Resnick's Bone and Joint Imaging [4 ed.] 0323523277, 9780323523271

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DONALD RESNICK, MD

Professor Emeritus Department of Radiology University of California, San Diego San Diego, California

JON A. JACOBSON, MD

Professor of Radiology Lenox Hill Radiology, New York City University of California, San Diego San Diego, California

CHRISTINE B. CHUNG, MD

Professor of Radiology Director, Musculoskeletal Imaging Research University of California, San Diego La Jolla, California

MARK J. KRANSDORF, MD

Professor of Radiology Mayo Clinic College of Medicine and Science Rochester, Minnesota; Consultant Mayo Clinic Scottsdale, Arizona

MINI N. PATHRIA, MD

Professor of Clinical Radiology University of California, San Diego San Diego, California

Resnick’s Bone and Joint Imaging FO U RT H E D I T I O N

Elsevier 3251 Riverport Lane St. Louis, Missouri 63043 RESNICK’S BONE AND JOINT IMAGING, FOURTH EDITION ISBN: 978-­0-­323-­52327-­1 Copyright © 2025 by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notice Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds or experiments described herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. To the fullest extent of the law, no responsibility is assumed by Elsevier, authors, editors or contributors for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Previous editions copyrighted 2005, 1996, and 1989.

Content Strategist: Melanie Tucker Senior Content Development Specialist: Kate Mannix Publishing Services Manager: Julie Eddy Senior Project Manager: Rachel E. McMullen Design Direction: Brian Salisbury Third World Compiler: Sigfrido Ernesto Garcia Printed in India Last digit is the print number: 9 8 7 6 5 4 3 2 1

To our residents and fellows for their motivation, enthusiasm, and, most importantly, inspiration

P R E FA C E Nearly two decades have passed since the prior edition of this text, Bone and Joint Imaging, Third Edition. With that in mind, we are excited to present the Fourth Edition, knowing that the time is right to again gather in one volume the considerable information that allows accurate assessment of a variety of imaging methods applied to the analysis of disorders of the musculoskeletal system. Once again, there has been rapid growth in the scope of musculoskeletal imaging, not so much in terms of new or changing disease processes but rather, in the manner in which the many advanced imaging methods are being applied. In this edition, there is a new emphasis on MR imaging and, especially, ultrasonography, without sacrificing the significant information provided by conventional radiography and CT scanning. The organization of this work follows that in the Third Edition, with some changes. The material related to basic science and diagnostic imaging techniques, which appeared in early chapters in the previous work, can now be found throughout the book in each of the individual chapters. Also, the first three sections of the current edition relate

to traumatic, articular, and infectious disorders, topics deserving early attention, as they are generally encountered most frequently in clinical practice. Subsequently, nine other sections can be found, covering almost all categories of disease that affect bones, joints, and soft tissues. In each of the chapters, an initial Summary of Key Features is followed by several Key Concepts boxes in which the most important information is provided in bullet format. At the end of each chapter, as before, a short list of references can be found. The editors of this text, along with four additional authors, have worked tirelessly to organize and condense a vast amount of information pertinent to musculoskeletal imaging in an attempt to produce a text whose size would not discourage any interested person from first picking it up and then, hopefully, peeking inside. We believe further that whether one reads only a few sections of this book or spends time consuming large portions of it, an improved understanding of the imaging findings related to a vast number of musculoskeletal disorders will result. That was clearly our purpose and motivation.

ACKNOWLED GMENTS We are greatly indebted to a number of individuals without whom this project would not be possible. This includes the contributing authors from the previous edition of Bone and Joint Imaging, whose work laid the foundation for this current edition: Murray K. Dalinka, MD Jerry R. Dwek, MD Frieda Feldman, MD Steven R. Garfin, MD Thomas G. Goergen, MD Amy Beth Goldman, MD Guerdon D. Greenway, MD Parviz Haghighi, MD Tamara Miner Haygood, MD, PhD Thomas E. Herman, MD Michael Kyriakos, MD John E. Madewell, MD William H. McAlister, MD M.B. Ozonoff, MD Michael J. Pitt, MD David J. Sartoris, MD Donald E. Sweet, MD Barbara N. Weissman, MD Their efforts are very much appreciated. A very special thanks must go to Melanie Tucker, Senior Content Strategist, and her associates at Elsevier—Kate Mannix, Senior Content Development Specialist and Rachel McMullen, Senior Project Manager. We would also like to acknowledge those individuals whose dedication, commitment, and energy often go unnoticed but who keep the system running smoothly and on time.

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CONTRIBUTORS Robert D. Boutin, MD Clinical Professor of Radiology Department of Radiology Stanford University School of Medicine Stanford, California Muscle Disorders Michael G. Fox, MD, MBA, FACR Professor of Radiology Mayo Clinic Arizona Phoenix, Arizona Advanced Imaging of Spinal Disorders Leon Lenchik, MD Professor of Radiology Wake Forest University School of Medicine Winston-Salem, North Carolina Muscle Disorders Nicholas C. Nacey, MD Associate Professor of Radiology and Medical Imaging Division of Musculoskeletal Radiology University of Virginia Health System Charlottesville, Virginia Advanced Imaging of Spinal Disorders

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SECTION 1  Traumatic Disorders

1 Physical Injury: Concepts and Terminology S U M M A R Y O F K E Y F E AT U R E S • P  hysical trauma is a common cause of acute skeletal abnormalities and is associated with a wide range of delayed complications. • The radiographic characteristics of fractures in the various skeletal sites are explained on the basis of biomechanical principles. • Special types of fractures include pathologic, stress, greenstick, torus, bowing, and transchondral fractures; trabecular microfractures; and osseous infractions accompanying subluxations and dislocations.

• T  rauma can affect synovial joints, symphyses, synchondroses, and the bone’s soft tissue supporting structures, including inserting tendons and entheses. • A variety of skeletal muscle alterations are related to physiologic stress and acute or chronic injury. • Characteristic skeletal abnormalities appear in abused children.

INTRODUCTION

accuracy for assessing purely soft tissue injuries. CT scanning is most commonly used to assess traumatic abnormalities in regions of complicated anatomy, such as the spine, face, pelvis, glenohumeral and sternoclavicular joints, and the midfoot and hindfoot, or in the setting of intraarticular fractures to assess articular congruity. Advances in CT technology—such as rapid multislice helical scanning, metal suppression algorithms, and three-­dimensional reformatted images— ensure rapid examination and multidimensional display of abnormalities (Fig. 1.2). CT angiography is widely used for the identification and possible treatment of posttraumatic vascular abnormalities, including dissection, disruption, and occlusion of major vessels, arteriovenous fistulas, and pseudoaneurysms. Mechanisms leading to vascular injury include a tear from the presence of a sharp bone fragment, compression related to hematoma or swelling within a tight fascial compartment, a shearing type of injury, and entrapment in the fracture fragments with angulation and occlusion. The vessels that are injured most commonly are in close proximity to a bone and held in a relatively fixed position by fascial or muscular attachment (Fig. 1.3). Scintigraphy is used in the evaluation of patients with skeletal trauma, particularly in the diagnosis of early stress fractures and multifocal abnormalities and in patients unable to undergo MR imaging. The vast majority of fractures are detected by bone scintigraphy within hours of the injury, with some delay in the identification of scintigraphic abnormalities in older patients, particularly those with osteoporosis. Scintigraphy can be used in age-­indeterminate fractures to assess acuity. The minimal time required for the bone scan to return to normal after fracture is about 5 to 7 months; in 90% of cases, the scan is normal by 2 years after the injury. Radionuclide alterations are not specific for fracture because they also occur in soft tissue, synovial, and ligamentous injuries as well as a variety of nontraumatic etiologies. Thus, the role of scintigraphy in skeletal trauma has largely been supplanted by MR imaging. The extreme sensitivity of MR imaging to bone, cartilage, and soft tissue injury makes it an indispensable supplementary technique for the initial diagnosis of injury in trauma patients whose initial radiographs

  

Physical injury contributes to a wide variety of alterations in bones, joints, and soft tissues. In addition to fractures, dislocations, subluxations, and capsular, tendinous, muscular, and ligamentous tears, trauma can affect the growth plates of immature skeletons as well as the hyaline cartilaginous and fibrocartilaginous joint structures. Further complications of trauma, covered in other chapters, include complex regional pain syndrome, osteolysis, osteonecrosis, many of the osteochondroses, neuropathic osteoarthropathy, infection, and heterotopic bone formation. Trauma has also been implicated in the development of certain neoplasms, such as aneurysmal bone cysts. Nonmechanical trauma to the musculoskeletal system can result from thermal and electrical injury, irradiation, and chemical substances.

DIAGNOSTIC TECHNIQUES The sensitivity and widespread availability of conventional radiography have led to its routine use in the initial assessment of skeletal injuries. Stress radiography obtained during the application of manual stress, gravity stress, or weight bearing can be effective in uncovering ligamentous injury that is not apparent on initial radiographs (Fig. 1.1). This technique is used most commonly for injuries to the acromioclavicular joint, knee, ankle, and foot. In the evaluation of trauma in children, comparison views provide important information in less than 5% of cases and should be obtained selectively. They are most useful in the evaluation of Salter-­Harris type I growth plate injuries and in the assessment of bowing fractures and injuries about the elbow. The role of computed tomography (CT) in the diagnosis of skeletal trauma is prominent. CT imaging is excellent for defining the presence and extent of fractures or dislocations as well as detecting intraarticular effusions and osteochondral bodies. CT scans afford a reasonable assessment of the soft tissues following trauma, though both magnetic resonance (MR) imaging and ultrasonography (US) show higher

1

2

SECTION 1  Traumatic Disorders

are either negative or have equivocal findings (Fig. 1.4). MR imaging is also well suited to the assessment of osteochondral and stress fractures. In chronic skeletal trauma, MR imaging plays an important role in identifying complications such as osteonecrosis, nonunion, and superimposed infection. The use of MR imaging for the assessment of both acute and chronic soft tissue injuries has greatly expanded due to its high accuracy in identifying sites of trauma and characterizing such injuries. In subsequent chapters, the role of MR imaging in assessing specific injuries will be emphasized. Although US plays a limited role in the assessment of bony trauma, it is also a powerful technique for assessment of soft tissue injuries and is extensively used due to its wide availability, portability,

and high accuracy. US is sensitive for detecting joint effusions, evaluating tendons and ligaments, and assessing muscle injury.

FRACTURES Epidemiology The likelihood, location, and configuration of a fracture after an injury depend on a number of factors, including the age and sex of the person, the type and mechanism of the injury, and the presence of any predisposing factors that might alter the bones or soft tissues of the musculoskeletal system. Birth-­related trauma in a newborn, sports-­related activities in an adolescent or young adult, occupation-­related stresses in a mature adult, and normal activities in the elderly are typical situations leading to skeletal injury.

Terminology KEY CONCEPTS  • A  n open fracture is at high risk of infection. • Incomplete fractures that do not involve the entire bone circumference occur most frequently in children. • Comminuted fractures have more than one fracture line within a bone. • Movement between the two ends at a fracture can result in angulation, displacement, distraction, shortening, and/or rotation.

Fig. 1.1  Stress radiography. Application of manual stress may allow detection of ankle ligament injuries not apparent on routine radiographs. This anteroposterior radiograph obtained during varus stress of the plantarflexed foot demonstrates varus tilt of the talus with respect to the tibia with widening the superolateral mortise, indicative of an injury to the calcaneofibular ligament.

A

Basically, a fracture is a break in the continuity of bone, cartilage, or both. Each fracture is associated with soft tissue injury, the character and degree of which have additional therapeutic implications. A trans-­chondral fracture is one that involves a cartilaginous surface. If the cartilage alone is involved, the term chondral fracture is used; a fracture involving cartilage and subjacent bone is termed an osteochondral fracture. In a closed (simple) fracture, the skin is intact and thus prevents communication between the fracture and the outside environment. An open fracture allows communication between the fracture and the outside environment because of the disruption of skin. Bone fragments may or may not protrude through the cutaneous defect. Although

B Fig. 1.2  Right hip fracture-dislocation. ­ Although the initial radiograph (A) shows a displaced fracture-­ dislocation of the right femoral head and neck with peripheral extrusion of a portion of the femoral head (arrow), the 3D CT reformatted image (B) viewed from a posterior approach clearly demonstrates the abnormal relationship of the displaced femoral head (arrow) relative to the femoral neck and acetabulum. 3D CT reformatted images are particularly helpful for surgical planning for complex injuries.

CHAPTER 1  Physical Injury: Concepts and Terminology closed and open fractures are clinically distinguishable, specific findings accompanying an open fracture may be apparent on radiographs (Box 1.1). Open fractures have a higher rate of disturbances in healing, in part related to an increased frequency of infection. A complete fracture occurs when the entire circumference of a tubular bone or both cortical surfaces of a flat bone have been disrupted. In an incomplete fracture, a break in the cortex does not extend

completely through the bone. Incomplete fractures occur in the resilient elastic bones of children and young adults. They may be further classified into various types, including bowing, greenstick, and torus fractures. The descriptive nomenclature of fractures can be amplified by the use of terms denoting the direction of the fracture line with reference to the shaft (long bones) or cortex (irregular bones). Four basic types of linear fractures involving the shaft of a tubular bone are recognized: transverse, oblique, oblique-­transverse, and spiral. A comminuted fracture has more than two fracture fragments regardless of the total number of such fragments. Comminuted fractures may result from a variety of different mechanisms. However, in general, the greater the applied force and the more rapid its application, the greater is the energy absorption by the bone and the more severe the comminution. Crush fractures result in severe comminution and associated soft tissue injury. Certain distinctive subtypes of comminuted fractures exist. A butterfly fragment (Fig. 1.5) is a wedge-­shaped fragment arising from the shaft of a long bone at the apex of the force. A segmental fracture (Fig. 1.6) is one in which two distinct fracture lines isolate a segment of the shaft of a tubular bone. Segmental fractures have special implications in terms of the adequacy of the blood supply and the healing rate. The alignment of a fracture refers to the longitudinal relationship of one fragment to another. If the fragments have not moved in any plane relative to each other, the fracture is said to be in anatomic or near anatomic alignment. By convention, angulation of the distal fragment is described in relation to the proximal one. Such angulation may be medial or lateral, dorsal or volar, or, in the forearm, radial or ulnar.

BOX 1.1  Radiographic Signs of Open A

Fractures

B

Soft tissue defect Bone protruding beyond soft tissues Subcutaneous or intraarticular gas Foreign material beneath skin Absent pieces of bone

Fig. 1.3  CT angiography. (A) Lateral radiograph of the distal femur shows an open displaced femoral shaft fracture with large amounts of gas in the soft tissues and greater than full shaft width posterior displacement of the distal fragment. (B) Three-­dimensional CT angiogram of the lower extremities demonstrates interruption of the left superficial femoral artery (arrow) at the level of the osseous injury.

A

3

B Fig. 1.4  Occult fracture of the distal radius. (A) Initial posteroanterior radiograph was interpreted as normal. (B) Coronal T1-­weighted MR image displays an undisplaced intraarticular fracture of the distal radius (arrows). An additional fracture is seen at the proximal pole of the hamate (arrowhead).

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SECTION 1  Traumatic Disorders

Fig. 1.5  Butterfly fracture fragment. A comminuted fracture of the midportion of the shaft of the tibia contains a wedge-­shaped butterfly fragment (arrow) arising from the lateral cortex. Note the valgus angulation of the distal fragments of the tibial and fibular fractures.

Midline

Midline

A

B

Fig. 1.7  (A) Varus angulation; the distal fragment is angulated toward the midline. (B) Valgus angulation; the distal fragment is angulated away from the midline.

*

Fig. 1.6  Segmental fracture of the tibia. A segment of the central shaft of the tibia (asterisk) has been isolated in this injury by superior and inferior fractures. There is also an oblique fracture (arrow) of the proximal fibula.

Varus refers to angulation of the distal fracture fragment toward the midline of the body, and valgus refers to its angulation away from the midline (Fig. 1.7). Apex anterior angulation at the fracture site means that the apex of the fracture is directed anteriorly (ventrally). Conversely, apex posterior angulation indicates that the apex of the fracture site is directed posteriorly (dorsally). Fracture position describes the relationship of the fracture fragments, exclusive of angulation, to the normal anatomic situation. Deviation from anatomic position is called displacement, which is described in terms of

Fig. 1.8  Bayonet deformity. Observe the fractures of the shafts of the tibia and fibula. The distal tibial fragment is displaced posteriorly, with overriding of the tibial fracture fragments. Note that the distal fragment (arrow) invaginates into the region of the syndesmosis with widening between the proximal tibia and fibula, indicating syndesmotic injury.

apposition and rotation. Apposition considers the degree of bone contact at the fracture site. A fracture with complete, or 100%, apposition is considered undisplaced. Partial degrees of surface contact can be roughly quantitated by using percentages (e.g., 25%, 50%, or 75% apposition). If the fracture surfaces are separated, the amount of distraction can be measured. Overlapping fracture surfaces with resultant shortening are described as a bayonet deformity (Fig. 1.8). Visualization of rotatory displacement of a

CHAPTER 1  Physical Injury: Concepts and Terminology fracture (i.e., rotation about the long axis of a bone) is facilitated by including the joints both proximal and distal to the fracture on the film (Fig. 1.9). An avulsion fracture occurs when an osseous fragment is pulled from the parent bone by a tendon or ligament (Fig. 1.10). An impaction fracture results when one fragment of bone is driven into an apposing fragment (Fig. 1.11). Two specific types of impaction fractures are recognized. A depression fracture results when the impacting forces occur between one hard (i.e., stronger) bone surface and an apposing softer

Fig. 1.9  Rotatory displacement. Radiograph of the forearm reveals that the wrist is in a posteroanterior position and the elbow is in a lateral attitude. Fractures of the shafts of the radius and ulnar are observed (arrows), with disparate diameters of the fracture ends at the radial fracture reflecting rotation.

(i.e., weaker) surface. A compression fracture is a type of impaction fracture characteristically involving the vertebral bodies.

Fracture Healing After a fracture, a series of events takes place that leads to osseous healing in most cases (Fig. 1.12). Three indistinctly separated phases of healing are recognized: an inflammatory phase (representing approximately 10% of the entire healing time), a reparative phase (about 40%), and a remodeling phase (the longest phase, accounting for 50% to as

Fig. 1.11  Impaction fracture. A sclerotic line (arrows) extends across the lateral aspect of the subcapital region related to an impacted fracture with valgus angulation of the shaft relative to the head. Note the excessive vertical orientation of the femoral head trabeculae related to the lateral impaction.

A

Fig. 1.10  Avulsion fracture. The biceps femoris tendon and fibular collateral ligament are attached to the large fracture fragment (arrow) avulsed at the fibular head. Overlying soft tissue swelling is present.

5

B

C

Fig. 1.12  Normal fracture healing. (A) After the injury, bleeding is related to osseous and soft tissue damage. A hematoma, followed by clot formation, develops within the medullary canal between the fracture ends and beneath the periosteal membrane, which may have been torn. (B) Callus formation takes place and consists of external bridging callus at the periosteal surface, intramedullary callus, and primary callus at the ends of the fracture fragments. (C) Callus envelops the bone ends rapidly and produces increasing stability at the fracture site.

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SECTION 1  Traumatic Disorders

much as 70% of healing time). Initially, bleeding from the damaged ends of the bones and neighboring soft tissues results in the formation of a hematoma within the medullary canal between the fracture ends and beneath the elevated periosteum. Bleeding is followed by clot formation that leads to an intense, acute inflammatory response. The reparative phase begins with organization of the fracture hematoma and invasion by fibrovascular tissue, which replaces the clot and lays down the collagen fibers and matrix that will later become mineralized to form the woven bone of the provisional or primary callus. Callus rapidly envelops the bone ends, increasing stability at the fracture site. The remodeling phase is associated with resorption of unnecessary segments of callus and proliferation of trabeculae along lines of stress. Many local factors can modify the healing process: degree of trauma, degree of bone loss, type of bone involved, extent of immobilization, presence of infection, presence of an underlying pathologic process, use of radiation therapy, presence of poor vascularity or frank osteonecrosis, and occurrence of intraarticular extension. Systemic factors such as the age of the patient and the presence of metabolic bone disease also can be influential in fracture repair. Imaging findings that indicate successful healing include progressive loss of the fracture line, bridging or buttressing callus crossing the fracture, and reestablishment of cortical and marrow continuity. In some instances, the healing process is markedly slowed (delayed union) or arrested altogether (nonunion). Because the rate of fracture healing depends on many local and systemic factors, no definition of delayed union has been uniformly accepted, although clinical application of the term implies that the healing attempt is proceeding. Nonunion generally indicates that the fracture site has failed to heal completely during a period of approximately 9 to 12 months after the injury and that either a pseudarthrosis (consisting of a synovium-­lined cavity and synovial fluid, typically related to persistent motion at the nonunion site) or fibrocartilaginous union has developed. Nonunion of clavicular, scaphoid, humeral, ulnar, tibial, and femoral fractures is encountered most commonly (Fig. 1.13). Delayed union and nonunion of fractures should be distinguished from malunion. A malunited fracture is one that has healed, albeit in an improper position (e.g., excessive angular or rotational deformity). Malunion of a fracture in a child may be a temporary phenomenon that spontaneously disappears with further skeletal growth and remodeling.

A

B

Fig. 1.13  Abnormal fracture healing. (A) Classic hypertrophic nonunion is evident at the ulnar shaft fracture (arrow) with prominent external callus and enlarged irregular bone ends. (B) A different patient with proximal humeral nonunion (arrows) shows the atrophic form of nonunion with minimal callus at the fracture site.

Special Types of Fractures Pathologic Fractures

A pathologic fracture is one in which the bone is disrupted at a site of preexisting abnormality, typically by a load that would not fracture normal bone. Any process that focally weakens the bone structurally can result in a pathologic fracture, the most typical cause being an osseous tumor. Of the tumorous causes of pathologic fracture, skeletal metastasis predominates. Radiographic distinction between a pathologic and a nonpathologic fracture is not difficult when a fracture line traverses a large area of osseous destruction, when there is visible underlying cortical erosion, or when the adjacent or distant bones are riddled with additional lesions (Fig. 1.14). When a smaller lesion is present, the fracture itself may obscure the area of lysis or sclerosis, especially in the presence of malalignment at the fracture site. The absence of a history of significant trauma and the presence of symptoms and signs indicating a preexisting abnormality are clinical aids to the diagnosis of a pathologic fracture. If a pathologic fracture is suspected, CT scanning and MR imaging can be employed to evaluate the region for an underlying lesion. Diagnostic difficulty may be encountered in a patient who has a nonpathologic fracture because resorption, osteolysis, or rotation about the fracture site may create the illusion of an underlying lesion (Fig. 1.15).

Fig. 1.14  Pathologic fracture. Oblique fracture line (arrows) through a primary Langerhans cell sarcoma can be detected in the distal portion of the femur. Note the mixed osteolysis and osteosclerosis of the underlying tumor as well as cortical irregularity and periostitis (arrowhead) related to this rare neoplasm.

Trabecular Microfractures (Bone Bruises) The use of MR imaging to evaluate musculoskeletal injuries led to the identification of intraosseous regions of altered marrow signal, known as trabecular microfractures or bone bruises. These injuries, which are typically located close to a joint surface, result from compression or

CHAPTER 1  Physical Injury: Concepts and Terminology

7

*

A

B Fig. 1.15  Pseudopathologic fracture. (A) Anteroposterior radiograph of the left hip shows a femoral neck fracture with an apparent region of osteolysis (arrow) at the superior neck. (B) Axial CT scan shows that the defect is related to angulation at the fracture site creating a gap (asterisk) between the fracture fragments at the anterosuperior neck.

* *

* *

B

A

Fig. 1.16  Trabecular microfracture (bone bruise). Sagittal intermediate-weighted (A) and fluid-­sensitive (B) MR images show the characteristic finding of a bone bruise. In this case, it involves mainly the posterior portion of the lateral femoral condyle. The lesion shows patchy high signal intensity in part B that extends to the subchondral bone (asterisks).

impaction forces. Resolution of the MR abnormalities associated with bone bruises generally occurs over one to several months and may coincide with a decrease in or disappearance of the patient’s symptoms. The characteristics of these trabecular microfractures on MR images are remarkably constant and are those of poorly marginated regions of low signal intensity marrow on T1-­weighted images and high signal intensity on fluid-­sensitive sequences, typically at the subchondral region (Fig. 1.16). The detection of bone bruises at specific anatomic sites provides secondary evidence that other injuries may be present; examples include the occurrence of bone bruises in the lateral femoral condyle and posterolateral portion of the tibia in patients with injuries to the anterior cruciate ligament, bone bruises in the lateral femoral condyle in persons with injuries to the medial collateral ligament of

the knee, and bone bruises in the lateral femoral condyle and medial portion of the patella in patients with lateral patellar dislocation.

Stress Fractures KEY CONCEPTS  • • • •

S tress fractures result from repetitive trauma. The lower extremity is the most common location of stress fractures. Fatigue fractures (overuse) develop in normal bone. Insufficiency fractures develop in bone with diminished elastic resistance or healing capacity. • The most common etiology of insufficiency fracture is osteoporosis.

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SECTION 1  Traumatic Disorders

Stress fractures can occur in normal or abnormal bone subjected to repeated loading of bone, resulting in microdamage without adequate or proportionate bone repair. The injury results from repetitive loads, each less than that which would cause an acute fracture of bone, occurring at a frequency, rate, or force beyond the bone’s ability to adapt. Two types of stress fracture are recognized: fatigue fracture, which results from the application of repetitive stress on a bone with normal elastic resistance, and insufficiency fracture, which occurs when normal stress is placed on a bone with deficient elastic resistance. Fatigue fractures frequently share the following features: the activity is new or different, the activity is strenuous, and the activity is repeated with a frequency that ultimately produces symptoms and signs. Fatigue fractures are relatively common in athletes and military recruits undergoing basic training. They are especially frequent in runners and ballet dancers, and their sites of involvement often can be predicted by an analysis of the specific sporting activity. Typical examples are the fatigue fractures that occur in the metatarsal bones of military recruits (“march” fractures) and in the lower extremities in athletes, joggers, and dancers. The causes of insufficiency fractures are diverse and include osteo­ porosis, rheumatoid arthritis, Paget disease, osteomalacia or rickets, hyperparathyroidism, renal osteodystrophy, osteogenesis imperfecta, osteopetrosis, fibrous dysplasia, and irradiation. Of these causes, underlying osteoporosis, prior radiation therapy, and rheumatoid arthritis are most common. A distinctive form of insufficiency fractures affecting the lateral femoral cortex has been described related to long-­term ingestion of bisphosphates causing a cessation of bone remodeling induced by the drug (Fig. 1.17). Fatigue and insufficiency fractures are not infrequent after certain surgical procedures that result in altered stress or an imbalance of muscular force on normal or abnormal bones. Common examples are noted in the metatarsal bones after bunion surgery and in the lower extremities after arthrodesis or arthroplasty.

Fig. 1.17  Insufficiency fracture: bisphosphonate use. The radiograph shows an incomplete transverse fracture of the lateral femoral cortex (arrow) caused by long-­term use of bisphosphonate therapy for osteo­ porosis. Note the multiple regions of undulating and beak-like bone proliferation along the lateral femoral cortex below the fracture.

The clinical findings of stress fractures are typically localized tenderness, soft tissue swelling, and activity-­related pain that is relieved by rest. The bones in the lower extremity are affected more frequently than those in the upper extremity. The specific site of stress fractures is influenced by the type of physical activity causing the injury. More than one site can be involved simultaneously, more than one stress fracture can occur in a single bone, and symmetrical changes are not unusual. The radiographic abnormalities are influenced by the location of the fracture and the interval between the time of injury and the radiographic examination. In a diaphysis, a linear cortical radiolucent area is frequently associated with periosteal and endosteal cortical thickening (Fig. 1.18). In some cases, multiple radiolucent striations that extend partially or completely across the cortex are seen. In an epiphyseal or metaphyseal location or in a cancellous area, focal sclerosis representing condensation of trabeculae is the typical finding, and periostitis is not prominent (Fig. 1.19). With healing at either site, the sclerosis may become more diffuse and, eventually, it and the fracture line can disappear. Radionuclide examination is very sensitive for early detection of stress injury to bone. The finding of abnormal scintigraphic patterns in athletic individuals indicates increased stress and can be seen prior to the development of an actual fracture. A shin splint is one of these conditions. Shin splints represent periosteal disruptions of varying length, possibly caused by the rupture of Sharpey’s fibers that extend from the muscle through the periosteum into the cortical structure of bone. In patients with shin splints, poorly marginated regions of mildly increased radionuclide accumulation are seen over an elongated area at the cortex of the tibia. This pattern of abnormality differs from that typically seen in an acute stress fracture, in which a more focal fusiform area of increased activity is apparent. Uncommonly, stress fractures are predominantly longitudinal in orientation, resulting in long areas of intense activity, most frequently at the tibia (Fig. 1.20). MR imaging has comparable sensitivity and superior specificity with respect to bone scintigraphy in the assessment of stress injury. In the initial stages of stress injury, only superficial periostitis is seen.

Fig. 1.18  Stress fracture: radiographic abnormalities in diaphyses. Note the irregular radiolucent areas (arrows) in the anterior cortex of the midshaft of the tibia. Cortical thickening and periosteal new bone formation about these incomplete fractures are evident.

CHAPTER 1  Physical Injury: Concepts and Terminology As the injury progresses, marrow alterations become evident on fluid-­ sensitive sequences, followed by loss of marrow signal on T1-­weighted images. After these initial changes, cortical lucencies and striations may become evident, though they can be difficult to appreciate on MR images. A frank intramedullary fracture line appears only after the cortical toughening mechanisms are overcome (Fig. 1.21). Intramedullary stress fractures typically appear as a linear zone of low signal intensity surrounded by a broader, poorly defined area of slightly higher (though still low) signal intensity on T1-­weighted MR images and as a linear

area of low signal intensity surrounded by a broader region of high signal intensity on fluid-­sensitive images. Soft tissue and muscle edema are typically present. Specific examples of activities that cause stress fractures are listed in Table 1.1. Calcaneal or other tarsal stress fracture. Insufficiency fractures of the calcaneal tuberosity can accompany osteoporosis, rheumatoid arthritis, neurologic disorders, and other diseases (Fig. 1.22). Fatigue fractures of the calcaneus are less common but do occur, particularly

A

B

C

D

Fig. 1.19  Stress fracture: radiographic abnormalities in metaphyses and epiphyses. Bandlike focal sclerosis (arrows) is typical of a stress fracture in the proximal portion of the tibia.

A

9

E

Fig. 1.21  Magnetic resonance (MR) grading of stress injury. (A) Symptoms develop prior to MR abnormalities and the bone appears normal. (B) Initial MR finding of stress injury is superficial periostitis. (C) Marrow edema initially appears on fluid-­sensitive sequences followed by alterations on T1-­weighted images. (D) With ongoing injury, faint regions of intracortical lucencies and striations become apparent. (E) Ultimately, a frank intramedullary fracture line develops.

B Fig. 1.20  Stress fracture: scintigraphy of stress fracture. (A) Images of the lower legs during the delayed portion of a bone scan show intense longitudinally oriented increased tracer accumulation at the distal tibia. (B) Anteroposterior radiograph demonstrates a long intramedullary band of sclerosis (arrows) exiting the medial tibial cortex related to a longitudinal insufficiency fracture of the tibia. Note the periostitis at the medial cortex at the fracture line.

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SECTION 1  Traumatic Disorders

TABLE 1.1  Activities That Lead to Stress

Fractures at Specific Locations Location

Activity or Event

Sesamoids of metatarsal bones

Prolonged standing

Metatarsal shaft

Marching, stamping on ground, prolonged standing, ballet, sequelae of bunionectomy

Navicular

Stamping on ground, marching, long-­distance running

Calcaneus

Jumping, parachuting, prolonged standing, recent immobilization

Tibia   Midshaft and distal shaft Long-­distance running   Proximal shaft (children)

Running

Fibula   Distal shaft

Long-­distance running

  Proximal shaft

Jumping, parachuting

Patella

Hurdling

Femur  Shaft

Ballet, long-­distance running

 Neck

Ballet, marching, long-­distance running, gymnastics

Fig. 1.22  Calcaneal stress fracture. Note the vertically oriented sclerotic line (arrows) at the calcaneal tuberosity. The fracture line courses perpendicular to the weight-­bearing trabeculae, typical of an insufficiency fracture.

Pelvis  Sacrum

Long-­distance running

  Obturator ring

Stooping, bowling, gymnastics

Lumbar vertebra (pars interarticularis)

Ballet, lifting heavy objects, scrubbing floors

Cervicothoracic spinous process

Clay shoveling

Ribs

Carrying a heavy pack, golfing, rowing, coughing, sequelae of radical neck surgery

Clavicle

Sequelae of radical neck surgery

Coracoid of scapula

Trapshooting

Humerus Proximal physis (children) Throwing a ball Distal shaft

Throwing a ball

Ulna  Olecranon

Pitching a ball

  Coronoid shaft

Pitchfork work, propelling a wheelchair

Hook of hamate

Holding a golf club, tennis racquet, baseball bat

Modified from Daffner RH, Pavlov H. Stress fractures: current concepts. Am J Roentgenol. 1992;159(2):245–252.

among military recruits. Sagitally oriented fractures in the tarsal navicular bone occur in physically active persons, especially basketball players and runners (Fig. 1.23). Stress fractures in the other tarsal bones are less common. Fibular stress fracture. Changing muscular stress can result in a “runner’s fracture.” Jumping can also produce fibular stress fractures; classically, the proximal portion of the bone is affected in jumping, whereas the distal shaft is injured in runners.

Fig. 1.23  Tarsal navicular stress fracture. The anteroposterior radiograph of the foot shows a sagitally oriented stress fracture (arrow) in the tarsal navicular bone. There is sclerosis at the lateral pole, suggesting ischemia or early avascular necrosis.

Tibial stress fracture. Stress fractures of the proximal diaphysis of the tibia can occur during running (Fig. 1.24); stress fractures of the middle and distal tibial diaphysis can occur during running, marching, and ballet dancing. The posteromedial portion of the cortex is affected more frequently than the anterolateral portion. Shin splints relate to multifocal stress injury along the anterior tibial cortex; the resulting pain is milder and more diffuse than that of a stress fracture.

CHAPTER 1  Physical Injury: Concepts and Terminology

11

A

B Fig. 1.25  Femoral neck stress fracture. Coronal T1-­weighted (A) and fluid-­sensitive (B) MR images of the pelvis reveal a fatigue fracture in the medial portion of the left femoral neck with a short fracture line on the compressive side of the bone (arrow), surrounded by marrow edema. Fig. 1.24  Tibial stress fracture. Observe a transverse fracture of the posterior tibia (arrow) at the proximal metadiaphysis in an avid runner. There is sclerosis surrounding the fracture, along with periostitis.

Femoral stress fracture. Stress fractures of the shaft or neck of the femur can result from numerous activities, including long-­distance running, ballet dancing, and marching. Two types of stress fracture of the femoral neck are described. The more common compression type is found in younger patients, appearing as a haze of callus in the inferior aspect of the medial femoral neck, and is stable in most cases (Fig. 1.25). The less common tensile type develops in older patients at the superior femoral neck, which can become displaced. Uncommonly, stress fractures of the subchondral bone at the femoral head may be observed in osteoporotic patients and during pregnancy; these can lead to articular surface collapse and can be difficult to differentiate from osteonecrosis. Metatarsal stress fracture. The metatarsal bones are frequent sites of stress fracture, which may be caused by marching, ballet dancing, prolonged standing, foot deformities, and surgical resection of adjacent metatarsal bones. The middle and distal portions of the shafts of the second and third metatarsal bones are affected most often (Fig. 1.26), but any metatarsal bone can be involved. In the first and fifth metatarsals, the base of the bone is most commonly fractured. Stress fractures can involve the metatarsal heads and lead to sclerosis and flattening of subchondral bone, findings that resemble those of Freiberg infraction. Pubic rami and symphysis stress fracture. Stress fractures of the pubic arch and parasymphyseal bone are encountered in pregnant women, joggers, long-­ distance runners, and marathoners. Similar fractures occur in patients with osteoarthritis of the hip, those who have undergone hip arthroplasty, and those with traumatic or iatrogenic sacroiliac joint instability, as well as after irradiation and in association with osteoporosis and rheumatoid arthritis (Fig. 1.27). Complications of such stress fractures include osteolysis simulating malignancy. Other pelvic stress fractures. Insufficiency fractures of the sacrum in patients with postmenopausal or senile osteoporosis or rheumatoid arthritis and in those who have received corticosteroid medications or radiation therapy are common. Sacral insufficiency fractures may lead to significant clinical manifestations that simulate the findings associated with skeletal metastasis, including sciatica and severe low

back or groin pain. These can be unilateral or bilateral, with vertical fracture lines typically located in the sacral ala close to the sacroiliac joint or joints, leading to subtle interruption of the superior cortical surface or the arcuate lines of the sacrum. Horizontal fracture lines also may be evident, typically at the S2 level. Bilateral alar fractures connected by a horizontal fracture line produce the “butterfly” or “H” pattern of increased scintigraphic uptake in the sacrum. CT shows irregular bands of sclerosis at sacral insufficiency fractures that are typically undisplaced (Fig. 1.28). MR images reveal low signal intensity bands on T1-­weighted images and extensive edema in the adjacent marrow on fluid-­sensitive sequences. Sacral insufficiency fractures may be an isolated finding, although they are frequently associated with other insufficiency fractures of the pelvis, including of the pubic rami, pubic symphysis, ilium, and acetabular roof. Fatigue fractures of the sacrum are less common than insufficiency fractures. These occur predominantly in runners and are typically limited to the upper sacrum, extending from the superior sacral cortex to the first or second ventral sacral foramen (Fig. 1.29). Upper extremity stress fracture. These fractures are far less frequent than stress fractures in the bones of the lower extremity. The majority of upper extremity stress injuries are seen in children at an open physis, typically related to throwing. In adults, typical sites include the coracoid process of the scapula in trap shooters; the acromion of the scapula in golfers; the ulna in bowlers, tennis players, baseball pitchers, and golfers; the hook of the hamate in tennis players, golfers, and baseball players; the olecranon in baseball pitchers and javelin throwers; the phalangeal tufts in guitar players; the phalanges of the hand in bowlers; and the inferior edge of the glenoid fossa in baseball pitchers. Stress fracture of the neural arch of the vertebra (spondylolysis). Spondylolysis represents a defect in the pars interarticularis of the vertebra, most commonly at the L5 level. It may or may not be associated with slippage of one vertebral body onto the adjacent one; this slippage is termed spondylolisthesis. It has been estimated that 3% to 7% of vertebral columns reveal at least one area of spondylolysis. The etiology of spondylolysis is multifactorial, but the most important factor implicated in the formation of such defects is excessive stress during childhood and adolescence. Spondylolysis is discussed in further detail in Chapter 53.

12

SECTION 1  Traumatic Disorders

A

B

C

Fig. 1.26  Second metatarsal stress fracture. (A) Note patchy bone sclerosis and periostitis at the neck of the second metatarsal (arrows) compatible with a fatigue-type of stress fracture. (B) Long-axis T1-­weighted MR image shows a stress fracture traversing the full width of the shaft (arrow) with irregular cortical thickening related to periosteal new bone formation. (C) Corresponding fluid-­sensitive MR image reveals increased signal in the bone and soft tissues (arrow).

* Fig. 1.28  Sacral stress fracture. The typical CT features of an insufficiency fracture of the sacrum are shown in this elderly woman. The axial CT image shows a vertical band of patchy sclerosis in the left lateral sacral ala (arrows) adjacent to the sacroiliac joint. In more advanced cases, cortical disruption, fracture diastasis, and displacement may be evident.

Fig. 1.27  Multiple stress fractures: pelvis. In this middle-­aged female runner with osteoporosis, disordered eating, and amenorrhea (female athlete triad), there is an acute fracture at the junction of the superior pubic ramus and acetabulum (arrow), with disruption of the medial acetabular wall and protrusio deformity. A healed insufficiency fracture is seen at the inferior pubic ramus (asterisk). The patient had undergone cephalomedullary femoral fixation for a prior fracture at the lesser trochanter and medial femoral neck.

Greenstick, Torus, and Bowing Fractures In an immature skeleton, fractures that do not completely traverse the entire circumference of a bone are not infrequent. Incomplete fractures

can be seen in skeletally mature patients, particularly in thin bones, but far less commonly than in young children. A greenstick fracture is one that perforates one cortex and ramifies within the medullary bone (Fig. 1.30). The name is derived from this fracture’s resemblance to a young tree branch that, when broken, is disrupted on its outer surface but remains intact on its inner surface. Typical locations of greenstick fractures are the proximal metaphysis or diaphysis of the tibia and the middle third of the radius and ulna. A torus (buckling) fracture results from an injury insufficient in force to create a complete discontinuity of bone but sufficient to produce buckling of the cortex (Fig. 1.31). Torus fractures are common in metaphyseal regions of long bones. Radiographs may be interpreted as normal unless subtle bulging of the cortex is identified. With the application of both compressive and angular forces, a combination of greenstick and torus fractures may result; this is termed a lead pipe fracture.

CHAPTER 1  Physical Injury: Concepts and Terminology

A

13

B Fig. 1.29  Sacral stress fracture. (A) Fatigue fracture (arrows) of the left upper sacrum in a runner can be seen on the T1-­weighted oblique coronal MR image. (B) Corresponding fluid-­sensitive image shows marrow edema adjacent to the injury, partially obscuring the fracture line.

Fig. 1.30  Greenstick fracture. Observe that the fracture (arrow) involves one side of the fibula and extends incompletely through the bone.

Bowing injuries are a plastic response, usually due to longitudinal stress that is insufficient to result in a frank visible fracture. They occur virtually exclusively in children when the bone is less brittle, typically in the thin bones, such as the clavicle, radius, and ulna. Bowing is due to plastic deformation, whereby osseous bending results in permanent bowing of the bone. Radiographs reveal lateral or anteroposterior bending of the affected bone without any discrete fracture line (Fig. 1.32). The abnormality may be subtle and necessitate comparison radiographs of the opposite side for correct diagnosis. Sequential radiographs of a plastic bowing deformity may show periostitis or thickening of the involved cortices. Scintigraphic uptake or marrow edema on MR images is seen following such injuries. A bowed bone generally

Fig. 1.31  Torus fracture. Note the buckling of the ulnar-­sided cortices of the radius and ulna (arrows), with relative preservation of the contralateral cortical surface.

remains bowed, resists attempts at reduction, holds an adjacent fracture in angulation, and prevents relocation of an adjacent dislocation.

Toddler’s Fractures Infants and toddlers frequently develop an acute ­onset limp without a clear history of specific injury. The classic toddler’s fracture is a nondisplaced oblique fracture of the distal diaphysis of the tibia. The fracture line can be very subtle and easily overlooked on radiographs; scintigraphy or follow-­up radiographs showing periostitis indicate that the tibia has been injured (Fig. 1.33). Although this fracture is the most common pattern of injury, other causes of these clinical manifestations are occult fractures of the fibula, femur, metatarsal bones (particularly the first) and, less commonly, calcaneus. Most toddler’s fractures occur between the ages of 1 and 3 years; the remainder occur before the age of 1 year.

14

SECTION 1  Traumatic Disorders apparent because of a varying degree of radiodensity. Secondary radiographic signs consisting of soft tissue swelling and joint effusion can be apparent with either chondral or chondro-­osseous fragments. After the injury, the detached portion of the articular surface can remain in situ, be slightly displaced, or become loose or free within the joint cavity (Fig. 1.34). Radiographic identification of loose osteocartilaginous bodies or those attached to the synovial lining requires a careful search of the recesses and dependent portions of the joint. Such bodies are common in the olecranon, coronoid, and radial fossae in the elbow; the axillary and subscapular recesses in the glenohumeral joint; the acetabular fossa and recesses about the femoral neck of the hip; and the posterior recesses in the knee. Detection of osteocartilaginous bodies should stimulate a search for their site of origin. Osteochondral injuries are a well-­recognized component of a variety of momentary or persistent subluxations and dislocations. Classic examples include injuries to the glenoid region of the scapula and humeral head with dislocation of the glenohumeral joint, injuries to the patella and lateral femoral condyle with dislocation of the patella (Fig. 1.35), and injuries to the femoral head with dislocation of the hip.

Osteochondritis Dissecans Fig. 1.32  Bowing deformities of bone. Note the bowing of the ulna (arrows) associated with a fracture of the adjacent radius.

KEY CONCEPTS  • T he most common locations of osteochondritis dissecans are the inner non–weight-­bearing surfaces of the medial femoral condyle, patella, and talar dome. • The bone fragment can be stable, unstable in situ, or displaced. • Fluid separating the osteochondritis dissecans fragment from the parent bone suggests instability. • An unstable fragment can displace and migrate, producing osteochondral bodies in the joint.

Fig. 1.33  Toddler’s fracture: tibia. A follow-­up radiograph obtained in a 2-­year-­old refusing to bear weight reveals periostitis (arrows) along the tibial shaft related to a nondisplaced fracture of the distal tibia. The initial radiograph (not shown) revealed a questionable hairline lucency in this region.

Acute Chondral and Osteochondral Fractures Shearing, rotational, or tangentially aligned impaction forces generated by abnormal joint motion may produce fractures of one or both of the two apposing joint surfaces. Acute injuries can produce fragments consisting of cartilage alone (chondral fractures) or cartilage and underlying bone (osteochondral fractures). A purely cartilaginous fragment creates no direct radiographic abnormalities, whereas one containing calcified cartilage and bone becomes

Osteochondritis dissecans is characterized by fragmentation and possible separation of a portion of the articular surface. The age at onset varies from childhood to middle age, but an onset in adolescence is most common. Patients may be entirely asymptomatic; however, pain aggravated by movement, limitation of motion, clicking, locking, and swelling may be apparent. Single or multiple sites can be affected. The condition is generally thought to be the eventual result of an osteochondral fracture that was initially caused by shearing, rotatory, or tangentially aligned impaction forces. Considerable interest has developed in determining the stability of the osteochondral fragment. MR imaging is most useful in this regard, with high signal intensity deep to the osteochondral fragment on fluid-­sensitive images indicative of fluid or granulation tissue, which is strong but not infallible evidence of an unstable lesion. The presence of fluid encircling the fragment or focal cystic areas beneath the fragment is the best indicator of instability (Fig. 1.36). Similarly, the absence of a zone of high signal intensity at the interface of the fragment and the parent bone is a reliable sign of lesion stability. Unstable lesions are characterized by (1) the presence of a line of high signal intensity at the interface between the osseous fragment and the adjacent bone, (2) an articular fracture indicated by joint fluid of high signal intensity passing through the subchondral bone plate, (3) a focal osteochondral defect filled with joint fluid, and (4) a 5-­mm or larger fluid-­filled cyst deep to the lesion. MR arthrography also may be useful in the evaluation of osteochondritis dissecans and in establishing fragment stability. Femoral condyle. One of the most common locations of osteochondritis dissecans is the condylar surface of the distal femur,

CHAPTER 1  Physical Injury: Concepts and Terminology

A

B

C

15

D

Fig. 1.34  Acute chondral and osteochondral fractures: fragment components. Fragments can consist of cartilage alone (A) or both cartilage and bone (B). Chondral or osteochondral fragments can remain in situ (B), be displaced within the articular cavity (C), or become embedded at a distant synovial site (D) and evoke a local inflammatory reaction.

A

B

Fig. 1.35  Acute osteochondral fracture: lateral patellar dislocation. (A) On axial CT image, note the osteochondral fracture with missing bone (arrow) at the median ridge of the patella and shallowness of the trochlea. (B) Sagittal reformatted CT image shows the displaced osteochondral fragment (arrow) lying within the intercondylar notch. Note the large effusion within the joint.

accounting for as many as 75% of cases (Fig. 1.37). With regard to femoral involvement, men are affected more frequently than women, and the average age at the onset of symptoms and signs is 15 to 20 years, although the age range is highly variable. Unilateral changes predominate over bilateral changes by a ratio of approximately 3:1. The medial condyle is affected most frequently, with the defect occurring at the inner non–weight-­bearing surface, although other sites may be involved (Fig. 1.38). The osseous component of the lesion is detectable with routine radiography or standard CT. Purely chondral lesions can be visualized with high-­resolution MR imaging, particularly in the presence of an effusion; they are often better appreciated following arthrography. The major differential diagnosis is an insufficiency fracture of the femoral condyle, formerly referred to as spontaneous osteonecrosis of the knee. This latter lesion occurs in older persons, is associated with a sudden onset of clinical manifestations, and almost invariably involves the weight-­bearing portion of the medial femoral condyle in the setting of underlying meniscal dysfunction. Patella. Compared with osteochondritis dissecans of the femoral condyle, involvement of the patella is rare. The typical site of the lesion is the median ridge of the patella. The lateral facet is affected in approximately 30% of cases, and the most medial, or “odd,” facet is

generally spared. The middle or lower portion of the bone is affected almost universally, whereas the superior portion is uninvolved. The cause of the lesion appears to be traumatic. The lesions are optimally identified on lateral and axial radiographs, where they appear as osseous defects near the convexity between the condylar articular surfaces of the patella (Fig. 1.39). The major differential diagnoses are a dorsal defect of the patella and osteochondral fractures related to direct injury or recurrent dislocation. A dorsal defect of the patella, which likely represents an anomaly of ossification in the spectrum of a bipartite or multipartite patella, is associated with a round and lytic defect with well-­defined margins in the superolateral aspect of the bone (see Chapter 52). This defect occurs in both sexes, may be bilateral, and is typically asymptomatic; it demonstrates intact cartilage on arthrography. Dislocation of the patella is associated with an osteochondral fracture on the medial side of the patella and, less frequently, at the lateral margin of the lateral femoral condyle. Talus. Osteochondritis dissecans is common in the talar dome. The middle third of the lateral border of the talus and the posterior third of the medial border of the talus are the two most common sites of injury, and they are involved with approximately equal frequency. Centrolateral (or anterolateral) lesions are commonly encountered

16

SECTION 1  Traumatic Disorders

A

B

Fig. 1.36  Osteochondritis dissecans of the medial femoral condyle. Coronal T1-­weighted (A) and fluid-­ sensitive (B) MR images reveal a lesion involving the inner surface of the medial condyle (arrows). The fragment is ossified, and the junction between it and the parent bone demonstrates intermediate signal intensity in part A and high signal intensity in part B. The abnormalities are consistent with granulation tissue or fluid in this junctional area. Signal alterations at the overlying cartilage are noted, although it may not be completely interrupted medially. These findings indicate a loose in situ fragment.

abnormalities include flattening, cystic and sclerotic changes, and fragmentation of the capitulum. The resulting bone fragments may remain at their site of origin or become partially or completely detached. Free intraarticular bodies may migrate to any region of the elbow, although they often lodge in the fossa of the distal end of the humerus. CT scanning, CT arthrography, ultrasonography, MR imaging, and MR arthrography have all been used to assess this lesion (Fig. 1.41). With regard to the differential diagnosis, Panner disease, related to irregular ossification of the capitulum, is seen in a younger age group.

Other Sites Posttraumatic osteochondral fractures, osteochondritis dissecans, and osteonecrosis can be identified at other sites, including other tarsal bones, tibia, humeral head, acetabulum, and glenoid cavity.

Fractures of the Shafts of Long Tubular Bones

Fig. 1.37  Osteochondritis dissecans of the femoral condyle. Classic defect of the medial condyle (arrows).

in patients who have had previous episodes of ankle injury. Patients are usually in the second to fourth decades of life. Conventional radiographs can usually delineate the site of injury. The osseous defects may be quite subtle, consisting of slight irregularity of the articular surface, shallow excavations with or without adjacent sclerosis, and small “flake” fracture fragments (Fig. 1.40). CT arthrography and MR imaging better delineate the fracture site, define the condition of the overlying cartilage, and detect intraarticular osseous and cartilaginous bodies. Capitulum of the humerus. Osteochondritis dissecans about the elbow usually involves the capitulum (or capitellum). Radiographic

It is the application of an abnormal force to a bone, a process termed loading, that results in an injury. The ability of bone to absorb energy varies with the person’s age, sex, and metabolic status; the integrity of surrounding tissue; and the specific bone involved. The bones of children are more plastic (ductile) than the comparatively brittle bones of adults. This fact contributes to the occurrence of incomplete and bowing fractures in children, whereas these injuries are almost never seen in adults. Additional factors that contribute to the production of a fracture are the presence of a preexisting lesion and a previous surgical procedure. Four basic types of load can be applied to an object such as a long tubular bone: tension (distraction) forces act perpendicular to the cross-­section of the bone and pull trabeculae apart, compression forces act in a similar perpendicular direction and press trabeculae together, torsion (rotational) forces twist the bone, and bending forces lead to angulation (Fig. 1.42). Of these types of force, compression, torsion, and bending forces working independently or in

CHAPTER 1  Physical Injury: Concepts and Terminology

A

B

C

D

17

E

Fig. 1.38  Osteochondritis dissecans of the femoral condyles: sites of occurrence. (A) Classic (medial condyle). (B) Extended classic (medial condyle). (C) Inferocentral (medial condyle). (D) Inferocentral (lateral condyle). (E) Anterior (lateral condyle).

A

B Fig. 1.39  Osteochondritis dissecans of the patella. (A) Sunrise radiograph reveals bone fragmentation at the central patella (arrow). (B) Axial fluid-­sensitive MR image shows the bone fragment (arrows) with adjacent high signal intensity between the fragment and the underlying osseous bed. The articular cartilage of the patella is irregular and thinned at the margins of the bone fragment.

A

B

Fig. 1.40  Osteochondritis dissecans of the talus: medial lesion. (A) Note the lucent lesion of the medial talar dome (arrows) as the osteochondral abnormality on the anteroposterior radiograph. (B) Corresponding coronal T1-­weighted fat-­suppressed MR arthrogram image shows high signal contrast undermining the undisplaced fragment (arrows), indicating instability.

combination are common causes of bone injury. The fracture configuration or pattern depends on the interaction of a particular load and a specific bone. Several types of fracture configurations are recognized (Table 1.2).

• Transverse fracture (mechanism: bending, or angular, forces in long bones; tensile, or traction, forces in short bones). A transverse fracture line, which occurs at a right angle to the shaft, is usually the result of a bending force (Fig. 1.43). Tensile failure of the bone takes place on its convex side (opposite the input force), with subsequent compressive failure on its concave side. Often, the cortex on the compressive side fails before the transverse fracture is complete, resulting in cortical splintering. Transverse fractures (i.e., avulsion fractures) can also be caused by traction forces at sites of tendon or ligament insertion into bone. • Oblique fracture (mechanism: combination of compression, bending, and torsion forces). Combined forces consisting of compression, torsion, and, to a lesser extent, bending typically lead to an oblique fracture. Such a fracture resembles a spiral fracture superficially; differentiation between the two is important, however, because steep oblique fractures have a higher frequency of nonunion, whereas spiral fractures usually heal uneventfully. In an oblique fracture, the ends of the bones are short and blunt without the vertical segment characteristic of a spiral fracture. • Oblique-­transverse fracture (mechanism: combination of axial compression and bending forces). This combination of forces can lead to several different types of fracture: if the compression forces are larger than the bending forces, an oblique fracture is produced; if the bending forces are sufficiently large, a purely transverse fracture is seen; and if both the compression and the bending forces are of sufficient magnitude, an oblique-­transverse fracture results

18

SECTION 1  Traumatic Disorders

*

Fig. 1.41  Osteochondritis dissecans of the capitulum of the humerus. (A) Anteroposterior radiograph in a Little League pitcher shows a rounded lucency at the central capitulum (arrow). (B) Corresponding T1-­ weighted MR image shows the lesion well (asterisk), although the overlying cartilage is not well assessed on this sequence. LOADING MODE Tension

Compression

Bending

Torsion

unless the fracture is distracted, no clear space is evident between the fragments (Fig. 1.45). • Diaphyseal impaction fracture (mechanism: axial compression force). In certain locations, such as the humerus, femur, and tibia, an axially applied load drives the diaphyseal bone, with its thick and rigid cortex, into the thin metaphyseal bone. Examples of this injury are a supracondylar fracture of the femur and a comminuted fracture of the tibial plateaus. • Comminuted fracture (mechanism: variable). Indirect or direct application of force, usually of high energy, leads to multiple osseous fragments of varying size.

DISLOCATIONS Terminology

Transverse

Oblique

Butterfly

Spiral

FRACTURE TYPE Fig. 1.42  Biomechanics of fractures in long tubular bones: basic types of load. (From Browner BD, Jupiter JB, Levine AM, Trafton PG, eds. Skeletal Trauma: Fractures, Dislocations, Ligamentous Injuries. Philadelphia: WB Saunders; 1992:101.)

(Fig. 1.44). These fractures tend to be shorter than the long oblique fractures described earlier. A butterfly fragment may be an added component of the oblique-­transverse fracture pattern. • Spiral fracture (mechanism: torsion force). Spiral fractures result from twisting or rotational forces, perhaps combined with axial compression. They are usually observed in the humerus, femur, and tibia. The fracture lines approximate an angle of 40 to 45 degrees, and the direction of the spiral denotes the direction of the rotational forces. In a spiral fracture, long, sharp, pointed ends with a long vertical segment connecting the fracture lines are characteristic, and

Dislocation is complete loss of contact between two osseous surfaces that normally articulate. Subluxation is a partial loss of this contact. Closed subluxation or dislocation exists when the skin and soft tissues remain intact over the injured joint; open dislocation or subluxation exists if associated soft tissue injury exposes the joint to the outside environment (Fig. 1.46). Subluxations and dislocations are usually caused by physical trauma, although they can also occur when congenital or acquired conditions produce muscle imbalance. Many dislocations and subluxations related to trauma are associated with fracture of a neighboring bone. Typical examples of such fractures are the Hill-­Sachs lesion of the humeral head after anterior dislocation of the glenohumeral joint and fractures of the acetabulum that accompany posterior dislocation of the hip. The terminology used to describe a dislocation or subluxation varies with the anatomic complexity of the involved joint. When the joint is composed of two bones, the joint injury derives its name from that joint (e.g., dislocation of the hip). When the joint comprises more than two bones, the dislocation is still named after the involved articulation if it affects the two major bones. If the smallest of the three bones is dislocated, the injury is named after that bone (e.g., dislocation of the patella). The term diastasis refers to abnormal separation of a joint that is normally only slightly movable (e.g., the symphysis pubis; Fig. 1.47).

CHAPTER 1  Physical Injury: Concepts and Terminology

19

TABLE 1.2  Biomechanics of Fractures in Long Tubular Bones Fracture Pattern

Mechanism of Injury

Location of Soft Tissue Hinge

Energy Load

Common Sites

Transverse

Bending

Concavity

Low

Diaphyses

Oblique

Compression, bending, and torsion

Concavity (often destroyed)

Moderate

Radius, ulna, tibia, fibula

Oblique-­transverse

Compression and bending

Concavity or side of butterfly

Moderate

Femur, tibia, humerus

Spiral

Torsion

Vertical segment

Low

Tibia, humerus

Diaphyseal impaction

Compression

Variable

Variable

Humerus, femur, tibia

Comminuted

Variable

Destroyed

High

Variable

From Gonza ER, Harrington IJ. Biomechanics of Musculoskeletal Injury. Baltimore: Williams & Wilkins; 1982:2.

Fig. 1.43  Long bone transverse fracture. A sagittal CT reformatted image of the lower extremity shows a transverse fracture of the femoral shaft with mild comminution in a patient struck by an automobile. The distal fragment is displaced full shaft-­width posteriorly, is angulated anteriorly, and shows overriding related to shortening. The distal fragment is interposed into the posterior musculature, and the neurovascular bundle (arrows) is deviated by the displaced bone.

Fig. 1.44  Long bone oblique fracture. Short oblique (tapping) fracture (arrows) of the midshaft of the ulna resulting from a direct blow.

TRAUMA TO SYNOVIAL JOINTS Traumatic Synovitis and Hemarthrosis KEY CONCEPTS 

Biomechanics Conventional classification schemes define four types of joint motion: gliding and angular movements, circumduction, and rotation. They may occur independently or, far more frequently, in various combinations. In any location, the precise characteristics of joint movement are governed principally by the shape of the articular surfaces (Table 1.3). In general, increasing freedom of movement is achieved at the expense of joint stability. Traumatic dislocation of a joint implies that the joint capsule and protective ligaments have been damaged. Alternatively, the capsule may be stripped from one of its osseous sites of attachment, or a stretched ligament may lead to avulsion of a bone fragment. Although trauma can produce dislocation of any articulation, the most commonly involved sites are the glenohumeral joint, elbow, ankle, hip, and interphalangeal joints.

• D  isplacement of fat pads about the joint indicates the presence of an effusion or mass within the articulation. • Effusion is easiest to appreciate at the knee and elbow. • The presence of fat within a traumatic effusion (lipohemarthrosis) strongly suggests the presence of a fracture. • The most common fracture associated with lipohemarthrosis in the knee is an impaction fracture of the lateral tibial plateau.

A joint effusion appearing within the first few hours after trauma is usually related to a hemarthrosis; nonbloody effusions generally appear 12 to 24 hours after injury. Bloody or nonbloody effusions occurring after trauma are associated with radiographic findings related to displacement of intraarticular fat pads and edema of extraarticular fat planes. Typical examples of these findings are widening of the suprapatellar pouch in cases of knee trauma and displacement of the fat pads about the distal end of the humerus

20

SECTION 1  Traumatic Disorders

*

* *

Fig. 1.45  Long bone spiral fracture. Spiral fracture (arrows) of the distal tibia shows the sharp pointed ends and criss-­crossing connected fracture lines typical of rotational injury. Note the focal soft tissue swelling related to fracture blisters (asterisks) adjacent to the fracture.

Fig. 1.47  Diastasis. Abnormal widening of the symphysis pubis (asterisk) related to pelvic trauma is apparent. A midline vertical fracture of the sacrum (arrows) is also present.

TABLE 1.3  Morphologic Classification of Synovial Joints Type of Joint Motion

Examples

Plane

Uniaxial

Intermetatarsal, intercarpal

Hinge

Uniaxial

Humeroulnar, interphalangeal

Pivot

Uniaxial

Proximal radioulnar, median atlantoaxial

Bicondylar

Uniaxial (minimal Knee, temporomandibular movement also in a second axis)

Ellipsoid

Biaxial

Radiocarpal, metacarpophalangeal

Sellar

Biaxial

First carpometacarpal, ankle, calcaneocuboid

Spheroidal

Triaxial

Hip, glenohumeral

Modified from Williams PL, Warwick R. Gray’s Anatomy. 36th ed. (British). Philadelphia: WB Saunders; 1980:430.

Lipohemarthrosis

Fig. 1.46  Open dislocation. Lateral dislocation of the tibiotalar joint is associated with a soft tissue defect medially with the distal tibia protruding through the skin. Note the punctate foci of soft tissue gas (arrows) at the lateral ankle.

(Fig. 1.48). Displacement and distortion of these fat planes indicates the presence of fluid or a mass in the joint; in the clinical setting of trauma, detection of these changes should encourage a thorough search for a subtle fracture or subluxation. CT scanning and MR imaging in cases of acute hemarthrosis document characteristic findings of a fluid level, or interface, between two components of the bloody joint effusion. The upper component is serum, and the lower component relates to the cellular components of blood; each component has different CT and MRI findings.

Radiographic examination using a horizontal beam technique may demonstrate a fat-­blood fluid level after injury to the joint. Most commonly, this finding is seen in a knee or glenohumeral joint, although it may also be noted in other joints. Bloody synovial fluid containing fat droplets and bone marrow spicules is highly suggestive of an intraarticular fracture. Infrequently, a hemorrhagic effusion containing fat may be observed in patients without fracture, probably related to significant cartilaginous, ligamentous, or articular fat pad injury. In the knee, subtle tibial plateau fractures are the most common source of the fat. Lipohemarthroses also can be detected with CT scanning or MR imaging. The most superior zone contains floating fat that is high signal on T1-­ weighted images and suppresses with spectral fat saturation. The central zone contains serum and an inferior zone contains dependent red blood cells (Fig. 1.49). A thin band of signal void, representing a chemical shift artifact, may be visible at the interface of fat and serum. Occasionally, MR images show only small bubbles of floating fat rather than a frank fatty layer (Fig. 1.50).

CHAPTER 1  Physical Injury: Concepts and Terminology

TRAUMA TO SYMPHYSES Traumatic insult to symphyses, including the symphysis pubis, manubriosternal joint, and intervertebral disc, is not infrequent. Subluxation (i.e., diastasis) or dislocation of the symphysis pubis leads to a break in the anterior pelvic ring and is commonly combined with a second injury causing pelvic disruption, such as fracture of the ilium or sacrum or diastasis of the sacroiliac joint. Subluxation or dislocation of the manubriosternal joint usually indicates significant trauma and may be seen after automobile collisions in which the chest strikes the steering

21

wheel. Atraumatic displacement at this site occasionally occurs owing to the exaggerated thoracic kyphosis associated with generalized osteoporosis, osteomalacia, renal osteodystrophy, or plasma cell myeloma. Violation of the cartilaginous endplate and subchondral bone plate of the vertebral body may allow intraosseous displacement of disc material (cartilaginous, or Schmorl, nodes). These nodes can result in an obvious compression fracture of the vertebral body or subtle injury at the discovertebral junction. Typically, the cranial disc protrudes into the vertebra, although both cranial and caudal discs may be involved. The intravertebral disc material may be associated with surrounding osseous compression and reactive bone formation. Another form of injury of the discovertebral junction occurs at the site of attachment of the annulus fibrosus to the rim of the vertebral body. In a developing skeleton, this union is far more solid than that between the cartilage in the vertebral rim and the ossified portion of the vertebral body. Thus, in a young patient, injury with prolapse of the contiguous intervertebral disc can lead to displacement of the ossified portion of the vertebral rim as a result of separation of the osteocartilaginous junction between the rim and the remaining vertebral body, forming a limbus vertebral fragment (Fig. 1.51). Injuries of the intervertebral disc may be combined with fractures of the vertebral bodies and posterior elements, leading to spinal instability. Spinal trauma is discussed in further detail in Chapter 53.

TRAUMA TO SYNCHONDROSES (GROWTH PLATES) Mechanism and Classification KEY CONCEPTS 

Fig. 1.48  Traumatic effusion. Displacement of the anterior and posterior fat pads about the elbow (arrows) after trauma usually indicates intraarticular fluid or blood. The posterior fat pad is more specific for effusion, as it is normally not visible, whereas thin anterior fat pads can be seen in the absence of intraarticular fluid. Note “sail” appearance of abnormally elevated anterior fat pads and the fracture of the neck of the radius.

• T he traditional Salter-­Harris classification divides fractures involving a physeal plate into five categories. • The Salter-­Harris II fracture, which involves the physeal plate and one side of the metaphysis, is the most common type. • Type IV and type V injuries can damage the physis sufficiently to interfere with normal skeletal growth. • MR imaging is the most accurate method for assessing premature physeal fusion.

* *

A

B Fig. 1.49  Lipohemarthrosis. (A) On a cross-table ­ lateral radiograph, a straight radiodense fluid line (arrows) at a fat-blood ­ interface can be a helpful clue to the underlying but subtle tibial plateau fracture (arrowhead). (B) Axial fluid-sensitive ­ MR image shows a lipohemarthrosis characterized by a superior layer of suppressed fat (white asterisk) followed by a layer of serum (black asterisk) and an inferior layer of cellular components of blood.

22

SECTION 1  Traumatic Disorders

A

Fig. 1.50  Lipohemarthrosis. On a coronal T1-­weighted MR image of the knee, several small globules of fat (arrows) are seen in the suprapatellar pouch, related to an osteochondral injury from a patellar dislocation.

Fig. 1.51  Schmorl nodes and limbus vertebra. The lateral radiograph reveals the typical appearance of Schmorl nodes (arrows). These cartilaginous nodes are generally well defined, circular or lobulated, close to the discovertebral junction, and accompanied by a rim of bone sclerosis. A limbus fragment (arrowhead) is seen at L4 related to a triangular displaced portion of the anterior ring apophysis.

The growth plate of an immature skeleton is especially vulnerable to injury; approximately 6% to 15% of fractures of the tubular bones of children younger than 16 years involve the growth plate and neighboring bone. Forces that produce ligamentous tear or joint dislocation in adults may lead to growth plate injury in children and adolescents because the joint capsule and ligamentous structures are approximately two to five times stronger than the cartilaginous plate. Four types of stress may produce growth plate injury: shearing or avulsive forces

C

B

D

E

Fig. 1.52  Growth plate injury: classification system. (A) Type I. A split in the growth plate occurs through the zone of hypertrophic cells. The periosteum is intact. (B) Type II. The growth plate is split, and the fracture enters the metaphyseal bone and creates a triangular fragment. The periosteum about the fragment is intact, whereas that on the opposite side may be torn. (C) Type III. A vertical fracture line extends through the epiphysis to enter the growth plate. It then extends transversely across the hypertrophic zone of the plate. (D) Type IV. A fracture extends across the epiphysis, growth plate, and metaphysis. Note the incongruity of the articular surface and violation of the germinal cells of the growth plate. (E) Type V. Compression of a portion of the growth plate may not be associated with immediate radiographic abnormalities.

account for approximately 80% of injuries; splitting or compressive stresses account for the remainder. Sites most typically affected are the phalanges; the distal tibial, fibular, ulnar, and radial growth plates; and the proximal humeral growth plate. Growth plate injuries may occur acutely as a result of a single episode of trauma or chronically as a consequence of prolonged stress, particularly that associated with athletics. Associated metaphyseal failure is more common in sites where the metaphysis is not protected from compression stress. Metaphyseal fragility is also accentuated by any condition associated with osseous weakening, such as hyperparathyroidism or the hypervascularity of the normal growth spurt. Avulsion injury to the growth plate is commonly observed at sites of apophyses. Examples include the lesser trochanter and the medial epicondyle of the distal portion of the humerus. The vulnerability of any specific apophysis to avulsion injury is governed by its development and maturation and depends on the time of appearance and fusion of the apophysis. Although several classification systems of growth plate injuries have been proposed, that of Salter and Harris is accepted most widely. This system originally separated physeal injuries into five types according to their radiographic appearance (Fig. 1.52). The Salter-­Harris classification has subsequently been expanded to include nine types of injuries, but the initial scheme remains more widely used in clinical practice. Type I (6%). A type I injury represents pure epiphyseal separation, with the fracture isolated to the growth plate itself. This injury has a favorable prognosis and most frequently occurs in children younger than 5 years, at a time when the growth plate is wide. The proximal humerus and femur and the distal humerus are most commonly

CHAPTER 1  Physical Injury: Concepts and Terminology

23

* A A

B

Fig. 1.53  Growth plate injury: Salter I. (A) Lateral radiograph of the right wrist in a child following a fall on an outstretched hand shows widening of the distal radial physis (arrow) and displacement of the pronator quadratus fat pad (asterisk). (B) Comparison to the normal contralateral wrist accentuates these abnormalities.

Fig. 1.54  Growth plate injury: Salter II. Observe the widening of the ulnar side of the growth plates at the bases of the second and third proximal phalanges and the small metaphyseal fracture fragments (arrows).

affected. Radiographic recognition of this injury is not difficult when the growth plate is widened and the epiphysis is displaced. If spontaneous reduction of the separation takes place, the radiographic diagnosis is challenging. Helpful signs are soft tissue swelling, particularly when centered at the physeal level, and minimal widening or irregularity of the growth plate. Comparison radiographs of the opposite (uninvolved) side aid in detecting subtle growth plate changes (Fig. 1.53). MR images show abnormal fluid accumulation within the damaged physis and adjacent marrow and soft tissue edema. Type II (75%). A type II injury, the most common type of growth plate injury, results from a shearing or avulsion force that splits the growth plate for a variable distance before entering the metaphysis and separating a small fragment of the metaphyseal bone—the Thurston Holland or corner sign (Fig. 1.54).

B

Fig. 1.55  Growth plate injury: Salter II. Coronal T1-­weighted (A) and fluid-­sensitive (B) MR images of the ankle show widening of the medial side of the distal tibial physis and a metaphyseal fracture fragment at the lateral side. The periosteum remains intact (arrows) overlying the metaphyseal fracture in such injuries, allowing easy reduction. There is also a fracture at the tip of the fibula.

The periosteum on the side of the metaphyseal fracture remains intact, but that on the opposite side is disrupted in conjunction with growth plate separation (Fig. 1.55). Because of the intact periosteum, the fracture fragment is usually easily reduced. The usual age at injury is 10 to 16 years, and common sites of involvement are the distal ends of the radius, tibia, fibula, femur, and ulna, in order of decreasing frequency. The prognosis after this injury is generally good because of the absence of subsequent growth disturbance. Type III (8%). In a type III injury, the fracture line extends vertically through the epiphysis to the growth plate and then horizontally across the growth plate itself, usually on one side or the other. Type III injuries are especially common in children between the ages of 10 and 15 years and most frequent in the medial or lateral distal tibia, with less frequent involvement of the proximal tibia and distal femur. Radiography usually allows prompt recognition of the fracture, although CT imaging is widely employed in such injuries to evaluate congruity of the articular surface. Displacement is generally minimal, and growth arrest and deformities are rare. Type IV (10%). A vertically oriented splitting force can produce a fracture that extends across the epiphysis, the growth plate, and the metaphysis to create a fragment that consists of a portion of both the epiphysis and the metaphysis (Fig. 1.56). This injury is most common at the distal humerus and tibia. The radiographic diagnosis is facilitated by the presence of considerable metaphyseal and epiphyseal bone within the fragment. However, in younger children in whom the epiphysis is unossified or only partially ossified, the injury may be mistaken for a type II fracture. A type IV injury often requires open reduction and careful realignment to prevent subsequent growth arrest and joint deformity. Type V (1%). A crushing or compressive injury to the end of a tubular bone can lead to a rare type V growth plate fracture. Injury to the vascular supply of the plate occurs without any immediate radiographic signs, though MR imaging can show marrow edema in such injuries. This injury leads to focal areas of diminished or absent bony growth, which, in the presence of normal development in adjacent areas, can lead to angular deformity. Premature osseous fusion of the injured portion of the plate may be identified, particularly when MR imaging is used (see later discussion). This injury is more prominent in older children and adolescents, particularly those 12 to 16 years old. The physes of the distal portions of

24

SECTION 1  Traumatic Disorders

*

A

B

Fig. 1.56  Growth plate injury: Salter IV. Coronal T1-­weighted (A) and fluid-­sensitive (B) MR images of the left knee show a fracture line (arrows) extending vertically through the epiphysis and metaphysis with surrounding marrow edema. Note the low-­grade injury of the medial collateral ligament (asterisk).

the femur and tibia and proximal portion of the tibia are usually affected. Type VI. An injury (e.g., physical trauma, burn, infection) to the perichondrium can produce reactive bone formation external to the growth plate. The resultant osseous bridge may act as a barrier to growth of the adjacent portion of the plate, leading to progressive osseous angulation. Type VII. This relatively common type of injury consists of a fracture limited to an epiphysis in the absence of involvement of the growth plate or metaphysis. Transchondral fractures and osteochondritis dissecans are examples of type VII injuries. Type VIII. This injury affects metaphyseal growth and remodeling mechanisms in an immature skeleton, primarily as a result of effects on the blood supply. Type IX. An injury to the periosteum of the diaphysis may, in rare circumstances, result in disruption of normal diaphyseal growth and remodeling. Segmental comminuted fractures, wringer injuries, and severe burns are examples of the type of trauma that can lead to this kind of injury. Some degree of growth deformity develops in approximately 25% to 30% of patients with growth plate injuries. In up to 10% of patients, this deformity is significant. The prognosis is related to the age of the patient, the anatomy of the vascular supply to the region, the type of injury, and the immediacy and adequacy of the reduction. In general, the younger the patient at the time of injury, the poorer is the prognosis for residual deformity. Types I, II, and III injuries have a relatively good prognosis, whereas type IV injuries carry a guarded prognosis and types V and VI injuries have a poor prognosis. Common radiographic residua of growth disturbances related to previous physeal injury include transphyseal linear ossific striations and growth recovery lines that are modified in appearance according to the sites of arrested physeal growth. Significant sequelae include growth impairment, premature growth plate fusion, epiphyseal malposition and rotation, and osteonecrosis. Premature partial arrest of growth is produced by a bridge of bone, or bone bar, that extends from the metaphysis to the epiphysis across a portion of the physis (Fig. 1.57). Continued growth of the remaining portion of the physis results in increasing angular deformity. Type IV

injuries characteristically lead to closure of a portion of the physis; type V injuries may result in premature closure of the entire growth plate. MR imaging allows accurate assessment of the extent of the initial injury as well as the extent of physeal arrest (Fig. 1.58).

Specific Injuries Slipped Capital Femoral Epiphysis

Slippage of the capital femoral epiphysis is typically observed between the ages of 10 and 17 years in boys and 8 and 15 years in girls. Boys are affected more frequently than girls, and Black patients are affected more frequently than Whites; overweight children have an especially high occurrence. About 20% to 35% of patients with slipped capital femoral epiphysis have bilateral involvement, which is more frequent in girls. A variety of contributing factors have been emphasized in the pathogenesis of this injury: • Trauma. Although trauma is an important precipitating event in infants and young children, it appears to be a minor factor in older children. Fewer than 50% of patients have a history of significant injury. • Adolescent growth spurt. The association between slipped capital femoral epiphysis and the adolescent growth spurt involves the relatively wide physis during this period and its change in configuration from a horizontal to an oblique plane, with increased shearing stress. • Hormonal influences. The list of endocrine diseases associated with this femoral disorder includes hypothyroidism, hypoestrogenic states, acromegaly, gigantism, cryptorchidism, and pituitary and parathyroid tumors. Despite these observations, no clear evidence exists that levels of growth hormone are abnormal in patients with slipped capital femoral epiphysis. • Weight and activity. One of the most striking characteristics of patients with slipped capital femoral epiphysis is a tendency to be overweight. Obesity increases the shearing stress on the growth plate and can lead to slippage, even during usual activity. The propensity for epiphyseal slippage appears to be greater in physically active adolescents than in those who are less active. By convention, reference is made to the movement of the femoral head with respect to the shaft in cases of slipped capital femoral

CHAPTER 1  Physical Injury: Concepts and Terminology epiphysis. The femoral head is usually located in a posterior and medial direction with respect to the remainder of the femur; other directions can be seen. Radiographic analysis remains essential to the diagnosis of slipped capital femoral epiphysis. Both anteroposterior and frog-­leg or lateral projections are mandatory; abnormalities on the frontal projection alone may be subtle, even in the presence of significant epiphyseal displacement. Comparison radiographs of the opposite side can be very useful. On the anteroposterior view, osteoporosis of both the femoral head and the femoral neck is common. The margin of the metaphysis may seem blurred or indistinct, and the growth plate may appear widened. A tangential line along the lateral border of the femoral neck may fail to intersect any part of the epiphysis or may cross only a small portion of it (Fig. 1.59). MR imaging is more sensitive for the early diagnosis of this condition, demonstrating physeal widening, physeal fluid, and marrow edema prior to frank slippage, when routine radiographs are still normal. In chronic stages of slipped capital femoral epiphysis, routine radiography shows reactive bone formation along the medial and posterior portions of the femoral neck, a buttressing phenomenon similar to that which occurs in degenerative joint disease. Sequelae of slipped capital femoral epiphysis include severe varus deformity, shortening and broadening of the femoral neck, osteonecrosis, chondrolysis, and premature degenerative joint disease. Osteonecrosis has been described in 6% to 15% of patients with this disorder. Chondrolysis may be observed in as many as 25% of patients with epiphyseal slippage and is more frequent in Black than White patients, in females than males, and in persons with severe slippage. It usually occurs within 1 year of the slippage and may be evident in untreated or treated persons. Radiographs outline osteoporosis and concentric narrowing of the interosseous space, followed by eburnation and osteophytosis of apposing osseous margins. Some joint space recovery may be seen after a period of months in approximately one-­third of patients. Its cause is unknown.

A

25

Growth Plate Injuries About the Knee Growth plate trauma in the distal portion of the femur may be related, in many cases, to birth or to athletic or automobile injuries. Examples include the wagon-­wheel fracture resulting when children catch their legs between the spokes of wagon or bicycle wheels and the clipping injury of adolescent football players. Salter-­Harris types II and III injuries are especially common. Injury to the proximal tibial physis is relatively rare.

Fig. 1.58  Growth plate injury: physeal bar. Sagittal gradient echo MR image demonstrates an ossific bridge (arrow) involving the posterior aspect of the distal femoral physis resulting from a previous Salter-­ Harris IV injury to this physis.

B

Fig. 1.57  Growth plate injury: premature partial arrest of growth from previous fracture. (A) Lateral radiograph at the time of initial injury shows a growth plate fracture with anterior physeal widening and a posterior metaphyseal component. (B) Sagittal fluid-­sensitive MR image shows partial arrest of the growth plate with edema and an angular deformity with tenting (arrow) of the physis. Growth arrest is uncommon following Salter II injuries but can take place when the injury is severe or remains unreduced for an extended period.

26

SECTION 1  Traumatic Disorders

A

B Fig. 1.59  Slipped capital femoral epiphysis: radiographic abnormalities. (A) Anteroposterior radiograph of the pelvis shows subtle findings at the right femoral physis (arrow), including mild osteoporosis of the proximal portion of the femur, an indistinct metaphyseal margin, and failure of the lateral femoral neck line to intersect the physis. (B) In the frog-­leg view of the right hip, the degree of posterior slippage is readily apparent. Note the widened growth plate.

*

A

B Fig. 1.60  Growth plate injury: ankle, juvenile fracture of Tillaux. Frontal (A) and lateral (B) radiographs show a subtle fracture (arrow) involving the anterolateral portion of the epiphysis with widening of the lateral physis. It represents a Salter-­Harris type III injury in a partially fused physis. Note the effusion (asterisk) on the lateral radiograph.

Growth Plate Injuries About the Ankle Injuries to the growth plate in the distal portion of the tibia are common. Type II injury is most frequent, followed in order of decreasing frequency by types III, IV, and I lesions. Of physeal injuries at this site, 10% to 12% are followed by growth disturbance. Adolescent fractures at the partially fused distal tibia epiphysis represent approximately 5% to 10% of all injuries in this location. The primary mechanism of injury appears to be external rotation of the foot, although plantar flexion has also been suggested. The resulting injury has several variations, including a two-­plane fracture pattern (Tillaux or Kleiger fracture) that involves only the epiphysis, and a three-­plane fracture pattern in which an additional metaphyseal fracture is present. The juvenile fracture of Tillaux classically involves the lateral portion of the distal tibial epiphysis and conforms to a Salter-­Harris type

III injury because of lateral extension of the fracture through the open physis (Fig. 1.60) A triplane fracture resembles two different types of Salter-­Harris injury (a type III lesion on the anteroposterior, radiograph and a type II lesion on the lateral radiograph), although, in reality, it is a variation of a type IV injury pattern. Two, three, or four fragments may result, with two fragments being most common. Because of the complexity of the injury, CT imaging is an excellent technique for delineating the site and extent of involvement (Fig. 1.61).

Growth Plate Injuries About the Shoulder Disruption of the epiphysis and physis in the proximal portion of the humerus is relatively infrequent. Its occurrence in adolescent baseball pitchers as an epiphysiolysis is termed Little League shoulder syndrome.

CHAPTER 1  Physical Injury: Concepts and Terminology

A

27

B

Fig. 1.61  Growth plate injury: triplane ankle fracture. Coronal (A) and sagittal (B) reformatted CT images show an injury that has the appearance of a type III lesion on coronal image (black arrows). On the sagittal image, a type II lesion is apparent. Note the slight posterior displacement of the distal tibial epiphysis and gap at the articular surface (white arrows).

Separation of the proximal humeral epiphysis may result from an injury at birth, particularly during a difficult delivery. The epiphysis of the inner margin of the clavicle ossifies at approximately 18 to 20 years of age and, with closure of the growth plate, merges with the shaft of the clavicle at approximately 25 years of age. Injury to the medial end of the clavicle in an immature skeleton can produce an epiphyseal separation that may be misdiagnosed as sternoclavicular joint dislocation. Physeal injuries about the shoulder may account for pseudodislocations of the acromioclavicular joint in children. Such injuries include displacement of the distal portion of the clavicle from its periosteal sleeve and avulsion of the epiphysis of the coracoid process.

Growth Plate Injuries About the Elbow Accurate diagnosis of elbow injury in an immature skeleton is complicated by the presence of multiple ossification centers. A mnemonic that can be used to remember the sequence of appearance of some of these ossification centers is CRITOL: C, capitulum (1 year); R, radial head (3 to 6 years); I, internal or medial epicondyle (5 to 7 years); and T, trochlea (9 to 10 years); O, olecranon center of the ulna (6 to 10 years); and L, the final center to appear, lateral epicondyle (9 to 13 years). Normally, the metaphysis of the distal portion of the humerus and the capitulum are anteverted about 140 degrees relative to the shaft of the humerus. A line drawn along the anterior cortex of the humerus on a lateral radiograph—the anterior humeral line—should intersect the middle third of the capitular ossification center. In the presence of supracondylar fractures of the humerus (the most common fracture about the elbow in children), posterior displacement or angulation of the distal fragment allows the anterior humeral line to pass through the anterior third of the ossification center or even anterior to the capitulum (Fig. 1.62). Because of absent or incomplete ossification of the developing centers about the elbow in infants and children, complete assessment of injuries may not be possible with conventional radiography. Fracture of the lateral condyle occurs frequently and represents a Salter-­Harris type IV injury. The fracture line splits the epiphysis and separates a portion of the adjacent metaphysis and the capitulum.

Fig. 1.62  Elbow injury: supracondylar fracture of the humerus. On a lateral radiograph, elevation of the intracapsular fat pads and a subtle supracondylar fracture line (arrow) are seen. The plane of the anterior cortex of the humerus intersects the anterior third of the capitular ossification center, indicative of minimal posterior displacement at the fracture site.

Separation of the medial epicondyle ossification center is a result of stress placed on the flexor pronator tendon that attaches to this site; this represents approximately 10% of all elbow injuries. In some instances, the epicondyle may become entrapped within the joint (Fig. 1.63). In this situation, the displaced epicondylar ossification center can simulate a normal trochlear center. However, the appearance of a trochlear center without a medial epicondylar center is inconsistent with the normal sequence of ossification about the distal portion of the humerus.

28

SECTION 1  Traumatic Disorders

A

B Fig. 1.63  Intraarticular displacement of the medial epicondyle of the humerus. (A) The lateral radiograph shows a large effusion. (B) The anteroposterior radiograph shows swelling and medial joint widening. Note the intraarticular position of the avulsed medial epicondyle (arrows).

A

B Fig. 1.64  Growth plate injury of the distal portion of the humerus. Although an anteroposterior radiograph (A) appears to delineate dislocation of the elbow with medial displacement of the ulna and radius, a lateral radiograph (B) identifies the metaphyseal ossific flake (arrow) and normal alignment of the radius and capitulum, findings indicating that separation of the distal humeral growth plate has occurred.

Separation, with or without fracture, of the entire distal humeral epiphysis may be mistaken for fracture of the lateral humeral condyle or dislocation of the elbow (Fig. 1.64). In most cases, a Salter-­Harris type I or II injury is present. Radiographs usually reveal normal alignment of the radial shaft and capitellar ossification center, normal alignment of the radius and ulna, and malalignment of these bones with the humerus.

Other Growth Plate Injuries The relative frequency of some physeal injuries is indicated in Table 1.4.

Chronic Stress Injuries A variety of musculoskeletal manifestations related to the chronic application of stress can occur in professional and recreational athletes. Growth plates in the distal portions of the radius and ulna, proximal

portion of the humerus, distal aspect of the femur, and distal end of the tibia are affected most commonly. The general radiographic abnormalities accompanying the chronic stress are similar in each of these locations. Part or all of the physis appears widened and irregular, with varying degrees of accompanying sclerosis in the adjacent metaphysis (Fig. 1.65). Superficially, these radiographic abnormalities resemble those occurring in rickets, hypophosphatasia, or metaphyseal dysplasia. In some cases, a unilateral or asymmetrical distribution of changes provides an important diagnostic clue. MR imaging shows physeal widening, intraphyseal fluid, and adjacent marrow edema in such cases. During skeletal maturation, focal zones of periphyseal edema may be seen, particularly about the knee joint, but the relationship of such regions of edema with clinical symptoms is unclear. It is postulated that the edema may correspond to regions of imminent physeal closure (Fig. 1.66).

CHAPTER 1  Physical Injury: Concepts and Terminology

29

TABLE 1.4  Relative Frequency of Physeal

Injuries

Frequency (%)

Typical Agea (yr)

Distal portion of radius

49.9

9–14

Distal portion of humerusb

16.7

Birth–5c

Distal portion of tibia

11.0

Age Range (yr)

6d

3–10

12

8–13

Distal portion of fibula

9.1

Distal portion of ulna

5.7

Proximal portion of radius

4.2

9–10

8–13

Proximal portion of humerus

3.1

14–15

10–16

Distal portion of femur

1.2

11–12

10–15

Proximal portion of ulna

0.7

Proximal portion of tibia

0.5

13–15

Proximal portion of femur

0.1

2–6

Other

0.8

12–15 aGirls,

because of earlier skeletal maturity and advanced skeletal age relative to boys, have injuries at an average age 1 to 2 years younger than boys. bThe majority of these fractures are lateral condyle lesions. cDistal humeral fracture-­separations. dLateral humeral condyle fracture-­separations. From Shapiro F. Epiphyseal growth plate fracture-­separations: a pathophysiologic approach. Orthopedics. 1982;5(6):720–736.

Fig. 1.66  Focal periphyseal edema. Coronal fluid-­sensitive MR image of the knee in an active 13-­year-­old girl shows focal edema (arrows) adjacent to the distal femoral physis.

TRAUMA TO SUPPORTING STRUCTURES, SYNDESMOSES, AND ENTHESES Tendon and Ligament Injury and Healing In most regions of the body, tendons are subjected to tensile loading. Acute failure of a tendon may occur at the myotendinous junction between muscle and tendon or at the osseous site of tendinous attachment; the latter sometimes results in an avulsion fracture (e.g., mallet finger). Failure within the tendon itself is rare unless preexisting tendon degeneration is present. Tendon tears or ruptures can appear at virtually any site in the body. Typical examples are injuries to the tendons in the hands and feet and to the patellar, triceps, peroneal, quadriceps, rotator cuff, and Achilles tendons. In many cases, a significant traumatic event initiates the tendon injury, although spontaneous rupture has been documented, especially in patients with rheumatoid arthritis and systemic lupus erythematosus and in those receiving local corticosteroid injections. Ligament tears or ruptures are also widely distributed and are particularly noteworthy about the wrist, ankle, elbow, and knee. In these cases, radiography may require supplementation with stress radiography. MR imaging and ultrasonography are the modalities of choice for tendon and ligament evaluation.

Avulsion Injuries KEY CONCEPTS  • A  vulsion fractures occur due to traction injury of bone at ligament and tendon insertions. • In the immature skeleton, the relative weakness of the physeal plates compared with the tendon results in a high frequency of apophyseal avulsion fractures. • The pelvic apophyses are particularly vulnerable to avulsion injury. • Apophyseal avulsions can heal with abundant heterotopic ossification, simulating malignancy.

Fig. 1.65  Growth plate injury: chronic stress involving the olecranon in a pitcher. Note the physeal widening and irregularity of the physis (arrow).

Abnormal tensile stress on ligaments and tendons caused by a single violent injury or repetitive injuries may lead to characteristic avulsions at their sites of attachment to bone. For example, avulsion of a portion

30

SECTION 1  Traumatic Disorders

A

B

Fig. 1.67  Avulsion injury: cruciate ligament avulsion. (A) Observe the posterior bony fracture fragment (arrow) associated with a lipohemarthrosis in this cross-­table lateral radiograph. (B) Sagittal CT imaging reconstruction shows a posterior tibial avulsion fracture (arrow) related to the site of attachment of the posterior cruciate ligament.

of the calcaneus, patella, or ulnar olecranon may accompany an exaggerated pull of the Achilles, quadriceps, or triceps tendon, respectively. Avulsion injuries of the proximal portion of the humerus, which generally occur during dislocation of the glenohumeral joint, may involve either of the tuberosities related to tendinous traction by the various components of the rotator cuff. Avulsion fractures frequently accompany ligamentous, tendinous, and other injuries about the knee (Fig. 1.67). The size of the avulsed fragment is quite variable; in adults, only small osseous flecks may be pulled from the parent bone, whereas in children or adolescents, an entire apophysis may undergo avulsion. Because tendinous, ligamentous, and capsular tissue is much stronger than physeal cartilage, forces that might produce a ligamentous or tendinous injury or dislocation in an adult may lead to apophyseal avulsion in a child. In an older child or adolescent with more extensive ossification of the skeleton, the size of the displaced bone fragment may be larger and, thus, facilitate the proper diagnosis and interpretation of the injury. Apophyseal avulsions can occur at many different skeletal sites, although those of the pelvis and hip are encountered most frequently. Several avulsion injuries about the pelvis and hip in young athletes have characteristic radiographic features, including avulsion injuries of the anterior superior iliac spine, which occur in sprinters as a result of stress at the origin of the tensor fasciae or the sartorius muscle; avulsion injuries of the anterior inferior iliac spine, which relate to stress at the origins of the straight and reflected heads of the rectus femoris muscle (Fig. 1.68); avulsion injuries of the apophysis of the lesser trochanter caused by stress by the psoas major muscle during strenuous hip flexion; avulsion injuries of the apophysis of the ischial tuberosity resulting from violent contraction of the hamstring muscles, often occurring in soccer players and hurdlers; avulsion injuries of the greater trochanter of the femur produced by gluteal muscle contraction; avulsion of the apophysis of the iliac crest secondary to severe contraction of the abdominal muscles associated with abrupt directional change during running; and avulsion injuries near the symphysis pubis related to the adductor muscle (adductor longus, adductor brevis, gracilis) insertion sites. Follow-­up radiographs may show considerable new bone formation or healing with incorporation of the fragment into the parent bone that, in some cases, is associated with bizarre skeletal overgrowth (Fig. 1.69).

Fig. 1.68  Avulsion injury: pelvis. The avulsed fragment (arrow) at the anterior inferior iliac spine is related to stress at the origin of the rectus femoris muscle.

Diastasis The term diastasis implies a separation of normally joined bony elements; it is frequently applied to syndesmoses and, specifically, to injuries of the ligaments that connect the distal tibia and fibula. Complete or partial diastasis can occur depending on the extent of damage to the tibiofibular and interosseous ligaments. Radiographs usually reveal abnormal separation of the tibia and fibula in which the space between the medial cortex of the fibula and the posterior edge of the peroneal groove is greater than 5.0 to 5.5 mm on an anteroposterior radiograph (Fig. 1.70). The diastasis is accentuated with weight-­bearing stress radiography. Soft tissue ossification and even ankylosis between the tibia and the fibula may subsequently occur. The term diastasis is likewise applied to separation of apposing bone surfaces about symphyses (e.g., symphysis pubis).

CHAPTER 1  Physical Injury: Concepts and Terminology

31

*

Fig. 1.69  Avulsion injury: pelvis. Bulky bone formation is seen adjacent to the left ischial tuberosity (arrows) related to a chronic avulsion fracture of the ischial apophysis related to stress at the origin of the hamstring muscles.

Fig. 1.70  Diastasis at tibiofibular syndesmosis. There is widening of the space between the distal tibia and fibula (asterisk) related to a syndesmotic injury. Note the fracture of the medial malleolus and high fibular fracture (arrows).

TRAUMA TO SKELETAL MUSCLE Trauma to skeletal muscle may result from any type of accidental injury, but it is encountered most often in the setting of physical exertion, particularly athletic endeavors. Intense and prolonged eccentric exercise, in which the muscle lengthens as it contracts, produces the common muscle strain injury, but this mechanism is only one of a spectrum of injuries that can affect skeletal muscle. A brief overview of common muscle injuries is presented next: the entire spectrum of muscle injuries and their related imaging findings are discussed in detail in Chapter 26.

Direct Muscle Injury Muscle lacerations result from direct penetrating injury, whereas a contusion results from a direct blow compressing the muscle without any break in the overlying skin. Of these, contusions are more common, typically related to impact during sports or following a fall. The gastrocnemius and quadriceps muscles are typical sites of involvement. Injury results in capillary rupture, hematoma formation, and interstitial hemorrhage. Contusions vary in severity, and the muscle is still able to function, even in severe cases.

Indirect Muscle Injury Indirect injuries to muscle occur from overzealous use during physical exercise. Skeletal muscles transmit their contractile forces to adjacent structures through tendinous attachments. The junctional region between muscle fibers and the tendinous attachment, termed the myotendinous or musculotendinous junction, is the typical site of muscle strain injury (Fig. 1.71). Certain muscles are prone to strain injury and show several typical characteristics. First, such muscles commonly perform eccentric actions. Second, the muscles commonly are long and act across two joints. Third, muscles that have a higher proportion of type II (fast-­twitch) fibers and are involved in activities requiring sudden acceleration or deceleration are typically affected. Fourth, the precise architecture of the muscle alters the risk for strain injury. Pennate muscles, in which the fibers insert at an angle to the tendon, are at higher risk than parallel muscles, in which the fibers converge at the tendon at the end of the muscle.

Fig. 1.71  Skeletal muscle injury: myotendinous strain. Axial fluid-­ sensitive MR image reveals increased signal intensity of the medial gastrocnemius muscle and thickening and edema of its superficial tendon (arrows).

Rhabdomyolysis Rhabdomyolysis is a relatively common syndrome of muscle injury in which muscle necrosis alters the integrity of the cell membrane and allows cellular contents to escape into the general circulation. Causative factors include burns, crush injuries, prolonged muscle compression, drug overdose, and extremely intense exercise, especially in hot climates. Rhabdomyolysis is a common complication of inadequately managed compartment syndrome. Compartment syndrome is characterized by elevated pressure within an anatomically confined space that leads to irreversible damage to its contents (i.e., muscle and neurovascular components). Common causes are trauma with hemorrhage, fractures, increased capillary permeability after thermal burns, and intense physical activity.

32

SECTION 1  Traumatic Disorders

TRAUMATIC ABUSE OF CHILDREN (NONACCIDENTAL TRAUMA) KEY CONCEPTS  • A  single-­view “babygram” image is not an adequate screening survey for child abuse. • The most specific skeletal findings in child abuse are metaphyseal corner fractures and fractures of the posteromedial ribs. • Comminuted skull fractures and multiple fractures of the long bones at varying stages of healing also suggest nonaccidental trauma. • Child abuse can be challenging to differentiate from some forms of osteogenesis imperfecta.

A

Skeletal abnormalities can be detected in 50% to 70% of cases of child abuse; their detection plays a critical role in diagnosis of nonaccidental trauma. The proper workup of a child suspected of having been physically abused includes a radiographic survey of all of the long bones, the pelvis, the spine, the ribs, and the skull. A single radiograph of the entire skeleton is diagnostically inadequate. Skeletal injuries that strongly suggest child abuse include metaphyseal corner fractures of the long bones, posteromedial rib fractures, and multiple skull fractures. Those that are bilateral and cross sutures are particularly suggestive of child abuse (Fig. 1.72). Other “unusual” fractures—such as those of the sternum, lateral aspect of the clavicle, scapula, and vertebral bodies, and posterior osseous elements caused by squeezing the thoracic cage—are highly suggestive of nonaccidental trauma.

B

C Fig. 1.72  Abused child syndrome: radiographic abnormalities. (A) Three-dimensional ­ surface rendering of the cranium shows multiple fractures (arrows) involving the frontal bones bilaterally. (B) Metaphyseal irregularity and corner fractures (arrowhead) are more immediate radiographic clues to child abuse. (C) Rib fractures (arrows) are frequent in an abused child. (Courtesy Jerry R. Dwek, MD, San Diego, CA.)

CHAPTER 1  Physical Injury: Concepts and Terminology Less specific findings include single or multiple fractures at other sites: in order of decreasing frequency, at the humerus, femur, tibia, and small bones of the hand and foot. Other findings include overabundant callus formation, bilateral acute fractures, and fractures in the lower extremities in infants and young children who are not walking, though these features are less specific. Scintigraphy can be a useful adjunct to identify multifocal fractures, though its utility at the metaphyseal region is limited due to normal intense growth plate uptake. The most distinctive skeletal injuries related to child abuse are corner fractures at the metaphyses of the long bones. Diaphyseal or metaphyseal fractures—most commonly, transverse—can be seen in various stages of healing. Traumatic insult to the child’s skeleton can produce elevation of the periosteal membrane, which is loosely attached to the diaphysis of tubular bones. Although the resultant periostitis is a delayed radiographic finding, it should be emphasized that firm attachment of the periosteal membrane to the metaphyses of the tubular bones can lead to an immediate radiographic abnormality— single or multiple metaphyseal bone fragments consisting of a disc of bone and calcified cartilage. These metaphyseal infractions, which are highly specific for abuse, may be quite subtle and require multiple projections for adequate visualization. Reactive bone formation with sclerosis can be a prominent change associated with periostitis and metaphyseal fracture. Physeal injuries also occur. Subperiosteal bone formation may be apparent between 7 and 14 days after diaphyseal, metaphyseal, or physeal injury. Late skeletal findings include metaphyseal cupping, growth disturbances, subluxation, and diaphyseal widening caused by subperiosteal apposition. Extensive extraosseous alterations also may be present, including myositis, pancreatitis, hepatic and renal injuries, ocular lesions such as retinal detachment, and intracranial and subdural hematomas. Cranial and visceral abnormalities are typically assessed using CT imaging. Disorders or conditions that must be differentiated from nonaccidental trauma are the normal periostitis of infancy, metaphyseal changes of normal growth, metaphyseal fraying related to rickets, osteogenesis imperfecta, Menkes syndrome (kinky hair syndrome), types of congenital insensitivity to pain, metaphyseal dysplasias, and infantile cortical hyperostosis. Of these, the milder forms of the osteogenesis imperfecta spectrum are the most challenging to distinguish from child abuse, often requiring genetic testing or collagen analysis.

FURTHER READING Ayoub DM, Hyman C, Cohen M, Miller M. A critical review of the classic metaphyseal lesion: traumatic or metabolic? Am J Roentgenol. 2014;202(1):185–196. Beck BR, Bergman AG, Miner M, et al. Tibial stress injury: relationship of radiographic, nuclear medicine bone scanning, MR imaging, and CT severity grades to clinical severity and time to healing. Radiology. 2012;263(3):811–818. Behrens SB, Deren ME, Matson A, Fadale PD, Monchik KO. Stress fractures of the pelvis and legs in athletes: a review. Sports Health. 2013;5(2): 165–174. Blankenbaker DG, De Smet AA, Vanderby R, McCabe RP, Koplin SA. MRI of acute bone bruises: timing of the appearance of findings in a swine model. Am J Roentgenol. 2008;190(1):W1–W7.

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Daffner RH, Pavlov H. Stress fractures: current concepts. Am J Roentgenol. 1992;159(2):245–252. Dijkman BG, Sprague S, Schemitsch EH, Bhandari M. When is a fracture healed? Radiographic and clinical criteria revisited. J Orthop Trauma. 2010;24:S76–S80. Dwek JR. The radiographic approach to child abuse. Clin Orthop Relat Res. 2011;469(3):776–789. Ecklund K, Jaramillo D. Patterns of premature physeal arrest: MR imaging of 111 children. Am J Roentgenol. 2002;178(4):967–972. Hesper T, Zilkens C, Bittersohl B, Krauspe R. Imaging modalities in patients with slipped capital femoral epiphysis. J Child Orthop. 2017;11(2):99–106. Jacobs JC, Archibald-­Seiffer N, Grimm NL, Carey JL, Shea KG. A review of arthroscopic classification systems for osteochondritis dissecans of the knee. Orthop Clin North Am. 2015;46(1):133–139. Jaimes C, Jimenez M, Shabshin N, Laor T, Jaramillo D. Taking the stress out of evaluating stress injuries in children. Radiographics. 2012;32(2):537–555. Jarraya M, Hayashi D, Roemer FW, et al. Radiographically occult and subtle fractures: a pictorial review. Radiol Res Pract. 2013:2013. Jawetz ST, Shah PH, Potter HG. Imaging of physeal injury: overuse. Sports Health. 2015;7(2):142–153. John SD, Moorthy CS, Swischuk LE. Expanding the concept of the toddler’s fracture. Radiographics. 1997;17(2):367–376. Kemp AM, Dunstan F, Harrison S, et al. Patterns of skeletal fractures in child abuse: systematic review. BMJ. 2008;337:a1518. Kirby MW, Spritzer C. Radiographic detection of hip and pelvic fractures in the emergency department. Am J Roentgenol. 2010;194(4):1054–1060. Mosher TJ. MRI of osteochondral injuries of the knee and ankle in the athlete. Clin Sports Med. 2006;25(4):843–866. Pathria MN, Chung CB, Resnick DL. Acute and stress-­related injuries of bone and cartilage: pertinent anatomy, basic biomechanics, and imaging perspective. Radiology. 2016;280(1):21–38. Pathria MN. Radiologic analysis of trauma. In: Nahum A, Melvin JW, eds. Accidental Injury: Biomechanics and Prevention. 2nd ed. New York, NY: Springer-­Verlag; 2002:103–120. Peh WC, Khong PL, Yin Y, et al. Imaging of pelvic insufficiency fractures. Radiographics. 1996;16(2):335–348. Pierce JL, McCrum EC, Rozas AK, Hrelic DM, Anderson MW. Tip-­of-­the-­ iceberg fractures: small fractures that mean big trouble. Am J Roentgenol. 2015;205(3):524–532. Rios AM, Rosenberg ZS, Bencardino JT, Rodrigo SP, Theran SG. Bone marrow edema patterns in the ankle and hindfoot: distinguishing MRI features. Am J Roentgenol. 2011;197(4):W720–W729. Rogers LF. Radiology of Skeletal Trauma. 3rd ed. New York, NY: Churchill Livingstone; 2002. Rogers LF, Poznanski AK. Imaging of epiphyseal injuries. Radiology. 1994;191(2):297–308. Sanders TG, Medynski MA, Feller JF, Lawhorn KW. Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 2000;20(suppl 1):S135–S151. Shane E, Burr D, Abrahamsen B, et al. Atypical subtrochanteric and diaphyseal femoral fractures: second report of a task force of the American Society for Bone and Mineral Research. J Bone Miner Res. 2014;29(1):1–23. Stevens MA, El-­Khoury GY, Kathol MH, et al. Imaging features of avulsion injuries. Radiographics. 1999;19(3):655–672. Zbojniewicz AM, Laor T. Focal periphyseal edema (FOPE) zone on MRI of the adolescent knee: a potentially painful manifestation of physiologic physeal fusion? Am J Roentgenol. 2011;197(4):998–1004. Zbojniewicz AM, Stringer KF, Laor T, Wall EJ. Juvenile osteochondritis dissecans: correlation between histopathology and MRI. Am J Roentgenol. 2015;205(1):W114–W123.

2 Physical Injury: Upper Extremity S U M M A R Y O F K E Y F E AT U R E S • F  ractures and dislocations of the upper extremity are common in both children and adults. • The vast majority of fractures in the upper extremity are adequately evaluated with conventional radiology, although specialized projections can facilitate fracture detection, particularly in regions of complex anatomy, such as the upper extremity articulations. • The wide range of mobility in the upper extremities, particularly the shoulder and wrist, makes them vulnerable to a number of

instability patterns, including posttraumatic dislocation that occurs in characteristic directions in each joint. • Injuries about the elbow are often associated with a joint effusion elevating the intraarticular fat pads. There are few other reliable soft tissue indicators of injury in the upper extremity. • Computed tomography and magnetic resonance imaging play an increasingly important role in the diagnosis and classification of acute injuries and in detecting delayed complications such as nonunion and osteonecrosis.

INTRODUCTION

there is considerable displacement. CT is the imaging modality of choice when this injury is suspected, allowing detection of more subtle injuries and simultaneous assessment of the upper mediastinal structures.

  

Routine radiographic findings are emphasized in this chapter, although reference is made to the assessment of such injuries with other methods such as computed tomography (CT) and magnetic resonance (MR) imaging. Both techniques are fundamental to the evaluation of internal derangements of joints. This survey of physical injuries focuses on the upper extremity, proceeding in a proximal to distal direction. It is not meant to compete with standard references but rather to provide an overview of the more important physical injuries occurring in the upper extremity.

CLAVICLE AND PERICLAVICULAR JOINTS Sternoclavicular Joint Dislocation The sternoclavicular joint is the only articulation between the axial skeleton and upper extremity. Sternoclavicular joint injuries are rare, accounting for only about 2% to 3% of all shoulder dislocations. Traumatic dislocation of the sternoclavicular joint requires a direct or indirect force of great magnitude. These are classified into anterior and posterior according to the direction of displacement of the clavicle; anterior dislocation is more common. Anterior, or presternal, dislocations are caused by forces that move the shoulder backward and outward or downward. Serious complications are rare after this type of dislocation, although a “cosmetic bump” may remain indefinitely. Posterior, or retrosternal, dislocations of the sternoclavicular joint are accompanied by life-­threatening complications in up to 30% of patients related to clavicular impingement on the neurovascular structures, esophagus, and trachea at the upper mediastinum (Fig. 2.1). A pneumothorax or hemothorax may be an associated finding. Patients with findings indicating mediastinal compression require urgent diagnosis and surgical intervention. Asymmetry in clavicular height and malalignment at the sternoclavicular joint can be recognized on cranially angulated anteroposterior (AP) radiographs when

34

Fracture of the Clavicle KEY CONCEPTS  • F ractures of the clavicle are common injuries, particularly in children and young adults. • The most common fracture pattern is a midshaft fracture with superior apex angulation and superior displacement of the proximal fragment. • Fractures of the distal clavicle may be associated with coracoclavicular ligament injury and marked elevation. • Fractures of the medial end of the clavicle are caused by a direct blow and are best evaluated with CT imaging. • Nonunion of clavicle fractures is typically hypertrophic, and the bulky callus can result in compression of neurovascular structures.

Fractures of the clavicle are common, particularly among children and young adults (Fig. 2.2). Classification of clavicle fractures is based on their location as well as the degree of displacement and comminution, and the presence or absence of articular involvement. The clavicle is divided into three segments: (1) a distal segment consisting of the outer 25% to 30% of the bone at and distal to the coracoclavicular ligaments, (2) an intermediate segment consisting of the middle 40% to 50% of the bone, and (3) an inner segment consisting of the medial 25% of the bone. Approximately 75% to 80% of clavicular fractures involve the middle segment, 15% to 20% involve the distal segment, and 5% affect the inner segment. In midshaft and distal fractures, the mechanism of injury is usually a fall onto an outstretched hand or a fall on the shoulder that drives the humerus and scapula downward. Fractures of the midshaft typically show superior apex angulation with elevation of the medial

CHAPTER 2  Physical Injury: Upper Extremity

35

* A

A

* B

B Fig. 2.1  Sternoclavicular joint: posterior dislocation. (A) Frontal sternoclavicular joint radiograph with cranial angulation shows asymmetry in the position of the medial margins of the left clavicle (arrow, on the injured side), located inferior to the right clavicle (arrowhead). (B) Axial CT scan confirms posterior dislocation with the left clavicular head (arrow) compressing the mediastinal vascular structures (arrowhead).

Fig. 2.3  Clavicular fracture: intermediate segment. (A) Frontal radiograph of a right clavicle demonstrates the typical fracture configuration of a displaced midshaft clavicle fracture. Note that the medial portion of the clavicle (arrow) is pulled upward by the sternocleidomastoid muscle; the lateral portion (asterisk) is pulled downward by the weight of the arm and inward by the pectoralis major and latissimus dorsi muscles. (B) Fracture comminution and displacement are more evident on the cranially angulated view.

*

Fig. 2.2  Clavicle fracture. An angulated fracture of the clavicle (arrow) is shown in a skeletally immature child. Note the typical superior apex angulation seen with clavicle fractures.

segment. These fractures are readily diagnosed with conventional radiographs and are best characterized on AP radiographs obtained with 15 to 20 degrees of cranial angulation (Fig. 2.3). Fractures of the distal portion of the clavicle are classified according to the location of the fracture relative to the coracoclavicular ligaments and the integrity of those ligaments. Fractures distal to the ligaments are typically undisplaced and intraarticular. Fractures at the ligaments show variable patterns depending on the extent of comminution and ligamentous integrity. A characteristic avulsed flange of bone arising from the inferior cortex distal clavicular fragment may be evident in injuries due to avulsion by the coracoclavicular ligaments.

Fig. 2.4  Clavicular fracture: distal segment. A fracture of the distal clavicle with complete disruption of the coracoclavicular ligaments allows superior migration of the proximal segment of the clavicle. The sharp tip of the proximal fragment (arrow) is elevated and tenting the overlying skin. Note that the small distal clavicle fragment (asterisk) remains aligned with the acromion.

Fractures of the distal clavicle located just proximal to the ligaments tend to elevate (Fig. 2.4). Associated fractures of the coracoid process and ribs may be evident. Medial clavicular fractures are uncommon. Medial fractures typically result from a direct blunt injury

36

SECTION 1  Traumatic Disorders

and are best evaluated with CT. These are divided into extraarticular fractures, which are often transverse and do not become displaced because of ligamentous and musculature attachments, and intraarticular fractures, which enter the sternoclavicular joint. CT is the imaging modality of choice for evaluating medial clavicular fractures. Clavicle fractures are typically managed conservatively, though surgical fixation is gaining popularity in adults as it leads to better cosmetic outcome and a lower rate of nonunion, which can be seen in up to 15% of midshaft fractures. Fractures that are elevated have a poorer prognosis related to more significant displacement at the fracture site and a higher rate of nonunion. Nonunion of midshaft clavicular fracture is typically hypertrophic with exuberant callus that can be associated with compression of the adjacent neurovascular structures, particularly in the region of the costoclavicular space. Posttraumatic nonunion of the clavicle must be differentiated from congenital pseudarthrosis, which usually manifests as a painless swelling overlying the middle third of the bone, more frequently on the right side, during infancy and early childhood; callus and periosteal bone formation are absent.

Normal

Type I

Type IV

Type II

Type V

Acromioclavicular Joint Acute Injury

Subluxation or dislocation of the acromioclavicular joint is a common injury that accounts for approximately 10% of all shoulder dislocations. Injury to the acromioclavicular joint can result from indirect or, more commonly, direct force applied to the acromion, typically related to a fall on the shoulder. These are classified according to the extent of ligament damage. The initial classification system used three grades of injury but was subsequently expanded to include six grades of injury (Fig. 2.5). A type I injury is associated with stretching or tearing limited to the superior acromioclavicular capsule and does not result in malalignment. A type II injury is associated with disruption of the entire acromioclavicular capsule, allowing widening of the joint. The coracoclavicular complex, consisting of the trapezoid and conoid ligaments, may be sprained but remains intact, limiting superior and posterior subluxation to a few millimeters. A type III injury is characterized by disruption of both the acromioclavicular and coracoclavicular ligaments, allowing further elevation of the clavicle with respect to the acromion (Fig. 2.6). Types IV, V, and VI injuries are more severe, exhibiting considerable damage to the deltoid and trapezius muscles and their aponeuroses that act as dynamic stabilizers of the joint; thus, they require surgical management (Table 2.1). Fractures of the coracoid process can be associated with the higher-­grade acromioclavicular joint dislocations. Coracoclavicular ligamentous calcification or ossification can appear after the injury regardless of the type of treatment initiated.

Posttraumatic Osteolysis Posttraumatic osteolysis of the distal portion of the clavicle can be a delayed complication of acute injury or caused by repetitive trauma from activities such as weightlifting. The precise etiology is unclear, though it is likely caused by varying combinations of hypermobility, overuse leading to stress injury of the bone, and hyperemia. Subtle resorption of the distal clavicle cortex is followed by subchondral cyst formation and clavicular bone erosion, producing widening of the acromioclavicular joint, typically in a unilateral fashion (Fig. 2.7). The natural course of posttraumatic osteolysis is variable but typically continues for 12 to 18 months.

Conjoined tendon of biceps and coracobrachialis Type III Type VI Fig. 2.5  Acromioclavicular joint: classification of injuries. Type I: A mild force applied to the point of the shoulder does not disrupt either the acromioclavicular or the coracoclavicular ligaments. Type II: A moderate to heavy force applied to the point of the shoulder disrupts the acromioclavicular ligaments but the coracoclavicular ligaments remain intact. Type III: When a severe force is applied to the point of the shoulder, both the acromioclavicular and the coracoclavicular ligaments are disrupted. Type IV: In this major injury, the acromioclavicular and coracoclavicular ligaments are disrupted, and the distal end of the clavicle is displaced posteriorly into or through the trapezius muscle. Type V: A violent force has been applied that not only ruptures the acromioclavicular and coracoclavicular ligaments but also disrupts the deltoid and trapezius muscle attachments and creates a major separation between the clavicle and the acromion. Type VI: Another major injury is the rare inferior dislocation of the distal end of the clavicle to the subcoracoid position, resulting in extensive soft tissue disruption. (From Rockwood CA Jr, Matsen FA III, eds. The Shoulder. 2nd ed. Philadelphia: WB Saunders; 1998:495.)

Shoulder Injuries about the shoulder are among the most commonly encountered traumatic abnormalities, although their precise patterns vary according to the person’s age.

Glenohumeral Joint Dislocation Even under normal circumstances, the glenohumeral joint is relatively unstable; this instability results in a spectrum of injuries. Glenohumeral joint dislocations are classified according to the direction of movement of the humerus relative to the glenoid.

CHAPTER 2  Physical Injury: Upper Extremity

37

* Fig. 2.6  Acromioclavicular joint dislocation: type III injury. Observe the superior displacement of the left clavicle with respect to the acromion on a bilateral acromioclavicular view done upright with weights. The inferior margins of the clavicle and the acromion (arrowheads) are no longer aligned. Widening of the acromioclavicular joint and an increased distance between the clavicle and the coracoid process (asterisk) are apparent. The contralateral right side shows the normal relationships of these structures.

TABLE 2.1  Acromioclavicular Injuries Type

Radiographic Findings

Structural Findings

I

Normal

Acromioclavicular ligament sprain

II

Minimal superior subluxation of the clavicle

Acromioclavicular ligament disruption, coracoclavicular ligament sprain

III

25%–100% superior subluxation or dislocation of the clavicle

Acromioclavicular ligament disruption, coracoclavicular ligament disruption

IV

Posterior displacement of the clavicle into or through trapezius muscle

Acromioclavicular ligament disruption, coracoclavicular ligament disruption, clavicular detachment of deltoid and trapezius muscles

V

>100% superior dislocation of the clavicle

Acromioclavicular ligament disruption, coracoclavicular ligament disruption, more extensive clavicular detachment of the deltoid and trapezius muscles

VI

Displacement of the clavicle below the acromion or coracoid process

Acromioclavicular ligament disruption, coracoclavicular ligament disruption, clavicular detachment of the deltoid and trapezius muscles

Fig. 2.7  Osteolysis of the distal clavicle and type II injury. Cortical resorption and bone erosion at the distal end of the clavicle (arrow) represent osteolysis. Note the normal cortex at the end of the acromion (arrowhead). There is widening of the acromioclavicular joint and superior displacement of the clavicle related to a subacute type II injury that occurred 4 months previously.

Anterior Dislocation KEY CONCEPTS  • 9 5% of glenohumeral joint dislocations result in anterior displacement of the humerus relative to the glenoid, typically associated with inferior and medial displacement of the humerus. • Anterior dislocations are classified as subcoracoid, subglenoid, subclavicular, and intrathoracic, with the latter two considered rare. • The Hill-­Sachs lesion is an impaction fracture on the posterolateral humeral head that is best seen on the internal rotation view. • The Bankart lesion is a fracture or a soft tissue injury at the anterior-­inferior glenoid. • Anterior glenohumeral joint dislocations may be recurrent; CT and MR imaging are used to evaluate the extent of bone and soft tissue injury to plan surgical management in such cases.

Fig. 2.8  Glenohumeral joint: anterior subglenoid dislocation. The humeral head is displaced anteriorly and inferiorly, and the posterior humeral head and greater tuberosity are fractured (arrow), with displaced fracture fragments (arrowheads).

Anterior dislocation accounts for more than 95% of glenohumeral joint dislocations. Anterior dislocations are classified as subcoracoid (the most common type), subglenoid (second in frequency; Fig. 2.8), subclavicular, and intrathoracic (rare). Intrathoracic dislocations are generally accompanied by fractures of the proximal portion of the humerus. In all of these forms, the humeral head is displaced anteriorly

38

SECTION 1  Traumatic Disorders

*

*

*

A

B

C

Fig. 2.9  Glenohumeral joint: anterior subcoracoid dislocation. (A) Anteroposterior radiograph shows anterior and medial displacement of the humeral head relative to the glenoid (asterisk). (B) Scapular Y view radiograph reveals the abnormal position of the humeral head, which is located anterior to the glenoid cavity (asterisk). Impaction of the anterior glenoid rim against the posterolateral aspect of the humeral head (arrowhead) has produced a small Hill-­Sachs lesion. (C) Axillary radiograph reveals an anterior dislocation of the humeral head relative to the glenoid (asterisk) and impaction of the posterior humeral head (arrowhead). Although the dislocation is well shown on this radiograph, axillary projections are difficult to obtain while the humeral head is still displaced.

and inferiorly relative to the glenoid. Anterior dislocations are best evaluated radiographically by the inclusion of a lateral scapular projection, an axillary projection, or both, in addition to standard frontal views of the shoulder (Fig. 2.9). Anterior dislocations are associated with a compression fracture on the posterolateral aspect of the humeral head that is produced by impaction of the humerus against the anterior rim of the glenoid fossa. This osseous defect of the humerus is called a Hill-­Sachs lesion. This fracture is observed in many cases of anterior dislocation of the glenohumeral joint; its frequency and size increase following recurrent dislocation. Radiographs obtained in internal rotation are necessary because such rotation of the humerus produces a tangential view of the osseous defect (Fig. 2.10). A second type of injury accompanying anterior dislocation of the humeral head involves the anterior rim of the glenoid fossa and is called a Bankart lesion (Fig. 2.11). Although large osseous fractures of the glenoid are apparent on radiographs, smaller fractures are best seen on CT images. The Bankart lesion may include only the labral and cartilaginous structures. Conventional MR imaging and MR arthrography are the methods of choice for detecting alterations limited to the soft tissues related to dislocation. A number of other osseous and nonosseous injuries can accompany anterior dislocations of the glenohumeral joint. An avulsion fracture of the greater tuberosity of the humerus occurs in 10% to 15% of cases. Disruption of the rotator cuff may complicate anterior dislocation of the glenohumeral joint, particularly in patients who are older than 40 years. Injuries to the brachial plexus or its branches—specifically, the axillary nerve—occur in 7% to 45% of anterior glenohumeral joint dislocations; such injuries are more common in older patients and those with large hematomas. Approximately 40% of anterior glenohumeral joint dislocations are recurrent and are more likely in cases of subcoracoid and subglenoid dislocations and in younger persons.

Fig. 2.10  Glenohumeral joint: Hill-­Sachs lesion. In a patient with a previous anterior dislocation, an internal rotation view reveals the extent of the Hill-­Sachs lesion (arrows).

Surgical reconstruction is typically needed for the treatment of patients with recurrent anterior glenohumeral joint dislocation. CT imaging is widely used to quantify the size of the Bankart lesion and extent of bone loss at the glenoid to determine the optimal surgical approach to such patients (Fig 2.12).

CHAPTER 2  Physical Injury: Upper Extremity

Posterior Dislocation Posterior dislocation of the glenohumeral joint is rare, accounting for approximately 2% to 4% of all shoulder dislocations. Many cases of posterior dislocation result from seizures; in these instances, bilateral dislocations may be evident. Posterior glenohumeral dislocation is challenging to diagnose on AP radiographs, as the findings are subtle and easily overlooked. More than 50% of cases of posterior glenohumeral dislocation are unrecognized on initial clinical and radiographic

Fig. 2.11  Glenohumeral joint: Bankart lesion. In addition to a Hill-­ Sachs lesion (arrow), note the fragmentation of the anterior-­inferior glenoid rim (arrowhead), representing an osseous Bankart lesion.

evaluation despite the presence of a history of trauma, pain, swelling, and limitation of motion. Physical examination reveals a posteriorly displaced humeral head that is held in internal rotation. Absence of external rotation and limitation of abduction are present in virtually all cases. On the AP radiograph, the fixed internally rotated position of the humeral head produces a “lightbulb” appearance, as the head is centered on the humeral shaft in this position. Posterior dislocation of the humeral head also distorts the normal elliptic radiodense area created by overlapping of the head and glenoid fossa. An empty—or “vacant”—glenoid cavity may be seen due to posterior displacement of the humeral head, creating a space between the anterior rim of the glenoid and the humeral head that is frequently greater than 6 mm. In addition, the normal parallel pattern of the articular surfaces of the glenoid concavity and the humeral head convexity is lost (Fig. 2.13). An important radiographic sign of posterior dislocation is the presence of a second cortical line in the humeral head, the trough line, which that runs parallel and lateral to the subchondral articular surface of the humeral head. This line represents the margin of a trough­like impaction fracture of the humeral head created when it contacts the posterior glenoid rim during dislocation (Fig. 2.14). The trough line is analogous to the Hill-­Sachs lesion seen in association with anterior glenohumeral joint dislocation and is diagnostic of a posterior dislocation. Additional views are mandatory to properly profile the glenohumeral joint to establish the diagnosis. The axillary view is particularly helpful for diagnosis of posterior dislocation and is more reliable than the standard scapular Y view. Associated injuries include stretching of the posterior capsule, fracture of the posterior aspect of the glenoid rim, avulsion fracture of the lesser tuberosity of the humerus, and stretched or detached subscapularis tendon. CT scanning, MR imaging, and MR arthrography are widely used to evaluate bone and soft tissue injuries associated with acute (or chronic) posterior dislocations of the glenohumeral joint.

*

A

39

B

Fig. 2.12  Glenohumeral joint: recurrent anterior dislocation. (A) Three-dimensional ­ (3D) reformatted CT image of the posterior shoulder in a patient with multiple previous dislocations shows a large Hill-Sachs ­ lesion (asterisk) at the posterior humeral head adjacent to the greater tuberosity. (B) 3D reformatted CT image of the scapula shows flattening related to a Bankart fracture (arrow) at the anterior glenoid, resulting in deformity of the normal convexity of the glenoid rim with loss of bone stock.

40

SECTION 1  Traumatic Disorders

Superior and Inferior Dislocation Superior dislocation of the glenohumeral joint is rare and difficult to distinguish from a high-­riding humeral head from chronic cuff tear unless the acromion is fractured. It is caused by extreme forward and upward force on an adducted arm that can produce extensive damage to the rotator cuff, capsule, biceps tendon, and surrounding

*

musculature, as well as fracture of the acromion, clavicle, coracoid process, or humeral tuberosities. Inferior dislocation of the glenohumeral joint (luxatio erecta) is also rare. A direct axial force on a fully abducted arm or a hyperabduction force leading to leverage of the humeral head across the glenoid is responsible for this type of dislocation. After this injury, the superior aspect of the articular surface of the humeral head is directed inferiorly and does not contact the inferior glenoid rim. As a result, the arm is held over the patient’s head (Fig. 2.15). There is extensive injury to the inferior glenohumeral capsule and there is a high risk of neurovascular injury in this form of dislocation. Drooping shoulder. A special type of inferior displacement of the humeral head is termed the drooping shoulder (Fig. 2.16); this should not be confused with a dislocation. Inferior drooping can be associated with up to 40% of uncomplicated fractures of the proximal humerus, although the cause is not clear. The humeral head is inferiorly displaced relative to the glenoid but is not shifted medially or rotated. Recognition of this common condition eliminates the possibility of an erroneous diagnosis of fracture-­dislocation of the proximal humerus. Conservative therapy leads to disappearance of the drooping shoulder over a period of weeks.

Fracture of the Proximal Portion of the Humerus

Fig. 2.13  Glenohumeral joint: posterior dislocation. Findings on the anteroposterior radiograph include distortion of the normal elliptic radiodense region created by the overlying humeral head and glenoid fossa, a “vacant” glenoid cavity (asterisk), loss of parallelism between the articular surfaces of the glenoid cavity and humeral head, internal rotation of the humerus, and an impaction fracture of the anteromedial humeral head (arrow).

A

The type of injury is dependent, to a large extent, on the age of the person. In the immature skeletons of children or adolescents, physeal separation with or without associated fracture is encountered. In young adults, glenohumeral joint dislocation or subluxation predominates. It is in middle-­aged adults (>45 years) and in the elderly that fractures of the proximal portion of the humerus are typically seen, usually in the setting of underlying osteoporosis (Table 2.2). There are several classification systems employed for proximal humeral fractures. However, they all show considerable interobservor variability, even if CT is employed to evaluate the fracture, limiting their usefulness in clinical practice. The widely used Neer

B Fig. 2.14  Glenohumeral joint: posterior dislocation and trough line. (A) Anteroposterior radiograph shows the humeral head held in internal rotation. Note the vertical band of sclerosis within the humeral head running parallel to the posterior glenoid, indicative of an impacted fracture producing the trough line (arrows). (B) Axillary radiograph reveals posterior dislocation of the humerus relative to the glenoid and an impaction fracture (arrows) involving the anteromedial portion of the humeral head. Note the irregularity of the cortical margin of the posterior aspect of the glenoid rim (arrowhead).

CHAPTER 2  Physical Injury: Upper Extremity

41

*

A

B Fig. 2.15  Glenohumeral joint: inferior dislocation. (A) Anteroposterior radiograph obtained following an inferior dislocation of the glenohumeral joint demonstrates the classic position of the arm directed superiorly, held over the head. (B) Three-­dimensional reformatted CT angiogram image shows the inferiorly directed humeral head far below the glenoid fossa (asterisk), displacing the subclavian artery inferiorly (arrow).

Fig. 2.16  Glenohumeral joint: drooping shoulder. Fracture of the greater tuberosity (arrow) of the humerus is associated with inferior subluxation of the head with respect to the glenoid cavity.

classification of fractures of the proximal humerus emphasizes the presence or absence of significant displacement of one or more of four major osseous segments: the articular segment containing the anatomic neck, the greater tuberosity, the lesser tuberosity, and the shaft and surgical neck. A displaced fracture exists if any of the four segments is separated by more than 1 cm from its neighbor or is angulated more than 45 degrees. These measurements are somewhat arbitrary and can be difficult to assess accurately on conventional radiographs, particularly in comminuted fractures. Undisplaced fractures or fractures with minimal displacement that do not meet

these criteria are considered one-­part fractures. Approximately 80% of fractures of the proximal portion of the humerus are undisplaced because of the protection afforded by the periosteum, joint capsule, and rotator cuff (Fig. 2.17). Two-­part fractures, in which only a single segment is displaced, represent approximately 15% of all fractures of the proximal humerus (Fig. 2.18). Three-­part and four-­part fractures each account for approximately 3% to 4% of all humeral fractures. Surgical management or hemiarthroplasty is employed for the majority of four-­part fractures. The term fracture-­dislocation is used to indicate that the articular segment of the humerus is displaced beyond the joint space (Fig. 2.19). Impaction fractures of the humeral articular surface against the anterior or posterior rim of the glenoid cavity in cases of glenohumeral joint dislocation were considered earlier in this chapter. More severe fragmentation or comminution can accompany central impaction of the humeral head against the glenoid cavity. Complications of fractures of the proximal humerus include lipohemarthrosis, production of intraarticular osteocartilaginous fragments, inferior displacement of the humeral head (drooping shoulder), and osteoarthritis. Delayed union or nonunion can occur with any type of fracture of the proximal portion of the humerus and may be accompanied by significant angulation at the fracture site. Osteonecrosis is reported in 7% to 50% of cases and is most typical with displaced fractures at the humeral neck that disrupt the medial metaphyseal cortex, severe fractures (four-­part fractures), or fracture-­dislocations (Fig. 2.20). Less commonly, injury to the nearby brachial plexus and the axillary artery may be seen.

Fracture of the Scapula Scapular fractures are infrequent, accounting for 3% to 5% of shoulder girdle injuries. They are typically caused by high-­energy trauma and are usually associated with additional injuries involving the ribs, clavicle, lung, head, or spine. Scapular fractures may involve one or more of the following anatomic regions: glenoid fossa and articular surface,

42

SECTION 1  Traumatic Disorders

TABLE 2.2  Fractures of the Humeral Metaphyses and Shaft Site

Characteristics

Complications

Proximal

Middle-­aged and elderly adults Defined by Neer classification as one-­part to four-­part, based on the degree and location of displacement and angulation

Lipohemarthrosis Drooping shoulder related to hemarthrosis and/or capsule, muscle, or nerve injury Osteonecrosis, especially with four-­part fractures Osteoarthritis Heterotopic ossification Rotator cuff tear Brachial plexus and, less commonly, axillary artery injury Painful arc of motion

Middle

Delayed union or nonunion when the fracture is transverse or distracted Adults > children Most common at the junction of the distal and middle thirds Radial nerve injury in 5%–15% of cases Brachial artery injury Associated fractures in 25% of cases (ulna, clavicle, or proximal humerus) Characteristic displacements related to sites of muscular attachment

Supracondylar

Children >> adults Extension (95%) and flexion (5%) types Paradoxical posterior fat pad sign

Brachial artery injury Median, ulnar, or radial nerve injury Malalignment Heterotopic ossification Volkmann’s ischemic contracture

A

B

Fig. 2.17  Fractures of the proximal humerus: undisplaced. Fractures involve the surgical neck and greater tuberosity of the humerus (arrows). There is mild impaction but less than 1 cm of displacement and less than 45 degrees of angulation between the fracture fragments. There is no displacement of the fracture at the medial humeral cortex (arrowhead),suggesting that vascularity is intact. The articular surface is not affected. The fracture was managed conservatively with good results.

neck, body, spinous process, acromion, and coracoid process (Fig. 2.21). They are found most frequently in the scapular body, followed by the neck and other regions of the bone.

Intraarticular Fractures Scapular fractures are divided according to whether they affect the articular surface of the glenoid. The majority of scapular fractures requiring surgical fixation involve the joint surface. CT scanning is often used to identify the presence or absence of intraarticular

extension. Approximately 10% to 30% of scapular fractures involve the articular surface, at either the rim or the glenoid fossa. A fracture of the rim of the glenoid occurs in approximately 20% of traumatic glenohumeral joint dislocations. Either the anterior glenoid rim (in anterior dislocations) or the posterior glenoid rim (in posterior dislocations) may be affected. Larger portions of the glenoid fossa may be fractured when the humeral head is driven against the glenoid cavity by a direct force, often associated with extensive comminution of the scapular body (Fig. 2.22).

43

CHAPTER 2  Physical Injury: Upper Extremity

*

Fig. 2.18  Fractures of the proximal humerus: two-­part fracture. Fractures involve the surgical neck and base of the greater tuberosity of the humerus (arrows). There is >1 cm of shortening at the fracture with medial displacement and angulation of the head fragment relative to the shaft. Notice the drooping of the humeral head relative to the glenoid.

Fig. 2.20  Osteonecrosis: humeral head. After a fracture of the proximal portion of the humerus, osteonecrosis of the humeral head occurred, resulting in patchy bone sclerosis with humeral head flattening due to collapse of the articular surface (asterisk). There are also healed fractures of the glenoid neck and upper ribs (arrowheads).

5 6 4 2

*

Fig. 2.19  Fracture-­dislocation of the glenohumeral joint. Anterior (subcoracoid) dislocation of the humeral head (asterisk) at the glenohumeral joint is associated with displaced fractures of the surgical neck and base of the greater tuberosity of the humerus (arrows).

1

3

Extraarticular Fractures

Fig. 2.21  Scapular fracture: sites of injury. Fractures of the scapula may involve the glenoid fossa and articular surface (1), the neck (2) or body (3) of the bone, or the scapular spine (4), acromion (5), or coracoid process (6). They are most common in the scapular body and neck.

Approximately 50% to 70% of scapular fractures involve the neck, body, and spine of the scapula. These extraarticular fractures make up the majority of scapular fractures. They are typically managed conservatively unless they are significantly displaced and angulated or there are additional fractures to the shoulder girdle, resulting in an unstable floating glenoid. A fracture in the neck of the scapula characteristically occurs after a direct blow to the shoulder. The fracture line, which may

be impacted, extends from the supraclavicular notch above to the coracoid process below. Isolated fractures of the scapular spine are infrequent and, when present, are a result of direct trauma. Fractures of the acromion generally follow direct blunt trauma, although muscular traction can rarely produce a similar lesion. On radiographs, a fracture line is evident, either adjacent to the

44

SECTION 1  Traumatic Disorders

A

B

Fig. 2.22  Scapular fracture: intraarticular. (A) Anteroposterior radiograph shows a horizontal fracture involving the glenoid (arrow), extending into the scapular neck and scapular body (arrowhead). (B) Three-­ dimensional reformatted CT image en face to the glenoid shows the articular surface disruption (arrows) and comminution of the scapular body.

acromioclavicular joint or at the base of the acromion process. Displaced acromion fractures can result in significant impingement of the rotator cuff. Neurologic injury, although rare, is also a recognized complication. Fractures of the coracoid process are caused by a direct injury from a dislocating humeral head or a direct force on the tip of the coracoid process itself, or in relation to an avulsion injury. Fracture of the coracoid tip, which may be displaced inferiorly, may result from traction avulsion by the short head of the biceps brachii muscle or the coracobrachialis muscle. Fractures related to avulsion by the coracoclavicular ligaments are more common. These occur at the base of the coracoid process related to a high-­grade acromioclavicular separation. In such cases, the coracoid fragment may be undisplaced or displaced superiorly along with the clavicle (Fig. 2.23). AP radiographs may not demonstrate the coracoid process fracture clearly and should be supplemented with a lateral scapular view, axillary projection, or both. CT imaging is helpful for diagnosis of fractures of both the coracoid process and acromion.

*

Fracture of the Humeral Diaphysis Fractures of the humeral diaphysis account for about 3% to 5% of all fractures (see Table 2.2), most commonly in elderly patients related to a fall. In younger patients, humeral shaft fractures more often result from either high-­energy trauma, such as a motor vehicle collision, athletic injury, and assault, or related to penetrating injury. In proximal shaft fractures, characteristic patterns of displacement are seen related to the muscular forces acting on the fragments (Fig. 2.24). In fractures occurring above the insertion of the tendon of the pectoralis major muscle, the proximal fragment is displaced into abduction and external rotation as a result of the action of the rotator cuff musculature; fractures occurring in the interval between the insertion of the pectoralis major tendon proximally and the deltoid muscle insertion distally result in adduction of the proximal fragment and lateral displacement of the distal fragment; and fractures occurring distal to the insertion of the deltoid muscle result in abduction of the proximal fragment and proximal displacement of the distal fragment. Approximately three-­fourths of all humeral fractures involve the middle third of the bone, distal to the deltoid muscle insertion. These

Fig. 2.23  Scapular fracture: fracture of the coracoid process. Frontal radiograph demonstrates fracture of the base of the coracoid process (arrows) extending toward the scapular spine. Note the superior displacement of the fracture accompanied by superior offset of the clavicle relative to the acromion (asterisk), suggesting that this fracture was avulsed by the coracoclavicular ligaments during a grade 3 equivalent acromioclavicular joint separation.

may not be significantly displaced. Transverse fractures of the humeral shaft are most frequent and represent 50% to 70% of all diaphyseal fractures of the humerus; oblique or spiral fractures, each representing about 20% of all humeral diaphyseal fractures, result from torsional forces; and segmental and comminuted fractures constitute the other patterns of humeral shaft fracture. Among the complications of fracture of the humeral diaphysis, neurologic injury is most common. Radial nerve palsy occurs in as many as 18% of closed fractures of the humeral shaft

CHAPTER 2  Physical Injury: Upper Extremity

Deltoid m.

A

45

Pectoralis major m.

B

C

Fig. 2.24  Effects of muscular forces in cases of humeral fracture above the pectoralis muscle. (A), below the pectoralis muscle but above the deltoid muscle (B), and below the deltoid muscle (C). (From Browner BD, Levine AM, Jupiter JB, Trafton PG, eds. Skeletal Trauma, vol 2. 2nd ed. Philadelphia: WB Saunders; 1998:1526.)

and is associated most often with transverse fractures of the diaphysis, particularly those occurring in the junction of the middle and distal thirds of the bone as the nerve spirals around the humerus, approximately 10 cm above the elbow joint (Fig. 2.25). Injury to the median or ulnar nerve is rare in cases of humeral diaphyseal fracture. Vascular compromise occurs in less than 5% of patients with fracture of the humeral shaft. Delayed union or nonunion of humeral shaft fractures is also encountered. In general, transverse, segmental, or open fractures unite more slowly than do spiral, oblique, or comminuted fractures. Fractures of the distal humerus often involve the elbow joint and are discussed subsequently.

ELBOW Fractures and dislocations about the elbow represent 5% to 8% of all skeletal injuries. Either direct injury, such as impact on the radius and ulna, or indirect injury, such as that transmitted through the bones of the forearm from a fall on an outstretched hand, lead to elbow fractures and dislocations.

Elbow Dislocation The elbow joint is the third most common site of dislocation (after the glenohumeral joint and interphalangeal joints of the fingers), and the most common site of dislocation in children. The most commonly reported mechanism of injury is hyperextension, typically combined with rotation. In cases of dislocation involving both the radius and the ulna, posterior dislocation (Fig. 2.26) is most frequent (approximately 80% to 90% of all elbow dislocations). In adults, this injury may be complicated by fracture of the coronoid process of the ulna, the capitellum of the humerus, or the radial head. In children and adolescents, the medial epicondylar ossification center is frequently avulsed and may become entrapped during reduction (see Fig. 1.63). Isolated fractures of the coronoid process of the ulna are rare and are typically caused by shearing injury related to posterior dislocation of the elbow as there are no muscular or tendinous attachments at the coronoid process to produce avulsion fractures. The presence of a coronoid fracture in the

Fig. 2.25  Humerus shaft fracture. Fracture of the distal humerus (arrow) shows varus angulation at the distal fragment. The patient sustained a radial nerve injury with this fracture, which is located in the region where the radial nerve courses around the humeral shaft to enter the anterior compartment.

46

SECTION 1  Traumatic Disorders

A

B

Fig. 2.26  Elbow: posterolateral dislocation of both the radius and the ulna. (A) Anteroposterior radiograph shows lateral displacement of the radius and ulna relative to the humerus. (B) Lateral radiograph shows posterior displacement of the radius and ulna with respect to the humerus.

*

A

B Fig. 2.27  Elbow: coronoid process fracture. (A) Lateral radiograph shows a fracture of the coronoid process (arrow), indicating that there has been an elbow dislocation that has reduced. (B) Anteroposterior radiograph shows extension of the coronoid fracture to the medial ulna and malalignment with mild lateral shift of the forearm bones relative to the humerus and widening of the lateral joint (asterisk).

setting of a normally aligned elbow should suggest the diagnosis of a dislocation that has reduced (Fig. 2.27). Medial, lateral, and anterior dislocations of the elbow are not common. In infants and young children, separation of the entire distal humeral epiphysis may be confused with elbow dislocation (see Fig. 1.64). Correct diagnosis of this injury rests on two observations: (1) a normal relationship between the capitellum and radius and (2) medial displacement of the radius and ulna with respect to the humerus.

Radial Head Dislocation Isolated radial head dislocation without an associated fracture in the ulna is rare in adults but is common in children, with anterior dislocation of the radius relative to the capitellum. In children, subluxation of the radial head, which is usually but not invariably transient, is termed nursemaid’s elbow or pulled elbow, related to displacement of the annular ligament relative to the radius. Routine radiographs are normal in this condition. Rarely, the annular ligament becomes entrapped in the

CHAPTER 2  Physical Injury: Upper Extremity joint and surgical reduction is required. Isolated dislocation of the ulna at the elbow is unusual. The combination of an ulnar shaft fracture and radial head dislocation at the elbow joint is termed Monteggia fracture-­dislocation (Fig. 2.28). Various types of Monteggia fracture-­dislocations are recognized (Table 2.3). These patterns emphasize the typical occurrence of

*

Fig. 2.28  Type I Monteggia fracture-­dislocation. Note the fracture of the upper third of the ulna (arrow), with anterior angulation at the fracture site and anterior dislocation of the radial head, which is no longer congruent with the capitulum (asterisk).

47

injuries to more than one structure in the forearm. Monteggia fracture-­ dislocation is a common injury in adults (but rare in children) and is easily overlooked.

Fracture of the Distal Portion of the Humerus Fractures of the distal humerus can be subdivided according to whether they are extraarticular or intraarticular. Supracondylar fractures are extraarticular injuries that are particularly common in children (see Fig. 1.62). Transcondylar fractures resemble supracondylar fractures but occur slightly further distally and are intraarticular in location, with a transverse fracture line that traverses both condylar surfaces (Fig. 2.29). Other intraarticular fractures of the distal portion of the humerus include epicondylar, condylar, and intercondylar types. Epicondylar fractures are intraarticular but do not disrupt the condylar surface (Fig. 2.30). The epicondyles, as well as other osseous structures throughout the elbow, are injured more frequently in children or adolescents than in adults. In a mature skeleton, the medial epicondyle is fractured more commonly than the lateral epicondyle; the injury is related in most cases to a direct force applied to the epicondyle. Injury to the adjacent ulnar nerve also may be apparent. Isolated fractures of the lateral epicondyle are very rare in adults. Condylar fractures are relatively uncommon and occur predominantly in children. Fractures of the lateral condyle are more frequent than those of the medial condyle (Fig. 2.31). Each can be associated with significant instability and restriction of motion, especially if the fracture fragment is large. In this regard, a classification system has been devised on the basis of the size of the fragment and the presence or absence of disruption of the lateral trochlear ridge. This structure, which separates the trochlea and capitellum, is important in providing medial and lateral stability to the elbow. In type I fractures of the condyles, the lateral trochlear ridge is not disrupted, whereas in type II fractures, the larger fracture fragment contains the separated condyle and a portion of this ridge. This latter pattern of injury allows translocation of the radius and ulna in a mediolateral direction and is termed a fracture-­dislocation.

TABLE 2.3  Fractures of the Radial and Ulnar Shafts Site

Characteristics

Complications

Ulna (alone)

“Nightstick” fracture: direct blow to the forearm, distal > middle > proximal segments of the ulna

Displacement at the fracture site (uncommon)

Injury to branches of the radial nerve (approximately 20% of Monteggia injury: cases) Type I: Fracture of the middle or upper third of the ulna with anterior dislocation of the radial head (65%) Type II: Fracture of the middle or upper third of the ulna with posterior dislocation of the radial head (18%) Type III: Fracture of the ulna just distal to the coronoid process with lateral dislocation of the radial head (16%) Type IV: Fracture of the upper or middle third of the ulna with anterior dislocation of the radial head and proximal radial fracture (1%) Radius (alone)

Proximal and middle segments: Uncommon because usually associated with an ulnar fracture Galeazzi injury: fracture of the radial shaft with dislocation or subluxation of the distal radioulnar joint caused by a direct blow or a fall on the outstretched hand (rare) with pronation of the forearm; variable degrees of displacement at the fracture site

Angulation Entrapment of the extensor carpi ulnaris Delayed union or nonunion

Radius and ulna

Closed or open Nondisplaced or displaced (displacement more common in adults than children)

Delayed union or nonunion (especially of ulna) Infection in open fractures Nerve and vascular injuries, especially in open fractures and those with severe displacement Compartment syndrome Synostosis between the radius and ulna

48

A

SECTION 1  Traumatic Disorders

B

A

B

Fig. 2.30  Humeral fracture: epicondylar. (A) Fracture of the medial epicondyle. (B) Fracture of the lateral epicondyle.

C

D

Fig. 2.29  Humeral fracture: supracondylar and transcondylar. (A–B) Supracondylar fracture (extension type), probably caused by a fall on an outstretched hand with the elbow in extension. (A) On a lateral view, the fracture line extends obliquely upward from a more distal point anteriorly to a more proximal point posteriorly. Posterior and proximal displacement of the distal fragment results, in part, from the force of the triceps muscle attaching to the ulna. Observe the sharp margin of the proximal fragment, which projects into the antecubital fossa; this accounts for the associated injuries to the brachial artery and median nerve. (B) On an anteroposterior view, the fracture line is generally transverse in configuration. Displacement and angulation at the fracture site are of variable degree. (C–D) Transcondylar fracture (extension type). The fracture line passes through the condyles of the humerus and is intracapsular in location. (C) On a lateral view, posterior displacement of the distal fragment predominates. (D) On a frontal view, the fracture line is commonly transverse and inferior to that of a supracondylar fracture.

Intercondylar fractures of the distal portion of the humerus result in comminuted and complex fracture lines that generally include one component that traverses the supracondylar region of the humerus in a transverse or oblique fashion and a second component, vertical or oblique in nature, that violates the articular surface (Fig. 2.32). The resulting configuration of the fracture is thus T-­ or Y-­s haped. The extent of articular displacement determines management; the majority of intercondylar fractures

A

B

Fig. 2.31  Humeral fracture: condylar. (A) Fracture of the medial condyle. (B) Fracture of the lateral condyle.

require surgery to restore articular congruity. CT is the preferred modality for assessing the articular surface in condylar and intercondylar fractures (Fig. 2.33).

Fracture of the Olecranon Fractures of the olecranon, which represent approximately 20% of all elbow injuries in adults, result from direct injury, indirect injury, or a combination of the two (Fig. 2.34). The presence of fracture comminution and/or displacement of the olecranon fracture fragment determine whether the fracture needs to be managed surgically. The traction from the triceps muscle accounts for

CHAPTER 2  Physical Injury: Upper Extremity

A

49

B

Fig. 2.32  Humeral fracture: intercondylar. (A) Comminuted fracture that has led to separation of the trochlear and capitular fragments. (B) Anteroposterior radiograph of a patient with an intercondylar fracture (arrows) shows the typical T-­shaped configuration associated with this injury. Rotation at the fracture site and incongruity of the articular surface are potential complications.

Fig. 2.34  Ulnar fracture: olecranon. A mildly displaced olecranon fracture has led to a gap at the proximal ulnar articular surface (arrow). A joint effusion is present with elevation of the anterior and posterior fat pads (arrowheads).

Fracture of the Head and Neck of the Radius KEY CONCEPTS 

*

A

*

B

Fig. 2.33  Humeral fracture: intercondylar. (A) Coronal reformatted CT image depiction of an intercondylar fracture shows a vertical splitting fracture entering the joint (arrowhead), disrupting the articular surface. (B) Fracture pattern with separation of the medial (black asterisk) and lateral (white asterisk) elbow columns is well shown on the three-­ dimensional reformatted CT image.

displacement of the olecranon fragment or fragments. Complications of olecranon fractures include a decreased range of elbow motion, osteoarthritis, nonunion, and ulnar nerve damage. Significant posterior displacement of the olecranon fragment, combined with anterior movement of the remaining portion of the ulna and the radial head, is a more serious injury in the spectrum of fracture-­ dislocation of the elbow.

• M  ost common fracture seen at the elbow in adults. • Typically due to a fall on an outstretched hand and can be caused by valgus injury or elbow dislocation. • Elevation of the fat pads indicates that an elbow effusion is typically present, an important clue to intraarticular injury. • Fractures of the radial head and neck are well seen on the special radial head projection that should be obtained if there is an unexplained posttraumatic effusion. • The need for surgical treatment is determined by the degree of comminution, depression, and angular deformity of the articular surface.

Radial head and neck fractures are the most common elbow injury seen in adults, representing up to 50% of fractures affecting the elbow. The diagnostic importance of a positive fat pad sign (see Fig. 1.48), as well as the use of oblique and specialized radiographic projections such as the radial head view, are well recognized in identifying undisplaced fractures of the radial head and neck (Fig. 2.35). These fractures result principally from axial loading related to a fall on an outstretched hand. The radial head and neck also can be fractured during a valgus injury, in which case ligament or osseous injury at the ulnar collateral ligament is typically present (Fig. 2.36) or in association with elbow dislocation. Radial head fractures are classified into four types using the Mason Johnston classification. Type I is undisplaced or displaced less than 2 mm. Type II shows displacement of 2 or more mm or involvement of greater than 30% of the radial head. Type III is defined by comminution. Type IV shows associated proximal radial dislocation. Impaction fractures of the radial neck, without involvement of the radial head, are encountered frequently and typically managed conservatively. Complications after radial head fractures are infrequent and consist of limited range of motion, osteoarthritis, and, in more severe injuries,

50

SECTION 1  Traumatic Disorders

Fig. 2.35  Radial fracture: head of the radius. An angulated radial head projection is used to demonstrate a radial head fracture (arrow). Note the elevation of the posterior fat pad, indicating an elbow effusion in the setting of trauma (arrowhead).

Fig. 2.36  Radial fracture: neck of the radius. A transverse fracture of the neck of the radius (arrow) is associated with an avulsion fracture of the medial epicondyle (arrowhead), suggesting a valgus injury at the elbow joint.

heterotopic ossification. Such fractures, however, may be part of a more complex or widespread injury, such as elbow dislocation, fracture of the capitellum, and subluxation of the distal radioulnar joint (Essex-­ Lopresti injury). The Essex-­Lopresti injury consists of a comminuted and displaced radial head fracture and disruption of the distal radioulnar joint.

FOREARM Injuries involving a single anatomic structure in the forearm are uncommon (see Table 2.3). In common with the pelvis, mandible, and ankle, the forearm can be considered a ring structure because of the myotendinous, ligamentous, and articular connections of the radius and ulna. Disruption of the forearm ring at one site is usually accompanied by disruption at a second (or even third) site. When both disruptions are fractures, accurate diagnosis with routine radiography is not difficult. When a fracture is accompanied by a frank dislocation, routine radiographic diagnosis is also straightforward as long as the entire forearm from elbow to wrist is surveyed. When subluxation is a component of the injury pattern, however, the initial radiographic examination may be interpreted as showing only a single lesion, particularly if the subluxation is transient or appears only in certain positions of the forearm. In such cases, CT or MR imaging can be helpful, particularly for assessment of subtle injuries at the distal radioulnar joint.

Fracture of Both the Radius and the Ulna Fractures involving both bones of the forearm are common and usually result from direct injury. In adults, fractures of both bones of the forearm typically affect the middle diaphyseal segments, although the peripheral segments also may be affected. The fractures of the radius and ulna may occur at the same level or at different levels; those at the same level have a higher risk of bridging and forming a synostosis (Fig. 2.37). In children, the distal third of the diaphyses of the radius and ulna are involved most commonly; the site of a radial fracture is generally more distal than that of an ulnar fracture. Considerable

Fig. 2.37  Fractures of the diaphyses of the radius and ulna: both-­ bone forearm fracture. Note the transverse fractures of the shafts of the radius (arrow) and ulna (arrowhead). Fractures at the same level involving both forearm bones are at risk for rotary deformity and synostosis formation.

CHAPTER 2  Physical Injury: Upper Extremity

51

displacement, angulation, and rotation at the fracture sites are common and lead to deformity and loss of function. Other complications of both-­bone forearm fractures include delayed union or nonunion, neurologic and vascular injury, and compartment syndrome.

Fracture of the Ulna Fractures involving the diaphysis of the ulna may occur as part of Monteggia fracture-­dislocation (see previous discussion) or as an isolated phenomenon. Isolated fractures of the ulnar shaft are common; typically, they result from a direct injury and are designated nightstick fractures (Fig. 2.38). Significantly displaced fractures of the ulnar diaphysis are usually associated with dislocations of the proximal or distal radioulnar joint.

Fracture of the Radius Fractures of the diaphysis of the radius occur most commonly as part of Galeazzi fracture-­dislocation (see later discussion) and rarely as an isolated phenomenon. Isolated fractures of the proximal portion of the radial shaft result from direct trauma and are less common than those of the ulna.

WRIST AND HAND Fracture of the Distal Portions of the Radius and Ulna KEY CONCEPTS  • C aused by fall on outstretched hand. • In pediatric patients, fracture is often incomplete, with compressive buckling limited to dorsal cortex best seen on a lateral radiograph. • The most common etiology of insufficiency fracture is osteoporosis. • In older women with osteoporosis, the most common pattern is a Colles fracture, with dorsal displacement and angulation of the articular surface. • The need for surgical fixation is determined by the degree of comminution, angular deformity, involvement of articular surface, and any associated ulnar or carpal fracture at imaging. • The majority are treated with closed reduction and casting; CT is useful for surgical planning when there is major articular surface disruption.

The most common mechanism of injury to the wrist is a fall on an outstretched hand. Fractures of the distal regions of the radius and ulna are approximately 10 times more frequent than those of the carpal bones; the latter are especially infrequent in children. In children, the most common pattern of fracture is an incomplete compressive injury of the dorsal radial cortex, best seen on the lateral view as a buckling deformity. These fractures are easily overlooked at the time of injury and recognized only on follow-­up radiographs as metaphyseal sclerosis and periostitis become evident. Incomplete greenstick tensile fractures of the volar cortex are less common but tend to be more unstable. Complete fractures of the distal radius involving both cortices result in more displacement and angulation but still have an excellent prognosis. Injuries involving the distal radial physis are classified according to the Salter-­Harris classification. The radial physis can undergo stress injury caused by repetitive trauma, leading to widening and irregularity that can simulate rickets. This type of stress injury is referred to as a gymnast wrist. Many eponyms have been used to describe fractures of the distal ends of the radius and ulna in adults; major characteristics of these fractures are described in Table 2.4. Although these designations are still used, descriptions related to the intraarticular or extraarticular nature of the fracture, the number of fracture fragments, and the presence and degree of displacement or angulation are becoming more

Fig. 2.38  Fractures of the diaphyses of the radius and ulna: isolated fracture of the ulna (nightstick fracture). Note the oblique, slightly displaced fracture of the distal portion of the ulna (arrow).

common. CT and MR imaging are useful supplements to standard radiography in assessing fracture comminution, depression and incongruity of articular surfaces, and associated soft tissue abnormalities. The classic Colles fracture is a transverse fracture, with or without comminution, that extends from the volar to the dorsal surface of the distal part of the radius and is accompanied by impaction and displacement of the dorsal surface of the radius (Fig. 2.39). The typical mechanism is a fall on an outstretched hand. Fracture of the ulnar styloid process occurs in approximately 50% to 60% of cases; fracture extension into the distal radioulnar joint occurs in most cases. Radial shortening and dorsal inclination of the articular surface of the radius (which normally has a volar inclination of 5to15 degrees) are important sequelae of Colles fractures that, if not corrected, may influence subsequent wrist function. Complications are diverse and common, including unstable reduction, articular incongruity, subluxation or dislocation of the distal radioulnar joint, median nerve compression, ulnar nerve injury, entrapment of flexor tendons, complex regional pain syndrome, carpal malalignment, delayed union, or nonunion. A distal radial fracture similar in position to Colles fracture but associated with volar (or palmar) angulation or displacement of the distal fragment is known as Smith fracture. Smith fracture is much less common than Colles fracture. Complications of Smith fractures are similar to those of Colles fractures and may include injury to the extensor tendons. Shearing injuries producing intraarticular fractures limited to the dorsal or volar rims of the distal radius are referred to as Barton or reverse Barton fractures, typically associated with carpal translation along with the fracture fragment. Differentiation from Colles fracture can be accomplished based on findings on a lateral radiograph of the wrist. Barton fracture involves the dorsal rim of the distal portion of the radius, generally related to dorsiflexion and pronation of the forearm

52

SECTION 1  Traumatic Disorders

TABLE 2.4  Fractures of the Distal Portions of the Radius and Ulna Fracture

Mechanism

Characteristics

Complications

Colles

Dorsiflexion

Fracture of the distal radius with dorsal displacement Varying amounts of radial displacement, angulation, and shortening Ulnar styloid fracture in about 50%–60% of cases Associated injuries to the carpus, elbow, humerus, femur (in osteoporotic patients)

Subluxation or dislocation of the distal radioulnar joint Injury to the median or, less commonly, radial or ulnar nerve Extensor tendon rupture Deformity Osteoarthritis

Smith (reverse Colles)

Variable

Fracture of the distal radius with palmar displacement Less common than Colles fracture Varying amounts of radial comminution, articular involvement Associated fracture of the ulnar styloid process

Similar to Colles fracture

Barton

Dorsiflexion and pronation

Intraarticular fracture of the dorsal rim of the radius

Similar to Colles fracture

Reverse Barton

Dorsiflexion with tension failure of volar lip

Intraarticular fracture of the volar rim of the radius

Similar to Colles fracture

Hutchinson (chauffeur)

Avulsion by the radial collateral ligament

Intraarticular fracture of the styloid process of the radius Usually nondisplaced

Scapholunate dissociation Ligament damage Osteoarthritis Osteoarthritis

Die-­punch fracture

Axial loading

Depressed fracture of central articular surface below lunate

Radiocarpal fracture dislocation

Dorsiflexion

Uncommon and severe injury Entrapment of neurovascular structures Associated fractures of the dorsal rim and styloid process of the and tendons radius, ulnar styloid process May be irreducible

Ulnar styloid process

Dorsiflexion or avulsion by ulnar collateral ligament or triangular fibrocartilage complex

Usually associated with radial fractures, can be isolated Usually undisplaced

A

Nonunion

B Fig. 2.39  Wrist fracture: Colles fracture. (A) Observe the transverse fracture of the distal portion of the radius, with intraarticular extension into the radiocarpal joint (arrowhead). (B) On the lateral projection, dorsal angulation of the articular surface of the radius is apparent and caused by compaction of bone dorsally (arrow). The ulnar styloid process is intact, and no evidence of subluxation of the distal portion of the ulna can be seen.

CHAPTER 2  Physical Injury: Upper Extremity

Fig. 2.40  Wrist fracture: Barton fracture. The dorsal rim of the distal portion of the radius is fractured (arrowhead). It is displaced proximally and posteriorly, with dorsal subluxation of the carpus (arrow).

on a fixed wrist (Fig. 2.40). It extends in an oblique fashion from the dorsal surface of the radius proximally to the articular surface of the radius distally without violating the volar surface of the radius and is accompanied by dorsal displacement of the carpus. The reverse Barton fracture is more common than the Barton fracture. The reverse Barton is a coronal fracture affecting the volar rim of the distal radius while the dorsal cortex remains intact. Carpal translation is a prominent feature of this injury. An oblique intraarticular fracture of the styloid process of the radius is often referred to as Hutchinson fracture or, because of its original occurrence when starting the crank of a car engine suddenly reversed during a backfire, chauffeur’s fracture (Fig. 2.41). An axial loading injury producing depression limited to the lunate facet of the distal radius is known as a die-­punch fracture. There is no universally accepted classification system for distal radial fractures or clear-­cut indications for conservative management versus surgical fixation. The majority of distal radial fractures can be managed with closed reduction and casting with good outcomes, particularly in pediatric patients. Surgical fixation is used most frequently in older patients with intraarticular fractures involving their dominant extremity. Features to assess that guide treatment include the degree of comminution, displacement and angulation, the extent of gap and depression at the articular surface, and associated fractures of the ulna and carpal bones.

Dislocation of the Distal Radioulnar Joint Dislocations of the distal radioulnar joint may be an isolated injury or occur in association with a fracture of the radius. The combination of a distal radioulnar dislocation with a fracture of the shaft of the radius is termed a Galeazzi fracture-­dislocation (Fig. 2.42). The fracture typically affects the radial shaft; less commonly, the fracture involves the distal end of the radius. Fractures of the radial neck and head, which may be associated with dislocation of the inferior radioulnar joint, are not

53

Fig. 2.41  Wrist fracture: radial styloid process. There is an intraarticular fracture of the distal radius (arrow) limited to the styloid process, without extension to the ulnar cortex of the radius. Note the undisplaced fracture of the ulnar styloid.

regarded as Galeazzi fracture-­dislocations unless the radial shaft is also fractured. Dislocation of the ulna usually occurs in a distal, dorsal, and medial direction; volar dislocation is less frequent.

Carpal Instability KEY CONCEPTS  • T hree smooth carpal arcs present at the wrist indicate normal intercarpal alignment. • Scapholunate dissociation results in widening of the interspace between the scaphoid and the lunate related to incompetence of the scapholunate ligament, often associated with volar rotation of the scaphoid. • The dorsal intercalary segment carpal instability pattern of carpal instability results in dorsal tilt of the lunate and an increased scapholunate angle. • The volar intercalary segment carpal instability pattern of carpal instability results in volar tilt of the lunate and a decreased scapholunate angle. • Perilunate and lunate dislocations are the early and late stages of a lesser arc injury; both are best appreciated on the lateral projection. • The classic perilunate dislocation involves dislocation of all of the carpal bones except the lunate dorsal to the radius, leaving the lunate behind to rest in its expected position with respect to the radius. • The classic lunate dislocation involves an isolated dislocation of the lunate bone volar to the radius and remaining carpal bones.

Normal Carpal Alignment Two important concepts regarding the radiographic anatomy of the wrist should be emphasized. First, on a posteroanterior view, three smooth carpal arcs define the normal intercarpal relationships (Fig. 2.43). Arc 1 follows the proximal surfaces of the scaphoid, lunate, and triquetrum; arc 2 is located along the distal surfaces of these same carpal bones; and arc 3 defines the curvature of the proximal surfaces of the capitate and hamate. In the normal situation, with the wrist in neutral position, these curvilinear arcs are roughly parallel, without

54

SECTION 1  Traumatic Disorders

2

*

3

1

Fig. 2.43  Carpal arcs. Three smooth carpal arcs define the normal intercarpal relationships of the wrist. Offsets in these lines indicate carpal fracture and/or instability.

Fig. 2.42  Galeazzi fracture-­dislocation. Transverse radial fracture (arrow) is associated with shortening and volar angulation, with dorsal dislocation of the distal end of the ulna (asterisk).

disruption, and the interosseous spaces are approximately equal in size. Second, a lateral radiograph of a normal wrist (in neutral position) is characterized by a specific relationship of the longitudinal axes of the radius, scaphoid, lunate, capitate, and third metacarpal. A continuous line can be drawn through the axes of the radius, lunate, and capitate, with an angle between 0 and 30 degrees. This line intersects a second line through the longitudinal axis of the scaphoid and creates an angle of 30 to 60 degrees. Alterations in these relationships (as well as others) indicate carpal instability, which is related to trauma in most instances.

Carpal Instability The complex anatomy and motions of the carpal bones predispose the wrist to a number of instability patterns. Carpal instability is considered to be present when symptomatic malalignment exists and the normal kinematics are disrupted during any portion of the arc of motion of the wrist. A number of classification systems for wrist instability have been proposed; the Mayo classification is most commonly used by hand surgeons. This classification divides carpal instability into four types; (1) dissociative, when malalignment occurs within the proximal or distal row; (2) nondissociative, when malalignment takes place at the radiocarpal or midcarpal joint; (3) complex, when there are both dissociative and nondissociative patterns; and (4) adaptive, when instability is caused by abnormal morphology of the distal radius or ulna. Instability patterns also can be defined as either static, when malalignment among the carpal bones is evident on routine radiographs, or dynamic, when such malalignment requires manipulation. Although

a wide range of instability patterns are encompassed in this scheme, only the most common characteristic and distinct patterns of carpal instability are discussed here. Scapholunate dissociation (rotatory subluxation of the scaphoid) is the most common form of dissociative instability. It should be suggested when the distance between the scaphoid and lunate is 3 mm or wider and can be diagnosed almost unequivocally when this distance is 4 mm or more (Fig. 2.44). Radiographs with a clenched fist highlight the gap between the two bones. In addition to widening of the scapholunate space and palmar tilting of the scaphoid, rotatory subluxation of the scaphoid is associated with other radiographic findings. These include, on a posteroanterior view, a ring produced by the cortex of the distal pole of the scaphoid and a foreshortened scaphoid. Two patterns of complex carpal instability that interrupt the normal carpal relationships in the sagittal plane and manifest in lunate tilt on the lateral view require emphasis (Fig. 2.45). Dorsal intercalary segment instability (DISI) is the more common of the two. In this pattern, the lunate is tilted dorsally, the scaphoid is tilted in a palmar direction, and the scapholunate angle is greater than 70 degrees (Fig. 2.46). The second pattern, volar intercalary segment instability (VISI), occurs when the lunate is tilted in a palmar direction and the scapholunate angle is decreased below the normal value of approximately 35 degrees (Fig. 2.47). Dorsiflexion instability commonly occurs after scaphoid fractures with scapholunate separation or dissociation as well as after fractures of the proximal portion of the radius. Palmar flexion instability may be seen after disruption of the lunotriquetral interosseous ligament, excision of the triquetrum, and sprains of the midcarpal joint that damage the extrinsic ligaments.

Carpal Dislocation Close inspection of the functional anatomy of the wrist and the patterns of injury indicates that a predictable sequence of events generally occurs after trauma. Lesser arc injuries occur in four stages, with each successive stage indicating increased carpal instability (Fig. 2.48). A stage I injury represents scapholunate dissociation with rotatory subluxation of the scaphoid; a stage II injury is characterized by

CHAPTER 2  Physical Injury: Upper Extremity

55

*

A

B Fig. 2.44  Scapholunate dissociation (rotatory subluxation of the scaphoid). (A) Findings on the posteroanterior view include scapholunate widening, malalignment of the proximal carpal arc between the scaphoid and lunate (arrowheads), and a foreshortened scaphoid (asterisk). (B) The scapholunate space (arrowhead) widens even further with ulnar deviation.

A

B

C

Fig. 2.45  Lateral (static) carpal instability. (A) Normal intercarpal rela­tions between the lunate and capitate (solid black line), and scaphoid (dotted red line) in the lateral projection. (B) Malalignment pattern of dorsal interca­lary segment instability (dashed black line, lunate axis; dashed red line, scaphoid axis). (C) Malalignment pat­ tern of volar intercalary segment instability.

perilunate dislocation; a stage III injury creates lunotriquetral ligamentous disruption; and a stage IV injury is associated with lunate dislocation. Greater arc injuries represent fracture-­dislocation patterns as this arc passes through the scaphoid, capitate, hamate, and triquetrum. A common pattern of carpal injury is a perilunate dislocation or transscaphoid perilunate fracture-­dislocation. In perilunate dislocation, the lunate remains aligned with the distal end of the radius and the other carpal bones dislocate, usually dorsally (Fig. 2.49). When the wrist is hyperextended, the dorsal cortex of the distal radial articular surface fixes the lunate in place and apposes the scaphoid waist. A fall on a hyperextended hand, which creates abnormal force through the radius, can produce a fracture of the scaphoid and, with sufficient stress, dislocation of the carpus. The distal fragment of the scaphoid may move with the distal carpal row, and the proximal fragment may

*

Fig. 2.46  Dorsal intercalary segment instability. Observe the dorsal tilt of the lunate (asterisk) and increased scapholunate angle on the lateral radiograph.

move with the proximal carpal row. With continued hyperextension force, the capitate may force the lunate ventrally, thus converting the perilunate dislocation into a lunate dislocation in which the lunate is displaced in a palmar direction and the capitate appears to be aligned with the distal end of the radius (Fig. 2.50).

56

SECTION 1  Traumatic Disorders

*

1 1 2 2

Fig. 2.47  Volar intercalary segment instability. Findings include palmar tilt of the lunate (asterisk) and distal pole of the scaphoid with a decreased scapholunate angle.

Fracture of the Carpal Bones

Fig. 2.48  Wrist injuries: greater and lesser arcs. The locations of the greater (1) and lesser (2) arcs are shown, as are the common sites of carpal fractures that can be produced experimentally. A pure greater arc injury consists of a transscaphoid, transcapitate, transhamate, transtriquetral fracture-­dislocation; a pure lesser arc injury is a perilunate or lunate dislocation. Various combinations of these injury patterns are seen clinically.

KEY CONCEPTS  • T he scaphoid is the most commonly fractured carpal bone. Because of its retrograde blood supply, proximal fractures have a high rate of complications, including nonunion and osteonecrosis. • Undisplaced scaphoid fractures can be difficult to see on conventional radiography. Obtain follow-­up radiographs or advanced imaging for posttraumatic snuffbox tenderness. • The second most common carpal fracture is at the dorsal surface of the triquetrum, best seen on the lateral radiograph. • Fractures of the hook of the hamate can be due to trauma or overuse. These are best evaluated with cross-­sectional imaging techniques, such as CT.

Approximately 65% of all carpal bone fractures involve the scaphoid bone (Fig. 2.51). These are often undisplaced and can be difficult to identify on the initial radiographs. Follow-­up radiographs after 7 to 10 days are recommended if there is snuffbox tenderness following a wrist injury, or CT and MR imaging can be utilized for initial diagnosis of occult scaphoid fractures. Fractures of the scaphoid are classified principally according to their location (proximal pole, waist, distal body, tuberosity, distal articular), because the site of involvement affects the likelihood of osteonecrosis and the rate of healing. In general, the prognosis of distal fractures is better than that of proximal fractures. The most frequent scaphoid fractures occur in the waist (approximately 70%) or proximal pole (approximately 20%). The frequency of delayed union or nonunion is greatest in fractures of the proximal pole and in those associated with displaced fragments. Radiographic abnormalities of scaphoid include bone sclerosis, cyst formation, widening of the scapholunate space, bone resorption, and, subsequently, radiocarpal and intercarpal osteoarthrosis (Fig. 2.52). The frequency of osteonecrosis after scaphoid fractures is approximately 10% to 15%; this frequency rises to 30% to 40% in the case of nonunion. MR imaging, with or without intravenous contrast, is often used for assessment of scaphoid viability, though the accuracy of MR imaging for the diagnosis of osteonecrosis remains controversial.

*

Fig. 2.49  Perilunate dislocation. Observe the alignment of the lunate (arrowheads) with the distal end of the radius and dorsal displacement of the capitate (asterisk) and the rest of the carpal bones.

Isolated fractures of the other carpal bones are less frequent. Triquetral fractures represent 3% to 4% of all carpal fractures. The dorsal surface of the triquetrum is typically fractured, related either to contact with the hamate or ulnar styloid process or to avulsion by the extrinsic carpal ligaments (Fig. 2.53). Isolated fractures of the lunate constitute 2% to 7% of all carpal fractures. Hamate fractures account for 2% to 4% of all carpal fractures and may involve any portion of the bone. Fractures of the hook of the hamate deserve emphasis. These injuries may result from a fall on a dorsiflexed wrist with force transmitted

CHAPTER 2  Physical Injury: Upper Extremity

*

A

57

*

B Fig. 2.50  Lunate dislocation. (A) Anteroposterior view of the wrist shows disruption of the carpal arcs at the proximal carpal row and an abnormal contour of the lunate (asterisk), which appears triangular. (B) On the lateral view, note the volar displacement and rotation of the lunate (asterisk), with the capitate (solid arrow) remaining above the radius, though it is slightly subluxed dorsally relative to the central radial concavity (arrowhead), illustrating the difficulty of classifying such lesions as purely lunate or perilunate dislocations.

joint, often associated with fractures at the base of the first metacarpal (Fig. 2.55). The Bennett fracture-­dislocation results in a triangular intraarticular avulsion fracture at the ulnar base of the first metacarpal. The fragment remains attached to the volar capsular structures and remains in situ while the shaft fragment is pulled dorsally and radially. A second intraarticular fracture of the proximal first metacarpal, the Rolando fracture, is comminuted and results in a Y-­or T-­shaped fracture line.

Metacarpophalangeal Joint

Fig. 2.51  Carpal scaphoid fracture. An acute transverse fracture at the waist of the scaphoid (arrows) shows minimal displacement between the fracture fragments.

through the transverse carpal and pisohamate ligaments, or from a direct force, such as occurs in athletes who use rackets, bats, or clubs. Overuse injury can result in stress fractures of the hamate that are often incomplete. Accurate clinical and radiographic diagnosis is difficult— specialized radiographic projections and techniques, particularly CT scanning, may be required (Fig. 2.54). Complications of fractures of the hook of the hamate include nonunion, osteonecrosis, injuries to the ulnar or median nerve, and tendon rupture.

Thumb Carpometacarpal Joint

Dislocation of the carpometacarpal joint is not rare at the thumb and results in disruption of the capsular ligaments that stabilize this critical

Dislocations and collateral ligament injuries of the first metacarpophalangeal joint are important complications of trauma. Gamekeeper’s thumb, related to a sudden valgus stress applied to the metacarpophalangeal joint of the thumb resulting in injury to the ulnar collateral ligament or its osseous insertions, has received the most attention. Initially described as an occupational hazard in English game wardens, the injury is now recognized as occurring in various settings, including skiing. Initial radiographs may be negative, although small avulsed fracture fragments from the base of the proximal phalanx can be delineated in up to a third of cases (Fig. 2.56). In gamekeeper’s thumb injuries, attenuation or disruption of the ulnar collateral ligament may be accompanied by interposition of the adductor aponeurosis between the torn ligament and bone (Stener lesion), best evaluated with MR imaging or ultrasonography.

Fingers Metacarpal Fractures

Fractures of the metacarpal bones, which predominate in the first and fifth digits, are generally classified according to anatomic location: metacarpal head, metacarpal neck, metacarpal shaft, and metacarpal base. Metacarpal neck fractures typically result from axial loading while the metacarpophalangeal joint is flexed, with the majority affecting the fifth metacarpal (boxer fracture). These fractures typically show shortening and volar angulation of the distal fragment (Fig. 2.57). Less commonly, direct blows and rotational injuries result in transverse or spiral fractures of the metacarpal shaft, respectively. Spiral fractures may result in rotary malalignment that can be difficult to recognize

58

SECTION 1  Traumatic Disorders

A

B Fig. 2.52  Carpal scaphoid fracture: nonunion and osteonecrosis. (A) Posteroanterior radiograph shows a nonunited fracture (arrow) in the proximal scaphoid with volume loss and increased density of the proximal portion of the scaphoid bone. A small bone fragment above the ulna (arrowhead) is an intraarticular body. (B) T1-weighted MR image shows low signal within the proximal fragment along with secondary osteoarthrosis at the radioscaphoid joint and cystic change in the capitate (arrowhead).

into hyperextension. The index finger is most commonly involved. In cases of complex dislocation, radiographs may reveal a widened joint space following reduction, indicative of interposition of the volar plate or capsular structures within the joint. An adjacent sesamoid can also become displaced into the joint space. Dislocations of the proximal interphalangeal joints are very common and may occur with or without an adjacent phalangeal fracture. These dislocations can occur in a dorsal or volar direction, dorsal dislocation being far more common, accounting for up to 90% of all dislocations at this joint (Fig. 2.58). Dorsal dislocation results from a hyperextension injury; ligamentous and volar plate disruption is a frequent associated finding.

Phalangeal Fractures

Fig. 2.53  Carpal fracture: dorsal surface of the triquetrum. Lateral radiograph shows a small flake of bone avulsed from the dorsal surface of the triquetrum with overlying soft tissue swelling (arrowhead).

on radiographs. Metacarpal base fractures are related to high-­energy trauma, are often intraarticular, and may be associated with carpometacarpal subluxation or dislocation.

Metacarpophalangeal and Interphalangeal Joint Dislocation Metacarpophalangeal joint dislocation at the fingers occurs considerably less frequently than dislocation of a proximal interphalangeal joint. It results from a fall on an outstretched hand that forces the joint

Phalangeal fractures are more frequent than metacarpal fractures. They typically involve the distal phalanges, followed in order of frequency by the proximal phalanges and the middle phalanges. Proximal phalangeal fractures result from similar mechanisms as metacarpal shaft fractures and typically affect the shaft, though subcondylar neck fractures at the proximal phalanx are also common, especially in children. Proximal phalangeal fractures are often unstable and require surgical fixation more frequently than those affecting the other phalanges. Middle phalangeal fractures are typically related to proximal interphalangeal joint dislocation. These include volar plate fractures related to dorsal dislocation of a proximal interphalangeal joint and dorsal avulsion fractures related to avulsion by the extensor central slip attachment following palmar dislocation (Fig. 2.59). Comminuted basal pilon fractures from axial loading also affect the middle phalanx. Distal phalangeal fractures include crushing injuries of the tuft related to a direct blow, the mallet fracture, in which the dorsal base of the distal phalanx is avulsed by the extensor tendon, and the jersey finger, in which the volar base of the distal phalanx is avulsed by the flexor profundus tendon (Fig. 2.60). In the immature skeleton, physeal separation at the base of the distal phalanx can be associated with injury to the overlying nail bed, resulting in an open fracture at risk for secondary infection.

CHAPTER 2  Physical Injury: Upper Extremity

59

A Fig. 2.55  Fracture-­dislocation of the first carpometacarpal joint. Radiograph shows an oblique intraarticular fracture of the first metacarpal (or Bennett fracture), which is proximally and radially displaced relative to the trapezium (arrow). There is also a displaced trapezium fracture (arrowhead).

B Fig. 2.54  Carpal fracture: hamate. (A) Carpal tunnel radiograph shows a fracture of the hook of the hamate (arrow) with volar displacement of the hook fragment. (B) Axial CT image in a different patient shows a minimally displaced fracture at the base of the hook (arrowhead) that was not evident on radiographs.

Fig. 2.56  Gamekeeper’s thumb. Note the displacement and rotation of a triangular fracture fragment (arrowhead) arising from the ulnar aspect of the proximal phalanx of the thumb.

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SECTION 1  Traumatic Disorders

Fig. 2.59  Middle phalangeal fracture. Dorsal subluxation of the fourth proximal interphalangeal joint with a small volar plate avulsion fracture (arrow). Small avulsion fractures near the proximal interphalangeal or distal interphalangeal joint can result from traction on the volar plate. Fig. 2.57  Metacarpal fracture: boxer fracture. An oblique fracture at the neck of the fifth metacarpal (arrow) with minimal shortening and volar angulation.

A

Fig. 2.58  Interphalangeal joint dislocation. Dorsal dislocation of the fifth proximal interphalangeal joint without fracture.

B

Fig. 2.60  Distal phalangeal fractures. (A) Mallet fracture (arrow) at the dorsal base of the third distal phalanx related to avulsion by the extensor digitorum tendon. (B) Jersey finger fracture (arrowhead) at the volar base of the fourth distal phalanx related to avulsion by the flexor digitorum profundus tendon.

CHAPTER 2  Physical Injury: Upper Extremity

FURTHER READING Alyas F, Curtis M, Speed C, Saifuddin A, Connell D. MR imaging appearances of acromioclavicular joint dislocation. Radiographics. 2008;28(2):463–479. Bruno F, Arrigoni F, Palumbo P, Natella R, Maggialetti N, Reginelli A, Splendiani A, Di Cesare E, Bazzocchi A, Guglielmi G, Masciocchi C. The acutely injured wrist. Radiologic Clinics. 2019;57(5):943–955. Cibulas A, Leyva A, Cibulas G, Foss M, Boron A, Dennison J, Gutterman B, Kani K, Porrino J, Bancroft, LW, Scherer K. Acute shoulder injury. Radiologic Clinics. 2019;57(5):883–896. Carroll EA, Schweppe M, Langfitt M, Miller AN, Halvorson JJ. Management of humeral shaft fractures. J Am Acad Orthop Surg. 2012;20(7):423–433. Cockenpot E, Lefebvre G, Demondion X, Chantelot C, Cotten A. Imaging of sports-­related hand and wrist injuries: sports imaging series. Radiology. 2016;279(3):674–692. Flores DV, Goes PK, Gómez CM, Umpire DF, Pathria MN. Imaging of the acromioclavicular joint: anatomy, function, pathologic features, and treatment. Radiographics. 2020 Sep;40(5):1355–1382. Goldfarb CA, Yin Y, Gilula LA, Fisher AJ, Boyer MI. Wrist fractures: what the clinician wants to know. Radiology. 2001;219(1):11–28. Gyftopoulos S, Albert M, Recht MP. Osseous injuries associated with anterior shoulder instability: what the radiologist should know. Am J Roentgenol. 2014;202(6):W541–W550. Kani KK, Mulcahy H, Chew FS. Understanding carpal instability: a radiographic perspective. Skelet Radiol. 2016;45(8):1031–1043.

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Little JT, Klionsky NB, Chaturvedi A, Soral A, Chaturvedi A. Pediatric distal forearm and wrist injury: an imaging review. Radiographics. 2014;34(2):472–490. Melenevsky Y, Yablon CM, Ramappa A, Hochman MG. Clavicle and acromioclavicular joint injuries: a review of imaging, treatment, and complications. Skelet Radiol. 2011;40(7):831–842. Morell DJ, Thyagarajan DS. Sternoclavicular joint dislocation and its management: A review of the literature. World J Orthop. 2016;7(4):244. Nellans KW, Kowalski E, Chung KC. The epidemiology of distal radius fractures. Hand Clin. 2012;28(2):113–125. Rogers LF. Radiology of Skeletal Trauma. 3rd ed. New York: Churchill Livingstone; 2002. Ropp AM, Davis DL. Scapular fractures: what radiologists need to know. Am J Roentgenol. 2015;205(3):491–501. Sandstrom CK, Kennedy SA, Gross JA. Acute shoulder trauma: what the surgeon wants to know. Radiographics. 2015;35(2):475–492. Scalcione LR, Gimber LH, Ho AM, Johnston SS, Sheppard JE, Taljanovic MS. Spectrum of carpal dislocations and fracture-­dislocations: imaging and management. Am J Roentgenol. 2014;203(3):541–550. Scalcione LR, Pathria MN, Chung CB. The athlete’s hand: ligament and tendon injury. Semin Musculoskel R. 2012;16(4):338–350. Sheehan SE, Dyer GS, Sodickson AD, Patel KI, Khurana B. Traumatic elbow injuries: what the orthopedic surgeon wants to know. Radiographics. 2013;33(3):869–888. Wieschhoff GG, Sheehan SE, Wortman JR, Dyer GS, Sodickson AD, Patel KI, Khurana B. Traumatic finger injuries: what the orthopedic surgeon wants to know. Radiographics. 2016;36(4):1106–1128.

3 Physical Injury: Pelvis and Hip S U M M A R Y O F K E Y F E AT U R E S • T  raumatic injuries involving the pelvis, hip, and femur are common and a major cause of posttraumatic morbidity and mortality and health care expenditure.

  

INTRODUCTION This survey of physical injuries at the pelvis, acetabulum, proximal femur, and femoral shaft proceeds in a proximal to distal direction. It is not meant to compete with standard references but rather to provide an overview of the more important physical injuries occurring at the pelvis, hip, and femur. Although routine radiographic findings are emphasized in this chapter, computed tomography (CT) and magnetic resonance (MR) imaging techniques are also fundamental to the evaluation of traumatic injuries of the pelvis and hip. This chapter focuses primarily on fractures related to acute trauma; stress fractures of the pelvic region are discussed in further detail in Chapters 1, 29, and 59.

FRACTURES OF THE PELVIS General Considerations The bony pelvis is intimate with vital internal organs, and the evaluation of these organs is mandatory in cases in which osseous or ligamentous disruption is apparent. Hemorrhage caused by vascular injury to arteries, urinary tract injury, compression of peripheral nerves, and disruption of viscera are among the significant complications of pelvic fractures and dislocations. Excessive bleeding may accompany unstable pelvic fractures and is a significant cause of mortality and morbidity, particularly in elderly patients. The causes of excessive bleeding in the elderly include atherosclerosis, increased fracture comminution in the setting of brittle bones, fragility of the periosteum preventing tamponade, and the use of anticoagulant medications. The detection of active bleeding on contrast-­enhanced CT imaging, CT and conventional angiography, and interventional image-­guided procedures such as coil placement play a major role in the detection and treatment of vascular injury. Injuries to the urinary tract are typically associated with significant anterior disruption such as symphyseal diastasis, displaced fractures of the pubic rami, or both. Urethral damage is somewhat more frequent than injury to the bladder, typically involving the membranous or bulbous urethra. Bladder injury can take the form of contusion, intraperitoneal rupture, extraperitoneal rupture, or combined injury (Fig. 3.1). Damage to the peripheral nerves occurs in approximately 10% of patients after injuries to the bony pelvis, and this frequency increases in those with sacral fractures. Imaging examinations directed at the detection of such complications are as fundamental to the proper analysis of pelvic fractures and dislocations as is imaging of the bones themselves.

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• Th  e incidence of injuries involving the pelvic girdle is increasing with an aging population. • Imaging plays a major role in the diagnosis and classification of injuries in this region.

Classification of Pelvic Fractures KEY CONCEPTS  • D  amage to nonosseous structures such as the genitourinary tract and pelvic vasculature results in significant morbidity and mortality in patients with pelvic fractures. • Fractures of the pelvis are divided into stable and unstable categories based on how many sites of disruption are present at the pelvic ring. • Pelvic ring disruption can take the form of fractures or disruption of the symphyseal and sacroiliac articulations. • Single breaks in the pelvic ring tend to be stable. • Double breaks in the pelvic ring tend to be unstable.

Fractures of the pelvis, which account for approximately 3% of all fractures, have been classified in several ways, based on such factors as the site of involvement, direction of force, mechanism of injury, and presence or absence of instability. The major forces acting on the pelvic ring are anterior compression, lateral compression, vertical shear, and complex forces. The flattened planes of the symphyseal and sacroiliac articulations provide little osseous stability; the stability of the pelvic ring is considered to depend primarily on the integrity of its ligamentous structures, especially those located posteriorly. Instability is most characteristic of injuries resulting from vertical shear and complex forces. Several classification systems are used for fractures involving the pelvic ring. The Key and Conwell system is simple to use and divides pelvic fractures into four categories. Stable fractures do not disrupt the osseous ring or disrupt it in only one location, whereas mildly unstable and grossly unstable fractures disrupt the ring in two or more locations. Acetabular fractures form a separate category because the management in these injuries is directed toward reestablishing articular congruity. This system is no longer widely used because it lacks sufficient precision to guide the orthopedic surgeon. The Tile classification also divides pelvic injuries into stable and unstable categories, but it subdivides the unstable group into those injuries that produce only rotational instability as compared to more serious injuries that result in both rotational and vertical instability. Rotational instability occurs as a result of a combination of anterior and posterior injuries allowing the iliac wing to rotate, typically externally with anteroposterior (AP)

CHAPTER 3  Physical Injury: Pelvis and Hip

63

Fig. 3.2  Rotational instability. Axial CT shows bilateral widening of the anterior aspect of the sacroiliac joints (arrows), more pronounced on the right, with normal alignment posteriorly. This pattern of injury allows the iliac wings to rotate externally.

* A

*

A

B

Fig. 3.3  Stable pelvic fractures. (A) Type I injury: avulsion fracture. This injury may involve the anterior superior iliac spine (1), anterior inferior iliac spine (2), or ischial tuberosity (3). (B) Type I injury: fracture of a single pubic ramus or iliac wing (Duverney fracture). A single break in the superior or inferior pubic ramus (1 and 2), certain fractures of the ilium (3), and some types of fractures of the sacrum (4) or coccyx (5) do not lead to disruption of the pelvic ring.

B Fig. 3.1  Posttraumatic bladder rupture. (A) AP radiograph shows disruption of the pubic symphysis with a displaced symphyseal fragment (asterisk), a vertical fracture of the right sacrum disrupting the arcuate lines (arrow), and diastasis at the left sacroiliac joint (arrowhead). (B) Axial CT after IV contrast administration shows contrast material extravasation around the bladder extending laterally (arrows). The bladder contains gas (asterisk) related to catheterization.

compression, and internally with lateral compression. Such injuries typically involve damage to the anterior sacroiliac ligaments, with relative preservation of the posterior sacroiliac complex (Fig. 3.2). Vertical instability is less common, typically caused by multiple fractures in the setting of complete disruption of the posterior sacroiliac ligament complex on one side, allowing one hemipelvis to displace cranially or caudally. The widely used Young and Burgess classification divides injuries according to mechanism, describing varying degrees of instability related to lateral compression, AP compression, vertical shearing, and combined forces (Table 3.1). This system excludes fractures that involve the acetabulum, and such injuries will be discussed separately. It should be emphasized that all of these classification systems were devised based on radiographic analysis; a recent series analyzing pelvic fracture patterns using CT imaging identified numerous additional patterns of injury that do not conform to these traditional systems.

Stable Pelvic Fractures Stable injuries, which do not involve the pelvic ring or fracture it in only one site, represent approximately 30% of all injuries that involve the bony pelvis. This category includes apophyseal avulsion fractures, isolated pubic rami fractures, transverse fractures of the sacrum and coccyx, and fractures isolated to the iliac wing (Fig. 3.3).

Avulsion Fractures of the Pelvis Avulsion fractures of the pelvis and hip occur at sites of muscular and tendinous insertions in both skeletally immature and adult populations, though the vast majority of such injuries are found in adolescents with unfused apophyses, most commonly related to injury during sports. The most common locations for apophyseal avulsion fractures are the ischial tuberosity, anterior superior iliac spine, and anterior inferior iliac spine. The ischial tuberosity is the most commonly injured, related to excessive tension by the hamstring and adductor magnus tendons. Ischial apophyseal fragments are larger than those associated with other apophyseal avulsions, appearing as a prominent arcuate-­shaped fragment of bone displaced inferior to the ischium. Because a large portion of the ischial apophysis is located posterior to the ischial body, the bony defect at the underlying ischium may appear insignificant relative to the size of the displaced fragment. The sartorius tendon and portions of the tensor fascia lata insert at the anterior superior iliac spine and are responsible for avulsion fractures at this region (Fig. 3.4). The anterior inferior iliac spine is the attachment site for the rectus femoris tendon

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SECTION 1  Traumatic Disorders

TABLE 3.1  Pelvic Fracture Classification Type of Injury

Morphologic Characteristics

Stable Pelvic Fractures Avulsion fractures

Apophyseal avulsion in adolescence

Pubic ramus

Single ramus Ipsilateral superior and inferior pubic rami

Low sacrum

Transverse sacrum Coccyx

Duverney

Iliac wing fracture

Unstable Pelvic Fractures Type of injury

Morphologic characteristics

Lateral compression (all forms)

Transverse overlapping pubic rami fractures Oblique pubic rami fractures

Lateral compression 1

Impacted buckle fracture of sacrum (minor or no instability when underlying bone is osteopenic)

Lateral compression 2

Iliac crescent fracture

Lateral compression 3

Lateral compression 1-­2 with AP compression injury on contralateral side

AP compression (all forms)

Diastasis of pubic symphysis (Young and Burgess classification) Vertical pubic rami fractures (Tile classification)

AP compression 1

2.5 cm diastasis, widening anterior SI joint

AP compression 3

>5 cm diastasis, widening of both anterior and posterior SI joint

Vertical shear

Fractures of pubic rami and SI disruption with vertical displacement of hemipelvis

Combined

Complex pelvic fracture with combined elements of above

AP, Anteroposterior; SI, sacroiliac. Modified from Khurana B, Sheehan SE, Sodickson AD, Weaver MJ. Pelvic ring fractures: what the orthopedic surgeon wants to know. Radiographics. 2014;34(5):1317–1333.

Fig. 3.4  Apophysis avulsion fracture. AP radiograph of the pelvis shows inferior displacement of the anterior superior iliac apophysis (arrow) related to a traction injury by the sartorius. Note the open iliac wing and ischial apophyses in this adolescent.

and is often avulsed during sprinting or kicking sports (see Fig. 1.68). Less common sites of apophyseal avulsion fractures include the iliac wing apophysis (abdominal muscles), the pubic symphysis (adductor muscles, gracilis), and the lesser trochanter (iliopsoas tendon). Apophyseal avulsion fractures are usually diagnosed on radiographs, which show the fracture well if the apophysis is ossified and the avulsed bone is displaced. Avulsions of the superior and inferior iliac spines may be overlooked on AP radiographs; shallow oblique radiographs can be helpful. CT or MR imaging can be used to identify such injuries before apophyseal ossification, if the radiographs are equivocal, and to further assess the regional soft tissues (Fig. 3.5).

Fig. 3.5  MR image of ischial avulsive injury. Coronal fluid-­sensitive MR image of the pelvis shows widening, irregularity, and fluid within the right ischial apophysis (arrows), with surrounding soft tissue edema related to a subacute avulsion injury at the hamstring insertion. (Courtesy Dr. Jerry R. Dwek, MD, San Diego, CA.)

Fractures of the Pubic Rami A single pubic ramus fracture or ipsilateral fractures of the superior and inferior ramus are considered stable injuries. Fractures of the pubic rami are common, occur in elderly patients after a fall or in the form of stress fractures in athletes and after hip surgery, and are somewhat more frequent in the superior ramus than the inferior ramus. Bilateral

CHAPTER 3  Physical Injury: Pelvis and Hip rami fractures are typically seen in the setting of more significant pelvic injury and are often associated with fractures of the posterior pelvis.

Fracture of the Sacrum Isolated transverse fractures of the sacrum and coccyx located below the sacroiliac joints do not disrupt the pelvic ring and are therefore considered mechanically stable. Neurologic compromise related to malalignment of the sacral canal, resulting in compression or disruption of the sacral nerve roots is a recognized complication. Transverse fractures of the sacrum should be distinguished from vertical fractures, which may be associated with additional osseous and ligamentous injuries, and from insufficiency stress fractures, which occur in an osteopenic skeleton and have both a vertical and a horizontal configuration. It has been estimated that over half of sacral fractures are overlooked on radiographs, particularly in osteoporotic patients. In all instances of sacral fracture, careful radiographic analysis of the foramina and arcuate lines is required.

Duverney Fracture An isolated fracture of the iliac wing, or Duverney fracture, follows a high-­force direct lateral compression injury such as a fall, pedestrian struck by a moving vehicle, or an unrestrained passenger being thrown to the side during a motor vehicle accident (Fig. 3.6). Iliac wing fractures are often depressed and comminuted and associated with significant swelling and hemorrhage. Although the fracture is mechanically stable, concomitant injuries to the local adjacent soft tissues, vasculature, and abdominal structures contribute to significant morbidity, particularly in osteoporotic patients who tend to show a higher degree of comminution at the fracture.

Unstable Pelvic Fractures KEY CONCEPTS  • T he principal mechanisms responsible for unstable pelvic injury include AP compression, lateral compression, and vertical shear. • The majority of unstable pelvic fractures result from lateral compression. • Lateral compression injuries produce horizontal pubic rami fractures and impaction fractures of the sacrum; they ultimately result in diastasis of the sacroiliac joint opposite the side of impact. • Anterior compression injuries produce symphysis diastasis, vertical pubic rami fractures, and, ultimately, diastasis of the sacroiliac joints. • Vertical shear injuries result in craniocaudad displacement of the injured portion of the pelvis.

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Unstable injuries of the pelvis disrupt the pelvis in at least two places (Fig. 3.7). Unstable pelvic injuries are generally classified by the mechanism of injury into those resulting from anterior compression, lateral compression, or vertically directed forces. Of these, the most common mechanism is lateral compression. More extensive disruptions of the pelvis result from complex injury patterns and massive crushing injuries in which the osseous ring is disrupted in multiple locations or completely shattered.

Lateral Compression Lateral compression causes over 50% of all pelvic ring fractures. A force directed from the lateral side results in oblique or horizontal pubic rami fractures and impaction fractures of the sacrum (Fig. 3.8). The impaction fracture at the sacrum in low-­grade lateral compression injuries is often difficult to appreciate on radiographs. On CT imaging, sacral impaction fractures often produce only subtle buckling of the anterior sacral cortex rather than a frank lucent fracture line. With further lateral compression, the ipsilateral iliac wing rotates inward, resulting in an ipsilateral fracture of the posterior iliac wing and crushing of the ipsilateral sacroiliac ligaments when the force is particularly severe. With even greater force, the contralateral sacroiliac ligaments tear, allowing sacroiliac diastasis and external iliac rotation away from the direction of the force.

Anterior Compression Anterior compression injuries represent 20% of all pelvic fracture patterns and are accompanied by urethral or visceral damage in about 30% to 40% of cases. Anterior compression injuries initially result in diastasis of the pubic symphysis or vertical fractures of the pubic rami. Straddle injuries are typified by disruption of the anterior portion of the pelvis in at least two places; bilateral vertical fractures involving both pubic rami or a unilateral fracture of both rami combined with symphyseal diastasis fulfills this criterion. With greater force, the degree of symphysis diastasis and/or pubic rami fracture displacement increase. Diastasis of the symphysis pubis greater than 15 mm should raise the strong possibility of disruption of the posterior aspect of the pelvic ring as well. As the injury progresses from the anterior to the posterior pelvic ring, it results in diastasis of the anterior sacroiliac joints, which can be unilateral or bilateral. The sacroiliac injury affects the anterior joint initially, widening the anterior joint and allowing external rotation of the iliac bone. The posterior sacroiliac ligaments fail when the injury is extremely violent. Wide diastasis of the pubic symphysis and disruption of both sacroiliac joints is often referred to as an “open-­book” injury (Fig. 3.9).

Vertical Shearing

Fig. 3.6  Duverney fracture. AP radiograph of the pelvis demonstrates a mildly displaced fracture (arrows) limited to the right iliac wing. The fracture appears sclerotic because of overlapping of bone fragments.

Vertical shearing injuries at the pelvis are uncommon and represent less than 15% of all injuries to the bony pelvis. These develop from a vertically directed force to the pelvis as the result of direct impact to the ischium from high-­energy trauma or direct impact on an extended leg when falling from a height. The force results in vertically oriented fractures of the pubic rami and sacrum with craniocaudad displacement of fracture fragments. In younger patients, the bone may remain intact and the injury can take place at the pubic symphysis and sacroiliac ligaments. The term Malgaigne fracture is often applied to a variety of injuries that have ipsilateral disruption of the anterior and posterior regions of the pelvic ring related to vertical instability. Forms of this injury include (1) a vertical fracture of both pubic rami combined with either dislocation of the sacroiliac joint

66

A

SECTION 1  Traumatic Disorders

B

C

D

Fig. 3.7  Unstable pelvic injury. (A) Note the disruption of the pelvis in two locations as a result of bilateral vertical fractures involving both pubic rami. (B) Vertical fractures of both pubic rami on one side combined with a sacral fracture lead to disruption of the pelvic ring in two locations. (C) Vertical fractures of both pubic rami on one side combined with dislocation of the sacroiliac joint produce disruption of the pelvic ring in two locations. (D) Disruption of the pelvic ring as a result of bilateral dislocations of the sacroiliac joint and diastasis of the symphysis pubis.

A

Fig. 3.9  Anterior compression. The AP pelvic radiograph demonstrates wide diastasis of the pubic symphysis and marked widening of the right sacroiliac joint (arrows).

FRACTURES OF THE ACETABULUM KEY CONCEPTS 

B Fig. 3.8  Lateral compression. (A) Radiograph reveals a horizontal fracture at the right superior pubic ramus (arrow) and a minimally impacted fracture of the left symphysis (arrowhead). (B) Axial CT image shows buckling at the anterior sacral cortex (arrows) related to bilateral impaction fractures that are difficult to appreciate on the radiographs.

or fracture of the ilium or sacrum, and (2) symphyseal dislocation combined with either dislocation of the sacroiliac joint or fracture of the ilium or sacrum (Fig. 3.10). The key finding in vertical shearing injuries is cephalad displacement of the iliac crest on the injured side, which is most apparent on outlet views of the pelvis or on coronal CT reformatted images.

• F ractures of the acetabulum are considered separately from other pelvic fractures because articular incongruity at the hip joint has a significant impact on management and prognosis. • On radiographs, careful analysis of the normal lines contributing to the acetabulum helps identify acetabular injuries. • The Judet and Letournel classification divides acetabular fractures into 10 categories based on detailed analysis of the fracture pattern. • CT plays a critical role in classifying acetabular injuries.

Acetabular fractures result from the impact of the femoral head against the acetabular roof, central regions of the acetabulum, or its rims (walls). Although the radiographic examination is an important step in the initial evaluation of acetabular fractures, CT imaging plays a vital role in the assessment and classification of acetabular trauma. On radiographs, delineation of six bony landmarks remains fundamental to a proper assessment of the extent of injury: acetabular dome (roof), medial acetabular wall (quadrilateral plate), anterior acetabular rim, posterior acetabular rim, iliopectineal (anterior) column, and ilioischial (posterior) column (Fig. 3.11). With CT imaging, the integrity of each of these structures can be determined with great accuracy, as well as the congruity of the articular surfaces of the acetabular dome

CHAPTER 3  Physical Injury: Pelvis and Hip

67

A

*

B Fig. 3.10  Vertical shear. (A) The AP pelvic radiograph demonstrates complete disruption of the left sacroiliac joint, allowing the left iliac wing to displace cranially. There are fractures at the left pubic rami. (B) The CT image shows dislocation of the left sacroiliac joint with the ilium completely displaced anterior to the sacrum (asterisk). Note the fracture of the right iliac wing (arrow) and contrast extravasation (arrowheads) from bladder rupture.

and quadrilateral surface, and the presence of intraarticular osseous fragments and associated fractures of the bony pelvis (Fig. 3.12). Articular surface incongruity following acetabular fractures results in high rates of posttraumatic osteoarthrosis of the hip joint. Other complications of acetabular fractures include ischemic necrosis of the femoral head, heterotopic ossification, and hemorrhage, as well as urinary tract, bowel, and peripheral nerve injury. Although numerous classification systems are described for fractures involving the acetabulum, the Judet and Letournel classification is most widely used. This system divides acetabular fractures into five elemental types. The designation elemental fractures is used to describe injuries to one structural component of the acetabulum or its supporting structures; such fractures involve the posterior wall, are transverse, involve the anterior or posterior column, or affect the anterior wall, in decreasing order of frequency. Isolated posterior wall fractures are encountered commonly, typically related to posterior hip dislocation, whereas isolated fractures of the anterior wall are rare. Fractures may involve the anterior or posterior column alone, or a transverse fracture may involve both columns. There are five additional variations of these basic elemental patterns related to associated fractures, resulting in a total of 10 separate fracture types. This second grouping refers to various combinations of elementary fractures with other fractures, including fractures of the posterior wall combined with transverse fractures, fractures of both columns, T-­shaped fractures, and other fracture patterns, again in decreasing order of frequency.

Fig. 3.11  Acetabular lines. The normal acetabular lines are illustrated on a normal hip radiograph. These include the acetabular roof (dotted line), ilioischial line (white line), iliopectineal line (black line), medial wall (dashed line), posterior wall (white arrows), and anterior wall (black arrows).

HIP DISLOCATION AND SUBLUXATION KEY CONCEPTS  • H  ip dislocations are classified as posterior, anterior, or central. • The most common direction of hip dislocation is posterior, resulting in posterior/superior displacement of the femoral head relative to the acetabulum. • The hallmark of a posterior dislocation is a fracture of the posterior wall of the acetabulum. • Anterior dislocations typically result in the femoral head displacing toward the obturator foramen. • Central dislocations are rare and show complex patterns of acetabular fractures.

Dislocation of the femoral head with or without an acetabular fracture usually follows considerable trauma and represents approximately 5% of all articular dislocations. Hip dislocations are generally classified as posterior, anterior, or central. More than 80% of hip dislocations are posterior, whereby the femoral head dislocates posteriorly relative to the acetabulum, typically related to a high-­impact injury such as a motor vehicle accident or a fall from a height.

Posterior Hip Dislocation Posterior dislocation of the hip often results from a “dashboard injury,” in which the flexed knee strikes the dashboard during a head-­on automobile collision. Concomitant injury to the hip, capsule, paraarticular soft tissues, sciatic nerve, and femoral head vasculature is common. The femoral head typically migrates superiorly, and the leg is held in a shortened, internally rotated, and adducted position. Uncommonly,

68

SECTION 1  Traumatic Disorders

A

B

Fig. 3.12  Acetabular fracture. (A) The AP radiograph illustrates a right acetabular fracture disrupting the inner acetabular roof and the iliopectineal and ilioischial lines. (B) Three-­dimensional CT image shows, in vivid fashion, the transverse plane of the fracture with disruption of both the anterior and posterior columns.

*

A

B

Fig. 3.13  Hip dislocation: posterior dislocation. (A) Radiograph shows posterosuperior displacement of the femoral head and a large displaced fragment (white arrow) arising from the posterior acetabular lip. An impaction fracture of the inferior aspect of the femoral head (black arrows) is also apparent. (B) Axial CT scan shows the posterior wall fracture fragment (arrow) extending to involve the posterior edge of the acetabular roof (asterisk). Note the small fragments within the joint.

posterior dislocation of the hip takes place without superior femoral head migration; such injuries are challenging to recognize on the AP radiograph but are well shown on lateral radiographs or CT images. Fractures of the posterior lip of the acetabulum are commonly present and highly suggestive of this injury. These may consist of a small cortical fragment at the peripheral rim of the acetabulum, a large osteochondral portion involving the posterior articular surface, or, less commonly, extension from the posterior rim to also involve the acetabular dome or medial wall. Osteochondral impaction fractures of the anterior aspect of the femoral head also may be present, typically located at or below the fovea (Fig. 3.13). Whereas large posterior acetabular rim fractures are readily detected on radiographs, particularly with the use of oblique Judet views, small acetabular rim fractures and osteochondral impaction fractures of the femoral head are better evaluated with CT images. The posterior

rim fractures are often comminuted and can displace, resulting in intraarticular fragments. A persistently widened hip joint following reduction suggests abnormally placed intraarticular fragments on fragments; however, intraarticular bone fragments can be difficult to identify on conventional radiography. CT imaging is well suited for identifying displaced intraarticular osseous fragments. Occasionally, CT images demonstrate a few small bubbles of gas within the hip joint following a dislocation, even following a closed injury (Fig. 3.14). Although intraarticular hemarthrosis or lipohemarthrosis and posterior soft tissue edema are apparent on both CT and MR images, associated tearing of the acetabular labrum, hip capsule, and ligaments, as well as muscle strains of the external rotator, quadratus femoris, and gluteal muscles, is better evaluated with MR imaging. Advanced imaging should be obtained following reduction of the hip to minimize the risk for osteonecrosis, which is increased when

CHAPTER 3  Physical Injury: Pelvis and Hip

69

Fig. 3.14  Hip dislocation: posterior dislocation. The transverse CT image shows intraarticular gas (black arrow) and fat (white arrow) layering at the top of an effusion. Intraarticular bone fragments are seen at the medial joint (arrowhead). There is irregularity from a displaced posterior wall fracture and bone fragments in the posterior soft tissues, which are thickened related to dislocation.

reduction is delayed beyond 6 hours. Long-­term complications of posterior hip dislocation include femoral head osteonecrosis, premature osteoarthrosis of the hip joint, and heterotopic ossification in the adjacent soft tissues.

A

Anterior Hip Dislocation Anterior dislocation of the hip represents 5% to 10% of all hip dislocations and is caused by a high-­energy force placing the femur in forced abduction, extension, and external rotation. Anterior dislocations can be superior or inferior relative to the acetabular plane. The leg position with anterior dislocation is typically abducted and externally rotated rather than adducted and internally rotated as it is with posterior hip dislocation Anterior inferior dislocations represent 90% of anterior hip dislocation. In this injury, radiographs clearly show the abnormal position of the femoral head; on frontal radiographs, an anteriorly displaced femoral head typically moves inferomedially and overlies the obturator foramen. Rarely, the femoral head may even approach the level of the pubic symphysis. Anterior superior dislocations are rare and may be difficult to distinguish from posterior dislocation in radiographs unless one notes the characteristic posture of the leg. In both types of anterior hip dislocations, osteochondral impaction fractures of the superior aspect of the femoral head are common, and additional associated fractures of the acetabular rim, greater trochanter, or femoral neck may be observed. Major ligament injury to the intrinsic and extrinsic hip capsule is present and in cases of obturator dislocation, injury to the obturator nerve can lead to denervation myopathy of the adductor muscles (Fig. 3.15).

Central Hip Fracture-­Dislocation Central acetabular fracture-­dislocation usually results from a force applied to the lateral side of the trochanter and pelvis, with the stress applied to the medial acetabular wall through the femoral head. The intrapelvic displacement of the femoral head results in various patterns of acetabular fracture, complicating this injury, and associated nerve injury and hemorrhage into the pelvis are commonly observed. If the injury extends to involve the acetabular roof, posttraumatic osteoarthrosis of the joint is common. Radiographs show the medial displacement of the femoral head, but CT scanning is the preferred imaging method for assessment of these injuries. Uncommonly, simultaneous

R 1 7 3

* *

B

P119

Fig. 3.15  Hip dislocation: anterior dislocation. (A) Radiograph reveals an inferomedial position of the femoral head overlying the obturator foramen. (B) Axial fluid-­sensitive MR image obtained 3 weeks later for persistent leg weakness shows edema within the adductor muscles (asterisks) resulting from subacute denervation myopathy related to injury to the obturator nerve.

bilateral central acetabular fractures can be seen following a seizure. The central acetabulum is also a common site for pathologic fractures; these tend to be highly comminuted and allow greater displacement of the femoral head into the pelvis (Fig. 3.16).

Transient Hip Subluxation The hip may undergo transient posterior subluxation and then reduce spontaneously, particularly during athletic activities such as football and soccer. Recognizing such injuries is challenging unless there is a fracture at the posterior acetabular rim, indicating the femoral head is displaced posteriorly impacting the acetabulum. Characteristic soft tissue findings that accompany this injury include tearing of the iliofemoral ligament at its femoral neck insertion and avulsion injuries of the posterior labrum, transverse ligament, and ligamentum teres (Fig. 3.17).

70

SECTION 1  Traumatic Disorders Although many fractures of the proximal femur are the result of major trauma, a significant number are caused by relatively minor injury such as a fall from standing height, particularly among osteoporotic elderly patients. Fractures involving the proximal femur are increasing in frequency as the population ages and are a major cause of morbidity, mortality, and health care expenditure. Among the elderly, there is an associated excess mortality rate as high as 10% to 30% within the year following such an injury. Treatment of such fractures has therefore become more aggressive with early surgical fixation of fractures, ideally within 48 hours, in an attempt to limit periods of immobility and improve outcome.

*

Classification

Fig. 3.16  Hip dislocation: central dislocation. Radiograph reveals medial displacement of the femoral head (arrow) into the pelvis at the site of a pathologic fracture of the acetabulum related to extensive acetabular bone destruction from multiple myeloma. Multiple additional lesions are present, including large lesions at the right femur (asterisk) and left ischium, which is also fractured (arrowhead).

*

Fig. 3.17  Transient hip subluxation. Oblique axial fluid-­sensitive MR image of the right hip shows extensive edema posterior to the joint related to a reduced posterior subluxation. A fracture at the posterior acetabular wall is present (asterisk), along with tearing of the posterior labrum and capsule (arrow).

FRACTURES OF THE PROXIMAL FEMUR KEY CONCEPTS  • F ractures at the proximal femur are associated with high morbidity and mortality, particularly in elderly patients. • These can be divided into intracapsular (femoral head, subcapital, transcervical) and extracapsular (intertrochanteric, subtrochanteric) locations. • Fractures that are intracapsular are more common and more likely to disrupt the circumflex femoral arteries, leading to osteonecrosis. • Proximal femoral fractures may be occult on radiographs, particularly in osteopenic patients. • If radiographic findings are negative, MR or CT imaging is recommended if a proximal femoral fracture is clinically suspected (inability to bear weight).

No classification system for fractures of the proximal femur is uniformly accepted. Although numerous anatomic designations, including femoral head, subcapital, transcervical, basicervical, intertrochanteric, pertrochanteric, and subtrochanteric, are used to define the location of the fracture, there is variability in the use of these designations. Femoral head fractures involve the articular surface, subcapital fractures occur immediately beneath the articular surface, transcervical fractures pass across the middle of the femoral neck, basicervical fractures occur at the base of the femoral neck, intertrochanteric fractures and pertrochanteric fractures are located between the greater and lesser trochanters, and subtrochanteric fractures occur below the lesser trochanter. These locations can be organized into two groups: intracapsular fractures (those at the femoral head, subcapital, and transcervical regions) and extracapsular fractures (those trochanteric and subtrochanteric regions). Basicervical fractures may be intracapsular or extracapsular based on the precise location and orientation of the fracture line. Intracapsular femoral fractures are approximately twice as frequent as those that are extracapsular. Intracapsular fractures are far more likely to be associated with disruption of the femoral blood supply derived from the medial and lateral circumflex femoral arteries, resulting in secondary osteonecrosis (Fig. 3.18).

Intracapsular Fractures of the Hip Femoral head. Complete fractures separating and displacing a portion of the articular surface of the femoral head are rare, typically associated with high-­energy trauma resulting in a posterior dislocation of the hip (Fig. 3.19). These occur as a result of mechanical shearing of the head against the acetabulum or, less commonly, avulsion by the ligamentum teres and can be described using the Pipkin classification. Complete femoral head fractures can be classified into those that are located solely below the fovea and those that involve the articular surface above the fovea. Fractures that extend above the fovea have a higher rate of complications such as osteonecrosis and posttraumatic arthrosis. Associated fractures of the femoral neck or acetabulum can accompany these injuries. Osteochondral impaction fractures of the femoral head related to hip dislocation are more common than widely displaced femoral head fractures. These are located at the anteroinferior head following posterior hip dislocation and at the superior head following anterior dislocation. Stress fractures of the femoral head involve the subchondral bone plate and lead to sclerosis, flattening, and collapse of the weight-­bearing surface. These are typically insufficiency fractures related to osteoporosis and challenging to distinguish from osteonecrosis. Fatigue fractures of the femoral head are far less common than those at the femoral neck. Femoral neck. Fractures of the femoral neck at the subcapital and basicervical regions in elderly persons with osteopenia, particularly women with osteoporosis, have received great attention. Classification of femoral neck fractures according to the direction of impaction and

CHAPTER 3  Physical Injury: Pelvis and Hip

Intracapsular

Femoral head

Subcapital

Femoral neck

71

Basicervical

Extracapsular Pertrochanteric Intertrochanteric Subtrochanteric Fig. 3.18  Proximal femoral fractures. The top row illustrates the various locations of intracapsular fractures of the proximal femur. These can be associated with disruption of femoral head vascularity with subsequent osteonecrosis. The bottom row illustrates fracture locations that do not typically result in avascular necrosis because they are below the capsular reflections at the femoral neck.

Fig. 3.19  Femoral head fracture. Axial CT image shows a fracture of the anterior aspect of the right femoral head (arrow) with 180 degrees of rotation of the fragment. The femoral head was fractured related to a posterior hip dislocation. Note the small bony fragments posterior to the hip joint.

degree of displacement on prereduction radiographs is commonly performed using the Garden system. Four types of fractures are identified: type I, incomplete or impacted at the lateral cortex with valgus angulation; type II, complete without osseous displacement; type III, complete but with medial impaction of fracture fragments resulting in varus angulation; and type IV, complete with total displacement of fracture fragments. Type I and II fractures can be challenging to visualize on radiographs. Careful analysis of the femoral neck cortices to identify small areas of step-­off, buckling, and/or cracking is needed, with particular attention to the lateral and posterior cortices (Fig. 3.20). Although bandlike sclerosis at the femoral neck and loss of the smooth curved contour of the femoral neck suggest a fracture, these findings can be simulated by osteophytes at the edge of the femoral head. A bent appearance of the normally linear primary compressive trabeculae at the level of the femoral neck also may be a clue that a valgus-impacted femoral neck fracture is present. Types III and IV fractures are readily visualized on radiographs but are associated with a higher rates of osteonecrosis and therefore managed more aggressively, often with hemiarthroplasty rather than percutaneous pinning (Fig. 3.21).

Undisplaced fractures of the proximal portion of the femur may escape detection on initial routine radiographic examination. It is recommended that patients unable to bear weight after a fall with negative radiograph findings undergo advanced imaging to exclude an occult fracture of the femoral neck (Fig. 3.22). MR imaging has traditionally been considered more sensitive than CT scanning for femoral neck fractures; however, data are limited comparing MR imaging with current CT technology, which affords thinner slices and high-­quality reconstructions. The greater availability of CT imaging and the option to simultaneously and rapidly evaluate large regions of the body often lead to CT scanning being used rather than MR imaging for first-­line screening. MR imaging is clearly more sensitive than CT scanning for associated soft tissue injuries, although these typically do not affect immediate surgical management. Under normal circumstances, femoral neck fractures reveal evidence of healing in the first 6 to 12 months. Complications are not uncommon, and nonunion occurs in approximately 5% to 25% of cases; ischemic necrosis of the femoral head occurs in 10% to 30% of cases. MR and CT imaging have been used not only for the initial diagnosis of the fracture but also as a means of detecting osteonecrosis and other complications. CT imaging is excellent for evaluating nonunion but is less sensitive than MR imaging for the early detection of avascular necrosis. MR imaging is accurate for the diagnosis of delayed posttraumatic osteonecrosis; however, its role in the preoperative detection of femoral head ischemia following a proximal femoral fracture has not been established.

Extracapsular Fractures of the Hip Trochanteric fractures. KEY CONCEPTS  • C omplete intertrochanteric fractures are usually displaced, shortened with varus angulation, and managed surgically. • Incomplete fractures of the greater trochanter are typically undisplaced and may be managed conservatively. • MR imaging of incomplete greater trochanteric fractures frequently shows more extensive injury than is evident on radiographs, although the impact of MR imaging on management remains controversial. • Isolated fractures of the lesser trochanter in adults are typically pathologic.

72

SECTION 1  Traumatic Disorders

A

B Fig. 3.20  Fracture of the femoral neck. (A) On the radiograph, observe the band of increased radiodensity at the femoral neck and subtle buckling of the medial and lateral femoral cortices (arrows). (B) Coronal CT formatted image shows the cortical irregularities (arrows) and slight lateral impaction with relatively vertical femoral head trabeculae, consistent with a Garden type I fracture.

Fig. 3.21  Fracture of the femoral neck. An obvious left femoral neck fracture is seen with considerable displacement between the fracture fragments, consistent with a Garden IV fracture.

Trochanteric fractures predominate in elderly patients, with a somewhat higher frequency in women. Fracture comminution is common and leads to multiple fragments of bone, which may include the greater trochanter, lesser trochanter, or both. The terms intertrochanteric (fracture close to the base of the femoral neck that run between the trochanters) and pertrochanteric (fractures run through the trochanters themselves, often leading to separation and displacement of trochanteric fragments) describe fractures in this region; these are often used interchangeably, and many authors refer to all fractures in this region as intertrochanteric. No uniform classification system exists for intertrochanteric fractures, although most classification systems in use emphasize the number of separate

Fig. 3.22  Occult fracture of the femoral neck. A coronal T1-­weighted MR image of the right hip in a patient with normal radiographs after a fall shows a transverse fracture at the right femoral neck (arrows) with marrow edema extending distally.

fragments as a guide to predicting instability and the need for surgical fixation. Complete intertrochanteric fractures are readily visible on radiographs, although precise analysis of fracture pattern is complicated by fracture comminution, as well as by the typical displacement, shortening, and varus angulation that occur with such injuries (Fig. 3.23). External rotation of the femur may produce the false appearance of a lytic lesion of the femur. Incomplete fractures limited to the greater trochanter are infrequent and are generally related to injury from a low-­impact fall, particularly in elderly persons. Incomplete rather

CHAPTER 3  Physical Injury: Pelvis and Hip than complete fractures appear to be associated with a better prognosis. Fractures limited to the trochanter are not usually significantly displaced, and their detection may be difficult on radiographs. It has been shown that MR imaging in an apparently isolated greater trochanteric fracture shows linear marrow edema presumed to represent fracture extension directed toward the intertrochanteric ridge, femoral shaft, or medial femoral neck in up to 90% of patients (Fig. 3.24). Some authors have suggested that the MR finding of fracture extension beyond the midline of the femur is an indication for surgical fixation; however, this recommendation has not been validated, and the treatment implications of fracture extent based on MR imaging remain controversial. Isolated traumatic fractures of the lesser trochanter are uncommon after the lesser trochanteric apophysis fuses in adolescence. An isolated

73

lesser trochanteric fracture in an adult should prompt careful analysis for an underlying marrow infiltrative process because pathologic fractures are not uncommon in this region and are typically related to metastatic disease (Fig. 3.25). Subtrochanteric region. Fractures of the femur that commence or extend immediately below the trochanters are considered subtrochanteric in location and involve the portion of the femur between the lesser trochanter and a point 5 to 6 cm distal to its base. Approximately 5% to 10% of fractures of the proximal portion of the femur involve the subtrochanteric region. These fractures occur in older patients after relatively minor injuries or in younger patients following major trauma. Pathologic fractures also occur in this region of the femur, are often transverse rather than oblique, and occur in the setting of minimal trauma. Insufficiency fractures of the lateral femur in the subtrochanteric region and midfemoral shaft are well recognized in Paget disease and as a complication of long-­term bisphosphate therapy (see Fig. 1.17). Fractures of the subtrochanteric region are challenging to treat because of the high biomechanical stresses in this region and the strong muscular forces on the proximal bone, resulting in a high rate of nonunion and implant failure (Fig. 3.26).

* Fig. 3.23  Femur fracture: intertrochanteric. The complete intertrochanteric fracture is evident, with impaction and varus angulation at the fracture site.

A

Fig. 3.25  Pathologic fracture at the lesser trochanter. An avulsion fracture of the lesser trochanter (arrow) related to metastatic disease is shown. Note the osteolysis at the adjacent femur (asterisk) and irregularity of the medial femoral cortex.

B Fig. 3.24  Femur fracture: greater trochanter fracture. (A) The radiograph shows an undisplaced fracture (arrow) that appears to be limited to the greater trochanter. (B) Corresponding coronal T1-­weighted MR image shows more extensive fracture lines (black arrows) extending medially, approaching the lesser trochanter.

74

SECTION 1  Traumatic Disorders

A

B

LT

Fig. 3.26  Subtrochanteric fracture. (A) The injury radiograph shows a reverse obliquity intertrochanteric fracture extending well below the lesser trochanter at the lateral cortex (arrow). (B) Follow-­up radiograph 2 months after anatomic reduction with placement of cephalomedullary fixation shows failure of fixation with shortening and redisplacement at the fracture.

TABLE 3.2  Traumatic Fractures of the Femoral Shaft Site

Characteristics

Complications

Any level

Major violence with associated injuries to the femur, tibia, patella, acetabulum, hip, and knee Open or closed Spiral, oblique, or transverse fracture with a possible butterfly fragment and comminution

Refracture Peroneal nerve injury from skeletal traction Vascular injury (femoral artery) Thrombophlebitis Nonunion (1% of cases), malunion, or delayed union Infection Fat embolization (approximately 10% of cases)

Proximal

Associated with osteoporosis and Paget disease Less common than midshaft fractures Commonly extend into the subtrochanteric region

Malalignment Nonunion

Middle

Most common site Transverse fracture is most typical

Distal and supracondylar

Less common than midshaft fractures

FEMORAL SHAFT FRACTURES Because the femoral shaft is the strongest portion of the longest and most resilient bone in the human body, fracture requires violent force. Strong muscle attachments to the greater and lesser trochanters lead to abduction, flexion, and external rotation of the proximal femoral fragment and insertion of the adductor muscles on the medial portion of the distal femoral fragment leads to its medial angulation. All of these factors contribute to the varus deformity that typifies fractures involving the middle segment of the femoral diaphysis. Traumatic femoral shaft fractures can be classified in several ways, including on the basis of whether they are open or closed, fracture morphology, and the portion of the shaft involved (Table 3.2). Femoral shaft fractures may be classified as simple (with transverse, oblique, or spiral components), segmental, or comminuted (see Fig. 1.43). Although transverse or oblique fractures of the femoral diaphysis

Malalignment Arterial injury

are very common, comminuted fractures with one or more butterfly fragments are also encountered regularly. Occult injuries of the knee occur in 5% to 15% of femoral shaft fractures and, in adolescents, may include physeal injuries in the distal end of the femur. Femoral neck fractures, often undisplaced, are also associated with femoral shaft fractures and are not infrequently overlooked. Complications of femoral shaft fractures include arterial injuries, malunion, refracture, and fat embolization (see Fig. 1.3). Fatigue fractures of the femoral shaft can take place at the medial cortex related to repetitive traction by the adductor musculature. Adductor avulsive injuries (also termed adductor insertion avulsion syndrome or thigh splints) can show considerable periosteal new bone formation, simulating an aggressive neoplasm (Fig. 3.27). MR imaging shows extensive marrow and soft tissue edema in these injuries. The underlying fracture lines are often longitudinal and intracortical and may be overlooked on MR imaging but are easiest to visualize on CT scans.

CHAPTER 3  Physical Injury: Pelvis and Hip

Fig. 3.27  Adductor avulsive injury. Radiograph of the left femur in an avid athlete demonstrates cortical irregularity and periostitis at the medial femoral cortex (arrows) related to stress injury at the adductor insertion.

FURTHER READING Abrassart S, Stern R, Peter R. Morbidity associated with isolated iliac wing fractures. J Trauma Acute Care Surg. 2009;66(1):200–203. Alam A, Willett K, Ostlere S. The MRI diagnosis and management of incomplete intertrochanteric fractures of the femur. Bone Joint J. 2005;87(9):1253–1255. Alton TB, Gee AO. Classifications in brief: Young and Burgess classification of pelvic ring injuries. Clin Orthop Relat Res. 2014;472:2338–2342. Brandser E, Marsh JL. Acetabular fractures: easier classification with a systematic approach. AJR. 1998;171(5):1217–1228. Carnesale PG, Stewart MJ, Barnes SN. Acetabular disruption and central fracture-dislocation of the hip: A long-term study. JBJS. 1975;57(8):1054– 1059. Chiang CC, Wu HT, Lin CF, Tzeng YH, Huang CK, Chen WM, Liu CL. Analysis of initial injury radiographs of occult femoral neck fractures in elderly patients: a pilot study. Orthopedics. 2012;35(5):e621–e627. Dreizin D, Smith EB. CT of sacral fractures: classification systems and management. Radiographics. 2022;42(7):1975–1993. Droll KP, Broekhuyse H, O’Brien P. Fracture of the femoral head. JAAOS. 2007;15(12):716–727.

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Durkee NJ, Jacobson J, Jamadar D, Karunakar MA, Morag Y, Hayes C. Classification of common acetabular fractures: radiographic and CT appearances. AJR. 2006;187(4):915–925. Fairbairn KJ, Mulligan ME, Murphey MD, Resnik CS. Gas bubbles in the hip joint on CT: an indication of recent dislocation. AJR. 1995;164(4):931–934. Gabbe BJ, Esser M, Bucknill A, Russ MK, Hofstee DJ, Cameron PA, Handley C. The imaging and classification of severe pelvic ring fractures. Bone Joint J. 2013;95(10):1396–1401. Geusens E, Van Breuseghem I, Pans S, Brys P. Imaging in trauma of the pelvis and hip region. JBR BTR. 2004;87(4):190–202. Haq RU, Dhammi IK, Srivastava A. Classification of pelvic fractures and its clinical relevance. J Orthop Traumatol Rehabil. 2014;7(1):8. Khurana B, Sheehan SE, Sodickson AD, Weaver MJ. Pelvic ring fractures: what the orthopedic surgeon wants to know. Radiographics. 2014;34(5):1317–1333. Kim SJ, Ahn J, Kim HK, Kim JH. Is magnetic resonance imaging necessary in isolated greater trochanter fracture? A systemic review and pooled analysis. BMC musculoskeletal disorders. 2015;16(1):395. Learch TJ, Pathria MN. Greater trochanter fractures: MR assessment and its influence on patient management. Emergency Radiology. 2000;7(2):89–92. Lovelock JE, Monaco LP. Central acetabular fracture dislocations: an unusual complication of seizures. Skeletal radiology. 1983;10(2):91–94. Moorman III CT, Warren RF, Hershman EB, Crowe JF, Potter HG, Barnes R, O’Brien SJ, Guettler JH. Traumatic posterior hip subluxation in American football. JBJS. 2003;85(7):1190–1196. Pfeifer K, Leslie M, Menn K, Haims A. Imaging findings of anterior hip dislocations. Skeletal radiology. 2017;46(6):723–730. Rehman H, Clement RG, Perks F, White TO. Imaging of occult hip fractures: CT or MRI? Injury. 2016;47(6):1297–1301. Rogers LF. Radiology of Skeletal Trauma. 3rd ed. New York: Churchill Livingstone; 2002. Rossi F, Dragoni S. Acute avulsion fractures of the pelvis in adolescent competitive athletes: prevalence, location and sports distribution of 203 cases collected. Skeletal radiology. 2001;30(3):127–131. Sadro CT, Sandstrom CK, Verma N, Gunn ML. Geriatric trauma: A radiologist’s guide to imaging trauma patients aged 65 years and older. Radiographics. 2015;35(4):1263–1285. Sanders TG, Zlatkin MB. Avulsion injuries of the pelvis. Semin. Musculoskelet. Radiol. 2008;12(01):042–053. Scheinfeld MH, Dym AA, Spektor M, Avery LL, Dym RJ, Amanatullah DF. Acetabular fractures: what radiologists should know and how 3D CT can aid classification. Radiographics. 2015;35(2):555–577. Schicho A, Schmidt SA, Seeber K, Olivier A, Richter PH, Gebhard F. Pelvic X-ray misses out on detecting sacral fractures in the elderly: Importance of CT imaging in blunt pelvic trauma. Injury. 2016;47(3):707–710. Shah R, Shelat N, El-Khoury GY, Bennett DL. Avulsion injuries of the pelvis. J Am Osteopath Coll Radiol. 2016;5(4):5–11. Sheehan SE, Shyu JY, Weaver MJ, Sodickson AD, Khurana B. Proximal femoral fractures: what the orthopedic surgeon wants to know. Radiographics. 2015;35(5):1563–1584. Tannast M, Pleus F, Bonel H, Galloway H, Siebenrock KA, Anderson SE. Magnetic resonance imaging in traumatic posterior hip dislocation. J. Orthop.Trauma. 2010;24(12):723–731. Theumann N, Verdon J, Mouhsine E, Denys A, Schnyder P, Portier F. Traumatic injuries: imaging of pelvic fractures. European radiology. 2002;12(6):1312–1330.

4 Physical Injury: Lower Extremity S U M M A R Y O F K E Y F E AT U R E S • T  raumatic injuries involving the knee, tibia/fibula, ankle, and foot are common and often complicated by instability, premature arthrosis, and nonunion because of their exposed position, limited soft tissue coverage, and the demands of weight-­bearing. • Despite their small size, many avulsion fractures found at the lower extremity are important indicators of associated ligament injury and potential instability.

• Th  e foot and ankle are the most common sites for missed skeletal injury because of their complex anatomy. Computed tomography plays an important role in the diagnosis and characterization of skeletal injuries in this region.

INTRODUCTION

Fracture of the Distal Femur

  

This discussion of physical injuries at the knee, tibial and fibular shafts, ankle, and foot proceeds in a proximal to distal direction and provides an overview of the most important physical injuries affecting the lower extremity. The lower extremity is the most common site of missed fractures in clinical practice and many significant injuries, particularly at the ankle and foot, can be subtle. Conventional radiography is emphasized, but advanced imaging techniques, particularly computed tomography (CT), play an important role in the diagnosis, classification, and presurgical planning, as many of the injuries discussed later affect regions of complex anatomy (Fig.4.1).

KNEE KEY CONCEPTS  • T he presence of a lipohemarthrosis within the knee joint is an important radiographic finding indicating the presence of an intraarticular fracture. • Fractures of the distal femur are seen most commonly following high-­ energy trauma or in the setting of osteoporosis. • The proximal tibia is the most common site of fracture at the knee joint and shows a variety of fracture patterns. • Injury to the proximal fibula can be associated with knee or ankle injury. • Several small avulsion fractures about the knee joint are useful indicators of knee ligament injury.

Injuries to the knee are common and can be caused by direct or indirect trauma. The majority of significant injuries about the knee are associated with an effusion, but some injuries, particularly extracapsular injuries such as those involving the proximal fibula, may show only nonspecific soft tissue swelling. The importance of identifying lipohemarthrosis as an indicator of an intraarticular fracture is discussed in Chapter 1. At the knee, lipohemarthrosis occurs in 35% to 45% of intraarticular knee fractures, and its presence should prompt additional radiographic projections or CT scanning if a fracture is not identified on the initial radiographic survey because it is a highly specific indicator of bony injury (Fig. 4.2).

76

Fractures of the distal femur can be classified as supracondylar, intercondylar, or condylar. Most of these injuries result from axial loading combined with varus or valgus stress and rotation. Although distal femur fractures are commonly associated with high-­energy trauma in young males, the majority actually occur in elderly osteopenic females after a fall onto the bent knee (Fig. 4.3). Patients with knee arthroplasty are also at risk for distal femoral fracture. Supracondylar fractures (without intraarticular extension) are commonly transverse or slightly oblique in configuration, with varying degrees of displacement and comminution of the fracture fragments. Supracondylar fractures accompanied by a vertical fracture line extending into the knee, typically into the intercondylar notch or trochlea, are referred to as intercondylar fractures. In condylar fractures, sagittal or coronal fracture lines are isolated to the region of a single condyle (Fig. 4.4).

Fracture of the Proximal Tibia KEY CONCEPTS  • T he proximal tibia is the most common site of fracture at the knee joint and shows a variety of fracture patterns. • The most common cause of an unexplained lipohemarthrosis is an occult fracture of the lateral tibial plateau. • Fractures of the lateral tibial plateau are best evaluated by CT. • The Schatzker classification is commonly used to classify fractures of the tibial plateau. • The Segond fracture at the lateral tibia is strongly associated with anterior cruciate ligament injury.

Fractures of the proximal tibia may be extraarticular or intraarticular. Cross-­table lateral and oblique radiography, CT scanning, or magnetic resonance (MR) imaging is frequently required for the diagnosis and accurate assessment of proximal tibial fractures, which are often accompanied by soft tissue injury about the knee. Important imaging considerations related to tibial fractures include the detection of lipohemarthrosis, avulsion fractures and sites of ligamentous detachment (femoral condyle, fibular head, intercondylar eminence), meniscal

CHAPTER 4  Physical Injury: Lower Extremity

77

* *

A

B

C

Fig. 4.1  Intraarticular fracture of distal tibia: advanced imaging. (A) Mortise radiograph of the right ankle shows irregularity of the distal lateral tibia (arrows). (B) Axial CT scanning through the injury shows a large avulsion fracture fragment (asterisk) arising from the anterolateral tibia at the insertion site of the anterior tibiofibular ligament (Tillaux fracture). (C) Three-­dimensional surfaced-rendered CT image shows the avulsed fracture fragment (asterisk) and a gap at the articular surface (arrowhead). Note the undisplaced fracture of the distal fibula (arrow) not visible on the radiograph.

Fig. 4.2  Lipohemarthrosis. Cross-­ table lateral radiograph shows a large effusion with a fat–fluid level (arrows) indicating the presence of an intraarticular fracture.

injuries, abnormal widening of the joint space during the application of stress, and disruption of the articular surface.

Tibial Plateau Fracture Tibial plateau fractures predominate in middle-­ aged and elderly persons when the relatively stronger condylar portion of the femur impacts against the plateau. Depression and displacement at the articular surface are the most important factors determining the need for surgical intervention; these are best evaluated with CT imaging (Fig. 4.5). The Schatzker classification system is widely used by orthopedic

Fig. 4.3  Fracture of the distal portion of the femur. Cross-­table lateral radiograph demonstrates a comminuted intercondylar fracture of the distal femur with offset at the trochlea (arrows) in an elderly osteopenic patient. Note the associated lipohemarthrosis.

surgeons to plan surgical fixation of tibial plateau fractures. It divides fractures into six types, with higher numbers reflecting increasing fracture severity. Type I is split lateral tibial plateau fracture, type II is a depressed lateral tibial plateau fracture, type III is a depressed and split lateral tibial plateau fracture, type IV is limited to the medial plateau,

78

SECTION 1  Traumatic Disorders

*

A

B

Fig. 4.4  Condylar fracture. (A) Lateral radiograph shows a fracture of the posterior femur involving the articular surface (arrows). (B) Axial CT image shows the fracture is limited to the lateral femoral condyle (asterisk).

A

B Fig. 4.5  Fracture of the proximal portion of the tibia: lateral plateau fracture. (A) Valgus stress has led to a fracture with central depression of the tibial plateau (arrows), as shown on a frontal radiograph. (B) Coronal CT reformatted image shows the central depression of the lateral tibial plateau (arrowheads) and mild fracture comminution.

and type V affects both plateaus, with the additional separation of the entire articular surface from the shaft in type VI. Because tibial plateau fractures are related to valgus stress far more commonly than varus stress, isolated lateral plateau fractures (75% to 80% of all fractures of the tibial plateau) and combined lateral and medial plateau fractures (10% to 15%) are more frequent than isolated medial plateau fractures (5% to 10%).

Tibial Spine Fracture Fractures of the tibial spine or intercondylar eminence are indicative of possible damage to the cruciate ligaments of the knee. Varying degrees of osseous displacement are seen. Either the anterior tibial spine or,

less commonly, the posterior tibial spine is affected; rarely, both are involved. Avulsion injuries of the anterior tibial spine occur more commonly in children and adolescents than in adults. Such fractures in adults are typically accompanied by ligamentous and meniscal injury, whereas in children, they may be an isolated phenomenon (Fig. 4.6). Routine radiography supplemented with tunnel or notch views, radiographs obtained during the application of stress, arthrography, and MR imaging are important in the assessment of these injuries.

Segond Fracture An avulsion fracture of the lateral tibial cortex, termed a Segond fracture, occurs with the knee in flexion because of internal rotation of

CHAPTER 4  Physical Injury: Lower Extremity

79

Fracture of the Proximal Fibula

*

Fig. 4.6  Fracture of the proximal portion of the tibia: intercondylar eminence fracture. Sagittal MR image reveals a fracture (arrowheads) of the proximal portion of the tibia and a large effusion (asterisk). The anterior cruciate ligament (arrow) inserts on the fracture fragment, which is minimally elevated.

the tibia. The soft tissue structure responsible for the avulsion varies as several ligaments and tendinous slips insert along the lateral tibia. The fracture fragment arises from the cortex just distal to the joint line and is typically thin, vertically oriented, and less than 1 cm long, and can be appreciated only on the anteroposterior radiograph (Fig. 4.7A). It is important to recognize this fracture as disruption of the anterior cruciate ligament occurs in 75% to almost 100% of patients with a Segond fracture. Another fracture strongly associated with anterior cruciate ligament injury is an osteochondral impaction fracture of the lateral femoral condyle, resulting in a “deep notch” (Fig. 4.7B). Less common fractures suggesting anterior cruciate ligament injury include avulsion fractures at the posterior medial tibial plateau related to the semimembranosus insertions and impaction fractures of the far posterior tibial plateau. An uncommon avulsion fracture that appears similar to the Segond fracture but occurs at the medial tibia, referred to as a “reverse Segond fracture,” is associated with injury to the medial collateral ligament rather than the anterior cruciate.

Posterior Cruciate Ligament Avulsion Fracture The posterior cruciate ligament can be injured during a hyperextension or rotational injury or by a direct blow to the tibia from a fall or dashboard injury that drives the tibia posteriorly relative to the femur. Such injuries can result in a midsubtance tear of the posterior cruciate ligament or bony avulsion of its tibial insertion at the posterior tibia. The fracture fragment is located posterior to the tibial spines and best appreciated on the lateral radiograph or CT image (see Fig. 1.67).

Tibial Tuberosity Fracture Fractures of the tibial tuberosity most commonly affect adolescent males approaching fusion of the tibial apophysis with the tibial shaft. These are typically caused by forcible quadriceps contraction placing tension on the tubercle, disrupting the relatively weak growth plate between this secondary ossification center and the anterior tibia. The fracture may be hinged open, may be displaced proximally, may involve the articular surface, or may be associated with disruption of the entire proximal tibial physis (Fig. 4.8).

Fibular head or neck fractures can result from a direct blow, a varus force (in which an avulsion fracture of the proximal pole or styloid process of the fibula occurs), a valgus force (which is accompanied by a fracture of the lateral tibial plateau and injury to the medial collateral ligament), and a twisting force at the ankle (in which pronation and external rotation may lead to a fracture in the fibular neck). Displaced fractures or those with significant lateral capsular disruption may be associated with injury to the peroneal nerve. Avulsion fractures of the proximal fibula are markers of injury of the lateral knee capsule. Oblique fractures that include the lateral margin of the fibular head are caused by avulsion by the biceps femoris tendon and fibular collateral ligament (Fig. 4.9). The “arcuate sign” refers to a smaller avulsion fracture limited to the fibular tip that is often displaced proximally, indicating avulsion injury by the arcuate complex. Despite its small size, this is an important fracture to recognize because it indicates significant soft tissue injury of the posterolateral knee ligaments and is often associated with cruciate ligament damage.

Fracture of the Patella Patellar fractures most commonly result from a direct blow related to a fall or dashboard injury; these may be open because of the subcutaneous position of the patella. Indirect forces related to contraction of the quadriceps muscles can also cause patellar fracture. The most common fracture pattern is transverse. The amount of separation between the fragments, which correlates with extensor mechanism dysfunction, and the extent of articular surface step-off determine whether surgical fixation is necessary. Vertical and comminuted (stellate) fractures are less frequent and usually result from direct injury (Fig. 4.10). A vertical fracture should be differentiated from bipartite patella, in which a well-­corticated separate ossification center is seen at the superolateral quadrant. In children, fragmentation of the lower pole of the patella, referred to as Sinding-­Larsen-­Johansson disease, is a stress-­related phenomenon that may also mimic a fracture. It should be differentiated from an acute patellar sleeve fracture resulting from avulsion of the lower pole of the patella; these injuries are predominantly chondral and underestimated on radiography.

Patellar Dislocation KEY CONCEPTS  • L ateral dislocation of the patella relative to the trochlea is a common injury, particularly in young females. • The patella is typically reduced at presentation, making clinical diagnosis difficult. • Characteristic fractures indicate that a dislocation has taken place, including osteochondral and avulsion fractures of the medial patella and impaction fractures of the lateral femur. • MR imaging is preferred over CT scanning following patellar dislocation because it is more sensitive for chondral and retinacular injury. • Patellofemoral dislocation can be repetitive in patients with underlying patellofemoral maltracking dysfunction.

Osteochondral fractures of the medial patellar facet and peripheral marginal fractures of the medial patella are typically related to patellar dislocation. Lateral dislocation, which may be transient, predominates; consequently, the patella may no longer be dislocated on initial radiographs. Identification of these characteristic associated fractures, which are best seen on axial radiographs, therefore assumes diagnostic importance. In addition to patellar fracture, osteochondral shearing injury of the lateral femoral condyle and nonarticular impaction

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SECTION 1  Traumatic Disorders

A

B Fig. 4.7  Segond fracture and deep notch sign. (A) Anteroposterior radiograph in a patient with an acute anterior cruciate ligament tear shows a Segond fracture (arrow) at the proximal lateral margin of the tibia. (B) In a different patient, an impaction fracture of the lateral femoral condyle producing a deepened notch (arrowheads) is seen on the lateral radiograph.

*

Fig. 4.8  Tibial tuberosity fracture. The lateral radiograph shows a displaced fracture of the tibial tuberosity that extends onto the tibial articular surface (arrows) in an adolescent. Note the large effusion (asterisk). (Courtesy Robert Boutin, Stanford, CA.)

fracture of the lateral femoral cortex are common following patellar dislocation. The MR imaging features of patellar dislocation include hemarthrosis, intraarticular chondral or osteochondral bodies, osteochondral fractures, marrow edema of the medial aspect of the patella and the anterior aspect of the lateral femoral condyle, and disruption of the medial patellar retinaculum (Fig. 4.11). Traumatic dislocation of the patella can be produced by a direct blow or an exaggerated contraction of the quadriceps mechanism. Abnormalities predisposing to dislocation include an abnormally high

*

Fig. 4.9  Proximal fibula fracture. Anteroposterior radiograph of the knee shows a fracture involving the fibular head with overlying swelling at the lateral knee effacing the subcutaneous fat (asterisk). The fracture fragment (arrow) includes the insertion sites of the fibular collateral ligament and biceps femoris tendon.

patella (patella alta), deficient height of the lateral femoral condyle, shallowness and dysplasia of the trochlea, genu valgum or recurvatum, lateralized insertion of the patellar tendon, excessive tibial torsion, and muscle imbalance.

Knee Dislocation Knee dislocation is a rare but serious injury because it produces gross joint instability and has a strong association with neurovascular injury to popliteal vasculature and peroneal nerve. Anterior, posterior, lateral, medial, and rotatory patterns of displacement are recognized. Anterior dislocation of the tibia relative to the femur is the most common type

CHAPTER 4  Physical Injury: Lower Extremity

Fig. 4.10  Patellar fracture. Comminuted stellate patellar fracture with displacement associated with prepatellar swelling.

A

*

81

Fig. 4.12  Knee dislocation. Lateral radiograph in a patient with anterior knee dislocation shows anterior displacement of the tibia relative to the femur.

(30% to 50% of all knee dislocations) (Fig. 4.12). Posterior dislocations are next in frequency. Radiographic diagnosis is obvious when the knee is still dislocated, but in most cases the knee has been reduced, either spontaneously or by emergency personnel. In such cases, the MR finding of simultaneous multiple ligament injury allows accurate diagnosis. As a general rule, detection of injury of all four major ligament groups of the knee (anterior cruciate, posterior cruciate, medial stabilizers, and lateral stabilizers) indicates that dislocation of the joint has occurred. The presence of injuries to three ligament groups or to both cruciate ligaments simultaneously also suggests that a dislocation has occurred, particularly in the presence of associated fractures and residual malalignment (Fig. 4.13). The reported incidence of associated injury to the popliteal artery varies from 7% to 64%. Delayed diagnosis of vascular injury can result in necrosis necessitating limb amputation, so vascular integrity must be assessed carefully in any patient with suspected knee dislocation. A combination of clinical assessment, augmented by high-­resolution CT angiography in patients with diminished pulses or ankle-­brachial index, is typically used to delineate the status of the popliteal artery following knee dislocation. Nerve injury occurs in approximately 25% of knee dislocations, most commonly affecting the peroneal nerve. Transection of the larger nerves can be appreciated on ultrasonography or MR imaging, but stretching injuries are typically diagnosed clinically.

Proximal Tibiofibular Joint Dislocation

B Fig. 4.11  Patellar dislocation. (A) Axial radiograph shows an avulsion fracture at the medial aspect of the patella (arrow). (B) Axial fluid-sensitive MR image shows a joint effusion, marrow edema (representing a bone bruise) in the anterior aspect of the lateral femoral condyle (arrowhead), irregularity of the medial margin of the patella with partial disruption of the inserting medial retinaculum (asterisk), and a chondral abnormality (arrow) in the patella.

Although uncommon, proximal tibiofibular joint dislocation may be seen in parachuting, hang-­gliding, skydiving, and horseback riding injuries. Dislocation at the proximal tibiofibular joint accompanying ipsilateral knee, tibial shaft, and ankle fractures is often overlooked as attention is directed toward the other more easily recognized injuries (Fig. 4.14). The most common direction of fibular displacement is anterolateral, resulting in loss of congruity and widening of the joint space, often in association with ligament injuries at the lateral knee. Less frequently, posteromedial dislocation of the fibular head may be noted, often with associated peroneal nerve injury. Proximal tibiofibular subluxation is easily overlooked on radiographs, and there is no effusion in the knee cavity with this injury. Shallow oblique radiographs,

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SECTION 1  Traumatic Disorders

Fig. 4.13  Knee dislocation. Sagittal intermediate-weighted MR image in a patient with a recent knee dislocation shows disruption of both the anterior (arrow) and posterior (arrowhead) cruciate ligaments. The joint is distracted, and the tibia is anteriorly displaced relative to the femur.

Fig. 4.15  Tibial and fibular shaft fractures. Anteroposterior radiograph of the tibia/fibula shows comminuted fractures at the midshafts of the tibia (arrow) and fibula (arrowhead), with shortening and displacement at the fracture sites.

comparison views of the contralateral side, and CT imaging are helpful when the injury is suspected.

TIBIAL AND FIBULAR DIAPHYSES KEY CONCEPTS  • T he tibia is the most commonly fractured long bone. • Tibial shaft fractures are often accompanied by fibular shaft fractures, either at the same or different level. Additional injuries to the knee and ankle also may be present. • Tibial shaft fractures have a high incidence of nonunion, particularly if the fracture is open. • Isolated fractures of the shaft of the fibula are uncommon; an associated ankle injury should be excluded.

Fig. 4.14  Proximal tibiofibular joint dislocation. Anteroposterior radiograph of the tibia and fibula shows a distal fibular shaft fracture (arrow). The proximal tibiofibular joint (arrowhead) is widened, with lateral displacement of the fibula, resulting in loss of normal overlap of the tibia and fibula. There is overlying swelling at the lateral knee.

Of all the long tubular bones (conventionally defined as the humerus, femur, tibia, and fibula), the tibia is fractured most commonly (Table 4.1), typically as a result of a fall, sports injury, or, less commonly, high-­ energy vehicular trauma. In general, the more severe the force, the more likely it is that both the tibia and fibula will fracture. Tibial and fibular fractures occurring together may appear at the same level, although it is common for them to occur at different levels (Fig. 4.15). Isolated fractures of the fibular shaft are uncommon and result from a direct blow. An apparently isolated fibular fracture is often one component of a more complicated injury involving the ankle as well (see later discussion). Additional injuries of the ipsilateral knee and ankle are not uncommon

CHAPTER 4  Physical Injury: Lower Extremity

83

TABLE 4.1  Fractures of the Tibial and Fibular Shafts Site

Characteristics

Complications

Tibia

Direct or indirect trauma Associated fractures of the fibula, especially in direct and severe trauma Transverse or comminuted fracture in direct trauma, oblique or spiral fracture in indirect trauma, sometimes segmental fractures Middle and distal thirds > proximal third Minor, moderate, or major categories of injury, the last associated with comminuted and open fractures Prognosis related to the amount of displacement, degree of comminution, open or closed fracture, and infection Childhood fractures: Toddler’s fracture—spiral fracture, undisplaced Proximal metaphyseal fracture—associated with genu valgum deformity

Delayed union (no osseous union at 20 wk) in 5%–15% of cases Nonunion (no osseous union at 6 mo–1 yr) is most common in the distal third of the tibia Infection with or without nonunion Vascular injury (to the anterior tibial artery or, less commonly, the posterior tibial artery) Compartment syndrome (anterior > posterior or lateral compartment) Nerve injury (uncommon, peroneal and posterior tibial nerves) Refracture (especially in athletes) Leg shortening Osteoarthritis (if fracture extends into the joint) Reflex sympathetic dystrophy syndrome

Fibula

Isolated fractures are rare and related to direct injury Associated fractures of tibia and ankle injuries

Related to those of the associated tibial or ankle injury

children, adults have a 10% incidence of delayed union or nonunion (Fig. 4.16). The most important risk factor for nonunion is the presence of an open fracture, which increases the risk of infection and also predisposes to ischemia of the underlying bone by disrupting the overlying soft tissue vascular supply to the tibial periosteum. Additional complications of tibial (and fibular) shaft fractures include malunion, infection, neurovascular injury, and compartment syndromes.

ANKLE KEY CONCEPTS  • D  isruption of the ring formed by the tibia, fibula, talus, and ligaments in more than one location results in ankle instability. • Ankle injuries are commonly classified by the Weber classification based on the location of the fibular fracture or by the Lauge-­Hansen classification based on the mechanism of injury. • The most common fracture seen at the ankle is an oblique fracture of the distal fibula that is higher posteriorly and courses inferiorly toward the tibiotalar joint. • Injuries at the medial ankle may be associated with fibular fractures that are located far proximally. • Tibiotalar dislocation is the end stage of ankle injury and usually occurs in a posterior direction.

Fig. 4.16  Tibial nonunion. An anteroposterior radiograph of the distal calf and ankle shows a nonunited distal tibial fracture (arrow) with hypertrophic nonbridging callus. There is a plate fixating a healed fibular fracture.

and may be clinically occult, so the adjacent joints should be assessed with dedicated radiographs. Survey radiographs of the femur and pelvis also may be appropriate when a severe injury of the tibia and fibula has occurred. In children, distinctive fractures of the tibial shaft include a spiral fracture in the first 3 years of life, designated a toddler’s fracture, and a fracture involving the proximal metaphysis of the bone. Fractures of the proximal metaphyseal region of the tibia may be associated with a subsequent valgus deformity at the fracture site.

Tibial Nonunion The tibial shaft is the most common site of nonunion among long bone fractures. Whereas tibial shaft fractures generally heal quickly in

Fractures About the Ankle Stability of the ankle joint depends on the integrity of a ring formed by the tibia, fibula, and talus, united by the surrounding ligaments (Fig. 4.17). A single break in the ring does not allow subluxation of the talus in the mortise, whereas two or more breaks in the ring, whether fractures or a fracture in combination with a ruptured ligament, allow abnormal talar motion. Displacement of the talus in the ankle joint may be evident on routine radiographs, including the mortise view, although application of stress to the ankle with gravity or manual pressure during the radiographic examination can be of considerable diagnostic help (Fig. 4.18).

Weber Classification The Weber classification of ankle fractures, also known as the Danis-­ Weber classification, is based solely on the location of the fibular fraction and classifies these into three types (Fig. 4.19). The type A fracture

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SECTION 1  Traumatic Disorders

occurs below the level of the tibiotalar joint and does not cause instability. The type B fracture starts at the level of the distal tibial plafond and extends proximally in an oblique direction to involve the level of the syndesmosis; this is the most common fracture type and shows variable degrees of instability (Fig. 4.20). A type C fracture is a high fibular fracture located above the tibial plafond, often associated with syndesmotic rupture and diastasis. This classification system is easy to use, but it is simplistic because it considers only the fibular injury and is inadequate for guiding management. The AO classification system is an expansion of the Weber classification and subdivides the three patterns of fibular fractures depending on associated injuries affecting

4

1

A

2 3

B

C

Fig. 4.17  Ankle: stable and unstable characteristics. (A) The stability of the ankle joint is determined by the status of a ring comprising the mortise and surrounding ligaments. The latter include the deep and superficial deltoid ligaments (1), the anterior (2) and posterior (not shown) talofibular ligaments, the calcaneofibular ligament (3), the anterior (4) and posterior (not shown) tibiofibular ligaments, the inferior transverse ligament (not shown), and the interosseous membrane and ligament (not shown). (B) A single break in this ring does not allow displacement of the mortise. (C) Two or more breaks in the ring allow displacement of the mortise.

the medial malleolus and posterior malleolus. The AO classification is designed for guiding surgical therapy with instrumentation. These classification systems are based on the radiographic appearance of the injury, without implying any specific injury mechanism.

Lauge-­Hansen Classification The Lauge-­Hansen classification, which organizes ankle fractures by mechanism of the injury, was developed based on fractures created in cadavers by manual force. This classification was developed to guide manual reduction of ankle injuries by reversing the direction of forces producing the injury but is of diminishing value in the era of modern surgical fixation. Despite its complexity, poor interobserver agreement rate, and inability to reliably predict instability, it is still widely used and enhances our understanding of injuries of the ankle. Ankle fractures are classified into five major fracture groups reflecting different mechanisms of injury. Within each of these five groups are stages of injury designated by Roman numerals; the higher the number, the greater the applied force and resultant damage. Each fracture group is designated by two terms. The first term is either pronation or supination, which refers to the position of the foot at the time of injury. The foot is pronated when the forefoot is outwardly rotated and everted and the hindfoot is abducted. Supination represents inward rotation and inversion of the forefoot with adduction of the hindfoot. The second term reflects the direction in which the talus is displaced or rotated relative to the mortise formed by the distal tibia and fibula. Five directions of talar displacement are possible: external rotation (in which the talus is displaced externally and laterally rotated), internal rotation (in which the talus is displaced internally and medially rotated), abduction (in which the talus is displaced laterally without significant rotation), adduction (in which the talus is displaced medially without significant rotation), and dorsiflexion (in which the talus is dorsiflexed on the tibia).

*

A

B

Fig. 4.18  Ankle instability: stress radiography. (A) A mortise radiograph of the left ankle shows an oblique fracture of the distal fibula (arrow). The mortise appears congruent on this examination obtained at rest. (B) Stress radiograph obtained with manual stress shows lateral displacement of the talus with respect to the tibia resulting in widening of the medial “clear” space (asterisk), indicative of injury of the deltoid ligament.

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CHAPTER 4  Physical Injury: Lower Extremity

IV

I

II

II III

Type A Type B Type C Fig. 4.19  Weber classification of ankle fractures. Line  drawings showing the status of the anterior tibiofibular ligament (cross-hatch) and three patterns of fibular fracture (red line) used to classify ankle injury. See text for details.

Fig. 4.21  Ankle injuries: supination–external rotation injury. External rotation forces applied to a supinated foot initially result in rupture of the anterior tibiofibular ligament (stage I). As the forces continue, a short oblique fracture of the distal portion of the fibula occurs (stage II). Stage III involves a fracture of the posterior aspect of the tibia. Stage IV is a fracture of the medial malleolus.

*

Fig. 4.20  Weber B fracture. An oblique fracture of the distal fibula (arrows) is seen ending at the level of the plafond with soft tissue swelling overlying the lateral ankle (asterisk). In the Lauge-­Hansen classification, this fibular fracture configuration corresponds to a supination external rotation injury. This is the most common pattern of fibular fracture.

1. Supination–external rotation (SER) injury (stages I to IV). The SER category constitutes over 60% of all ankle injuries (Fig. 4.21). External rotation of the supinated foot forces the talus against the fibula, tearing the anterior tibiofibular ligament (stage I). As the mechanism of injury continues, a short oblique fracture of the distal portion of the fibula occurs (stage II). Stage III is a fracture of the posterior malleolus of varying size or a tear of the posterior tibiofibular ligament. Stage IV is characterized by fracture of the medial malleolus or tear of the deltoid ligament (Fig. 4.22). When the third and fourth stages are limited to the soft tissues, the severity of the injury is commonly undergraded on radiography, resulting in inadequate fixation and long-­term instability. 2. Supination-­adduction (SAD) injury (stages I and II). The SAD category constitutes about 20% of all ankle injuries (Fig. 4.23). Supination causes tension on the lateral ligaments, and with forcible adduction, either a lateral ligament rupture or a transverse fracture of the distal portion of the fibula occurs (stage I). The characteristic transverse fibular fracture usually arises just distal to the tibiotalar articulation. Continued pressure from the medially directed talus results in fracture of the medial malleolus or rupture of the deltoid

Fig. 4.22  Ankle injuries: supination–external rotation injury, stage IV. Anteroposterior radiograph reveals an oblique fibular fracture (arrowhead) and fracture of the medial malleolus (arrow). The mortise is incongruent and the talus is laterally shifted.

ligament (stage II). The medial malleolar fracture is often oblique or nearly vertical (Fig. 4.24). 3. Pronation–external rotation (PER) injury (stages I to IV). These injuries are described, along with pronation-­abduction injuries, in the following paragraph. 4. Pronation-­abduction (PAB) injury (stages I to III). PER (Fig. 4.25) and PAB (Fig. 4.26) injuries constitute about 20% of all injuries occurring about the ankle. The two groups are commonly considered together because PER stage I and II injuries and PAB stage I and II injuries cannot be distinguished radiographically. Forceful external rotation or abduction of the talus results in either deltoid

86

SECTION 1  Traumatic Disorders

III II

III

IV

I I

Fig. 4.23  Ankle injuries: supination-­ adduction injury. Adduction forces applied to a supinated foot initially result in a traction or avulsion fracture of the distal portion of the fibula or rupture of the lateral ligaments (stage I). As forces continue, fracture of the medial malleolus or rupture of the deltoid ligament occurs (stage II). The fibular fracture is typically transverse, and that of the medial malleolus is oblique or nearly vertical.

II

I

Fig. 4.25  Ankle injuries: pronation–external rotation injury. Forces of external rotation applied to a pronated foot initially result in rupture of the deltoid ligament or fracture of the medial malleolus (stage I). As forces continue, the anterior tibiofibular ligament is ruptured (stage II). A high fibular fracture (stage III) and fracture of the posterior tibial margin (stage IV) are the final stages in this mechanism of injury.

I

II

III

II

Fig. 4.26  Ankle injuries: pronation-­abduction injury. The first two stages of this injury are identical to those of the pronation–external rotation fracture complex. Stage III is a transverse supramalleolar fibular fracture that may be comminuted laterally.

Fig. 4.24  Ankle injuries: supination-­adduction injury, stage II. Note the transversely oriented fibular fracture and the nearly vertical fracture of the medial malleolus.

ligament rupture (60%) or fracture of the medial malleolus (40%) (PER or PAB stage I). In a PER or PAB stage II lesion, rupture of the distal tibiofibular syndesmosis also occurs. This latter injury may be purely ligamentous or may be an avulsion. PAB stage III injuries are stage I and II injuries combined with a transverse supramalleolar fibular fracture (Fig. 4.27). PER stage III injuries consist of stage I and II abnormalities plus a short spiral fracture of the fibula more than 2.5 cm above the tibiotalar joint (Fig. 4.28). This fibular fracture is usually 6 to 8 cm above the ankle and may be even more proximal in location. PER stage IV injuries are stage III injuries in combination with a fracture of the posterior tibial margin.

A fibular fracture occurring above the joint line and proximal to the distal tibiofibular synostosis may be an important manifestation of an ankle injury. Dupuytren fracture is one type that occurs in this position and involves the lower portion of the fibular shaft. When it results from a PER injury, the fracture extends from the anterior edge of the fibula in a posteroinferior direction; in a PAB injury, the fracture is oblique and extends from the lateral surface of the bone in an inferomedial direction; and in an SER injury, the fibular fracture is oblique, located approximately 4 cm from the distal tip of the fibula, and extends from the anterior edge of the bone in a posterosuperior direction. Maisonneuve fracture is a second type and involves the proximal portion of the fibular shaft (Fig. 4.29). 5. Pronation-­dorsiflexion (PDF) injury (stages I to IV). Their mechanism is forced dorsiflexion of the pronated foot (Fig. 4.30). In stage I a fracture of the medial malleolus is seen. In stage II a second fracture arises from the anterior tibial margin. A supramalleolar fracture of the fibula characterizes stage III, and in stage IV, this is accompanied by a relatively transverse fracture of the posterior aspect of the tibia that connects with the anterior tibial fracture.

CHAPTER 4  Physical Injury: Lower Extremity

87

Fig. 4.27  Ankle injuries: pronation-­abduction injury, stage III. Findings include a transverse supramalleolar fibular fracture (arrowhead) and fractures of the medial malleolus and anterior tibial tubercle (arrow).

Fig. 4.29  Maisonneuve fracture. The lateral radiograph shows an oblique fracture of the fibula (arrow), located well above the level of the ankle joint. An ankle MR image (not illustrated) showed deltoid ligament and syndesmotic injuries.

*

Fig. 4.28  Ankle injuries: pronation–external rotation injury, stage IV. Findings include fracture of the medial malleolus (arrow) and a high fracture of the fibula (arrowhead), well above the level of the ankle joint. The distal syndesmosis is widened (asterisk), with loss of tibial and fibular overlap.

A common fracture pattern found at the ankle after high-­energy trauma such as a fall from a height or motor vehicle accident is the comminuted pilon (pestle) fracture of the distal tibia. Pilon fractures are produced predominantly by axial loading as the talus is driven into the tibial plafond (Fig. 4.31). Pilon fractures are high-­energy injuries resulting in comminution and depression of the distal tibial joint surface. Because rotation is not a prominent finding in pilon fractures, the syndesmosis can be normal, and the fibula remains intact and normal in up to 25% of such injuries.

Tibiotalar Dislocation Subluxations and dislocations of the tibiotalar joint are divided into posterior, anterior, medial, and lateral types. Posterior dislocation of the talus relative to the tibia is most common, occurring after a high-­energy axial load that drives the foot posteriorly, trapping the wider anterior portion of the talus behind the distal tibia (Fig. 4.32). Tibiotalar dislocations, particularly those in a medial or lateral direction, are commonly associated with fractures of the adjacent malleolar surfaces. Anterior tibiotalar dislocation is uncommon, but its association with neurovascular injury should be appreciated. Superior dislocation of the talus into the tibiofibular syndesmosis is also recognized, resulting in gross syndesmotic diastasis. Another rare type of ankle dislocation, sometimes referred to as a Bosworth fracture-­dislocation, results from severe external rotation of the foot leading to a fibular fracture and posterior displacement of the distal fibula, which becomes locked behind the tibia.

88

SECTION 1  Traumatic Disorders

III

III II

I

II

IV

A

B

C

Fig. 4.30  Ankle injuries: pronation-­dorsiflexion injury. (A) Initially, a fracture of the medial malleolus occurs (stage I). Subsequent injuries include a fracture of the anterior tibial margin (stage II), a supramalleolar fracture of the fibula (stage III), and a transverse fracture of the posterior aspect of the tibia that connects with the anterior tibial fracture (stage IV). (B and C) Stage IV injury. Routine radiograph (B) and sagittal T1-­weighted MR image (C) show the characteristics of the distal tibial fracture (arrows).

HINDFOOT KEY CONCEPTS  • T he most common fractures seen at the talus involve the talar body, including its posterior and lateral processes. • Fractures of the talar neck can disrupt the blood supply of the proximal talar body and result in avascular necrosis and talar collapse. • The majority of calcaneal fractures are intraarticular fractures caused by axial loading resulting in posterior facet depression and flattening of the Bohler angle. • Extraarticular avulsion fractures of the calcaneus involving the anterior, middle, or posterior calcaneus can be small and overlooked on radiographs.

Fracture and Dislocation of the Talus Fractures of the talus can be divided into minor cortical avulsion fractures and major fractures that affect the head, neck, or body of the talus. Avulsion fractures are typically the result of a twisting or rotational force combined with flexion or extension stresses and can affect the superior surface of the talar neck or the lateral, medial,

and posterior aspects of the body. A longitudinal compression force in combination with acute plantar flexion accounts for the avulsion fracture of the anterosuperior surface of the talar neck related to the insertion of the talonavicular ligament. Eversion stress may lead to osseous avulsion at the site of attachment of the deep fibers of the deltoid ligament to the body of the talus. Supination injuries can lead to small avulsions at the insertion site of the anterior talofibular ligament. Major fractures are subdivided based on whether they involve the head, neck, or body of the talus. Such fractures result from higher-­ energy trauma such as a fall from a height or sudden hyperextension of the forefoot (e.g., sudden application of the brakes in an automobile to avoid an accident). CT scanning is generally regarded as the best of the advanced imaging methods for detecting and fully assessing these injuries. The talar body is the most common site of talar fracture; such fractures may involve the lateral or posterior process, the articular surface, or all regions, especially in instances of fracture comminution. Disruption of the talar body where the bone projects beneath the tip of the lateral malleolus may result from severe dorsiflexion and external rotation. Fractures of the lateral process of the talus are thought to result from inversion of the ankle with the foot in dorsiflexion. They are intraarticular, are related most often to a fall from a height, and are a recognized injury of snowboarders (Fig. 4.33). The posterior process may be fractured during severe plantarflexion of the foot because of compression between the posterior surface of the tibia and the calcaneus. Fractures involving the posterior process of the talus may be difficult to differentiate from the os trigonum. Fractures of the talar head are uncommon and may be accompanied by navicular fracture or talonavicular subluxation. Fractures of the neck of the talus are best appreciated on the lateral view, though they can be challenging to identify on routine radiographs when they are undisplaced because they are often oblique relative to standard radiographic projections (Fig. 4.34). Dorsiflexion related to a force from below or, more rarely, a direct blow to the talus produces this fracture. Fractures of the talar neck are at high risk of avascular necrosis because the blood supply to the more proximal talus is easily disrupted, leading to avascular necrosis of the body. It is estimated that as many as 89% to 90% of displaced talar neck fractures develop avascular necrosis, particularly when there is an associated dislocation. The appearance of a linear subchondral lucent area (Hawkins sign) in the talar dome on radiographs obtained 1 to 3 months after a talar neck fracture relates to hyperemia and continuity of the blood supply and should not be misinterpreted as a crescent sign of osteonecrosis. Other complications of talar neck fractures include delayed union or nonunion, infection, and posttraumatic osteoarthritis of adjacent articulations. The talus articulates with the tibia, calcaneus, and navicular bone at the tibiotalar, subtalar, and talonavicular joints, respectively. Subluxations or dislocations affecting the talus can involve one, two, or three of these joints and are generally accompanied by fractures of the talus. Tibiotalar dislocation has already been discussed. Talocalcaneal dislocation is less common and often associated with a fracture of the talar neck or body (Fig. 4.35). Medial subtalar dislocations are most frequent and represent approximately 55% to 80% of all subtalar dislocations. Lateral subtalar dislocations are second in frequency, followed by anterior and posterior subtalar dislocations, which are both rare. Talonavicular dislocation is typically seen in conjunction with calcaneocuboid malalignment. Total dislocation of the talus, in which all three of its articulations are dislocated, leading to talar extrusion, is a rare injury that is typically open.

CHAPTER 4  Physical Injury: Lower Extremity

A

89

B

Fig. 4.31  Pilon fracture of distal tibia. (A) Findings on the anteroposterior radiograph include a severely comminuted distal tibial fracture with depression of its distal articular surface (arrowheads) and joint incongruity. The syndesmosis remains intact and the fibula is normal. (B) Three-­dimensional surface-rendered CT image shows extensive articular surface comminution and vertical fracture lines extending to the distal tibial shaft.

*

Fig. 4.32  Tibiotalar dislocation. The talus is posteriorly displaced relative to the tibial shaft. Fractures of the posterior tibia (asterisk) and distal fibula (arrow) are also posteriorly displaced with the talus.

Fracture of the Calcaneus Calcaneal fractures account for 60% of all tarsal fractures, making the calcaneus the most common site of tarsal injury. Although the majority of calcaneal fractures can be identified on radiographs, the complexity of calcaneal anatomy and fracture patterns is better appreciated on CT imaging. Fractures of the calcaneus can be broadly classified into those that are intraarticular, affecting the posterior facet (∼75%), and those

Fig. 4.33  Lateral talar process fracture. An anteroposterior ankle radiograph shows an oblique fracture line (arrow) in the lateral talar process. Note its location just below the fibular tip.

that are extraarticular (∼25%); the former are associated with a poorer prognosis. Intraarticular fractures generally occur as a result of axial loading from a fall landing on the foot in which the talus is driven into the

90

SECTION 1  Traumatic Disorders posterior-­superior fragment. Intraarticular fractures of the calcaneus are best assessed on CT imaging, which displays the precise number and orientation of the fracture lines and the degree of displacement, depression, and rotation of the fracture fragments (Fig. 4.37). Extraarticular calcaneal fractures result from several different mechanisms, the most important of which are twisting forces resulting in bony avulsion. Generally, extraarticular fractures are divided depending on whether they involve the anterior, middle, or posterior calcaneus. Extraarticular fractures at the midcalcaneus include fractures of the midtuberosity, sustentaculum tali, and lateral process but do not enter the subtalar joint. Posterior fractures at the calcaneal tuberosity and medial tubercle generally can be seen on radiographs, whereas anterior fractures affecting the anterior process and lateral calcaneal wall near the calcaneocuboid joint tend to be smaller and more challenging to identify (Fig. 4.38).

Fracture of Other Tarsal Bones Fig. 4.34  Talar injuries: fracture of the talar neck. Observe the vertical fracture line at the talar neck fracture (arrow), with slight displacement (arrowhead) leading to widening of the posterior edge of the subtalar joint. An acute fracture of the posterior tubercle of the talus is also seen.

*

Fractures elsewhere in the tarsus are less common. Typical sites of injury in the tarsal navicular bone are its dorsal surface near the talonavicular joint, followed by the medial tuberosity and body of the bone. Fractures of the navicular may be combined with injuries of the calcaneus and cuboid, typically related to a midfoot sprain injury, resulting in avulsion fractures and capsular injury at the talonavicular and calcaneocuboid joints without significant malalignment. When this injury is severe, resulting in frank dislocation, it is referred to as a Chopart dislocation. Longitudinal fractures of the navicular are typically related to fatigue; these can be complicated by avascular necrosis of the lateral fragment (Fig. 4.39). Cuboid fractures also can be seen following eversion injury as the bone is compressed between the calcaneus and metatarsals.

MIDFOOT AND FOREFOOT KEY CONCEPTS 

Fig. 4.35  Talar fracture-­dislocation. A fracture of the talar neck is associated with extrusion of the talar body (asterisk), with dislocation of the tibiotalar and posterior subtalar joints. The displaced talar fragment is inverted, with its superior articular surface (arrowheads) directed inferiorly. Note the soft tissue gas (arrow), indicating an open injury.

cancellous bone of the calcaneus; this mechanism of injury explains the presence of bilateral calcaneal fractures (5% to 10% of all calcaneal fractures), as well as the simultaneous occurrence of spinal injuries (1% to 2% of all calcaneal fractures). Axial loading drives the lateral process of the talus into the calcaneus, leading to failure of the central calcaneus at the angle of Gissane, resulting in posterior facet depression and flattening of the Bohler angle on the lateral radiograph (Fig. 4.36). Intraarticular calcaneal fractures may be accompanied by peripheral displacement of the lateral calcaneal wall, resulting in tearing of the superior peroneal retinaculum or an avulsion fracture at its lateral fibular insertion, allowing lateral dislocation of the peroneal tendons. When fracture lines extend to the posterior margin of the tuberosity, the injury is more unstable, as the Achilles tendon retracts the

• T he Lisfranc fracture–dislocation results in tarsometatarsal joint instability and malalignment between the second metatarsal base and middle cuneiform. • Radiographic findings in a Lisfranc fracture–dislocation can be subtle, and this serious injury is often overlooked. • Metatarsal fractures can be caused by overuse or acute injury and typically affect the shaft and neck. • The “turf toe” injury is a ligamentous disruption of the first metatarsophalangeal joint best assessed with MR imaging. • Sesamoid fractures can be difficult to distinguish from a developmentally partitioned sesamoid bone.

Tarsometatarsal Dislocation The Lisfranc fracture–dislocation of the tarsometatarsal joints is an important injury that can be subtle and is overlooked in 20% of patients at initial presentation. Normally, the metatarsal bases are joined by ligamentous connections, except between the bases of the first and second metatarsal bones (Fig. 4.40). The strong ligamentous connection between the medial cuneiform and second metatarsal base is referred to as the Lisfranc ligament. The Lisfranc ligament is actually a complex of structures consisting of a weak dorsal band, a stout oblique interosseous ligament extending obliquely between the medial cuneiform and the second metatarsal base, and strong plantar bands that run in a similar direction. The interosseous and plantar components are most important for anchoring the base of the second metatarsal, and both

CHAPTER 4  Physical Injury: Lower Extremity

A

91

B

Fig. 4.36  Calcaneal injuries: measurement of the Bohler angle. (A) The lateral radiograph shows a fracture of the calcaneus with depression and flattening of the Bohler angle. This angle is formed by the intersection of two lines: the first line (solid) is drawn from the highest part of the anterior process of the calcaneus and the highest point of the posterior articular surface; the second line (dashed) is drawn between the latter point and the most superior part of the calcaneal tuberosity. The Bohler angle normally measures between 25 and 40 degrees. In this example, it is decreased because of a complex intraarticular calcaneal fracture. (B) An anteroposterior radiograph of the ankle in the same patient shows a fracture arising from the lateral fibular cortex (arrow) where a fragment has been avulsed by the superior peroneal retinaculum.

A

B Fig. 4.37  Calcaneal injuries: intraarticular fracture. (A) Although routine radiography reveals an intraarticular fracture of the calcaneus, the status of the posterior subtalar joint is difficult to determine. (B) Reformatted sagittal CT image shows depression and rotation of the posterior facet articular surface (arrowhead), with extension of fracture lines to the posterior tuberosity (arrow).

are typically injured when there is significant displacement. The second metatarsal base is also stabilized by its recessed position between the cuneiforms. Injuries to the tarsometatarsal joints can result from direct or, more commonly, indirect trauma. In the latter situation, violent abduction of the forefoot can lead to lateral displacement of the four lateral

metatarsal bones, with or without a fracture at the base of the second metatarsal and the cuboid. Associated dorsal displacement is more frequent than plantar displacement. The hallmark of a Lisfranc fracture– dislocation is widening of the distance between the first and second metatarsal bases and, more importantly, malalignment between the medial border of the middle cuneiform and second metatarsal base.

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SECTION 1  Traumatic Disorders

A

B

Fig. 4.40  Lisfranc fracture–dislocation. (A) Normal ligamentous anatomy. (B) Lateral dislocation of the second through fifth metatarsal bones may be associated with fractures of the base of the second metatarsal bone, the remaining metatarsals, cuneiform bones, and cuboid.

Fig. 4.38  Calcaneal injuries: extraarticular fracture. Small avulsion fracture at the lateral calcaneus at the insertion of the calcaneocuboid ligament (arrowhead).

Fig. 4.41  Lisfranc fracture–dislocation. There is a small fracture fragment at the base of the second metatarsal bone at the insertion site of the Lisfranc ligament (white arrow). Note the very subtle lateral displacement of the second metatarsal base. The medial edge of the second metatarsal base (black arrow) is slightly offset laterally relative to the medial edge of the middle cuneiform (arrowhead). This degree of offset is easily overlooked.

Fig. 4.39  Stress fracture of the navicular bone. A vertical fracture line (arrow) is seen at the mid-navicular in an avid runner.

Disruption of the alignment of the second metatarsal bone and second cuneiform is caused by lateral displacement of the metatarsal, resulting in a step-­off between these bones, often accompanied by small avulsion fractures at the sites of insertion of the Lisfranc ligament. This finding can be subtle and is more obvious with weight-­bearing or stress radiography (Fig. 4.41). Offset at the third metatarsal can be recognized as well. Alterations in the normal alignment of the bases of the fourth and fifth metatarsal bones with the cuboid and changes in the alignment of the base of the first metatarsal bone with the medial cuneiform are more variable. The first metatarsal bone may be spared (partial injury), dislocate in the same direction as the other metatarsal bones (homolateral dislocation) or in the opposite direction (divergent dislocation), depending on the precise vectors of the force (Fig. 4.42).

CHAPTER 4  Physical Injury: Lower Extremity

93

Fig. 4.43  Metatarsal bone fracture: base of the fifth metatarsal. An undisplaced transverse fracture line (arrow) is identified at the proximal base of the fifth metatarsal.

Fig. 4.42  Convergent Lisfranc fracture–dislocation. There is lateral dislocation of the all the metatarsals relative to the tarsal bones.

Fracture of the Metatarsal Bones Metatarsal fractures, which may result from direct or indirect forces or occur in response to chronic stress or neuropathic osteoarthropathy, may be transverse, oblique, spiral, or comminuted. Stress fractures of the metatarsal bone are common and typically involve the metatarsal neck (see Fig. 1.26). Traumatic fractures of the shaft and neck of the bone commonly result from a heavy object falling on the foot. Fractures of the metatarsal head are less common, result from direct injury, and are usually accompanied by fractures of adjacent metatarsal necks or shafts. Over half of all traumatic metatarsal fractures involve the proximal half of the fifth metatarsal. Fractures of the base of the fifth metatarsal bone are of three basic types: an avulsion fracture of the tuberosity that may or may not involve the metatarsal-­cuboid joint, a transverse fracture at the metadiaphyseal junction, or transverse fracture of the proximal diaphysis. The avulsion fracture of the tuberosity is the most common type, has a good prognosis, and is typically managed conservatively. These fractures, many of which involve the cuboid-­metatarsal joint, result from an indirect injury associated with sudden inversion of the foot. The osseous fragment varies considerably in size, and the fracture line may be limited to the proximal tip and not affect the joint (Fig. 4.43). Differentiating a tuberosity fracture from the normal apophysis of the fifth metatarsal bone can be difficult in children; the latter is oriented in a longitudinal direction, and the radiolucent line between it and the parent bone does not enter the cuboid-­metatarsal space. Fractures at the proximal diaphymetaphyseal region of the fifth metatarsal (true Jones fracture) result from either direct or indirect forces and are uncommon. The diaphyseal type, which is sometimes also referred to as a Jones fracture, is typically a stress injury related to overuse and has a propensity for refracture, delayed union, and nonunion.

Fig. 4.44  Turf-­toe injury. A sagittal fluid-­sensitive MR image of the great toe shows an effusion in the metatarsophalangeal joint. There is irregularity and abnormal signal at the plantar capsule (arrowhead) and the sesamoid (arrow) is proximally retracted.

Injuries of the Metatarsophalangeal Joints and Toes Dislocations at the metatarsophalangeal joints can occur in any direction. The first metatarsophalangeal joint is commonly affected. Similarly, patterns of dislocation of the interphalangeal joints in the foot are variable, but the interphalangeal joint of the hallux is typically affected. The “turf toe” injury is a hyperextension injury resulting in injury to the plantar ligaments between the sesamoids and proximal phalanx and is most commonly seen in football players who play on artificial turf (Fig. 4.44). This injury is difficult to recognize on radiographs unless the sesamoids are proximally retracted; it is best assessed with MR imaging. Fractures of the sesamoid can take place with this injury or in isolation (Fig. 4.45). These can be difficult to distinguish from a bipartite sesamoid, though the overall size of the sesamoid bone is larger when it is bipartite, the cleft runs coronally dividing the sesamoid into two roughly equal segments, and its edges are corticated. Sesamoiditis refers to marrow edema, sclerosis, and fragmentation of the sesamoid that may be ischemic or traumatic, often related to

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SECTION 1  Traumatic Disorders

Fig. 4.45  Sesamoid fracture. A sesamoid view of the great toe shows volume loss and fragmentation of the medial sesamoid (arrow).

overuse; this imprecise term is often used to describe sesamoid abnormalities of uncertain etiology. Regarding the toes, of particular importance are displaced intraarticular fractures (which may require surgical reduction) and, in children, physeal injuries of the distal phalanx.

FURTHER READING Antonova E, Le TK, Burge R, Mershon J. Tibia shaft fractures: costly burden of nonunions. BMC Musculoskelet Disord. 2013;14(1):42. Badillo K, Pacheco JA, Padua SO, Gomez AA, Colon E, Vidal JA. Multidetector CT evaluation of calcaneal fractures. Radiographics. 2011;31(1):81–92. Bowes J, Buckley R. Fifth metatarsal fractures and current treatment. World J Orthop. 2016;7(12):793. Bryson WN, Fischer EJ, Jennings JW, Hillen TJ, Friedman MV, Baker JC. Three-column classification system for tibial plateau fractures: what the orthopedic surgeon wants to know. Radiographics. 2021;41(1):144–155. Capps GW, Hayes CW. Easily missed injuries around the knee. Radiographics. 1994;14(6):1191–1210. Chaturvedi A, Mann L, Cain U, Chaturvedi A, Klionsky NB. Acute fractures and dislocations of the ankle and foot in children. RadioGraphics. 2020;40(3):754–774. Davis DL, Vachhani P. Traumatic extra-capsular and intra-capsular floating fat: Fat-fluid levels of the knee revisited. J Clin Imaging Sci. 2015;5:60. Dupuis CS, Westra SJ, Makris J, Wallace EC. Injuries and conditions of the extensor mechanism of the pediatric knee. Radiographics. 2009;29(3):877–886. Ehlinger M, Ducrot G, Adam P, Bonnomet F. Distal femur fractures. Surgical techniques and a review of the literature. Orthop Traumatol: Surgery & Research. 2013;99(3):353–360.

Gottsegen CJ, Eyer BA, White EA, Learch TJ, Forrester D. Avulsion fractures of the knee: imaging findings and clinical significance. Radiographics. 2008;28(6):1755–1770. Gwinner C, Märdian S, Schwabe P, Schaser KD, Krapohl BD, Jung TM. Current concepts review: fractures of the patella. GMS Interdiscip Plast Reconstr Surg DGPW. 2016;5. Ha AS, Porrino JA, Chew FS. Radiographic pitfalls in lower extremity trauma. AJR. 2014;203(3):492–500. Huang GS, Yu JS, Munshi M, Chan WP, Lee CH, Chen CY, Resnick D. Avulsion fracture of the head of the fibula (the “arcuate” sign): MR imaging findings predictive of injuries to the posterolateral ligaments and posterior cruciate ligament. AJR. 2003;180(2):381–387. Kfuri M, Schatzker J. Revisiting the Schatzker classification of tibial plateau fractures. Injury. 2018;49(12):2252–2263. Larsen P, Elsoe R, Hansen SH, Graven-Nielsen T, Laessoe U, Rasmussen S. Incidence and epidemiology of tibial shaft fractures. Injury. 2015;46(4):746–750. Markhardt BK, Gross JM, Monu J. Schatzker classification of tibial plateau fractures: use of CT and MR imaging improves assessment. Radiographics. 2009;29(2):585–597. Melenevsky Y, Mackey RA, Abrahams RB, Thomson III NB. Talar fractures and dislocations: a radiologist’s guide to timely diagnosis and classification. Radiographics. 2015;35(3):765–779. Okanobo H, Khurana B, Sheehan S, Duran-Mendicuti A, Arianjam A, Ledbetter S. Simplified diagnostic algorithm for Lauge-Hansen classification of ankle injuries. Radiographics. 2012;32(2):E71–E84. Pierce JL, McCrum EC, Rozas AK, Hrelic DM, Anderson MW. Tip-ofthe-iceberg fractures: small fractures that mean big trouble. AJR. 2015;205(3):524–532. Rogers LF. Radiology of Skeletal Trauma. 3rd ed. New York: Churchill Livingstone; 2002. Siddiqui NA, Galizia MS, Almusa E, Omar IM. Evaluation of the tarsometatarsal joint using conventional radiography, CT, and MR imaging. Radiographics. 2014;34(2):514–531. Sanders TG, Paruchuri NB, Zlatkin MB. MRI of osteochondral defects of the lateral femoral condyle: incidence and pattern of injury after transient lateral dislocation of the patella. AJR. 2006;187(5):1332–1337. Smitaman E, Davis M. Hindfoot fractures: injury patterns and relevant imaging findings. RadioGraphics. 2022;42(3):661–682. Tartaglione JP, Rosenbaum AJ, Abousayed M, DiPreta JA. Classifications in brief: Lauge-Hansen classification of ankle fractures. Clinical Orth and Rel Res. 2015;473:3323–3328. Topliss CJ, Jackson M, Atkins RM. Anatomy of pilon fractures of the distal tibia. Bone & Joint J. 2005;87(5):692–697. Verhage SM, Rhemrev SJ, Keizer SB, van Ufford HQ, Hoogendoorn JM. Interobserver variation in classification of malleolar fractures. Skeletal Radiol. 2015;44(10):1435–1439. Walker RE, McDougall D, Patel S, Grant JA, Longino PD, Mohtadi NG. Radiologic review of knee dislocation: from diagnosis to repair. AJR. 2013;201(3):483–495. Wei CJ, Tsai WC, Tiu CM, Wu HT, Chiou HJ, Chang CY. Systematic analysis of missed extremity fractures in emergency radiology. Acta Radiologica. 2006;47(7):710–717. Zeltser DW, Leopold SS. Classifications in brief: Schatzker classification of tibial plateau fractures. Clin Orthop Relat Res. 2013;471(2):371–374.

SECTION 2  Articular Disorders

5 Overview: Target Area Approach to Arthritis

S U M M A R Y O F K E Y F E AT U R E S • D  istribution, or localization, of radiographic abnormalities in many articular disorders allows accurate radiographic diagnosis.

  

INTRODUCTION

Juvenile Idiopathic Arthritis (see Fig. 5.1B)

Accurate radiographic diagnosis of joint disease is based on two fundamental parameters: morphology of the articular and juxtaarticular lesions and joint distribution. Morphologic features depend on the pathologic and histologic characteristics of the disease. The precise joint distribution, although not fully understood in certain disorders, provides important diagnostic information that often allows one disease process to be differentiated from another. This distribution as displayed on radiographs is designated the target area approach. The target area approach dictates locations that are predominantly involved in a disease process, not those that are involved exclusively. The pattern of distribution, when coupled with the morphology of the lesions, ensures a confident diagnosis in most patients with articular disease. The target area approach to analysis of articular disease is summarized in this chapter.

Symmetric or asymmetric distribution may be evident. Juvenile idiopathic arthritis can affect any joint of the hand, including the distal interphalangeal joints. The degree of osteoporosis, joint space narrowing, and osseous erosion is variable, and bony proliferation (periostitis and intraarticular fusion) may be a prominent finding.

HAND

The distribution of this disease varies widely. Findings are often bilateral and asymmetric; however, the changes may be unilateral or even ray-like in distribution (in which one or more joints in one or two fingers are involved). In many patients, the extent of distal interphalangeal joint abnormalities is striking. Osteoporosis may be absent, and intraarticular osseous fusion and periarticular osseous excrescences can be evident, allowing differentiation from rheumatoid arthritis.

The joints of the hand are the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints of the second to fifth digits, and the metacarpophalangeal and interphalangeal joints of the thumb.

Rheumatoid Arthritis (see Fig. 5.1A) Both hands are affected in a relatively symmetric fashion. Major alterations appear in all five metacarpophalangeal joints, the proximal interphalangeal joints, and the interphalangeal joint of the thumb. Abnormalities in the distal interphalangeal joints are less frequent, are mild, and rarely occur in the absence of changes in more proximal locations. The earliest changes most frequently are apparent in the second and third metacarpophalangeal joints and the third proximal interphalangeal joint. Fusiform soft tissue swelling, regional osteoporosis, diffuse loss of interosseous space, and marginal and central bony erosions are the observed findings.

Ankylosing Spondylitis (see Fig. 5.1C) Bilateral and asymmetric findings predominate. Distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints as well as the interphalangeal joint of the thumb can be affected. Osteoporosis, joint space diminution, osseous erosions, and deformities are less striking in this disease than in rheumatoid arthritis. Osseous proliferation can be exuberant.

Psoriatic Arthritis (see Fig. 5.1C)

Reactive Arthritis (see Fig. 5.1C) Asymmetric changes are most typical. Monoarticular or pauciarticular disease can affect any joint of the hand, although lower extremity involvement is far more common. The features are virtually identical to those of psoriatic arthritis.

Osteoarthrosis (see Fig. 5.1D) Bilateral symmetric or asymmetric findings can be observed. Unilateral involvement is rare. Distal interphalangeal and proximal interphalangeal joints generally are affected to a greater degree than are metacarpophalangeal joints. Further, changes are rarely isolated to

95

96

A

SECTION 2  Articular Disorders

Rheumatoid arthritis

F

B

Juvenile idiopathic arthritis

C

Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis

D

Osteoarthrosis

E

Inflammatory (erosive) osteoarthritis

G H I Gouty arthritis Systemic lupus Scleroderma and CPPD crystal deposition disease erythematosus polymyositis Fig. 5.1  Target areas of the hand. (A) Rheumatoid arthritis. (B) Juvenile idiopathic arthritis. (C) Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. (D) Osteoarthrosis. (E) Inflammatory (erosive) osteoarthritis. (F) Systemic lupus erythematosus. (G) Scleroderma and polymyositis. (H) Gouty arthritis. (I) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease.

the metacarpophalangeal joints and, in this location, the only typical feature is diffuse loss of joint space. In interphalangeal joints, loss of interosseous space, subchondral eburnation, marginal osteophytes, and small capsular ossicles appear. Findings suggesting a disease other than osteoarthrosis are marginal erosions in distal or proximal interphalangeal joints, or in both, and prominent osteophytes or erosions in metacarpophalangeal joints.

Inflammatory (Erosive) Osteoarthritis (see Fig. 5.1E) A bilateral symmetric or asymmetric distribution is encountered. Distal interphalangeal and proximal interphalangeal joint abnormalities predominate over those in the metacarpophalangeal joints. In many of the joints, morphologic alterations are indistinguishable from those of noninflammatory osteoarthrosis. In the inflamed joints, however, soft tissue swelling and centrally located depression, or collapse, of the subchondral bone plate are typical. Subsequent bone ankylosis of the intraarticular space can occur.

has been observed in some patients with scleroderma. A similar pattern of joint disease rarely is encountered in patients with polymyositis and, in this disease, deformities of the thumb may be encountered. In both of these diseases, more characteristic findings, such as soft tissue calcification and tuft resorption, usually are evident.

Gouty Arthritis (see Fig. 5.1H) A bilateral and asymmetric process predominates. Changes may appear in distal interphalangeal, proximal interphalangeal, or metacarpophalangeal joints, consisting of lobulated soft tissue masses, eccentric intraarticular and extraarticular osseous erosions, preservation of joint space, proliferation of bone (overhanging edges), and lack of osteoporosis.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.1I)

A deforming, nonerosive arthropathy with a bilateral and symmetric distribution affecting metacarpophalangeal and interphalangeal joints of all of the digits, including the thumb, characterizes one type of joint abnormality in this disease. Initially, such deformities are reversible but, with time, they may become fixed. Osteonecrosis at one or more metacarpal heads is a second (although rare) pattern of hand involvement.

Idiopathic calcium pyrophosphate dihydrate (CPPD) crystal deposition disease or that associated with hemochromatosis produces bilateral, relatively symmetric changes that predominate at the metacarpophalangeal joints. In both disorders, changes are most frequent in the second and third metacarpophalangeal joints; in hemochromatosis, the first, fourth, and fifth digits are involved more commonly than in idiopathic CPPD crystal deposition disease. Further, in hemochromatosis, beaklike osseous excrescences arising from the radial aspect of the metacarpal heads are distinctive.

Scleroderma and Polymyositis (see Fig. 5.1G)

Other Diseases

A bilateral erosive arthritis showing a predilection for the distal interphalangeal and, to a lesser extent, the proximal interphalangeal joints

Multicentric reticulohistiocytosis can lead to significant abnormalities of both hands, which usually are most striking in the distal

Systemic Lupus Erythematosus (see Fig. 5.1F)

CHAPTER 5  Overview: Target Area Approach to Arthritis

TABLE 5.1  Major Compartments of the

Wrist

Compartment

Location

Radiocarpal

Between the distal end of the radius and the proximal carpal row

Midcarpal

Between the distal and the proximal carpal rows

Common carpometacarpal

Between the distal carpal row and the bases of the four ulnar metacarpals

First carpometacarpal

Between the trapezium and the base of the first metacarpal

Inferior radioulnar

Between the distal ends of the radius and ulna, separated from the radiocarpal compartment by the triangular fibrocartilage of the wrist

Pisiform-­triquetral

Between the pisiform and triquetrum

interphalangeal and, to a lesser extent, the proximal interphalangeal joints. Thermal injuries, including frostbite and burns, may produce alterations that also predominate in distal locations. In some cases, the joints of the thumb are spared in frostbite. Hyperparathyroidism (and renal osteodystrophy) can lead to a peculiar “erosive” arthritis of the digits related to subchondral bone resorption that affects distal interphalangeal, proximal interphalangeal, or metacarpophalangeal joints of both hands. In most cases, the changes are combined with subperiosteal resorption in the phalanges. Historically, in rheumatic fever, a deforming, nonerosive arthropathy (Jaccoud arthropathy) predominates in the fourth and fifth digits. Septic arthritis of the metacarpophalangeal joints may follow a fistfight in which the fist is cut when it strikes the opponent’s teeth.

WRIST The major joints or compartments of the wrist are summarized in Table 5.1 and Fig. 5.2A.

Rheumatoid Arthritis (see Fig. 5.2B) A bilateral and symmetric process usually is evident. Although initial abnormalities often predominate about the distal ulna, all compartments of the wrist become involved at a relatively early stage. This pancompartmental distribution is an important characteristic of the wrist involvement in rheumatoid arthritis.

Juvenile Idiopathic Arthritis (see Fig. 5.2C) The pattern of wrist involvement is variable. In some forms of juvenile idiopathic arthritis, all the carpal bones migrate toward the bases of the metacarpals, reflecting joint space loss in the midcarpal and common carpometacarpal compartments. In fact, eventual osseous fusion of the proximal and distal carpal rows and bases of the four ulnar metacarpals may be seen, with relative sparing of the first carpometacarpal and radiocarpal compartments. A similar pattern of disease may be apparent in some patients with adult-­onset Still disease.

Ankylosing Spondylitis, Psoriatic Arthritis, and Reactive Arthritis (see Fig. 5.2D) Asymmetric findings in the wrist can appear during the course of any of these three disorders. Pancompartmental changes may be seen. Although similar to rheumatoid arthritis, these disorders are associated with less frequent and extensive wrist disease, the absence of osteoporosis, and the presence of poorly defined osseous excrescences, or “whiskers.”

97

Osteoarthrosis (see Fig. 5.2E) In the absence of significant accidental or occupational trauma, osteoarthrosis of the wrist is virtually limited to the first carpometacarpal and trapezio-­ trapezoid-­ scaphoid (triscaphe) area of the midcarpal joint. At the first carpometacarpal joint, radial subluxation of the metacarpal base may be evident, whereas at the triscaphe region, narrowing and eburnation may be the only findings. In the presence of occupational or accidental trauma, more widespread alterations of the wrist may be detected. Posttraumatic abnormalities eventually may become severe and widespread, leading to a pattern that is designated scapholunate advanced collapse.

Inflammatory (Erosive) Osteoarthritis (see Fig. 5.2E) Changes predominate at the first carpometacarpal joint and triscaphe region, a distribution identical to that in noninflammatory osteoarthrosis. At these sites, joint space narrowing and eburnation predominate, although rarely, erosive abnormalities may be detected.

Scleroderma (see Fig. 5.2F) Selective involvement of the first carpometacarpal compartment may be noted in some patients with scleroderma. The changes consist of scalloped erosions of the base of the metacarpal and adjacent trapezium. Similar alterations of the first carpometacarpal joint may be encountered in systemic lupus erythematosus, polymyositis, and Ehlers-­Danlos syndrome. In scleroderma, intraarticular and periarticular calcification can be observed about the altered joint.

Gouty Arthritis (see Fig. 5.2G) In longstanding gout, bilateral symmetric or asymmetric changes can be observed in the wrist. A pancompartmental distribution, similar to that in rheumatoid arthritis, may be apparent. Of diagnostic significance, the common carpometacarpal compartment may be the site of the most extensive abnormality in this disease, leading to scalloped erosions of the bases of one or more of the four ulnar metacarpals. Additional findings, such as the absence of osteoporosis and the presence of eccentric erosions with sclerotic margins, lobulated soft tissue masses, and preservation of joint space, also aid in the differentiation of gouty arthritis from rheumatoid arthritis.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.2H) CPPD crystal deposition disease leads to bilateral symmetric or asymmetric changes that reveal a distinct predilection for the radiocarpal compartment of the wrist. At this site, extensive narrowing of the space between the distal portion of the radius and scaphoid, with deepening of the scaphoid fossa of the radius, may be seen. Elsewhere in the wrist, the triscaphe or lunate-­capitate area of the midcarpal compartment and the first carpometacarpal compartment may show severe involvement. Of great importance in correct diagnosis of this disorder is the presence of calcification in the triangular fibrocartilage and elsewhere in the wrist.

Other Diseases In septic arthritis of the wrist, one compartment may be initially involved, although pancompartmental disease is the rule in neglected infection. CPPD deposition disease is associated with curvilinear calcification in the flexor carpi ulnaris tendon, adjacent to the pisiform.

FOREFOOT The joints of the forefoot are the distal interphalangeal, proximal interphalangeal, and metatarsophalangeal joints of the second to fifth digits,

98

SECTION 2  Articular Disorders

CCMC

CMC

MC

RC IRU

A. Wrist joints

B.

D. Ankylosing spondylitis, psoriatic

E. Osteoarthrosis and inflammatory

G. Gouty arthritis

H. CPPD crystal deposition disease

arthritis, and reactive arthritis

Rheumatoid arthritis

(erosive) osteoarthritis

C. Juvenile idiopathic arthritis

F. Scleroderma

Fig. 5.2  Joints and target areas of the wrist. (A) The trapezioscaphoid region of the midcarpal joint is separated by a vertical line from the remainder of this joint. The pisiform-­triquetral compartment is not shown. (B) Rheumatoid arthritis. (C) Juvenile idiopathic arthritis. (D) Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. (E) Osteoarthrosis and inflammatory (erosive) osteoarthritis. (F) Scleroderma. (G) Gouty arthritis. (H) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. CMC, First carpometacarpal compartment; CCMC, common carpometacarpal compartment; IRU, inferior radioulnar compartment; MC, midcarpal compartment; RC, radiocarpal compartment.

and the interphalangeal and metatarsophalangeal joints of the great toe. The major joints or compartments of the forefoot are summarized in Fig. 5.3.

Rheumatoid Arthritis (see Fig. 5.3A) A bilateral and symmetric process of the forefoot represents one of the earliest and most frequent radiographic findings in rheumatoid arthritis. Typically, the predominant changes occur at one or more metatarsophalangeal joints and the interphalangeal joint of the great toe. Significant involvement of the proximal interphalangeal and distal interphalangeal joints of the second to fifth toes is infrequent. At the metatarsophalangeal joints, abnormalities are most commonly encountered on the medial aspect of the metatarsal heads of the second to fourth digits and on the medial and lateral aspects of the metatarsal

head of the fifth digit; involvement at the fifth metatarsophalangeal joint is an early site of joint damage and should be especially scrutinized for erosions, particularly the lateral and plantar aspects. At the interphalangeal joint of the great toe, a typical erosion appears on the medial aspect of the distal portion of the proximal phalanx.

Ankylosing Spondylitis, Psoriatic Arthritis, and Reactive Arthritis (see Figs. 5.3B–C) In ankylosing spondylitis, symmetric or asymmetric abnormalities may appear at the metatarsophalangeal joints and the interphalangeal joint of the great toe. Psoriatic arthritis can be associated with a bilateral symmetric or asymmetric or unilateral process, with or without a ray-­ like pattern, leading to considerable abnormalities of the forefoot. The most severe changes are commonly seen at the metatarsophalangeal

CHAPTER 5  Overview: Target Area Approach to Arthritis

99

joints and the interphalangeal joint of the great toe. Prominent erosions and intraarticular osseous fusion can be evident at other interphalangeal joints as well. These changes in the interphalangeal joints in psoriatic arthritis allow differentiation from rheumatoid arthritis in most cases. Asymmetric or unilateral abnormalities of the forefoot are frequent in reactive arthritis. Fewer joints are affected in this disorder than in rheumatoid arthritis or psoriatic arthritis, although any joint of the forefoot is a potential site of abnormality. Selective involvement of the interphalangeal joint of the great toe can be encountered, similar to that seen in psoriatic arthritis.

Osteoarthrosis (see Fig. 5.3D) The first metatarsophalangeal joint is affected most frequently in osteoarthrosis with changes that include loss of interosseous space, bone eburnation, osteophytosis, and even hallux valgus deformity in a unilateral or bilateral distribution.

Gouty Arthritis (see Fig. 5.3E) A

Rheumatoid arthritis

B

Ankylosing spondylitis

Bilateral symmetric or asymmetric changes in gouty arthritis can appear in any joint of the forefoot. The characteristic distribution includes the first metatarsophalangeal joint and, to a lesser degree, the interphalangeal joint of the great toe; an erosion at the medial aspect of the distal first metatarsal is characteristic. Prominent changes about other metatarsophalangeal and interphalangeal joints are not infrequent, however. At any involved site, a large soft tissue mass commonly indicates the presence of a tophus.

Neuropathic Osteoarthropathy (see Fig. 5.3F) Neuropathic osteoarthropathy, particularly in diabetic patients, frequently affects the forefoot in a bilateral distribution. Metatarsophalangeal joint abnormalities predominate, although with progressive disease, a great degree of phalangeal resorption may be evident. Other causes of neuropathic osteoarthropathy, such as leprosy and alcoholism, occasionally produce a similar pattern of disease.

MIDFOOT AND HINDFOOT The major joints of the midfoot and hindfoot are shown in Fig. 5.4A.

D

Osteoarthrosis

C

Psoriatic arthritis and reactive arthritis

Rheumatoid Arthritis (see Fig. 5.4B) Rheumatoid arthritis frequently affects all the joints of the midfoot, commonly in association with changes at the metatarsophalangeal joints. Bilateral and symmetric abnormalities predominate. The most typical sites of involvement are the talonavicular portion of the talocalcaneonavicular joint, the tarsometatarsal joints, and the posterior subtalar joint.

Juvenile Idiopathic Arthritis (see Fig. 5.4B) Any of the joints of the midfoot can be affected in juvenile idiopathic arthritis. Bony ankylosis of the tarsal bones and bases of the metatarsal bones of both feet may eventually occur.

Osteoarthrosis (see Fig. 5.4C) Abnormalities of the first tarsometatarsal joint in one or both feet represent the most typical pattern of osteoarthrosis in the midfoot. The findings, consisting of joint space narrowing, bone sclerosis, and osteophytosis, can simulate those of gout.

Gouty Arthritis (see Fig. 5.4D) E

Gouty arthritis

F

Neuropathic osteoarthropathy Fig. 5.3  Target areas of the forefoot. (A) Rheumatoid arthritis. (B) Ankylosing spondylitis. (C) Psoriatic arthritis and reactive arthritis. (D) Osteoarthrosis. (E) Gouty arthritis. (F) Neuropathic osteoarthropathy.

Although any of the compartments of the midfoot can be affected, gouty arthritis shows a predilection for the tarsometatarsal joints. A bilateral symmetric or asymmetric process is most frequent. Prominent osseous erosions of the bases of one or more metatarsal bones are especially characteristic.

100

SECTION 2  Articular Disorders

CN

CN

CC

CC TCN

TCN

CN

TCN

TCN

CN

A

TMT ST

ST

TMT

TMT

TMT

TMT

TMT

CC

Joints of the midfoot and hindfoot

B

CC

C

Rheumatoid arthritis and juvenile idiopathic arthritis

Osteoarthrosis

TMT

TCN

TCN

TMT

D

Gouty arthritis

E

CPPD crystal deposition disease

Fig. 5.4  Joints and targets of the midfoot and hindfoot. (A) Joints of the midfoot and hindfoot. (B) Rheumatoid arthritis and juvenile idiopathic arthritis. (C) Osteoarthrosis. (D) Gouty arthritis. (E) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. CC, Calcaneocuboid; CN, cuneonavicular; ST, posterior subtalar; TCN, talocalcaneonavicular; TMT, tarsometatarsal.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.4E) Considerable osseous fragmentation in a bilateral distribution about the talonavicular aspect of the talocalcaneonavicular joint represents an infrequent but distinctive pattern in this disorder. The resulting

abnormalities simulate those of neuropathic osteoarthropathy in diabetes mellitus.

Neuropathic Osteoarthropathy The midfoot or hindfoot is a common site of involvement in diabetes mellitus. Tarsal disintegration with extension to the bases of the

101

CHAPTER 5  Overview: Target Area Approach to Arthritis

1

1 2

2

2

3

3

3

5

5 4

A

5 4

B

Potential calcaneal targets

4

C

Rheumatoid arthritis

1

Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis

1

1 2

2

2

3

3

3

5

5

5 4

D

1

4

4

CPPD crystal deposition disease, F Hyperparathyroidism xanthomatosis, and diffuse idiopathic skeletal hyperostosis Fig. 5.5  Target areas of the calcaneus. (A) The five potential target areas on the calcaneus (see text for identification of numbered areas). (B) Rheumatoid arthritis. (C) Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. (D) Gouty arthritis. (E) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, xanthomatosis, and diffuse idiopathic skeletal hyperostosis. (F) Hyperparathyroidism.

Gouty arthritis

E

metatarsal bones may be combined with changes at one or more metatarsophalangeal joints. In some cases, bone fragmentation and subluxation at the tarsometatarsal joints simulate the appearance of a traumatic Lisfranc fracture–dislocation.

CALCANEUS Five potential target areas exist on the calcaneus: (1) superior surface, (2) posterior surface above the attachment of the Achilles tendon, (3) posterior surface at the site of attachment of the Achilles tendon, (4) plantar surface at or near the site of attachment of the plantar aponeurosis, and (5) plantar surface anterior to the attachment of the aponeurosis (Fig. 5.5A). Of note, there is a synovium-­lined sac, the retrocalcaneal bursa, that is intimate with the posterosuperior aspect of the calcaneus, lying between the Achilles tendon and the surface of the bone. A small collection of fat in this region produces a characteristic normal radiolucent area, the retrocalcaneal recess, which is obliterated in the presence of retrocalcaneal bursitis.

Rheumatoid Arthritis (see Fig. 5.5B) Retrocalcaneal bursitis leads to unilateral or bilateral calcaneal erosions in both site 1 and site 2. An adjacent soft tissue mass projecting into the pre-­Achilles fat pad, related to the distended bursa, is frequently evident. Plantar osseous erosions may be seen, but large bone erosions along the plantar surface of the calcaneus are distinctly unusual. Associated Achilles tendinosis and even intratendinous rheumatoid nodules can produce changes at site 3.

Ankylosing Spondylitis and Psoriatic Arthritis (see Fig. 5.5C) Similar abnormalities occur in both ankylosing spondylitis and psoriatic arthritis, frequently in a bilateral distribution. Retrocalcaneal bursitis leads to osseous erosions at sites 1 and 2, which resemble the findings in rheumatoid arthritis, although reactive bone formation may be more prominent. On the plantar aspect of the bone, at sites 4 and 5, poorly marginated erosions, reactive bone sclerosis, and poorly defined enthesophytes may be detected. The outgrowths are more irregular and fuzzy and the degree of bone sclerosis is more prominent in these disorders than in rheumatoid arthritis. Achilles tendinosis can affect site 3.

Reactive Arthritis (see Fig. 5.5C) In reactive arthritis, unilateral or bilateral alterations can be encountered. Retrocalcaneal bursitis produces erosions at sites 1 and 2 that resemble the findings in rheumatoid arthritis. On the plantar aspect of the bone, osseous erosions and poorly defined bone formation occur at sites 4 and 5. The irregular enthesophytes that develop may become better defined over time.

Gouty Arthritis (see Fig. 5.5D) Tophaceous nodules in and about the Achilles tendon can lead to erosions at sites 2 and 3. The findings are combined with other, more typical changes at the metatarsophalangeal and interphalangeal joints.

102

SECTION 2  Articular Disorders

PF

M

A

PF

M

L

B

Rheumatoid arthritis

PF

M

L

Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis

C

L

Osteoarthrosis (especially in men)

PF PF

M

M

L

D

PF

L

PF

M

M

L

L

E

Hyperparathyroidism and Wilson disease Fig. 5.6  Target areas of the knee. (A) Rheumatoid arthritis. (B) Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. (C) Osteoarthrosis. (D) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. (E) Hyperparathyroidism and Wilson disease. L, Lateral femorotibial space; M, medial femorotibial space; PF, patellofemoral space. CPPD crystal deposition disease

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.5E) Calcific collections consisting of CPPD crystals can be deposited in the Achilles tendon and plantar aponeurosis of one or both feet in this disorder. The deposits are linear and may be of considerable length. Similar abnormalities may be seen in calcium hydroxyapatite crystal deposition disease.

Xanthomatosis (see Fig. 5.5E) Tendinous xanthomas can appear in the Achilles tendon and the plantar aponeurosis in a unilateral or bilateral distribution. They produce eccentric soft tissue masses that do not calcify. On rare occasions, they may erode subjacent bone.

Diffuse Idiopathic Skeletal Hyperostosis (see Fig. 5.5E) Well-­defined outgrowths of variable size occur at the sites of bony attachment of the Achilles tendon and plantar aponeurosis (sites 3 and 4).

Other Diseases Hyperparathyroidism can lead to subligamentous erosion at site 4, as well as subtle defects elsewhere in the calcaneus, including site 1 (see Fig. 5.5F). Haglund syndrome is characterized by a prominent posterosuperior border of the calcaneus, the Haglund bump, associated with retrocalcaneal bursitis at sites 1 and 2.

KNEE It is useful to analyze separately three major areas or spaces of the knee: the medial femorotibial space (M), the lateral femorotibial space (L), and the patellofemoral space (PF). Anteroposterior radiographs allow analysis of the medial and lateral femorotibial compartments, analysis

that can be improved by obtaining radiographs with the patient standing with or without knee flexion. Lateral and axial radiographs allow evaluation of the patellofemoral compartment.

Rheumatoid Arthritis (see Fig. 5.6A) Rheumatoid arthritis usually leads to alterations that are bilateral and symmetric and affect both medial and lateral femorotibial compartments to an equal degree. Diffuse loss of interosseous space in the medial and lateral femorotibial compartments may be combined with osteoporosis, marginal or central osseous erosions, and subchondral bone sclerosis. Depression of the osteoporotic bone of the tibia in combination with ligamentous abnormalities may create varus or, more characteristically, valgus angulation of the knee. Involvement of the patellofemoral space is often combined with involvement of the other two compartments in the knee in rheumatoid arthritis. Although not invariably present, tricompartmental abnormalities that are of equal severity with absence of osteophytes are most suggestive of rheumatoid arthritis.

Ankylosing Spondylitis, Psoriatic Arthritis, and Reactive Arthritis (see Fig. 5.6B) Any of these three disorders can affect one or both knees. A tricompartmental distribution may be encountered, although the degree of joint space narrowing, osteoporosis, and osseous erosion is less than in rheumatoid arthritis, and the extent of periosteal proliferation, or “whiskering,” may be pronounced.

Osteoarthrosis (see Fig. 5.6C) A unilateral or bilateral distribution can be seen. Asymmetric involvement of the medial and lateral femorotibial compartments

CHAPTER 5  Overview: Target Area Approach to Arthritis predominates, frequently in combination with significant patellofemoral compartment disease. Thus, bicompartmental rather than tricompartmental findings are evident on radiographs. In most men with osteoarthrosis of the knee, the medial femorotibial compartment is more severely affected, and the asymmetric nature of the process may lead to varus deformity. Severe alterations in the lateral femorotibial compartment and valgus deformity are more common in women with osteoarthrosis of the knee. Isolated abnormalities of the patellofemoral compartment are relatively unusual in osteoarthrosis of the knee, although such abnormalities are sometimes seen in women. The detection of joint space narrowing, bone sclerosis, and osteophytosis in this location in the absence of similar changes in either the medial or lateral femorotibial compartment should initiate a search for CPPD crystal deposition disease.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.6D)

103

axial migration of the femoral head with respect to the acetabulum. This finding is usually accompanied by marginal and central osseous erosions and cysts and even localized bone sclerosis. Osteophytosis is not a prominent feature. Over time, acetabular protrusion and coxa profunda are seen, with a diminutive and eroded femoral head that no longer occupies the entire expanded acetabular surface.

Ankylosing Spondylitis (see Fig. 5.7B) A bilateral and symmetric pattern consisting of axial migration of the femoral head as a result of diffuse loss of joint space is seen. Although this pattern is identical to that occurring in rheumatoid arthritis, the presence of osteophytosis, commencing on the superolateral aspect of the femoral head and progressing as a collar about the femoral head– neck junction, is distinctive of ankylosing spondylitis. Additional findings include subchondral cysts, mild acetabular protrusion, and partial or complete intraarticular bony ankylosis.

Osteoarthrosis (see Fig. 5.7C)

The distribution of abnormalities of the knee in patients with CPPD crystal deposition disease is somewhat variable. Usually both knees are affected. The medial femorotibial and patellofemoral compartments are commonly affected simultaneously, a distribution that is identical to that in osteoarthrosis. In these cases, the greater extent of osseous destruction and fragmentation, and the presence of chondrocalcinosis and gastrocnemius tendon calcification may allow accurate differentiation of CPPD crystal deposition disease from osteoarthrosis. Lateral femorotibial compartment changes, with or without medial femorotibial compartment abnormalities, also can be encountered in this disease and, in some instances, may lead to valgus deformity of the knee. Further, findings isolated to the patellofemoral compartment are observed in some patients. In fact, a “degenerative”-­like arthropathy of the patellofemoral compartment, appearing in the absence of significant medial or lateral femorotibial space alterations, raises the possibility that this disease is present, especially in men.

Unilateral or bilateral alterations are seen. Most commonly, loss of interosseous space results in superior migration of the femoral head with respect to the acetabulum. Less frequently, medial loss of joint space is seen, which may be associated with mild protrusio acetabuli deformity. Rarely, axial migration of the femoral head indicates diffuse loss of the cartilaginous surfaces of the femur and acetabulum. In all cases of osteoarthrosis, femoral osteophytes, particularly at the femoral head–neck junction, acetabular osteophytes, bone sclerosis, and subchondral cyst formation are common, and thickening, or buttressing, of the medial femoral cortex is apparent.

Other Diseases In addition to subperiosteal resorption of bone along the medial aspect of the tibia, hyperparathyroidism can produce distinctive types of articular abnormality on knee radiographs. Subchondral resorption of bone may be evident in any compartment. The changes, consisting of poorly defined “erosion” and sclerosis, may be especially marked in the patellofemoral areas (see Fig. 5.6E). Wilson disease may also lead to patellofemoral compartmental abnormalities.

The arthropathy of CPPD crystal deposition disease may involve one or both hips. It is characterized by symmetric loss of joint space with axial migration, bone sclerosis, subchondral cyst formation, and osteophytosis. The degree of bone collapse and fragmentation may be extreme, and the resulting radiographic features may be misinterpreted as neuropathic osteoarthropathy or osteonecrosis. Additional findings, such as chondrocalcinosis of the acetabular labrum and symphysis pubis detectable on pelvic radiographs, provide helpful clues to the correct diagnosis.

HIP

Osteonecrosis

Gouty Arthritis Hip involvement is unusual in gouty arthritis. Rarely, osseous erosion or osteonecrosis can be seen.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (see Fig. 5.7D)

In evaluating articular disorders that affect the hip, it is useful to define the nature or location of any accompanying joint space loss. With diminution of the articular space, the femoral head migrates in one of three basic directions with respect to the acetabulum. If the loss is confined to the superior aspect of the joint, the femoral head moves in an upward, or superior, (S) direction; if the loss is confined to the inner third of the joint, the femoral head migrates in a medial (M) direction; and if the joint space loss involves the entire joint surface, the femoral head migrates in an axial (A) direction along the axis of the femoral neck (Fig. 5.7A). Certain disorders are associated with characteristic patterns of femoral head migration.

Although osteonecrosis of one or both femoral heads can accompany a vast number of diseases, the joint space is remarkably preserved in most cases, even in the presence of significant bony collapse and fragmentation. In longstanding cases, secondary osteoarthrosis can result, owing to the incongruity of the apposing articular surfaces. In these instances, loss of joint space usually predominates in the superior aspect of the joint, leading to superior migration of the femoral head with respect to the acetabulum. Occasionally, loss of joint space is more diffuse. With secondary osteoarthrosis, the underlying features of osteonecrosis predominate.

Rheumatoid Arthritis (see Fig. 5.7B)

In Paget disease, bone involvement about the hip can lead to secondary degenerative joint disease. The radiographic findings are influenced by the distribution of the pagetic changes; the pattern of joint space loss may differ when the acetabulum is affected alone, when both the

In rheumatoid arthritis, the entire articular surface of the femoral head and acetabulum is typically affected in a bilateral and symmetric fashion. Thus, diffuse loss of the interosseous space occurs with

Other Diseases

104

SECTION 2  Articular Disorders

A

S

M

A

M

Patterns of migration

A

M

C

S

A

B

S

Rheumatoid arthritis and ankylosing spondylitis

A

S

A

M

S

M

D

Osteoarthrosis

CPPD crystal deposition disease Fig. 5.7  Target areas of the hip based on patterns of migration and sites of joint space loss (see text for explanation). (A) Patterns of migration of the femoral head. (B) Rheumatoid arthritis and ankylosing spondylitis. (C) Osteoarthrosis. (D) Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. A, Axial migration; M, medial migration; S, superior migration.

acetabulum and femur are affected, and when the femur is the only site of involvement. Because of these variations, any pattern of femoral head migration can appear in Paget disease. Regional migratory osteoporosis and transient osteoporosis of the hip are self-­limited conditions that can produce periarticular osteoporosis that improves spontaneously over several months. A unilateral distribution is typical, and when transient osteoporosis affects a woman in the third trimester of pregnancy, almost invariably the left hip is involved. Preservation of joint space is a feature of regional osteoporosis that allows its differentiation from infection. Furthermore, in most patients with these forms of osteoporosis, an insufficiency-­type stress fracture appears in the subchondral bone with possible subsequent collapse of the subchondral bone plate. Infections of the hip can have a bacterial, mycobacterial, or fungal cause. The radiographic features and prognosis are influenced by the age of onset. In infants, pyogenic arthritis of the hip requires immediate attention to prevent permanent epiphyseal damage. Joint space loss, which is generally diffuse in nature and unilateral in distribution, is a fundamental finding in all infectious disorders. Other findings include osteoporosis and marginal and central osseous erosions. Pigmented villonodular synovitis (a diffuse form of tenosynovial giant cell tumor) and synovial chondromatosis are two disorders that can produce monoarticular disease of the hip. In both conditions, soft tissue swelling and osseous erosions may appear in the absence of joint space narrowing and osteoporosis, although the last two findings are evident in some cases. The presence of cystic erosions of the femoral

neck in both conditions and the detection of calcific or ossific foci in some cases of synovial chondromatosis are important diagnostic clues. Cartilage atrophy, secondary to disuse, immobilization, or paralysis, produces diffuse loss of joint space and axial migration of the femoral head. Osteoporosis is evident. Irradiation can lead to collapse of the femoral head, fragmentation of the acetabulum, acetabular protrusion, and concentric joint space loss.

SHOULDER In the shoulder region, potential target areas can be affected in various articular disorders: the glenohumeral (GH) joint, the acromioclavicular (AC) joint, the rotator cuff (RC), and the undersurface of the distal end of the clavicle at the site of attachment of the coracoclavicular (CC) ligament (Fig. 5.8A).

Rheumatoid Arthritis (see Fig. 5.8B) Several target areas on both sides of the body can be involved in rheumatoid oarthritis. Glenohumeral joint alterations consist of osteoporosis, diffuse loss of joint space, and marginal osseous erosions, predominantly on the superolateral aspect of the humeral head. Acromioclavicular joint erosion with widening of the articular space is a recognized manifestation of this disease. The margins of the distal end of the clavicle may assume a tapered appearance. Similarly, scalloped erosion on the undersurface of the distal end of the clavicle opposite the coracoid process is an additional manifestation of rheumatoid

105

CHAPTER 5  Overview: Target Area Approach to Arthritis

AC CC

AC CC

RC

GH

A

AC RC

CC

GH

RC

GH

Rheumatoid arthritis and ankylosing C Osteoarthrosis spondylitis Fig. 5.8  Target areas of the shoulder. (A) Major target areas on the shoulder. See text for details. (B) Rheumatoid arthritis and ankylosing spondylitis. (C) Osteoarthrosis. AC, Acromioclavicular joint; CC, coracoclavicular ligament; GH, glenohumeral joint; RC, rotator cuff.

Potential shoulder targets

B

arthritis. Associated tears of the rotator cuff tendons and subacromial-­ subdeltoid bursitis are well-­ known complications of rheumatoid arthritis.

Ankylosing Spondylitis (see Fig. 5.8B) The changes about the shoulder in ankylosing spondylitis resemble those in rheumatoid arthritis. Glenohumeral joint involvement leads to joint space narrowing and osseous erosion. A large bony defect, the “hatchet” deformity, can appear on the superolateral aspect of the humeral head, which is distinctive. The absence of osteoporosis and the presence of bony proliferation about the osseous erosions are additional characteristics of ankylosing spondylitis that are helpful in diagnosis.

Osteoarthrosis (see Fig. 5.8C) Acromioclavicular joint degeneration is frequent in middle-­aged and elderly persons in whom intraarticular disc degeneration is almost universal. Changes consist of articular space narrowing, osteophytes, and bone eburnation. Osteoarthrosis of the glenohumeral joint also may be seen, most often after significant accidental or occupational trauma has occurred. Typical abnormalities include osteophytosis, which is predominantly at the inferior joint margin, joint space narrowing, bone sclerosis, labral degeneration and degenerative tearing, intraarticular bodies, acquired retroversion of the glenoid articular surface, and loss of glenoid bone stock. Disruption of the rotator cuff is frequent in elderly persons, producing elevation of the humeral head.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease Both the glenohumeral and the acromioclavicular joints can be affected in this disease. Fibrocartilage or hyaline cartilage calcification, joint space narrowing, bone sclerosis, and osteophytosis can appear at either shoulder location.

Calcium Hydroxyapatite Crystal Deposition Disease The deposition of calcium hydroxyapatite crystals in the shoulder is responsible for calcific “tendinitis” and subsequent periarticular cloud-­ like calcification in the subacromial-­subdeltoid bursa. Such deposition also may be instrumental in a distinctive arthropathy, the Milwaukee shoulder syndrome, that is characterized by destruction of bone and cartilage and deterioration of the rotator cuff.

Other Diseases Alkaptonuria (ochronosis) can lead to an arthropathy resembling osteoarthrosis of the glenohumeral joint in one or both shoulders. similarly, in acromegaly, osteophytosis may be evident in this site, especially on the inferior aspect of the humeral head. Hyperparathyroidism leads to osseous resorption of the distal end of the clavicle and adjacent acromion, as well as of the inferior aspect of the clavicle at the site of attachment of the coracoclavicular ligament. Posttraumatic changes include osteolysis of the distal end of the clavicle.

SACROILIAC JOINT The most important aspect in the differential diagnosis of diseases that affect the sacroiliac joint is the distribution of the abnormalities. Findings can be bilateral and symmetric, bilateral and asymmetric, or unilateral (Fig. 5.9). In nearly every instance, the synovial portion of the joint (where the sacrum and ilium subchondral bone plates are closely apposed) is affected to a greater degree than is the ligamentous portion.

Rheumatoid Arthritis (see Fig. 5.9B–C) Abnormalities of the sacroiliac joint in rheumatoid arthritis are generally a minor feature of the disease. Bilateral asymmetric or unilateral changes predominate, consisting of joint space narrowing, superficial osseous erosions, minor bone sclerosis, and absence of widespread bony ankylosis. Insufficiency fractures about the sacroiliac joint are a well-­known feature of rheumatoid arthritis.

Juvenile Idiopathic Arthritis The prevalence and appearance of sacroiliac joint changes in juvenile idiopathic arthritis depend on the subgroup of disease present. Changes usually are not prominent unless juvenile-­onset ankylosing spondylitis or another juvenile spondyloarthropathy is evident. In this case, a bilateral and symmetric distribution is encountered.

Ankylosing Spondylitis (see Fig. 5.9A) The classic sacroiliac joint findings in this disease are bilateral and symmetric. Bone erosions, bone sclerosis, and bony ankylosis of the synovial joint are frequently combined with poorly defined osseous margins in the ligamentous aspect of the joint. Iliac abnormalities predominate.

106

A

SECTION 2  Articular Disorders

Symmetric

B

Asymmetric

C

Unilateral

Fig. 5.9  Distribution of sacroiliac joint changes. (A) Symmetric. (B) Asymmetric. (C) Unilateral.

Psoriatic Arthritis and Reactive Arthritis (see Fig. 5.9A–C) The distribution of abnormalities is variable in psoriatic arthritis and reactive arthritis. Changes may be bilateral and symmetric, bilateral and asymmetric, or unilateral. Unilateral alterations of the sacroiliac joint are most typical of reactive arthritis and septic arthritis. Osseous erosion and bony sclerosis in psoriatic arthritis and reactive arthritis are similar to the findings in ankylosing spondylitis, although joint space narrowing and bony ankylosis occur with decreased frequency. Proliferation of bone in the ilium and sacrum above the synovial aspect of the joint may be prominent, particularly in reactive arthritis.

Osteoarthrosis (see Fig. 5.9A–C) Osteoarthrosis of the sacroiliac joint can be unilateral or bilateral. Unilateral abnormalities of this joint in conjunction with osteoarthrosis of the contralateral hip may be encountered. Findings include joint space narrowing, bone sclerosis, and osteophytosis, often focally involving the middle of the joint on anteroposterior radiographs or with inferior osteophytes. Erosions are not prominent, and paraarticular rather than intraarticular bone ankylosis predominates.

Gouty Arthritis (see Fig. 5.9A–C) Abnormalities of the sacroiliac joint can be seen in patients with long-­ standing tophaceous gout. Bilateral symmetric, bilateral asymmetric, or unilateral alterations consisting of large bone erosions and reactive bone sclerosis are found.

Other Diseases Sacroiliitis accompanying inflammatory bowel diseases is bilateral and symmetric and cannot be differentiated from that seen in ankylosing spondylitis (see Fig. 5.9A). In hyperparathyroidism, subchondral resorption of bone, especially in the ilium, produces bilateral and symmetric changes consisting of joint space widening and reactive bone sclerosis (see Fig. 5.9A); the diffuse and uniform joint space widening can be significant. Unilateral abnormalities are typical of sacroiliac joint infection (see Fig. 5.9C). Such infection is not infrequent in intravenous drug users. Osteitis condensans ilii produces bilateral and symmetric alterations in young women, the findings consisting of well-­ defined triangular sclerosis of the inferior aspect of the ilium (see Fig. 5.9A). Sacroiliac joint involvement also may accompany familial Mediterranean fever, relapsing polychondritis, Behçet syndrome, alkaptonuria, immobilization, and disuse.

6 Osteoarthrosis S U M M A R Y O F K E Y F E AT U R E S • Th  e term osteoarthrosis is used to describe degeneration of a synovial joint with characteristic pathologic abnormalities in articular cartilage and subchondral bone. • Inflammatory changes and synovitis are not present or represent only a minor histologic feature of synovial joint degeneration.

• C  haracteristic imaging features of osteoarthrosis include nonuniform joint space narrowing and osteophyte formation, with later subchondral cyst formation and bone sclerosis.

INTRODUCTION

are considerable deficiencies in our knowledge. Indeed, careful and continued assessment of many examples of so-­called primary osteoarthrosis eventually discloses at least subtle mechanical deviation in the involved articulation that has led to secondary degeneration of the joint. Articular degeneration may result from either an abnormal concentration of force across a joint with a normal articular cartilage matrix (e.g., injury, obesity, malalignment, dysplasia, neuropathy) or a normal concentration of force across an abnormal joint (e.g., meniscal tear, crystal deposition, osteonecrosis, metabolic diseases, preexisting arthritis). Eventually, abnormalities of force and articular structure appear together. The possible causes of osteoarthrosis are diverse (Table 6.1) and, further, these causes are not the same for each articulation. Both systemic and local factors are important, working together or separately.

  

Osteoarthrosis is a common degenerative disorder that involves synovial joints both in the central and in the peripheral skeleton. The suffix“-osis” rather than “-itis” implies that inflammatory changes are not present or, at most, are a minor histologic feature of this disorder. In certain varieties of osteoarthrosis, however, inflammatory changes are encountered such that osteoarthritis is the preferred designation (e.g., inflammatory osteoarthritis). Furthermore, degeneration of cartilaginous joints, fibrous joints, and entheses also is frequent, requiring terminology other than osteoarthrosis. Osteoarthrosis produces characteristic pathologic abnormalities in articular cartilage and subchondral bone, whereas alterations in the synovial membrane generally are mild. Associated imaging findings include joint space loss, bone eburnation and cyst formation, and osteophytosis. Subluxation, malalignment, fibrous ankylosis, and intraarticular osseous and cartilaginous bodies are among the potential complications of osteoarthrosis. The most common sites of extraspinal osteoarthrosis are the interphalangeal and metacarpophalangeal joints of the hand, first carpometacarpal and triscaphe areas of the wrist, acromioclavicular joint, hip, knee, and tarsometatarsal and metatarsophalangeal joints of the great toe.

ETIOLOGY KEY CONCEPTS  • S ystemic factors that may predispose to osteoarthrosis include genetics, obesity, age, sex, activity and occupation, nutritional and metabolic status, and osteoporosis. • Local factors that may predispose to osteoarthrosis include trauma, preexisting articular disease, and deformity.

Historically, osteoarthrosis was often classified into primary (idiopathic) and secondary types. Primary osteoarthrosis was regarded as a process in which articular degeneration occurs in the absence of any obvious underlying abnormality, whereas secondary osteoarthrosis was regarded as articular degeneration produced by alterations from a preexisting affliction. This classification into primary and secondary osteoarthrosis is misleading because it may indicate only that there

Systemic Factors Genetics

Genetic patterns have been recognized in some forms of osteoarthrosis (e.g., generalized osteoarthrosis with Heberden nodes), although the specific genetic factors have not been clearly identified in most forms of osteoarthrosis.

Obesity The role of obesity in the development of articular degeneration remains controversial. Studies of large populations of patients with degenerative joint disease reveal a great number of obese patients, but whether obesity causes osteoarthrosis or results from it is still debated. Accumulating data strongly support an association between obesity and osteoarthrosis of the knee; such an association for osteoarthrosis of the great toe and hand appears likely, but despite evidence to the contrary, an association between obesity and osteoarthrosis of the hip has not been established. Although it appears logical that excessive body weight should accentuate stresses across weight-­bearing articulations, extreme obesity may lead to patient immobility and decreased active joint motion, thereby diminishing any predisposition to develop degenerative articular alterations.

Age Strong evidence exists that degenerative joint disease occurs with increasing frequency in older persons, perhaps related to the

107

108

SECTION 2  Articular Disorders

TABLE 6.1  Main Causative Factors According to Location of Osteoarthritis INTRINSIC FACTORS

Affected Joint(s)

Age

Female Sex

Heredity

Fingers: DIP and nodal generalized osteoarthritis

+

++

++

Fingers: PIP and non­nodal generalized osteoarthritis

+

First carpometacarpal

+

First metatarsophalangeal

(+)

Hip

(+)

Knee

(+)

Glenohumeral

(+)

EXTRINSIC FACTORS

Obesity

Inflammation

+

++

Trauma

Minor Mechanical Disturbance

Dysplasia or Angulation

+ + ++ +

+

+ +

Ankle

+

Wrist

+

++

+

DIP, Distal interphalangeal; PIP, proximal interphalangeal. From Peyron JG: Epidemiologic and etiologic approach of osteoarthritis. Semin Arthritis Rheum 8:288–306, 1979.

diminished capacity of aging cartilage to resist mechanical stress because of changing physical and biochemical properties. The correlation of joint degeneration and advancing age is not linear. Rather, an age-­related predisposition to degenerative joint disease appears to increase exponentially after the age of 50 or 60 years.

Sex The pattern of degenerative joint disease is also influenced by the sex of the patient. Although the frequency of the disease is approximately equal in both sexes, men younger than 45 years are affected more commonly than are women of this age. In addition, women demonstrate severe disease more frequently than men and are more commonly afflicted with primary generalized osteoarthrosis, Heberden nodes, and inflammatory osteoarthritis.

Activity and Occupation Although normal use of a joint is thought to be beneficial to its integrity, it is generally assumed that either inactivity or excessive activity leads to articular degeneration. Certain occupations that are characterized by chronic and repetitive articular abuse are reportedly associated with degenerative joint disease at specific locations. Ballet dancers may develop osteoarthrosis in the ankles and joints of the feet. Osteoarthrosis has also been reported in the knees of football players, the patellofemoral joints of cyclists, and the hips of farmers. The deleterious effects of excessive repetitive impulse loading on joints (and bones) are perhaps best exemplified by the articular abnormalities in workers using vibrating tools (Fig. 6.1).

Nutritional and Metabolic Status The recognition of degenerative joint abnormalities in Kashin-­Beck disease has stimulated interest in the role of nutritional factors in the development of articular degeneration. In this disease, which is endemic in Siberia and other parts of the Far East, defective growth and maturation of epiphyses are associated with osteonecrosis and the appearance of osteoarthrosis-­like aberrations. Although the exact cause of Kashin-­Beck disease is not known, it has been attributed to the toxic effects of fungus-­contaminated grain, to selenium deficiency,

Fig. 6.1  Occupation-­ induced degenerative joint disease. In this pneumatic driller with 10 years of professional experience, cystic lesions are seen in the lunate and scaphoid. (Courtesy S. Sintzoff, MD, Brussels, Belgium.)

to chronic ingestion of excessive quantities of iron, and to defective mineral content of grain. An increased frequency of degenerative joint disease has been described in patients with a variety of endocrine disorders, such as diabetes mellitus and acromegaly. Vitamin C and vitamin D tissue levels have been reported to influence the frequency of osteoarthrosis. Degenerative joint disease can complicate various metabolic disorders, including Paget disease, alkaptonuria, hemochromatosis, Wilson disease, gout, calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, mucopolysaccharidoses, and osteopetrosis.

CHAPTER 6  Osteoarthrosis

Osteoporosis Although osteoporosis and degenerative joint disease are both common in older persons, increasing evidence supports an inverse correlation between the two processes. Secondary evidence of this dissociation is provided by reports that indicate differences in the patient populations affected by osteoporosis and osteoarthrosis; the former condition is evident in short and slender women and the latter in obese women. A reduction in bone mass in subchondral locations may lead to an increase in the tissue’s ability to absorb stress and a decrease in degenerative abnormalities.

Local Factors Trauma

Major or minor traumatic episodes appear to be important in producing abnormal stress across a joint, leading to its degeneration. Repetitive trauma is significant in athletic and occupation-­induced degenerative joint disease. It is also implicated in the appearance of joint degeneration in association with ligament laxity (Ehlers-­Danlos syndrome), loss of protective sensory feedback (neuropathic osteoarthropathy), extraarticular malalignment, and intraarticular malalignment (epiphyseal injury or slipping). Single episodes of trauma can also lead to incongruity of apposing articular surfaces, with resultant degenerative joint disease. Traumatic factors may explain the presence of more severe articular degeneration in the upper extremity on the dominant side than on the nondominant side, the lesser frequency of osteoarthrosis in joints that are located ipsilateral to and immediately above the site of amputation of a portion of the leg, and the absence of significant joint degeneration in an immobilized or paralyzed limb.

Preexisting Articular Disease or Deformity Degenerative changes in cartilage and bone may be superimposed on any primary articular process that has led to incongruity of and abnormal stress on the joint surfaces. Thus osteoarthrosis may follow inflammatory joint disease (e.g., rheumatoid arthritis and septic arthritis). Similarly, degenerative joint abnormalities may accompany hemophilia and other bleeding disorders, crystal-­induced arthropathy, osteonecrosis, and congenital disorders (e.g., acetabular dysplasia or epiphyseal dysplasia).

PATHOGENESIS Traditionally, osteoarthrosis is thought to begin in the articular cartilage. Physical forces apparently disrupt the cartilage matrix and adversely affect the chondrocytes. The alterations in the matrix are almost certainly related to enzymatic destruction. An alternative theory emphasizes the initial role of subchondral bony abnormalities in the pathogenesis of degenerative joint disease. According to this theory, overload produces microfractures in the subchondral bony trabeculae.

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Repair of these fractures leads to increased stiffness of the bone, a reduction in its shock-­absorbing efficiency, and exposure of overlying cartilage to increased force. This theory gains support from the clinical observations that some patients with osteoarthrosis demonstrate increased bone density when radiography, computed tomography (CT), or photon absorption techniques are used; that persons with disorders characterized by increased bone density (Paget disease, osteope­ trosis) may have degeneration of neighboring articulations; and that patients with osteoporosis of the femoral head may have a lower rate of occurrence of osteoarthrosis of the hip. After the appearance of degeneration in the cartilage or subchondral bone, a vicious circle of events occurs that aggravates the articular insult, resulting in progression of disease. Cartilaginous destruction increases joint instability, provoking further stress on cartilage and bone. In synovium-­lined joints, damage confined to cartilage generally shows a poor reparative response, whereas that extending to subchondral bone is accompanied by the appearance of cartilaginous tissue formed by vascular invasion. This tissue is not as sound mechanically as the original hyaline surface; it resembles fibrocartilage and accounts for such events as restoration of joint space, disappearance of bone eburnation and cysts, and improved joint congruity. Although traditionally the importance of inflammation in the pathogenesis of osteoarthrosis has not been emphasized, there are recent investigations that have indicated that inflammatory changes including synovitis are seen in some cases of osteoarthrosis and, further, such inflammation contributes to the joint damage, in part by affecting the extracellular matrix about the chondrocytes. The subchondral bone may represent a source of inflammatory mediators that govern regional pain and lead to degradation of the deep layers of articular cartilage.

RADIOGRAPHIC-­PATHOLOGIC CORRELATION (TABLE 6.2) Synovial Joints KEY CONCEPTS  • O  steoarthrosis involves a synovial joint often in a segmental or nonuniform distribution. • Cartilaginous abnormalities include articular cartilage degeneration, clefts, thinning, and defects. • Subchondral bone abnormalities include a destructive phase (eburnation, cyst formation, osseous remodeling) and a productive phase (marginal, central, periosteal, synovial, and capsular osteophytes). • Synovial membrane abnormalities are uncommon or mild with osteoarthrosis.

TABLE 6.2 Osteoarthrosis Radiographic-­Pathologic Correlation Pathologic Abnormality

Radiographic Abnormality

Cartilaginous fibrillation and erosion

Localized loss of joint space

Increased cellularity and hypervascularity of subchondral bone

Bony eburnation

Synovial fluid intrusion or bony contusion

Subchondral cysts

Revascularization of remaining cartilage and capsular traction

Osteophytes

Periosteal and synovial membrane stimulation

Osteophytes and buttressing

Compression of weakened and deformed trabeculae

Bony collapse

Fragmentation of osteochondral surface

Intraarticular osseous bodies

Disruption and distortion of capsular and ligamentous structures

Deformity and malalignment

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SECTION 2  Articular Disorders

Segmental Distribution of Abnormalities The morphologic features of osteoarthrosis often have a segmental or nonuniform distribution, especially in the large weight-­bearing articulations of the lower extremity. In these joints, there are regions of the articular surface that are consistently loaded, leading to pressurization of the interstitial fluid in the normally well-­ hydrated articular cartilage. This is a protective mechanism of the cartilage that shields the collagen-­proteoglycan matrix from the stresses placed on the joint surface. Osteoarthrosis is one response to a situation in which this protective mechanism is compromised. The pathologic and imaging features of this disorder are not the same in these loaded, or pressurized, segments and the less loaded regions of the joint. Therefore, although morphologic alterations are encountered in both segments, their nature and magnitude have a segmental or nonuniform distribution. It is this very distribution that represents an important characteristic of osteoarthrosis, allowing its pathologic and imaging differentiation from other disorders. The resulting structural abnormalities are most pronounced in the cartilage and subchondral bone.

Cartilaginous Abnormalities Characteristic changes in articular cartilage accompany osteoarthrosis (Fig. 6.2). Involved cartilage appears discolored (brown-­gray or yellow-­ gray) and thinned. Irregular crevices or cracks and larger areas of erosion develop, and ulcers of variable depth are seen, some of which are deep enough to expose the subchondral bone. Denuded areas appear, uncovering the subchondral bone. Eventually, loss of entire segments of the cartilaginous coat may be evident. Progressive erosion of cartilage is depicted on imaging studies as loss of the articular space, localized predominantly in the area of the joint that has been subjected to excessive pressure. Thus joint space narrowing dominates in the superolateral aspect of the hip and in the medial femorotibial compartment of the knee. In certain sites, joint space diminution may be more diffuse (osteoarthrosis of the interphalangeal or metacarpophalangeal joints). With these few exceptions, however, it is the focal or nonuniform nature of the loss of joint space that allows differentiation of osteoarthrosis from processes, such as rheumatoid arthritis, that lead to diffuse joint space loss.

Subchondral Bone Abnormalities Subchondral bone abnormalities in osteoarthrosis can be divided into a destructive phase (regressive remodeling) and a productive phase (progressive remodeling). Characteristics of the destructive

Fig. 6.2  Cartilaginous abnormalities: pathologic findings. Drawing depicts the irregular cracks or crevices (arrowheads) that may appear in the chondral surface. Terms such as fibrillation and fissuring are frequently applied to these findings.

phase are bony eburnation, cyst formation, and flattening and deformity of the subchondral bone plate, which predominate in the pressure segment of the joint; characteristics of the productive phase are osteophytes, which predominate in the nonpressure segment of the joint. Eburnation. After cartilage loss, bony eburnation becomes evident in the closely applied osseous surfaces, appearing dense and sclerotic, apparently related to deposition of new bone on preexisting trabeculae and to trabecular compression and fracture with callus formation. The loss of resilient cartilage and the restriction of joint motion heighten and localize the abnormal stress on the weakened hyperemic subchondral bone, leading to trabecular fracture, flattening, and collapse. Cyst formation. Cysts are a prominent finding in osteoarthrosis (as well as in other articular disorders) (Fig. 6.3). These lesions have been termed subchondral cysts, subarticular pseudocysts, and geodes. Any designation using the term cyst is not entirely accurate in that a cyst implies a cavitary lesion with an epithelial lining. Subchondral cysts are not surrounded by such a lining, nor are they uniformly cavitary. The term geode, which is popular in Europe, is a geologic term and is likewise not very appropriate; geodes are small, hollow rocks lined with crystals. Here, the designation subchondral cyst is used, despite its obvious inadequacies. Cystic spaces appear between thickened trabeculae in the subchondral bone in the pressurized joint segment. These cysts commonly are multiple, of variable size, and piriform in shape. Histologically, some cysts are noncavitary, containing myxoid and adipose tissue mixed with loose fibrous elements; others possess central cavitation containing proteinaceous material, are surrounded by fibrous tissue, and are well demarcated by adjacent eburnated bone. Communication of these cysts with the articular space may or may not be identifiable; when present, such communication may allow gas to pass from the joint into the cyst, creating a pneumatocyst (Fig. 6.4). The pathogenesis of these cystic lesions is not clear, with the emergence of two fundamental theories of pathogenesis: synovial fluid intrusion and bony contusion (Fig. 6.5). On imaging studies, the cystic lesions create multiple radiolucent areas of varying size on apposing surfaces of bone in the pressure segment of the joint, findings that must be differentiated from the subchondral lucent lesions that accompany other disorders (Table 6.3). In rheumatoid arthritis, cysts occur initially at chondro-­osseous junctions as a result of erosion of cartilage-­free

Fig. 6.3  Subchondral bone cysts: pathologic findings. Drawing reveals the typical appearance of multiple subchondral cysts of varying size in areas of cartilaginous degeneration or disappearance. They are surrounded by sclerotic bone.

CHAPTER 6  Osteoarthrosis

A

B Fig. 6.4  Subchondral cyst. This 38-­year-­old man developed knee pain and swelling after a fall. An enlarging lesion in the proximal end of the tibia was evident over a 2-­year period. Subsequently, the lesion stabilized and the symptoms disappeared. (A) Anteroposterior radiograph reveals a well-­circumscribed radiolucent area in the proximal portion of the tibia with a sclerotic border. (B) Axial CT image after the introduction of air into the articular cavity shows a large cyst containing gas (arrowhead) and one or two smaller cysts (arrows). The gas (i.e., air) within the cyst documents that it communicated with the joint cavity.

bone by inflammatory synovial tissue, or pannus, and are accompanied by early loss of articular space. They frequently are multiple, lack sclerotic margins, and subsequently extend over large segments of the joint surface. In CPPD, crystal deposition disease, multiple large and widespread cystic lesions are characteristic. They resemble the cysts in degenerative joint disease, except that they are larger, more numerous, and more frequently associated with disruption, collapse, and fragmentation of the subchondral bone plate. Chondrocalcinosis and calcification of other articular structures and tendons may also be present in CPPD crystal deposition disease. In osteonecrosis, cysts appear within the pressure segment of the articulation, related to osteoclastic resorption of necrotic trabeculae, with fibrous replacement of bone. Collapse of the subchondral bone plate and preservation of the joint space are additional features of osteonecrosis. Subchondral cysts also are a known sequela of bone injury, although its precise mechanism is not known. An intraosseous ganglion is another subchondral radiolucent

111

lesion that may simulate a degenerative cyst (Fig. 6.6). This lesion, which is commonly encountered in middle-­aged adults, is characterized by mild, localized pain and the absence of a significant history of trauma, is generally solitary, and is located in the epiphysis of a long bone, a carpal bone, or a subarticular region of a flat bone (particularly the acetabulum). Subchondral cysts in degenerative joint disease must also be distinguished from a variety of primary and secondary neoplasms of bone, including chondroblastoma (10-­to 30-­year-­old age group, solitary lesion) and giant cell tumor (20-­to 40-­year-­old age group, solitary eccentric trabeculated lesion). Osteophytosis. Osteophytes are a characteristic abnormality of osteoarthrosis, usually dominating in the nonpressurized portions of the joint. They may be marginal (peripheral), central, periosteal, or capsular in type. Marginal Osteophytes. Vascularization of the subchondral bone marrow in the peripheral portions of the joint produces calcification of the adjacent cartilage and stimulates endochondral ossification that leads to marginal osteophytes. As the osteophyte grows, it leaves behind remnants of the original calcified cartilage (and subchondral bone plate) as a telltale indicator of the location of the original joint surface, which can be identified histologically and radiographically (Fig. 6.7). Radiographically, marginal osteophytes appear as lips of new bone around the edges of the joint. They may be smooth, pitted, or undulating, and are of variable size. The excrescences frequently predominate on one side of the joint. Marginal osteophytes develop initially in areas of relatively normal joint space and usually are unassociated with significant adjacent bone sclerosis or cyst formation; joint space loss, bone eburnation, and subchondral cysts are findings that are characteristic of pressurized segments of the joint. Central (interior) osteophytes. The presence of osteophytes in the central, or interior, portions of the articular space is a less well-­ recognized manifestation of osteoarthrosis (Fig. 6.8). In central areas where remnants of articular cartilage still exist, hypervascularity of subchondral bone stimulates endochondral ossification. The resulting excrescences (which are most prominent in the hip and knee) are button­like or flat and are often demarcated at their bases by remnants of the original calcified cartilage. Central osteophytes frequently lead to a bumpy articular contour on radiographic examination (Fig. 6.9). The small excrescences can be misinterpreted as evidence of intraarticular osseous (loose) bodies or cartilage calcification (chondrocalcinosis). Periosteal and synovial osteophytes. In certain articulations, bone may develop from the periosteum or its intraarticular counterpart, the synovial membrane. This phenomenon is most characteristic in the femoral neck, where it is termed buttressing, and predominates on the medial aspect of the femoral neck (Fig. 6.10). Associated bone excrescences may project circumferentially, producing a radiodense line across the femoral neck that simulates a fracture. Capsular osteophytes. Osteophytes (or enthesophytes) accompanying osteoarthrosis may develop at the site of bony attachment of the joint capsule (and articular ligaments) (Fig. 6.11), a phenomenon that is particularly characteristic in the interphalangeal joints of the hand where the osteophytes resemble the wings of a seagull (seagull sign).

Synovial Membrane Abnormalities Synovial membrane alterations occur in osteoarthrosis but, in most cases, are not the major histologic abnormalities, despite recent emphasis suggesting that some forms of this disease are inflammatory and that inflammatory pathways may explain some of the cartilaginous and bony alterations that are encountered (see previous discussion). With increasing severity of osteoarthrosis, cartilaginous and osseous

112

SECTION 2  Articular Disorders

1

2 Fig. 6.5  Pathogenesis of subchondral cysts. Two fundamental theories are illustrated. The theory of synovial intrusion (1) states that abnormal stress on cartilage (arrow) leads to cartilaginous degeneration. Synovial fluid is driven into the subchondral bone through gaps in the chondral surface and bone plate (arrowhead), producing cysts that initially communicate with the joint and subsequently may become occluded with fibrous tissue. The theory of bony contusion (2) also holds that cartilage loss occurs as a result of abnormal stress (arrow). Subsequently, fracture and vascular insufficiency of the bone itself (arrowhead) produce cysts, which may communicate with the joint secondarily.

TABLE 6.3  Differential Diagnosis of Subchondral Cystic Lesions Disorder

Probable Mechanism of Cyst Formation

Radiographic Appearance

Osteoarthrosis

Synovial fluid intrusion Bony contusion

Multiple radiolucent lesions within pressure segment of joint Surrounding sclerotic margin Accompanying joint space narrowing and bony sclerosis

Rheumatoid arthritis

Pannus invasion of bone

Multiple radiolucent lesions begin at chondro-­osseous junction and become widespread No surrounding sclerotic margin Accompanying joint space narrowing and osteoporosis

Calcium pyrophosphate dihydrate crystal deposition disease

Synovial intrusion Bone contusion

Widespread radiolucent lesions, frequently large Surrounding sclerotic margin Accompanying joint space narrowing, bony sclerosis, collapse, and fragmentation

Osteonecrosis

Osteoclastic resorption of necrotic trabeculae

Single or multiple radiolucent lesions within pressure segment of joint Accompanying bony sclerosis, collapse, and fragmentation

Intraosseous ganglion

Intraosseous penetration of a soft tissue ganglion Single or loculated radiolucent lesion in pressure or nonpressure Primary intraosseous process, perhaps related to synovial segment of joint intrusion, synovial rests, or intramedullary mucoid degeneration Surrounding sclerotic margin owing to vascular insufficiency resulting from trauma Accompanying soft tissue mass

Neoplastic disorders Neoplastic proliferation with destruction and displacement of Chondroblastoma trabeculae Giant cell tumor Clear cell chondrosarcoma Skeletal metastasis

Variable, depending on the nature of the neoplasm

CHAPTER 6  Osteoarthrosis

113

A

Fig. 6.6  Intraosseous ganglion. An intraosseous ganglion, confirmed at surgery, is located adjacent to the ankle near the medial malleolus (arrows). It is lucent and surrounded by a thin rim of sclerosis, and apparently does not communicate with the articular cavity.

B

C

Fig. 6.7  Marginal osteophytes: pathologic findings. The marginal osteophyte develops as a lip of bone (arrow) as a result of vascularization of the subchondral marrow with the inception of endochondral ossification. As it grows, it leaves behind a remnant of the original calcified cartilage (arrowheads).

debris that originated from the articular surfaces may become embedded in the synovial membrane, acting as a local irritant and producing synovial proliferative changes. Infrequently, synovial abnormalities in osteoarthrosis may become so severe that they resemble the changes of rheumatoid arthritis. In the interphalangeal joints of the fingers, such synovial inflammation is present in inflammatory (erosive) osteoarthritis (see the later discussion in this chapter). Small synovial effusions may be encountered in osteoarthrosis. Sizable joint effusions that occur in the absence of trauma or osseous collapse should stimulate an investigation to exclude

Fig. 6.8  Central osteophytes: pathologic findings. (A) Reduplication of cartilage and bone. In the central portions of the articulation, hypervascularity of subchondral bone can lead to stimulation of remnants of cartilage, producing endochondral ossification. The flat outgrowths that develop (arrows) are often demarcated by the original zone of calcified cartilage (arrowheads). (B) Shifting of cartilage and bone border. In this situation, the osteophyte develops (arrows) without leaving behind a zone of calcified cartilage. (C) On a photograph of a macerated coronal section of the femoral head in a patient with osteoarthrosis, the osteophytes (solid arrows) are developing by reduplication and shifting of the cartilage-­bone junction. In places, a calcified zone of cartilage is identified (red arrowheads). A marginal osteophyte is also apparent (open arrow).

a superimposed articular process, such as infection or crystal deposition disease.

Abnormalities of Other Articular Structures In certain joints (knee, wrist, and sternoclavicular, acromioclavicular, and temporomandibular joints), fibrocartilaginous discs or menisci are present that may show considerable degeneration, particularly in older persons or after significant trauma (see Chapters 58, 59, and 60). Degeneration may also appear in the fibrocartilaginous labrum of the hip and glenohumeral joint. In some instances, these changes occur

114

SECTION 2  Articular Disorders cleft­like cavities appear in the central portion of the joint, usually after the age of 10 to 20 years (Fig. 6.12). They subsequently widen and become more irregular and may contain gas, leading to a vacuum phenomenon. Age-­related degenerative changes in the manubriosternal joint are similar.

Syndesmoses and Entheses

Fig. 6.9  Central osteophyte. Anteroposterior knee radiograph shows a central osteophyte (arrow) of the lateral femoral condyle with incidental interference screws related to prior reconstruction of the anterior cruciate ligament.

Fig. 6.10  Periosteal and synovial osteophytes: buttressing. Note the bone formation along the medial aspect of the femoral neck (arrows) in addition to other changes of osteoarthrosis, including joint space narrowing, bone sclerosis, and subchondral cyst formation.

At syndesmoses (e.g., tibiofibular and radioulnar interosseous membranes and ligaments), fibrous degeneration and bone proliferation may become apparent. At osseous sites of tendon attachment, a degenerative enthesopathy becomes apparent (Fig. 6.13). The degree of bone proliferation may be considerable, resulting in radiographically detectable bone excrescences (e.g., ischial tuberosity, trochanters) and enthesophytes (e.g., calcaneus, ulnar olecranon, patella). Tendon and ligament calcification also may be noted (e.g., sacrospinous and sacrotuberous ligaments). These changes may be generalized in diffuse idiopathic skeletal hyperostosis. Inflammatory enthesopathies are common in ankylosing spondylitis and other spondyloarthropathies but, unlike degenerative enthesophytes, the resulting bone outgrowths will appear irregular with erosions and indistinct margins on radiography.

Differential Diagnosis Osteoarthrosis is associated with joint space loss, bony sclerosis, and subchondral cysts in the pressurized (or stressed) segment of the joint and with osteophytes in the nonpressurized segment (Table 6.4). Osteoporosis, osseous erosion, and sizable joint effusions are not typical of this disease. In rheumatoid arthritis, joint effusion, osteoporosis, and uniform joint space loss are characteristic. In the spondyloarthropathies, irregular, poorly defined bone proliferation and intraarticular bony ankylosis may be noted. In gouty arthritis, bulky, asymmetric masses; eccentric, well-­ circumscribed osseous erosions; and preservation of the articular space are common. In CPPD crystal deposition disease, findings are very similar to those of osteoarthrosis, although intraarticular and extraarticular calcification, involvement of unusual joints, large tumor­like cystic lesions, progressive abnormalities with bone fragmentation and collapse, and absence of osteophytosis are characteristic features. Neuropathic osteoarthropathy is characterized by severe fragmentation and collapse of the articular surfaces, extensive bony sclerosis, multiple cartilaginous and osseous intraarticular bodies, large joint effusions, and joint subluxation and malalignment. The presence of both osteoarthrosis and osteonecrosis together can lead to diagnostic difficulty. This situation may relate to either osteonecrosis developing as a secondary phenomenon in cases of osteoarthrosis or osteoarthrosis occurring as a secondary phenomenon in cases of osteonecrosis (Fig. 6.14). Bone necrosis may be apparent on histologic examination of the eburnated surface in the pressurized segment of an osteoarthritic joint. Flattening and collapse of the subchondral bone plate, however, may be apparent in osteoarthrosis without indicating the presence of significant osteonecrosis. Radiographic abnormalities tend to be centered at the joint with osteoarthrosis, whereas the femoral head findings of osteonecrosis often predominate, even with secondary osteoarthrosis.

in the absence of any other articular abnormalities, whereas in other instances, findings of osteoarthrosis are evident.

COMPLICATIONS OF OSTEOARTHROSIS

Cartilaginous Joints

Angular deformity in osteoarthrosis is not unexpected in view of the nonuniform nature of the joint involvement. Focal loss of articular space is characteristic and may produce, for example, varus (and, less

Two major extraspinal cartilaginous joints, or symphyses, are the symphysis pubis and the manubriosternal joint. In the symphysis pubis,

Malalignment and Subluxation

CHAPTER 6  Osteoarthrosis

115

B

A

Fig. 6.11  Capsular osteophytes: pathologic and radiographic findings. (A) Drawing of a section through an osteoarthritic distal interphalangeal joint reveals capsular osteophytes (arrows) arising from the distal and middle phalanges. These bone outgrowths are sometimes termed enthesophytes rather than osteophytes. Note that the outgrowths extend proximally and are associated with small ossicles (arrowhead). Additional findings include cartilaginous destruction and subchondral sclerosis. (B) Radiograph shows the capsular osteophyte (arrow) arising from the distal phalanx. Joint space narrowing and bone sclerosis are also seen.

commonly, valgus) deformity of the knee. Changes in bone, capsule, and supporting tissue allow progressive subluxation, examples of which are lateral displacement of the tibia on the femur, lateral displacement of the femoral head in the acetabulum, and radial and proximal displacement of the first metacarpal base on the trapezium.

Fibrous and Bony Ankylosis

Fig. 6.12  Symphyseal degeneration. Radiograph of the symphysis pubis reveals subchondral bone sclerosis and osteophytes (arrows), consistent with degenerative arthrosis.

Fig. 6.13  Degenerative enthesopathy: calcaneus. Radiograph depicts the irregular osseous proliferation that can occur at sites of tendon and ligament attachment to the calcaneus (arrows).

Although fibrous ankylosis may be prominent at some sites of osteoarthrosis (sacroiliac joint), bony ankylosis is unusual. An exception to this is the occasional appearance of intraarticular bony ankylosis in association with inflammatory (erosive) osteoarthritis of the interphalangeal joints of the hand. Paraarticular bony ankylosis related to prominent osteophytes or overriding osseous surfaces related to malalignment may simulate intraarticular osseous fusion, as in the sacroiliac joints.

Intraarticular Cartilaginous and Osseous Bodies Osteocartilaginous bodies (or joint mice) within a joint can arise from several sources: transchondral fractures, disintegration of the articular surface, and synovial metaplasia (Fig. 6.15). Fragmentation of the joint surface can accompany a variety of disease processes, including osteoarthrosis. Cartilaginous and osseous debris may remain on the joint surface or become dislodged, or free or loose, in the joint cavity. Debris subsequently may become embedded at a distant synovial site, eliciting a local inflammatory response. Intraarticular bodies may be adherent or loose and moveable within a joint and joint recess. On radiographs, the osteocartilaginous bodies can increase or decrease in size, disappear, or remain unchanged. Osteochondral bodies commonly migrate to and become lodged in saclike articular regions, such as the acetabular fossa of the hip, olecranon fossa of the elbow (Fig. 6.16), or subscapular recess (Fig. 6.17) and axillary pouch of the glenohumeral joint. These bodies must be differentiated from other disease processes, such as idiopathic synovial chondromatosis. Idiopathic synovial chondromatosis is commonly associated with a large number of osteocartilaginous bodies of approximately equal size,

116

Osteoporosis

Joint Space Osseous Narrowing Erosions

Osseous Cysts Sclerosis

Bone Osteophytosis ­Whiskering

Intraarticular Osseous Fusion

Osteoarthrosis

–

Focal

–

+

+

+

–

–

Inflammatory osteoarthritis

–

Focal

+

+

+

+

–

DIP, PIP joints

Rheumatoid arthritis

+

Diffuse

+

+

–

–

–

Carpal, tarsal areas

Gouty arthritis

–

May be absent

+

+

+

+

–

Rare

Pyrophosphate arthropathy

–

Diffuse

–

+

+

±

–

Spondyloarthropathies

±

Diffuse

+

+

+

–

Osteonecrosis

–

Absent

–

+

+

Neuropathic osteoarthropathy

–

Variable

–

±

+

Osseous Fragmentation, Collapse Typical Location In large joints

–

Rare

DIP, PIP, MCP joints of hand; first CMC and trapezioscaphoid joints of wrist; first MTP, TMT joints of foot; knee; hip; apophyseal joints of spine DIP, PIP, MCP joints of hand; first CMC and trapezioscaphoid joints of wrist

PIP, MCP joints of hand; wrist; MTP joints of foot; knee; elbow; glenohumeral joint; cervical spine ±

MTP, IP joints of foot; DIP, PIP, MCP joints of hand; wrist; elbow; knee

–

+

MCP joints of hand; radiocarpal joint of wrist; knee

+

+

–

Spine; sacroiliac joint; various articulations of the appendicular skeleton

–

–

–

+

Hip; glenohumeral joint; until late knee; sites of trauma

±

–

–

+

Sites depend on underlying disorder

CMC, Carpometacarpal; DIP, distal interphalangeal; IP, interphalangeal; MCP, metacarpophalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal; TMT, tarsometatarsal.

SECTION 2  Articular Disorders

TABLE 6.4  Differential Diagnosis of Osteoarthritic Changes

CHAPTER 6  Osteoarthrosis

117

B

A

Fig. 6.14  Osteoarthrosis versus osteonecrosis. (A) Osteoarthrosis with collapse and fragmentation. In this patient with long­standing disease, considerable collapse of the weight-­bearing surface of the femoral head is evident. Note superior, or upward, migration of the femoral head with respect to the acetabulum, a large medial osteophyte (arrow), acetabular osteophytes, and buttressing. The changes are those of osteoarthrosis; the extent of bony collapse, though perhaps indicating secondary osteonecrosis, should not lead to an erroneous diagnosis of primary osteonecrosis. (B) Osteonecrosis with secondary cartilaginous destruction. In this patient, segmental collapse of the femoral head (arrows) is evident. Note diffuse loss of joint space, related either to secondary osteoarthrosis or to chondrolysis. Although bone sclerosis and buttressing are evident, the findings do not resemble those of primary osteoarthrosis as femoral findings predominate.

2

3

1

whereas osteochondral bodies in osteoarthrosis, a phenomenon that is sometimes designated secondary synovial osteochondromatosis, leads to fewer bodies (generally lateral

Commonly involved alone or in conjunction with medial or lateral femorotibial disease

Hyperparathyroidism

Medial = lateral*

Involved owing to subchondral resorption, crystal-­induced arthropathies, or unknown mechanism

*Subchondral resorption can produce collapse of bone in the medial or lateral femorotibial compartment, or both.

134

SECTION 2  Articular Disorders

A

B

Fig. 6.49  Osteoarthrosis of the ankle. (A) Anteroposterior mortise radiograph and (B) lateral ankle radiograph delineate posttraumatic joint space narrowing, sclerosis, and osteophytosis (arrow), the last predisposing to anterior ankle impingement. Note a large plantar calcaneal enthesophyte (arrowhead) and abnormally enlarged Achilles tendon (curved arrow) related to extensive tendinosis.

Fig. 6.51  Osteoarthrosis of the posterior subtalar joint after calcaneal fracture. In this 58-­year-­old man, hindfoot pain began approximately 4 years after a fracture of the calcaneus. A coronal reformatted CT image reveals depression of the posterosuperior surface of the calcaneus and the site of previous fracture (arrow). Note the narrow posterior subtalar joint (arrowhead), with osteophytes and bone fragmentation, and the close relationship of the fibula and the calcaneus. Compare with the opposite normal side.

Fig. 6.50  Osteoarthrosis of the first tarsometatarsal joint. Radiograph shows joint space narrowing, sclerosis, and osteophytes at the first (medial) tarsometatarsal joint and, to a lesser extent, the second tarsometatarsal space.

accumulate in these interphalangeal joints, leading to inflammation. The deposition of monosodium urate crystals in the osteoarthritic joints of the fingers, leading to articular inflammation (i.e., gout), may also be seen. Patients are generally elderly; indeed, they are older than the typical population with gout. Many of them are receiving diuretic therapy. The radiographic diagnosis of secondary gout in patients with osteoarthrosis of the interphalangeal joints of the fingers may be difficult.

Differential Diagnosis Inflammatory osteoarthritis is associated with proliferative and erosive abnormalities of interphalangeal joints. The erosions of inflammatory osteoarthritis are unusual in their distribution within an involved joint; they frequently predominate in the central portion. This central localization differs from the marginal localization associated with other erosive arthritides of the interphalangeal joints, such as rheumatoid arthritis, psoriatic arthritis, multicentric reticulohistiocytosis, and gout. The most difficult aspect of the differential diagnosis is distinguishing inflammatory osteoarthritis and psoriatic arthritis. In addition to the central location of erosions in the inflamed joints, the additional presence of a background of ordinary osteoarthrosis in many

A

B Fig. 6.52  Osteoarthrosis of the first metatarsophalangeal joint. (A) Frontal radiograph reveals joint space narrowing, sclerosis, and osteophytosis (arrows) about the first metatarsophalangeal joint. Note dorsal osteophytes (arrowheads) in (B), a lateral radiograph.

A

B

C

Fig. 6.53  Inflammatory (erosive) osteoarthritis: interphalangeal joint abnormalities. (A) Drawing depicts the usual appearance of inflammatory osteoarthritis of the interphalangeal joints. Findings resemble those of noninflammatory osteoarthritis, including traction osteophytes (solid arrows), ossicles (arrowhead), and eburnation. Erosive changes are also apparent, particularly in the central aspect of the joint (open arrows) (compare with Fig. 6.11). (B) In a more advanced case, disruption of the entire central aspect of the joint (arrows) is typical. Note the changes in the proximal interphalangeal joint, which are identical to those of noninflammatory osteoarthrosis. (C) The eventual result may be intraarticular osseous fusion, as seen in the distal interphalangeal joint.

136

SECTION 2  Articular Disorders

interphalangeal joints characterizes inflammatory osteoarthritis. This differs from psoriatic arthritis, in which marginal erosions and poorly defined bony proliferation may be distributed in an asymmetric, unilateral, or even ray­like pattern. Intraarticular bony ankylosis, which accompanies inflammatory osteoarthritis, may also be evident in psoriatic arthritis and, less commonly, in rheumatoid arthritis. Finally, in patients with nodal osteoarthrosis who develop inflammatory clinical manifestations, the possibility of secondary crystal deposition, including calcium hydroxyapatite, CPPD, and monosodium urate, should be considered

FURTHER READING Alizai H, Walter W, Khodarahmi I, et al. Cartilage imaging in osteoarthritis. Semin Musculoskelet Radiol. 2019;23:569. Berenbaum F. Osteoarthritis as an inflammatory disease (osteoarthritis is not osteoarthrosis). Osteoarthritis Cartilage. 2013;21:16. Bock GW, Garcia A, Weisman MH, et al. Rapidly destructive hip disease: clinical and imaging abnormalities. Radiology. 1993;186:461. Boegård T, Jonsson K. Radiography in osteoarthritis of the knee. Skeletal Radiol. 1999;28:605. Boegård T, Rudling O, Petersson IF, et al. Correlation between radiographically diagnosed osteophytes and magnetic resonance detected cartilage defects in the tibiofemoral joint. Ann Rheum Dis. 1998;57:401. Burke MJ, Fear EC, Wright V. Bone and joint changes in pneumatic drillers. Ann Rheum Dis. 1977;36:276. Crain DC. Interphalangeal osteoarthritis characterized by painful inflammatory episodes resulting in deformity of the proximal and distal articulations. JAMA. 1961;175:1049. Dalinka MK, Kricun ME, Zlatkin MB, et al. Modern diagnostic imaging in joint disease. AJR Am J Roentgenol. 1989;152:229. Dihlmann W, Hering L. Dense bone about the sacroiliac joint: a radiological review of the differential diagnosis. Eur J Radiol. 1998;27:241. Dixon T, Benjamin J, Lund P, et al. Femoral neck buttressing: a radiographic and histologic analysis. Skeletal Radiol. 2000;29:587. Ehrlich GE. Inflammatory osteoarthritis. II. The superimposition of rheumatoid arthritis. J Chronic Dis. 1972;25:635. Feldman F, Johnston A. Intra-­osseous ganglion. AJR Am J Roentgenol. 1973;118:328. Felson DT. Osteoarthritis as a disease of mechanics. Osteoarthritis Cartilage. 2013;21:10. Foreman SC, Gersing AS, von Schacky CE, et al. Chondrocalcinosis is associated with increased knee joint degeneration over 4 years: data from the Osteoarthritis Initiative. Osteoarthritis Cartilage. 2020;28:201. Jacobson JA, Girish G, Jiang Y, Resnick D. Radiographic evaluation of arthritis: inflammatory conditions. Radiology. 2008;248:378. Jacobson JA, Girish G, Jiang Y, Resnick D. Radiographic evaluation of arthritis: degenerative joint disease and variations. Radiology. 2008;248:737. Jaffe HL. Metabolic, Degenerative and Inflammatory Diseases of Bones and Joints. Philadelphia: Lea & Febiger; 1972.

Karasick D, Wapner KL. Hallux rigidus deformity: radiologic assessment. AJR Am J Roentgenol. 1991;157:1029. Kellgren JH, Moore R. Generalized osteoarthritis and Heberden’s nodes. BMJ. 1952;1:181. Kindynis P, Haller J, Kang HS, et al. Osteophytes of the knee: Anatomic, radiologic, and pathologic investigation. Radiology. 1990;174:841. Mankin HJ. The reaction of articular cartilage to injury and osteoarthritis. Part 1. N Engl J Med. 1974;291:1285. Mankin HJ. The reaction of articular cartilage to injury and osteoarthritis. Part 2. N Engl J Med. 1974;291:1335. Martel W, Braunstein EM. The diagnostic value of buttressing of the femoral neck. Arthritis Rheum. 1978;21:161. Martel W, Snarr JW, Horn JR. The metacarpophalangeal joints in interphalangeal osteoarthritis. Radiology. 1973;108:1. Martel W, Stuck KJ, Dworin AM, et al. Erosive osteoarthritis and psoriatic arthritis: a radiologic comparison in the hand, wrist, and foot. AJR Am J Roentgenol. 1980;134:125. McCarty DJ, Halverson PB, Carrera GF, et al. “Milwaukee shoulder”— association of microspheroids containing hydroxyapatite crystals, active collagenase, and neutral protease with rotator cuff defects. I. Clinical aspects. Arthritis Rheum. 1983;24:464. Milgram JW. The development of loose bodies in human joints. Clin Orthop. 1977;124:292. Neer CS. Anterior acromioplasty for the chronic impingement syndrome in the shoulder. J Bone Joint Surg Am. 1972;54:41. Resnick D. Patterns of migration of the femoral head in osteoarthritis of the hip: roentgenographic-­pathologic correlation and comparison with rheumatoid arthritis. AJR Am J Roentgenol. 1975;124:62. Resnick D, Niwayama G. Entheses and enthesopathy: Anatomical, pathological, and radiological correlation. Radiology. 1983;146:1. Resnick D, Niwayama G, Coutts RD. Subchondral cysts (geodes) in arthritic disorders: pathologic and radiographic appearance of the hip joint. AJR Am J Roentgenol. 1977;128:799. Resnick D, Niwayama G, Goergen TG. Comparison of radiographic abnormalities of the sacroiliac joint in degenerative disease and ankylosing spondylitis. AJR Am J Roentgenol. 1977;128:189. Roemer FW, Crema MD, Trattnig S, et al. Advances in imaging of osteoarthritis and cartilage. Radiology. 2011;260:332. Roemer FW, Demehri S, Omoumi P, et al. State of the art: Imaging of osteoarthritis - Revisited 2020. Radiology. 2020;296:5–21. Rose CP, Cockshott WP. Anterior femoral erosion and patello-­femoral osteoarthritis. J Can Assoc Radiol. 1982;33:32. Thomas RH, Resnick D, Alazraki NP, et al. Compartmental evaluation of osteoarthritis of the knee: a comparative study of available diagnostic modalities. Radiology. 1975;116:585. Trueta J. Studies of the Development and Decay of the Human Frame. Philadelphia: WB Saunders; 1968. Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg [Am]. 1984;9:358. Zhang Y, Hannan MT, Chaisson CE, et al. Bone mineral density and risk of incident and progressive radiographic knee osteoarthritis in women: the Framingham study. J Rheumatol. 2000;27:1032.

7 Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts S U M M A R Y O F K E Y F E AT U R E S • I n rheumatoid arthritis, involvement of synovial-­lined articulations, bursae, and tendon sheaths predominate. • With the spondyloarthropathies (ankylosing spondylitis, psoriatic arthritis, and reactive arthritis), in addition to involvement of

synovial-­lined spaces, there is characteristic involvement of the entheses or cartilaginous joints, or both.

  

INTRODUCTION The general imaging and pathologic abnormalities associated with articular involvement in rheumatoid arthritis and the spondyloarthropathies (ankylosing spondylitis, psoriatic arthritis, reactive arthritis) are similar in many respects. Involvement of synovial and cartilaginous joints, bursae, tendon sheaths, entheses, tendons, ligaments, soft tissues, and bones can be encountered in any of these disorders. The distribution and extent of abnormalities differ among these diseases, however. In rheumatoid arthritis, alterations in synovium-­lined articulations, bursae, and tendon sheaths frequently overshadow those in cartilaginous joints and sites of tendon and ligament attachment to bone. In ankylosing spondylitis, psoriatic arthritis, and reactive arthritis, abnormalities can be severe at cartilaginous articulations, including the discovertebral and manubriosternal joints and symphysis pubis. In addition, in those three conditions, a peculiar enthesopathy produces bone erosion and proliferation at tendo-­osseous junctions.

RHEUMATOID ARTHRITIS Overview The major abnormalities of rheumatoid arthritis appear in synovial articulations of the appendicular skeleton, particularly the small joints of the hand and foot, the wrist, the knee, the elbow, and the glenohumeral and acromioclavicular joints. The synovial articulations of the axial skeleton also may be affected, especially the apophyseal and atlantoaxial joints of the cervical spine. Changes are generally distributed symmetrically on the right and left sides of the body and consist of fusiform soft tissue swelling, regional osteoporosis, uniform loss of joint space, and marginal and central erosions. The synovium of bursae and tendon sheaths is also affected, whereas involvement of cartilaginous articulations and entheses is less frequent and extensive, with the exception of the discovertebral joints of the cervical spine.

Synovial Joints KEY CONCEPT  • F our fundamental radiographic abnormalities characterize early stages of articular involvement in rheumatoid arthritis: fusiform soft tissue swelling, regional osteoporosis, uniform loss of joint space, and marginal erosions of bone.

Rheumatoid arthritis is a chronic autoimmune disorder of unknown cause whose fundamental target tissue is the synovium that lines joints, tendon sheaths, and bursae. The precise trigger for the disease is likely multifactorial, including a genetic predisposition, with an association with certain histocompatibility antigens (e.g., human leukocyte antigen [HLA]-­DR4). The resulting cellular immune response includes the formation of an erosive pannus and inflammatory mediators that induce joint destruction (Table 7.1).

Synovial Membrane The earliest recognizable pathologic abnormality in rheumatoid arthritis is acute synovitis, which is associated with congestion and edema of the synovial membrane (Fig. 7.1) resulting in a thickened and injected synovial membrane. The bulky and hypervascular synovial tissue pro­ jects into the joint lumen as villous fronds that maintain contact with the synovial fluid. Characteristic conventional radiographic abnormalities accompany these early pathologic and histologic alterations (Fig. 7.2). Accumulation of synovial inflammatory tissue within the joint, an increase in intraarticular fluid, capsular distention, and surrounding soft tissue edema lead to one early radiographic finding of the disease— fusiform soft tissue swelling. In response to the hyperemia provoked by synovial inflammation, regional or periarticular osteoporosis—the second early radiographic sign of rheumatoid arthritis—becomes evident. This finding produces thinning and small areas of discontinuity (dot-­dash pattern) in the subchondral bone plate.

Articular Cartilage After an acute inflammatory episode, the inflamed synovium soon spills from the peripheral portion and marginal pockets of the joint and extends across the cartilaginous surface. Owing to enzymatic destruction of cartilage, interference with proper cartilaginous nutrition, or both factors, diffuse loss of the interosseous space becomes evident (see Fig. 7.2). Classically, joint space diminution is a relatively early finding in the disease, and it may appear within a period of weeks or months in some patients. Along with soft tissue swelling and periarticular osteoporosis, diffuse joint space narrowing is one of three early radiographic characteristics of rheumatoid arthritis.

Subchondral Bone Two alterations in subchondral bone that occur in the early stages of rheumatoid arthritis are osteoporosis and marginal erosion.

137

138

SECTION 2  Articular Disorders

Pathologic

Radiologic

Synovial inflammation and production of fluid

Soft tissue swelling and widening of joint space

as magnetic resonance (MR) imaging may detect marrow edema and even the bone erosions themselves at an earlier time. Single or multiple subchondral lucent cystlike areas in patients with early or more advanced rheumatoid arthritis are also well recognized, related to such factors as intraosseous extension of pannus, nutritional and metabolic injury of bone, and true intraosseous rheumatoid nodules. These cystic areas are particularly prominent in patients with rheumatoid arthritis who maintain a high level of physical activity and in whom the designation of rheumatoid arthritis of the robust reaction type has been employed (Fig. 7.3). These cysts, which may represent one mechanism of joint decompression (Fig. 7.4), are usually multiple, distributed symmetrically, of small size, and without sclerotic margins. Subchondral cysts are sometimes observed in the absence of classic marginal bone erosions, articular space loss, and osteopenia. In these instances, the radiographic manifestations resemble those of gout.

Hyperemia

Osteoporosis

Pannus destruction of cartilage

Narrowing of joint space

Fibrous Capsule

Osteoporosis, which can progress with time, is related to a combination of disuse of the articulation, osteoclastic resorption of the subchondral spongy trabeculae, and steroid-­induced bone changes. The initial erosions in rheumatoid arthritis occur at the marginal unprotected areas of the articulation, where pannus is intimate with bone that does not possess protective cartilage. Such erosions may be a very early manifestation of the disease, occurring within 1 or 2 years of the onset of joint symptoms. Of note, however, advanced imaging methods such

TABLE 7.1  Abnormalities of Synovial Joints

in Rheumatoid Arthritis

The fibrous capsule of the synovial joint reveals only minor alterations in patients with rheumatoid arthritis. After prolonged inflammation, capsular contraction can aggravate the malalignment and subluxation provoked by changes in supporting structures.

Pannus destruction of “unprotected” Marginal bony erosions bone at margin of joint Pannus destruction of subchondral bone

Bony erosions and formation of subchondral cysts

Fibrous and bony ankylosis

Bony ankylosis

Laxity of capsule and ligaments and muscular contraction and spasm

Deformity, subluxation, dislocation, fracture, fragmentation, and sclerosis

1

4

Synovial Membrane, Cartilage, and Bone in Advanced Rheumatoid Arthritis The pathologic and conventional radiographic changes in the synovial joints of patients with rheumatoid arthritis do not always pro­ gress relentlessly. Even in later phases, after irreversible damage has

2

3

5

6

Fig. 7.1  Synovial joint abnormalities in rheumatoid arthritis: pathologic overview. In a normal joint (1), observe the articular cartilage and synovial membrane. At the edges of the articulation (arrowheads), synovium abuts bone that does not possess protective cartilage. The very early abnormalities of rheumatoid arthritis (2) consist of synovial proliferation (open arrows), soft tissue edema (solid arrows), and osteoporosis. At a slightly later stage (3), the inflamed synovial tissue, or pannus (open arrow), has extended across the cartilaginous surface and is leading to chondral erosion. Capsular distention, soft tissue edema, and osteoporosis are seen. Small osseous erosions at the margins of the joint are appearing (arrowheads). In more advanced stages (4, 5), large marginal and central erosions and “cysts” are noted (arrowheads). In advanced rheumatoid arthritis (6), fibrous ankylosis of the joint is typical.

139

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

A

C

B

Fig. 7.2  Synovial joint abnormalities in rheumatoid arthritis: sequential radiographic changes in metacarpophalangeal joints. A, The earliest abnormalities consist of soft tissue swelling (solid arrows), periarticular osteoporosis, loss of a portion of the subchondral bone plate on the metacarpal head (open arrow), and minimal joint space narrowing. B, With progression, increases in soft tissue swelling (solid arrows) and osteoporosis are associated with marginal erosions of the metacarpal heads (open arrow). C, The later stages of rheumatoid arthritis are characterized by complete obliteration of the articular space and large central and marginal osseous erosions (open arrows).

1

3

2

Fig. 7.3  Pseudocystic rheumatoid arthritis. In some patients with rheumatoid arthritis, particularly men, multiple large radiolucent lesions (arrows) about involved articulations can occur, a pattern of disease that is termed robust-­type rheumatoid arthritis.

occurred, the changes may remain static for an indefinite period. In the late stage of rheumatoid arthritis, fragments of cartilage and bone are found embedded in the synovial tissue, with resulting radiographic abnormalities resembling those in neuropathic osteoarthropathy, osteoarthrosis, gout, osteochondritis dissecans, osteonecrosis, or idiopathic synovial osteochondromatosis. Osteoarthrosis can be a prominent secondary phenomenon in the synovial joints of patients with rheumatoid arthritis. Therefore, the possibility of underlying rheumatoid arthritis should be considered whenever radiographs reveal osteoarthrosis with unusual features (e.g., uniform joint space narrowing) or in unusual sites (Fig. 7.5).

Fig. 7.4  Mechanism of decompression of joints with raised intraarticular pressure. The three potential pathways are (1) subchondral cystic lesions, (2), synovial cysts, and (3) fistulas or sinus tracts.

Bursae and Tendon Sheaths Synovial inflammation in rheumatoid arthritis also occurs in the synovial lining of tendon sheaths and bursae (Table 7.2). Bursal involvement in this disease may occur in more than 5% of patients, particularly in the popliteal region of the knee, olecranon bursa, subacromial-­ subdeltoid bursa, and retrocalcaneal bursa, but also about the wrist and foot. Tenosynovitis is especially prominent in the dorsum of the hand and wrist, the fingers, and the foot. In some instances, bursitis and tenosynovitis occur as isolated or predominant manifestations of the disorder. Furthermore, in association with tenosynovitis, the tendon itself may be affected and become disposed to a variety of complications, including weakening, subluxation, entrapment, and rupture. The most common conventional radiographic finding associated with tenosynovitis and bursitis is soft tissue swelling or a mass, a finding

140

SECTION 2  Articular Disorders

T

Fig. 7.6  Abnormalities of the tendon sheath in rheumatoid arthritis. US long axis to a common extensor tendon (T) of the wrist shows hypoechoic distention of the tendon sheath (arrows), representing tenosynovitis.

Fig. 7.5  Synovial joint abnormalities in rheumatoid arthritis: productive changes in bone and secondary osteoarthrosis. On a radiograph of a coronal section of a cadaveric knee, observe the abnormalities related to bone production in the form of osteophytes (solid arrow) and subchondral sclerosis (open arrow). These findings should not be regarded as evidence of a diagnosis other than rheumatoid arthritis. In this case, involvement of both the medial femorotibial space and lateral femorotibial space, with predominant involvement of the latter area, aids in the accurate diagnosis of rheumatoid arthritis. Fragmentation of the articular surface, with the formation of a large intraarticular body (arrowhead), is seen.

TABLE 7.2  Abnormalities of Bursae and

Tendon Sheaths in Rheumatoid Arthritis Pathologic

Radiologic

Synovial inflammation and production of fluid

Soft tissue swelling

Hyperemia

Osteoporosis

Pannus destruction of subjacent bone

Surface resorption of bone

that is more ideally characterized with ultrasonography (US) (Fig. 7.6) and MR imaging. Erosion of subjacent bone can be observed, particularly in the posterosuperior aspect of the calcaneus (in relation to retrocalcaneal bursitis) (Fig. 7.7), the olecranon process (in relation to olecranon bursitis), the ulnar styloid (in relation to the extensor carpi ulnaris tenosynovitis) (Fig. 7.8), and the inferior surface of the acromion and distal end of the clavicle (in relation to subacromial bursitis).

Cartilaginous Joints and Entheses KEY CONCEPTS  • D  iscovertebral changes predominate in the cervical spine. • Presence of discovertebral erosions and vertebral subluxations in the absence of osteophytosis is typical.

Although involvement of cartilaginous joints, such as the symphysis pubis and manubriosternal and discovertebral articulations, and of entheses, such as those related to the spinous processes of the vertebrae, the inferior surface of the calcanei, the iliac wings, the ischial tuberosities, and the femoral trochanters, is observed in rheumatoid

arthritis, the frequency and severity of such involvement are far less striking than in the spondyloarthropathies. Of the cartilaginous joints, the alterations of the discovertebral junction in rheumatoid arthritis are most notable (Table 7.3) and predominate in the cervical region. The pathogenesis of these alterations is unclear with the following suggestions (Fig. 7.9): (1) discovertebral abnormalities occur as a secondary manifestation of synovial inflammation in the adjacent neurocentral articulations (joints of Luschka) in the cervical spine and the neighboring costovertebral articulations in the thoracic spine (the synovial school); (2) discovertebral alterations relate to traumatic insults produced by instability of the posterior elements of the spine (the traumatic school); or (3) discovertebral alterations in rheumatoid arthritis, as in ankylosing spondylitis, are produced by a primary enthesopathy (the enthesopathic school). The resulting abnormalities are characteristic (Fig. 7.10).

Tendons and Ligaments Inflammatory and degenerative changes and laxity resulting from distortion of tendons and ligaments by the intraarticular process contribute to the typical joint deformities that accompany long-­standing rheumatoid arthritis. “Spontaneous” tendon ruptures are a known manifestation of rheumatoid arthritis that are encountered most frequently in the hand and wrist, although ruptures of other tendons can occur, including the Achilles, patellar, tibialis posterior, and rotator cuff tendons. Joint subluxation, malalignment, and deformity in rheumatoid arthritis can be attributed to inflammatory destruction of intraarticular structures leading to surface incongruity, capsular and ligamentous weakening leading to laxity, tendinosis and tenosynovitis leading to contracture and rupture, and muscular contraction. Articular deformity is most characteristic at the wrist; the metacarpophalangeal, metatarsophalangeal, and interphalangeal articulations of the hand and foot; and the atlantoaxial region. Although such subluxation in rheumatoid arthritis is almost invariably associated with typical joint alterations, a deforming, nonerosive arthropathy may be encountered similar to that in systemic lupus erythematosus (Fig. 7.11).

Soft Tissues Edema

In patients with rheumatoid arthritis, widespread peripheral edema can occur in association with generalized factors such as anemia, fluid retention, and hypoalbuminemia, as well as localized factors, including obstruction of venous and lymphatic channels, reduced numbers of lymphatic vessels, and increased capillary permeability. Clinically,

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

A

141

B

Fig. 7.7  Abnormalities of bursae in rheumatoid arthritis. A–B, Retrocalcaneal bursitis. Soft tissue swelling (open arrows) represents a fluid-­filled, distended retrocalcaneal bursa. Subjacent osseous erosion (arrowhead, B) can be seen.

TABLE 7.3  Abnormalities of Discovertebral

Cartilaginous Joints in Rheumatoid Arthritis Potential Mechanism

Pathogenesis

Synovial inflammation

“Pannus” is derived from joints of Luschka (cervical region) and costovertebral articulations (thoracic region)

Trauma

Apophyseal joint instability leads to traumatic disruption of the discovertebral junction with cartilaginous node formation

Enthesopathy

Inflammation at ligamentous and capsular attachments leads to adjacent osseous erosion

lymphedema in patients with rheumatoid arthritis affects men and women with equal frequency and usually involves an entire limb, especially an upper extremity. The appearance of lymphedema in rheumatoid arthritis simulates that in a more recently described syndrome, remitting seronegative symmetric synovitis with pitting edema (RS3PE) syndrome.

Rheumatoid Nodules Fig. 7.8  Abnormalities of tendon sheaths in rheumatoid arthritis. Surface resorption of bone beneath an inflamed extensor carpi ulnaris tendon sheath at the wrist produces typical defects along the outer aspect of the ulnar styloid (arrowheads).

The most frequent soft tissue lesion in rheumatoid arthritis is a subcutaneous nodule, although such nodules are associated with a wide variety of disorders, including rheumatic fever, collagen vascular disorders, sarcoidosis, Weber-­Christian disease, gout,

142

SECTION 2  Articular Disorders

A

B

C

Fig. 7.9  Abnormalities of the discovertebral junctions of the cervical spine in rheumatoid arthritis. A, The normal situation. B, Proponents of the synovial school of thought suggest that inflammatory tissue in the neurocentral joints of Luschka (solid arrow) spreads across the discovertebral junction, a process leading to osseous erosion (open arrows). C, Proponents of the traumatic school of thought believe that instability of the apophyseal joints resulting from synovial inflammation (arrowhead) produces recurrent discovertebral trauma, which leads to cartilaginous nodes with surrounding sclerosis (open arrows).

Fig. 7.10  Discovertebral lesions in the cervical spine in rheumatoid arthritis. Sagittal sectional radiograph in a cadaver reveals, at one discovertebral level, prominent erosions about the neurocentral joints (arrows). At a lower level, widespread discovertebral erosions and disc space loss are apparent. Above, bone ankylosis (arrowhead) has led to obliteration of an intervertebral disc. The apophyseal joints are not well evaluated in this radiograph.

dermatologic processes, xanthomatosis, and various infections. One or more subcutaneous nodules are detectable in approximately 20% to 35% of patients with rheumatoid arthritis. The nodules are most commonly located between the skin and an underlying bony prominence. Typical locations include the olecranon, the proximal portion of the ulna, the lateral aspects of the fingers, the gluteal and Achilles tendon regions, and the areas about the femoral trochanters and ischial tuberosities. Almost invariably, rheumatoid nodules are associated with seropositivity for rheumatoid factor and a

propensity for severe erosive disease and vasculitis. They may be identified before the clinical onset of arthritis and are asymptomatic. Subcutaneous nodules vary in size from a few millimeters to greater than 5 cm; they are firm and nontender, and nodules are frequently attached to the deep fascia or the periosteum, but they can be freely movable. Radiographically, subcutaneous rheumatoid nodules are associated with lobulated, eccentric soft tissue masses. These masses infrequently calcify, a diagnostic point that may be helpful in distinguishing them from gouty tophi, which can contain calcification. In unusual instances, rheumatoid nodules can lead to erosion of subjacent bone, producing scalloped defects in the cortex of the proximal portion of the ulna, metacarpals, metatarsals, or other bones that can simulate the appearance of a variety of benign soft tissue neoplasms, as well as gout, tenosynovial giant cell tumor, ganglion, and xanthoma. Rheumatoid nodules appear hypoechoic, with variable hyperemia at US. With MR imaging, rheumatoid nodules typically demonstrate a nonspecific low to intermediate signal intensity on T1-­weighted MR images and heterogeneous low to high signal intensity on fluid-sensitive MR images, and they show enhancement of signal intensity after the intravenous administration of a gadolinium-­containing agent (Fig. 7.12). On US, rheumatoid nodules appear hypoechoic with possible hyperemia (see Fig. 7.12C). An atypical variant of rheumatoid disease, rheumatoid nodulosis, is characterized by the presence of multiple subcutaneous nodules and the absence of significant synovitis or systemic manifestations. Men are usually affected. Serologic tests for rheumatoid factor are commonly positive in these persons, and biopsy of the nodules and synovium reveals typical histologic changes of rheumatoid arthritis.

Synovial Cysts Synovial cysts are a well-­known manifestation of rheumatoid arthritis. They are most commonly encountered in the popliteal region of the knee, where the extension of the synovial inflammation extends from the knee joint into a communicating semimembranosus–medial gastrocnemius bursa producing a popliteal, or Baker, cyst, which at times

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

A

143

C

B

Fig. 7.11  Joint malalignment in rheumatoid arthritis: typical digital deformities of the hand. A, Swan-­ neck deformity (hyperextension at the proximal interphalangeal joint and flexion at the distal interphalangeal joint). B, Boutonnière deformity (flexion at the proximal interphalangeal joint and hyperextension at the distal interphalangeal joint). C, Rarely, severe subluxation of the hand in rheumatoid arthritis is associated with only minor intraarticular abnormality. Note the ulnar deviation and flexion at the metacarpophalangeal joints with swan-­neck deformities. Minor degrees of joint space narrowing are evident, but erosions are not prominent.

T

A

B

C

Fig. 7.12  Soft tissue nodules in rheumatoid arthritis: MR imaging and US. This 65-­year-­old woman with rheumatoid arthritis had multiple subcutaneous nodules, including one in the plantar aspect of the left heel. A, T1-­weighted transverse MR image reveals the soft tissue nodule in the left heel (arrowhead), surrounded by fat. B, After the intravenous administration of gadolinium-­containing contrast agent, an identical T1-­weighted MR image shows diffuse enhancement of the nodule (arrowhead). C, US shows a hypoechoic rheumatoid nodule (arrows) adjacent to the Achilles tendon (T). (B, Courtesy S. Moreland, MD, San Diego, CA.)

may be very extensive (Fig. 7.13). Synovial cysts also have been described at other sites, including the calf, knee, ankle, plantar aspect of the foot, hip, hand and wrist, elbow, and shoulder. Clinically, it may be difficult to differentiate signs and symptoms related to synovial cysts about the knee from those caused by thrombophlebitis. Furthermore, rupture of a synovial cyst is accompanied by swelling and edema that may lead to stasis, inflammation of the wall of the vein, and thrombophlebitis.

Sinus Tracts Cutaneous-­articular sinus tracts are recognized as an occasional feature of rheumatoid arthritis, leading to a finding that has been designated

“fistulous” rheumatism. In affected patients, erythematous periarticular nodules erupt and form draining sinuses, often multiple, in the vicinity of the hands and feet.

Muscles In rheumatoid arthritis, generalized muscle weakness is common, although other symptoms and signs related to muscle involvement are rare. Possible causes of muscle involvement in this disease include muscle atrophy, steroid myopathy, peripheral neuropathy, and acute or chronic myositis. Toxic myopathy precipitated by various therapeutic agents is also well recognized.

144

SECTION 2  Articular Disorders

A

B

C Fig. 7.13  Popliteal cyst in rheumatoid arthritis. Axial fluid-­sensitive MR image (A) and transverse (B) and sagittal extended field-of-view (C) US show the distended semimembranosus-medial gastrocnemius bursa (arrows). Note the characteristic communicating neck (arrowhead) between the tendon of the semimembranosus muscle and that of the medial head of the gastrocnemius muscle, and extension of the cyst distally between the muscle belly of the medial gastrocnemius and the subcutaneous fat.

TABLE 7.4  Mechanisms and Sites of

Pathologic Fractures in Rheumatoid Arthritis Mechanism

Typical Sites

Synovial inflammation with erosion of bone

Odontoid process, carpal scaphoid bone, distal portion of ulna

Mechanical erosion of bone

Ribs, articular surfaces of small bones in hands and feet, medial aspect of humeral neck

Intraosseous cystic lesions

Proximal portion of ulna, femoral neck, femur, and tibia about the knee

Bone deformation

Acetabulum

Generalized osteopenia

Insufficiency fractures of vertebral bodies, pelvis, tubular bones of lower extremity, small bones of foot

Osteonecrosis

Femoral head, vertebral bodies

Osteomyelitis

Variable

Digital Vessels Necrotizing arteritis in mesenteric, renal, and cerebral locations, subacute arteritis in skeletal muscles, and fibromuscular hyperplasia in peripheral vessels are all recognized in rheumatoid arthritis. Vasculitis complicated by digital gangrene and acro-­osteolysis can be seen in rheumatoid arthritis as well as in other collagen vascular disorders.

Bones Generalized osteoporosis is a common manifestation in patients with rheumatoid arthritis. producing bone weakening that contributes to a variety of fractures (Table 7.4). These fractures may occur after

minimal trauma or spontaneously (e.g., insufficiency fractures) in either spinal sites (compression fractures of vertebral bodies) or extraspinal locations (Fig. 7.14). Typical locations include the femur, tibia, fibula, calcaneus, sacrum, and para acetabular and para symphyseal regions. Accurate diagnosis of insufficiency fractures can be difficult and requires a high index of clinical suspicion, quality radiographs, and even scintigraphy, CT scanning, or MR imaging. Fractures through eroded bone (Fig 7.15) can occur with minor injury.

SPONDYLOARTHROPATHIES KEY CONCEPTS  • S pondyloarthropathies include a number of disorders that involve the spine and sacroiliac joints. • Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis are the three primary disorders in this group. • Spondyloarthropathies often produce abnormalities in cartilaginous joints and entheses in addition to synovial joints. • Bone proliferation is a characteristic feature of the spondyloarthropathies.

Overview Spondyloarthropathy is a term introduced to label a group of disorders that involve the axial skeleton, especially the spine and sacroiliac joints. Initial clinical abnormalities, however, may appear either in the axial skeleton or extra axial skeleton. These clinical manifestations and their imaging counterparts reflect arthritis, osteitis, and enthesitis. The last of these should be emphasized. An enthesis is a site of tendon, ligament, or capsular attachment to bone; enthesitis reflects alterations at these sites related to inflammation, and the clinical and

145

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

A

B

C

Fig. 7.14  Insufficiency-­type stress fractures in rheumatoid arthritis. A, Radiograph demonstrates a classic insufficiency fracture of the calcaneus (arrow) appearing as vertically oriented region of bony sclerosis. T1-­ weighted sagittal (B) and fluid-­sensitive coronal MR (C) images in a different patient show a characteristic linear jagged insufficiency fracture (arrow) with surrounding bone marrow edema.

TABLE 7.5  Rheumatoid Arthritis Versus the

Spondyloarthropathies Characteristic

Fig. 7.15  Fractures through sites of bone erosion in rheumatoid arthritis. This radiograph documents a fracture of the carpal scaphoid bone through a site of erosion (arrowhead). Ischemic necrosis of the proximal pole of the bone is evident. (From Resnick D, Cone R. Pathological fractures in rheumatoid arthritis: sites and mechanisms. Radiographics. 1984;4:549.)

imaging abnormalities related to enthesitis may dominate in any of the spondyloarthropathies. In short, although the articular manifestations of the spondyloarthropathies resemble those of rheumatoid arthritis, the distribution of abnormalities with predilection for the spine and sacroiliac joints, the potential severity of involvement in cartilaginous joints and entheses, and the propensity for bone proliferation are characteristic and differentiating features of the spondyloarthropathies (Table 7.5). The three major spondyloarthropathies are ankylosing spondylitis, psoriatic arthritis, and reactive arthritis (formerly known as Reiter syndrome). To this list can be added inflammatory bowel disease, juvenile spondyloarthropathy, uveitis, and undifferentiated spondyloarthropathy.

Rheumatoid SpondyloarArthritis thropathies

Synovial joint involvement

+

+

Soft tissue swelling

+

+

Osteoporosis

+

±

Marginal erosions

+

+

Central erosions and cysts

+

+

Bony ankylosis

±

+

Bony proliferation

–

+

Malalignment and subluxation

+

±

Bursal and tendon sheath involvement

+

+

Soft tissue swelling

+

+

Bony erosions

+

+

Bony proliferation

–

+

Cartilaginous joint involvement

±

+

Bony erosions

±

+

Bony proliferation

±

+

Bony ankylosis

±

+

Enthesopathy

±

+

Bony erosions

±

+

Bony proliferation

±

+

+, Common; ±, less common; –, rare or absent.

Although the specific criteria allowing diagnosis of the spondyloarthropathies vary from one source to another, there are certain diagnostic features that are uniformly emphasized. The histocompatibility complex antigen HLA-­B27 is encoded by the major gene predisposing to the spondyloarthropathies, being present in more than 90% of patients with ankylosing spondylitis, although

146

SECTION 2  Articular Disorders

its frequency in other forms of spondyloarthropathy is less, and, further, other genes also modulate disease predisposition. The presence of sacroiliitis on imaging studies represents a second fundamental criterion for the spondyloarthropathies. Additional diagnostic criteria emphasize sausage digit (dactylitis), inflammatory back pain, enthesitis (e.g., of the heel), arthritis, ophthalmologic abnormalities such as uveitis, and inflammatory bowel disease. Reliable diagnostic criteria, however, are difficult to develop owing to the heterogeneous group of disorders that currently make up the spondyloarthropathies and the fact that clinical and imaging manifestations may dominate in either the axial or peripheral skeleton. Despite this variability in site selection, the discovertebral junctions throughout the spine, the symphysis pubis, the manubriosternal joint, and the tendinous and ligamentous attachments in the calcaneus, pelvis, trochanters of the femur, tuberosities of the humerus, and patella are altered to a much greater extent in ankylosing spondylitis, psoriatic arthritis, and reactive arthritis than in rheumatoid arthritis. With regard to the morphology of the skeletal abnormalities, the imaging and pathologic characteristics of joint involvement in ankylosing spondylitis, psoriatic arthritis, and reactive arthritis are fundamentally similar and can be distinguished from those in rheumatoid arthritis. In synovial articulations, the absence of osteoporosis and the presence of bony proliferation and intraarticular bony ankylosis in the spondyloarthropathies are most helpful in differentiating the changes from those of rheumatoid arthritis. In cartilaginous joints, the extent of osseous erosion and bone proliferation in the former disorders is also helpful in the differential diagnosis. At sites of tendon and ligament attachment to bone, an inflammatory enthesopathy (i.e., enthesitis) leading to osseous destruction and repair is characteristic of the spondyloarthropathies.

Synovial Joints The predominant target area in the synovial joints in the spondyloarthropathies is the synovial membrane (Table 7.6). Fibroplasia, which is followed by cartilaginous metaplasia and chondro-­ossification, can

TABLE 7.6  Abnormalities of Synovial Joints

in the Spondyloarthropathies Pathologic

Radiologic

Synovial inflammation and production of fluid

Soft tissue swelling and widening of the joint

Mild to moderate hyperemia

Variable osteoporosis

Pannus destruction of cartilage

Narrowing of the joint space

Pannus destruction of “unprotected” Marginal bony erosions bone at the margin of a joint Pannus destruction of subchondral bone

Bony erosions and formation of subchondral cysts

Fibroplasia, cartilaginous metaplasia, chondro-­ossification, capsular ossification

Bony ankylosis

Bony proliferation in response to damage

Marginal “whiskering,” periostitis, subchondral sclerosis

Noninflammatory proliferation of the Cortical atrophy, osteolysis periosteum

lead to intraarticular bony ankylosis, a feature that may be apparent in any of the spondyloarthropathies but is most typical of ankylosing spondylitis and psoriatic arthritis (Fig. 7.16). Detection of osseous fusion at sites other than the carpal and tarsal areas is relatively unusual in rheumatoid arthritis. In the spondyloarthropathies, subchondral eburnation, irregular excrescences (“whiskers”) at the margins of the joint (Fig. 7.17A), and periostitis of adjacent diaphyses, particularly in the phalanges and the metacarpal and metatarsal bones, are distinctive (see Fig. 7.17B). Bone erosion in ankylosing spondylitis, psoriatic arthritis, and reactive arthritis may be superficial and quickly obscured by the profound tendency toward bone proliferation. Such erosion can be preceded by marrow edema detectable with MR imaging.

Bursae and Tendon Sheaths Inflammation in synovium-­lined bursae and tendon sheaths also occurs in the spondyloarthropathies. Retrocalcaneal bursitis is particularly characteristic of and often associated with Achilles tendinopathy and enthesitis (Fig. 7.18). Tenosynovitis, a frequently encountered manifestation of rheumatoid arthritis, may be a prominent feature in the spondyloarthropathies. Considerable soft tissue swelling in this clinical situation can produce a sausage-­shaped finger or toe (Fig. 7.19).

Cartilaginous Joints and Entheses The tendency for the spondyloarthropathies to affect cartilaginous articulations and sites of tendon and ligament attachment to bone is well known (Table 7.7). At the manubriosternal joint and symphysis pubis, progressive fibrosis and bone formation lead to trabecular thickening and intraarticular ossification. Similar abnormalities in the discovertebral joint produce “osteitis” of the anterior vertebral margin, which is accompanied by erosion and sclerosis of bone and progressive discal ossification associated with syndesmophyte formation (Fig. 7.20). The pathogenesis of destructive lesions at single or multiple discovertebral junctions during the course of ankylosing spondylitis is not clear, and several mechanisms probably contribute to these lesions. These include an increasing enthesopathy, pressure destruction of the intervertebral disc related to kyphosis, cartilage node formation, and improper healing (so-­called pseudarthrosis) about a fracture site. The last-­mentioned mechanism is expected in long standing disease in which a rigid vertebral column, caused by widespread bony ankylosis, is predisposed to fracture in a manner similar to that of a long tubular bone. Continued motion at the fracture site leads to improper fracture healing, in which callus formation, hemorrhage, fibrous proliferation, and mild inflammatory changes are seen. An enthesopathy occurring at other tendinous and ligamentous connections to bone in patients with spondyloarthropathies is responsible for the prominent clinical and imaging manifestations in the plantar aspect of the calcaneus, pelvis, patella, iliac crest, ischial (Fig. 7.21) and humeral tuberosities, and femoral trochanters. At these sites, edema, a decrease in hematopoietic tissue, and inflammatory changes in the adjacent bone marrow are associated with osseous erosion and sclerosis. Bony deposition can eventually obscure the eroded surface and produce a poorly defined, or “fluffy,” osseous contour.

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

1

4

2

3

5

6

Fig. 7.16  Synovial joint abnormalities in spondyloarthropathies: pathologic overview. Normal synovial joint is depicted at the upper left (1). Early changes (2) consist of synovial inflammation (open arrows) and soft tissue edema (solid arrows). Osteoporosis may not be evident. Subsequently (3), synovial inflammatory tissue, or pannus, extends across and beneath the chondral surface (open arrows) and leads to cartilaginous erosion or disruption. At later stages (4, 5), marginal and central osseous erosions develop (arrowheads). Associated bony proliferation (curved arrow) becomes evident. Finally (6), intraarticular bony ankylosis may develop.

147

148

SECTION 2  Articular Disorders

A

B

Fig. 7.17  Synovial joint abnormalities in spondyloarthritis: radiographic changes of bone proliferation. Radiographs show (A) “whiskering” at the joint margins (arrows) and (B) chronic bone proliferation resulting in diaphyseal periostitis (arrows) in a patient with psoriatic arthritis.

* Fig. 7.18  Bursal and tendon abnormalities in spondyloarthropa­ thies. US long axis to the distal Achilles tendon shows abnormal increased thickness and hypoechogenicity of the tendon (arrow) with cortical erosion (arrowhead) at the tendon attachment. Note fluid distention of the retrocalcaneal bursa (asterisk).

Fig. 7.19  Abnormalities of tendon sheaths in spondyloarthropathies. The soft tissue swelling and periostitis (arrows) involving the proximal phalanx of the fourth finger are entirely consistent with tenosynovitis, a characteristic finding of the spondyloarthropathies. (Courtesy D. Goodwin, MD, Hanover, NH.)

CHAPTER 7  Rheumatoid Arthritis and Spondyloarthropathies: Imaging and Pathologic Concepts

TABLE 7.7  Abnormalities of Cartilaginous Joints and Entheses in the Spondyloarthropathies Pathologic

Radiologic

Inflammation of subchondral bone

Bony erosion and sclerosis

Bony proliferation

Bony ankylosis

Inflammation of capsular, ligamentous, and tendinous attachments

Bony erosion and sclerosis

A

B

Fig. 7.20  Cartilaginous joint (discovertebral junction) abnormalities in spondyloarthropathies. A, Radiograph of a coronal section of the spine in a cadaver with ankylosing spondylitis reveals typical syndesmophytes extending as linear osseous bridges from one vertebral body to the next (arrows). B, In a photograph of a corresponding section from another cadaver with ankylosing spondylitis, the nature of the syndesmophytes is evident (arrows)—they represent chondrification and ossification of the annulus fibrosus.

149

150

SECTION 2  Articular Disorders

A

B

C Fig. 7.21  Abnormalities of entheses in spondyloarthropathies. A, Radiograph shows poorly defined erosion and reactive bone formation in the ischial tuberosities (arrows) in a patient with ankylosing spondylitis, corresponding to enthesitis and corresponding adjacent bone marrow edema on (B) T1-­weighted and (C) fluid-­sensitive MR images (arrows), Note additional involvement of the right greater trochanter at the gluteal tendon entheses (arrowhead).

FURTHER READING Ball J. Enthesopathy of rheumatoid and ankylosing spondylitis. Ann Rheum Dis. 1971;30:213. Baraliakos X, Conaghan PG, D’Agostino M-A. Imaging in rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and osteoarthritis. Eur J Rheumatol. 2019;6:38. Bywaters EGL. Pathology of the spondyloarthropathies. In: Calin A, ed. Spondyloarthropathies. New York: Grune & Stratton; 1984. Chang EY, Chen KC, Huang BK, et al. Adult inflammatory arthritides: what the radiologist should know. Radiographics. 2016;36:1849. Cruickshank B. Pathology of ankylosing spondylitis. Clin Orthop. 1971;74:43. Ginsberg MH, Genant HK, Yu TF, et al. Rheumatoid nodulosis: An unusual variant of rheumatoid disease. Arthritis Rheum. 1975;18:49. Jaffe HL. Metabolic, Degenerative and Inflammatory Diseases of Bones and Joints. Philadelphia: Lea & Febiger; 1972:779. Kaye BR, Kaye RL, Bobrove A. Rheumatoid nodules: review of the spectrum of associated conditions and proposal of a new classification, with a report of four seronegative cases. Am J Med. 1984;76:279. Martel W. Pathogenesis of cervical discovertebral destruction in rheumatoid arthritis. Arthritis Rheum. 1977;20:1217. Martel W, Hayes JT, Duff IF. The pattern of bone erosion in the hand and wrist in rheumatoid arthritis. Radiology. 1965;84:204. Mathew AJ, Krabbe S, Kirubakaran R, et al. Utility of magnetic resonance imaging in diagnosis and monitoring enthesitis in patients with spondyloarthritis: An OMERACT systematic literature review. J Rheumatol. 2019;46:1207.

Rapoport AS, Sosman JL, Weissman BN. Lesions resembling gout in patients with rheumatoid arthritis. AJR Am J Roentgenol. 1976;126:41. Rauschning W. Popliteal cysts and their relation to the gastrocnemiosemimembranosus bursa: Studies on the surgical and functional anatomy. Acta Orthop Scand. 1979;179(suppl):9. Resnick D. Inflammatory disorders of the vertebral column: seronegative spondyloarthropathies, adult-­onset rheumatoid arthritis, and juvenile chronic arthritis. Clin Imaging. 1989;13:253. Resnick D. Cone R: Pathological fractures in rheumatoid arthritis: Sites and mechanisms. RadioGraphics. 1984;4:549. Resnick D, Niwayama G. On the nature and significance of bony proliferation in “rheumatoid variant” disorders. AJR Am J Roentgenol. 1977;129:275. Resnick D, Niwayama G, Coutts R. Subchondral cysts (geodes) in arthritic disorders: Pathologic and radiographic appearance of the hip joint. AJR Am J Roentgenol. 1977;128:799. Schils JP, Resnick D, Haghighi PN, et al. Pathogenesis of discovertebral and manubriosternal joint abnormalities in rheumatoid arthritis: A cadaveric study. J Rheumatol. 1989;16:291. Schneider R, Kaye JJ. Insufficiency and stress fractures of the long bones occurring in patients with rheumatoid arthritis. Radiology. 1975;116:595. Sugimoto H, Takeda A, Hyodoh K. Early stage rheumatoid arthritis: Prospective study of the effectiveness of MR imaging for diagnosis. Radiology. 2000;216:569. Wu PC, Fang D, Ho EKW, et al. The pathogenesis of extensive discovertebral destruction in ankylosing spondylitis. Clin Orthop. 1988;230:154.

8 Rheumatoid Arthritis S U M M A R Y O F K E Y F E AT U R E S • C  haracteristic distribution of rheumatoid arthritis is a symmetric disorder with predilection for the hands, wrists, knees, shoulders, and hips (see Fig. 8.1). • Axial skeletal involvement predominates in the cervical spine. • Radiographs show characteristic morphologic features of rheumatoid arthritis.

• U  ltrasonography and magnetic resonance imaging ideally show soft tissue abnormalities, such as synovial hypertrophy. • Sjögren syndrome consists of rheumatoid arthritis, keratoconjunctivitis sicca, and xerostomia.

INTRODUCTION

of the diagnosis of rheumatoid arthritis. To this point, the recent emphasis on other diagnostic imaging techniques such as magnetic resonance (MR) imaging and ultrasonography (US) as more sensitive indicators of synovitis (see later discussion) will likely influence the selection of future diagnostic criteria for rheumatoid arthritis.

  

Rheumatoid arthritis is a common articular disorder that is typically characterized by a symmetric polyarticular disease of the synovial joints of the appendicular skeleton, with prominent abnormalities of the proximal interphalangeal and metacarpophalangeal joints of the hand, the wrist, the metatarsophalangeal joints of the foot, the posterior and plantar aspects of the calcaneus, the knee, the elbow, and the glenohumeral and acromioclavicular joints, abnormalities that are commonly combined with changes in the cervical spine. The disorder is variable in its course, ranging from a rapidly progressive inflammatory process (leading to destruction of cartilage and bone) to a slowly evolving and progressive disease. Estimates suggest that about 1% of adults develop rheumatoid arthritis, with the highest frequency in women beyond the age of 65 years. Risk factors include but are not limited to genetic predisposition, smoking, and periodontal disease.

DIAGNOSTIC CRITERIA Diagnostic criteria for rheumatoid arthritis have been modified related to the introduction of disease-­modifying therapeutic agents. The current criteria, as before, emphasize the presence of synovitis; however, the diagnostic importance of bone erosions has been lessened through the belief that the disorder can be treated effectively before such erosions appear. In the proper target population (consisting of patients with synovitis in at least one joint that is not better explained by another disorder), a scoring system for the diagnosis of rheumatoid arthritis emphasizes such factors as a typical distribution of joint involvement, positive results for serologic markers (such as rheumatoid factor and anti-citrullinated protein antibody), and positive test results for acute-­phase reactants. These criteria no longer include the application of conventional radiography to the establishment

CLINICAL ABNORMALITIES Although rheumatoid arthritis can occur in persons of all ages, it predominates in those between the ages of 25 and 55 years. Women are affected more commonly than men, with the female-­to-­male ratio being approximately 2:1 to 3:1. Various prodromal symptoms have been noted in rheumatoid arthritis, including fatigue, anorexia, weight loss, malaise, and muscular pain and stiffness. These findings can be obscured by prominent articular complaints, which are frequently an early manifestation of the disease. Joint pain and stiffness may initially involve a single joint for a period of weeks or months before more generalized articular findings become evident. In these instances of monoarthritis, clinical diagnosis can be extremely difficult. With the appearance of polyarticular disease, the correct diagnosis becomes more apparent. Articular involvement manifests as pain that is aggravated by motion, swelling, and stiffness, and limitation of movement. The most typically affected joints are the proximal interphalangeal and metacarpophalangeal joints of the hand, the wrist, the metatarsophalangeal joints of the foot, the knee, the joints of the shoulder, the ankle, and, to a lesser extent, the hip; any joint can be involved, however (Fig. 8.1). Although symmetry is the hallmark of joint involvement, some exceptions exist, especially in the early stages of the disease and in patients with neurologic deficits (e.g., unilateral muscle weakening or paralysis may protect the ipsilateral side from the effects of articular disease).

TABLE 8.1  Types of Bony Erosion in the Hand and Wrist in Rheumatoid Arthritis Type

Mechanism

Common Sites

Marginal erosion

Pannus destruction of bare areas (without protective cartilage) of bone

Metacarpophalangeal and proximal interphalangeal joints, radial styloid, midportion of scaphoid, triquetrum, capitate, trapezium

Compressive erosion

Collapse of osteoporotic bone by muscular forces

Metacarpophalangeal joints

Surface resorption

Erosion of bone beneath inflamed tendons

Outer aspect of distal end of ulna, dorsal aspect of first metacarpal bone, proximal phalanx of first digit

151

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SECTION 2  Articular Disorders

Fig. 8.2  Metacarpophalangeal and proximal interphalangeal joints: target areas. In the four ulnar digits, early osseous erosions may appear at the radial and ulnar aspects of the metacarpophalangeal and proximal interphalangeal joints. The initial changes occur on the radial aspect of the phalanges and metacarpal heads at the second and third metacarpophalangeal joints, and on the radial and ulnar aspects of the phalanges at the third proximal interphalangeal articulation. Distal interphalangeal joint changes are less common and less severe.

disease. The last feature is evident in 50% to 70% of patients with Sjögren syndrome and may be identical to rheumatoid arthritis. Fig. 8.1  General distribution of disease in rheumatoid arthritis. Rheumatoid arthritis is characteristically a symmetric arthritis of the small joints of the hands (proximal interphalangeal and metacarpophalangeal joints), feet (metatarsophalangeal joints and interphalangeal joint of the great toe), wrists (all compartments), knees, ankles, elbows, glenohumeral and acromioclavicular joints, and hips (arrows). In the axial skeleton, the articulations of the cervical spine are typically affected (arrow). Less consistent involvement occurs in the thoracolumbar spine, sacroiliac and temporomandibular joints, symphysis pubis, and manubriosternal joint (arrowheads).

Subcutaneous nodules are evident in approximately one-­fourth of patients with rheumatoid arthritis. They appear at pressure points, especially the juxtaarticular regions of the elbow, although they may appear in distant body sites, including the lungs, pleurae, and abdominal wall. Subcutaneous nodules usually have an insidious onset and persist unchanged for months or years. Ulceration, drainage, and sepsis can occur in association with these lesions. Muscular weakness and atrophy may be prominent in patients with rheumatoid arthritis. These muscular abnormalities may be related to disuse or inflammatory changes. Inflammatory and noninflammatory vascular lesions also occur and can lead to complications, including peripheral neuropathy, bowel perforation, myocardial infarction, Raynaud phenomenon, gangrene, and pulmonary hypertension. Furthermore, several types of peripheral neuropathies occur in this disease. Felty syndrome consists of rheumatoid arthritis, splenomegaly, and leukopenia. Additional clinical manifestations include a typical onset in the fifth, sixth, or seventh decade of life, weight loss, anemia, lymphadenopathy, chronic leg ulceration, and abnormal skin pigmentation. Women are affected more frequently than men, and the disease is rare in Black persons. The articular manifestations of Felty syndrome are similar to those of severe rheumatoid arthritis. Sjögren syndrome is a triad consisting of keratoconjunctivitis sicca, xerostomia, and connective tissue

ABNORMALITIES AT SPECIFIC LOCATIONS Hand KEY CONCEPTS  • M  etacarpophalangeal and proximal interphalangeal joints are involved. • Earliest changes are seen in the second and third metacarpophalangeal joints and third proximal interphalangeal joint. • Distal interphalangeal joint changes are infrequent and mild. • A variety of finger, thumb, and wrist deformities are encountered.

The joints of the hand are affected in almost all persons with rheumatoid arthritis. Metacarpophalangeal and proximal interphalangeal joint alterations predominate. The second and third metacarpophalangeal joints and the third proximal interphalangeal joint may reveal the earliest abnormalities (Figs. 8.2, 8.3, and 8.4). Fusiform soft tissue swelling, periarticular osteoporosis, concentric loss of articular space, and marginal erosions become evident at many or all of the proximal interphalangeal and metacarpophalangeal joints. US (Fig. 8.5) and MR imaging ideally show synovial hypertrophy; activity of synovitis can be demonstrated with increased vascularity with color Doppler imaging and enhancement after intravenous gadolinium administration with MR imaging. Whereas US may show bone erosions, MR imaging is more sensitive and specific for such findings (Fig. 8.6). Marginal erosions about the distal interphalangeal joints are generally small in comparison to those at the more proximal digital joints. In addition to marginal erosions (Fig. 8.7), two other types of bone erosion have been noted in the hands of patients with rheumatoid arthritis: compressive (pressure) erosions and superficial surface resorption (Table 8.1). Although fibrous ankylosis is characteristically the ultimate fate of severe arthritis of the metacarpophalangeal and proximal interphalangeal joints, occasional examples of intraarticular osseous fusion can be seen in these locations. In almost all such instances, the proximal

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CHAPTER 8  Rheumatoid Arthritis

A

C

B

Fig. 8.3  Metacarpophalangeal joint abnormalities: early changes. (A) Initially, the bones appear normal, with preservation of the subchondral bone plate on the radial aspect of the metacarpal head. (B) Subsequently, small radiolucent areas appear beneath the metacarpal head and are related to thinning of the bone plate with focal discontinuity or gaps (arrowheads). Tiny erosions and surface irregularity of the proximal phalanx are also evident (arrow). (C) At a later stage, obvious osseous defects are seen (arrowheads). Note the mild periosteal proliferation (arrow).

PP MC

A

B

Fig. 8.4  Proximal interphalangeal joint abnormalities: early changes. Initial radiographic changes include soft tissue swelling, joint space narrowing, and marginal erosions (arrowheads). Note that the erosive changes are more extensive on the proximal phalanx than on the middle phalanx.

Fig. 8.5  Metacarpophalangeal joint synovial hypertrophy: US. US dorsal to the metacarpophalangeal joint shows hypoechoic synovial hypertrophy (arrows, A) with hyperemia on color Doppler imaging (B). MC, Metacarpal head; PP, proximal phalanx.

154

SECTION 2  Articular Disorders

Wrist KEY CONCEPTS  • E arly involvement of the distal ulna is characteristic. • Pancompartmental changes in the wrist are seen at an early stage. • Multiple deformities of the wrist accompany long standing rheumatoid arthritis.

A

B Fig. 8.6  Metacarpal head erosions. Axial T1-­weighted (A) and fluid-­ sensitive (B) MR images show bone erosion (arrowhead) and synovial hypertrophy (arrows), with marrow edema of the third metacarpal head.

interphalangeal joint is ankylosed; bony ankylosis of the metacarpophalangeal articulation is exceedingly unusual, with the exception of that in the thumb. Deviation and deformity of the fingers and thumb are common complications of rheumatoid arthritis. Loosening or disruption of the distal attachment of the extensor tendon to the terminal phalanx may result in the development of a typical mallet, or drop, finger. Flexion of the proximal interphalangeal joint combined with hyperextension at the distal interphalangeal joint produces a boutonnière deformity of the digit. Swan-­neck deformity consists of hyperextension of the proximal interphalangeal joint and flexion of the distal interphalangeal joint. A variety of metacarpophalangeal articular deformities and deviations (Fig. 8.8) may appear in rheumatoid hands, including ulnar drift, extensor tendon subluxation, and palmar subluxation and flexion of the joint. Ulnar deviation at the metacarpophalangeal joints has been recorded in 25% to 65% of hands in patients with rheumatoid arthritis, and palmar subluxation has been noted in 20% to 68%. A relationship between radial deviation of the wrist and ulnar deviation at the metacarpophalangeal joints has been noted to produce the zigzag deformity of the hand in rheumatoid arthritis. The thumb malalignments are collapse deformities (boutonnière deformity) related to disturbance of function at the first metacarpophalangeal joint; swan-­neck deformity, related to disturbance of function at the first carpometacarpal joint; and boutonnière deformity (Z-­shaped deformity, or hitchhiker’s thumb).

Clinical findings may be related to synovitis in any of the compartments of the wrist, adjacent tenosynovitis, and attenuation or injury of soft tissue, tendinous, and ligamentous structures. Extensor carpi ulnaris tenosynovitis creates a painless swelling on the ulnar aspect of the wrist. Subsequent clinical features in rheumatoid arthritis relate to dorsal subluxation of the distal portion of the ulna; carpal tunnel syndrome, attributable to synovitis in the carpal tunnel, with dysesthesias along the course of the median nerve; and rupture of one or more extensor tendons. Erosion and swelling around the distal end of the ulna and the ulnar styloid process are early manifestations of rheumatoid arthritis (Figs. 8.9 and 8.10), and are related to abnormalities of the prestyloid recess of the radiocarpal compartment, the inferior radioulnar compartment, and the extensor carpi ulnaris tendon and sheath (Fig. 8.11). Synovial inflammation is well demonstrated with US and MR imaging (Fig. 8.12), and when located within the radiocarpal compartment, leads to rheumatoid erosion of the distal end of the radius (i.e., radial styloid process) and the adjacent scaphoid bone. Erosion of the triquetrum and pisiform bones is also common in early rheumatoid arthritis. Soon, all of the compartments of the wrist are involved. This pancompartmental distribution is characteristic of rheumatoid arthritis (Fig. 8.13) and allows differentiation from the selective compartmental changes encountered in a variety of other disorders that affect the wrist. In some cases, intraarticular involvement throughout the wrist in rheumatoid arthritis can lead to massive bone fusion of all of the carpal bones (Fig 8.14). Rheumatoid nodules also may be present (Fig. 8.15). Incongruity in cartilaginous and osseous surfaces, laxity of the articular capsule and ligaments, and muscular and tendinous imbalance can cause malalignment of the wrist in rheumatoid arthritis. The proximal row of carpal bones migrates in a medial (ulnar) and palmar direction along the inclined articular surface of the distal end of the radius. Imbalance of the muscles and tendons contributes to radial deviation at the wrist, and imbalance of the tendons also may be associated with ulnar deviation at the metacarpophalangeal joints, producing a zigzag deformity of the hand. Both palmar flexion instability (palmar, or volar, intercalated segment instability) and dorsiflexion instability (dorsal intercalated segment instability) occur in the wrist in rheumatoid arthritis, although the latter is more frequent. Rheumatoid arthritis deformities on the ulnar aspect of the wrist include distal and dorsal subluxation of the ulna and diastasis of the inferior radioulnar compartment. The caput ulnae syndrome consists of pain, limited motion, and dorsal prominence of the distal end of the ulna. The abnormally located, eroded head of the ulna projects into the compartments of the extensor tendons on the dorsum of the wrist and produces fraying of the tendon surfaces and, possibly, tendon rupture.

Elbow The elbow is frequently involved in rheumatoid arthritis; this is commonly bilateral but may be more marked in the dominant extremity, and it is usually associated with polyarthritis. Clinical symptoms and signs are variable but can lead to considerable

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CHAPTER 8  Rheumatoid Arthritis

PP

MC

A

C

B

Fig. 8.7  Metacarpophalangeal joint synovial hypertrophy and bone erosion. US (A–B) of the metacar­ pophalangeal joint shows hypoechoic synovial hypertrophy (arrows) with hyperemia on color Doppler imaging and marginal bone erosion (arrowhead), with the latter identified on (C) radiography. MC, Metacarpal head; PP, proximal phalanx. B

A

U

A

C

A. Erosions related to inferior radioulnar compartment B. Erosions related to prestyloid recess C. Erosions related to extensor carpi ulnaris tendon sheath

B

Fig. 8.9  Abnormalities of the distal end and styloid process of the ulna: sites of early soft tissue swelling and osseous erosion. (A) Soft tissue swelling about the distal end of the ulna (U) may appear as distention of the prestyloid recess of the radiocarpal compartment (arrowhead), the inferior radioulnar compartment (solid arrow), or the extensor carpi ulnaris tendon sheath (open arrow). (B) Early osseous erosions appear at three distinct areas in the distal portion of the ulna.

Fig. 8.8  Metacarpophalangeal joint deformities. Ulnar deviation and dislocation at the metacarpophalangeal joints (arrows) are shown with chronic inflammatory changes at the wrist (open arrows). There is associated radial deviation of the radiocarpal joint that, in combination with the ulnar deviation of the metacarpophalangeal joints, produces the classic zigzag deformity.

156

SECTION 2  Articular Disorders disability as a result of limitation of both flexion and extension of the joint. Additional clinical manifestations include antecubital soft tissue masses related to synovial cysts with compression of adjacent nerves, rheumatoid nodules, and olecranon bursitis, which is seen not only in rheumatoid arthritis but also in gout and in association with trauma or infection. Synovial inflammation in the elbow with progressive destruction of cartilage and bone produces soft tissue swelling with a positive fat pad sign, periarticular osteoporosis, joint space narrowing, and bone erosions (Fig. 8.16). US and MR imaging (see Fig. 8.16) show synovitis and bone erosions, as well as other soft tissue abnormalities such as olecranon bursitis (Fig. 8.17). More severe changes are characterized by extensive osteolysis of large portions of the humerus, radius, and ulna. Prominent cystic lesions of the olecranon may occur (Fig. 8.18) and can lead to fracture spontaneously or after minor trauma.

Glenohumeral Joint

Fig. 8.10  Tenosynovitis of the extensor carpi ulnaris. Note soft tissue swelling along the ulnar aspect of the wrist related to inflammation of the tendon sheath of the extensor carpi ulnaris, with surface resorption of the subjacent styloid process of the ulna (arrow), associated with extensive bone erosions of the metacarpal heads (arrowheads) in this patient with rheumatoid arthritis.

Clinical symptoms of disability related to glenohumeral joint involvement in rheumatoid arthritis are not infrequent. Pain, tenderness, and restricted motion may be evident. Associated subacromial-­subdeltoid bursitis may result in prominent soft tissue swelling. Acute tearing of

t

A

B

C

ECU

U

D

U

E

F

Fig. 8.11  Tenosynovitis of the extensor carpi ulnaris. T1-­weighted (A), fluid-­sensitive (B), and T1-weighted fat-suppressed contrast-­enhanced (C) axial MR images show enhancing synovitis (arrow) surrounding the extensor carpi ulnaris tendon (t). US long axis (D) and short axis (E) show hypoechoic tenosynovitis with flow on color Doppler imaging, and a bone erosion (arrowhead). Radiograph (F) shows soft tissue swelling. ECU, Extensor carpi ulnaris; U, ulna.

CHAPTER 8  Rheumatoid Arthritis

157

B

A

C

R L

C

D

E

Fig. 8.12  Synovial hypertrophy: MR imaging and US. T1-­weighted (A), and fluid-­sensitive (B) coronal MR images show predominant midcarpal joint synovitis and marrow edema, with less involvement of other wrist compartments (arrows). US (C and D) shows hypoechoic synovial hypertrophy (arrows) with flow on color Doppler imaging and an erosion (arrowhead). Radiograph (E) shows osteopenia and midcarpal joint space narrowing. C, Capitate; L, lunate; R, radius.

Fig. 8.13  Pancompartmental abnormalities of the wrist in rheumatoid arthritis. Radiograph demonstrates typical pancompartmental involvement of the wrist with osseous fusion of multiple carpal and metacarpal bones (arrows), ulnocarpal abutment, and extensive involvement of the thumb metacarpophalangeal joint in this patient with rheumatoid arthritis.

Fig. 8.14  Pancompartmental abnormalities of the wrist in rheumatoid arthritis. Radiograph shows osseous fusion between the radius and lunate (arrow), associated with pancompartmental joint space narrowing, ulnocarpal abutment, and additional involvement of multiple metacarpophalangeal joints, worst in the index finger (arrowhead), at the second metacarpophalangeal joint. Uniform joint space narrowing is also noted at the other metacarpophalangeal joints and midcarpal joint.

158

SECTION 2  Articular Disorders A deep bone erosion may develop on the medial aspect of the surgical neck of the humerus as a result of the abnormal pressure exerted by the adjacent glenoid margin, and this erosion may eventually lead to a pathologic fracture of the humeral neck. Rotator cuff muscle atrophy or tendon tear is common in long standing rheumatoid arthritis and is caused by the damaging effect of the inflamed synovial tissue on the undersurface of the tendons adjacent to the greater tuberosity, resulting in a high-­riding humeral head. Both US and MR imaging can show synovial hypertrophy and bone erosions, as well as associated subacromial-­subdeltoid bursitis.

Acromioclavicular and Coracoclavicular Joints A

Pain, tenderness to direct palpation, and local soft tissue swelling can indicate rheumatoid involvement of the acromioclavicular joint. Soft tissue swelling superior to the joint and subchondral osteoporosis and erosions predominating on the clavicle, especially its inferior margin, are early findings. Subsequently, larger erosive changes are detected and may progress to extensive osteolysis of the outer third of the clavicle (see Fig. 8.19A). An elongated, shallow erosion can be seen along the undersurface of the distal end of the clavicle in rheumatoid arthritis. US and MR imaging can be used to further analyze these abnormalities, although the findings often lack specificity.

Forefoot KEY CONCEPTS 

B

C Fig. 8.15  Rheumatoid nodule. Fluid-sensitive (A) and T1-weighted fat-suppressed contrast-enhanced (B) axial MR images show a rheumatoid nodule (arrow), appearing hypoechoic at US (C) (cursors). Note enhancing tenosynovitis in B.

the tendons of the rotator cuff in rheumatoid arthritis may produce clinical findings simulating infection. Progressive destruction of the chondral surface of the glenoid cavity and humeral head leads to diffuse loss of joint space, which may be accompanied by marginal bone erosions and subchondral cystic lesions (Fig. 8.19). Particularly characteristic are superficial irregularities, deep erosive changes, and cystic changes on the superolateral aspect of the humeral head adjacent to the greater tuberosity. This last abnormality resembles a Hill-­Sachs compression fracture occurring after an anterior glenohumeral joint dislocation and the marginal erosions of other synovial processes, such as ankylosing spondylitis.

• Changes predominate at the metatarsophalangeal joints, and these changes may be the initial radiographic manifestations of the disease. • An early site of involvement is the fifth metatarsal head. • Abnormalities in the second through fifth interphalangeal joints are rare. • Fibular deviation of the toes (with the exception of the fifth toe) at the metatarsophalangeal joints is characteristic in chronic disease.

Clinical abnormalities of the forefoot are especially common in rheumatoid arthritis (80% to 90% of patients) and may be the initial manifestation of the disease (10% to 20% of patients). The metatarsophalangeal joints of the lateral digits are affected most frequently. Intermittent or constant pain, tenderness, and soft tissue swelling can be prominent findings. Characteristic deformities include spreading of the metatarsal bones, hallux valgus, lateral deviation of the toes at the metatarsophalangeal joints, hammer toe, and cock toe. Additional findings in rheumatoid arthritis include insufficiency (stress) fractures, peripheral neuropathy, tendon injury and rupture, widespread edema, rheumatoid nodules, and hallux rigidus. Radiologic abnormalities of the forefoot are also frequent and are commonly the initial manifestation of the disease. The earliest alterations appear at the metatarsophalangeal joints (Figs. 8.20 and 8.21), particularly the fifth metatarsal head (Fig. 8.22). Changes predominate on the medial aspect of the metatarsal head, with the exception of the fifth digit, where soft tissue swelling and subjacent osseous erosion on the lateral aspect of the bone can be very early and important findings (see Fig. 8.22C). Early radiographic alterations at the metatarsophalangeal joints consist of soft tissue swelling, periarticular osteoporosis, concentric joint space narrowing, and marginal and central osseous defects. Both US (Fig. 8.23) and MR imaging can show synovial hypertrophy, erosions, and other soft tissue abnormalities such as bursitis and tenosynovitis. Adventitious bursae are not uncommon in the forefoot, plantar to the metatarsal heads (Fig. 8.24). Later abnormalities include fibular deviation of the toes (with the exception of

159

CHAPTER 8  Rheumatoid Arthritis

f f

f

U

H

A

C

B

H

R

D

E

H U

H

F

G

Fig. 8.16  Rheumatoid arthritis: synovial hypertrophy and bone erosions. Anteroposterior (A) and lateral (B) radiographs show distention of the anterior and posterior joint recesses (arrows) superiorly displacing the intraarticular fat pads (f), with bone erosions (arrowheads). US of the posterior joint recess (C) and over the radial head (D) shows hypoechoic synovial hypertrophy (arrows), with bone erosions (arrowheads) and hyperemia on color Doppler imaging (C and E). T1-­weighted (F), fluid-­sensitive (G), and T1-weighted fat-suppressed contrast-enhanced (H) axial MR images show enhancing synovial hypertrophy (arrow) and bone erosions (arrowhead). H, Humerus; R, radius; U, ulna.

the fifth digit), and dorsiflexion and lateral subluxation or dislocation of the proximal phalanges at the metatarsophalangeal articulations (Fig. 8.25).

Midfoot Pes planovalgus deformity is common in rheumatoid arthritis and may relate to rupture of the tibialis posterior tendon. Radiographic abnormalities in the midfoot are also common, with a predilection for the talocalcaneonavicular joint.

Heel Clinical lesions of the heel encountered in rheumatoid arthritis and the spondyloarthropathies are retrocalcaneal bursitis, Achilles tendinosis, paratendinitis and paratenonitis, and plantar fasciopathy. Retrocalcaneal bursitis can produce a soft tissue mass on the posterosuperior aspect of the calcaneus that obliterates the normal radiolucent region extending between the top of the bone and the Achilles tendon, with the mass projecting into the inferior portion of the pre-­Achilles fat pad (Fig. 8.26). Subjacent well- or poorly defined erosion of the calcaneus

160

SECTION 2  Articular Disorders on both its posterior and superior aspects is characteristic. Achilles tendinosis leads to enlargement and blurring of the tendon. Well-­defined calcaneal excrescences and small bone erosions are also observed on the plantar aspect of the bone in patients with rheumatoid arthritis. Poorly marginated plantar outgrowths with adjacent bone sclerosis, as seen in the spondyloarthropathies, are rare in rheumatoid arthritis. US (Fig. 8.27) and MR imaging can show the soft tissue abnormalities about the heel in rheumatoid arthritis, including tendon abnormalities and bursitis.

T

Knee

U

The knee is frequently affected in rheumatoid arthritis, often at an early stage of the disease. Pain and swelling appear. Characteristically, diffuse abnormalities occur in both the medial and the lateral femorotibial compartments and may be combined with similar changes in the patellofemoral compartment. This bicompartmental or tricompartmental distribution is an important clue to the correct diagnosis. Diffuse and uniform joint space narrowing between the femur and tibia is characteristic (Fig. 8.28). Osteophytes are lacking unless there is secondary osteoarthrosis, although uniform joint space narrowing predominates. Bone erosions on the medial and lateral margins of the tibia (Fig. 8.29), and subchondral erosions and cysts are additional radiographic findings. Occasionally, the lateral femorotibial compartment is involved more severely than the medial one and may lead to a valgus deformity of the knee. An enlarging joint effusion and synovitis may be accompanied by synovial cysts, especially in the popliteal region, ideally characterized by US and MR imaging.

Fig. 8.17  Rheumatoid arthritis: olecranon bursitis. US in the sagittal plane over the olecranon of the ulna (U) shows hyperechoic distention of the olecranon bursa (arrow) with hyperemia. T, Triceps brachii.

Hip Clinical abnormalities of the hip are far less frequent than those of the knee and increase with the duration and severity of rheumatoid

H

A

B

Fig. 8.18  Rheumatoid arthritis: ulnar cyst. Reformatted sagittal CT images at the levels of the trochlea and trochlear notch (A) and the capitellum and radial head (B) show joint recess distention from synovial hypertrophy (arrows), large intraosseous cysts in the ulna (open arrow), and bone erosions (arrowhead).

CHAPTER 8  Rheumatoid Arthritis

A

161

B

C

D

Fig. 8.19  Rheumatoid arthritis: shoulder. Radiograph (A), coronal reformatted CT image (B), and T1-­ weighted (C) and fluid-­sensitive (D) coronal MR images show uniform glenohumeral joint space narrowing, with bone erosions (arrowhead) and acromioclavicular joint space widening (open arrow). Note chronic tearing of the supraspinatus tendon (arrow).

arthritis. Pain, tenderness, shortening of the limb, gait abnormalities, and decreased range of motion, particularly internal rotation, extension, and abduction, are observed. Radiographic abnormalities of the hip are generally bilateral and symmetric. The most typical early abnormality is concentric loss of joint space. The femoral head moves centrally along the axis of the femoral neck (axial migration). Joint effusion, synovial hypertrophy, and erosions characteristic of inflammatory arthritis are demonstrated on MR imaging (Fig. 8.30). Eventually, the joint space may be completely obliterated, and the femoral head and acetabulum protrude into the pelvis (Fig. 8.31). Bilateral acetabular protrusion and coxa profunda are particularly characteristic of rheumatoid arthritis. Both US and MR imaging can show a joint effusion, synovial hypertrophy, and bursitis when present.

Osteonecrosis of the femoral head is not uncommon and generally occurs in patients with rheumatoid arthritis who are being treated with corticosteroids. The radiographic appearance of osteonecrosis of the femoral head with osseous collapse, cyst formation, and sclerosis without joint space loss is identical to that of osteonecrosis occurring in patients without rheumatoid disease. MR imaging features include a demarcation line about the periphery of the necrotic bone with an inner portion that is of high signal on fluid-sensitive images and an outer portion of persistent low signal (the double line sign), variable internal marrow signal, and possible subchondral collapse (see Chapter 40).

Sacroiliac Joint As opposed to the frequent and severe clinical and imaging abnormalities that characterize sacroiliac joint disease in ankylosing

162

SECTION 2  Articular Disorders

Cervical Spine KEY CONCEPTS  • C hanges predominate in the upper portion of the cervical spine, especially at the atlantoaxial junction. • Atlantoaxial joint subluxation can have a horizontal or vertical pattern. • Additional characteristic findings include discovertebral erosion, loss of intervertebral disc space, odontoid process erosion, subaxial vertebral subluxations, and spinous process erosion.

Cervical spine involvement is common in rheumatoid arthritis and can lead to severe pain and disability, as well as a variety of neurologic manifestations, although some patients with significant radiographic evidence of disease may be entirely asymptomatic. Symptoms and signs related to cervical spine abnormalities develop in approximately 60% to 80% of rheumatoid arthritis patients at some time during their illness. These clinical findings include pain, weakness, abnormal mobility, and neurologic manifestations (e.g., paresthesias, paresis, muscle wasting, and quadriplegia).

Specific Sites of Cervical Spine Involvement

B Fig. 8.20  Abnormalities of the forefoot: target areas. In addition to characteristic involvement of the medial and lateral aspects of the fifth metatarsal, osseous erosions of rheumatoid arthritis initially appear on the medial aspect of the first to fourth metatarsal bones and the medial aspect of the distal portion of the proximal phalanx of the great toe.

Fig. 8.21  Forefoot involvement. Radiograph shows erosions of all of the metatarsal heads (arrows), particularly the medial aspects. Note the prominent changes at the interphalangeal joint of the great toe (arrowheads) and the relative absence of findings in other interphalangeal articulations.

spondylitis, changes in this location are relatively infrequent and mild in rheumatoid arthritis. When such changes are present, they lack the bilateral symmetry that is frequent in ankylosing spondylitis. Joint space narrowing is often mild. Osseous erosions have a predilection for the iliac aspect of the joint; they are superficial and well marginated. Far more important than sacroiliac joint involvement in rheumatoid arthritis is the occurrence of insufficiency fractures about the osseous pelvis, especially in the sacrum and ilium near the sacroiliac joint, parasymphyseal and para acetabular regions, and pubic rami.

The entire cervical spine is affected by the rheumatoid process; changes may be evident as far cephalad as the base of the occiput and as far caudad as the C7–T1 junction (Box 8.1). Further, synovial and cartilaginous articulations, the joints of Luschka, tendinous and ligamentous attachments, and soft tissues of the cervical region can exhibit significant abnormalities in this disease. In patients who can undergo complete conventional radiographic evaluation, the frequency of radiographic changes of the cervical spine is consistently high and may reach 85%. Radiographic abnormalities in the cervical spine have been reported to correlate with those in the peripheral joints and with the presence of serum rheumatoid factor and subcutaneous nodules. Such abnormalities dominate in the upper cervical region. Careful radiographic technique is important; in an apparently normal cervical spine, considerable subluxation at the C1–C2 junction can be revealed with the addition of a lateral view of the flexed neck. Occipitoatlantoaxial articulations. Various types of malalignment in the atlantoaxial region have been described in rheumatoid arthritis (Fig. 8.32). The major types include anterior atlantoaxial subluxation, vertical subluxation (also known as cranial settling and atlantoaxial impaction), lateral subluxation, and posterior subluxation. Subluxations of all types have been noted in 40% to 85% of patients with rheumatoid arthritis. Abnormal separation between the anterior arch of the atlas and the odontoid process (dens) of the axis, designated anterior atlantoaxial subluxation, is a characteristic finding in rheumatoid arthritis that may be evident at an early stage of the disease when other cervical spine abnormalities, including odontoid erosion, are not apparent. Generally, the interosseous distance between the posterior aspect of the anterior arch of the atlas and the anterior aspect of the odontoid process does not exceed 2.5 mm in adults. Measurement of the inferior aspect of this articulation is used most often. Anterior atlantoaxial subluxation occurs in 20% to 25% of patients with rheumatoid arthritis (Fig. 8.33). The pathogenesis of anterior atlantoaxial subluxation relates to the presence of transverse ligament laxity caused by synovial inflammation and hyperemia of the adjacent articulations. Vertical subluxation, or cranial settling, at C1–C2 also can be observed in patients with rheumatoid arthritis and, when extensive, can be fatal. This complication has been associated with neurologic symptoms and signs related to entrapment of the first and second

CHAPTER 8  Rheumatoid Arthritis

A

163

C

B

Fig. 8.22  Fifth metatarsophalangeal joint involvement. Radiographs from three separate patients (A–C) show erosions of the lateral aspect of the fifth metatarsal head (arrow). Note additional soft tissue swelling (open arrow) and fourth metatarsal head erosions (arrowhead) in (C).

M

P

Fig. 8.23  Fifth metatarsophalangeal joint involvement. US of the fifth metatarsophalangeal joint shows an erosion (arrows) of the metatarsal head (M). (P), Proximal phalanx.

cervical nerve roots, impairment of cranial nerves, bulbomedullary compression, occlusion of the branches of the spinal and vertebral arteries, and hydrocephalus. Atlantoaxial impaction is diagnosed by applying one or more radiographic measurements that assess the relationship of the tip of the odontoid process to landmarks at the base of the skull. In general, vertical subluxation is a later manifestation than anterior atlantoaxial subluxation. With descent of the anterior process of the atlas with respect to the odontoid process during cranial settling, the degree of anterior atlantoaxial subluxation diminishes, and even the pannus in the area may decrease. When severe, cranial settling is easily diagnosed on radiographs obtained in a lateral projection or with computed tomography (CT) scanning or MR imaging. Cranial settling has been observed in 5% to 22% of patients with rheumatoid arthritis. In general, vertical translocation of the dens results from disruption and collapse of the osseous and articular structures that exist between the occiput and the atlas and between the atlas and the axis. Lateral subluxation of the atlantoaxial joints also has been observed in patients with rheumatoid arthritis. In these patients, asymmetry is recorded between the odontoid process (and body of the axis) and the

atlas. This complication is diagnosed when the lateral masses of the atlas are displaced more than 2 mm with respect to those of the axis, and it is observed in 10% to 20% of patients with rheumatoid arthritis. The sequence of events that leads to lateral subluxation of the atlantoaxial joints includes articular space narrowing, bone erosion, disruption of the articular capsules, and, in severe cases, collapse of the lateral masses of the axis. Odontoid process erosions have been detected in 14% to 35% of patients with rheumatoid arthritis, related to synovial inflammation in adjacent articulations (Fig. 8.34). Thus bone erosions predominate in the portions of the odontoid process that are intimate with the synovium-­lined spaces between the anterior arch of C1 and the anterior aspect of the odontoid process and between the posterior surface of the odontoid process and the transverse ligament. Defects of the odontoid tip at sites of ligamentous attachment and defects of the base of the odontoid process related to the nearby lateral atlantoaxial joints can also be seen. Further erosion of the odontoid process, which is usually associated with atlantoaxial subluxation, can lead to considerable osteolysis. Subaxial articulations. Subluxation and dislocation are observed at one or more subaxial levels in patients with rheumatoid arthritis. These abnormalities have been noted in 9% of patients with chronic and severe articular disorders. When localized to one area, changes are particularly characteristic at the C3–C4 and C4–C5 levels; however, multilevel subluxations are more typical and produce a doorstep or stepladder appearance on lateral radiographs. Anterior subluxation is far more frequent than posterior subluxation. Apophyseal joint abnormalities in the subaxial region, including joint space narrowing and superficial erosions, are common. During flexion of the neck, instability produces tilting of the lateral masses of one vertebra on the next, with abnormal widening of the articular spaces. Generally, fibrous ankylosis is the terminal event; however, bony ankylosis of one or more articulations may be seen.

164

SECTION 2  Articular Disorders

A

Fig. 8.25  Forefoot deformities. Fibular deviation and subluxation of the phalanges typically occur at the first to fourth digits. The relatively mild nature of the osseous erosions in comparison to the degree of deformity evident in this patient is somewhat unusual.

B

Diffuse locations. Diffuse involvement of the entire cervical spine is common, particularly in long standing rheumatoid arthritis (see Box 8.1). The resulting radiographic picture, which consists of atlantoaxial subluxation, odontoid and apophyseal joint erosions, subaxial subluxation, intervertebral disc space narrowing, marginal sclerosis of vertebrae, and spinous process destruction, is virtually pathognomonic of this disease.

Thoracic and Lumbar Spine When compared with the distinctive alterations of the cervical spine, which represent a common and well-­known manifestation of rheumatoid arthritis, abnormalities of the thoracic and lumbar spine, including those in the apophyseal joints and discovertebral junctions, are relatively uncommon. Patients with rheumatoid arthritis who are receiving corticosteroid medication are predisposed to ischemic necrosis of bone. Although the femoral head is the typical site of this complication, vertebral bodies in the thoracic and lumbar segments of the spine can be affected, leading to vertebral collapse and the accumulation of intraosseous gas (vacuum vertebral body).

C Fig. 8.24  Adventitious bursitis. US (A) and fluid-­sensitive (B) and T1-weighted fat-suppressed contrast-­enhanced (C) sagittal MR images show adventitious bursitis (arrows). Note a needle (arrowheads) in (A) used for aspiration.

Discovertebral joint abnormalities observed in the cervical spine in rheumatoid arthritis include intervertebral disc space narrowing, subchondral osseous irregularity, and adjacent bone eburnation. Multiple levels of the cervical spine are typically affected. A characteristic manifestation of rheumatoid discitis is the absence of osteophytosis, which distinguishes the cervical spinal abnormalities of rheumatoid arthritis from those of degenerative disc disease. Spinous process erosions and destruction of one or more spinous processes may be detected, particularly in the lower cervical (and upper thoracic) region. Tapered and sharpened spinous elements may be related to inflammation of the adjacent supraspinous ligaments or neighboring bursae.

COEXISTENT OSSEOUS AND ARTICULAR DISEASE Septic Arthritis Infections are frequent in patients with rheumatoid arthritis, especially after the introduction of steroids and immunosuppressive agents. Pulmonary infections, skin infections, osteomyelitis, and septic arthritis have all been noted. The reported frequency of suppurative arthritis in patients with rheumatoid disease varies from less than 1% to 12% or higher. Indeed, rheumatoid arthritis appears to be the most common predisposing factor to septic arthritis, especially polyarticular infection. Pyarthrosis is more frequent in elderly rheumatoid arthritis patients with severe disability. The most frequently reported infecting organism is Staphylococcus aureus. Septic arthritis complicating rheumatoid disease often affects multiple joints. The onset of pyarthrosis in a person with rheumatoid arthritis may produce only subtle clinical changes; a source of infection, onset of chills, or any deterioration in the clinical state should arouse suspicion of a superimposed articular infection. The

CHAPTER 8  Rheumatoid Arthritis

A

B

Fig. 8.26  Abnormalities of the calcaneus: posterosuperior and inferior aspects. (A) Soft tissue radiograph defines a thickened Achilles tendon and a fluid-­filled retrocalcaneal bursa (open arrows) that projects into the pre-­Achilles fat pad. Focal osteoporosis of the neighboring calcaneus is evident. (B) Observe the erosion of the posterosuperior aspect of the calcaneus (arrowhead) and a well-­defined plantar calcaneal enthesophyte (arrow). (A, Courtesy J. Weston, MD, Lower Hutt, New Zealand.)

Ach

C

Fig. 8.27  Heel abnormalities: US. US long axis to the distal Achilles tendon (Ach) shows distention of the retrocalcaneal bursa (arrows) and a calcaneal (C) erosion (arrowhead), with adjacent hyperemia.

165

166

SECTION 2  Articular Disorders

Fig. 8.28  Knee abnormalities. Radiographs show uniform joint space narrowing of all knee compartments (arrows) with periarticular osteopenia and no significant osteophyte formation.

Fig. 8.29  Knee abnormalities. Radiograph shows a marginal erosion (arrow) of the medial aspect of the tibia.

A

B

C

Fig. 8.30  Hip abnormalities. (A) Radiograph and coronal (B) T1-weighted ­ and (C) fluid-sensitive ­ MR images show uniform joint space narrowing, erosions, bone marrow edema, joint effusions, and synovial hypertrophy (arrows) in both hips.

CHAPTER 8  Rheumatoid Arthritis

167

2

3 1 3 4

Fig. 8.31  Hip abnormalities. Radiograph shows uniform joint space narrowing with axial migration of each femoral head (arrows). Note acetabular protrusion on the left and, to a lesser extent, on the right.

BOX 8.1  Cervical Spine Abnormalities in

Rheumatoid Arthritis

Occipitoatlantoaxial Articulations Atlantoaxial subluxation Odontoid erosion and fracture Apophyseal joint erosion, sclerosis, and fusion Subaxial Articulations Subaxial subluxation Apophyseal joint erosion, sclerosis, and fusion Intervertebral disc space narrowing Erosion and sclerosis of vertebral body margins Spinous process erosion Osteoporosis

importance of early diagnosis is underscored by the fact that infection is the most common cause of death in patients with rheumatoid arthritis. Radiographic evidence of any rapid deterioration of a joint should be suspected. Asymmetric joint disease and poorly defined and rapid destruction of bone are other useful signs of infection in a patient with rheumatoid arthritis (Box 8.2).

Crystal Deposition Diseases The coexistence of rheumatoid arthritis and gout is not common, although it is being reported with increasing frequency. Typically, men are affected. Gout is the initial disease, and rheumatoid arthritis develops years later. The coexistence of rheumatoid arthritis and calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is also encountered occasionally. It appears likely, however, that the coexistence of true rheumatoid arthritis and CPPD crystal deposition disease is merely a chance occurrence.

Collagen Vascular Disorders Rheumatoid arthritis can be combined with several collagen vascular disorders in various overlap syndromes and in mixed connective tissue disease. In some of these disorders, specific laboratory parameters allow an accurate diagnosis. In others, the exact nature of the disease is more perplexing, and diagnosis is complicated by the occurrence of

Fig. 8.32  Abnormalities of the cervical spine: directions of atlantoaxial subluxation. Varying types of subluxation may occur at the atlantoaxial articulations in patients with rheumatoid arthritis. Most typically, anterior movement of the atlas with respect to the axis (1) is seen. Vertical translocation of the odontoid process, or cranial settling (2), can also occur. Lateral subluxation (3) can be recorded on frontal radiographs as asymmetry becomes apparent between the odontoid process and the lateral masses of the atlas. In addition, the anterior arch of the atlas can move inferiorly (4) with respect to the odontoid process, a finding associated with cranial settling. Finally, in the presence of severe erosion of the odontoid process, the anterior arch can move posteriorly against the eroded bone or, rarely, behind the eroded odontoid process.

rheumatoid arthritis–like clinical and radiographic features in patients with pure collagen vascular disorders.

IMAGING ASSESSMENT OF DISEASE DIAGNOSIS, EXTENT, AND PROGRESSION The initial diagnosis of rheumatoid arthritis is often based on clinical findings that allow effective treatment before structural damage of joints becomes evident. Such treatment at an early stage of the disease is critical because reduction of joint inflammation is known to limit damage to cartilage and subchondral bone. Although conventional radiography has long been considered to be the gold standard in monitoring the effects of articular inflammation in rheumatoid arthritis, its sensitivity to the early structural alterations of the disease is low and, further, conventional radiography does not allow assessment of disease activity. These limitations have led to a great deal of interest in more sensitive diagnostic imaging methods such as US and MR imaging. The European League Against Rheumatism (EULAR) has outlined specific recommendations related to the use of imaging techniques in the clinical management of rheumatoid arthritis, some of which are repeated here: 1. When there is diagnostic doubt, conventional radiography, US, or MR imaging can be used to improve the diagnostic certainty above clinical criteria alone. 2. US and MR imaging are superior to the clinical examination in the detection of joint inflammation. 3. Conventional radiography of the hands and feet should be used as the initial imaging technique to detect damage; however, US and/ or MR imaging should be considered if conventional radiography does not show damage and may be used to detect joint damage at an earlier time point.

168

SECTION 2  Articular Disorders

A

B

C

D

Fig. 8.33  Abnormalities of the cervical spine: anterior atlantoaxial subluxation. Radiographs in (A) extension and (B) flexion show widening of the anterior atlantodens interval (arrow) only in flexion. Similar but less pronounced findings related to the patient’s supine position, are shown with MR imaging in extension (C) and flexion (D).

3

1

2

Fig. 8.34  Abnormalities of the cervical spine: odontoid process erosions. Odontoid process erosions occur in areas that are intimate with the synovial articulations between the anterior arch of the atlas and the dens (1) and between the dens and the transverse ligament of the atlas (2), and in areas that are intimate with the ligamentous attachments (3) at the tip of the odontoid process.

BOX 8.2  Radiographic Features of Septic

Arthritis Complicating Rheumatoid Arthritis Monoarticular or polyarticular distribution Predilection for knee involvement Asymmetric changes Progressive soft tissue swelling and joint effusion Rapid and poorly defined bony erosion

4. Bone marrow edema detectable by MR imaging is a strong independent predictor of subsequent radiographic progression in early rheumatoid arthritis. 5. Inflammation seen on imaging may be more predictive of a therapeutic response than clinical features of disease activity; imaging may be used to predict response to treatment.

6. Given the improved detection of inflammation by US and MR imaging than by clinical examination, they may be useful in monitoring disease activity. 7. Monitoring of functional instability of the cervical spine by lateral radiographs obtained in flexed and neutral positions of the neck should be performed in patients with clinical suspicion of cervical involvement; when these radiographs are positive or specific neurologic symptoms and signs are present, MR imaging should be performed. 8. US and MR imaging can detect inflammation that predicts subsequent joint damage, even when clinical remission is present and can be used to assess persistent inflammation. With regard to specific imaging techniques, US allows the evaluation of abnormalities of both bone and soft tissues. US appears to be more sensitive than conventional radiography and equally sensitive to MR imaging in the detection of bone erosions, especially in the metacarpophalangeal and metatarsophalangeal joints (see Figs. 8.7, 8.11, 8.16, and 8.23). US can be used effectively in the detection of synovitis, with results comparable to those of MR imaging in this regard, and US is sensitive to the presence of hypervascularity through the use of color or power Doppler techniques. MR imaging is effective in the detection of synovitis in joints, tendon sheaths, and bursae, especially through the use of high-field strength magnets and intravenous gadolinium-­based contrast agents (see Figs. 8.6, 8.11, 8.12, 8.15, 8.16, 8.19, and 8.24). As noted earlier, the identification of bone marrow edema is predictive for the subsequent development of bone erosions. Both MR imaging and CT scanning can be effective in the analysis of some of the complications of rheumatoid arthritis, including synovial cysts, other paraarticular masses, rheumatoid nodules, tendon ruptures, entrapment neuropathies, and insufficiency fractures, and CT scans can display morphologic features of joint disease in a vivid and more accurate way when compared to conventional radiographs. There is reported variability in the MR imaging protocols that are being used to assess joint involvement in patients with rheumatoid arthritis. Disagreement exists regarding the choice of target sites and imaging parameters, as well as the necessity for intravenous contrast agents. Generally, the hands, wrists, and feet are selected for analysis (although other symptomatic joints may also be assessed). The choice of field of view (i.e., imaging of each extremity separately or both extremities at once) and of imaging

CHAPTER 8  Rheumatoid Arthritis planes is not uniform. Although the differentiation of synovitis and joint fluid usually can be accomplished through the use of T1-­weighted and fluid-sensitive MR images alone, intravenous gadolinium-­ based contrast agents make this distinction much easier. Features of an inflamed synovial membrane in MR images include a thickened frond like tissue with slightly higher signal than fluid in T1-­weighted images and high signal on fluid-sensitive images, as well as hyperintensity in T1-­weighted images immediately after intravenous contrast administration. Of note, delayed imaging after intravenous injection of the contrast medium is characterized by seepage of contrast agent across the inflammatory pannus, with an increase in the signal intensity of joint fluid on T1-­weighted images. The enhancement of joint fluid occurs within minutes, reaches a plateau in about 30 minutes, and persists for at least 60 minutes. The MR imaging features of chronic synovial hypertrophy are more complex and variable, including fatty infiltration in the synovial membrane (secondary lipoma arborescens), frond-like regions of intermediate or low signal intensity related to fibrosis, and nodular synovial proliferation (i.e., rice bodies). With regard to bone erosions, MR imaging is sensitive, although misdiagnosis is possible as the normal surface of some bones, such as the metacarpal and metatarsal heads, contains flattened and undulating margins that simulate the appearance of bone erosions. With MR imaging, however, marrow edema is a reliable predictive feature for the future development of bone erosions. Evaluation of rheumatoid spines with MR imaging deserves special emphasis. Although this technique can be used to assess any spinal segment, most reports have emphasized changes in the cervical region, especially the craniocervical junction. MR imaging allows assessment of the relationship of the occiput, atlas, and axis, and is therefore useful in delineating the extent of subluxation in this spinal segment. MR imaging allows direct visualization of the spinal cord so that sites of physical distortion of the cord by displaced vertebrae, inflammatory masses, or both, can be detected. The severity of myelopathy correlates better with MR imaging findings than with findings on conventional radiography. Medullary compression by the tip of the odontoid process in instances of cranial settling is far better delineated in MR images than on standard radiographs. In instances of cord compression, areas of abnormal MR signal intensity within the spinal cord itself, perhaps reflecting edema, have been detected in rheumatoid arthritis patients.

DIFFERENTIAL DIAGNOSIS General Abnormalities The diagnosis of rheumatoid arthritis is obvious when radiographic examination reveals a symmetrically distributed articular disorder characterized by osteoporosis, fusiform soft tissue swelling, concentric joint space loss, and marginal and central erosions affecting the proximal interphalangeal and metacarpophalangeal joints of the hands, the wrists, the metatarsophalangeal joints of the feet, the knees, and the elbows.

Remitting Seronegative Symmetric Synovitis With Pitting Edema (RS3PE Syndrome) Patients with RS3PE syndrome are generally elderly, with an acute onset of bilateral and symmetric synovitis involving predominantly the hands and wrists, along with evidence of tenosynovitis and pitting edema of the dorsum of the hands. Patients are more often male and are typically seronegative for rheumatoid factor, and most possess the

169

human leukocyte antigen (HLA)-­B27 antigen. Other clinical features include the involvement of large joints and flexion contractures of the wrists, fingers, and elbows. Although the remitting course, the remarkable response to low-­dose corticosteroids, and the absence of joint destruction are clearly different from the characteristics of rheumatoid arthritis, many similarities exist between RS3PE syndrome and polymyalgia rheumatica.

Spondyloarthropathies Rheumatoid arthritis characteristically has articular lesions that differ in distribution and morphology from those of the spondyloarthropathies. Ankylosing spondylitis (which shows a predilection for the axial skeleton, although it may also produce appendicular articular disease), psoriatic arthritis (which may affect the axial and appendicular skeleton, as well as the distal interphalangeal articulations), and reactive arthritis (which leads to asymmetric arthritis of the lower extremity, with or without sacroiliac and spinal alterations) may each be associated with prominent findings in synovial and cartilaginous joints and entheses. In the synovial joints, the absence of osteoporosis and the presence of bony proliferation and intraarticular osseous fusion are commonly encountered in the spondyloarthropathies, findings that differ from the features of rheumatoid arthritis. Similarly, ankylosing spondylitis, psoriatic arthritis, and reactive arthritis can produce significant and extensive abnormalities of the cartilaginous joints and entheses; these sites are much less frequently and severely affected in rheumatoid arthritis. Widespread spondylitis and sacroiliitis are also characteristic of the spondyloarthropathies.

Gout Gouty arthritis is associated with a form of asymmetric articular disease of the appendicular skeleton that is characterized by soft tissue masses, eccentric osseous erosions, bony proliferation, preservation of joint space, and absence of osteoporosis, features that usually are easily differentiated from those of rheumatoid arthritis.

Collagen Vascular Disorders The arthropathy of systemic lupus erythematosus is a deforming, nonerosive process that is initially reversible. Marginal and central bone erosions and diffuse joint space narrowing are unusual in this disease unless coexistent rheumatoid arthritis is present. In contrast, the deformities in rheumatoid arthritis are almost universally associated with joint space narrowing and bone erosion. In scleroderma, articular changes may be especially prominent in the distal interphalangeal joints of the fingers and the first carpometacarpal and inferior radioulnar compartments of the wrist. They are generally associated with tuft resorption and soft tissue and capsular calcification. Mixed connective tissue disease and overlap syndromes can lead to radiographic abnormalities common to more than one collagen vascular disorder.

CPPD Crystal Deposition Disease CPPD crystal deposition disease is radiographically manifested as articular and periarticular calcification and pyrophosphate arthropathy. The calcification involves various structures, including cartilage (chondrocalcinosis), and is most prominent in the knees, wrists, metacarpophalangeal joints, and symphysis pubis. Pyrophosphate arthropathy leads to joint space narrowing, subchondral sclerosis and cyst formation, and bone collapse and fragmentation. The arthropathy of hemochromatosis is very similar to that of idiopathic CPPD crystal deposition disease.

170

SECTION 2  Articular Disorders

Abnormalities at Specific Sites

Glenohumeral Joint

Hand and Wrist

Marginal erosions of the humeral head are seen in rheumatoid arthritis, ankylosing spondylitis, and infection, as well as in other disorders. In ankylosing spondylitis, the size of the defect may be considerably larger than that in rheumatoid arthritis. Septic arthritis of the glenohumeral joint is usually monoarticular.

Symmetric changes at the metacarpophalangeal and proximal interphalangeal joints are common in rheumatoid arthritis (Table 8.2). Psoriatic arthritis leads to significant abnormalities of the distal interphalangeal joints, as well as the more proximal articulations. Osteoarthrosis (inflammatory or noninflammatory) most typically affects the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints. Gouty arthritis can involve any joint of the hand, including the distal interphalangeal joints. CPPD crystal deposition disease has a predilection for the metacarpophalangeal articulations. Rheumatoid arthritis can manifest initially as soft tissue swelling, joint space narrowing, and osseous erosions in one or two locations of the wrist. Soon, however, pancompartmental alterations become evident. In patients without a significant history of accidental or occupational trauma, osteoarthrosis leads to articular abnormalities that are invariably confined to the first carpometacarpal compartment, the triscaphe region of the midcarpal compartment, or both. CPPD crystal deposition disease favors the radiocarpal compartment; scleroderma may selectively involve the first carpometacarpal and inferior radioulnar compartments; and gout produces pancompartmental disease, with predominant involvement of the common carpometacarpal compartment.

Acromioclavicular Joint Resorption of the distal end of the clavicle and widening of the acromioclavicular joint are observed in rheumatoid arthritis, ankylosing spondylitis, infection, other collagen vascular disorders, and hyperparathyroidism, as well as after trauma.

Forefoot The most common sites of articular disease of the forefoot in rheumatoid arthritis are the metatarsophalangeal joints and the interphalangeal joint of the great toe. Although these same articulations are involved in psoriatic arthritis, reactive arthritis, and gout, extensive abnormalities of other interphalangeal joints in one or more digits should be evident in these disorders (Table 8.3). Further, forefoot abnormalities are usually symmetric in distribution in rheumatoid arthritis and asymmetric in psoriatic arthritis, reactive arthritis, and gouty arthritis.

TABLE 8.2  Compartmental Analysis of Hand and Wrist Diseasea DIP Joints Rheumatoid arthritis

PIP Joints +

Inferior Pisiform-­ Common First MCP Radiocarpal Radioulnar Midcarpal Triquetral Carpometacarpal Carpometacarpal Joint Joint Joint Joints Joint Joint Joint +

+

+

+

+

+

+

Osteoarthrosis

+

+

+

+b

+

Inflammatory osteoarthritis

+

+

±

+b

+

+b

+

CPPD crystal deposition disease Gouty arthritis

+

+

Sclerodermad

+

+

+

+

+

+

+

+c

+

+

+

+

aOnly

the typical locations for each disease are indicated. a predilection for trapezioscaphoid area of the midcarpal joint. cVery severe abnormalities may be present in this compartment. dSome patients have coexistent rheumatoid arthritis. DIP, Distal interphalangeal; MCP, metacarpophalangeal; PIP, proximal interphalangeal. bHas

TABLE 8.3  Compartmental Analysis of Forefoot Diseasea Metatarsophalangeal Joints

Interphalangeal Joint of Great Toe

Other Interphalangeal Joints

Rheumatoid arthritis

+

+

Gouty arthritis

+

+

+

Psoriatic arthritis

+

+b

+

Reactive arthritis

+

+b

+

Osteoarthrosis

+c

aOnly

the typical locations of each disease are indicated. destructive changes may be observed. cHas a predilection for the metatarsophalangeal joint of the first digit. bSevere

171

CHAPTER 8  Rheumatoid Arthritis

Heel Retrocalcaneal bursitis producing soft tissue swelling and subjacent osseous erosion occurs not only in rheumatoid arthritis but also in ankylosing spondylitis, psoriatic arthritis, and reactive arthritis (Table 8.4). The changes are virtually indistinguishable in these four disorders, and tendon thickening can be seen in any one of them. Nodular prominence of the Achilles tendon also can be encountered in gout (as a result of tophi) and hyperlipoproteinemia (secondary to xanthoma).

Knee In rheumatoid arthritis, diffuse involvement of the medial and lateral femorotibial compartments is seen, with or without patellofemoral compartment changes. In osteoarthrosis, nonuniform alterations of the medial and lateral femorotibial compartments (the medial side is usually the dominant side of involvement, especially in men) can be combined with patellofemoral compartment disease. In CPPD crystal deposition disease, patellofemoral abnormalities, occurring alone or in combination with medial and lateral femorotibial alterations, are typical. A varus deformity is especially characteristic of osteoarthrosis, whereas valgus deformity is not uncommon in rheumatoid arthritis and CPPD crystal deposition disease. Marginal erosions of the femur and tibia are evident in rheumatoid arthritis, the spondyloarthropathies, gout, and infection, especially tuberculosis. In gout and tuberculosis, such erosions may be unaccompanied by joint space narrowing.

Hip Concentric loss of the articular space and axial migration of the femoral head with respect to the acetabulum are typical of rheumatoid involvement of the hip. In osteoarthrosis, superior or medial migration is more frequent than axial migration. Axial migration of the femoral head can accompany the hip alterations of CPPD crystal deposition disease and ankylosing spondylitis, although both of these disorders are associated with osteophytes and bone sclerosis. Acetabular protrusion is a common manifestation of severe rheumatoid hip disease. It is associated with diffuse loss of the interosseous space and an eroded and often diminutive femoral head. Protrusio acetabuli also can be encountered in patients with osteoarthrosis, familial or idiopathic protrusion deformities (Otto pelvis), ankylosing spondylitis, infection, osteomalacia, and Paget disease (Box 8.3).

Sacroiliac Joint Sacroiliac joint abnormalities are not common or prominent in rheumatoid arthritis. When evident, they are generally asymmetric in

distribution and consist of minor subchondral erosions, minimal bone eburnation, and absent or focal intraarticular bony ankylosis (Table 8.5). These characteristics differ from those of ankylosing spondylitis (bilateral symmetric disease with extensive bone erosions, sclerosis, and ankylosis), psoriatic arthritis and reactive arthritis (bilateral symmetric or asymmetric disease or unilateral disease with changes identical to those of ankylosing spondylitis), gout (bilateral or unilateral abnormalities with large erosions), osteoarthrosis (bilateral or unilateral disease with prominent subchondral sclerosis), osteitis condensans ilii (bilateral symmetric alterations of the lower part of the ilium with significant bony eburnation), hyperparathyroidism (bilateral symmetric abnormalities with widening of the interosseous space and bone erosions and sclerosis), and infection (unilateral disease with poorly defined osseous margins and reactive sclerosis).

Spine Rheumatoid arthritis produces infrequent abnormalities of the thoracic and lumbar spine. Rheumatoid changes in the cervical spine consisting of apophyseal joint erosion and malalignment, intervertebral disc space narrowing with adjacent eburnation and without osteophytes, and multiple subluxations (including at the atlantoaxial junction) are virtually diagnostic when they occur as a group. They differ from the cervical alterations of ankylosing spondylitis (widespread apophyseal joint ankylosis and syndesmophytes), psoriatic arthritis (apophyseal joint narrowing, eburnation, and prominent anterior vertebral bone formation), diffuse idiopathic skeletal hyperostosis (flowing ossification and excrescences along the anterior aspect of the spine, with preservation of intervertebral disc height), and juvenile idiopathic arthritis (apophyseal joint ankylosis with hypoplasia of the vertebral bodies and intervertebral discs). Atlantoaxial subluxation alone is not a pathognomonic sign of rheumatoid arthritis, however. It is also observed in

BOX 8.3  Causes of Protrusio Acetabuli Rheumatoid arthritis Ankylosing spondylitis Osteoarthrosis (medial migration pattern) Infection Paget disease Osteomalacia Irradiation Acetabular trauma

TABLE 8.4  Abnormalities of the Heel Retrocalcaneal Bursitis With Posterosuperior Calcaneal Erosion

Achilles Tendinosis

Enthesophyte at Posterior Attachment of Achilles Tendon

Well-­Defined Plantar Calcaneal Enthesophyte

Poorly Defined Plantar Calcaneal Enthesophyte

Rheumatoid arthritis

+

+

+

Ankylosing spondylitis

+

+

+

+a

Psoriatic arthritis

+

+

+

+a

Reactive arthritis

+

+

Gouty arthritis

+b

+c

Xanthoma

+b

+c

aPoorly

defined enthesophytes may become better defined with healing. of the calcaneus can occur beneath a tophus or xanthoma. cNodular thickening of the tendon may be seen. bErosion

+

+a

172

SECTION 2  Articular Disorders

TABLE 8.5  Comparison of Sacroiliac Joint Abnormalities in Rheumatoid Arthritis and

Ankylosing Spondylitis

Rheumatoid Arthritis

Ankylosing Spondylitis

Distribution

Asymmetrical or unilateral

Bilateral and symmetric

Erosions

Superficial

Deep

Sclerosis

Mild or absent

Moderate or severea

Bony ankylosis

Rare, segmental

Common, diffuse

aSclerosis

may disappear in long standing disease.

ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and juvenile chronic arthritis, as well as after trauma or local infection (Grisel syndrome).

SJÖGREN SYNDROME General Features The classic triad of Sjögren syndrome consists of keratoconjunctivitis sicca (dry eyes), xerostomia (dry mouth), and rheumatoid arthritis. In some patients, however, rheumatoid arthritis is replaced by another disorder such as systemic lupus erythematosus, periarteritis nodosa, progressive systemic sclerosis, or polymyositis. The diagnosis is established by the presence of two of the three major components.

Clinical Abnormalities Sjögren syndrome is a common disorder, affecting about 500,000 to 2 million persons in the United States. It is far more frequent in women than in men, and the average age at the time of diagnosis is 40 to 50 years. The two most common clinical patterns are (1) slowly progressive development of the sicca complex in a patient with chronic rheumatoid arthritis and (2) a more rapid development of oral and ocular dryness accompanied by episodic parotitis in an otherwise healthy person. Parotid gland enlargement is evident in approximately 50% of patients. Articular symptoms and signs may or may not be present. Clinical manifestations are almost invariably those of rheumatoid arthritis. In 10% to 15% of patients with rheumatoid arthritis, keratoconjunctivitis sicca develops after an average duration of arthritis of 9 years. Subcutaneous nodules are apparent in approximately 60% of patients with arthritis and are histologically typical of rheumatoid nodules. The eventual outcome of the joint disease is similar to that in uncomplicated rheumatoid arthritis. Additional manifestations of Sjögren syndrome include Raynaud phenomenon (20%), splenomegaly, and leukopenia suggestive of Felty syndrome, infections, vasculitis, peripheral neuropathy, glomerulonephritis, and purpura.

Radiographic Abnormalities The major articular findings are those of rheumatoid arthritis and consist of soft tissue swelling, periarticular osteoporosis, marginal erosions, joint space narrowing, and intraarticular cystic lesions. Typical target sites are the same as those of rheumatoid arthritis.

FURTHER READING Abrar DB, Schleich C, Brinks R, et al. Differentiating rheumatoid and psoriatic arthritis: A systematic analysis of high-resolution magnetic resonance imaging features- preliminary findings. Skeletal Radiol. 2021;50:531–541. Adams ME, Li DKB. Magnetic resonance imaging in rheumatology. J Rheumatol. 1985;12:1038.

Bloch KJ, Buchanan WW, Whol MJ, et al. Sjögren’s syndrome: A clinical, pathological and serological study of sixty-­two cases. Medicine. 1965;44:187. Braunstein EM, Weissman BN, Seltzer SE, et al. Computed tomography and conventional radiographs of the cranio-­cervical region in rheumatoid arthritis: A comparison. Arthritis Rheum. 1984;27(26). Castillo BA, El Sallab RA, Scott JT. Physical activity, cystic erosions, and osteoporosis in rheumatoid arthritis. Ann Rheum Dis. 1965;24:522. Chang EY, Chen KC, Huang BK, et al. Adult inflammatory arthritides: What the radiologist should know. RadioGraphics. 2016;36:1849. Colebatch AN, Edwards CJ, Ostergaard M, et al. EULAR recommendations for the use of imaging of the joints in the clinical management of rheumatoid arthritis. Ann Rheum Dis. 2013;72:804. El-­Khoury GY, Larson RK, Kathol MH, et al. Seronegative and seropositive rheumatoid arthritis: Radiographic differences. Radiology. 1988;168:517. El-­Khoury GY, Wener MH, Menezes AH, et al. Cranial settling in rheumatoid arthritis. Radiology. 1980;137:637. Felty AR. Chronic arthritis in the adult associated with splenomegaly and leukopenia: A report of 5 cases of an unusual clinical syndrome. Johns Hopkins Hosp Bull. 1924;35:16. Fries JF, Bloch DA, Sharp JT, et al. Assessment of radiologic progression in rheumatoid arthritis: A randomized controlled trial. Arthritis Rheum. 1986;29:1. Gasson J, Gandy SJ, Hutton CW, et al. Magnetic resonance imaging of rheumatoid arthritis in metacarpophalangeal joints. Skeletal Radiol. 2000;29:324. Gelman MI, Ward JR. Septic arthritis: A complication of rheumatoid arthritis. Radiology. 1977;122:17. Heywood AWB, Meyers OL. Rheumatoid arthritis of the thoracic and lumbar spine. J Bone Joint Surg Br. 1986;68:362. Kaye JJ, Callahan LF, Nance Jr EP, et al. Rheumatoid arthritis: Explanatory power of specific radiographic findings for patient clinical status. Radiology. 1987;165:753. Kursunoglu-­Brahme S, Riccio T, Weisman MH, et al. Rheumatoid knee: Role of gadopentetate-­enhanced MR imaging. Radiology. 1990;176:831. Martel W. The pattern of rheumatoid arthritis in the hand and wrist. Radiol Clin North Am. 1964;2:221. Martel W. Pathogenesis of cervical discovertebral destruction in rheumatoid arthritis. Arthritis Rheum. 1977;20:1217. Monsees B, Destouet JM, Murphy WA, et al. Pressure erosions of bone in rheumatoid arthritis: A subject review. Radiology. 1985;155:53. Park WM, O’Neill M, McCall IW. The radiology of rheumatoid involvement of the cervical spine. Skeletal Radiol. 1979;4:1. Resnick D. Patterns of migration of the femoral head in osteoarthritis of the hip: Roentgenographic-­pathologic correlation and comparison with rheumatoid arthritis. AJR Am J Roentgenol. 1975;124:62. Resnick D. Rheumatoid arthritis of the wrist: The compartmental approach. Med Radiogr Photogr. 1976;52:50. Resnick D, Feingold ML, Curd J, et al. Calcaneal abnormalities in articular disorders: Rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis and Reiter’s syndrome. Radiology. 1977;125:355. Rowbotham EL, Grainger AJ. Rheumatoid arthritis: Ultrasound versus MRI. Am J Roentgenol. 2011;197:541.

CHAPTER 8  Rheumatoid Arthritis Schils JP, Resnick D, Haghighi PN, et al. Pathogenesis of discovertebral and manubriosternal joint abnormalities in rheumatoid arthritis: A cadaveric study. J Rheumatol. 1989;16:291. Sharp JT. An overview of radiographic analysis of joint damage in rheumatoid arthritis and its use in metaanalysis. J Rheumatol. 2000;27:254. Sharp JT, Young DY, Bluhm GR, et al. How many joints in the hands and wrists should be included in a score of radiologic abnormalities used to assess rheumatoid arthritis? Arthritis Rheum. 1985;28:1326. Stiskal MA, Neuhold A, Szolar DH, et al. Rheumatoid arthritis of the craniocervical region by MR imaging: Detection and characterization. AJR Am J Roentgenol. 1995;165:585.

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Sugimoto H, Takeda A, Hyodoh K. Early-­stage rheumatoid arthritis: Prospective study of the effectiveness of MR imaging for diagnosis. Radiology. 2000;216:569. Weissberg D, Resnick D, Taylor A, et al. Rheumatoid arthritis and its variants: Analysis of scintiphotographic, radiographic, and clinical examinations. AJR Am J Roentgenol. 1978;131:665. Weissman BNW, Alibadi P, Weinfeld MS, et al. Prognostic features of atlanto-­ axial subluxation in rheumatoid arthritis. Radiology. 1982;144:745. Wolfe BK, O’Keeffe D, Mitchell DM, et al. Rheumatoid arthritis of the cervical spine: Early and progressive radiographic features. Radiology. 1987;165:145.

9 Juvenile Idiopathic Arthritis S U M M A R Y O F K E Y F E AT U R E S • J uvenile idiopathic arthritis encompasses a number of conditions. • One form, juvenile-­onset adult-­type seropositive rheumatoid arthritis, shows imaging features similar to those of adult rheumatoid arthritis. • Another form, termed Still disease, is seronegative and has several forms: systemic, polyarticular, and oligoarticular or pauciarticular disease.

• U  nlike adult rheumatoid arthritis, radiographic findings with Still disease include late development of joint space narrowing and erosions and presence of osseous ankylosis and epiphyseal overgrowth. • Another form of juvenile idiopathic arthritis appears similar to adult-­type spondyloarthritis, such as ankylosing spondylitis and psoriatic arthritis.

INTRODUCTION

tests (e.g., rheumatoid factor, anti-citrullinated protein antibody, antinuclear antibodies, and human leukocyte antigen [HLA]-­B27). Despite this, a significant number of patients do not fit neatly into the proposed classification categories and their disease is often listed as undifferentiated arthritis. Conversely, certain specific disorders are not included as part of juvenile idiopathic arthritis such as septic arthritis, bleeding diatheses, neoplasms such as leukemia and neuroblastoma, collagen vascular disorders, Sjögren syndrome, rheumatic fever, and some rarer conditions. In the following pages, a few of the subgroups of juvenile idiopathic arthritis are first described, including those separated by their seropositivity or seronegativity with regard to rheumatoid factor and those associated with psoriasis or enthesitis, followed by a review of some of the most characteristic imaging findings that are encountered in this heterogeneous disorder.

  

Juvenile idiopathic arthritis is a disorder encompassing a variety of conditions of unknown etiology that affect articular structures in children, adolescents, and teenagers, generally with a disease onset below the age of 16 years and persistence of symptoms for over 6 weeks. Although the specific imaging features of juvenile idiopathic arthritis depend on the subgroup of patients being evaluated, certain characteristics are sufficiently common in most patients to allow differentiation of juvenile idiopathic arthritis from various adult diseases. Loss of articular space and osseous erosions are relatively late manifestations of juvenile disease. Metaphyseal radiolucency, periostitis, intraarticular bony ankylosis, epiphyseal compression fractures, subluxation or dislocation, and growth disturbances are common. Although changes may be observed in many different skeletal sites, abnormalities of the hand, wrist, foot, knee, hip, cervical spine, mandible, and temporomandibular joint are especially characteristic. A number of other disorders, however, can simulate the imaging features of juvenile idiopathic arthritis. In 1897, Still, an English pediatrician, described in detail an articular condition in 22 children that appeared to be distinct from the adult type of rheumatoid arthritis because of its predilection for large joints rather than small ones, its propensity for producing joint contractures and muscle wasting, and its association with significant extraarticular manifestations such as splenomegaly, lymphadenopathy, anemia, fever, pleuritis, and pericarditis. Since that report, the term Still disease has been frequently used to describe rheumatoid arthritis in children. It is now recognized that a number of separate disorders can lead to chronic arthritis in children and that in many patients, scrutiny of the clinical and imaging features allows a more precise diagnosis.

CLASSIFICATION There is no uniformly acceptable classification system for juvenile idiopathic arthritis. Popular systems have been provided by the European League Against Rheumatism (EULAR) and by the International League of Associations for Rheumatology (ILAR) (Box 9.1 and Table 9.1). Such systems often rely upon clinical findings coupled with information related to family history and results of laboratory

174

Juvenile-­Onset Adult-­Type (Seropositive) Rheumatoid Arthritis An articular disease that resembles and behaves like its adult counterpart has been noted in 5% to 10% of children with juvenile idiopathic arthritis (Fig. 9.1A). This subtype is more common in girls than in boys and is more common after the age of 10 years. The clinical onset is usually polyarticular (involvement of five or more joints), with early involvement of the interphalangeal and metacarpophalangeal joints of the hand, the wrist, the knee, and the metatarsophalangeal and interphalangeal joints of the foot. Rarely, oligoarthritis rather than polyarthritis is seen. Subcutaneous nodules, particularly about the forearm and elbow, can be detected in approximately 20% to 30% of children; such nodules are rare in other forms of juvenile idiopathic arthritis. Iridocyclitis is not present. Radiologic changes in juvenile-­onset adult-­type rheumatoid arthritis include soft tissue swelling, periarticular osteoporosis, and periostitis in the hands and feet. Periosteal bone formation can involve large segments of the metaphyses of the phalanges, metacarpals, and metatarsals. The frequency and severity of periostitis account for the fundamental difference between juvenile-­onset and adult-­onset disease. Significant osseous erosions are also encountered in children with this subtype of disease. Of note, the appearance of significant erosive abnormality in the absence of joint space loss is an important diagnostic sign of juvenile-­onset rheumatoid arthritis. The prognosis of

CHAPTER 9  Juvenile Idiopathic Arthritis

175

polyarthritis in children who become seropositive for rheumatoid factor is generally poor.

BOX 9.1  Juvenile Idiopathic Arthritis Classification*

Seronegative Chronic Arthritis (Still Disease)

Juvenile-­onset adult-­type (seropositive) rheumatoid arthritis Seronegative chronic arthritis (Still disease) Classic systemic disease Polyarticular disease Oligoarticular or monoarticular disease Enthesitis-­related arthritis Psoriatic arthritis Miscellaneous arthritis

In this most common (∼70%) subtype of juvenile idiopathic arthritis, systemic or articular (or both) symptoms and signs develop in the absence of positive serologic test results for rheumatoid factor. Within this subgroup are certain clinical varieties, such as classic systemic disease, polyarticular disease, and oligoarticular or monoarticular disease, accounting for great variability in the available classification systems.

Classic Systemic Disease

* The classification systems for juvenile idiopathic arthritis developed by European League Against Rheumatism, International League of Associations for Rheumatology, and American College of Radiology are not consistent. Box 9.1 represents only one system of classification.

This pattern, which is usually seen in boys and girls younger than 5 years and represents approximately 10% to 20% of cases of juvenile idiopathic arthritis, is associated with severe extraarticular clinical manifestations. An acute febrile onset may or may not be accompanied by arthritis. Affected children have toxic symptoms along with

TABLE 9.1  Juvenile Idiopathic Arthritis Clinical and Radiographic Features Disorder

Clinical Features

Sites of Articular Involvement

Radiographic Features

Juvenile-­onset adult-­type (seropositive) rheumatoid arthritis

Female predominance >10 yr old Polyarticular involvement ± Subcutaneous nodules ± Vasculitis Seropositive for rheumatoid factor

MCP and IP joints of the hand Wrist Knee MTP and IP joints of the foot Cervical spine

Soft tissue swelling Osteoporosis Periostitis Erosions ± Joint space loss Atlantoaxial subluxation

  Systemic disease

Affects males and females equally younger than 5 yr Systemic manifestations Mild articular manifestations

Unusual and mild joint involvement*

  Polyarticular disease

Affects males and females equally Variable age Polyarticular involvement Symmetric

MCP and IP joints of the hand Wrist Knee Ankle Intertarsal, MTP, and IP joints of the foot Cervical spine

Soft tissue swelling Osteoporosis Periostitis Growth disturbances ± Erosions ± Joint space loss Intraarticular bony ankylosis Apophyseal joint ankylosis with hypoplasia of the cervical vertebrae and discs Scoliosis

  Oligoarticular or monoarticular disease

Female predominance Young age Iridocyclitis ± Systemic manifestations Asymmetric

Knee Ankle Elbow Wrist

Soft tissue swelling Osteoporosis Growth disturbances ± Joint space loss ± Erosions

Enthesitis-­related arthritis

Male predominance 10–12 yr old Polyarticular or pauciarticular involvement Predilection for the lower extremity Asymmetric ± Back pain ± Iridocyclitis ± Family history HLA-­B27 positive

Ankle Knee Intertarsal joints Calcaneus Hip ± Sacroiliac joint ± Spine

± Sacroiliitis ± Spondylitis Joint space loss Intraarticular bony ankylosis Erosions Bony proliferation

Still disease

*When present, findings are similar to those of polyarticular or oligoarticular disease. IP, Interphalangeal; MCP, metacarpophalangeal; MTP, metatarsophalangeal.

176

SECTION 2  Articular Disorders

A

B

Fig. 9.1  Juvenile idiopathic arthritis: subtypes of disease. A, Juvenile-­onset adult-­type (seropositive) rheumatoid arthritis in an 18-­year-­old girl with seropositive rheumatoid arthritis for approximately 6 years. Observe that the radiographic abnormalities are similar to those seen in adult-­onset disease. Involvement occurs in all the compartments of the wrist and in the metacarpophalangeal and proximal interphalangeal joints, with less striking changes in the distal interphalangeal joints. Radiographic changes include soft tissue swelling, periarticular osteoporosis, joint space narrowing, and marginal erosions. At some metacarpophalangeal joints, considerable erosive alterations are not accompanied by severe loss of joint space (arrows). Also note the intraarticular osseous fusion at several proximal interphalangeal joints and periostitis of the phalangeal shafts (arrowheads). B, Seronegative chronic arthritis (Still disease): polyarticular disease. An 11-­year-­old girl, seronegative for rheumatoid factor, had symmetric articular disease of the hands, wrists, knees, feet, and cervical spine. The radiograph outlines considerable generalized osteoporosis, periarticular soft tissue swelling, superficial erosions of carpal bones and metacarpal heads with shape irregularities, joint space narrowing, epiphyseal collapse, and enlargement of the epiphyses, particularly those of the distal end of the radius and distal portion of the ulna (arrows). The crenated or “crinkled” appearance of the carpus and metacarpal heads is distinctive. Flexion contractures of several digits are evident.

irritability, listlessness, anorexia, and weight loss. A rash accompanies the fever in approximately 80% to 90% of children. Generalized lymphadenopathy and hepatosplenomegaly can simulate findings in leukemia or lymphoma. Pericarditis and myocarditis represent serious manifestations of Still disease. Although joint manifestations are common, they are generally mild. Radiologic findings are unusual, though chronic, and disabling articular changes occasionally become evident.

Polyarticular Disease Polyarticular arthritis (see Fig. 9.1B) may occur at the onset of Still disease or as a later complication in a child with systemic manifestations. This pattern, which is associated with antinuclear antibody positivity, is evident in approximately 15% to 20% of patients with juvenile idiopathic arthritis, but it is the most heterogeneous subtype. Boys and girls are affected in equal numbers. Symmetric or asymmetric involvement of the metacarpophalangeal and proximal interphalangeal joints of the hands, the wrists, the knees, the ankles, and the intertarsal, metatarsophalangeal, and interphalangeal joints of the feet is typical. The cervical

spine is frequently a site of early abnormality and is characteristically the only region of the vertebral column affected. In the initial stages of polyarthritis, radiographic findings are soft tissue swelling, osteoporosis, and advanced skeletal maturation. In the hands and feet, abnormalities in the shape (squaring) of the carpal and tarsal bones are frequently combined with initial loss of joint space and subsequent intraarticular bony ankylosis. Synovitis of the flexor tendon sheaths may produce periostitis of the diaphyses and metaphyses of the phalanges, metacarpals, and metatarsals. Premature fusion of the epiphyses of the bones is not uncommon and accounts for the characteristic growth defects. The epiphyses may appear enlarged or ballooned in relation to the diaphyses, and a decrease in bone length is characteristic. Osseous erosion is unusual. In larger articulations such as the knee, osteoporosis and epiphyseal overgrowth are more typical. In the hip, enlargement and osteoporosis of the femoral capital epiphysis, failure of growth and premature fusion of the femoral neck, coxa valga deformity, hypoplasia of the iliac bones, and protrusio acetabuli are seen. Apophyseal joint erosions, narrowing, and bony ankylosis predominate in the upper cervical region.

CHAPTER 9  Juvenile Idiopathic Arthritis Associated hypoplasia of the vertebral bodies and intervertebral discs is characteristic.

Oligoarticular or Monoarticular Disease The oligoarticular or monoarticular disease pattern, which is observed in young children and may represent 30% to 70% of all cases of juvenile idiopathic arthritis, is generally confined to the large joints, most frequently the knees, ankles, elbows, and wrists. This clinical pattern of arthritis carries with it a serious threat of blindness from iridocyclitis. Additional systemic manifestations are infrequent, although lymphadenopathy, splenomegaly, fever, and rash are occasionally observed. In recent years, distinct subtypes of this disease pattern have been identified on the basis of clinical and immunogenetic evidence, and an overlap of findings in oligoarticular and polyarticular seronegative forms of juvenile idiopathic arthritis has been observed, leading again to inconsistencies in disease classification. Furthermore, a monoarticular type of juvenile idiopathic arthritis also has been reported. In children who initially exhibit monoarticular disease, oligoarticular disease or, infrequently, polyarthritis may develop. In general, it cannot be predicted whether more widespread articular abnormality will develop in children with monoarthritis. In monoarticular or oligoarticular Still disease, radiographically demonstrable abnormalities of bone growth may appear at an early stage. Increased size and accelerated maturation of epiphyseal ossification centers, longitudinal overgrowth of bones adjacent to an affected articulation, and regional atrophy and remodeling of bone are observed. Soft tissue swelling and osteoporosis are seen, but bone erosion is a late manifestation.

Enthesitis-­Related Arthritis This pattern of juvenile idiopathic arthritis, characterized by a combination of enthesitis and arthritis, is typically seen in boys after the age of 6 years and is accompanied by seropositivity for the histocompatibility antigen HLA-­B27. The mean age at disease onset is 10 to 12 years. Enthesitis, which is often remitting and mild, predominates in the posterior and plantar aspects of the calcaneus and the tarsus, and arthritis is most prevalent in the joints of the lower extremity, including the hip. In addition, clinical manifestations may be encountered in the sacroiliac joints, leading to a diagnosis of juvenile-­onset ankylosing spondylitis, but radiographic changes in these articulations and those of the spine are difficult to interpret in young children and are frequently delayed until the latter part of the second decade of life. It

177

is clear that clinical and imaging findings of enthesitis-­related arthritis overlap those of the spondyloarthropathies as in ankylosing spondylitis, psoriasis (see following discussion), inflammatory bowel disease, and reactive arthritis.

Psoriatic Arthritis The inclusion of this subgroup of juvenile idiopathic arthritis is controversial. When employed, this subgroup is composed of children with dactylitis, nail changes, and arthritis, although the typical psoriatic skin disease may appear before or after these manifestations. Radiographic abnormalities can simulate those in adults with psoriatic arthritis, including distal interphalangeal joint destruction, phalangeal tuft resorption, and sacroiliitis. Juvenile-­onset psoriatic arthritis usually has an oligoarticular onset.

RADIOGRAPHIC ABNORMALITIES The radiographic abnormalities associated with juvenile idiopathic arthritis depend on the specific subgroup being investigated. In the following discussion, emphasis is placed on features that can be encountered in juvenile-­onset adult-­type (seropositive) rheumatoid arthritis and the polyarticular and oligoarticular types of seronegative chronic arthritis (Still disease). The many similarities among these forms of arthritis facilitate their discussion as a group in the following analysis.

General Features The general radiographic characteristics of juvenile idiopathic arthritis in comparison to adult-­onset disease are shown in Tables 9.2 and 9.3 and Fig. 9.2.

Soft Tissue Swelling Periarticular soft tissue swelling is a common early manifestation of arthritis, related in some cases to large joint effusions. Tenosynovitis leads to focal soft tissue swelling.

Osteopenia Juxtaarticular or diffuse osteoporosis may be encountered. In addition, band ­like metaphyseal lucent zones may be seen, particularly in the distal end of the femur, proximal portion of the tibia, and distal ends of the radius, tibia, and fibula, identical to those seen in childhood leukemia. Osteoporosis in juvenile idiopathic arthritis may lead to fractures, including compression fractures of the epiphyses, diaphyseal and

TABLE 9.2  Juvenile Idiopathic Arthritis Versus Adult-­Onset Rheumatoid Arthritis General Radiographic Characteristics* Finding

Juvenile Idiopathic Arthritis

Adult-­Onset Rheumatoid Arthritis

Soft tissue swelling

Common

Common

Osteoporosis

Common

Common

Joint space loss

Late manifestation

Early manifestation

Bony erosions

Late manifestation

Early manifestation

Intraarticular bony ankylosis

Common

Rare

Periostitis

Common

Rare

Growth disturbances

Common

Absent

Epiphyseal compression fractures

Common

Less common

Joint subluxation

Common

Common

Synovial cysts

Uncommon

Common

*Characteristics depend on the specific subgroups of juvenile idiopathic arthritis.

178

SECTION 2  Articular Disorders

TABLE 9.3  Comparison of Radiographic Abnormalities Juvenile Idiopathic Arthritis*

Finding Cervical Spine C1–C2 subluxation

+

Apophyseal joint ankylosis Hypoplasia of the vertebral bodies and intervertebral discs

Adult-­Onset Rheumatoid Juvenile-­Onset Adult-­Onset Ankylosing Arthritis Ankylosing Spondylitis Spondylitis ++

+

+

++

±

++

++

++

–

±

–

Thoracolumbar Spine Apophyseal joint ankylosis

±

–

++

++

Syndesmophytes

–

–

++

++

Sacroiliac Joints Erosions

+

+

++

++

Ankylosis

±

±

++

++

Peripheral Joints Early involvement

++

++

++

±

Erosions

±

++

+

+

Joint space narrowing

±

++

+

+

Bony proliferation and periostitis

++

±

++

++

*Characteristics of juvenile-­onset adult-­type rheumatoid arthritis and Still disease. ++, Very common; +, common; ±, uncommon; –, rare or absent.

A

B Fig. 9.2  Juvenile idiopathic arthritis: general radiographic abnormalities. A, Periostitis. Prominent periosteal proliferation of numerous phalanges (arrows) is associated with osteoporosis and periarticular soft tissue swelling. Joint space diminution and erosions are not significant features in this child. B, Epiphyseal compression fractures. The irregular outline of the metacarpal heads (arrows) is produced by compression of weakened osteoporotic bones.

CHAPTER 9  Juvenile Idiopathic Arthritis metaphyseal fractures of tubular bones, and compression fractures of vertebral bodies.

Joint Space Abnormalities Loss of the interosseous space in juvenile idiopathic arthritis is less frequent than in adult-­onset rheumatoid arthritis. The combination of osteoporosis and soft tissue swelling without cartilaginous (or osseous) destruction is an important radiographic characteristic of this disease. In later stages, intraarticular bony ankylosis is frequent, especially in the small joints of the hands and wrists.

Bone Erosion Destruction of bone is also a relatively late manifestation of juvenile idiopathic arthritis. Bone erosions may occur at the margins of the articulation (as in adult-­onset rheumatoid arthritis) or along the entire articular surface of the bone.

Periostitis Periostitis is a frequent and prominent manifestation of juvenile idiopathic arthritis, most common in the periarticular regions of the phalanges, metacarpals, and metatarsals. Periostitis can appear early in the course of the disease in combination with osteoporosis and soft tissue swelling, much like the appearance of osteomyelitis.

Growth Disturbances Epiphyseal enlargement from accelerated growth stimulated by hyperemia is frequent about the small and large articulations. This overgrowth is accentuated by the adjacent constricted appearance of the metaphysis and diaphysis. Accelerated osseous growth and maturation lead to an increase in the number and size of the carpal and tarsal bones. Disturbance of the normal growth of the diaphysis of tubular bones is a characteristic feature of juvenile idiopathic arthritis. In the

A

179

hands and feet, short, broad phalanges, metacarpals, and metatarsals simulate the changes in various bone dysplasias. In the lower extremities, leg length discrepancies are seen.

Epiphyseal Compression Fractures Compression fractures are evident in the weight-­bearing epiphyses of the lower extremities, as well as the epiphyses of the hands and feet. They are produced by abnormal stress (resulting from muscle spasm and joint subluxation) acting on weakened osteoporotic bone. Flattening and deformity of the epiphyseal ossification centers and formation of dense intraosseous foci as a result of trabecular compression are evident.

Joint Subluxation Subluxation and dislocation can be observed in any articulation but are most common in the hip. These complications result from large intraarticular effusions or, more importantly, from ligamentous destruction and muscle foreshortening secondary to fibrosis.

Soft Tissue Calcification Periarticular soft tissue calcific deposits may be recorded in this disease, appearing in the joint capsule, ligament, or muscle. The exact cause of periarticular calcification in juvenile idiopathic arthritis is not clear.

Abnormalities in Specific Locations A comparison of the radiographic abnormalities of chronic juvenile arthritis and those of similar diseases is presented in Table 9.3.

Hand Any articulation of the hand may be affected (Fig. 9.3). Swelling and regional osteoporosis can develop about the distal interphalangeal,

B

Fig. 9.3  Abnormalities of the hand. A, Typical changes in this child with polyarticular Still disease include periarticular soft tissue swelling and osteoporosis about the metacarpophalangeal and proximal interphalangeal joints and the wrist, mild joint space narrowing and erosive abnormalities, and periosteal bone formation in the phalanges. B, Note the extent of epiphyseal compression about the metacarpophalangeal and proximal interphalangeal joints, combined with osteoporosis, soft tissue swelling, and carpal involvement.

180

SECTION 2  Articular Disorders

proximal interphalangeal, and metacarpophalangeal joints. Periostitis of the metacarpal and phalangeal shafts, preservation of the joint space, and absence of significant erosions are most common. Epiphyseal collapse and deformity are also characteristic. A variety of finger deformities may eventually appear.

be enlarged and irregular in outline, and premature fusion of the growth plate may be evident. Articular space narrowing, osseous erosion, and osteophytosis may appear (Fig. 9.9). Protrusio acetabuli is more frequent in older children.

Wrist Abnormalities of the wrist are extremely common. Soft tissue prominence, osteoporosis, and irregular carpal ossification centers are seen (Fig. 9.4). Bone ankylosis of any of the compartments of the wrist may be prominent (Fig. 9.5). Growth disturbances and articular destruction can lead to significant wrist deformities, including ulnar deviation at the wrist.

Knee Radiographic abnormalities of the knee include osteoporosis, soft tissue swelling, and distention of the knee joint recesses (Fig. 9.6). Bone changes may include enlargement with ballooning of the distal femoral and proximal tibial epiphyses, flattening of the femoral condyles, widening of the intercondylar notch, joint space narrowing, and marginal or central osseous erosions (Fig. 9.7). These findings are virtually identical to those in hemophilia. Alterations in patellar shape consist of flattening of the inferior pole of the patella, which results in squaring of the bone.

Hip Involvement of the hip is common. Early imaging findings may be periarticular osteopenia and uniform joint space narrowing (Fig. 9.8). In younger patients, impairment of iliac bone development and coxa valga deformity are not infrequent. The femoral capital epiphysis may

Fig. 9.4  Abnormalities of the wrist. In this young child, erosions of multiple carpal bones have led to crenated osseous contours. Joint space narrowing and acceleration of bone maturation are seen.

Fig. 9.5  Abnormalities of the wrist: carpal ankylosis. Bilateral hand radiographs show bony ankylosis of the radiocarpal and midcarpal compartments (arrow). Joint space narrowing and partial ankylosis at the common carpometacarpal joint are also apparent.

CHAPTER 9  Juvenile Idiopathic Arthritis

A

B

C

181

D

Fig. 9.6  Abnormalities of the knee. A, Lateral radiograph shows distention of the suprapatellar recess (arrow), and (B) frontal radiograph shows widening of the intercondylar notch. Sagittal (C) intermediate-weighted and (D) contrast-enhanced MR images show heterogeneous but predominantly increased signal fluid and diffuse synovial hypertrophy (arrows).

clawing of the toes, hammertoes, hindfoot varus or valgus, pes cavus, and hallux valgus.

Sacroiliac Joint and Pelvis Although children with certain types of juvenile idiopathic arthritis, such as enthesitis and psoriatic arthritis, can have significant sacroiliac joint abnormalities (see Table 9.3), documenting the presence of an abnormal sacroiliac joint can be difficult because of the widened articular space and indistinct subchondral bone that characterize the normal sacroiliac joint in the pediatric age group. In some forms of this disease, enthesitis becomes prominent and can be observed in various locations, including the ischial tuberosities and femoral trochanters, leading to an irregular bone surface.

Cervical Spine

Fig. 9.7  Abnormalities of the knee. The major radiographic abnormalities in this 23-­year-­old woman who has had arthritis for approximately 10 years consist of diffuse joint space narrowing and marginal erosions (arrows). These simulate the findings in adult-­onset rheumatoid arthritis, but slight overgrowth of the femoral epiphysis indicates that the disease began at a relatively young age.

Foot and Ankle The radiographic abnormalities of the tarsus are similar to those in the carpus. Enlargement and irregularity of the tarsal bones, joint space narrowing, and intraarticular bony ankylosis can be seen. Metatarsophalangeal and interphalangeal joint alterations consist of osteoporosis, epiphyseal enlargement, brachydactyly, and periostitis (Fig. 9.10). Enthesitis about the calcaneus can be evident. Late deformities include

Radiographic abnormalities of the cervical spine are a significant feature of juvenile idiopathic arthritis (see Table 9.3; Fig. 9.11). Subluxation may develop in any vertebral segment but is most characteristic at the atlantoaxial level. Atlantoaxial instability in a child, however, is not diagnostic of juvenile idiopathic arthritis, being observed in trauma and in a variety of other conditions, including those causing hypoplasia of the odontoid process and congenital weakening of the surrounding ligaments, such as Down syndrome, and those associated with inflammation in the neck. Erosions of the anterior, posterior, and superior surfaces of the odontoid process also may be seen. Apophyseal joint space narrowing and bony ankylosis in association with subchondral erosions predominate in the upper cervical spine. Growth disturbances consist of decreased vertical and anteroposterior diameters of the vertebral bodies at the levels of apophyseal joint ankylosis. The adjacent intervertebral discs are also diminished in height (or completely obliterated) and may contain calcification. The resulting radiographic appearance in juvenile idiopathic arthritis is distinctive, with dwarf ­like alterations of both the vertebral bodies and the intervertebral discs and apophyseal joint ankylosis. Although apophyseal joint ankylosis can be seen in ankylosing spondylitis, the vertebral bodies are not significantly diminished in size in that disease nor are the intervertebral discs diminutive because disease onset generally occurs at a more advanced age. Congenital fusion of vertebral

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SECTION 2  Articular Disorders

A

C

B

D Fig. 9.8  Abnormalities of the hip. A, Anteroposterior radiograph shows left hip periarticular osteopenia and mild uniform joint space loss (arrow). Coronal (B) T1-­weighted, (C) fluid-­sensitive, and (D) T1-­weighted fat-suppressed contrast-­enhanced MR images show enhancing fluid signal synovial hypertrophy and bone marrow edema (arrow).

bodies (Klippel-­Feil deformity) may simulate the changes in juvenile idiopathic arthritis, although in the former disorder, the spinous processes of several vertebrae also may be incorporated into a single ossific mass. Fibrodysplasia ossificans progressiva can be accompanied by vertebral alterations, but additional abnormalities, such as soft tissue ossification, ensure an accurate diagnosis of that condition.

Mandible, Temporomandibular Joint, and Other Facial Structures Underdevelopment of the jaw (micrognathia) is not uncommon, occurring in approximately 10% to 20% of patients, and frequently occurs in association with temporomandibular joint abnormalities. Radiographic abnormalities include shortening of the body and vertical rami of the mandible, with widening of the mandibular notches. Both mandibular condyles are frequently flattened and poorly differentiated, although the temporomandibular joints themselves may appear normal. Articular space narrowing, bone erosion, and abnormal joint motion may be encountered in some persons. Antegonial notching of the mandible has been emphasized as an additional radiographic manifestation of juvenile idiopathic arthritis. This notching represents a concavity on the undersurface of the mandibular body just anterior to the angular process (gonion) (Fig. 9.12).

OTHER DIAGNOSTIC TECHNIQUES Other diagnostic techniques can be applied to the assessement of patients with juvenile idiopathic arthritis. Ultrasonography is more sensitive than conventional radiography in the detection of synovitis and joint effusions, especially in superficial articulations and the small joints of the hands and feet. This method also can be used to facilitate and monitor joint aspiration. Magnetic resonance (MR) imaging is also sensitive to the presence of synovitis and joint effusions, and the distribution and degree of synovial inflammation can be further enhanced through the intravenous administration of a gadolinium-­containing agent. Furthermore, the presence of marrow edema may be predictive of the subsequent appearance of bone erosions, as in adult-­type rheumatoid arthritis. MR imaging also may be helpful in the assessment of tendons, tendon sheaths, and even articular cartilage. It can provide additional information with regard to abnormalities in regions of complex anatomy such as the spine and sacroiliac joints.

SPECIAL TYPE OF JUVENILE IDIOPATHIC ARTHRITIS: ADULT-­ONSET STILL DISEASE Some adults may develop a disorder that is indistinguishable from Still disease, designated adult-­ onset Still disease. Pauciarticular

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183

abnormalities predominate, with a predilection for the knees, fingers, and wrists. Radiographic alterations develop in only a few patients. A distinctive radiographic pattern of articular disease of the wrist has been noted: narrowing of portions of the common carpometacarpal and midcarpal compartments without osseous erosions, which may culminate in bony ankylosis (Fig. 9.13). Similar patterns of ankylosis of the carpal (and tarsal) bones can be observed in children with juvenile idiopathic arthritis.

DIFFERENTIAL DIAGNOSIS Hemophilia

Fig. 9.9  Abnormalities of the hip. In a child with juvenile-­onset adult-­ type (seropositive) rheumatoid arthritis, note diffuse joint space narrowing, significant erosions of the femoral head and acetabulum, and osteoporosis.

Differentiating juvenile idiopathic arthritis and hemophilia based on conventional radiography can be difficult in the absence of clinical information. Soft tissue swelling, osteoporosis, subchondral osseous irregularity, joint space diminution, and growth disturbances may be evident in both disorders. In the knee, ankle, and elbow, the resulting radiographic picture may be identical in the two conditions. Polyarticular disease and significant involvement of the small joints of the hand and wrist are less frequent in hemophilia than in juvenile idiopathic arthritis, whereas radiodense joint effusions and multiple subchondral cystic lesions are somewhat more common in hemophilic arthropathy. Squaring or flattening of the inferior pole of the patella is more characteristic of juvenile idiopathic arthritis.

Idiopathic Multicentric Osteolysis Idiopathic multicentric osteolysis is a disorder characterized by multifocal articular destruction beginning in infancy or childhood. Although the clinical and radiographic features of idiopathic multicentric osteolysis are somewhat variable, pain and swelling of the hands, wrists, feet, ankles, and elbows are typical. Because of a remarkable predilection for the carpal and tarsal bones, the disorder is also referred to as carpal and tarsal osteolysis or disappearing carpal bones. Radiographic characteristics include osteoporosis, progressive osteolysis, and deformity, findings that may simulate the changes in juvenile idiopathic arthritis.

Mucopolysaccharidoses and Related Disorders Articular abnormalities accompanying mucopolysaccharidoses may simulate those in juvenile idiopathic arthritis, although characteristic findings are noted on skeletal surveys in patients with mucopolysaccharidoses. In many of these syndromes, periarticular involvement is apparent and leads to alterations in ligamentous and tendinous structures.

Other Disorders

Fig. 9.10  Abnormalities of the foot. Prominent growth disturbances such as these may accompany Still disease. Shortening of the metatarsal bones and deformity of some of the metatarsophalangeal joints are the most prominent findings.

Multiple epiphyseal dysplasia (and spondyloepiphyseal dysplasia) can lead to irregularity of many epiphyses and secondary degenerative joint abnormalities that could be confused with the changes of juvenile idiopathic arthritis. Progressive pseudo r­heumatoid arthritis of childhood (i.e., progressive pseudo r­ heumatoid chondrodysplasia) is a term applied to a hereditary arthropathy affecting the major and minor joints; findings include restricted articular motion, swelling about the interphalangeal articulations, platyspondyly, and irregularities of vertebral bodies. Infection or synovial hemangiomas can produce abnormalities of single articulations, which also simulate the findings of juvenile idiopathic arthritis. Other entities to be considered in the differential diagnosis of juvenile chronic arthritis include neuromuscular disorders and multicentric reticulohistiocytosis.

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SECTION 2  Articular Disorders

A

B

Fig. 9.11  Abnormalities of the cervical spine: apophyseal joint bony ankylosis. A–B, In two children with Still disease, apophyseal joint ankylosis is evident. The process is usually first apparent in the upper cervical region and progresses to the lower vertebrae. Hypoplasia of the vertebral bodies and intervertebral discs is prominent in both cases. Atlantoaxial subluxation is also evident in (A).

Fig. 9.12  Abnormalities of the mandible. In this child with juvenile idiopathic arthritis, note the short antegonial notches (arrows). Additional findings are articular changes in the temporomandibular joints (not well shown here).

Fig. 9.13  Adult-­ onset Still disease: wrist involvement. This 44-­year-­old woman has had Still disease since age 25 years. A frontal radiograph shows bony ankylosis of the midcarpal, common carpometacarpal, and intermetacarpal compartments of the wrist. The radiocarpal compartment is moderately narrowed. (Courtesy J. Esdaile, MD, Montreal, Quebec, Canada.)

CHAPTER 9  Juvenile Idiopathic Arthritis

FURTHER READING Ansell BM, Kent PA. Radiological changes in juvenile chronic polyarthritis. Skeletal Radiol. 1977;1:129. Berntson L, Fasth A, Andersson-­Gare B, et al. Construct validity of ILAR and EULAR criteria in juvenile idiopathic arthritis: a population based incidence study from the Nordic countries. J Rheumatol. 2001;28:2737. Brill PW, Kim HJ, Beratis NG, et al. Skeletal abnormalities in the Kniest syndrome with mucopolysacchariduria. AJR Am J Roentgenol. 1975;125:731. Bywaters EGL. Still’s disease in the adult. Ann Rheum Dis. 1971;30:121. Cassidy JT, Levinson JE, Bass JC, et al. A study of classification criteria for a diagnosis of juvenile rheumatoid arthritis. Arthritis Rheum. 1986;29: 274. Chlosta EM, Kuhns LR, Holt JF. The “patellar ratio” in hemophilia and juvenile rheumatoid arthritis. Radiology. 1975;116:137. Cohen PA, Job-­Deslandre CH, Lalande G, et al. Overview of the radiology of juvenile idiopathic arthritis (JIA). Eur J Radiol. 2000;33:94. Eisenstein EM, Berkun Y. Diagnosis and classification of juvenile idiopathic arthritis. J Autoimmunity. 2014;48-­49:31. Hemke R, Herregods N, Jaremko JL, et al. Imaging assessment of children presenting with suspected or known juvenile idiopathic arthritis: ESSRESPR points to consider. European Radiology. 2020;30:5237. Hervé-­Somma CMP, Sebag GH, Prieur A-­M, et al. Juvenile rheumatoid arthritis of the knee: MR evaluation with Gd-­DOTA. Radiology. 1992;182:93. Kahn PJ. Juvenile idiopathic arthritis. What the clinican needs to know. Bull Hosp Jt Dis. 2013;71:194. Martel W, Holt JF, Cassidy JT. Roentgenologic manifestations of juvenile rheumatoid arthritis. AJR Am J Roentgenol. 1962;88:400. Medsger Jr TA, Christy WC. Carpal arthritis with ankylosis in late onset Still’s disease. Arthritis Rheum. 1976;19:232.

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Munir S, Patil K, Miller E, et al. Juvenile idiopathic arthritis of the axial joints: a systematic review of the diagnostic accuracy and predictive value of conventional MRI. AJR. 2014;202:199. Poznanski AK, Hernandez RJ, Guire KE, et al. Carpal length in children—a useful measurement in the diagnosis of rheumatoid arthritis and some congenital malformation syndromes. Radiology. 1978;129:661. Ravelli A, Martini A. Juvenile idiopathic arthritis. Lancet. 2007;369:767. Richardson ML, Helms CA, Vogler III JB, et al. Skeletal changes in neuromuscular disorders mimicking juvenile rheumatoid arthritis and hemophilia. AJR Am J Roentgenol. 1984;143:893. Scheybani E, Khanna G, White AJ, et al. Imaging of juvenile idiopathic arthritis: a multimodality approach. RadioGraphics. 2013;33:1253. Schnedl WJ, Lipp RW, Trinker M, et al. Bone scintigraphy and magnetic resonance imaging in adult-­onset Still’s disease. Scand J Rheumatol. 1999;28:257. Senac Jr MO, Deutsch D, Bernstein BH, et al. MR imaging in juvenile rheumatoid arthritis. AJR Am J Roentgenol. 1988;150:873. Spranger J, Albert C, Schilling F, et al. Progressive pseudorheumatoid arthropathy of childhood (PPAC): a hereditary disorder simulating juvenile rheumatoid arthritis. Am J Med Genet. 1983;14:399. Stabrun AE, Larheim TA, Höyeraal HM, et al. Reduced mandibular dimensions and asymmetry in juvenile rheumatoid arthritis: pathogenetic factors. Arthritis Rheum. 1988;31:602. Still GF. On a form of chronic joint disease in children. Med Chir Trans. 1897;80:47. Tyler T, Rosenbaum HD. Idiopathic multicentric osteolysis. AJR Am J Roentgenol. 1976;126:23. Winchester P, Grossman H, Lim WN, et al. A new acid mucopolysaccharidosis with skeletal deformities simulating rheumatoid arthritis. AJR Am J Roentgenol. 1969;106:121.

10 Ankylosing Spondylitis S U M M A R Y O F K E Y F E AT U R E S • A  bnormalities are detected at the synovial and cartilaginous joints and at entheses, sites of tendinous and ligamentous attachment to bone, in both spinal and extraspinal locations. • The hallmark of the disorder is sacroiliitis, which is typically bilateral and symmetrical in distribution.

• S pondylitis leads to significant abnormalities at the discovertebral junction, apophyseal and costovertebral joints, and posterior ligamentous attachments.

INTRODUCTION

has been noted in some female patients. An insidious onset of disease, which occurs in 75% to 80% of patients, can lead to considerable delay in accurate diagnosis. Early clinical manifestations are generally noted in the back (70% to 80% of patients), although they may appear in the peripheral joints (10% to 20% of patients) or in the chest. Sciatic pain may be the initial symptom in 5% to 10% of patients. Constitutional findings include anorexia, weight loss, and low-­grade fever. The consensus is that in less than 20% of patients with adult-­onset ankylosing spondylitis does the disease progress to a condition of significant disability.

  

Ankylosing spondylitis is an immune-­mediated chronic inflammatory disorder with a genetic predisposition and probable environmental triggers that include certain microorganisms and biomechanical stress. The presence of human leukocyte antigen (HLA)-­B27 is the major genetic association in this disorder, although there are probably over 100 other genetic regions that contribute to its pathogenesis. Ankylosing spondylitis principally affects the axial skeleton, although the appendicular skeleton also may be significantly involved. Alterations occur in synovial and cartilaginous joints and in sites of tendon and ligament attachment to bone, known as entheses. Although ankylosing spondylitis is now the accepted name for this disease, many synonyms and eponyms have been used in the past, including Marie-­Strümpell disease, von Bechterew syndrome, and rheumatoid spondylitis. As discussed in Chapter 7, ankylosing spondylitis has recently been grouped under the general term of spondyloarthropathy or spondyloarthritis (SpA) as the classically used (modified) New York criteria for its diagnosis have been found not to be reliable or even applicable in the early stages of the disease. Furthermore, in these stages, active sacroiliitis may not be visible on conventional radiographs but is sometimes detectable with magnetic resonance (MR) imaging. This has led to the designation of axial SpA for spondyloarthropathies that affect the axial skeleton with or without radiographically evident alterations, and peripheral SpA when the peripheral skeleton is affected, often with prominent enthesitis. Such designations theoretically could lead to accurate diagnosis at an early disease stage when therapy is more effective. It is difficult to determine the true prevalence; however, ankylosing spondylitis is a common cause of back pain and disability, especially in young men. The prevalence of this disease in the general population is more difficult to determine, although figures of approximately 0.1% to 0.2% are commonly quoted, varying from one country to another. The precise ratio of the disease in men versus women is not known, with reports varying from 4:1 to 10:1. The true prevalence of ankylosing spondylitis in women may be much higher than these reports indicate, because the disease may be more subtle and difficult to diagnose in female patients.

CLINICAL ABNORMALITIES General Features The onset of ankylosing spondylitis generally occurs between the ages of 15 and 35 years in both men and women, although an earlier onset

186

Axial Skeletal Symptoms and Signs Clinical manifestations related to the spine and sacroiliac joints are characteristic of ankylosing spondylitis. Initially, transient aching pain and stiffness of variable intensity are observed in the low back region, but these symptoms may subsequently become persistent. With evolution of the disease, spread to higher levels of the vertebral column is frequent. Local pain and tenderness over the sacroiliac joints can be prominent in the early phases of the disease. With ankylosis of these joints, the clinical manifestations may become milder or disappear completely. Pain radiating into the lower extremities, not unlike sciatica, can be observed in approximately 50% of patients at some stage of the disorder. In the lumbar spine, paravertebral muscle spasm, straightening of the vertebral column, tenderness to percussion, and muscle atrophy are observed; in the thoracic spine, similar abnormalities may be accompanied by diminished chest expansion and exaggeration of the normal kyphotic curvature. Slight, moderate, or marked limitation of movement may be evident in the cervical spine. The head and neck protrude forward, and the patient may eventually be forced to constantly gaze at the floor. The cauda equina syndrome can be observed in patients with ankylosing spondylitis. Although its pathogenesis in this disease is not clear, the occurrence of loss of cutaneous sensation in the sacral and lower lumbar dermatomes, muscle weakness, and disturbed sphincter function may be related to arachnoiditis, with subsequent loss of meningeal elasticity.

Peripheral Skeletal Symptoms and Signs Peripheral articular manifestations are initially apparent in approximately 10% to 20% of patients and eventually occur in as many as 50%. In most persons, the manifestations are mild and transient, and asymmetric

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involvement of a few joints is typical. Asymmetry is more frequent, and residual destruction and deformity are less frequent, in ankylosing spondylitis than in rheumatoid arthritis. Involvement of the proximal or root joints (hips and shoulders) is particularly characteristic. Enthesitis can be a prominent clinical (and imaging) feature in persons with ankylosing spondylitis. Either focal or widespread entheseal involvement is encountered, accompanied by pain, tenderness to palpation, and swelling.

Extraskeletal Symptoms and Signs Iritis occurs in 20% of patients with ankylosing spondylitis and may be the initial feature of the disease. Spondylitic heart disease can lead to cardiac enlargement, conduction defects, and pericarditis, particularly in patients with chronic disease. Typically, aortic insufficiency caused by inflammation of the aortic valve and aorta resembles the finding in syphilitic aortitis. Pulmonary involvement in ankylosing spondylitis can manifest as a peculiar fibrosis and cavitation in the upper lobes that simulate the findings in tuberculosis. Additional systemic manifestations of ankylosing spondylitis include associations with inflammatory bowel disease (see Chapter 12) and amyloidosis.

RADIOGRAPHIC-­PATHOLOGIC CORRELATION General Distribution Ankylosing spondylitis affects synovial and cartilaginous joints, as well as sites of tendon and ligament attachment to bone (entheses). An overwhelming predilection exists for involvement of the axial skeleton, especially the sacroiliac, apophyseal, discovertebral, and costovertebral articulations (Fig. 10.1). Classically, changes are noted initially in the sacroiliac joints and next appear at the thoracolumbar and lumbosacral junctions; with disease chronicity, the midlumbar, upper thoracic, and cervical vertebrae may become involved. Radiographic abnormalities of the sacroiliac joint without vertebral changes are unusual. The combination of sacroiliac joint and cervical spine abnormalities without significant thoracic or lumbar spine changes appears to be more common in women than men. Spinal alterations without sacroiliac joint changes are unusual in classic ankylosing spondylitis in either men or women. In peripheral locations, radiographic changes predominate in the hips and glenohumeral joints, followed in descending order of frequency by the knees, hands, wrists, and feet, including the calcaneus. Bilateral abnormalities are common, although the degree of symmetry is less striking than in cases of rheumatoid arthritis. Radiographic abnormalities can be encountered in the symphysis pubis and in the manubriosternal, acromioclavicular, sternoclavicular, and temporomandibular joints. Changes are also evident at tendinous and ligamentous attachments to bone, especially in the spine, pelvic bones, and proximal femora.

General Radiographic and Pathologic Abnormalities Synovial Articulations

In general, the inflammatory process in ankylosing spondylitis is similar to that in rheumatoid arthritis but of lower intensity. Marked fibroplasia may be followed by cartilaginous metaplasia with chondral ossification, leading to intraarticular bony ankylosis. Capsular ossification also can lead to intraarticular bone ankyloses. The basic similarity of the pathologic alterations in synovial joints in ankylosing spondylitis and rheumatoid arthritis accounts for the overlap in their radiographic features. Both cause some degree of osteoporosis, joint space narrowing, and osseous erosion. Certain findings are more characteristic of ankylosing spondylitis than of rheumatoid arthritis, however. Prominent periarticular osteoporosis is not common in ankylosing spondylitis. Periostitis and bone proliferation, or

Fig. 10.1  Ankylosing spondylitis: distribution of articular disease. Initial abnormalities are most frequent in the sacroiliac joint and the thoracolumbar and lumbosacral junctions (arrowheads). Subsequent abnormalities are common in the entire vertebral column, tendinous and ligamentous insertions in the pelvis and proximal end of the femur, sternal joints, symphysis pubis, hips, and glenohumeral joints (arrows).

whiskering, may be seen. In ankylosing spondylitis, intraarticular bony ankylosis is common in the synovial joints of both the axial skeleton (sacroiliac, costovertebral, and apophyseal joints) and the extraaxial skeleton (hip, wrist, and articulations of the midfoot). In adult-­onset rheumatoid arthritis, fibrous ankylosis is more characteristic, except in the carpal and tarsal areas.

Cartilaginous Articulations In the cartilaginous joints of the axial skeleton (discovertebral junction, symphysis pubis, and manubriosternal articulation), the fundamental process appears to be inflammatory. At the junction of the intervertebral disc and the vertebral edge, chondrocytes undergo calcification and become vascularized and subsequently ossified, with production of syndesmophytes that extend from one vertebral body to another (Fig. 10.2). Eventually, extensive bony ankylosis of the entire articulation may be evident.

Entheses Inflammation at ligamentous and tendinous attachments (enthesitis) is a prominent feature of ankylosing spondylitis and the other spondyloarthropathies, and it is associated with erosion and eburnation of the subjacent bone. On radiographs, poorly defined erosive abnormalities with surrounding bone sclerosis are observed. As the lesions heal, the sclerosis decreases, the osseous surface becomes less irregular, and well-­defined bony excrescences appear (Fig. 10.3).

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SECTION 2  Articular Disorders

TABLE 10.1  Terminology Commonly

Applied to Spinal Abnormalities in Ankylosing Spondylitis

A

B

Fig. 10.2  Cartilaginous articulations: general radiographic and pathologic abnormalities of the discovertebral junction. Radiograph (A) and photograph (B) of a sagittal section of the spine (the left side of each picture is anterior) reveal typical syndesmophytes (arrowheads) extending from one vertebral body to another. Note their vertical direction and slender configuration.

Fig. 10.3  Enthesitis: general radiographic abnormalities of the ischial tuberosities. Radiographic findings include cortical irregularity, sclerosis, and irregular hyperostosis of the ischial tuberosities at the hamstring tendon footprints (arrows). Note sacroiliac joint fusion (arrowheads).

RADIOGRAPHIC AND PATHOLOGIC ABNORMALITIES AT SPECIFIC SITES Sacroiliac Joint KEY CONCEPTS  • B ilateral sacroiliitis occurs early and eventually is uniform and symmetric. • Iliac involvement about the sacroiliac joints predominates. • Complete bone ankylosis of the joint can result.

Term

Definition

Osteitis

Enthesopathy occurring at the discovertebral junction associated with erosion, bone sclerosis, and syndesmophytes

“Shiny corner sign”

Increased radiodensity of the corners of the vertebral body related to osteitis

Squaring

Straightened or convex anterior margin of the vertebral body related to erosion

Syndesmophyte

Ossification within the annulus fibrosus leading to thin, vertical, radiodense areas

Bamboo spine

Undulating vertebral contour caused by extensive syndesmophytes

Discitis

Erosive abnormalities of the discovertebral junction related to several mechanisms

Discal ballooning

Biconvex shape of the intervertebral disc related to osteoporotic deformity of the vertebral body

Trolley-­track sign

Three vertical radiodense lines on frontal radiographs related to ossification of the supraspinous and interspinous ligaments and apophyseal joint capsules

Dagger sign

Single central radiodense line on frontal radiographs related to ossification of the supraspinous and interspinous ligaments

Sacroiliitis is the hallmark of ankylosing spondylitis. It occurs early in the course of the disease. Although an asymmetric or, rarely, unilateral distribution may be evident on the initial radiographic examination, radiographic changes at later stages of the disease are bilateral and symmetric in about 90% of patients. Changes in the sacroiliac joint occur in both the synovial and ligamentous (superior and posterior) portions, predominating in the ilium. Initial changes consist of patchy periarticular osteoporosis and loss of definition, superficial erosion, and focal sclerosis of subchondral bone. A poorly defined subchondral bone plate is an important radiographic sign of sacroiliitis that is not observed in degenerative sacroiliac joint disease. Further erosive changes lead to considerable fraying of the osseous surface and widening of the interosseous space. As proliferative bony changes in the sacroiliac joint become more prominent, irregular bony bridges traverse portions of the articular cavity (Fig. 10.4). Subsequently, complete bone ankylosis of the joint can be observed. In late stages of the disease, bone sclerosis about the involved sacroiliac joints may disappear.

Spine KEY CONCEPTS  • S ee Table 10.1. • S ites of spine involvement include the discovertebral junctions, apophyseal joints, costovertebral joints, posterior ligamentous attachments, and atlantoaxial joints. • Although initially apparent at the thoracolumbar and lumbosacral junctions, changes can eventually be noted throughout the vertebral column. • Radiographic descriptions of abnormal ossification include the dagger sign, the trolley-track sign, and bamboo spine.

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B

A

C

D Fig. 10.4  Abnormalities of the sacroiliac joint: radiographic stages (four different patients). (A) Initial abnormalities consist of bilateral and uniform involvement of the sacroiliac joints with erosion and sclerosis (arrows). At later stages (B through D), there is sclerosis, progressive joint space narrowing, and then decreased sclerosis, as the sacroiliac joints become fused.

Discovertebral Junction Osteitis. Focal destructive areas along the anterior margin of the discovertebral junction at the superior and inferior portions of the vertebral body are an early and significant feature of ankylosing spondylitis and have been termed Romanus lesions. Osseous erosion (osteitis) of the corners of the vertebral body when combined with bone formation results in loss of the normal concavity of the anterior vertebral surface and thus vertebral squaring (Fig. 10.5). This change in vertebral configuration is much easier to assess in the lumbar spine. As the erosions heal, reactive sclerosis produces whitening, or a “shiny corner” configuration (see Fig. 10.5). Syndesmophytosis. Erosive vertebral abnormalities are associated with bone formation that extends across the margin of the intervertebral disc (Fig. 10.6). Thin vertical outgrowths are termed syndesmophytes and represent ossification of the annulus fibrosus itself. Syndesmophytes predominate on the anterior and lateral aspects of the spine. The vertical nature of the outgrowths and their connection to the vertebral edges allow their differentiation from spinal osteophytes (which are triangular and arise several millimeters from the discovertebral junction) and from the paravertebral ossification of psoriatic arthritis and reactive arthritis (which begins at a distance from the vertebral body and intervertebral disc). In the later phases of ankylosing spondylitis, extensive syndesmophytes produce the undulating vertebral contour that is termed the bamboo spine (Fig. 10.7). Discovertebral erosions and destruction. Destructive foci that appear throughout the discovertebral junction in ankylosing spondylitis, termed Andersson lesions, can be localized to one or two areas or can involve the

entire junction (Fig. 10.8). Lesions localized to the central subchondral portions of the discovertebral junction can be observed in ankylosed and nonankylosed spines. Histologic evaluation confirms the presence of intraosseous discal displacement (Schmorl, or cartilaginous, nodes) in many cases. Radiographic examination outlines irregularity of the central portion of the superior and inferior vertebral margins, and radiolucent areas with surrounding bone sclerosis are present in the vertebral bodies. Localized peripheral discovertebral lesions can also be caused by discal displacement, although inflammation in the outer fibers of the annulus fibrosus related to the spondylitic process may play a role in the development of these lesions. Destruction of the entire discovertebral junction of two neighboring vertebral bodies occurs almost exclusively in patients with advanced ankylosis (Fig. 10.9). Many patients relate a history of significant trauma, and radiographs, computed tomography (CT), or MR imaging obtained at the time of injury may reveal an associated fracture through the ankylosed apophyseal articulations, the neighboring articular processes, or, infrequently, the laminae or spinous process. Serial radiographs indicate an initial fracture of the spine and the subsequent development of bone destruction and sclerosis. An ankylosed spine in the later stages of this disease is prone to fracture, a vulnerability that is accentuated by adjacent vertebral osteoporosis (Fig. 10.10). The cervical spine is especially susceptible to fracture (60% to 75% of fractures), and neurologic complications or death may result. Conversely, fractures in the thoracic and lumbar spine in ankylosing spondylitis are often unrecognized clinically. Hyperextension injuries lead to spinal fractures that begin anteriorly in the vertebral body or, more commonly, the intervertebral disc; hyperflexion injuries produce spinal fractures that

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SECTION 2  Articular Disorders

Fig. 10.5  Osteitis: radiographic abnormalities. Osseous erosion and sclerosis have produced whitening of the corners and margins along the anterior surfaces of the vertebrae (arrows) with straightening of the anterior vertebral surface (arrowhead). Note sclerosis and fusion of the lumbar spine facet joints.

A

Fig. 10.7  Bamboo spine: radiographic abnormalities. Lumbar spine radiograph shows smooth, undulating syndesmosphytes creating the appearance of bamboo (arrows). Facet joint fusion is also present, as is osseous fusion of the sacroiliac joints (arrowheads).

B

Fig. 10.6  Syndesmophytes: radiographic abnormalities. (A) Lumbar spine and (B) cervical spine radiographs show bridging syndesmophyte formation (arrow) that extends in a vertical fashion from one vertebral body to the next. Note facet joint fusion.

CHAPTER 10  Ankylosing Spondylitis

A

B

191

C

Fig. 10.8  Discovertebral erosion and destruction: types of lesions. (A) Localized central discovertebral lesions. Defects with surrounding eburnation in the central portion of the discovertebral junction may reflect intraosseous displacement of disc material (cartilaginous nodes). (B) Localized peripheral discovertebral lesions. Defects may occur on the anterior or posterior aspect of the discovertebral junction. Their cause is obscure; they may be related to kyphosis with discal injury, cartilaginous node formation, or enthesitis. (C) Extensive central and peripheral discovertebral lesions. Destruction of the entire discovertebral junction is frequently the result of either widespread enthesitis or improper fracture healing.

Fig. 10.10  Spinal fractures. Acute midthoracic spinal fracture (arrows) is associated with subluxation.

A

B

Fig. 10.9  Discovertebral erosion and destruction: central and peripheral lesions—improper fracture healing or pseudarthrosis. (A) Lateral radiograph reveals a typical pseudarthrosis of the lower thoracic spine characterized by extensive osseous resorption and sclerosis (arrows). The appearance simulates that of an infection. (B) Sagittal reformatted computed tomography image shows the fracture to better advantage.

commence in the posterior osseous elements of the vertebra. Many of the resulting fractures become displaced. With continued movement at the fracture site, however, fibrous union can occur and result in improper fracture healing, or what has been labeled a pseudarthrosis. Discal calcification. Central or eccentric circular or linear calcific collections may appear within the intervertebral disc at single or multiple sites (Fig. 10.11). Similar deposits accompany other conditions of the vertebral column that are characterized by ankylosis, such as diffuse idiopathic skeletal hyperostosis (DISH) and juvenile idiopathic arthritis. Osteoporosis. In many patients with ankylosing spondylitis of long duration, osteoporosis of the vertebral bodies becomes apparent and, later, sometimes severe.

Apophyseal Joint Apophyseal joint inflammation is an essential abnormality in ankylosing spondylitis, and some investigators think that apophyseal joint

disease, including ankylosis, occurs before syndesmophyte formation. Further, an inverse relationship may exist between the extent of apophyseal joint involvement and the size of the syndesmophytes at the corresponding spinal level. Poorly defined bone erosions of apophyseal joints in the lumbar, thoracic, and cervical segments of the spine are accompanied by reactive subchondral bone formation. In any segment of the spine, apophyseal joint space narrowing is common as the disease process continues. Subsequently, apophyseal joint osseous fusion and capsular ossification are frequent (see Fig. 10.6), especially in the cervical spine (Fig. 10.12). The appearance is reminiscent of that in juvenile idiopathic arthritis, although hypoplasia of the vertebral bodies and intervertebral disc spaces, a prominent finding in juvenile idiopathic arthritis, is not observed in ankylosing spondylitis.

Costovertebral Joints The costovertebral joints may demonstrate erosion, sclerosis, and ankylosis (Fig. 10.13). Indistinctness and erosion of subchondral bone, bone sclerosis, and partial or complete osseous fusion are more easily defined with CT scanning.

Posterior Ligamentous Attachments Lesions affecting the posterior ligamentous attachments include calcification and ossification, producing the dagger sign, (Fig. 10.14) and subligamentous erosion.

Atlantoaxial Articulations Inflammatory changes of the synovial and adjacent ligamentous structures can lead to erosion of the dens. Although atlantoaxial subluxation can be observed in patients with ankylosing spondylitis, the frequency of this complication appears to be less than that in rheumatoid arthritis.

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SECTION 2  Articular Disorders

Fig. 10.13  Costovertebral joint ankylosis. Axial CT scan of a thoracic vertebra in a patient with ankylosing spondylitis reveals bone erosions and partial bone ankylosis (arrowhead) of the costovertebral joints on one side. Note the involvement of the ipsilateral rib with cortical thickening (arrows). Similar abnormalities may occur in osteoarthrosis.

Fig. 10.11  Discal calcification and ballooning. Long-­standing ankylosing spondylitis is characterized by syndesmophytosis, apophyseal joint ankylosis, discal calcification (arrows), osteoporosis, and ballooning, or biconvexity, of the intervertebral disc.

Fig. 10.12  Apophyseal joint ankylosis. In the cervical spine, note the apophyseal joint narrowing and fusion (arrow) extending from C2 to C7. Syndesmophytes (arrowhead) and osteoporosis are also seen.

Fig. 10.14  Posterior spinal ligamentous ossification. Frontal radiograph of the lumbar spine reveals ossification of the interspinous and supraspinous ligaments, which is producing a vertical central ossification (arrow), the dagger sign. Note osseous fusion of the sacroiliac joints (arrowheads).

CHAPTER 10  Ankylosing Spondylitis

193

Complications of Spinal Involvement

Additional Pelvic Sites

Neurospinal complications, including spinal cord compression and even death, are a recognized though infrequent manifestation of ankylosing spondylitis. Vertebral fractures, especially in the cervical region, are associated with significant morbidity and mortality related to deformity of the cord, as well as hematomas. Atlantoaxial instability, in either a horizontal or a vertical direction, can produce neurologic deficit and may be fatal. Spondylodiscitis has been associated with compression of the cord or nerve roots, especially in the lumbar segment. Although the mechanism is not clear, spinal stenosis is being recognized with increasing frequency in patients with ankylosing spondylitis. The cauda equina syndrome is also observed in some patients with ankylosing spondylitis, occurring late in the course of the disease. Typical clinical findings include cutaneous sensory impairment of the lower limbs and perineum with sphincter disturbances. Widening of the neural canal in the lumbar segment, dilatation of the dural sac, and thecal diverticula may also be seen (Fig. 10.15).

Enthesopathy, especially enthesitis, is especially prominent in certain pelvic sites, such as the ischial tuberosities (Fig. 10.17), iliac crests, and sacroiliac spaces above the true synovial joints; similar abnormalities occur at extrapelvic sites, such as the femoral

Symphysis Pubis Alterations of the symphysis pubis (Fig. 10.16) have been described in about 20% of patients with ankylosing spondylitis. These alterations simulate those occurring at the discovertebral junction, as both the symphysis pubis and discovertebral junction are cartilaginous joints. Bone erosion and sclerosis dominate.

A

Fig. 10.16  Abnormalities of the symphysis pubis. Note the narrowing and osseous fusion of the symphysis pubis with sclerosis of parasymphyseal bone.

B

Fig. 10.15  Abnormalities of the lumbar spine. (A) T1-­weighted and (B) fluid sensitive sagittal MR images of the lumbar spine show widening of the neural canal in the lumbar segment and dilatation of the dural sac (arrow).

194

SECTION 2  Articular Disorders

trochanters (see Fig. 10.17), humeral tuberosities, inferior clavicular margin at the site of attachment of the coracoclavicular ligament, anterior surface of the patella, and plantar aspect of the calcaneus. Osseous erosion with poorly defined bone margins and reactive sclerosis are the observed radiographic alterations, similar to those occurring in psoriatic arthritis, reactive arthritis, and inflammatory bowel disease.

Hip A bilateral (93%) and symmetric (73%) distribution, with concentric joint space narrowing (50%) and osteophytosis (58%), is characteristic (Table 10.2). An early and distinctive abnormality is

an osteophyte, or bump, on the lateral aspect of the femoral head. Osteophytes subsequently create a collar of bone around the femoral neck at the margin of the articular surface. Subsequent diffuse, or concentric, joint space narrowing produces axial migration of the femoral head with respect to the acetabulum. Protrusio acetabuli can eventually occur (Fig. 10.18). The combination of concentric diminution of the articular space and osteophytosis is characteristic of hip disease in ankylosing spondylitis, although it also may be observed in calcium pyrophosphate dihydrate crystal deposition disease, Paget disease, and, infrequently, uncomplicated osteoarthrosis. Concentric joint space narrowing is also seen in rheumatoid arthritis, but osteophytosis is not generally prominent in this disease. In some patients with ankylosing spondylitis, excessive heterotopic ossification following hip arthroplasty is encountered.

Glenohumeral Joint With the exception of the hip, the glenohumeral joint is the peripheral articular site most frequently affected in patients with longstanding ankylosing spondylitis (30% of patients). The abnormalities are more commonly bilateral than unilateral. Osteoporosis, diffuse joint space narrowing, and erosive changes, predominantly in the superolateral aspect of the humeral head, simulate the changes seen in rheumatoid arthritis. In some spondylitic patients, the entire outer aspect of the humerus is destroyed—the “hatchet” sign (Fig. 10.19).

Calcaneus Although clinically manifested heel abnormalities are infrequent in ankylosing spondylitis, radiographic changes of the calcaneus are common (Fig. 10.20). Bilateral abnormalities predominate. Well-­defined plantar or posterior calcaneal enthesophytes are a common manifestation but are similar in appearance to those in a normal population. Retrocalcaneal swelling (related to bursitis), posterior calcaneal erosion, and Achilles tendon thickening are also frequent findings. Bony erosion and proliferation resulting in poorly defined enthesophytes at the site of ligamentous attachment to bone on the inferior surface of the calcaneus are identical to the findings of psoriatic arthritis and reactive arthritis.

Fig. 10.17  Enthesitis. Osseous irregularity, bone proliferation, and reactive sclerosis are noted at the tendon attachments on the greater trochanter and ischial tuberosity (arrows). Note osseous fusion of the sacroiliac joint (arrowhead).

COEXISTENCE WITH OTHER DISORDERS The well-­documented association of ankylosing spondylitis and certain inflammatory bowel disorders, such as ulcerative colitis and Crohn disease, is discussed in Chapter 12.

TABLE 10.2  Differential Diagnosis of Hip Involvement Disease

Typical Distribution

Femoral Head Migration Osteophytosis

Miscellaneous Findings

Ankylosing spondylitis

Bilateral, symmetric

Axial

Lateral aspect of femur, collar at femoral head–femoral neck junction

Cysts, bony ankylosis, protrusion deformity, postoperative heterotopic ossification

Rheumatoid arthritis

Bilateral, symmetric

Axial

Rare

Osteoporosis, bone erosions, protrusion deformity

Osteoarthrosis

Unilateral or bilateral

Superior or medial

Lateral and medial Femoral and acetabular

Bone sclerosis, cysts, buttressing

Axial

Lateral and medial Femoral and acetabular

Bone sclerosis, cysts, collapse, fragmentation, calcification

Calcium pyrophosphate Bilateral, symmetric or dihydrate crystal deposition asymmetric disease

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A

195

B Fig. 10.18  Abnormalities of the hip: osteophytosis. (A) Observe the bone formation on the lateral margin of the femoral head (arrow), which has resulted in a bumpy contour. (B) The osteophytes have formed a collar about the femoral neck (arrows). Extensive concentric joint space narrowing has occurred. (From Dwosh IL, Resnick D, Becker MA. Hip involvement in ankylosing spondylitis. Arthritis Rheum. 1976;19:683.)

Fig. 10.19  Abnormalities of the shoulder: glenohumeral joint. Observe the large erosive abnormality along the lateral aspect of the humeral head (arrow), termed the hatchet sign. Also note bone proliferation (arrowheads) along the humeral cortex.

OTHER DIAGNOSTIC TECHNIQUES Ultrasonography Ultrasonography (US) may detect findings at the synovial articulations (effusion, synovial hypertrophy, hyperemia) of the extremities, but is relatively limited with regard to the axial skeleton given the depth of the joints and small joint recesses. Enthesitis of the extremities will appear as an abnormal hypoechoic tendon with possible hyperemia at its bony attachment showing cortical irregularity and erosions (Fig. 10.21). The latter findings assist in the differentiation

Fig. 10.20  Abnormalities of the calcaneus. Findings include erosion of the posterosuperior aspect of the bone (arrowhead) related to retrocalcaneal bursitis, as well as erosive and proliferative changes of the plantar aspect of the bone (arrow) related to an enthesopathy intimate with the attachment site of the plantar fascia.

between true inflammatory enthesitis and a degenerative enthesophyte with tendinosis, although correlation with radiography is extremely helpful to show the cortical erosion and cortical indistinctness at the tendon footprint in ankylosing spondylitis.

Scintigraphy Sacroiliac and spinal abnormalities in ankylosing spondylitis can be evaluated with radionuclide scintigraphy (Fig. 10.22). Qualitative analysis of the accumulation of bone-­seeking radiopharmaceutical preparations in the sacroiliac region is often difficult, however, because of

196

SECTION 2  Articular Disorders

the normal radionuclide activity in this location. In addition, uptake of the radionuclide in the sacrum and the sacroiliac joint is influenced by the age and sex of the patient, and ratios are not always uniform for the two sides of the body in normal persons. In patients with advanced disease, radionuclide uptake in the sacroiliac joints (as well as the spine) may not be abnormal. Single-­photon emission computed tomography (SPECT) also can be used for the detection of sacroiliitis, with reports indicating higher sensitivity than standard scintigraphy.

CT Scanning CT scanning has been found to be effective in the detection of some of the early alterations of the sacroiliac joints in ankylosing spondylitis. Compared with conventional radiography, CT scanning of these joints is more sensitive to the detection of bone erosions and bone sclerosis and more accurate in delineating joint space narrowing and intraarticular bone fusion (Fig. 10.23). Currently, however, MR imaging is judged superior to CT scanning in the assessment of early sacroiliitis. More clinically useful indications for CT scanning in patients with ankylosing spondylitis include detection of spinal fractures and spinal stenosis.

MR Imaging KEY CONCEPTS 

* Fig. 10.21  Ultrasonographic abnormalities in ankylosing spondylitis. US long axis to the distal Achilles tendon shows abnormal increased thickness and hypoechogenicity of the tendon (arrow), with cortical erosion (arrowhead) at the tendon attachment. Note fluid distention of the retrocalcaneal bursa (asterisk).

A

• F ocal subchondral bone marrow edema, although nonspecific, is the earliest sign of erosion at the sacroiliac joints. • Sacroiliac joint effusion and diffuse subchondral bone marrow edema are characteristic findings. • Chronic sacroiliitis is characterized by subchondral fatty marrow.

The role of MR imaging in the assessment of patients with ankylosing spondylitis has expanded greatly such that this imaging method is often employed after conventional radiography, especially in early stages of the disorder and when radiographs are not diagnostic. The major indications for MR imaging in ankylosing spondylitis relate to the assessment of the sacroiliac joints, spine, and entheses, as well as of the effects of therapy.

B Fig. 10.22  Scintigraphic abnormalities in ankylosing spondylitis. (A) In this patient with typical spondylitic changes in the sacroiliac joints, technetium-99m ­ pyrophosphate radionuclide scintigraphy shows marked increased focal uptake. Uptake about the hip corresponds to enthesitis. (B) In another patient with long-­ standing ankylosing spondylitis who had been injured in a fall, a focal area of markedly increased activity on bone scan corresponds to the site of a fracture and pseudarthrosis. The sacroiliac joints are ankylosed and are normal on scintigraphy.

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A

197

spondyitis. An additional finding seen in ankylosing spondylitis is the presence of high T1 intraarticular signal. Its sensitivity to bone erosions and joint space narrowing or ankylosis is debated and probably lower than the sensitivity of CT scanning to these findings. Of interest, the MR imaging appearance of inflammatory changes about the sacroiliac joints (as well as in the vertebral bodies) can change with time as fat accumulation at sites of inflammation is encountered (Fig. 10.25). Later, osseous sacroiliac joint fusion is well demonstrated on MR images (Fig. 10.26). With regard to the spine, MR imaging is useful in the assessment of inflammatory changes at the discovertebral joints (i.e., Romanus and Andersson lesions), the corners of the vertebral body (i.e., osteitis) (Fig. 10.27), and the apophyseal joints and spinous processes. Finally, MR imaging is effective in the identification of enthesitis, not just in the spine but elsewhere, including the innominate bones, femora, and other sites (Fig. 10.28). Although the choice of a small field of view is a general principle of MR imaging, large field-­of-­view images or even whole body images have been used to assess larger regions of the skeleton in patients with ankylosing spondylitis. In this regard, disease activity in the sacroiliac joints, spine, and entheses can be determined during a single examination. MR imaging has been applied successfully to the evaluation of spondylitic patients with the cauda equina syndrome. Dorsally situated arachnoid diverticula are directly visualized with this method. The fluid contents of the diverticula are well demonstrated, as are the accompanying osseous erosions of the posterior elements and bodies of affected vertebrae.

DIFFERENTIAL DIAGNOSIS Sacroiliitis

B Fig. 10.23  CT scanning in ankylosing spondylitis: sacroiliitis (two different patients). (A) An oblique axial image through the lower portion of the sacroiliac joint shows bilateral articular abnormalities, greater on the right side. These abnormalities consist of joint surface irregularity and erosion in the ilium, along with associated new bone formation. (B) Axial CT image in another patient shows narrowing of and sclerosis about the sacroiliac joints with partial osseous fusion (arrows). (A, Courtesy T. Learch, MD, Los Angeles, CA.)

With regard to the sacroiliac joints, most MR imaging protocols employ a true coronal imaging plane of the sacrum and a second imaging plane at right angles to the first plane. T1-­weighted sequences and fluid-­sensitive sequences, such as fat-­suppressed T2-­weighted or short-­tau inversion recovery (STIR) sequences, are standard. The role of intravenous injection of a gadolinium-­containing agent in the assessment of the sacroiliac joints (or spine) is controversial, with some investigators indicating that such injection is not needed. The findings of sacroiliac joint involvement vary according to the stage of the disease. MR imaging is especially sensitive to inflammation of these joints, manifest as a joint effusion and high signal on fluid-­ sensitive images involving the subchondral bone marrow (Fig.10.24). Focal periarticular marrow changes are often non-specific; however, more extensive high T2 signal is characterstic of ankylosing

The sacroiliac joint abnormalities in ankylosing spondylitis must be differentiated from those accompanying other disorders (Table 10.3). This can be accomplished by analyzing both the distribution and the morphology of the articular changes. Classically, a bilateral and symmetric distribution is observed in ankylosing spondylitis. Although a similar pattern may be evident in other spondyloarthropathies, asymmetric or, infrequently, unilateral alterations may accompany reactive arthritis and psoriatic arthritis. A bilateral and symmetric distribution is also associated with the sacroiliitis of inflammatory bowel disease (ulcerative colitis, Crohn disease, Whipple disease). In rheumatoid arthritis, sacroiliac articular abnormalities are generally absent or minor. Bilateral and symmetric alterations are also encountered in hyperparathyroidism (and renal osteodystrophy), osteitis condensans ilii, gouty arthritis, and osteoarthrosis. Unilateral abnormalities are most typical in infection. Poorly defined erosive abnormality with adjacent sclerosis (particularly in the ilium), associated joint space narrowing, intraarticular osseous fusion, and ligamentous ossification is the characteristic appearance of sacroiliac joint disease in classic ankylosing spondylitis and in the sacroiliitis of inflammatory bowel disease. In psoriatic arthritis and reactive arthritis, extensive bony eburnation may be unaccompanied by intraarticular osseous fusion. Subchondral resorption of bone, predominantly in the ilium, in conjunction with primary or secondary hyperparathyroidism leads to irregularity of the osseous surface, adjacent bone sclerosis, and widening of the interosseous joint space, that may simulate inflammatory sacroiliitis. In osteitis condensans ilii, a triangular segment of bony sclerosis is evident in the inferior aspect of the ilium. In chronic tophaceous gouty arthritis, large, gouged-­out defects with surrounding sclerosis are observed, whereas in osteoarthrosis, joint space narrowing, bony sclerosis, and anterior osteophytes are typical. Paraarticular bridging osteophytes and

198

A

SECTION 2  Articular Disorders

B Fig. 10.24  Acute sacroiliitis: MR imaging. (A) T1-­weighted and (B) fluid-­sensitive axial MR images show bilateral sacroiliac joint effusions, subchondral bone erosions, and diffuse periarticular bone marrow edema (arrows).

Fig. 10.25  Remote sacroiliitis and periarticular fat deposition: MR imaging. (A) Coronal T1-weighted and (B) axial fluid-sensitive MR images show bilateral periarticular fat signal about the sacroiliac joints (arrows), which show cortical irregularity and erosions.

Fig. 10.26  Sacroiliiac joint fusion: MR imaging. T1-­weighted MR image shows bilateral mature osseous fusion across the sacroiliac joints (arrows).

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A

199

B

Fig. 10.27  Lumbar osteitis: MR imaging. (A) T1-­weighted and (B) fluid-­sensitive sagittal MR images show focal osteitis of the corners of several vertebral bodies (arrows).

ligamentous ossification are the usual sacroiliac joint findings in DISH. The diffuse or uniform involvement of the sacroiliac joints and joint space widening are key radiographic features that also differentiate sacroiliitis from osteoarthritis.

Spondylitis Spinal abnormalities in classic ankylosing spondylitis initially appear in the thoracolumbar and lumbosacral junctions, and may subsequently extend throughout the thoracic and lumbar spine and into the cervical region. An identical distribution is encountered in the spondylitis of inflammatory bowel disease. Although the entire vertebral column may be altered in psoriatic arthritis and reactive arthritis, spotty involvement of the vertebral column is also encountered. Spondylitis without sacroiliitis is relatively rare in classic ankylosing spondylitis, although it may be observed in both psoriatic arthritis and reactive arthritis. The thin, vertically oriented syndesmophytes that are evident in most patients with classic ankylosing spondylitis and the spondylitis of inflammatory bowel disease differ considerably in appearance from the broad, asymmetric bony outgrowths seen in most patients with the spondylitis of psoriatic arthritis and reactive arthritis, the triangular outgrowths of spondylosis deformans, and the flowing anterolateral ossification of DISH (Table 10.4). The bony excrescences accompanying neuropathic osteoarthropathy, acromegaly, and fluorosis should not be confused with the syndesmophytes of ankylosing spondylitis. Vertebral (and sacroiliac joint) abnormalities in X-­linked hypophosphatemic vitamin D–resistant osteomalacia may simulate those in ankylosing spondylitis. Osteitis with sclerosis and erosion of the anterior corners of the vertebral bodies and squaring are encountered much more commonly in classic ankylosing spondylitis and the spondylitis of inflammatory bowel disease than in psoriatic arthritis and reactive arthritis. Discovertebral erosions and sclerosis, which are seen in

ankylosing spondylitis, are also observed in psoriatic arthritis. Similar lesions are evident in the cervical spine in patients with rheumatoid arthritis and throughout the spine in many disorders that are associated with cartilaginous (Schmorl) nodes. When severe, spondylitic erosions can simulate the findings in infectious spondylitis, although infection is generally localized to one or several spinal levels. Odontoid erosion and atlantoaxial subluxation are encountered in ankylosing spondylitis, usually in patients with long-­standing disease. Similar findings are observed in psoriatic arthritis and, less commonly, in reactive arthritis. In rheumatoid arthritis, these findings are combined with other diagnostic features in the cervical spine. In the cervical spine, the widespread apophyseal joint ankylosis accompanying ankylosing spondylitis resembles the findings in juvenile idiopathic arthritis. In the latter disorder, associated hypoplasia of the vertebral bodies and intervertebral discs is distinctive. Abnormalities of the cervical spine in other diseases can generally be differentiated from those in ankylosing spondylitis (Fig. 10.29).

Abnormalities of Extraspinal Synovial Articulations The abnormalities in the synovial joints of the appendicular skeleton in ankylosing spondylitis can resemble those in other articular disorders, with some differentiating characteristics (Table 10.5).

Enthesopathy Bony erosion with proliferation at the site of the osseous attachment of ligaments and tendons (i.e., enthesitis) is a typical lesion of ankylosing spondylitis, psoriatic arthritis, and reactive arthritis. Enthesopathy is less prominent in rheumatoid arthritis.

200

SECTION 2  Articular Disorders

TABLE 10.3  Distribution of Sacroiliac Joint

Abnormalities in Various Disordersa Bilateral Symmetric Distribution

Disorder

A

Bilateral Asymmetric Unilateral Distribution Distribution

Ankylosing spondylitis

+

–

–

Psoriatic spondylitis

+

+

+

Reactive arthritis

+

+

+

Inflammatory bowel disease

+

–

–

Rheumatoid arthritis

–

+

+

Osteitis condensans ilii

+

–

–

Hyperparathyroidism

+

–

–

Gouty arthritis

+

+

+

Osteoarthrosis

+

+

+

Infection

–

–

+

aOnly

the most typical patterns of distribution are indicated.

TABLE 10.4  Bony Outgrowths of the Spine Outgrowth

B

C Fig. 10.28  Pelvic enthesitis. (A) T1-­weighted and (B) fluid-­sensitive coronal MR images show pronounced bone marrow edema deep to the proximal hamstring tendon attachments with fluid signal at the enthesis, corresponding to ill-­defined cortical irregularity and bone proliferation, wel demonstrated on radiography (C) (arrows).

Definition

Representative Disorders Appearance

Syndesmophyte Ossification of the Ankylosing annulus fibrosus spondylitis Alkaptonuria

Vertical outgrowth extending from the edge of one vertebral body to the next

Osteophyte

Triangular outgrowth located several millimeters from the edge of the vertebral body

Hyperostosis at the Spondylosis attachment of deformans annular fibers

Flowing anterior Ossification of the Diffuse idiopathic Undulating skeletal outgrowth along ossification intervertebral hyperostosis the anterior and disc, anterior lateral aspects of longitudinal the spine ligament, and paravertebral connective tissue Paravertebral ossification

Ossification of Psoriatic paravertebral spondylitis connective tissue Reactive arthritis

Poorly defined or well-­defined outgrowth separated from the edge of the vertebral body and the intervertebral disc

201

CHAPTER 10  Ankylosing Spondylitis

A

B

C

E

D

F

Fig. 10.29  Differential diagnosis of cervical spine abnormalities. (A) Ankylosing spondylitis is characterized by syndesmophytes (arrows) and apophyseal joint ankylosis. (B) Psoriatic spondylitis leads to bony outgrowths (arrows) that predominate in the lower cervical spine. The apophyseal joints appear normal. (C) Diffuse idiopathic skeletal hyperostosis (DISH) is accompanied by extensive bone deposition on the anterior portion of the vertebral column. (D) Sternocostoclavicular hyperostosis is characterized by exuberant bone formation anteriorly and centrally, which obliterates the interface between vertebral bodies and intervertebral discs, and by apophyseal joint ankylosis. (E) Juvenile idiopathic arthritis is associated with hypoplasia of the vertebral bodies and intervertebral discs, apophyseal joint ankylosis, and a predilection for the upper cervical region. (F) Acromegaly leads to bone deposition that resembles that of spondylosis deformans and an increase in the anteroposterior dimension of the vertebral bodies.

TABLE 10.5  Abnormalities of Synovial Articulations

Disease

Symmetric Involvement

Soft Tissue Swelling

Osteoporosis

Joint Space Narrowing

Bony Ankylosis

Erosions and Cysts

Bony Proliferation or Whiskering

Ankylosing spondylitis

±

+

±

+

+

+

+

Rheumatoid arthritis

+

+

+

+

±

+

–

Psoriatic arthritis

±

+

–

+

+

+

+

Reactive arthritis

–

+

±

+

+

+

+

Gouty arthritis

±

+

–

±

–

+

+*

Septic arthritis

–

+

+

+

+

+

+†

*Irregular lips of bone are apparent. †Poorly defined fraying of bone is seen.

FURTHER READING Cawley MID, Chalmers TM, Kellgren JH, et al. Destructive lesions of vertebral bodies in ankylosing spondylitis. Ann Rheum Dis. 1972;31:345. Chang EY, Chen KC, Huang BK, Kavanaugh A. Magnetic resonance imaging of rheumatological diseases. Radiographics. 2016;36:1849. De Hooge M, van den Berg R, Navarro-­Compan V, et al. Magnetic resonance imaging of the sacroiliac joints in the early detection of spondyloarthritis: no added value of gadolinium compared with short tau inversion recovery sequence. Rheumatology. 2013;52:1220. Diekhoff T, Lambert R, Hermann KG. MRI in axial spondyloarthritis: understanding an “ASAS-positive MRI” and the ASAS classification criteria. Skeletal Radiology. 2022;51:1721. Dwosh IL, Resnick D, Becker MA. Hip involvement in ankylosing spondylitis. Arthritis Rheum. 1976;19:683. Fatemi G, Gensler LS, Learch TJ, et al. Spine fractures in ankylosing spondylitis: a case report and review of imaging as well as predisposing factors to falls and fractures. Semin Arthritis Rheum. 2014;44:20. Gelman MI, Umber JS. Fractures of the thoracolumbar spine in ankylosing spondylitis. AJR Am J Roentgenol. 1978;130:485.

Ginsburg WN, Cohen MD, Miller GM, et al. Posterior vertebral body erosion by cauda equina syndrome: an unusual manifestation of ankylosing spondylitis. J Rheumatol. 1997;24:1417. Jang JH, Ward MM, Rucker AN, et al. Ankylosing spondylitis: patterns of radiographic involvement – a re-­examination of accepted principles in a cohort of 769 patients. Radiology. 2011;258:192. Jevtic V, Kos-­Golja M, Rozman B, et al. Marginal erosive discovertebral “Romanus” lesions in ankylosing spondylitis demonstrated by contrast enhanced Gd-­DTPA magnetic resonance imaging. Skeletal Radiol. 2000;29:27. Kim NR, Choi J-­Y, Hong SH, et al. “MR corner sign”: value for predicting presence of ankylosing spondylitis. AJR. 2008;191:124. Kozin F, Carrera GF, Ryan LM, et al. Computed tomography in the diagnosis of sacroiliitis. Arthritis Rheum. 1981;24:1479. Laloo F, Herregods N, Varkas G, et al. MRI of the axial skeleton in spondyloarthritis. European Radiology. 2017;27:2024. Lukas C, Braun J, van der Heijde D, et al. Scoring inflammatory activity of the spine by magnetic resonance imaging in ankylosing spondylitis. J Rheumatol. 2007;34:862. McEwen C, DiTata D, Lingg C, et al. Ankylosing spondylitis and the spondylitis accompanying ulcerative colitis, regional enteritis, psoriasis, and Reiter’s disease: a comparative study. Arthritis Rheum. 1971;14:291.

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SECTION 2  Articular Disorders

Mitchell MJ, Sartoris DJ, Moody D, et al. Cauda equina syndrome complicating ankylosing spondylitis. Radiology. 1990;175:521. Oostveen J, Prevo R, den Boer J, et al. Early detection of sacroiliitis on magnetic resonance imaging and subsequent development of sacroiliitis on plain radiography: a prospective, longitudinal study. J Rheumatol. 1999;26:1953. Pipikos T, Kassimos D, Angelidis G, et al. Bone single photon emission/ computed tomography in the detection of sacroiliitis in seronegative spondyloarthritis: a comparison with magnetic resonance imaging. Mol Imaging Radionucl Ther. 2017;26:101.

Resnick D. Inflammatory disorders of the vertebral column: seronegative spondyloarthropathies, adult-­onset rheumatoid arthritis, and juvenile chronic arthritis. Clin Imaging. 1989;13:253. Smith J. Update on ankylosing spondylitis: current concepts in pathogenesis. Curr Allergy Asthma Rep. 2015;15:489. Vinson EN, Major NM. MR imaging of ankylosing spondylitis. Semin Musculoskelet Radiol. 2003;7:103.

11 Psoriatic Arthritis S U M M A R Y O F K E Y F E AT U R E S • P  soriatic arthritis produces distinctive abnormalities of synovial and cartilaginous joints, as well as abnormalities of the tendon and ligament attachments to bone (i.e., entheses). • The classic manifestation is that of a polyarticular disorder with a predilection for the distal interphalangeal joints of the fingers, although a variety of other clinical patterns may be observed.

• M  arginal erosions at synovial articulations, bone proliferation, including periostitis, and inflammatory enthesitis are characteristic imaging findings. • Sacroiliitis is typically bilateral and may be asymmetric or symmetric.

INTRODUCTION

The clinical nature of the articular disease is diverse. Abnormalities may be dominant in the peripheral skeleton, axial skeleton, or both. A monoarticular, pauciarticular, or polyarticular distribution may be encountered, and virtually any joint can be affected, although the small joints of the hands and feet are reportedly involved in 25% to 50% of patients with arthritis. In the hands and feet, soft tissue enlargement in the form of a sausage digit may be seen. In some patients, low back complaints predominate as a result of involvement of the spine and the sacroiliac joints. Sacroiliitis has been reported in as many as 30% to 35% of psoriatic patients with arthritis. In some of these patients, the dominant clinical and imaging feature is enthesitis, especially related to the Achilles tendon, plantar fascia, and tendinous attachments on the greater trochanter of the femur. Indeed, enthesitis is a common initial manifestation of psoriatic arthritis (∼15% of patients), and its frequency increases further with disease chronicity.

  

For many years after the original descriptions of psoriatic arthritis in the late 19th century, the joint abnormalities associated with psoriasis were considered to be part of the spectrum of rheumatoid arthritis. Although clinical features of psoriatic arthritis that include joint pain, swelling, dysfunction, and structural damage resemble those of rheumatoid arthritis, it is now known that psoriatic arthritis possesses distinctive clinical, imaging, and serologic features. Furthermore, recent evidence suggests that immunologically and pathologically, psoriatic arthritis and rheumatoid arthritis are different diseases.

PREVALENCE AND SPECTRUM The reported frequency of psoriatic arthritis in persons with skin psoriasis is inconsistent, ranging from 5% to 35%. Although clinical features are variable and difficult to classify, some investigators have described five broad clinical varieties of psoriatic arthritis (Box 11.1): (1) polyarthritis characterized by distal interphalangeal joint involvement; (2) a deforming type of arthritis characterized by widespread ankylosis and, occasionally, arthritis mutilans; (3) a symmetric seronegative polyarthritis simulating rheumatoid arthritis but without its laboratory parameters; (4) monoarthritis or asymmetric oligoarthritis; and (5) sacroiliitis and spondylitis resembling ankylosing spondylitis. Characteristic imaging abnormalities accompany these five types of disease, with certain features that allow accurate diagnosis.

CLINICAL ABNORMALITIES Psoriatic arthritis usually manifests in adults, most typically between the ages of 40 and 50 years, although the occurrence of psoriatic arthritis in children is increasingly being recognized. In most adult patients, a long history of psoriatic skin disease is evident, although in 5% to 15% of persons, the articular abnormalities coincide with or even antedate the appearance of skin lesions. Articular disease is much more prevalent in patients with moderate or severe skin abnormalities. Nail abnormalities appear to correlate most closely with articular disease, and such changes are generally apparent in the same digit that has significant distal interphalangeal joint abnormalities. In approximately 2% of persons, nail involvement occurs without skin involvement.

RADIOGRAPHIC ABNORMALITIES KEY CONCEPTS  • S ee Box 11.2. • S ynovial articulations: erosions (initially marginal), with destruction and later possible bone ankylosis. • Inflammatory enthesitis: whiskering at tendon and ligament attachments. • Erosions at cartilaginous joints. • Periostitis. • Sausage digit: soft tissue swelling of a digit. • Pencil-and-cup deformity: chronic joint erosion and destruction, typically involving the interphalangeal joints. • Ivory phalanx: sclerosis of a distal phalanx, characteristically in the toes. • Sacroiliac joint: bone erosions, sclerosis, and fusion (bilateral, asymmetric or symmetric).

Distribution of Radiographic Abnormalities Psoriatic arthritis can affect synovial and cartilaginous joints and entheses in both the appendicular and the axial skeleton (Fig. 11.1). Although the articular distribution of psoriatic arthritis is variable, an asymmetric or even unilateral appearance is much more common in psoriatic arthritis than in rheumatoid arthritis, although widespread involvement of one side of the body is almost invariably associated with

203

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SECTION 2  Articular Disorders

BOX 11.1  Varied Patterns of Psoriatic

Arthritis*

Polyarthritis with distal interphalangeal joint involvement Symmetric seronegative polyarthritis simulating rheumatoid arthritis Monoarthritis or asymmetric oligoarthritis Sacroiliitis and spondylitis Arthritis mutilans * In addition, patients with psoriatic arthritis may have coincidental rheumatoid arthritis.

changes on the other side. Both upper extremity and lower extremity joints are affected in psoriatic arthritis; in contrast, reactive arthritis involves predominantly the joints of the lower extremity. The distal interphalangeal and proximal interphalangeal joints (as well as the metacarpophalangeal and metatarsophalangeal joints) of the hand and foot are commonly affected. Abnormalities of the phalangeal tufts and calcaneus are also characteristic. Significant abnormalities of the hip and shoulder are relatively uncommon. In the axial skeleton, sacroiliac joint and spinal abnormalities predominate.

General Radiographic Abnormalities See Fig. 11.2.

BOX 11.2  Characteristics of Psoriatic

Arthritis

Involvement of synovial and cartilaginous joints and entheses Asymmetric distribution more common than symmetric distribution Involvement of interphalangeal joints of the hands and feet Sacroiliitis and spondylitis with paravertebral ossification Bone erosion with adjacent bone proliferation Intraarticular bone ankylosis Destruction of phalangeal tufts Enthesitis

Soft Tissue Swelling Fusiform soft tissue swelling is frequently evident about involved joints and reflects the presence of synovial effusions of variable size and soft tissue edema. Sausage like swelling of entire digits (i.e., sausage digit) or diffuse swelling of all or part of an extremity also may be encountered.

Osteoporosis Osteoporosis is not a prominent feature of psoriatic arthritis, although it may be demonstrated in early phases of the disease.

Joint Space Narrowing or Widening The articular space may be narrowed or widened. In large joints, such as the knee, ankle, elbow, and hip, diffuse loss of joint space is identical to that observed in rheumatoid arthritis. In the small joints of the fingers and toes, severe destruction of marginal and subchondral bone can lead to considerable widening of the articular space. This finding is uncommon in rheumatoid arthritis but may be seen in gout, inflammatory osteoarthritis, and multicentric reticulohistiocytosis.

Bone Erosion Erosive abnormalities are prominent in psoriatic arthritis. Initially, erosions predominate in the marginal areas of the articulation, but as they progress, central areas are also affected. In the small joints of the hands and feet, destruction or whittling of the head of one phalanx may produce a small, blunt osseous surface that projects into the expanded base of a neighboring phalanx, reminiscent of a pencil-­and-­cup or cup-­and-­ saucer arrangement. Similar changes are encountered at metacarpophalangeal and metatarsophalangeal locations. In some patients with psoriatic arthritis, complete dissolution of large segments of apposing bones, fragmentation with osseous debris, and disorganization of the joint resemble the changes of neuropathic osteoarthropathy.

Bone Proliferation

Fig. 11.1  Psoriatic arthritis: distribution of radiographic abnormalities. The most typical sites of abnormality are the interphalangeal joints of the hand and foot, metacarpophalangeal and metatarsophalangeal joints, calcaneus, sacroiliac joint, and spine (arrows). Not uncommon are changes in the knee; ankle; manubriosternal, sternoclavicular, acromioclavicular, and costovertebral joints; symphysis pubis; and tendinous connections (entheses) of the pelvis, elbow, and wrist. Significant alterations of the hip and glenohumeral joint are relatively unusual (arrowheads).

As in the other spondyloarthropathies, proliferation of bone is a striking feature of psoriatic arthritis. Irregular excrescences create a spiculated, frayed, or paintbrush appearance. Bone proliferation probably relates to an exaggerated healing response of the injured bone. The osseous erosion in rheumatoid arthritis is generally not associated with adjacent bony deposition. Although bone proliferation may accompany erosions in gouty arthritis, the resulting excrescences are generally well defined. Periostitis in the metaphyses and diaphyses of bones is not uncommon in psoriatic arthritis, particularly in the hands and feet. In these locations, periosteal bone formation, probably related to tenosynovitis, may lead to significant cloaking of an entire phalanx or a portion of a metacarpal or metatarsal bone. This change may appear early in the disease course, in association with soft tissue swelling, before significant abnormalities occur in the adjacent articulations. Condensation of bone on the periosteal and endosteal surfaces of the cortex and

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B

A

205

C

Fig. 11.2  General radiographic abnormalities. (A–C) Classic radiographic changes are depicted about the distal interphalangeal joints in three patients with psoriatic arthritis. These changes include soft tissue swelling, lack of osteoporosis, joint space narrowing, osseous erosions with accompanying bone proliferation (solid arrows), osteolysis with a pencil-­and-­cup appearance (open arrow), and tuft resorption (arrowhead).

trabecular thickening in the spongiosa can cause an entire phalanx to appear radiodense. This latter appearance is termed the ivory phalanx and is most common in the terminal phalanges of the toes. Exuberant bone formation, especially in the hands and feet, has been characterized as a specific form of psoriatic arthritis, designated psoriatic onycho-­pachydermoperiostitis (i.e., POPP syndrome). In this syndrome, nail involvement and soft tissue thickening are associated findings. The resulting radiographic features, which include periostitis and bone sclerosis, simulate the appearance of other disorders, including infection, reactive arthritis, and bizarre parosteal osteochondromatous proliferation (BPOP syndrome). Intraarticular osseous fusion is another manifestation of bone proliferation in psoriatic arthritis, and it is particularly prominent in the hands and feet. Although intraarticular osseous fusion is also observed in inflammatory osteoarthritis, septic arthritis, and even rheumatoid arthritis (carpal and tarsal areas), it is an important radiographic sign of the spondyloarthropathies. Bone proliferation occurs at sites where tendons and ligaments insert on bones. These locations include the posterior and inferior surfaces of the calcaneus, femoral trochanters, ischial tuberosities, medial and lateral malleoli, ulnar olecranon, and anterior surface of the patella.

Tuft Resorption Resorption of the tufts of the distal phalanges of the hands and feet is characteristic of psoriatic arthritis. Soft tissue swelling and adjacent interphalangeal joint abnormalities are frequent. The nail of the involved digit is almost always affected.

Malalignment and Subluxation Deformities of the hands and feet can be encountered in some patients with psoriatic arthritis. Telescoping of one bone on its neighbor may lead to the opera-­glass hand. In this situation, excess skin may be folded

over the involved joints and produce a concertina-­like appearance. Ulnar deviation at the metacarpophalangeal joints, fibular deviation at the metatarsophalangeal joints, and boutonnière and swan-­neck deformities are not as common in psoriatic arthritis as in rheumatoid arthritis.

Radiographic Abnormalities at Specific Sites Hand

The destructive arthritis of the distal interphalangeal joints of the hand (see Fig. 11.2) is the best-­known manifestation of psoriatic arthritis. At these sites, bilateral symmetric or asymmetric changes or unilateral changes are observed. Initial erosions occur at the margins of the articulation (Fig. 11.3) and proceed centrally (Fig. 11.4). The resulting irregular osseous surfaces may become separated from each other as a consequence of the extensive nature of the erosive process. This lack of apposition of adjacent bony margins distinguishes the radiographic picture of psoriatic arthritis from that of osteoarthrosis, in which closely applied undulating bone surfaces are the rule. The adjacent proximal interphalangeal joints are frequently affected. The metacarpophalangeal joints may be relatively spared. At any altered interphalangeal site, radiographic findings may include separated, eroded, well-­demarcated bone margins; protrusion of a blunted and distorted osseous surface into an adjacent expanded one (pencil-­and-­cup appearance) (Fig. 11.5); irregular periosteal bone proliferation in the form of inflammatory enthesitis (whiskering) and diffuse periostitis (Fig. 11.6); and intraarticular osseous fusion.

Wrist Abnormalities in the wrist in psoriatic arthritis are not as frequent as those in the fingers and are rarely encountered without more typical distal changes. In addition to erosions at synovial articulations, exuberant periosteal new bone formation may be evident (POPP syndrome) (Fig. 11.7).

206

SECTION 2  Articular Disorders

Forefoot The forefoot is commonly affected in psoriatic arthritis (Fig. 11.8). Bilateral asymmetric changes predominate in the interphalangeal and metatarsophalangeal joints and are characterized by marginal erosions, bony proliferation, alterations in joint space (narrow or wide), and lack of osteoporosis. Extensive destruction of the interphalangeal joint of the great toe is more characteristic of this articular disorder than of any other disease. Osteolysis of tufts and the phalangeal and metatarsal shafts may be encountered. In the terminal phalanges, extensive new bone formation may lead to increased osseous density of the entire bone (ivory phalanx).

Calcaneus As in the other spondyloarthropathies, erosion and proliferation of the posterior or inferior surface of the calcaneus, or both, may be prominent in psoriatic arthritis (Fig. 11.9). Retrocalcaneal bursitis with subjacent erosion of the posterosuperior surface of the calcaneus is associated with surrounding bony proliferation.

Sacroiliac Joint

Fig. 11.3  Radiographic abnormalities of the hand. Early involvement in the hand shows marginal erosions with an ill-­defined, frayed appearance of the bone (arrows). Contrast this appearance with the adjacent normal metacarpophalangeal joint.

Sacroiliitis develops in 30% or more of patients with psoriatic arthritis, especially in patients with severe skin involvement. Bilateral abnormalities of the sacroiliac joint are much more frequent than unilateral changes in psoriatic arthritis. Although asymmetric findings may be apparent, symmetric abnormalities predominate. Sacroiliitis can appear without spondylitis. Radiographic sacroiliac joint changes include bone erosions and sclerosis, predominantly in the ilium, and widening of the articular space (Fig. 11.10). Although significant joint space diminution and bony ankylosis can occur, these findings (particularly bone ankylosis) are less prevalent than in classic ankylosing spondylitis or the spondylitis associated with inflammatory bowel disease.

Spine As in reactive arthritis, paravertebral ossification about the lower thoracic and upper lumbar segments can occur in psoriatic arthritis (Fig. 11.11). Initially, ossification appears as a thick and fluffy, or thin and curvilinear, radiodense region on one side of the spine that parallels the lateral surface of the vertebral bodies and the intervertebral discs. It extends progressively at a variable rate and eventually may produce a large and bulky outgrowth that merges with the underlying osseous and discal tissue. Its greater size, unilateral or asymmetric distribution, and its location farther away from the vertebral column distinguish paravertebral ossification from the typical syndesmophytosis of ankylosing spondylitis and inflammatory bowel disease. In addition to the pattern and distribution of bony outgrowths, other features of psoriatic spondylitis differ from those of classic ankylosing spondylitis. Osteitis and squaring of the anterior surfaces of the vertebral bodies are relatively infrequent in psoriatic arthritis. Although apophyseal joint space narrowing, sclerosis, and bony ankylosis may be seen, the frequency of these findings is much less than that in ankylosing spondylitis. In addition, cervical spine abnormalities (Fig. 11.12) may become striking in some patients with psoriatic arthritis.

OTHER DIAGNOSTIC TECHNIQUES Scintigraphy Fig. 11.4  Radiographic abnormalities of the hand. Interphalangeal joint changes consist of articular space narrowing, intraarticular bone ankylosis, marginal and central bone erosions, flexion contractures, and osteolysis of the phalangeal tufts. Metacarpophalangeal joint abnormalities, although less marked, include joint space narrowing, marginal bone erosions, and bone proliferation.

Scintigraphy with bone-­seeking radiopharmaceutical agents can delineate an articular abnormality of psoriatic arthritis before its appearance on radiographic examination. Increased radionuclide accumulation predominates at the interphalangeal, metacarpophalangeal, and metatarsophalangeal joints of the hands and feet; however, calcaneal, sacroiliac joint, and spinal uptake can be considerable. The asymmetric

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207

Fig. 11.5  Radiographic abnormalities of the hand: pencil-­ and-­ cup appearance. Radiographs show chronic erosive changes of the distal interphalangeal joint with a pencil-­and-­cup appearance (arrow). Note uniform joint space narrowing of the metacarpophalangeal joint (arrowhead) and diffuse soft tissue swelling of the finger. Pancompartmental abnormalities of the wrist are also evident.

nature of the scintigraphic alterations in psoriatic arthritis frequently permits its differentiation from rheumatoid arthritis.

Ultrasonography The role of ultrasonography (US) in the assessment of psoriatic arthritis is limited to superficial structures. Synovitis is characterized as hypoechoic synovial hypertrophy with increased flow on color Doppler imaging and may be found distending joint recesses (Fig. 11.13), tendon sheaths (Fig. 11.14), and bursae. Inflammatory enthesitis will appear as a cortical irregularity and possible erosions at a thickened tendon (Fig. 11.15) or ligament (Fig. 11.16) attachment with possible hyperemia on color Doppler imaging. Correlation with radiography is important to distinguish the fuzzy appearance of inflammatory enthesitis from degenerative enthesophytes because they may appear similar at US.

Magnetic Resonance Imaging

Fig. 11.6  Radiographic abnormalities of the hand: periostitis. Radiographs show diffuse periostitis of the distal metacarpal bone, proximal phalanx, and middle phalanx (arrows). Note uniform joint space narrowing and destructive changes at the metacarpophalangeal joint, and uniform joint space narrowing of the proximal interphalangeal joint of the third digit.

Magnetic resonance (MR) imaging in patients with psoriatic arthritis reveal alterations similar to those of rheumatoid arthritis, although extracapsular inflammation is a finding that may differentiate psoriatic from rheumatoid arthritis (Fig. 11.17). Importantly, however, the degree of bone proliferation and marrow edema about involved articulations is much greater in psoriatic arthritis and, in some cases, is profound, indicative of osteitis. Furthermore, MR imaging is effective in the detection of enthesitis in both the peripheral and the axial skeleton, and it allows the detection of tenosynovitis in cases of dactylitis. As in ankylosing spondylitis, MR imaging can be applied to the assessment of spondylitis and sacroiliitis, and large field-­of-­view MR imaging or total body MR imaging can serve as an effective screening method for psoriatic arthritis and can be used to follow the effect of treatment.

208

A

SECTION 2  Articular Disorders

B Fig. 11.7  Radiographic and ultrasonographic abnormalities of the wrist: periostitis. Radiograph (A) and ultrasonographic image (B) of dorsal aspect of the wrist show exuberant and diffuse periosteal new bone formation (arrows), which should not be interpreted as osteophytes or post­traumatic findings. Correlation with radiography is extremely helpful when interpreting the ultrasonographic findings.

Fig. 11.9  Abnormalities of the calcaneus. Retrocalcaneal bursitis is manifested as erosion of the posterosuperior aspect of the calcaneus (arrows). A large plantar calcaneal enthesophyte is identified.

Fig. 11.8  Radiographic abnormalities of the forefoot. Findings include joint space narrowing and bone ankylosis of multiple interphalangeal joints and osseous erosion and proliferation, particularly about the interphalangeal joint of the great toe. Note the tuft osteolysis and sclerosis of bone in multiple digits.

ADDITIONAL DISEASES OF SKIN AND JOINTS Certain cutaneous disorders are associated with clinical and radiographic findings of arthritis, which in some cases simulate those of psoriatic arthritis. These include acne fulminans, acne conglobate, hidradenitis suppurativa, and pyoderma gangrenosum. Pustular lesions of the skin, especially those affecting the hand and foot (e.g., pustulosis palmaris et plantaris), have been linked to a variety of skeletal abnormalities that may affect the tubular bones of the extremities and the axial skeleton. Classic sites of involvement include the clavicle, sternum, and upper ribs, although other sites, such as the

discovertebral junction, ilium, and parasymphyseal bones, also may be involved. A variety of names have been applied to these findings, influenced by the age of the person and the distribution of the alterations; these designations include sternocostoclavicular hyperostosis, chronic recurrent multifocal osteomyelitis (CRMO), and synovitis-­ acne-­pustulosis-­hyperostosis-­osteitis (SAPHO syndrome), discussed elsewhere in the book. Acro-­osteolysis may accompany a variety of dermatologic conditions in addition to psoriatic arthritis; they include mycosis fungoides, pityriasis rubra pilaris, epidermolysis bullosa, erythema elevatum diutinum, and ichthyosiform erythroderma.

DIFFERENTIAL DIAGNOSIS Other Spondyloarthropathies (Ankylosing Spondylitis, Reactive Arthritis) The radiographic findings in psoriatic arthritis are fundamentally similar to those in the other two spondyloarthropathies, ankylosing

CHAPTER 11  Psoriatic Arthritis

A

B

209

C

Fig. 11.10  Abnormalities of the sacroiliac joint. (A) Radiograph and (B) CT image show asymmetric abnormalities. The left sacroiliac joint reveals sclerosis with extensive erosive change, giving the joint space a widened appearance. Minimal changes are present on the right side. In a different patient (C) with bilateral asymmetric involvement, more advanced changes are present on the right, with partial osseous fusion.

Fig. 11.11  Radiographic abnormalities of the thoracic and lumbar spine. Bulky outgrowths appear (arrows) and merge with the underlying vertebral bodies and intervertebral discs. Note the asymmetric distribution with the outgrowths almost confined to the left side. Surgical clips are evident.

spondylitis and reactive arthritis (Table 11.1). In all three disorders, synovial joint involvement is characterized by the absence of osteoporosis and the presence of soft tissue swelling, joint space abnormality, osseous erosion, and bony proliferation. In psoriatic arthritis and ankylosing spondylitis, intraarticular bone ankylosis is not uncommon. In each of these spondyloarthropathies, abnormalities of the cartilaginous joints, such as the symphysis pubis and discovertebral junction, consisting of erosion and bony proliferation, may be observed. Similarly, each of these diseases may be associated with entheseal abnormalities. The distribution of articular abnormalities differs among psoriatic arthritis, reactive arthritis, and ankylosing spondylitis. In psoriatic arthritis, an asymmetric polyarticular disorder involving the upper and

Fig. 11.12  Radiographic abnormalities of the cervical spine. Note the erosions at the discovertebral junction and apophyseal joints (arrows) and syndesmophytes (arrowheads).

lower extremities, with a predilection for the interphalangeal joints of the hands and the metatarsophalangeal and interphalangeal joints of the feet, is observed. In reactive arthritis, asymmetric disease of the articulations of the lower extremity is most characteristic, whereas in ankylosing spondylitis, appendicular skeletal involvement is less prominent than axial skeletal involvement. Spinal and sacroiliac joint alterations occur in psoriatic arthritis, reactive arthritis, and ankylosing spondylitis. In the first two disorders, symmetric or asymmetric abnormalities of the sacroiliac joints and large, broad excrescences of the spine may be seen. In ankylosing spondylitis (as well as in the sacroiliitis and spondylitis of inflammatory bowel disease), bilateral symmetric sacroiliac joint abnormalities are almost universal, and spinal changes typically consist of thin, linear, and symmetrically distributed outgrowths (i.e., syndesmophytes).

210

SECTION 2  Articular Disorders

DP MP R

A C

L

A

B Fig. 11.15  US: enthesitis. US of the dorsal finger in the sagittal plane (A–B) shows hypoechoic enlargement of the distal extensor tendon (arrows). Note cortical irregularity at the tendon attachment and hyperemia on color Doppler imaging. DP, Distal phalanx; MP, middle phalanx.

B Fig. 11.13  US: wrist synovitis. US of the dorsal aspect of the wrist in the sagittal plane (A) shows hypoechoic distention of the radiocarpal and midcarpal joint recesses (arrows) with increased flow on color Doppler imaging (B). C, Capitate; L, lunate; R, radius.

PP P

T

MP

F

C

Fig. 11.16  US: enthesitis. US of the lateral aspect of the finger in the coronal plane shows hypoechoic enlargement of the ulnar collateral ligament (arrow). Note cortical irregularity at the ligament attachments. MP, Middle phalanx; PP, proximal phalanx.

A

Rheumatoid Arthritis

B Fig. 11.14  US: tenosynovitis. (A) US of the medial aspect of the ankle short axis to the tibialis posterior (P) and flexor digitorum longus (F) tendons shows hypoechoic distention of the tendon sheaths (arrows) with increased flow on color Doppler imaging (B). C, Calcaneus; T, talus.

In some patients with psoriatic arthritis, the distribution of articular abnormalities in the appendicular skeleton is similar to that in rheumatoid arthritis, whereas in others, asymmetry and extensive distal interphalangeal articular alterations facilitate differentiation from rheumatoid arthritis. Further, in psoriatic arthritis, bony proliferation leading to fraying or irregularity of the periarticular bony surfaces, and intraarticular bone ankyloses are findings not typical of rheumatoid arthritis.

Other Disorders Erosive arthritis of the distal interphalangeal joints can be observed in many disease processes (Box 11.3). Additional imaging findings in most of these disorders generally allow accurate diagnosis.

R

A

B

C Fig. 11.17  MR imaging: synovitis and tenosynovitis. Axial T1-­weighted (A), fluid-­sensitive (B), and T1-weighted fat-suppressed contrast-enhanced (C) MR images show enhancing fluid-­signal synovitis involving the fifth metacarpophalangeal joint (arrow). Note pericapsular inflammation characteristic of psoriatic arthritis. Bone irregularity and subchondral bone marrow edema of the fifth metacarpal head are consistent with erosions. Flexor tenosynovitis of the thumb is also noted (arrowhead).

TABLE 11.1  Differential Diagnosis of Psoriatic Arthritis Psoriatic Arthritis

Reactive Arthritis

Rheumatoid Arthritis

Types of involved articulations

Synovial joints Symphyses Entheses

Synovial joints Symphyses Entheses

Synovial joints*

Distribution of arthritis

Appendicular and axial skeleton Polyarticular or pauciarticular Symmetric, asymmetric, or unilateral Upper and lower extremities Sacroiliac joints and entire spine

Appendicular and axial skeleton Polyarticular or pauciarticular Asymmetrical Lower extremities Sacroiliac joints and, less commonly, spine

Appendicular and axial skeleton Polyarticular Symmetric Upper and lower extremities Cervical spine

Nature of Lesions† Osteoporosis Soft tissue swelling Joint space narrowing

+

+

++

++

++

++

+

+

++

Severe periarticular osteolysis

++

+

+

Intraarticular bone ankylosis

++

++‡

+

Bone proliferation and periostitis

++

++

–§

Tuft resorption

++

–

–

*Symphyses and entheses are less commonly and less extensively involved in rheumatoid arthritis than in psoriatic arthritis or reactive arthritis. †–, absent; +, occasionally present; ++, commonly present. ‡Less frequent than in psoriatic arthritis. §Occasionally seen in male patients with rheumatoid arthritis and in those with both rheumatoid arthritis and diffuse idiopathic skeletal hyperostosis.

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SECTION 2  Articular Disorders

BOX 11.3  Causes of Erosive Arthritis of

Distal Interphalangeal Joints Psoriatic arthritis Inflammatory (erosive) osteoarthritis Gout Hyperparathyroidism Multicentric reticulohistiocytosis Scleroderma Thermal injuries

FURTHER READING Abrar DB, Schleich C, Brinks R, et al. Differentiating rheumatoid and psoriatic arthritis: a systemic analysis of high-resolution magnetic resonance imaging features-preliminary findings. Skeletal Radiology. 2021;50:531. Battistone MJ, Manaster BJ, Reda DJ, et al. The prevalence of sacroiliitis in psoriatic arthritis: new perspectives from a large, multicenter cohort. Skeletal Radiol. 1999;28:196. Bethapudi S, Halstead J, Ash Z, et al. Test yourself: answer psoriatic onycho-­ pachydermo periostitis (POPP). Skeletal Radiol. 2014;43:409. Forrester DM. The “cocktail sausage” digit. Arthritis Rheum. 1983;26:664. Gutierrez M, Fillippucci E, De Angelis R, Filosa G, Kane D, Grassi W. A sonographic spectrum of psoriatic arthritis: “the five targets.” Clin Rheumatol. 2010;29:133. Haroon M, Winchester R, Giles JT, et al. Clinical and genetic associations of radiographic sacroiliitis and its different patterns in psoriatic arthritis. Clin Exp Rheumatol. 2017;35:270. Helliwell PS, Hickling P, Wright V. Do the radiological changes of classic ankylosing spondylitis differ from the changes found in the spondylitis

associated with inflammatory bowel disease, psoriasis, and reactive arthritis? Ann Rheum Dis. 1998;57:135. Jacobson JA, Girish G, Jiang Y, Resnick D. Radiographic evaluation of arthritis: inflammatory conditions. Radiology. 2008;248:378. Liu J-­T, Yeh H-­M, Liu S-­Y, et al. Psoriatic arthritis: epidemiology, diagnosis, and treatment. World J Orthop. 2014;5:537. Maldonado-­Ficco H, Sheane B, Thavaneswaran A, et al. Magnetic resonance imaging in psoriatic arthritis: a descriptive study of indications, features, and effect on treatment change. J Clin Rheumatol. 2017;23:243. Martel W, Stuck KJ, Dworin AM, et al. Erosive osteoarthritis and psoriatic arthritis: a radiologic comparison in the hand, wrist, and foot. AJR Am J Roentgenol. 1980;134:125. McEwen C, Ditata D, Lingg C, et al. Ankylosing spondylitis and spondylitis accompanying ulcerative colitis, regional enteritis, psoriasis, and Reiter’s disease. Arthritis Rheum. 1971;14:291. Poggenborg RP, Ostergaard M, Terslev L. Imaging in psoriatic arthritis. Rheum Dis Clin N Am. 2015;41:593. Poggenborg RP, Eshed I, Ostergaard M, et al. Enthesitis in patients with psoriatic arthritis, axial spondyloarthritis, and healthy subjects. Ann Rheum Dis. 2015;74:823. Resnick D, Niwayama G. On the nature and significance of bony proliferation in “rheumatoid variant” disorders. AJR Am J Roentgenol. 1977;129:275. Schoellnast H, Deutschmann HA, Hermann J, et al. Psoriatic arthritis and rheumatoid arthritis: findings in contrast-­enhanced MRI. AJR. 2006;187:351. Schwenzer NF, Kotter I, Henes JC, et al. The role of dynamic contrast-­ enhanced MRI in the differential diagnosis of psoriatic and rheumatoid arthritis. AJR. 2010;194:715. Sundaram M, Patton JT. Paravertebral ossification in psoriasis and Reiter’s disease. Br J Radiol. 1975;48:628. Tan AL, Fukuba E, Halliday NA, et al. High-­resolution MRI assessment of dactylitis in psoriatic arthritis shows flexor tendon pulley and sheath-­ related enthesitis. Ann Rheum Dis. 2015;74:185.

12 Reactive and Enteropathic Arthropathies S U M M A R Y O F K E Y F E A T U R E S : R E A C T I V E A R T H R O P A T H I E S  • Reactive arthritis follows a gastrointestinal or urogenital infection. • Males between 15 and 35 years of age are most commonly affected. • Lower extremity asymmetric inflammatory arthritis is characteristic.

  

• The triad of urethritis, conjunctivitis, and arthritis may be present. • Imaging features resemble other spondyloarthropathies, such as ankylosing spondylitis and psoriatic arthritis.

S U M M A R Y O F K E Y F E A T U R E S : E N T E R O P A T H I C A R T H R O P A T H I E S  • Inflammatory arthritis is associated with ulcerative colitis, Crohn disease, and Whipple disease. • Imaging features of joint inflammation, enthesitis, and bone proliferation appear similar to those of ankylosing spondylitis and psoriatic arthritis.

• Sacroiliitis is typically bilateral and symmetric, similar to that seen in ankylosing spondylitis.

  

REACTIVE ARTHRITIS Reactive arthritis typically follows a recent gastrointestinal or urogenital infection and is associated with spinal and peripheral arthritis, as well as extraarticular symptoms and signs. The most common bacterial pathogens that have been implicated in reactive arthritis include Salmonella, Shigella, Campylobacter, Yersinia, and Chlamydia. Cultures of blood or synovial fluid and results of microbial tests, however, are typically negative, underscoring that this inflammatory articular disorder relates to a sterile reaction after an infectious trigger. Cases of reactive arthritis have been described following Covid-19 infection. Inflammation of the spine and sacroiliac joints in many patients explains the classification of reactive arthritis as a spondyloarthropathy, although reactive arthritis likely represents less than 5% of persons in this disease category. Patients with reactive arthritis are generally young adults and possess the human leukocyte antigen (HLA)-­B27 allele. One subtype of reactive arthritis, previously known as Reiter syndrome, is characterized by a classic clinical triad of urethritis, arthritis, and conjunctivitis. Reactive arthritis is accompanied by typical imaging features that it shares with the other spondyloarthropathies (i.e., psoriatic arthritis and ankylosing spondylitis). It is the distribution of articular abnormalities that allows a firm imaging diagnosis in some patients with reactive arthritis, specifically an asymmetrically distributed articular disorder of the lower extremities.

CLINICAL ABNORMALITIES Most patients with reactive arthritis are between 15 and 35 years of age. At any age, the disease is much more common in men than in women. Urethritis is frequently the initial manifestation of the disease. Circinate balanitis has been noted in many patients with the dysenteric and venereal forms of reactive arthritis. Early and transient conjunctivitis frequently accompanies acute attacks. Later and more severe ocular involvement may include episcleritis, keratitis, uveitis, iritis, retrobulbar neuritis, corneal ulceration, and intraocular hemorrhage. The characteristic skin lesion, which occurs in 5% to 30% of patients, is termed keratoderma blennorrhagicum, most commonly noted on the soles of the feet and the palms of the hands. Keratosis of the nails also may be observed,

simulating psoriasis. On the buccal mucosa and the tongue, superficial erythematous ulcerations may be evident in 5% to 10% of patients. Characteristically, an asymmetric arthritis of the lower extremity becomes evident, often within 1 to 3 weeks of the inciting episode of urethritis or diarrhea. Initially, the most commonly affected joints are the knee and the ankle, followed in descending order of frequency by the metatarsophalangeal joints, heel, shoulder, wrist, hip, and lumbar spine. The occurrence of heel pain and tenderness should be stressed as a common manifestation of reactive arthritis. The arthritic attacks are usually self-­limited and of short duration, although recurrences are frequent.

RADIOGRAPHIC ABNORMALITIES The general radiographic features of reactive arthritis are shown in Box 12.1. The synovial joints, symphyses, and entheses are affected. Typically, an asymmetric distribution, with a predilection for articulations of the lower extremity, is seen (Fig. 12.1). The most characteristic sites of abnormality are the small articulations of the foot, the calcaneus, the ankle, and the knee. Joint alterations in the upper extremity are less frequent, and abnormalities of the hip are uncommon. In the axial skeleton, the sacroiliac joints and spine are frequent targets.

General Radiographic Abnormalities KEY CONCEPTS  • S ee Fig. 12.2. • R adiographic characteristics of articular involvement are similar to those of the other spondyloarthropathies. • Bone erosions (initially marginal) and uniform joint space narrowing in synovial joints are similar to findings in other inflammatory arthritides. • The presence of enthesitis and bone proliferation is similar to findings in ankylosing spondylitis and psoriatic arthritis, abnormalities that are not seen in rheumatoid arthritis. • Involvement of cartilaginous joints occurs. • Lower extremity involvement predominates. • Sacroiliac joint involvement is typically bilateral but asymmetric.

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SECTION 2  Articular Disorders

BOX 12.1  Characteristics of Reactive

Arthritis

Involvement of synovial joints, symphyses, and entheses Asymmetric arthritis of the lower extremities Predilection for the small articulations of the foot, calcaneus, ankle, knee, and sacroiliac joint Bone erosion with adjacent proliferation Paravertebral ossification

Bone Erosion The most frequent sites of osseous erosion are the small joints of the foot, hand, and wrist; the knee; and the sacroiliac joint. Such erosions initially appear at the joint margins and may later involve the central portion of the articulation. Superficial resorption of bone may also occur beneath inflamed bursae and tendon sheaths.

Bony Proliferation Bony proliferation is characteristic of the spondyloarthropathies and is the most helpful radiographic feature in distinguishing these conditions from rheumatoid arthritis. Linear or fluffy periosteal bony proliferation, termed whiskering, is not uncommon in reactive arthritis, especially in the metacarpal, metatarsal, and phalangeal shafts; the malleolar region; and the knee. At sites of tendon and ligament attachment to bone (e.g., plantar aspect of calcaneus, ischial tuberosity), osseous surfaces frequently appear poorly defined or frayed. Adjacent periostitis is often encountered. Intraarticular bony ankyloses is uncommon but may be observed in the small joints of the hands and feet.

Specific Sites of Abnormality Forefoot

Radiographs of the feet frequently reveal asymmetric involvement of the metatarsophalangeal and interphalangeal joints (Fig. 12.3); the reported prevalence of these findings varies from 40% to 55%. At any location in the foot, osteoporosis, joint space loss, and marginal erosions with adjacent proliferation can be observed (Fig. 12.4). The sesamoid bones can undergo significant erosion and proliferation. Subluxation and deformity of the metatarsophalangeal articulations may be evident, an appearance that has been termed Lanois deformity.

Calcaneus Calcaneal alterations are characteristic (25% to 50% of patients). Both the posterior and the plantar aspects of the bone are affected, often bilaterally (Fig. 12.5). Poorly defined calcaneal erosions appear on the posterosuperior aspect of the bone related to retrocalcaneal bursitis. The adjacent Achilles tendon is frequently thickened. Plantar calcaneal enthesophytes are often large and irregular.

Hand and Wrist Fig. 12.1  Reactive arthritis: distribution of articular abnormalities. The most characteristic sites of involvement are the small articulations of the foot, calcaneus, ankle, knee, hand, and sacroiliac joint (arrows). Less commonly, the shoulder, elbow, hip, spine, symphysis pubis, and manubriosternal joint are affected (arrowheads).

Severe and widespread radiographic abnormalities of the upper extremity are distinctly unusual in reactive arthritis (Fig. 12.6). Wrist involvement is usually asymmetric (Fig. 12.7).

Sacroiliac Joint

Soft tissue prominence is related to intraarticular effusion, periarticular edema, and inflammation of bursal and tendinous structures. This finding is frequent about the interphalangeal joints of the toes and the fingers and may result in sausage like swelling of an entire digit, the sausage digit.

Sacroiliitis is common in reactive arthritis (Fig. 12.8). Although changes are generally bilateral, asymmetry is frequent. Unilateral sacroiliac joint abnormalities do occur, particularly early in the disease process. Although intraarticular bone fusion may eventually appear, this finding is less frequent than in classic ankylosing spondylitis and the sacroiliitis of inflammatory bowel disease (IBD).

Osteoporosis

Spine

Soft Tissue Swelling

Regional or periarticular osteoporosis accompanies acute episodes of arthritis. With recurrent or prolonged bouts of articular disease, osteoporosis may decrease in extent and severity, and it is not uncommon to detect severe cartilaginous and osseous lesions without adjacent osteoporosis.

Joint Space Narrowing Loss of the interosseous space, which usually is diffuse, is more frequent in the small articulations of the foot, hand, and wrist than in the knee and ankle.

An early finding in reactive arthritis (and psoriatic arthritis) is the appearance of paravertebral ossification about the lower three thoracic and upper three lumbar vertebrae (Fig. 12.9). On frontal radiographs, elongated vertical osseous bridges extend across the intervertebral disc but are separated by a clear space from the lateral margins of both the disc and the vertebral body. The outgrowths may be either well defined and linear or thick and fluffy and often skip from one side of the spine to the other. Involvement of large segments of the thoracic and lumbar spine, as well as the cervical spine, may eventually be noted.

CHAPTER 12  Reactive and Enteropathic Arthropathies

A

C

B

Fig. 12.2  General radiographic abnormalities of reactive arthritis in three different patients. Note the absence of osteoporosis and the presence of soft tissue swelling (arrowheads), periostitis and whiskering (A–B, solid arrows), osseous erosions, subluxation (B, open arrow), and bone production along the plantar aspect of the calcaneus (C).

A

B

Fig. 12.3  Abnormalities of the forefoot. (A) Radiograph of the third metatarsophalangeal joint outlines erosions of the metatarsal head (arrowheads) and adjacent bony proliferation (arrows). The joint space is not narrowed. (B) Radiograph of the forefoot reveals soft tissue swelling of the second digit (arrowheads), destruction of the distal interphalangeal joint, and intraarticular bone ankylosis of the proximal interphalangeal joint. Note the absence of osteoporosis.

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SECTION 2  Articular Disorders

The importance of recognizing paravertebral ossification is twofold: the finding may be an initial manifestation of the disease, and the abnormality is more diagnostic of reactive arthritis or psoriatic arthritis than of classic ankylosing spondylitis or the spondylitis associated with IBD. Further, apophyseal joint erosion, bone sclerosis, and osseous fusion are less than in reactive arthritis than in classic ankylosing spondylitis. Cervical spine abnormalities are not frequent in reactive arthritis.

OTHER DIAGNOSTIC TECHNIQUES As described in Chapter 10, advanced imaging methods, particularly magnetic resonance (MR) imaging, have been employed increasingly

Fig. 12.4  Abnormalities of the forefoot. Radiograph of great toe shows marginal erosions at the interphalangeal joint (arrows), with ill-­ defined bone proliferation and osteitis of the distal phalanx.

A

B

in the spondyloarthropathies, representing more sensitive methods than radiography in the detection of arthritis (Fig. 12.10) and enthesitis (see Fig. 12.5B), as well as bursitis and tenosynovitis.

DIFFERENTIAL DIAGNOSIS Other Spondyloarthropathies Although its general features resemble those of the other spondyloarthropathies (ankylosing spondylitis and psoriatic arthritis), reactive arthritis has a sufficiently characteristic articular distribution to allow accurate diagnosis in some cases. Specifically, an asymmetric arthritis of the lower extremity, sacroiliitis, and, less commonly, spondylitis,

Fig. 12.6  Abnormalities of the hand. Radiograph shows soft tissue swelling, bone erosions, and irregular bone proliferation at joints of the third digit (arrows).

C

Fig. 12.5  Abnormalities of the calcaneus. Images show enthesitis (arrows) as irregular bone proliferation on radiography (A), increased signal on the fluid-sensitive ­ magnetic resonance image (B), and uptake on a delayed bone scan image (C) at the Achilles and plantar aponeurosis attachments on the calcaneus.

CHAPTER 12  Reactive and Enteropathic Arthropathies

217

Fig. 12.7  Abnormalities of the wrist. The major radiographic abnormality is bone proliferation (arrows) about several compartments of the wrist. Soft tissue swelling is also evident.

Fig. 12.9  Abnormalities of the spine. Radiograph of the thoracolumbar spine shows paravertebral ossification. Note the asymmetric nature and lateral location of the outgrowths.

Fig. 12.8  Abnormalities of the sacroiliac joint. Bilateral and asymmetric alterations are observed in reactive arthritis. Erosions and reactive eburnation predominate in the ilium (arrows). Also, hyperostosis can be seen at the superior aspect of the joint (arrowhead).

are characteristic. In psoriatic arthritis, widespread involvement of the upper extremity may be apparent. In all of the spondyloarthropathies, the presence of soft tissue swelling, joint space narrowing, bone erosions, bony proliferation, and enthesitis is typical. These disorders all involve the sacroiliac joints, where bilateral symmetric changes may be seen. In psoriasis and reactive arthritis, however, asymmetry is more frequent than in ankylosing spondylitis and the sacroiliitis of IBD. Paravertebral ossification, rather than classic syndesmophytosis, is also more characteristic of psoriasis and reactive arthritis.

Fig. 12.10  Sacroiliitis: MR imaging. Oblique transverse T1-weighted fat-suppressed contrast-enhanced MR image reveals high signal intensity in the left sacrum and ilium, indicating sacroiliitis. (Courtesy G. Sandrini De Toni, MD, São Paulo, Brazil.)

and marginal erosions being observed. Bony proliferation is unusual, and the irregular, proliferative, erosive changes of the spondyloarthropathies are not seen in rheumatoid arthritis. Widespread and severe sacroiliac and thoracolumbar spinal changes are very uncommon in rheumatoid arthritis.

Rheumatoid Arthritis

Septic Arthritis and Osteomyelitis

The radiographic features of rheumatoid arthritis differ considerably from those of reactive arthritis. Rheumatoid arthritis is associated with bilateral and symmetric alterations, with early joint space narrowing

The early localized abnormalities of reactive arthritis may resemble those of bone and joint infection, a dilemma made more difficult owing to the clinical findings of a prior gastrointestinal or

218

SECTION 2  Articular Disorders

genitourinary infection in persons with reactive arthritis. Soft tissue swelling, osteoporosis, bony and cartilaginous destruction, and periostitis are evident in both reactive arthritis and infectious disease. Eventually, the polyarticular nature of reactive arthritis and the absence of recoverable microorganisms allow its accurate differentiation from infectious disease. With regard to the sacroiliac joint, unilateral distribution and involvement of the adjacent soft tissue suggest septic arthritis.

ENTEROPATHIC ARTHROPATHIES The appearance of musculoskeletal abnormalities in patients with gastrointestinal disorders has been recognized with increasing frequency. These abnormalities have been designated enteropathic arthropathies because of the close association of articular and intestinal findings (Table 12.1). Ulcerative colitis, Crohn disease (regional enteritis), and Whipple disease are three intestinal diseases whose rheumatologic manifestations are now well known. In addition, as discussed earlier in this chapter, reactive arthritis can follow a variety of intestinal infections, specifically those associated with Salmonella, Shigella, or Yersinia organisms. For some of these disorders, genetic factors appear to predispose certain persons to these articular manifestations. For example, approximately 90% of

patients with ulcerative colitis and Crohn disease in whom spondylitis or sacroiliitis develops demonstrate the genetically determined histocompatibility antigen HLA-­B27. Intestinal pathogens, such as Klebsiella, may also represent potential triggers for these musculoskeletal abnormalities.

ULCERATIVE COLITIS Musculoskeletal abnormalities are the most common extraintestinal manifestation of ulcerative colitis. The type of articular disease can be categorized as peripheral joint arthralgia and arthritis (10% to 15%), sacroiliitis and spondylitis (10% to 15%), and miscellaneous abnormalities (10% to 20%).

Peripheral Joint Arthralgia and Arthritis Although bowel disease is usually clinically evident before the onset of arthritis, articular abnormalities may appear before intestinal abnormalities in 10% to 15% of patients. A close temporal association exists between exacerbations of intestinal disease and joint inflammation. The articular findings can be categorized as an acute synovitis that is predominantly monoarticular or pauciarticular in distribution. Joints in the lower extremity are affected more frequently than those in the upper extremity. The knees are involved most commonly,

TABLE 12.1  Radiographic Manifestations of Enteropathic Arthropathies Disorder

Sacroiliitis

Spondylitis

Peripheral Joints

Other Manifestations

Ulcerative colitis

+

+

Soft tissue swelling Osteoporosis Joint space narrowing (r) Erosions, cysts (r)

Periostitis (r)

Crohn disease

+

+

Soft tissue swelling Osteoporosis Joint space narrowing (r) Erosions, cysts (r)

Periostitis (r) Osseous granulomas (r) Osteomyelitis (r)

Whipple disease

+

+

Soft tissue swelling Osteoporosis Joint space narrowing (r) Erosions, cysts (r)

Subcutaneous nodules (r)

Salmonella, Shigella, and Yersinia infections

+

+

Soft tissue swelling Osteoporosis Septic arthritis

Intestinal bypass surgery

+

+

Soft tissue swelling Osteoporosis Gout (r)

Osteomalacia (r)

Laënnec cirrhosis

Soft tissue swelling Osteoporosis

Soft tissue calcification (r)

Biliary cirrhosis

Soft tissue swelling Joint space narrowing Erosions Bone destruction Chondrocalcinosis (r)

Osteomalacia Xanthoma Periostitis (r)

Viral hepatitis

Soft tissue swelling (r)

Subcutaneous nodules

Pancreatic disease

Soft tissue swelling (r) Osteoporosis Erosions, cysts (r) Osteonecrosis, fat necrosis

Subcutaneous nodules Osteolysis Periostitis Metastasis

+, Present; r, rare.

CHAPTER 12  Reactive and Enteropathic Arthropathies followed by the ankles, elbows, wrists, shoulders, and small joints of the hands and feet. Asymmetric inflammation of the proximal interphalangeal joints of the toes is suggestive of colitic arthritis. The attacks are usually self-­limited, frequently resolving within 1 to 3 months. Radiographic findings are not specific (Fig. 12.11). Permanent joint abnormalities are infrequent, even in the setting of recurrent clinical attacks of arthritis.

Sacroiliitis and Spondylitis Spondylitis and sacroiliitis in ulcerative colitis are poorly correlated with activity of the bowel disease and, in fact, may manifest before, at the same time as, or after the onset of intestinal changes. The clinical features and radiographic abnormalities (Fig. 12.12) of spondylitis and sacroiliitis in patients with ulcerative colitis are identical to those of classic ankylosing spondylitis. Sacroiliac joint involvement is usually bilateral and symmetric in distribution.

Miscellaneous Abnormalities Clubbing of the fingers is a recognized complication of ulcerative colitis. In addition, enthesitis may be seen similar to that in ankylosing spondylitis (Fig. 12.13). Although the degree of bone marrow edema with MR imaging is a clue to the diagnosis of enthesitis avoiding the misdiagnosis of a tendon tear, correlation with radiography showing the ill-­defined bone cortex of inflammatory enthesitis helps ensure the proper diagnosis. On rare occasions, hypertrophic osteoarthropathy leading to periosteal bone formation in the tibia, fibula, radius, and ulna also may be apparent (Fig. 12.14).

CROHN DISEASE Musculoskeletal manifestations in Crohn disease can take several forms: peripheral joint arthralgia and arthritis, sacroiliitis and spondylitis, and miscellaneous abnormalities.

219

Peripheral Joint Arthralgia and Arthritis The reported frequency of enteropathic arthritis in patients with Crohn disease varies from less than 1% to 22%. Peripheral joint abnormalities in Crohn disease are equally frequent in men and women. The pattern of articular involvement is typically a mild, migratory synovitis of one or, less commonly, several joints that involves the lower extremity more frequently than the upper extremity. The knee is the most common site of abnormality, followed by the ankle, shoulder, wrist, elbow, and small joints of the hands and feet. Arthritis, which may be associated with erythema nodosum, can occur simultaneously with the onset of bowel disease or at any time during its course. Infrequently, it may precede intestinal alterations. The recrudescence of arthritis is commonly associated with an exacerbation of intestinal disease. Radiographic abnormalities are not specific.

Sacroiliitis and Spondylitis Sacroiliac joint and spinal changes develop in a significant number of patients with Crohn disease (3% to 16%); conversely, a high frequency of Crohn disease occurs in patients with ankylosing spondylitis. Men and women are affected with equal frequency. Symptoms and signs may antedate or follow the onset of bowel disease. Exacerbation of these findings does not appear to be related to activity of the bowel disease, nor does treatment of the intestinal disorder influence the progress of the arthritis. Serologic testing for the presence of HLA-­B27 antigen is positive in approximately 50% of patients with Crohn disease and sacroiliitis or spondylitis. The radiographic features of the spinal and sacroiliac articular abnormalities in Crohn disease are identical to those of classic ankylosing spondylitis. Bilateral sacroiliac joint narrowing and erosion and sclerosis of the ilium and sacrum are evident (Fig. 12.15). Findings at MR imaging are also similar to those in ankylosing spondylitis (Fig. 12.16). Spinal involvement can eventually lead to a bamboo spine.

Miscellaneous Abnormalities Digital clubbing has been detected in as many as 40% of patients with Crohn disease. Bilateral, symmetric periostitis, which is a manifestation of hypertrophic osteoarthropathy, is an extremely rare complication of Crohn disease. Granulomatous and infectious processes of bone have been reported in association with Crohn disease. Although an abscess of the psoas muscle is an infrequent complication of Crohn disease, with a prevalence of approximately 3% to 5%, some investigators regard Crohn disease as the leading cause of psoas abscesses.

WHIPPLE DISEASE Musculoskeletal manifestations are an important feature of the disease. These manifestations can be divided into peripheral joint arthralgia and arthritis, sacroiliitis and spondylitis, and miscellaneous abnormalities.

Peripheral Joint Arthralgia and Arthritis Acute migratory episodic arthralgia and arthritis are apparent in 60% to 90% of patients with Whipple disease, and these findings may antedate other changes of the disease. Articular abnormalities are usually transient and migratory, and large joints such as the knees, ankles, and glenohumeral joints are usually involved. Residual joint deformities are rare. Radiographic examinations of involved peripheral joints may be normal, although soft tissue swelling, osteoporosis, and joint space narrowing are occasionally evident (Fig. 12.17). Fig. 12.11  Ulcerative colitis: peripheral joint abnormalities. Observe a large joint effusion of the knee with displacement of the fat pads and prominence of the suprapatellar pouch (arrowheads).

Sacroiliitis and Spondylitis Sacroiliitis and spondylitis have been described in patients with Whipple disease. Although the exact frequency of these abnormalities is not

A

B

C

D Fig. 12.12  Ulcerative colitis: sacroiliac joint abnormalities. Radiograph (A) and CT image (B) show bilateral asymmetric erosions and sclerosis about the sacroiliac joints. Follow-­up radiograph (C) and T1-­weighted MR image (D) show fusion of the left sacroiliac joint. Note periarticular fat on the MR image (arrow), a finding seen with chronic sacroiliac joint inflammation.

A

B

GT

D

C

R

E

F

Fig. 12.13  Ulcerative colitis: enthesitis. Radiographs (A and B) show an ill-defined ­ cortex at the gluteal tendon insertion on the greater trochanter (arrow), corresponding to fluid-signal ­ abnormality of the tendon and adjacent marrow on the fluid-sensitive coronal MR image (arrow) (C). Note hypoechoic increased thickness of the gluteal tendons ­ (arrow) associated with cortical irregularity of the greater trochanter (GT) on ultrasonography (D). T1-weighted (E) and fluid-sensitive ­ (F) coronal MR images show additional enthesitis at the left hamstring tendon origin (curved arrow). Note sacroiliac joint fusion in (A) (arrowheads) and trochanteric marrow edema in (F) (arrow).

CHAPTER 12  Reactive and Enteropathic Arthropathies

221

Fig. 12.14  Ulcerative colitis: hypertrophic osteoarthropathy. Note the periostitis (arrows) of the diaphyses and metaphyses of the radius and ulna.

known, reports have suggested that sacroiliitis is observed in about 20% of patients with Whipple disease and that spondylitis is much less frequent. The HLA-­B27 antigen may be present in many of these patients with involvement of the axial skeleton.

Miscellaneous Abnormalities Subcutaneous nodules, particularly on extensor surfaces of the extremities, are evident in some patients with joint symptoms. Additional manifestations include clubbing of the fingers, hypertrophic osteoarthropathy, reflex sympathetic dystrophy, and myalgias.

PANCREATIC DISEASE Fat Necrosis Pancreatic disorders can be complicated by fat necrosis at multiple distant sites, with subsequent subcutaneous nodular skin lesions, panniculitis, polyarthritis, and medullary fat necrosis. The association of pancreatitis, panniculitis, and polyarthritis is known as the PPP syndrome. These manifestations appear most frequently in older men in association with carcinoma of the pancreas, although they can also occur with acute pancreatitis caused by either abdominal trauma or alcohol abuse, pancreatic pseudocysts, and pancreatic duct calculi. In many patients, joint pain and nodules precede abdominal pain. Articular abnormalities are characterized by a symmetric or asymmetric polyarthritis, which can be associated with pain, swelling, tenderness, warmth, and an effusion. A predilection for the ankles, elbows, knees, wrists, and small joints of the hands and feet is seen. Radiographic findings related to joint disease are absent or minimal; osteoporosis and soft tissue swelling may be seen, but joint space narrowing and osseous erosion are reported infrequently. Bone involvement can occur simultaneously with subcutaneous nodules and polyarthritis, or it can represent an isolated phenomenon.

Fig. 12.15  Crohn disease and ankylosing spondylitis: sacroiliac joint and spinal abnormalities. Frontal radiograph reveals bilateral symmetric sacroiliac joint changes with intraarticular bone fusion. Syndesmophytes are seen in the spine. (Courtesy of P. Ellenbogen, MD, Dallas, TX.)

Osteolytic lesions with moth-­eaten bone destruction and periostitis of the tubular bones of the extremities resemble the findings in osteomyelitis or osteonecrosis (Fig. 12.18). These changes occur in the long bones of the extremities, in the small bones of the hands and feet, or in both locations. In the bones of the hands and feet, cystic defects and a coarsened trabecular pattern may be apparent, and the epiphyses may be unaffected. MR imaging is sensitive to the early changes of intraosseous fat necrosis and shows multiple foci of abnormal signal (see Chapter 40). Although the exact pathogenesis of the articular and osseous findings associated with pancreatic disorders has not been delineated accurately, widespread fat necrosis is likely responsible for these abnormalities. Obstruction of pancreatic ducts by edema, calculi, or tumor or hormonal hypersecretion by acinar cell carcinomas and functioning metastases can lead to the release of excess circulating lipase into the bloodstream, which results in autodigestion of fat deposits at distant sites. Indeed, even fat globules in the synovial fluid have been identified.

Osteonecrosis Osteonecrosis is a recognized manifestation of pancreatic disease. This complication is most frequently associated with chronic or inactive pancreatitis. Abnormalities of the femoral and humeral heads are typical, although diaphyseal and metaphyseal infarction in long tubular bones may be seen.

222

SECTION 2  Articular Disorders

B

A

Fig. 12.16  Crohn disease and ankylosing spondylitis: sacroiliac joint abnormalities. T1-weighted (A) and fluid-­sensitive (B) MR images show diffuse subchondral bone marrow edema about the right sacroiliac joint (arrow); however, bilateral symmetric sacroiliac joint involvement would be more typical.

Fig. 12.17  Whipple disease: peripheral joint abnormalities. Observe the hip joint space narrowing and osseous cysts. Similar changes were seen in the contralateral hip. (From Chevallier PL, Vallat JP, Luthier F, et al.: Bilateral (coxopathy revealing Whipple disease: Apropos of a case. [Article in French.] Rev Rhum Mal Osteoartic. 1976; 43:663.) Fig. 12.18  Pancreatic disease: fat necrosis. Radiographic abnormalities include lytic defects of the metacarpals and phalanges, with associated periostitis. Soft tissue swelling is also evident. (Courtesy A. Brower, MD, Norfolk, VA.)

FURTHER READING Agarwal S, Sasi A, Ray A, et al. Pancreatic panniculitis polyarthritis syndrome with multiple bone infarcts. QJM. 2019;112:43. Atzeni F, Defendenti C, Ditto MC, et al. Rheumatic manifestations in inflammatory bowel disease. Autoimmunity Rev. 2014;13:20. Bentaleb I, Abdelghani KB, Rostom S, et al. Reactive arthritis: Update. Current Clinical Microbiology Reports. 2020;7:124. El-­Khoury GY, Kathol MH, Brandser EA. Seronegative spondyloarthropathies. Radiol Clin North Am. 1996;34:343.

Helliwell PS, Hickling P, Wright V. Do the radiological changes of classic ankylosing spondylitis differ from the changes found in the spondylitis associated with inflammatory bowel disease, psoriasis, and reactive arthritis? Ann Rheum Dis. 1998;57:135. Hirondel JL, Fournier L, Fretille A, et al. Intraosseous fat necrosis and metaphyseal osteonecrosis in a patient with chronic pancreatitis: MR imaging and CT scanning. Clin Exp Rheumatol. 1994;12:191. Karreman MC, Luime JL, Hazes JMH, et al. The prevalence and incidence of axial and peripheral spondyloarthritis in inflammatory bowel disease: a systematic review and meta-­analysis. J Crohn Colitis. 2017;11:631.

CHAPTER 12  Reactive and Enteropathic Arthropathies Khan MA. Axial arthropathy in Whipple’s disease. J Rheumatol. 1982;9:928. Leclerc-­Jacob S, Lux G, Rat AC, et al. The prevalence of inflammatory sacroiliitis assessed on magnetic resonance imaging of inflammatory bowel disease: a retrospective study performed on 186 patients. Alimentary Pharmacol Therapeutics. 2014;39:957. Loverdos I, Swan MC, Shekherdimian S, et al. A case of pancreatitis, panniculitis, and polyarthritis syndrome: Elucidating the pathophysiologic mechanisms of a rare condition. J Pediatr Surg Case Reports. 2015;3:223.

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Martel W, Braunstein EM, Borlaza G, et al. Radiologic features of Reiter’s disease. Radiology. 1979;132:1. Selmi C, Gershwin ME. Diagnosis and classification of reactive arthritis. Autoimmunity Rev. 2014;13:546. Slovis TL, Berdon WE, Haller JO, et al. Pancreatitis and the battered child syndrome: report of 2 cases with skeletal involvement. AJR Am J Roentgenol. 1975;125:456. Sundaram M, Patton JT. Paravertebral ossification in psoriasis and Reiter’s disease. Br J Radiol. 1975;48:628.

13 Gout S U M M A R Y O F K E Y F E AT U R E S • Th  e biochemical hallmark of the disease is hyperuricemia. • Idiopathic gout can be divided into four stages: asymptomatic hyperuricemia, acute gouty arthritis, intercritical gout, and chronic tophaceous gout. • Gouty arthritis is characterized by asymmetric polyarticular involvement, predominantly affecting the feet, hands, wrists, elbows, and knees.

• R  adiographic manifestations occur late in the course of the disease and include lobulated eccentric soft tissue masses, well-­defined erosions, and relative preservation of joint spaces. • Ultrasound and dual-­energy computed tomography have characteristic findings in cases of gout.

INTRODUCTION

Asymptomatic Hyperuricemia

  

Famous and influential people have suffered from the ravages of gout throughout history. Apparent descriptions of the disorder can be found in the Babylonian Talmud from more than 2000 years ago, as well as in the Bible. The disease was originally called podagra, a Greek derivative from pous (foot) and agra (attack). The current term gout is derived from the Latin word gutta (drop), a reflection of the early belief that an acute attack of the disease was the result of poison (malevolent humor) dropping into the joint.

CLINICAL FEATURES The biochemical hallmark of the disease is hyperuricemia, which may develop from excessive production of uric acid, a decrease in renal excretion of uric acid, or a combination of the two. Traditionally, gout has been classified into two types: (1) primary gout, in which the underlying hyperuricemia is the result of an inborn error of metabolism, and (2) secondary gout, in which the hyperuricemia is a consequence of any number of other disorders. More recently, it has been observed that a variety of metabolic defects account for the hyperuricemia and clinical disease in patients with so-­called primary gout. Diagnostic criteria for gout also have been suggested with recent emphasis on characteristics such as at least one episode of swelling, pain, and/or tenderness in a peripheral joint or bursa and the presence of monosodium urate crystals in a symptomatic joint, bursa, or tophus. Idiopathic gout occurs far more commonly in men than in women (20:1). The first attack of arthritis most frequently occurs during the fifth decade of life in men and in the postmenopausal period in women. Premenopausal women with gout usually have a family history of the disease or, infrequently, long-­term diuretic use. The hereditary nature of hyperuricemia and gout is well known, with the reported familial prevalence varying from 6% to 80%. Recent studies have led to the identification of at least 28 urate-­ associated loci. Genetic factors that contribute to hyperuricemia and gout are mostly involved with the renal urate transport system. Idiopathic gout can be divided into several stages, distinguishable by the amount and sites of crystal deposition and by the state of the inflammatory response.

224

Many persons have hyperuricemia for prolonged periods, even a lifetime, without any symptoms or signs. Indeed, hyperuricemia has been described in 2.3% to 17.6% of persons, 20% of whom will develop renal calculi or acute gout. The prevalence of gout increases substantially with advancing age and increasing serum urate concentration. Urolithiasis, articular attacks of gout, or both, mark the end of this phase.

Acute Gouty Arthritis Early in the course of gouty arthritis, the disorder is usually monoarticular or oligoarticular. Gout has a predilection for the joints of the lower extremity, particularly the first metatarsophalangeal and intertarsal joints, the ankles, and the knees. The first metatarsophalangeal joint is the most common site of initial involvement and may eventually be altered in 75% to 90% of patients with gout. Inflammatory changes in the spine, hip, shoulder, or sacroiliac joint are unusual and generally occur only in long-­standing articular disease. The onset and severity of arthritis in acute gout are often dramatic, and the clinical findings of acute gout may simulate those of septic arthritis. Pain, tenderness, and swelling occur within several hours and may persist for days to weeks.

Interval Phase of Gout (Intercritical Gout) The asymptomatic period between gouty attacks may last from months to years. With recurring attacks, the arthritis commonly becomes longer in duration, more frequent in occurrence, and polyarticular in distribution. Eventually, recovery between acute attacks becomes incomplete.

Chronic Tophaceous Gout Before the advent of effective therapy for hyperuricemia, clinical or radiographic evidence of gout (called tophi) developed in 50% to 60% of patients, but this frequency has now decreased sharply. Tophi (deposits of monosodium urate) commonly occur in the synovium and subchondral bone and are frequently noted on the helix of the ear and in the subcutaneous and tendinous tissues of the elbow, hand, foot, knee, and forearm. These deposits may appear as irregular, hard masses

CHAPTER 13  Gout and produce ulceration of the overlying skin, with extrusion of chalky masses or urate crystals.

GENERAL PATHOLOGIC FEATURES

or ossify and produce tendon rupture and nerve compression with paralysis.

GENERAL RADIOGRAPHIC FEATURES

Acute Gouty Arthritis Urate crystals, which can evoke an acute inflammatory response in the skin, subcutaneous tissues, and joints, are needle shaped, with strong negative birefringence when examined under polarized light. Modifications may occur in the shape of the urate crystals, with a rod­like appearance being more common than the classic needle­like configuration in subacute and chronic gout. The appearance of urate crystals differs considerably from that of calcium pyrophosphate dihydrate (CPPD) crystals; CPPD crystals are more rhomboid, variable in shape, and demonstrate weak positive birefringence when examined under polarized light.

Interval Phase of Gout Urate crystals may be identified in the synovial fluid between attacks of gout; usually, however, these crystals are extracellular. Similarly, urate crystals can occasionally be recovered from a noninvolved joint in patients with gouty arthritis at other locations and in those with little history of gouty arthritis. It appears that crystalline deposits are often inert, but if disrupted by mechanical factors or altered solubility, the crystals are capable of being released into the joint space and initiating an acute inflammatory response.

KEY CONCEPTS  • S ee Table 13.1. • T he erosions in gout characteristically are eccentric and punched out, often with sclerotic margins and overhanging edges. • Eccentric soft tissue swelling is a prominent radiographic finding. • Joint space is generally preserved until late.

Although radiographic alterations may accompany the initial bouts of acute gouty arthritis, routine radiographic evaluation reveals no abnormalities of the articular structures in a large percentage of patients with clinical evidence of gout and symptoms spanning many years. During the acute attack of arthritis, soft tissue prominence about the involved joint or joints coincides with the presence of synovial inflammation, capsular distention, and surrounding soft tissue edema. As the attack subsides, these radiographic abnormalities usually disappear. After years of intermittent episodic arthritis, chronic tophaceous gout may lead to permanent radiographic abnormalities.

Soft Tissue Abnormalities

Chronic Tophaceous Gout In chronic tophaceous gout, urate crystals in the synovial membrane are released into the synovial fluid, absorbed by the adjacent articular cartilage and, over time, penetrate the entire thickness of cartilage and collect in subchondral and deeper osseous areas. Adjacent regions of cartilage may be unaffected such that bone erosions centrally or at the margins of the joint may appear at a time when the joint space is preserved. Tophaceous deposits also occur in periarticular tissues, such as the joint capsules, tendons, ligaments, and bursae, particularly in the olecranon and prepatellar regions. Extraarticular collections may be noted in the helix or antihelix of the ear, skin of the fingertips, palms, soles, and other regions, including the tarsal plates of the eyelids, nasal cartilage, and cornea or sclerotic coats of the eye. These tophaceous nodules consist of multicentric deposition of urate crystals and intercrystalline matrix, as well as foreign body granulomatous reaction. As they become larger, tophi may calcify

Eccentric nodular soft tissue prominence accompanies soft tissue deposition of urate crystals in tophaceous gout (Fig. 13.1). This is most frequent in the feet, hands, ankles, elbows, and knees. Calcification of a tophus occurs but is infrequent.

Articular Space Abnormalities In gout, the joint space is remarkably well preserved in width until late in the course of articular disease (Fig. 13.2). Microtophi within the joint can cause an effusion to appear relatively dense. In addition, microtophi can coat the surface of the intraarticular structures, producing an arthrogram-­like appearance and simulating chondrocalcinosis (Fig. 13.3), although this finding also can be seen in CPPD crystal deposition. In advanced disease, joint space narrowing is frequent and may be uniform, similar to appearance in rheumatoid arthritis. Bony ankylosis has been observed but is extremely rare.

TABLE 13.1  Radiographic Features of Gouty and Rheumatoid Arthritis Distribution

225

Gouty Arthritis

Rheumatoid Arthritis

Asymmetric joint involvement

Symmetric joint involvement

Soft tissue swelling

Eccentric

Fusiform

Soft tissue calcification

Occasional

Rare

Osteoporosis

Absent or mild

Moderate or severe

Joint space loss

Frequently absent

Diffuse; occurs early in disease course

Bony erosions

Eccentric Frequent sclerotic margin Intraarticular and extraarticular Overhanging edge

Marginal Rare sclerotic margin Intraarticular No overhanging edge

Malalignment, subluxation

Rare

Common

226

SECTION 2  Articular Disorders

A

Fig. 13.2  Radiographic features of gout: articular space abnormalities. Observe that the articular space is only minimally narrowed (arrowhead), despite the presence of nodular soft tissue masses and eccentric osseous erosions (arrows). (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

B Fig. 13.1  Radiographic features of gout. Bilateral hand and foot radiographs show the hallmark features of gout, including well-­defined articular and periarticular erosions with sclerotic margins and overhanging edges, as well as prominent eccentric soft tissue swelling and masses (arrows).

Bone Mineralization Abnormalities Although osteoporosis of subchondral bone can be observed during an acute gouty attack, extensive loss of bone density is not characteristic.

Bone Erosions Bone erosions in gout are produced by tophaceous deposits and may be intraarticular, paraarticular, or located a considerable distance from the joint (Fig. 13.4). Intraarticular erosions usually commence in the marginal areas of the joint and proceed centrally; paraarticular erosions are eccentric in location, frequently beneath soft tissue nodules. Gouty erosions may be surrounded by a sclerotic border and produce a punched-out appearance. In about 40% of patients with gouty erosions of bone, an elevated bony margin, or lip, extends outward in the soft tissues, apparently covering the tophaceous nodule. The overhanging edge may relate to bone resorption beneath the gradually enlarging tophus, with periosteal

Fig. 13.3  Radiographic features of gout: articular space abnormalities. Note coating of the hyaline cartilage and menisci with microtophi producing an arthrogram-­like effect (arrows). The anatomic location and non-mineralized density differentiate this finding from chondrocalcinosis.

bony apposition at the outer aspect of the involved cortex. Although the appearance is not pathognomonic, it is strongly suggestive of gouty arthritis.

Subperiosteal Apposition of Bone and Proliferative Changes Bone proliferation is occasionally observed in gout (Fig. 13.5). Enlargement of the ends and shafts of involved bones can produce club-­shaped metacarpal, metatarsal, and phalangeal heads (termed mushrooming), an enlarged ulnar styloid, and thickened diaphyses.

Intraosseous Calcification Intraosseous calcific deposits have been observed in approximately 6% of patients with chronic gouty arthritis, especially in the hands and feet. These deposits represent intraosseous urate deposits that, in most cases, arise from the adjacent joint, penetrate the cartilaginous surface, and extend into the adjacent spongiosa. Radiographic findings include focal or diffuse calcific collections, usually involving subchondral or subligamentous bony areas, in association with adjacent joint disease,

CHAPTER 13  Gout

A

B

227

C

Fig. 13.4  Radiographic features of gout: erosive bony abnormalities. (A) Well-­defined marginal erosion is evident (arrow), without reactive sclerosis. The articular space is narrowed only minimally. (B) Well-­defined extraarticular erosion (arrow) demonstrates surrounding bony eburnation. Additionally, soft tissue calcification and bone proliferation (arrowhead) are evident. (C) Overhanging margin. This lip of bone (arrowhead) may be evident in intraarticular or extraarticular locations. (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

osseous destruction, and involvement of periarticular tissue (Fig. 13.6). The radiographic alterations resemble those of enchondromas or osteonecrosis or bone infarcts.

GENERAL ULTRASONOGRAPHIC FEATURES KEY CONCEPTS  • A  cute gouty arthritis may have nonspecific findings of joint effusion and synovitis. • Intraarticular microtophi appear as hyperechoic foci that may layer on the hyaline cartilage, producing the double line sign. • Soft tissue tophi have a very characteristic appearance, appearing as globular and hyperechoic regions with internal punctate bright echoes often associated with cortical erosion.

Ultrasonography (US) is well suited to evaluate findings of gout in the extremities. Gouty arthritis will show hypoechoic or anechoic fluid distention of a joint recess, commonly associated with hyperechoic microtophi. These microtophi can layer on the hypoechoic hyaline cartilage, producing what has been termed the double contour sign (Fig. 13.7), which is differentiated from the normal echogenic cartilage surface by a more granular appearance and persistent echogenicity, regardless of the insonation angle. Soft tissue tophi have a very characteristic appearance on US, appearing as a relative globular and hyperechoic region with internal, more reflective foci (Fig. 13.8), and often a surrounding hypoechoic or anechoic halo. When in a periarticular location, these foci are often associated with a cortical erosion, although tophi also may be associated with tendons, such as the patellar and popliteus tendons in the knee, as well as tendons about the ankle and foot (see examples in following text).

GENERAL COMPUTED TOMOGRAPHIC FEATURES Standard CT scanning can occasionally provide useful information in patients with gout, especially those with involvement of

areas of complex anatomy such as the hindfoot and midfoot, osseous pelvis, base of the skull, and spine. CT scanning has revealed tophaceous deposits with attenuation values similar to those of calcifications, and the differentiation of noncalcified and calcified tophi may be difficult with standard CT imaging. In recent years, a great deal of attention has been directed at the important role of dual-­energy CT imaging when the diagnosis of gout is not clear, in the differentiation of urate crystal deposition from calcification, and in the assessment of the response of urate deposits to treatment. With this technique, two x-­ray tubes with different peak kilovoltages (80 and 140 kVp) are used to simultaneously acquire two sets of images of a specific region of the body. By comparison of the material-­specific differences in attenuation on these two image acquisitions, differentiation of the chemical composition of the scanned tissue can be determined. Specifically, in gout, dual-­energy CT can be employed to differentiate between urate deposits and calcium or bone (Fig. 13.9).

GENERAL MAGNETIC RESONANCE IMAGING FEATURES Magnetic resonance (MR) imaging may be useful in assessing the full extent of the gouty process, especially in anatomically complex regions such as the spine, small bones of the hands and feet, and sacroiliac and temporomandibular joints. In the peripheral skeleton, MR imaging allows visualization of the extent of soft tissue, synovial, cartilage, and bone involvement (Fig. 13.10). MR imaging shows intermediate to low signal intensity in noncalcified gouty tophi on both T1-­weighted and fluid sensitive MR images. MR imaging following gadolinium administration shows heterogeneous enhancement, with no enhancement in areas of calcification and amorphous urate deposits and variably intense enhancement in the inflamed synovium. In certain articulations, MR imaging (as well as CT scanning) may reveal intraarticular deposits of monosodium urate crystals in characteristic locations. As one example, crystalline deposits of gout in the knee show predilection for the popliteus tendon at its femoral attachment, quadriceps and patellar tendons, and paracruciate regions.

228

SECTION 2  Articular Disorders

A

Fig. 13.6  Radiographic features of gout: intraosseous calcification. Observe the punctate and circular calcifications in the proximal phalanx and metatarsal of the great toe, as well as in the cuneiforms. Extensive soft tissue swelling and calcification about a destroyed first metatarsophalangeal joint and extensive phalangeal involvement are evident.

MT1

B Fig. 13.5  Radiographic features of gout: proliferative bony abnormalities. Considerable productive changes of bone are apparent at the (A) second metacarpophalangeal and third distal interphalangeal joints and (B) the olecranon (arrow). Note soft tissue swelling from olecranon bursal distention in (B).

DISTRIBUTION OF ARTICULAR INVOLVEMENT The imaging abnormalities in gouty arthritis are generally asymmetric and polyarticular. There is a predilection for the lower extremity, and involvement is common in the feet, hands, wrists, elbows, and knees. A few specific areas of involvement are discussed in the following paragraphs.

Common Sites of Disease Foot Abnormalities

The most characteristic site of abnormality in gout is the first metatarsophalangeal joint (Fig. 13.11). Any of the other metatarsophalangeal joints and the interphalangeal joints may reveal similar abnormalities. Extensive destruction in the tarsometatarsal (Fig. 13.12) and intertarsal

PP

Fig. 13.7  Ultrasonographic features of gout: double contour sign. US of the first metatarsophalangeal joint in the sagittal plane shows echogenic microtophi (arrowheads) outlining the surface of the hypoechoic hyaline cartilage and paralleling the echogenic subchondral bone plate (the double contour sign). Note intraarticular hyperemia representing synovitis. MT1, First metatarsal; PP, proximal phalanx.

joints is especially characteristic. Although MR imaging is a very sensitive method in detection of tophaceous gout, the location of abnormalities, as well as characteristic radiographic and US findings, is pathognomonic (Fig. 13.13). Tendon involvement may simulate extensive tendinosis on MR imaging; US demonstrates the characteristic tophus appearance (Fig. 13.14). Joint recess distention may appear dense from microtophi as displayed with US (Fig. 13.15).

Hand and Wrist Abnormalities Imaging of the hands and wrists in patients with gout may reveal widespread articular abnormalities involving the distal interphalangeal, proximal interphalangeal, and, to a lesser extent,

CHAPTER 13  Gout

229

PP MT1

Fig. 13.8  US features of gout: tophus. US of the medial aspect of the first metatarsophalangeal joint in the axial plane shows the characteristic appearance of a tophus, visualized as a globular heterogeneous hyperechoic area (arrows) with internal punctate reflective echoes (arrowheads). Note erosion (curved arrow) of the first metatarsal (MT1). PP, Proximal phalanx.

C

A

PP MT1

B

D

Fig. 13.9  Dual-energy ­ CT features of gout. (A) Radiograph; (B) axial CT image; (C) dual-energy ­ CT image; and (D) US show a tophus (arrow) extending in a proximal and medial direction from the first metatarsophalangeal joint. Note the increased density of the tophus on radiography and CT imaging, and the hyperechoic appearance with US. Urate crystal deposition appears green on the dual-energy ­ CT; a second focus of urate deposition is seen at the second metatarsophalangeal joint. MT1, First metatarsal; PP, proximal phalanx. (Courtesy of Girish Gandikota, Chapel Hill, NC.)

230

A

SECTION 2  Articular Disorders

C

B

D

Fig. 13.10  MR imaging features of gout. (A) Sagittal T1-­weighted MR image of the foot shows multiple soft tissue and intra­articular masses of intermediate signal intensity, with extensive osseous involvement. (B) Corresponding T1-weighted fat-suppressed contrast-enhanced MR image shows intense heterogeneous enhancement, with no enhancement in the areas of calcification and amorphous urate deposits and variably intense enhancement in the inflamed synovium. (C) Coronal fluid-sensitive MR image shows the tophi to have heterogeneous intermediate signal intensity. Note subcutaneous edema around the ankle. (D) Tophi show hyperintense signal on the sagittal fluid-sensitive MR image.

A

B Fig. 13.11  Forefoot abnormalities in gout. (A) Early involvement of the first metatarsophalangeal joint. Erosions predominate at the dorsomedial aspect of the metatarsal head (arrow) and are associated with soft tissue swelling, articular space narrowing (arrowhead), and osteophyte formation. (B) Severe forefoot abnormalities. Findings include extensive bony destruction, with overhanging margins (arrow) and pathologic fractures. (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

231

CHAPTER 13  Gout metacarpophalangeal joints (Figs. 13.16 and 13.17). Large erosions of the carpometacarpal joints are characteristic, although all the compartments in the wrist may eventually be affected. When osseous destruction is centered at joint, the findings may simulate infection; however, identification of an echogenic tophus with US (Fig. 13.18) or positive findings on dual-energy CT may obviate a joint aspiration. Both US and MR imaging can be used to evaluate isolated soft tissue abnormalities with gout, such as peritendinitis (Fig. 13.19).

Elbow Abnormalities Bursal inflammation commonly produces bilateral soft tissue swelling over the extensor surface of the elbow. The presence of microtophi will produce relatively dense soft tissue swelling. With US, findings range from diffuse echogenic microtophi to larger tophi with possible shadowing (Fig. 13.20). Erosive and proliferative changes may be seen in the subjacent olecranon of the ulna.

Knee Abnormalities The knee is the second most common joint to be involved with gout. Findings include joint effusion with possible microtophi coating the intraarticular structures (see Fig. 13.3). Marginal erosions in the knee may also occur on the medial or lateral aspect of the femur and tibia, or both, in the absence of significant narrowing of the articular space. Common locations for soft tissue tophi include the patellar tendon and popliteus tendon. Involvement of the patellar tendon can produce extensive soft tissue swelling that my clinically simulate a tumor (Fig. 13.21). Popliteal tendon involvement may show only subtle increased density at the popliteus groove of the femur on radiographs with possible erosion (Fig. 13.22). Similar to other sites, gouty involvement of a tendon may simulate severe tendinosis on MR imaging, whereas US will show the characteristic appearance of a tophus.

Uncommon Sites of Disease Sacroiliac Joint Abnormalities

Sacroiliac joint involvement in gout is infrequent (Fig. 13.23). It may be bilateral or unilateral, with morphologic changes similar to those occurring in the peripheral joints. Fig. 13.12  Midfoot abnormalities in gout. A typical site of alteration is the tarsometatarsal joints, where erosions may be extensive.

Spine Abnormalities Spinal manifestations of gout are extremely uncommon. Radiographic abnormalities in the cervical segment include erosions of the odontoid

PP MT1

D

A

B

C

E

Fig. 13.13  Tophus: first metatarsal. Coronal (A) T1-weighted, ­ (B) fluid-sensitive ­ fat-suppressed, and (C) T1-­ weighted fat-suppressed contrast-enhanced ­ MR images show enhancing soft tissue and osseous fluid signal abnormality (arrow). US (D and E) in axial plane over the first metatarsal show the characteristic heterogeneous hyperechoic tophus (arrows) with internal echogenic foci. Note first metatarsal erosion (curved arrow) and hyperemia in (E). MT1, First metatarsal; PP, proximal phalanx.

232

SECTION 2  Articular Disorders

T

B

A

C

Fig. 13.14  Tophus: tibialis posterior tendon. (A) Sagittal T1-­weighted and (B) short-axis fluid-­sensitive fatsuppressed MR images show abnormal extensive intermediate signal involving the tibialis posterior tendon with surrounding fluid signal (arrow). (C) US long axis to the tibialis posterior tendon (T) shows echogenic tophus with internal hyperechoic foci (arrow).

A

Fig. 13.16  Hand abnormalities in gout. Interphalangeal joint alterations include bone erosion and intraosseous defects (arrowheads). Soft tissue swelling is seen. (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

Tibia

Talus

B Fig. 13.15  Microtophi: ankle joint. (A) Lateral radiograph and (B) US of anterior aspect of the ankle in the sagittal plane show distention of the anterior joint recess (arrow). Note internal hyperechoic foci with US representing microtophi creating the dense effusion on radiography.

process or endplates of the vertebral bodies, disc space narrowing, and vertebral subluxation. Spinal cord compression at various spinal levels has been reported as a complication of gout.

COEXISTENT ARTICULAR DISORDERS Calcium Pyrophosphate Dihydrate Crystal Deposition Chondrocalcinosis can occur in patients with gout, particularly within the menisci of the knee, symphysis pubis, and triangular fibrocartilage of the wrist. Hyaline cartilage calcification or widespread

CHAPTER 13  Gout

Fig. 13.17  Wrist abnormalities in gout. Diffuse disease of all compartments of the wrist is evident. Erosions (arrows) are most prominent at the common carpometacarpal compartment (upper arrow). (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

B

A

chondrocalcinosis is rare in gouty arthritis. Crystal deposition coating the intraarticular structures can be seen in gout and CPPD crystal deposition.

233

DP

Osteoarthrosis In patients with osteoarthrosis of the interphalangeal joints of the hand (nodal osteoarthritis) in whom inflammation and radiographically evident erosions develop, diagnostic possibilities include secondary gout, calcium hydroxyapatite crystal deposition, CPPD crystal deposition, and inflammatory (erosive) osteoarthritis.

SPECIAL TYPES OF GOUTY ARTHRITIS Early ­Onset Idiopathic Gouty Arthritis The reported peak age of occurrence of idiopathic gout varies from 30 to 50 years. Gout has been reported in early life, but clinical and radiographic abnormalities in idiopathic gout in the first two decades of life are uncommon. Radiographic abnormalities in these young patients resemble the changes in adults with gout (Fig. 13.24). The joints involved most frequently are those in the feet and hands.

Gout Associated With Hereditary Disease Type I Glycogen Storage Disease

Patients with type I glycogen storage disease (glucose-­ 6-­ phosphatase deficiency), a rare hereditary disorder of childhood, may contract gouty arthritis if they live to adulthood. In some of these patients, arthritis develops in the first decade of life and is extremely disabling.

Lesch-­Nyhan Syndrome Lesch-­Nyhan syndrome includes spasticity, choreoathetosis, intellectual disability, and compulsive self-­mutilation manifested as finger and lip biting. Boys are affected, and the disorder is X-­linked (Fig. 13.25). Complete or virtually complete deficiency of hypoxanthine-­guanine phosphoribosyltransferase is associated with Lesch-­Nyhan syndrome.

MP

C Fig. 13.18  Tophus: distal interphalangeal joint. (A) Lateral radiograph shows osseous destruction centered at the distal interphalangeal joint (arrow), with a pathologic fracture of the middle phalanx. (B) Sagittal fluid-­ sensitive MR image shows extensive fluid signal abnormality (arrow). (C) US of the dorsal aspect of the finger shows the characteristic echogenic appearance of a tophus (arrows). DP, Distal phalanx; MP, middle phalanx.

Radiographic abnormalities of Lesch-­Nyhan syndrome reflect self-­ mutilation, with amputation of the soft tissues and osseous structures of the hands. Gouty erosions, delayed skeletal maturation, coxa valga deformities with subluxation of the hips, and soft tissue tophi have been described in this disorder. Additional findings include traumatic changes occurring after seizures, cerebral atrophy, and uric acid calculi in the urinary tract.

Saturnine Gout The accidental contamination of alcoholic beverages with lead has been recognized for centuries. In addition, lead was sometimes intentionally added to wine to improve its flavor or prevent spoiling, a practice that was subsequently ruled illegal. Gout occurring as a complication of chronic lead intoxication is called saturnine gout. Currently, this form of gout is principally associated with the ingestion of illegally manufactured alcohol (moonshine). It is caused in large part by decreased urate clearance by the kidneys as a result of lead nephropathy. Saturnine gout accounts for only a small number of cases of gout. Patients are typically

234

SECTION 2  Articular Disorders

T T

A

C

B

D Fig. 13.19  Peritendinitis: extensor tendons. US of the dorsal aspect of the wrist (A) short axis and (B) long axis to the extensor tendons (T) show hypoechoic peritendinitis with hyperechoic microtophi (arrows) and hyperemia. (C) Sagittal fluid-­sensitive and (D) axial T1-weighted fat-suppressed contrast-enhanced MR images show abnormal fluid signal surrounding the extensor tendons with a small peripheral-­enhancing fluid collection (arrow).

O

A

O

B

C Fig. 13.20  Olecranon bursitis. US (A) shows distention of the olecranon bursa with diffuse echogenic microtophi (arrows). US (B) and lateral radiograph (C) from a different patient show more nodular tophi (arrows), with partial shadowing on US and increased density on radiography. O, Olecranon.

CHAPTER 13  Gout

A

235

B

P T

C

D Fig. 13.21  Tophus: patellar tendon. Patellar tendon tophus (arrow) is shown on (A) radiography as soft tissue swelling of increased density, (B) sagittal intermediate-­weighted, and (C) fluid-­sensitive MR images as diffuse abnormal intermediate signal intensity, and (D) US long axis to the patellar tendon as hyperechoic with a hypoechoic halo (arrows). P, Patella; T, tibia.

male, Black, aged 45 to 55 years, often azotemic and anemic, but otherwise asymptomatic except for joint disease. Radiographic findings resemble those of idiopathic gout.

Gout Associated With Other Clinical Disorders (Secondary Gout) A number of other disorders may result in hyperuricemia and secondary gout. Myeloproliferative disorders, which are apparent in approximately 5% to 10% of patients with gout, include polycythemia vera, leukemia, lymphoblastoma, myeloid metaplasia, hemolytic anemia, sickle cell anemia, pernicious anemia, thalassemia, multiple myeloma, secondary polycythemia, infectious mononucleosis, and Waldenström hyperproteinemia, as well as some carcinomas. Hyperuricemia may be associated with a variety of endocrine disorders, including hyperparathyroidism, hypoparathyroidism, myxedema, and hypoadrenal states. Additional causes of hyperuricemia and gout are obesity, idiopathic hypercalciuria, psoriasis, myocardial infarction and vascular disease, renal disease, and near-­starvation states. Drug-­induced gout has been noted in association with diuretic, pyrazinamide, and salicylate therapy.

DIFFERENTIAL DIAGNOSIS Rheumatoid Arthritis Rheumatoid arthritis produces radiographic alterations that differ from those of gout, including symmetric joint involvement, fusiform

soft tissue swelling, early joint space loss, marginal erosions, and regional osteoporosis (see Table 13.1).

Psoriatic Arthritis Psoriatic arthritis may produce radiographic changes that resemble those of gout, and the presence of elevated serum uric acid levels may lead to further diagnostic difficulty. Articular manifestations of psoriatic arthritis include progressive destruction of the peripheral joints of the extremities, periosteal proliferation (i.e., whiskering) at the margins of the joint, enthesitis, paravertebral ossification, and sacroiliac disease.

Calcium Pyrophosphate Dihydrate Crystal Deposition Disease CPPD crystal deposition disease resulting from the presence of intraarticular crystals can produce an acute arthritis termed the pseudogout syndrome. The clinical symptoms are identical to those of gout, and radiographic abnormalities consist of articular and periarticular calcification and pyrophosphate arthropathy. The cartilage calcification (chondrocalcinosis) accompanying CPPD crystal deposition disease is frequently widespread and involves hyaline cartilage and fibrocartilage; chondrocalcinosis in gout is usually localized to one or two joints and generally involves fibrocartilage alone. Intraarticular crystal deposition coating intraarticular structures can be seen in both conditions. Pyrophosphate arthropathy leads to structural joint abnormalities that demonstrate an unusual predilection for the wrist, metacarpophalangeal joints, and knee; they include joint space narrowing, subchondral sclerosis and cyst formation, bone fragmentation and collapse, and

236

SECTION 2  Articular Disorders

B

A

T F

C

D Fig. 13.22  Tophus: popliteus tendon. Popliteal tendon tophus (arrows) is shown with (A) radiography as soft tissue swelling of increased density, coronal (B), and axial (C) fluid-­sensitive MR images as diffuse abnormal intermediate tendon signal, and (D) US long axis over the lateral aspect of the femur in the coronal plane as hyperechoic with a hypoechoic halo. Note erosive changes of the femur (arrowhead). F, Femur; T, tibia.

Amyloidosis Amyloidosis, which occurs in a primary form or as a secondary manifestation of another disease, can result in bone and joint lesions. Amyloid infiltration of the articular structures may cause soft tissue masses and focal erosive osseous lesions indistinguishable from those of gout.

Xanthomatosis

Fig. 13.23  Sacroiliac joint abnormalities in gout. Bilateral sacroiliac joint alterations (arrows) typical of gout include scalloped erosions and adjacent bony sclerosis. (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

variable osteophyte formation. Although the radiographic manifestations of pyrophosphate arthropathy may resemble those of gout, the presence of lobulated soft tissue masses, intact joint spaces, and osseous erosions in the latter disease usually permits differentiation of the two disorders.

Tendinous xanthomas are particularly frequent on the extensor surface of the hand and foot and in the patellar and Achilles tendon regions. Tuberous xanthomas occur in the subcutaneous tissues of the elbows and knees. Radiographic changes consist of eccentric soft tissue nodular masses with subjacent bone erosion, findings simulating gouty tophi (Fig. 13.26). Hypercholesterolemia in patients with xanthomatosis is an important laboratory abnormality.

Inflammatory (Erosive) Osteoarthritis and Multicentric Reticulohistiocytosis Destructive articular abnormalities of the interphalangeal joints, which are noted in both gout and psoriatic arthritis, are also apparent in inflammatory (erosive) osteoarthritis and multicentric reticulohistiocytosis. The former disease affects middle-­aged and elderly women and produces symmetric joint changes, usually confined to the interphalangeal joints of the fingers, the first carpometacarpal joint, and the triscaphe portion of the midcarpal joint.

CHAPTER 13  Gout

A

237

B

Fig. 13.24  Early onset gouty arthritis. Progressive abnormalities occurred over a 2-­year period in this 23-­year-­old man with gout. (A) Initial film reveals soft tissue swelling and bony destruction of the proximal phalanx (arrow). (B) Subsequent radiograph demonstrates increased severity of the bony and soft tissue changes. (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 9:265, 1977.)

Fig. 13.25  Lesch-­Nyhan syndrome. Destruction and partial amputation of the phalanges are seen.

Fig. 13.26  Xanthomatosis. Note the soft tissue masses with subjacent scalloped erosions of the phalanges (arrows). (From Resnick D. The radiographic manifestations of gouty arthritis. CRC Crit Rev Diagn Imaging. 1977;9:265.)

238

SECTION 2  Articular Disorders

The erosions in inflammatory osteoarthritis frequently commence in the central portion of the joint. The radiographic manifestations in multicentric reticulohistiocytosis include erosions with sharp margins and lack of osteoporosis. Multicentric reticulohistiocytosis produces symmetric joint lesions, and the articular space may be narrowed rapidly. These latter features do not commonly occur in gout.

FURTHER READING Barthelemy CR, Nakayama DA, Carrera GF, et al. Gouty arthritis: a prospective radiographic evaluation of sixty patients. Skeletal Radiol. 1984;11:1. Chen CKH, Chung CB, Yeh L, et al. Carpal tunnel syndrome caused by tophaceous gout: CT and MR imaging features in 20 patients. AJR Am J Roentgenol. 2000;175:655. Chen CKH, Yeh LR, Pan H-­B, et al. Intra-­articular gouty tophi of the knee: CT and MR imaging in 12 patients. Skeletal Radiol. 1999;28:75. Desai MA, Peterson JJ, Garner HW, et al. Clinical utility of dual-­energy CT for evaluation of tophaceous gout. Radiographics. 2011;31:1365. Girish G, Glazebrook KN, Jacobson JA. Advanced imaging in gout. Am J Roentgenol. 2013;201:515. Good AE, Rapp R. Chondrocalcinosis of the knee with gout and rheumatoid arthritis. N Engl J Med. 1967;277:286. Halla JT, Ball GV. Saturnine gout: a review of 42 patients. Semin Arthritis Rheum. 1982;11:307. Lally EV, Zimmermann B, Ho Jr G, et al. Urate-­mediated inflammation in nodal osteoarthritis: clinical and roentgenographic correlations. Arthritis Rheum. 1989;32:86.

Lesch M, Nyhan WL. A familial disorder of uric acid metabolism and central nervous system function. Am J Med. 1964;36:561. Mallinson PI, Reagan AC, Coupal T, et al. The distribution of urate deposition within the extremities in gout: a review of 148 dual-­energy CT cases. Skeletal Radiol. 2014;43:277. Martel W. The overhanging margin of bone: a roentgenologic manifestation of gout. Radiology. 1968;91:755. Matteo AD, Cipolletta E, Ausili M, et al. The popliteus groove in the lateral femoral condyle: a shelter for monosodium urate crystals? Ann Rheum Dis. 2017;76:1358. Neogi T, Jansen TLTA, Dalbeth N, et al. 2015 gout classification criteria: an American College of Rheumatology / European League against Rheumatism collaborative initiative. Ann Rheum Dis. 2015;74:1789. Nicolaou S, Yong-­Hing CJ, Galea-­Soler S, et al. Dual-­energy CT as a potential new diagnostic tool in the management of gout in the acute setting. AJR. 2010;194:1072. Ogdie A, Taylor WJ, Weatherall M, et al. Imaging modalities for the classification of gout: systematic literature review and meta-­analysis. Ann Rheum Dis. 2015;74:1868. Omoumi P, Zufferey P, Malghem J, So A. Imaging in gout and other crystal-­ related arthropathies. Rheum Dis Clin Am. 2016;42:621–644. Resnick D, Broderick TW. Intraosseous calcifications in tophaceous gout. AJR Am J Roentgenol. 1981;137:1157. Resnick D, Reinke RT, Taketa RM. Early-­onset gouty arthritis. Radiology. 1975;114:67. Seegmiller JE. Human aberrations of purine metabolism and their significance for rheumatology. Ann Rheum Dis. 1980;39:103. Strobl S, Halpern EJ, Abd Ellah M, et. al. Acute gouty knee arthritis: Ultrasound findings compared with dual-energy CT findings. Am J Roentgenol. 2018;210:1323.

14 Calcium Pyrophosphate Dihydrate Crystal Deposition Disease S U M M A R Y O F K E Y F E AT U R E S • Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is a disorder characterized by CPPD crystals in and about joints. • Chondrocalcinosis, or calcification of cartilage, is seen in CPPD crystal deposition disease and other conditions.

• CPPD crystals may deposit in ligaments, synovium, joint capsule, and tendons. • Joint damage resulting from CPPD crystal deposition is termed pyrophosphate arthropathy.

INTRODUCTION

Chondrocalcinosis: Term reserved for pathologically or radiographically evident cartilage calcification. In some instances, this calcification may indicate not CPPD crystal deposition but deposits of other crystals. Articular and periarticular calcification: Terms used for pathologically or radiographically evident calcification in and around joints. Chondrocalcinosis is but one of the possible manifestations of such calcification. Pyrophosphate arthropathy: Term used to describe a peculiar pattern of structural joint damage occurring in CPPD crystal deposition disease that simulates, in many ways, degenerative joint disease but is characterized by distinctive features.

  

Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is one of the most common of articular disorders, especially in elderly persons. As many as 50% of persons over the age of 80 years have CPPD crystal deposition in one or more of their joints, although such deposition is asymptomatic in most of them. In others, several different clinical patterns are encountered that simulate a variety of other rheumatologic disorders, leading to diagnostic difficulty. Therefore it is often the findings displayed on imaging studies, especially conventional radiography, that allow a specific diagnosis of CPPD crystal deposition disease. Of importance, however, chondrocalcinosis can no longer be considered the only significant imaging feature of this disease. Equally characteristic imaging findings include the presence of other intraarticular and periarticular calcifications and structural joint damage. The pattern and distribution of structural joint damage (i.e., pyrophosphate arthropathy) are especially distinctive and can often be differentiated from the features of degenerative joint disease to allow an accurate diagnosis of CPPD crystal deposition disease even in the absence of chondrocalcinosis. In 1961 and 1962, McCarty and others discovered nonurate crystals in the joint fluid of patients experiencing gout­like attacks of arthritis. These crystals were subsequently identified as CPPD by their x-­ray diffraction powder pattern. When clinical and radiographic findings in these patients were analyzed, it was recognized that the same disease had been described as chondrocalcinosis polyarticularis, reflecting the calcific deposits within cartilage. It thus became clear that patients with a distinctive gout­like pattern of arthritis (pseudogout syndrome) had crystal accumulation within joints (CPPD crystal deposition) that could cause cartilage calcification (chondrocalcinosis). Subsequently, other crystals were found to produce calcific collections in the knee.

TERMINOLOGY Some inconsistency exists in the terminology that has been used to describe this disorder; the following terms are employed most commonly at the current time. Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease: General term for a disorder characterized by the presence of Ca2P2O7 • 2H2O (CPPD) crystals in or around joints. Pseudogout: Term applied to one of the clinical patterns that may be associated with crystal deposition. This pattern, characterized by intermittent acute attacks of arthritis, simulates gout.

CLINICAL PATTERNS CPPD crystal deposition disease affects both men and women and is generally observed in middle-­aged and elderly patients. Various clinical patterns underscore the ability of this disease to simulate a variety of other conditions, and a patient may demonstrate several different clinical patterns during the course of the disease. A pattern of disease simulating gout and designated pseudogout occurs in about 10% to 25% of symptomatic patients with CPPD crystal deposition disease. This pattern, which is characterized by acute or subacute self-­limited attacks of arthritis, may be provoked by trauma, surgery, intraarticular injection, or medical illness. As one example, attacks of pseudogout may be observed after parathyroidectomy. A second clinical pattern characterized by almost continuous acute attacks of arthritis simulates rheumatoid arthritis (i.e., pseudo­rheumatoid arthritis) and is seen in about 5% of symptomatic patients. In about 50% to 60% of symptomatic patients, chronic articular disease with or without acute exacerbations simulate osteoarthrosis (i.e., pseudo-­osteoarthrosis). Additional less frequent clinical patterns of CPPD crystal deposition disease simulate neuropathic disorders, spondyloarthropathies, and other processes. Of importance, the vast majority of persons with CPPD crystal deposition that is evident with radiography or other imaging methods are asymptomatic (with regard to articular manifestations) at the time of the imaging studies, suggesting that such crystal deposition is a normal manifestation of aging.

CLASSIFICATION CPPD crystal deposition disease can be conveniently classified into cases that are hereditary, sporadic (idiopathic), or associated with

239

240

SECTION 2  Articular Disorders

other disorders. The importance of genetic factors in the pathogenesis of premature or extensive CPPD crystal deposition is underscored by innumerable reports of multiple kindreds with familial involvement. Indeed, several genetic loci have been associated with familial CPPD crystal deposition disease in recent years. Sporadic disease usually occurs in middle-­aged and elderly patients, and series with both male and female predominance have been recorded. Other disorders associated with CPPD crystal deposition disease are discussed in the next section.

ASSOCIATED DISEASES Many disorders have been reported in association with CPPD crystal deposition (Box 14.1). In most instances, the nature and significance of such associations cannot be assessed and they may merely represent the chance occurrence of two diseases. The most important disorders associated with CPPD crystal deposition disease are hyperparathyroidism, hemochromatosis, hypophosphatasia, and hypomagnesemia (including Bartter and Gitelman syndromes).

BOX 14.1  Conditions Associated With

CPPD Crystal Deposition

Group A: True association—high probability 1. Primary hyperparathyroidism 2. Familial hypocalciuric hypercalcemia 3. Hemochromatosis 4. Hemosiderosis 5. Hypophosphatasia 6. Hypomagnesemia 7. Bartter and Gitelman syndromes 8. Hypothyroidism 9. Gout 10. Neuropathic osteoarthropathy 11. Amyloidosis 12. Localized trauma a. Surgery for osteochondritis dissecans b. Hypermobility syndrome 13. Corticosteroid therapy (long-­term) 14. Aging Group B: True association—modest probability 1. Hyperthyroidism 2. Nephrolithiasis 3. Diffuse idiopathic skeletal hyperostosis 4. Ochronosis 5. Wilson disease 6. Hemophilic arthritis Group C: True association unlikely 1. Diabetes mellitus 2. Hypertension 3. Azotemia 4. Hyperuricemia 5. Gynecomastia 6. Inflammatory bowel disease 7. Rheumatoid arthritis 8. Paget disease of bone 9. Acromegaly From McCarty D. Crystals, joints, and consternation. Ann Rheum Dis. 1983;42(3):243–253.

PATHOGENESIS OF CRYSTAL DEPOSITION AND SYNOVITIS CPPD crystal deposition is generally first observed in articular cartilage, although deposits may be recognized in other articular tissues, such as synovium and capsule, as well as periarticular tissues, such as tendons and ligaments. The earliest site of crystal deposition is in the pericellular matrix around the chondrocyte lacunae in the midzonal area. The precise mechanism by which CPPD crystals are precipitated in cartilage is not fully understood, although the role of extracellular inorganic pyrophosphate produced by chondrocytes appears critical. Once the crystals are formed, they mediate tissue damage and inflammation by multiple mechanisms. The process of crystal shedding has been emphasized in some reports, a process that may become exaggerated in conditions associated with significant cartilage destruction, such as infection and neuropathic osteoarthropathy.

GENERAL PATHOLOGIC FEATURES The pathologic features associated with CPPD crystal deposition disease include crystal deposition in various articular and periarticular tissues and structural joint damage.

Crystal Deposition CPPD crystals may be apparent in cartilage, synovium, capsule, soft tissues, tendons, and ligaments. With regard to cartilage, crystalline deposits can occur in both fibrocartilage and hyaline cartilage (Fig. 14.1). Fibrocartilaginous collections of CPPD crystals are most frequently observed in the menisci of the knee, triangular fibrocartilage of the wrist, acetabular labra, symphysis pubis, and annulus fibrosus of the intervertebral disc. Additional sites of fibrocartilaginous deposition include the articular discs of the acromioclavicular and sternoclavicular joints and the glenoid labra. CPPD crystal deposition disease with calcification also occurs in tendons and ligaments, most often in the Achilles, triceps, quadriceps, gastrocnemius, and supraspinatus tendons and cruciate ligaments of the knees. Soft tissue deposits may become large, so-­called tophaceous pseudogout.

Structural Joint Damage The structural joint damage associated with CPPD crystal deposition disease resembles degenerative joint disease on pathologic as well as imaging examination. Cartilage fibrillation and erosion correlate with radiographically evident joint space narrowing. Subchondral bone contains thickened trabeculae and multiple cysts. When compared with the cystic lesions occurring in degenerative joint disease, the cysts of CPPD crystal deposition disease are larger, more numerous, and more widespread. Bone fragmentation and collapse, which are frequent in this disease, may be related to fracture of these cystic lesions. Intraarticular osseous bodies may be loose within the joint cavity or embedded in the cartilaginous and synovial tissue.

GENERAL RADIOGRAPHIC FEATURES KEY CONCEPTS  • Imaging features can be divided into calcification and pyrophosphate arthropathy. • Calcification occurs in cartilage (fibrocartilage and hyaline), synovium, capsules bursae, tendons, ligaments, soft tissues, and vessels. • Pyrophosphate arthropathy is characterized by degenerative-like changes that occur in an unusual distribution and are associated with prominent subchondral cysts.

241

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

H

F

H

H F

F

B

A

C

Fig. 14.1  Pathologic abnormalities: crystal deposition in cartilage. (A) Fibrocartilage and hyaline cartilage of the knee. Sagittal section reveals CPPD crystal deposition in the fibrocartilage (F) of the menisci and the hyaline cartilage (H) of the patella, femur, and tibia. (B) Fibrocartilage of the intervertebral disc. Fibrocartilage (F) calcification is apparent mainly in the annulus fibrosus in this sagittal section of the spine. (C) Fibrocartilage and hyaline cartilage of the wrist. In a coronal section, both fibrocartilage (F) and hyaline cartilage (H) are calcified.

Articular and Periarticular Calcification CPPD crystal deposition disease is associated with calcification of articular and periarticular structures (Fig. 14.2). Articular and periarticular calcific deposits may be located in cartilage, synovium, capsules, tendons, bursae, ligaments, soft tissues, and vessels, and may demonstrate some degree of symmetry from one side to the other. The frequency of radiographically demonstrable articular calcification is greatest in the knee, symphysis pubis, wrist, elbow, and hip. In patients who demonstrate calcification of some articulation on complete skeletal surveys, frontal radiographs of the knees alone detect calcification in approximately 90%; frontal radiographs of the knees and symphysis pubis detect calcification in approximately 98%; and frontal radiographs of the knees, symphysis pubis, and wrists detect calcification in approximately 100%. Thus an effective screening test for articular calcification consists of a posteroanterior radiograph of each wrist, an anteroposterior radiograph of the pelvis, and an anteroposterior radiograph of each knee.

4 1 2

3

Cartilaginous Calcification Chondrocalcinosis is most frequent in the knee, wrist, symphysis pubis, elbow, and hip, and may involve fibrocartilage or hyaline cartilage (Fig. 14.3). Fibrocartilaginous calcification is most common in the menisci of the knee, triangular fibrocartilage of the wrist, symphysis pubis, annulus fibrosus of the intervertebral disc, and acetabular and glenoid labra. Fibrocartilaginous deposits appear as thick, shaggy, irregular radiodense areas, particularly within the central aspect of the joint cavity. Hyaline cartilage calcification is most common in the wrist, knee, elbow, and hip. These deposits may be thin, linear or curvilinear, or punctate, and separated from the subjacent subchondral bone.

Synovial and Capsular Calcification Calcification within the synovial membrane is a common feature of CPPD crystal deposition disease (Fig. 14.4). Synovial deposits are most frequent in the wrist, particularly about the radiocarpal and distal radioulnar joints; knee; and metacarpophalangeal and metatarsophalangeal joints. These deposits may simulate idiopathic synovial chondromatosis. CPPD crystal deposition in joint capsules is most commonly observed in the elbow (Fig. 14.5) and metatarsophalangeal

Fig. 14.2  Articular and periarticular calcifications. Deposits may be located in the hyaline cartilage (1), fibrocartilage (2), synovial membrane (3), and joint capsule (4).

joints but is also observed in the metacarpophalangeal and glenohumeral joints.

Tendinous, Bursal, and Ligamentous Calcification Calcification is most often observed in the Achilles (Fig. 14.6), triceps, quadriceps, gastrocnemius, and supraspinatus tendons, as well as in the subacromial-­subdeltoid bursa. In tendons, calcifications may simulate the findings of calcific tendinitis related to calcium hydroxyapatite crystal deposition, except that they may be more linear and elongated.

242

SECTION 2  Articular Disorders

H

H L F

F

A

B F F

H

F

C

F

D

Fig. 14.3  Radiographic abnormalities: chondrocalcinosis. (A–C) Chondrocalcinosis of fibrocartilage (F) is apparent in the menisci of the knee, triangular fibrocartilage of the wrist, and annulus fibrosus of the intervertebral discs. It is thick and shaggy in character. Hyaline cartilage calcification (H), which is seen in the knee and wrist, is thin and parallels the osseous surface. Possible ligamentous calcification (L) is also noted in the wrist. (D) Hyaline cartilage (H) calcification in the elbow is seen in a frontal radiograph. (A, From Resnick D, Niwayama G, Goergen TG, et al: Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

Soft Tissue and Vascular Calcification In some patients, poorly defined calcific deposits are seen in the soft tissues and vessels. Soft tissue calcification is most common about the elbow, wrist, and pelvis. Tumorous calcific collections that resemble gouty tophi are occasionally observed (Fig. 14.7). The resulting radiographic findings, which have been designated tophaceous pseudogout, may resemble the abnormalities of idiopathic synovial chondromatosis, soft tissue chondrosarcoma or osteosarcoma, gout, soft tissue chondroma, periosteal or parosteal osteosarcoma, or calcium hydroxyapatite crystal deposition.

Pyrophosphate Arthropathy The structural joint changes associated with CPPD crystal deposition disease are both common and characteristic. These alterations may appear without adjacent or distant articular calcification. Pyrophosphate arthropathy is most common in the knee, wrist, and metacarpophalangeal joints. The distribution is usually bilateral, although symmetric changes may not be present. In some ways, pyrophosphate arthropathy is similar to degenerative joint disease with regard to

articular space narrowing, bony sclerosis, and cyst formation, but it differs from degenerative joint disease in five respects: 1. Unusual articular distribution: Although arthropathy is encountered in weight-­bearing joints, such as the knee and hip, it is also apparent in sites that are involved less commonly in degenerative joint disease, such as the wrist, elbow, and glenohumeral joint (Fig. 14.8). 2. Unusual intraarticular distribution: The distribution of pyrophosphate arthropathy in certain joints is characteristic (Fig. 14.9). Thus isolated or significant involvement of the radiocarpal or trapezio­ scaphoid joint of the wrist, patellofemoral compartment of the knee, and talocalcaneonavicular joint of the midfoot may signify CPPD crystal deposition disease. 3. Prominent subchondral cyst formation: The cysts associated with pyrophosphate arthropathy are numerous and may reach considerable size. They are typically multiple, subchondral in location, clustered in a group, and surrounded by sclerotic, smudged, and indistinct margins. When large, they may fracture or simulate neoplasm.

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

C S

243

S

T

Fig. 14.4  Radiographic abnormalities: synovial calcification. Observe the synovial (S) and capsular (C) calcification of the metacarpophalangeal joints. (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

Fig. 14.6  Radiographic abnormalities: tendinous calcification. Calcification within the Achilles tendon (T) is apparent. (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

C

H

Fig. 14.5  Radiographic abnormalities: capsular calcification. In the elbow, capsular calcification (C) is associated with hyaline cartilage calcification (H).

4. Destructive bone changes that are severe and progressive: Pyrophosphate arthropathy may be associated with extensive and rapid subchondral bone collapse and fragmentation and the appearance of single or multiple intraarticular osseous bodies (Fig. 14.10). These features resemble those of neuropathic osteoarthropathy. 5. Variable osteophyte formation: In some patients, large, irregular bony excrescences are noted about the involved joints; in others,

Fig. 14.7  Radiographic abnormalities: tophaceous pseudogout. Intraarticular and periarticular tumoral deposits are evident at the base of the thumb. (Courtesy G. El Khoury, MD, Iowa City, IA.)

joint space narrowing, sclerosis, and fragmentation may be unaccompanied by osteophyte formation and produce a polished, eburnated bony surface (Fig. 14.11).

244

SECTION 2  Articular Disorders

GENERAL MAGNETIC RESONANCE IMAGING FEATURES CPPD crystal accumulation typically leads to masses with predominantly low signal intensity, although these masses may show enhancement of

signal intensity after the intravenous administration of a gadolinium-­ containing contrast agent. Small collections of CPPD crystals in the menisci of the knee and the triangular fibrocartilage of the wrist are easily overlooked during magnetic resonance (MR) imaging examinations, as are those within the intervertebral disc. Low signal intensity is characteristic of such calcific collections. In the menisci of the knee, however, regions of intermediate signal intensity may simulate meniscal tears. Similarly, in hyaline cartilage, CPPD crystal deposits appear as hypointense foci (Fig. 14.12). Synovial calcifications and intraarticular debris (often composed of both CPPD and calcium hydroxyapatite crystals) are also apparent on MR imaging.

GENERAL ULTRASONOGRAPHY IMAGING FEATURES The primary role of ultrasonography (US) in evaluation of CPPD crystal deposition disease is to assess for joint effusion and possible synovitis (Fig. 14.13), similar to other arthritides, often followed by US-­ guided joint aspiration or synovial biopsy. Calcification of articular and periarticular structures can be visualized by US as echogenic foci with possible shadowing; however, radiographic correlation is essential to confirm a correct diagnosis. Chondrocalcinosis, appearing as punctate hyperechoic foci within hyaline and fibrocartilage, and identification of crystal deposition coating the hyaline cartilage (the double contour sign) can be seen, although the latter has also been described with gout.

IMAGING FEATURES IN SPECIFIC ARTICULATIONS Knee

Fig. 14.8  Characteristics of pyrophosphate arthropathy: unusual articular distribution. Changes in the elbow include joint space narrowing, subchondral cysts (solid arrow), deformity of the radial head (arrowhead), and fragmentation (open arrow). (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

A

The knee is the joint involved most commonly (Table 14.1). Chondrocalcinosis and synovial calcification may be combined with tendinous and ligamentous deposits in the quadriceps muscle, gastrocnemius muscle, and collateral and cruciate ligaments. Chondrocalcinosis of the menisci and hyaline cartilage with gastrocnemius tendon calcification is characteristic (Fig. 14.14). Additionally, intraarticular crystal deposition may coat the surface of the hyaline cartilage and menisci, creating an arthrogram-­like effect (Fig. 14.15). Pyrophosphate arthropathy most commonly involves the medial femorotibial compartment; the patellofemoral compartment is the

B Fig. 14.9  Characteristics of pyrophosphate arthropathy: unusual intraarticular distribution. (A) Observe the selective involvement of the radiocarpal compartment of the wrist (arrow). (B) Predilection for the patellofemoral compartment of the knee is apparent on this lateral radiograph.

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

A

245

B

Fig. 14.10  Characteristics of pyrophosphate arthropathy: destructive bone changes that are severe and progressive. Radiographs of the glenohumeral joint obtained 16 months apart outline the rapidity of joint destruction in this disease (arrows). (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

second most commonly involved area. More important, the distribution of knee compartmental alterations in CPPD crystal deposition disease differs from that of degenerative joint disease. Isolated or severe patellofemoral compartment changes or isolated lateral compartment alterations (especially in men) (Fig. 14.16), severe flattening of either the medial or lateral tibial condyles, and significant varus or valgus angulation are characteristics of knee involvement in this disease.

Wrist

A

B

Fig. 14.11  Characteristics of pyrophosphate arthropathy: variable osteophyte formation. (A) In some persons, large osteophytes (arrowhead) accompany joint space narrowing (arrow). (B) In other persons, joint space narrowing (arrow) occurs without osteophyte formation. Intraarticular bodies are apparent (arrowhead). (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

Calcification in the wrist is observed most commonly in the triangular fibrocartilage (Fig. 14.17); hyaline cartilage of the radiocarpal, midcarpal, and common carpometacarpal joints; synovium; and ligamentous structures, particularly between the scaphoid and lunate and between the lunate and triquetrum (see Fig. 44-­3B). Carpal malalignment with separation of the scaphoid and lunate may be observed, with disruption of the intervening interosseous ligament. The wrist arthropathy of CPPD crystal deposition disease demonstrates an unusual predilection for the radiocarpal compartment (Fig. 44-­18). Joint space narrowing, sclerosis, and discrete subchondral radiolucent lesions (Fig. 44-­19) are observed between the distal end of the radius and the proximal carpal row. The scaphoid moves proximally, deepening the scaphoid fossa in the distal articular surface of the radius, and the lunate may move distally and approach the capitate (Fig. 44-­20). The resulting appearance is similar to what has been termed scapholunate advanced collapse (SLAC) in instances of wrist injury, although posttraumatic SLAC is more often unilateral and is also seen in young persons. The compartmental distribution of CPPD arthropathy differs considerably from that of degenerative joint disease. The latter disorder affects predominantly the first carpometacarpal and trapezioscaphoid areas, with sparing of the radiocarpal compartment.

246

SECTION 2  Articular Disorders

A

C

B

Fig. 14.12  Chondrocalcinosis: radiography and MR imaging. (A) Anteroposterior and (B) lateral radiographs and (C) sagittal fluid-­sensitive MR image show chondrocalcinosis of the hyaline cartilage (arrowheads). Note chondrocalcinosis of the medial meniscus (arrow) and intraarticular bodies in a popliteal cyst (curved arrow).

R

L

third metacarpophalangeal joints and are characterized by joint space narrowing, sclerosis, cyst formation, and bony collapse, particularly of the metacarpal head. Although the second and third metacarpophalangeal joints are also involved in hemochromatosis, changes in these same joints in the fourth and fifth digits are not infrequent in hemochromatosis. Further, the absence of erosions of the metacarpal heads in CPPD crystal deposition disease differs from the findings in rheumatoid arthritis.

C

Hip Fig. 14.13  Wrist synovitis: US. Evaluation of the dorsal wrist in the sagittal plane shows hypoechoic distention of the radiocarpal (arrow) and midcarpal (arrowhead) joint recesses with hyperemia with color Doppler imaging representing synovitis. C, Capitate; L, lunate; R, radius.

TABLE 14.1  Most Frequent Sites of Clinical

and Radiographic Abnormalities in CPPD Crystal Deposition Disease Clinical Manifestations Calcification Hand

+

Wrist

+

Arthropathy +

+

Elbow

+ +

Shoulder

+

Hip

+

+

Knee

+

+

Ankle

+

Spine

+

Pelvis

+

+

Metacarpophalangeal Joints Radiographic abnormalities in this location include cartilaginous, capsular, and synovial calcifications, and arthropathy (see Fig. 14.17). The structural joint changes show a predilection for the second and

Both fibrocartilaginous calcification of the acetabular labra and hyaline cartilage calcification may be seen (Fig. 14.21). Joint space narrowing may involve the entire joint or be confined to its superolateral aspect. In the latter situation, the changes resemble those of osteoarthrosis, whereas with diffuse loss of joint space, the findings are similar to those of rheumatoid arthritis. Additional manifestations of hip involvement in CPPD crystal deposition disease are rapid and extensive destruction of the femoral head and acetabulum, subchondral cysts of variable size, fragmentation, protrusio acetabuli deformity, and tendon calcification.

Spine In the spine, CPPD crystal deposition disease frequently demonstrates intervertebral disc calcification, with deposits initially appearing in the outer fibers of the annulus fibrosus (Fig. 14.22). The nucleus pulposus is generally not involved. CPPD deposits are detected in other spinal tissues as well, including the ligamentum flavum, posterior longitudinal ligament, interspinous and supraspinous ligaments, and interspinous bursae. Disc space narrowing is a common finding in CPPD crystal deposition disease. The narrowing may be extensive, widespread, and associated with considerable vertebral sclerosis. In unusual circumstances, severe osseous destruction of the adjacent vertebral bodies is seen. CPPD crystal deposition in the spine is widespread, and destructive abnormalities of the cervical spine are occasionally apparent. In the atlantoaxial joint, CPPD crystal deposition may encircle the dens, causing inflammation (termed crowned dens syndrome) associated with joint space narrowing and cyst formation (Fig. 14.23). Tumorlike masses may compress the spinal cord, and the anterior longitudinal ligament may become calcified as well. Complications of involvement

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

247

Fig. 14.14  Chondrocalcinosis and gastrocnemius tendon calcification. Radiographs show meniscal chondrocalcinosis (arrows) and gastrocnemius tendon calcification (curved arrow). Also note synovial calcification in the suprapatellar recess (arrowhead).

Fig. 14.15  Intraarticular crystal deposition. Radiographs show linear intraarticular calcification outlining the hyaline cartilage and menisci (arrows). Note adjacent punctate hyaline cartilage chondrocalcinosis (arrowhead) and gastrocnemius tendon calcification (curved arrow).

of the cervical spine include atlantoaxial subluxation and spontaneous fractures of the odontoid process.

DIFFERENTIAL DIAGNOSIS

CLINICAL AND RADIOGRAPHIC CORRELATIONS

Chondrocalcinosis, particularly of the menisci of the knee, may relate not only to the presence of CPPD crystals but also to the deposition of other crystalline material, such as dicalcium phosphate dihydrate and calcium hydroxyapatite. Chondrocalcinosis of more than one meniscus, of both knees, or of more than one set of joints usually indicates CPPD crystal deposition. Additional causes of intraarticular radiodense lesions that may simulate CPPD crystal deposition include intraarticular bodies; meniscal ossicles of the knee; osteochondritis dissecans of the knee, ankle, or elbow; osteonecrosis; and idiopathic synovial chondromatosis.

Although calcification and arthropathy frequently coexist in the same joint, either radiographic finding can be identified in the absence of the other. More commonly, calcification precedes arthropathy, with calcification beginning in the fibrocartilage and subsequently involving the hyaline cartilage of large joints and eventually the hyaline cartilage of the small joints of the hands and feet. In some instances, however, arthropathy develops in patients who demonstrate neither local (in the same joint) nor distant (in any joint) calcification.

Intraarticular Calcification

248

SECTION 2  Articular Disorders

Fig. 14.16  Pyrophosphate arthropathy. Radiograph shows predominant severe patellofemoral articular changes.

Fig. 14.18  Wrist and hand abnormalities in CPPD crystal deposition disease. Radiograph shows severe radiocarpal and midcarpal degenerative changes (arrow). Note soft tissue calcification (curved arrow) and degenerative changes of the second and third metacarpophalangeal joints (arrowhead).

Periarticular Calcification Periarticular radiodense deposits may be associated with metastatic calcification, dystrophic calcification, or calcinosis. Such calcification may be seen in renal osteodystrophy, idiopathic tumoral calcinosis, collagen vascular diseases, milk-­alkali syndrome, and hypervitaminosis D. Calcific periarthritis or peritendinitis may be associated with the deposition of calcium hydroxyapatite crystals in tendons and bursae, particularly about the shoulder. Tendinous calcification in CPPD crystal deposition disease produces similar abnormalities, but the deposits may be more linear and elongated.

Pyrophosphate Arthropathy

Fig. 14.17  Wrist and hand abnormalities in CPPD crystal deposition disease. Radiograph shows triangular fibrocartilage chondrocalcinosis (arrowhead) and structural changes at the radiocarpal as well as the second and third metacarpophalangeal joints, where synovial and ligamentous calcifications are also noted (arrows).

The arthropathy of CPPD crystal deposition disease closely resembles degenerative joint disease but, as indicated previously, involves unusual joints and compartments and is associated with extensive bone sclerosis, multiple subchondral cysts, bone fragmentation, osseous debris, and variable osteophyte formation (Table 14.2). The degree of bone fragmentation, sclerosis, and collapse encountered in patients with CPPD crystal deposition disease is reminiscent of the changes accompanying other disorders such as neuropathic osteoarthropathy, steroid-­ induced arthropathy, osteonecrosis, and infection. Bone erosion is not a feature of CPPD crystal deposition disease. The absence of erosive change usually aids in distinguishing this condition from rheumatoid arthritis and related synovial disorders such as psoriatic arthritis and ankylosing spondylitis. The appearance of joint space narrowing, bony eburnation, osteophytosis, and sclerosis in CPPD crystal deposition disease may resemble the features of gout. Differentiation between gout and CPPD crystal deposition disease is further complicated by the occasional presence of periarticular calcification and chondrocalcinosis in gouty arthritis. In gouty arthritis,

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

A

B

249

C

Fig. 14.19  Wrist abnormalities in CPPD crystal deposition disease. (A) Radiograph and (B) T1-­weighted and (C) fluid-­sensitive coronal MR images show subchondral cysts (arrowheads). Note triangular fibrocartilage chondrocalcinosis (arrow).

osteoarthrosis, isolated patellofemoral compartment changes, especially in men, are an important diagnostic clue, suggesting the presence of pyrophosphate arthropathy. Patellofemoral compartment erosions may be noted in patients with primary hyperparathyroidism or renal osteodystrophy, but additional skeletal findings allow the diagnosis of these conditions.

Wrist Selective involvement of the radiocarpal compartment of the wrist is most characteristic of CPPD crystal deposition disease. Degenerative joint disease in the wrist usually produces changes in the first carpometacarpal and trapezioscaphoid areas rather than in the radiocarpal compartment. After injury, however, osteoarthrosis can appear in any region of the wrist, including the radioscaphoid, radiolunate, and lunate-­capitate spaces. Radiocarpal compartment changes may occasionally be seen in patients with gout or occupation-­related degenerative disease. Rheumatoid arthritis also involves this joint, but additional changes in other compartments of the wrist are generally apparent in that disease. Posttraumatic SLAC leads to structural abnormalities of the wrist that closely resemble those of CPPD crystal deposition disease. A unilateral distribution and, in some cases, the young age of the patient are clues that suggest SLAC is related to prior injury.

Metacarpophalangeal Joints

Fig. 14.20  Wrist abnormalities in CPPD crystal deposition disease. Radiograph shows radiocarpal and midcarpal joint changes consistent with pyrophosphate arthropathy, including scapholunate advanced collapse (arrow), triangular fibrocartilage chondrocalcinosis (arrowhead), and characteristic changes of the second and third metacarpophalangeal joints (curved arrow).

however, focal soft tissue swelling and bone erosion—findings not generally seen in CPPD crystal deposition disease—may be noted.

Knee Although the distribution of compartmental abnormalities in the knee in CPPD crystal deposition disease may be identical to that of

The metacarpophalangeal joints are frequently altered in CPPD crystal deposition disease. The changes in this location predominate over changes at the interphalangeal joints, whereas the converse is true in osteoarthrosis. The absence of osseous erosion of the metacarpal heads and proximal phalanges in CPPD crystal deposition disease allows its differentiation from rheumatoid arthritis. The arthropathies of idiopathic CPPD crystal deposition disease and hemochromatosis are very similar, but subtle differences have been defined. Although both disorders involve the second and third metacarpophalangeal joints, changes in the fourth and fifth digits are more prevalent in hemochromatosis. Peculiar hooklike osteophytes on the radial aspect of the metacarpal heads are also more characteristic of hemochromatosis than idiopathic CPPD crystal deposition disease.

250

SECTION 2  Articular Disorders

F

A

B

Fig. 14.21  Hip abnormalities in CPPD crystal deposition disease. (A) Fibrocartilage (F) calcification of the acetabular limbus is seen adjacent to a small subchondral cystic lesion (arrow). (B) Considerable flattening and deformity of the femoral head are associated with an elongated lateral acetabular osteophyte and new bone formation on the medial aspect of the femoral neck. The articular space is obliterated, and a large subchondral cyst (arrow) is evident. (From Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease [CPPD]: pseudogout. Radiology. 1977;122:1.)

Fig. 14.22  Spine abnormalities in CPPD crystal deposition disease: alterations of the intervertebral disc. In association with widespread disc calcification, disc space loss and bone eburnation are seen in this sagittal section of the lumbosacral junction.

CHAPTER 14  Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

A

251

B

Fig. 14.23  Spine abnormalities in CPPD crystal deposition disease: alterations at the atlantoaxial joint. Axial (A) and sagittal reformatted (B) CT images show synovial, capsular, and ligament calcification surrounding the odontoid process (arrows), which can be seen in the crowned dens syndrome. Note degenerative changes at the median anterior atlantoaxial joint.

TABLE 14.2  Differential Diagnosis of Pyrophosphate Arthropathy

Common sites

Pyrophosphate Arthropathy

Degenerative Joint Disease

Neuropathic Osteoarthropathy

Knee, wrist (radiocarpal), metacarpophalangeal

Hip, knee, interphalangeal of hand, wrist (first carpometacarpal, trapezioscaphoid), first metatarsophalangeal

Tabes: knee, ankle, hip, spine Diabetes: midfoot and forefoot Syringomyelia: upper extremity

Rheumatoid Arthritis Wrist (pancompartmental), metacarpophalangeal, interphalangeal of hand, metatarsophalangeal, knee, shoulder, cervical spine

Articular space narrowing

+

+

±

+

Sclerosis

+

+

+

–

Osteophytosis

±

+

±

–

Erosions

–

–

–

+

Cysts

+

+

±

+

Fragmentation

+

–

+

–

FURTHER READING Adamson III TC, Resnik CS, Guerra Jr J, et al. Hand and wrist arthropathies of hemochromatosis and calcium pyrophosphate deposition disease: distinct radiographic features. Radiology. 1983;147:377. Chang EY, Lim WY, Wolfson T, et al. Frequency of atlantoaxial calcium pyrophosphate dehydrate deposition at CT. Radiology. 2013;269:519. Chen C, Chandnani VP, Kang HS, et al. Scapholunate advanced collapse: a common wrist abnormality in calcium pyrophosphate dihydrate crystal deposition disease. Radiology. 1990;177:459. Dieppe PA, Alexander GJM, Jones HE, et al. Pyrophosphate arthropathy: a clinical and radiological study of 105 cases. Ann Rheum Dis. 1982;41:371. Jacques T, Michelin P, Badr S, et al. Conventional radiography in crystal arthritis. Radiol Clin. 2017;55:967. Leisen J. Calcium pyrophosphate dihydrate deposition disease: tumorous form. AJR. 1982;138:962. Martel W, Champion CK, Thompson GR, et al. A roentgenologically distinctive arthropathy in some patients with the pseudogout syndrome. AJR. 1970;109:587. Martel W, McCarter DK, Solsky MA, et al. Further observations on the arthropathy of calcium pyrophosphate crystal deposition disease. Radiology. 1981;141:1.

McCarty DJ, Hollander JL. Identification of urate crystals in gouty synovial fluid. Ann Intern Med. 1961;54:452. McCarty Jr DJ, Kohn NN, Faires JS. The significance of calcium phosphate crystals in the synovial fluid of arthritis patients: The “pseudogout” syndrome. Ann Intern Med. 1962;56:711. McCarty DJ, Silcox DC, Coe F, et al. Diseases associated with calcium pyrophosphate dihydrate crystal deposition. Am J Med. 1974;56:704. Moshrif A, Laredo JD, Bassiouni H, et al. Spinal involvement with calcium pyrophosphate deposition disease in an academic rheumatology center: A series of 37 patients. Seminars Arthritis Rheum. 2019;48:1113. Resnick D, Pineda C. Vertebral involvement in calcium pyrophosphate dihydrate crystal deposition disease. Radiographic-­pathologic correlation. Radiology. 1984;158:55. Resnick D, Niwayama G, Goergen TG, et al. Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease (CPPD): Pseudogout. Radiology. 1977;122:1. Rosenthal AK, Ryan LM. Calcium pyrophosphate deposition disease. New Engl J Med. 2016;374:2575. Utsinger PD, Zvaifler NJ, Resnick D. Calcium pyrophosphate dihydrate deposition disease without chondrocalcinosis. J Rheumatol. 1975;2: 258.

15 Calcium Hydroxyapatite Crystal Deposition Disease S U M M A R Y O F K E Y F E AT U R E S • C  alcium hydroxyapatite crystal deposition can lead to paraarticular accumulations, which in tendons are termed calcific tendinosis or tendinitis. • Calcific tendinosis most commonly involves the shoulder, although other sites are often affected.

• I ntraarticular deposition of calcium hydroxyapatite crystals, calcium pyrophosphate dihydrate crystals, or both (mixed calcium phosphate crystals) can cause joint alterations.

INTRODUCTION

PARAARTICULAR CRYSTAL DEPOSITION

The most frequent site of involvement is the shoulder, although other sites, including the wrist, hand, foot, elbow, hip, knee, neck, and lumbar spine, may be involved. The disease affects both men and women and is particularly common between 40 and 70 years of age. Although persons with such calcification may be asymptomatic, acute symptoms may appear and include pain, tenderness on pressure, local edema or swelling, restricted motion, and mild fever. Granular deposits of calcium material in fibrous connective tissue may be associated with necrosis, loss of fibrous structure, and surrounding inflammatory changes. The deposits appear milky or cheesy in consistency and chalk-­ like in quality. Paraarticular HA crystal deposition has been described as a three-­ phase (precalcific, calcific, and postcalcific phases) or four-­phase (precalcific, formative, resting, and resorptive phases) process, although there is great variability in the duration, pattern, and location of the calcification. Indeed, in recent years, migration of the calcific deposits has been emphasized, especially in the shoulder. Extension of the deposits into neighboring bursae, tendons, or bones, or combinations of these, has been described, often associated with increasing pain and regional inflammation (see later discussion).

Cause, Pathogenesis, and Classification

General Radiographic Features

  

Over the past 40 years, the development of methods such as polarizing microscopy that can identify crystalline deposits in and around joints has led to the elucidation of several disorders associated with tissue inflammation: needle-­shaped crystals of monosodium urate in patients with gout; calcium pyrophosphate dihydrate (CPPD) crystals in patients who have pseudogout syndrome; and crystalline depot corticosteroid preparations, which, when injected intraarticularly, can produce acute synovitis. Another group of crystals related to calcium hydroxyapatite (HA) or apatite-­like crystals also has been identified in periarticular or articular (e.g., synovial fluid, synovial membrane, cartilage) structures or in both. The presence of significant clinical manifestations in persons with calcium HA crystal deposition is not consistent, although severe regional pain and inflammation have been documented in many cases, especially about the shoulder. Furthermore, calcium HA crystals also may be observed in joint fluid and, in this location, can lead to articular manifestations.

The cause and pathogenesis of calcium HA crystal deposition in para­ articular tissues are not entirely clear. In the past, it was assumed that such collections resulted from the deposition of calcium in degenerated, injured, or necrotic tissue, perhaps related to a change in local pH values as a result of increased alkalinity or decreased carbon dioxide tension. More recently, documentation of familial cases, polyarticular involvement, and an increased frequency of certain histocompatibility antigens in these patients suggest that multiple local, systemic, metabolic, and genetic factors may be involved. Tenocyte metaplasia into chondrocytes has been another proposed cause of calcific tendinosis. Although the precise pathogenesis of calcium HA crystal deposition may vary among these many causes, tissue degeneration is a common theme. Calcium HA crystal deposition occurring in tendons is therefore commonly termed calcific tendinosis, and this designation is used for the remainder of this chapter; however, the term calcific tendinitis may be considered in the resorptive phase when tendon inflammation is present.

Clinical and General Pathologic Features Recurrent painful paraarticular calcific deposits in tendons are usually monoarticular in distribution, although they can be polyarticular.

252

KEY CONCEPTS  • H  A crystal deposition most commonly appears as a cloudlike density, usually within a tendon. • HA crystals may migrate into adjacent soft tissue and bone or may resorb.

The radiographic features of paraarticular calcium HA crystal deposition depend on the site of involvement and the stage of the process. Initially, the deposits may appear thin, cloud like, and poorly defined as they blend into the surrounding soft tissues. With time, they may appear denser, homogeneous, and more sharply delineated, with a linear or circular configuration (Figs. 15.1 and 15.2). Adjacent osseous tissues may be entirely normal, although osteoporosis and contour irregularities or frank erosions are sometimes apparent, with the latter indicating possible osseous extension (see later discussion). Sequential radiographic examinations in patients with calcific paraarticular deposits reveal varying patterns. In some patients, the deposits remain static for long periods. In other patients, the deposits may enlarge and change shape, or they may migrate into an adjacent bursa and resorb (Fig. 15.3). Alternatively, the calcification may diminish in size and disappear,

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

253

demonstrate bursal migration (if applicable) (Fig. 15.5) or intraosseous migration, and guide percutaneous lavage and aspiration as an effective treatment (see later discussion).

General Magnetic Resonance Imaging and Computed Tomography Features

A

It is the inflammatory response about the calcific foci that dominates the magnetic resonance (MR) imaging findings of this disorder because the calcification itself may be overlooked unless it is large. When visible, foci of calcification are of low signal intensity in the MR images (see Fig. 15.2). The calcification is better delineated with radiography or computed tomography (CT). Inflamed and edematous soft tissues and muscles appear as regions of high signal intensity on fluid-­sensitive sequences. Bone erosion from intraosseous migration is well shown by CT (Fig. 15.6) and, to a lesser extent, MR imaging. Reactive marrow edema may be intense, corresponding to regions of focal radionuclide uptake with bone scintigraphy (Fig. 15.7).

Calcific Tendinosis and Bursitis at Specific Sites Shoulder

B Fig. 15.1  Calcific tendinosis: infraspinatus. (A) In external rotation, HA calcification in the infraspinatus tendon (arrow) appears as a cloudlike density superimposed over the greater tuberosity. (B) In internal rotation, the infraspinatus calcification (arrow) is profiled adjacent to the posterior aspect of the greater tuberosity. Additional smaller calcifications in the supraspinatus tendon are also evident.

in the absence of symptoms. Reappearance of calcification also has been documented. Paraarticular amorphous calcific collections in association with some disorders, such as chronic renal or collagen vascular disease, may become massive and surround the joint.

General Ultrasonography Features KEY CONCEPTS  • C alcium HA most commonly appears as globular and hyperechoic, with shadowing in the formative phase and less shadowing in the resorptive phase. • HA crystals may migrate into an adjacent bursa, causing bursitis and subsequent resorption. • Ultrasonography-­guided lavage and aspiration is an effective treatment.

Ultrasonography (US) can effectively identify calcium HA deposition of the extremities. When located in the tendon, calcification will appear globular and hyperechoic. In the formative phase, the calcification will typically shadow (Fig. 15.4A), while in the resorptive phase, the calcification shows less or little shadowing (see Fig. 15.4B). US can also

The capsular, tendinous, ligamentous, and bursal tissues about the shoulder are the most common sites of calcific deposits. These deposits occur in about 3% of adults and are bilateral in almost 50% of persons. Clinical findings are apparent in about one-­third of patients. The imaging appearance of shoulder calcification depends on the exact location of the abnormal deposits; they are commonly encountered in the tendons of the rotator cuff, adjacent tendons, and bursae. The precise appearance and position of the calcification depend on the phase of the disease and the specific tendon in which the deposits are located (Fig. 15.8). The supraspinatus tendon is the most frequent site of calcification (Fig. 15.9). The deposits are located at the tendinous insertion on the promontory of the greater tuberosity. Radiodense lesions at this site may be seen in profile on external rotation radiographs of the shoulder. Calcification within the substance of the infraspinatus tendon also may be projected over the lateral aspect of the humeral head when the shoulder is internally rotated (see Fig. 15.1B). Calcification in the teres minor tendon is less common. Subscapularis tendon calcification is projected over the humeral head in external rotation because of the anterior position of the lesser tuberosity (Fig. 15.10). This calcification is evident tangentially adjacent to the lesser tuberosity in an axillary projection (see Fig. 15.2A). Although calcification in the tendon of the long head of the biceps brachii muscle may appear near its attachment to the superior aspect of the glenoid, calcification in this tendon is also seen along the shaft of the humerus at the junction of the tendon and muscle. Its appearance simulates that of an osseous body trapped in the sheath of the tendon. Many reports have emphasized the presence and extent of inflammation that occur when the calcific collections migrate from or within the tendon itself (Fig. 15.11). Such migration may occur beneath the floor of or within the subacromial-­subdeltoid bursa (leading to bursitis) (Fig. 15.12), within the bone itself (especially in the greater and lesser tuberosities of the humerus with extensive marrow edema) (see Fig. 15.7), and toward the myotendinous junction along the course of delaminated tears of the corresponding tendon. Other sites of tendon calcification about the shoulder are infrequent and include the pectoralis major tendon (Fig. 15.13), the teres major tendon, the tendon of the long head of the triceps muscle (with calcification adjacent to the inferior margin of the glenoid cavity), the deltoid attachment to the acromion, and the trapezius insertion (with calcification adjacent to the acromioclavicular joint). In some of these locations, such as the tendons of the pectoralis major and teres major

254

SECTION 2  Articular Disorders

A

C

B

D

Fig. 15.2  Calcific tendinosis: subscapularis. (A) Axillary radiograph shows amorphous calcification (arrow) at the lesser tuberosity within the subscapularis tendon. (B) Ultrasonography long axis to the subscapularis tendon shows hyperechoic calcification (arrow), with posterior acoustic shadowing. (C) T1-­weighted and (D) fluid-­sensitive axial magnetic resonance images show low signal calcification (arrow) within the subscapularis tendon.

A

B

Fig. 15.3  Calcific tendinosis: bursal migration. (A) External rotation shoulder radiograph shows calcification extending from the supraspinatus tendon into the adjacent subacromial-­subdeltoid bursa (arrow). (B) Radiograph several weeks later shows a more diffuse distribution of calcification within the bursa (arrow), with interval partial resorption.

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

255

muscles, erosion of the cortical surface of the adjacent bone, such as the humeral shaft, simulates the appearance of an aggressive lesion.

Hand and Wrist Calcification in the wrist is more frequent than in the hand, and deposits may be noted in or near the tendons of the flexor carpi ulnaris (adjacent to the pisiform), flexor carpi radialis (on the volar aspect of the radiocarpal joint), common flexors (near the volar aspect of the wrist), and extensor carpi ulnaris (adjacent to the distal end of the ulna and ulnar styloid). The most common site of calcification appears to be within the flexor carpi ulnaris tendon (Fig. 15.14).

D

T GT

Hip and Pelvis H

A

D

T GT

Calcific deposits are frequent in the gluteal insertions into the greater trochanter, where they appear as single or multiple cloud like linear, triangular, or circular radiodense areas on radiography. Similar to findings in the shoulder, calcification may extend into the adjacent bursae, becoming less dense on radiography and inciting bursitis. Inflammatory findings involving the tendon, adjacent soft tissues, and adjacent bone may simulate tendon or muscle injury and appear aggressive on MR imaging; however, noting the tendinous location of the calcification on correlative radiographs or CT provides the correct diagnoses. At the greater trochanter, calcification can be identified within the gluteus minimus tendon at the anterior facet of the greater trochanter (Fig. 15.15), and the gluteus medius tendinous attachment at the lateral and superoposterior facets (Figs. 15.16 through 15.18). Calcification in the femoral insertion of the gluteus maximus muscle leads to a radiodense shadow adjacent to the proximal posterior portion of the femur on radiography, with possible erosion of the femoral cortex and inflammatory changes on MR imaging (Fig. 15.19). Similar findings can be seen at the origin of the direct head of the rectus femoris muscle at the anterior inferior iliac spine (Fig. 15.20).

Neck

H

B Fig. 15.4  Calcific tendinosis: US. US images long axis to the supraspinatus tendon (T) in two different patients show (A) hyperechoic and shadowing calcification (arrows) in the formative phase, and (B) hyperechoic calcification with little shadowing (arrows) in the resorptive phase. D, Deltoid muscle; GT, greater tuberosity; H, humeral head.

Calcific tendinosis of the neck may appear within the longus colli muscle and tendon, the principal flexor of the cervical spine (Fig. 15.21). Tendinosis and paratendinitis in this region may result in acute neck and occipital pain, neck rigidity, and dysphagia. Imaging findings include prevertebral soft tissue swelling, particularly in the upper cervical region, as well as amorphous calcification, which is usually seen anterior to the second cervical vertebra, just inferior to the anterior arch of

D T

GT

A

B

Fig. 15.5  Calcific tendinosis: bursal migration. A, US image long axis to the supraspinatus tendon (T) shows hyperechoic calcification that has migrated into the subacromial-­s ubdeltoid bursa (arrow), also shown on a (B) radiograph with a fluid-­calcium level (arrow). D, Deltoid muscle; GT, greater tuberosity.

256

SECTION 2  Articular Disorders

D

GT

H

A

B

C

Fig. 15.6  Calcific tendinosis: intraosseous migration. (A) External rotation shoulder radiograph, (B) US image long axis to the supraspinatus tendon, and (C), coronal reformatted CT image show calcification (arrow), with adjacent bone erosion (arrowhead). D, Deltoid muscle; GT, greater tuberosity; H, humeral head.

B

A

C

D

E

Fig. 15.7  Calcific tendinosis: intraosseous migration. (A) External rotation shoulder radiograph shows intraosseous migration of calcification (arrow) with (B) uptake on a delayed bone scan image (arrow). (C) Coronal and (D) axial fluid-­sensitive MR images show low signal intraosseous migration of calcification (arrow), with surrounding marrow edema. (E) Axial CT image shows bone erosion related to intraosseous migration of calcification (arrow).

the atlas. Resorption of calcification is common and may be complete in 1 to 2 weeks, with disappearance of the soft tissue swelling.

Differential Diagnosis Tendinosis with paratendinitis and bursitis may produce soft tissue swelling without radiographically recognizable calcification. Stenosing tenosynovitis of the abductor pollicis longus and extensor pollicis

brevis tendons at the wrist (de Quervain disease) is one example. An example of noncalcific bursitis is Haglund syndrome, characterized by painful soft tissue swelling above the level of the Achilles tendon insertion in the calcaneus. Calcific tendinosis and bursitis must be distinguished from many disorders that produce periarticular or paraarticular calcification (Box 15.1). Such soft tissue deposits may relate to metastatic

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

257

SS

SS

IS IS SSc

TM

TM SSc

A

B

Fig. 15.8  Periarticular crystal deposition in the shoulder: sites of tendon calcification. (A) In external rotation, calcification in the supraspinatus (SS) tendon is observed adjacent to the greater tuberosity, whereas that in the infraspinatus (IS) and teres minor (TM) tendons overlies the greater tuberosity. Calcification in the subscapularis (SSc) tendon overlies the lesser tuberosity. (B) In internal rotation, calcification in the infraspinatus (IS) and teres minor (TM) tendons is seen lateral to the greater tuberosity, calcification in the supraspinatus (SS) tendon is projected over the greater tuberosity, and calcification in the subscapularis (SSc) tendon rotates medially, adjacent to the inner margin of the humeral head.

A

B

Fig. 15.9  Calcific tendinosis: supraspinatus and infraspinatus. (A) External rotation shoulder radiograph shows calcification in the supraspinatus tendon in profile (arrow), with infraspinatus tendon calcifications (arrowhead) superimposed over the greater tuberosity. (B) Internal rotation shoulder radiograph now shows infraspinatus tendon calcifications posteriorly seen in profile (arrowhead), with supraspinatus tendon calcifications (arrow) superimposed over the humeral head.

calcification, in which a disturbance of calcium and phosphorus metabolism is present; calcinosis, in which calcification of the skin and subcutaneous and connective tissues occurs in the presence of normal calcium metabolism (Fig. 15.22); and dystrophic calcification, in which calcium deposition occurs in devitalized tissues. Metastatic calcification is common in renal osteodystrophy (Fig. 15.23) and may also be seen in hypoparathyroidism, sarcoidosis,

hypervitaminosis D, milk-­alkali syndrome, and numerous other conditions. Calcific tendinosis and bursitis should be differentiated from causes of soft tissue ossification (Box 15.2). Frequently, such differentiation is possible because ossified masses reveal trabecular patterns. Soft tissue ossification is frequent after trauma (myositis ossificans), neurologic injury (Fig. 15.24), and burns.

258

SECTION 2  Articular Disorders

D

B LT

A

B

C

Fig. 15.10  Calcific tendinosis: subscapularis. (A) Anteroposterior shoulder radiograph shows calcification (arrow) superimposed over the proximal humerus. Gray-­scale (B) and color Doppler (C) US long axis to the subscapularis tendon show inhomogeneous hyperechoic calcification (arrows) with surrounding hyperemia. B, Biceps brachii long head tendon; D, deltoid muscle; LT, lesser tuberosity.

A

B

E

C

F

D

G

Fig. 15.11  Periarticular crystal deposition in the shoulder: phases of the disease. (A) Silent phase. Subclinical deposition of calcium occurs in the substance of the rotator cuff tendons. (B) Mechanical phase—elevation of the bursal floor. As the deposits increase in size, the floor of the subacromial-­subdeltoid bursa is raised. (C) Mechanical phase–subbursal rupture. Observe that rupture of the calcific deposits has occurred beneath the floor of the bursa. (D) Mechanical phase–intrabursal rupture. The entire deposit is being expelled into the subacromial-­subdeltoid bursa. (E) Adhesive periarthritis. Note the adduction of the shoulder with adhesive bursitis. (F) Intraosseous loculation. The calcific deposit has extended into the bone. (G) Dumbbell loculation. Rarely, a biloculated deposit may be seen as a result of pressure from the adjacent coracoacromial ligament. (Redrawn from Moseley HF: Shoulder lesions. 3rd ed. Edinburgh, E&S Livingstone, 1969.)

Calcific Tendinosis Treatment In the past, many techniques were used to treat calcific tendinosis and bursitis of the shoulder, with varying success. These techniques included heat and cold therapy, ultrasonic and diathermic procedures, needling and aspiration, steroid injections, surgery, and radiotherapy. Currently, US-­guided percutaneous lavage and aspiration (also termed barbotage) is commonly used to treat calcific tendinosis. Although there are several different variations to this procedure, most commonly, an 18- or 20-­gauge needle is guided into the calcification. A minimal amount of saline or anesthetic agent is injected to dilute the calcification, which is followed by aspiration of the calcification. A thin rim of calcification will remain, which subsequently gets resorbed (Fig. 15.25). When the calcification shows significant shadowing, initial

changes at US after aspiration may be lacking; however, resorption will still occur (Fig. 15.26). Variations of this technique include the use of multiple needles (one for lavage and the other for aspiration), as well as fenestration of the calcification. At the completion of the procedure, the adjacent bursa (if applicable) should be injected with corticosteroid to treat the subsequent bursitis. A decrease in calcium at imaging correlates with symptomatic improvement, with a success rate of approximately 90%.

INTRAARTICULAR CRYSTAL DEPOSITION The concept of intraarticular calcium HA crystal deposition has been emphasized in many reports. Investigations of elderly women who had

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

A

B

C

D

Fig. 15.12  Calcific tendinosis: bursal and intraosseous extension. (A) Anteroposterior shoulder radiograph shows calcification (arrows) extending from the supraspinatus tendon into the subacromial-­subdeltoid bursa and greater tuberosity (arrowhead). (B) Coronal fluid-­sensitive, (C) sagittal T1-­weighted, and (D) sagittal fluid-­ sensitive MR images show low signal calcification (arrow) within the supraspinatus tendon extending into the subacromial-­subdeltoid bursa and into the greater tuberosity (arrowhead). Note a small amount of bursal fluid.

B

B

P

A

C

Fig. 15.13  Calcific tendinosis: pectoralis major. (A) Anteroposterior shoulder radiograph shows calcification (arrow) superimposed over the proximal humerus. US (B) long axis and (C) short axis to the pectoralis major tendon (P) shows calcification (arrow). B, Biceps brachii long head tendon.

259

Fig. 15.14  Calcific tendinosis: flexor carpi ulnaris. Calcification (arrow) is apparent on the undersurface of the pisiform within the tendon of the flexor carpi ulnaris muscle.

A

C

B

D

E

Fig. 15.15  Calcific tendinosis: gluteus minimus. (A) Anteroposterior and (B) frog-leg ­ radiographs of the hip show calcification (arrow) at the anterior facet of the greater trochanter. Coronal T1-weighted ­ (C), coronal fluid-sensitive ­ (D), and axial fluid-sensitive ­ (E) MR images show low signal calcification (arrow) within the gluteus minimus tendon, with proximal edema.

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

A

C

B

261

D

Fig. 15.16  Calcific tendinosis: gluteus medius. (A) Anteroposterior radiograph shows amorphous calcification (arrow) at the lateral facet of the greater trochanter, consistent with the resorptive phase of calcific tendinosis. (B) Coronal T1-­weighted, (C) coronal fluid-­sensitive, and (D) axial fluid-­sensitive MR images show low signal calcification (arrow) within and superficial to the gluteus medius tendon, with adjacent edema and subgluteus maximus (trochanteric) bursitis (arrowhead).

A

B

C

D

Fig. 15.17  Calcific tendinosis: gluteus medius. (A) Anteroposterior radiograph shows calcification (arrow) at the lateral facet of the greater trochanter. (B) Coronal T1-­weighted and (C) coronal fluid-­sensitive MR images show low signal calcification (arrow) within the gluteus medius tendon, with edema and subgluteus medius bursitis. Note additional calcification of the hamstring tendons (arrowhead, D).

painful shoulders with decreased mobility or stability revealed radiographic evidence of disruption of the rotator cuff and demonstration of microspheroids containing calcium HA crystals in synovial fluid. This fluid also revealed activated collagenase and neutral protease activity. These findings led to the concept of the Milwaukee shoulder syndrome, in which intraarticular HA crystal deposition leads to the release of enzymes that attack the periarticular tissues, including the rotator cuff, with subsequent cuff disruption. Although the initial observations were related to disintegration of the glenohumeral joint, the concept subsequently was applied to other sites, including the knee, elbow, hip, and midtarsal articulations, at which rapid articular destruction could occur. This concept, however, remains controversial as other causes of such destruction have been proposed, including osteonecrosis and subchondral insufficiency fractures.

Radiographic and Pathologic Features Calcium HA crystal accumulation in joints can lead to intraarticular calcification. Although cartilage calcification, or chondrocalcinosis, has been noted occasionally, especially in the knee, calcium HA crystal deposition can also involve the synovial membrane, capsule, or both, and usually leads to amorphous or cloud like radiodense areas within the joint (Fig. 15.27). Furthermore, calcium HA crystal deposition can

occur in a joint that is otherwise normal, or it can develop in an articulation with preexisting abnormalities. Although usually evident in the small joints of the hand and wrist or foot, calcium HA crystal accumulation can cause calcification in large joints, such as the elbow, hip, knee, and glenohumeral articulation. Women are affected more frequently than men, and adults are affected much more commonly than children. Structural joint damage is observed in some patients with intraarticular calcium HA crystal accumulation. In elderly patients, radiographic findings in Milwaukee shoulder include loss of joint space, destruction of bone, subchondral sclerosis, intraarticular osseous debris, and joint disorganization (Fig. 15.28). Associated disruption of the rotator cuff allows the humeral head to become displaced superiorly with pressure erosion of the acromion. The resulting articular disease is termed cuff tear arthropathy by some investigators, who think that the initial alteration is not calcium HA crystal accumulation but rather, disruption of the rotator cuff, followed by leakage of synovial fluid, deterioration of cartilage nutrition, and mechanical derangement of the joint. An association between arthropathy in the shoulder and arthropathy in other joints, especially the knee, has been reported. Additional joints such as the hip and small joints of the hands and feet may be involved (Fig. 15.29).

262

SECTION 2  Articular Disorders

A

GT

B Fig. 15.18  Calcific tendinosis: gluteus medius. (A) Anteroposterior radiograph shows amorphous calcification (arrow) at the lateral facet of the greater trochanter, consistent with the resorptive phase of calcific tendinosis. (B) US long axis to the gluteus medius tendon (arrowheads) shows hyperechoic calcification (arrow), with partial shadowing within the gluteus medius tendon at the lateral facet of the greater trochanter (GT).

A

B

C

Fig. 15.19  Calcific tendinosis: gluteus maximus. (A) Anteroposterior radiograph with internal hip rotation shows amorphous calcification (arrow), consistent with the resorptive phase of calcific tendinosis. (B) Axial T1-weighted ­ and (C) fluid-sensitive ­ MR images show low signal calcification (arrow) within the gluteus maximus tendon near its femoral attachment with adjacent edema.

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

I

B

A

Fig. 15.20  Calcific tendinosis: rectus femoris. (A) Anteroposterior radiograph shows calcification (arrow) at the anterior inferior iliac spine. (B) US long axis to the direct head of the rectus femoris tendon (arrowheads) shows hyperechoic calcification (arrow) within the rectus femoris tendon at the anterior inferior iliac spine (I).

A

D

B

C

E

F

Fig. 15.21  Calcific tendinosis: longus colli. (A) Drawing of a sagittal section of the neck indicates the course of the longus colli muscle (arrow), which attaches to the anterior tubercle of the atlas and the anterior surface of the second through fourth cervical vertebrae. (B) Lateral radiograph shows soft tissue swelling, with calcification immediately below the anterior arch of C1. (C–D) Corresponding reformatted sagittal (C) and axial (D) CT scans of the spine show the calcification (arrows) to better advantage. (E–F) Corresponding sagittal T1-­weighted (E) and fluid-sensitive (F) MR images show the calcification as an area of low signal intensity (arrow). Note the surrounding inflammatory changes as well as marrow edema.

263

264

SECTION 2  Articular Disorders

BOX 15.1  Some Conditions Associated

with Paraarticular Calcification

Calcific tendinosis and bursitis Collagen vascular disease Hyperparathyroidism and renal osteodystrophy Hypoparathyroidism Hypervitaminosis D Milk-­alkali syndrome Idiopathic tumoral calcinosis Articular disorders: CPPD crystal deposition disease, gout, infection, synovial chondromatosis Sarcoidosis Primary soft tissue tumors (especially synovial sarcoma)

Fig. 15.23  Renal osteodystrophy. Large, radiodense collections about the elbow are typical of calcifications in this disorder.

BOX 15.2  Some Conditions Associated

With Soft Tissue Ossification Myositis ossificans traumatica Fibrodysplasia (myositis) ossificans progressiva Neurologic injury Burn Pseudomalignant osseous tumor of soft tissue

Fig. 15.22  Idiopathic tumoral calcinosis. Observe the large saclike collection of calcification about the hip.

Differential Diagnosis The radiographic manifestations of intraarticular calcium HA crystal deposition disease are similar to those of CPPD crystal deposition disease and what has been designated as rapidly progressive osteoarthrosis. Other disorders, such as alkaptonuria, infection, neuropathic osteoarthropathy, and idiopathic chondrolysis, resemble the arthropathy of calcium HA crystal deposition disease.

MIXED CALCIUM PHOSPHATE CRYSTAL DEPOSITION Inspection of synovial fluid or cartilage has documented the coexistence of calcium HA and CPPD crystals in numerous patients. When the crystals occur together, it is difficult to precisely identify their relative roles in the production of joint damage. The radiographic diagnosis of such mixed crystal disease is also difficult. A diagnostic clue is provided by cartilage calcification (chondrocalcinosis), which, when widespread, is much more characteristic of CPPD crystal deposition than calcium HA crystal accumulation. Conversely, in calcium HA crystal deposition, diffuse amorphous calcification within the joint is more typical.

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

Fig. 15.24  Heterotopic ossification after neurologic injury. In a paralyzed patient, ossification about the acetabulum and proximal portion of the femur can be seen.

B LT

A

C

LT

B

D

Fig. 15.25  Calcific tendinosis: lavage and aspiration. (A) Anteroposterior and (B) axillary radiographs show amorphous calcification (arrows) within the subscapularis tendon. (C) US long axis to the subscapularis tendon (left side of image is lateral) shows amorphous hyperechoic intratendinous calcification (arrows). (D) US shows the tip of a 20-­gauge needle (arrowheads) within the calcification. Note lower echogenicity within the calcification from the anesthetic agent and increased diameter during the active injection or lavage. B, Biceps brachii long head tendon; LT, lesser tuberosity.

265

266

SECTION 2  Articular Disorders

A

Fig. 15.27  Intraarticular crystal deposition. Radiograph reveals periarticular and intraarticular calcification involving the hand and wrist. The opposite side was affected similarly. A synovial biopsy of a proximal interphalangeal joint documented the presence of calcium HA crystal deposition.

B

H

C Fig. 15.26  Calcific tendinosis: lavage and aspiration. (A) US of the supraspinatus tendon shows echogenic and shadowing calcification (arrows). (B) A 20-gauge needle (arrowheads) is shown entering the calcification. (C) Three weeks after the single-puncture lavage and aspiration, the shell of calcification shown in (B) has resorbed (curved arrows). H, Humeral head.

Fig. 15.28  Intraarticular crystal deposition: Milwaukee shoulder syndrome. Note the joint space narrowing, subchondral sclerosis, and erosion of the undersurface of the clavicle and acromion.

CHAPTER 15  Calcium Hydroxyapatite Crystal Deposition Disease

A

267

B

Fig. 15.29  Intraarticular crystal deposition: arthropathy. (A) Radiograph of the hand reveals calcification within and around a distal interphalangeal joint associated with joint space narrowing and osteophytosis. (B) In a different patient, rapidly progressive hip disease resulted in dissolution of a large portion of the femoral head. (A, Courtesy V. Vint, MD, San Diego, CA.)

FURTHER READING Bonavita JA, Dalinka MK, Schumacher Jr HR. Hydroxyapatite deposition disease. Radiology. 1980;134:621. Dieppe PA, Doherty M, MacFarlane DG, et al. Apatite associated destructive arthritis. Br J Rheumatol. 1984;23:84. Fritz P, Bardin T, Laredo J-­D, et al. Paradiaphyseal calcific tendinitis with cortical bone erosion. Arthritis Rheum. 1994;37:718. Halverson PB, McCarty DJ. Clinical aspects of basic calcium phosphate crystal deposition. Rheum Dis Clin North Am. 1988;14:427. Hayes CW, Conway WF. Calcium hydroxyapatite deposition disease. Radiographics. 1990;10:1031. Hongsmatip P, Cheng KY, Kim C, et al. Calcium hydroxyapatite deposition disease: Imaging features and presentations mimicking other pathologies. European J Radiol. 2019;120:108653. Kekatpure AL, Sun J-­H, Sim G-­B, et al. Rapidly destructive arthrosis of the shoulder joints: radiographic, magnetic resonance imaging, and histopathologic findings. J Should Elbow Surg. 2015;24:922. Kraemer EJ, El-­Khoury GY. Atypical calcific tendinitis with cortical erosions. Skeletal Radiol. 2000;29:690. Marinetti A, Sessa M, Falzone A, et al. Intraosseous migration of tendinous caclifications: two case reports. Skeletal Radiol. 2018;47(1):131–136.

McCarty DJ, Halverson PB, Carrera GF, et al. “Milwaukee shoulder”: association of microspheroids containing hydroxyapatite crystals, active collagenase, and neutral protease with rotator cuff defects. I. Clinical aspects. Arthritis Rheum. 1981;24:464. Neer II CS, Craig EV, Fukuda H. Cuff-­tear arthropathy. J. Bone Joint Surg [Am]. 1983;65:1232. Orlandi D, Mauri G, Lacelli F, et al. Rotator cuff calcific tendinopathy: Randomized comparison of US-­guided percutaneous treatments using one or two needles. Radiology. 2017;295:518–527. Pereira BPG, Chang EY, Resnick DL, et al. Intramuscular migration of calcium hydroxyapatite crystal deposits involving the rotator cuff tendons of the shoulder: report of 11 patients. Skeletal Radiol. 2016;45:97. Rosenberg ZS, Shankman S, Steiner GC, et al. Rapid destructive osteoarthritis: clinical, radiographic, and pathologic features. Radiology. 1992;182:213. Sansone V, Consonni O, Maiorano E, et al. Calcific tendinopathy of the rotator cuff: the correlation between pain and imaging features in symptomatic and asymptomatic shoulders. Skeletal Radiol. 2016;45:49. ViGario DG, Keats TE. Localization of calcific deposits in the shoulder. AJR. 1970;108:806.

16 Hemochromatosis and Wilson Disease S U M M A R Y O F K E Y F E AT U R E S : H E M O C H R O M AT O S I S   • H  emochromatosis may be a primary or secondary condition that results in iron overload and subsequent iron accumulation in the liver, pancreas, heart, and skin. • Skeletal manifestations include osteoporosis, chondrocalcinosis, and a distinct arthropathy characterized by joint space narrowing, subchondral cyst formation, and osteophytosis.

• S keletal abnormalities resemble findings of calcium pyrophosphate dihydrate crystal deposition disease but are associated with more uniform joint space loss and a less progressive course.

  

S U M M A R Y O F K E Y F E A T U R E S : W I L S O N D I S E A S E  • W  ilson disease (hepatolenticular degeneration) is a rare autosomal recessive disorder likely related to a gene mutation (ATP7B) resulting in copper accumulation. • Organs affected include the basal ganglia in the brain (calcification), liver (cirrhosis), and cornea (Kayser-­Fleischer rings of greenish brown pigment).

HEMOCHROMATOSIS Disorders of iron storage can be conveniently divided into those that are primary (i.e., hereditary) and those that are secondary to iron overload states. Such overload states are associated with an increase in the availability of iron related to parenteral or oral intake or ineffective erythropoiesis. The most common cause of hemochromatosis is an inherited autosomal recessive disorder with variable penetrance that is thought to be a consequence of a mutation of the HFE protein, a protein that regulates the production of an iron regulatory hormone, hepcidin. This mutation results in an increased absorption of iron from the gastrointestinal tract. The clinical findings include a classic triad of abnormalities: bronze pigmentation of the skin, cirrhosis, and diabetes, leading to the descriptive term bronze diabetes. Specific clinical manifestations relate to tissue damage at the site of abnormal iron accumulation: iron within the parenchymal cells of the liver is associated with hypertrophy and cirrhosis, iron deposits in the pancreas result in diabetes, iron and melanin accumulations in the skin produce abnormal pigmentation, and cardiac deposition of iron results in heart failure. Secondary hemochromatosis is associated with an increased intake and accumulation of iron of known cause, such as alcoholic cirrhosis, multiple blood transfusions, refractory anemia, and chronic excess oral iron ingestion. Within this category of disease is erythropoietic hemochromatosis that results from excessive amounts of iron in the body related to an increase in the number and fragility of red blood cells (in conditions such as thalassemia and spherocytosis). In both primary and secondary hemochromatosis, significant iron overload occurs only after many years, so the onset of disease is generally between 40 and 60 years of age. Hemochromatosis is less frequent in women, presumably because of menstrual blood loss. The disease is diagnosed by detection of an elevated serum iron concentration and increased saturation of the plasma iron-­binding protein transferrin, combined with a typical histologic appearance on liver biopsy.

268

• D  istinctive skeletal abnormalities include osteopenia, bone fragmentation and cyst formation, ossicles, poorly defined subchondral bone, and osteochondritis dissecans, some of these abnormalities resembling those in hemochromatosis and idiopathic calcium pyrophosphate dihydrate crystal deposition disease.

  

CLINICAL FEATURES Most patients with primary, or hereditary, hemochromatosis become symptomatic between the ages of 40 and 60 years. The disorder is 8 to 20 times more frequent in men than in women, and women with this disorder frequently report absent or scanty menses. Initial clinical manifestations relate to the classic triad of the disease: cirrhosis, skin pigmentation, and diabetes. Subsequent complaints relate to ascites and cardiac failure. The impressive list of organs that are affected by hemochromatosis includes the heart, liver, pancreas, thyroid and pituitary glands, gonads, and skin. The arthropathy associated with hemochromatosis is more frequent in primary hemochromatosis than in secondary hemochromatosis and is manifested as a noninflammatory condition initially involving the small joints of the hands, particularly the second and third metacarpophalangeal joints, and eventually involving large articulations.

PATHOLOGIC FEATURES Articular abnormalities consist of two major features: abnormal amounts of hemosiderin granules and calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. Hemosiderin granules are seen in the lining cells in the synovial membrane. CPPD crystals also may be seen in the superficial layers of the synovial membrane. Chondrocalcinosis occurs either as an isolated phenomenon or in association with structural joint damage (Fig. 16.1). Calcification related to CPPD crystal deposition involves predominantly the fibrocartilage and hyaline cartilage of the knee but is also frequent in the symphysis pubis, wrist, and intervertebral disc. The bone abnormalities in hemochromatosis are similar to those noted in idiopathic CPPD crystal deposition disease.

CHAPTER 16  Hemochromatosis and Wilson Disease

B

A

269

C

Fig. 16.1  Radiographic findings in hemochromatosis: chondrocalcinosis. (A) Magnification radiography outlines calcium deposits (arrowhead) in the triangular fibrocartilage in the wrist. (B) Diffuse chondrocalcinosis of both fibrocartilage and hyaline cartilage is present in the knee. (C) In the symphysis pubis, chondrocalcinosis (arrowhead) of fibrocartilage is apparent.

RADIOGRAPHIC FEATURES KEY CONCEPTS • O  steoporosis • Chondrocalcinosis: hyaline cartilage and fibrocartilage similar to that in CPPD crystal deposition disease • Arthropathy: superficially similar to osteoarthrosis, although unique features of sites not typically involved in osteoarthrosis (such as the metacarpophalangeal joints, wrist, elbow, glenohumeral joint), large subchondral cysts, and uniform joint space loss, somewhat similar to CPPD arthropathy

Osteoporosis The reported frequency of osteoporosis varies from 25% to 58%, more commonly in primary hemochromatosis. Osteoporosis of the vertebral bodies produces biconcave deformities, or fish vertebrae, which are identical to those occurring in other forms of osteoporosis. In the appendicular skeleton, diffuse osteoporosis without a predilection for periarticular regions has been described.

Articular Calcification The reported frequency of chondrocalcinosis related to CPPD crystal deposition in patients with hemochromatosis varies from approximately 20% to 60%. It is most frequently seen in the wrist, knee, symphysis pubis, intervertebral discs shoulder, and hip, and it may involve fibrocartilage or hyaline cartilage (see Fig. 16.1). Although the distribution and extent of chondrocalcinosis in hemochromatosis may be identical to those associated with idiopathic CPPD crystal deposition disease, reports suggest that there is more involvement of the symphysis pubis, more prominent calcification of the hyaline cartilage, and good correlation between the severity of arthropathy and the degree of chondrocalcinosis in hemochromatosis compared with idiopathic CPPD crystal deposition disease. Fibrocartilage calcification, which is frequent in the triangular fibrocartilage of the wrist, menisci of the knee, symphysis pubis, and intervertebral disc, appears as thick, shaggy, irregular, radiodense regions. Hyaline cartilage calcification appears as linear or curvilinear radiodense areas paralleling the subchondral osseous surface. In the intervertebral disc, CPPD crystal deposition occurs initially in the outer fibers of the annulus fibrosus.

Structural Joint Damage or Arthropathy The reported frequency of arthropathy in hemochromatosis ranges from 24% to 50%. Although the arthropathy superficially resembles osteoarthrosis—with joint space narrowing, sclerosis, and osteophytosis—specific characteristics in its distribution and appearance enable

Fig. 16.2  Radiographic findings in hemochromatosis: metacarpophalangeal joint arthropathy. Involvement of all the metacarpophalangeal joints is characterized by articular space narrowing, surface irregularity, small cystic lesions, beaklike osteophytes, focal calcifications (arrowhead), and mild osteoporosis.

it to be recognized on radiographic examination. The arthropathy in hemochromatosis is almost identical to the arthropathy in idiopathic CPPD crystal deposition disease, and they share the following features: 1. Involvement of unusual articular sites: Arthropathy may produce abnormalities at joints that are not commonly involved in osteoarthrosis, such as the metacarpophalangeal joints, and midcarpal and radiocarpal compartments of the wrists, elbows, and glenohumeral articulations. 2. Formation of large subchondral cystic lesions: Arthropathy may be associated with multiple and sometimes large cysts in the subchondral bone. 3. Uniform loss of articular space: Arthropathy may be characterized by diffuse loss of articular space, an unusual finding in osteoarthrosis. Although it is difficult to differentiate the arthropathy of hemochromatosis and that of idiopathic CPPD crystal deposition disease, several subtle findings appear to be more typical of hemochromatosis: 1. Predilection for the metacarpophalangeal joints: These joints, especially in the second and third fingers, are the most characteristic sites of involvement in hemochromatosis (Fig. 16.2). Although both CPPD crystal deposition disease and hemochromatosis produce structural alterations in the metacarpophalangeal joints, more prevalent narrowing in these articulations (including those in the fourth and fifth digits) and peculiar hooklike osteophytes on the radial aspect of the metacarpal heads are characteristic of hemochromatosis. 2. Widespread abnormalities of the wrist: Involvement of the carpal bones may be noted in 30% to 50% of patients (Fig. 16.3). Although the radiocarpal compartment may be affected, as in idiopathic

270

SECTION 2  Articular Disorders CPPD crystal deposition disease, this compartment is occasionally unaffected in the arthropathy of hemochromatosis. 3. Slowly progressive alterations: The arthropathy of hemochromatosis may be slowly progressive. More rapid change, with fragmentation of bone, is more characteristic of idiopathic CPPD crystal deposition disease. 4. Unusual pattern of osteophytosis: Beaklike osteophytes of the metacarpal heads are particularly characteristic (Fig. 16.4). Similarly, osteophytes may be apparent about other involved articulations, such as the hip and glenohumeral joint. The arthropathy of hemochromatosis may be widespread and occur throughout the skeleton, including involvement of the hand and wrist, elbow, glenohumeral joint, hip, knee, ankle, foot, and spine. Radiographic abnormalities typically include joint space narrowing, bony eburnation, subchondral cyst formation, and osteophytosis. Chondrocalcinosis may or may not be apparent in the involved joint.

MAGNETIC RESONANCE IMAGING Fig. 16.3  Radiographic findings in hemochromatosis: wrist arthropathy. Observe the chondrocalcinosis (arrow) and diffuse narrowing of the radiocarpal, midcarpal, and first carpometacarpal joints.

The role of magnetic resonance (MR) imaging in cases of joint involvement in hemochromatosis is not clear at this time. MR imaging has not proved to be reliable in the detection of intraarticular iron, nor has a correlation been found among serum ferritin levels, severity of the arthropathy, or signal intensity values. MR imaging, however, can further document the structural articular abnormalities in this disease and may more accurately reveal the degree of inflammation when compared with conventional radiography.

DIFFERENTIAL DIAGNOSIS

Fig. 16.4  Radiographic findings in hemochromatosis: unusual pattern of osteophytosis. Note the beaklike excrescences (arrowheads), particularly on the radial aspect of the flattened and sclerotic metacarpal heads.

The chondrocalcinosis associated with hemochromatosis is almost identical to that associated with idiopathic CPPD crystal deposition disease and primary hyperparathyroidism. The chondrocalcinosis in hemochromatosis is readily differentiated from the other intraarticular and periarticular calcifications that can be observed in a variety of disorders. The arthropathy of hemochromatosis is easily differentiated from that of rheumatoid arthritis, spondyloarthropathies, and gout. It differs from osteoarthrosis in its distribution and appearance; involvement of unusual joints and the presence of uniform loss of articular space, multiple subchondral cysts, distinctive osteophytes, and mild collapse and flattening of bone allow the differentiation of hemochromatosis from osteoarthrosis in most patients. The arthropathy of hemochromatosis is almost identical to that of idiopathic CPPD crystal deposition disease (Table 16.1). Subtle differences in hemochromatosis may

TABLE 16.1  Hemochromatosis, Wilson Disease, and Idiopathic CPPD Crystal Deposition Disease Hemochromatosis

Wilson Disease

Idiopathic CPPD Crystal Deposition Disease

Osteopenia

+

+

–

Chondrocalcinosis

+a

?b

+

Additional calcification

±

?b

+

Joint space narrowing

+

+

+

Subchondral cysts

+

+

+

Rapid progression

±

–

+

Involvement of unusual articular sites

+c

+

+

aHemochromatosis

may be associated with more prominent hyaline cartilage calcification than noted in idiopathic CPPD crystal deposition disease. fragmentation in Wilson disease may resemble intraarticular and periarticular calcification. cWrist involvement in hemochromatosis may be more diffuse and metacarpophalangeal joint involvement may be more widespread than in idiopathic CPPD crystal deposition disease. CPPD, Calcium pyrophosphate dihydrate. bBone

CHAPTER 16  Hemochromatosis and Wilson Disease

A

A

271

B

Fig. 16.6  Radiographic findings in Wilson disease: bone irregularity and cyst formation. (A–B) Observe the osseous irregularity in the radial styloid process and base of a proximal phalanx (arrowhead). (Courtesy C. Alexander, MD, Auckland, New Zealand.)

B Fig. 16.5  Hemochromatosis versus idiopathic CPPD crystal deposition disease. (A) Hemochromatosis. Note the uniform loss of joint space at all metacarpophalangeal joints, including the fourth and fifth. Significant crumbling of the metacarpal heads is evident, especially in the third digit. Beaklike osseous excrescences are arising from the radial aspect of the metacarpal heads, particularly the third and fourth. Abnormal calcification is not apparent. (B) Idiopathic CPPD crystal deposition disease. Loss of joint space is evident in the second and third metacarpophalangeal joints, with relative sparing of those in the fourth and fifth digits. Slight flattening of the metacarpal heads and abnormal calcification about the metacarpophalangeal joints are seen. Small osteophytes are arising from the radial aspect of the second and third metacarpal heads, but they are not nearly as apparent as in (A).

include involvement of all the metacarpophalangeal joints, including the fourth and fifth, as well as the midcarpal and common carpometacarpal joints; the presence of osteoporosis and distinctive beak­like osteophytes; and the absence of rapidly progressive neuropathic-­like joint damage (Fig. 16.5).

WILSON DISEASE CLINICAL FEATURES Wilson disease may be slightly more common in men than in women. Symptoms and signs are usually apparent between the ages of 5 and 40 years, with 50% of patients symptomatic by the age of 15 years. The initial clinical manifestations are hepatic in 42%; neurologic in 34%;

psychiatric in 10%; and hematologic, endocrinologic, or renal in less than 10% of patients. Lenticular degeneration leads to neurologic symptoms, which include tremor, rigidity, dysarthria, incoordination, and personality change. Articular alterations in Wilson disease are unusual in children but may be observed in as many as 50% of adults. Most patients with articular involvement are 20 to 40 years of age. The joint abnormalities are frequently asymptomatic and are detected only by radiographic examination, although pain and swelling may occasionally be observed. Many joints are involved, including those in the hand, wrist, elbow, shoulder, hip, and knee. Osteopenia and possible fractures have been described in 25% to 50% of patients with Wilson disease.

RADIOGRAPHIC FEATURES The radiographic features of Wilson disease include osteopenia, which has been described in up to 50% of patients and may be associated with a high frequency of fractures. Rickets and osteomalacia, as well as Fanconi syndrome, also have been reported in patients with Wilson disease. The occurrence of chondrocalcinosis in Wilson disease is controversial and, at most, is rare. Articular manifestations in Wilson disease reportedly include subchondral bone fragmentation and cyst formation, cortical irregularities, and bone sclerosis in the wrist, hand, foot, hip, glenohumeral joint, elbow, and knee (Fig. 16.6). Radiodense lesions occur centrally and at the joint margins and may be associated with articular space narrowing. Distinct ossicles that possess complete cortices may appear (Fig. 16.7). The subchondral bone is irregular and indistinct, and focal areas of fragmentation of the articular surface can be observed in the metacarpophalangeal, interphalangeal, and wrist joints. Larger areas of fragmentation of the osseous surface are also noted. The cause of the bone fragmentation in Wilson disease is obscure. Because of their spasticity and tremors, patients with Wilson disease may be prone to minor injuries, producing cartilaginous and osseous damage. Joint hypermobility also has been reported. Additional radiographic characteristics of the arthropathy in Wilson disease are small joint effusions; joint space narrowing, including of the patellofemoral compartment in the knee; peculiar tongue­like osteophytes at bony prominences, such as those about the elbow and ankle; and fluffy periostitis of the trochanters and inferior surface of the calcaneus (Fig. 16.8).

272

SECTION 2  Articular Disorders

DIFFERENTIAL DIAGNOSIS The distribution of articular abnormality in Wilson disease includes a predilection for the small joints of the hands and wrists, particularly the metacarpophalangeal articulations; this distribution is not typical of osteoarthrosis. The bone fragmentation and irregular osseous surfaces in Wilson disease also differ from the findings in osteoarthrosis, although both disorders are associated with joint space narrowing and subchondral bony eburnation and cyst formation. The arthropathy of Wilson disease most resembles that of idiopathic CPPD crystal deposition disease and hemochromatosis. A definite association between Wilson disease and CPPD crystal deposition disease has not been proved.

FURTHER READING

Fig. 16.7  Radiographic features of Wilson disease: distinct ossicles. One or more ossicles (arrowhead) are present about the distal end of the ulna, a finding resembling chondrocalcinosis. (Courtesy M. Dalinka, MD, Philadelphia, PA.)

Fig. 16.8  Radiographic findings in Wilson disease: bony proliferation. Observe the fluffy bone production on the lesser trochanter (arrowhead). (From Golding DN, Walshe JM: Arthropathy of Wilson’s disease: study of clinical and radiological features in 32 patients. Ann Rheum Dis. 1977;36:99.)

Adamson III TC, Resnik CS, Guerra Jr J, et al. Hand and wrist arthropathies of hemochromatosis and calcium pyrophosphate deposition disease: distinct radiographic features. Radiology. 1983;147:377. Atkins CJ, McIvor J, Smith PM, et al. Chondrocalcinosis and arthropathy: Studies in haemochromatosis and in idiopathic chondrocalcinosis. Q J Med. 1970;39:71. Coffey AJ, Durkie M, Hague S, et al. A genetic study of Wilson’s disease in the United Kingdom. Brain. 2013;136:1476. Felitti VJ, Beutler E. New developments in hereditary hemochromatosis. Am J Med Sci. 1999;318:257. Finby N, Bearn AG. Roentgenographic abnormalities of the skeletal system in Wilson’s disease (hepatolenticular degeneration). AJR Am J Roentgenol. 1958;79:603. Frenzen K, Schafer C, Keyber G. Erosive and inflammatory joint changes in hereditary hemochromatosis arthropathy detected by low-­field magnetic resonance imaging. Rheumatol Int. 2013;33:2061. Hirsch JH, Killien C, Troupin RH. The arthropathy of hemochromatosis. Radiology. 1976;118:591. Mindelzun R, Elkin M, Scheinberg IH, et al. Skeletal changes in Wilson’s disease: a radiological study. Radiology. 1970;94:127. Moore EA, Vennart W, Jacoby RK, et al. Magnetic resonance manifestations of idiopathic hemochromatosis in the wrist. Br J Rheumatol. 1993;32:917. Narvaez J, Alegre-­Sancho JJ, Juanola X, et al. Arthropathy of Wilson’s disease presenting as noninflammatory polyarthritis. J Rheumatol. 1997;24:2494. Oke AR, Wong E, McCrae F, et al. Hereditary hemochromatosis arthropathy and Doppler ultrasound findings of synovitis. Rheumatology. 2017;56:1240. Scullion S, Grainger AJ, Greenspan A. Radiologic imaging of metabolic and endocrine disorders as they affect the hand and wrist. Semin Musculoskel Radiol. 2021;25:246. Sinigaglia L, Fargion S, Ludovica A, et al. Bone and joint involvement in genetic hemochromatosis: role of cirrhosis and iron overload. J Rheumatol. 1997;24:1809. Yu-­zhang X, Xue-­zhe Z, Xian-­hao X, et al. Radiologic study of 42 cases of Wilson’s disease. Skeletal Radiol. 1985;13:114.

17 Alkaptonuria and Oxalosis S U M M A R Y O F K E Y F E AT U R E S : A L K A P T O N U R I A • A  lkaptonuria is a rare hereditary disorder resulting from an inability to metabolize homogentisic acid. • Clinical and radiographic findings relate to homogentisic aciduria and ochronosis.

• T  ypical radiographic and pathologic findings of ochronosis involve both spinal and extraspinal sites.

  

S U M M A R Y O F K E Y F E AT U R E S : O X A L O S I S • C  alcium oxalate crystal deposition may occur as a rare hereditary disorder or, more commonly, related to renal malfunction.

  

ALKAPTONURIA Alkaptonuria is a rare autosomal recessive disorder characterized by a deficiency of the enzyme homogentisate 1,2 dioxygenase (HGD) that is caused by mutations in the HGD gene. Such mutations occur with increased frequency in certain countries such as Slovakia and the Dominican Republic. Owing to this deficiency in HGD, homogentisic acid, produced during the metabolism of phenylalanine and tyrosine, accumulates and is excreted in the urine. When the urine of affected persons is allowed to stand, the homogentisic acid is oxidized to a melanin-­like product, which causes the urine to gradually turn dark. Bluish-­black pigmentation of connective tissue becomes apparent at such sites as the skin, sclerae, and ears in patients with alkaptonuria. Such pigmentation in the joints of the appendicular and axial skeletons of affected individuals can lead to a distinctive arthropathy.

TERMINOLOGY For clarity, it is necessary to define several terms related to this disorder. Alkaptonuria: General name of a disease characterized by the absence of HGD and the accumulation of homogentisic acid in the urine. Ochronosis: The abnormal pigmentation, brown-­black in color, that may be observed in various connective tissues in patients with alkaptonuria. Ochronotic arthropathy: Structural damage that results from the pigmented deposits in the joints of the appendicular and axial skeletons.

GENERAL CLINICAL FEATURES In general, alkaptonuria is asymptomatic until adult life, although in children, discoloration of urine may be detected. Alkaptonuria almost inevitably progresses to ochronosis and arthropathy. Ochronotic pigmentation is observed infrequently before the age of 20 or 30 years, initially appearing as mild pigmentation of the ears or sclerae, although more widespread ocular abnormality may be apparent. In the ear, cartilage may appear thickened, with slate blue or gray discoloration. Discoloration of skin leading to staining of clothes is caused by perspiration in the axillary and genital areas.

• O  xalate deposition, termed oxalosis, occurs in renal and extra-­ renal sites.

Ochronotic arthropathy is a manifestation of long-­standing alkaptonuria. Symptoms and signs usually appear in the fourth decade of life and consist of pain and limitation of motion in the hip, knee, and shoulder. Joint effusions result from fragmentation of friable cartilage, with subsequent irritation of the synovial membrane. Stiffness and low back pain, obliteration of the normal lumbar curve, thoracic kyphosis, and restriction of motion are spinal manifestations of the disease. Additional symptoms and signs of alkaptonuria may relate to ochronotic deposition in other organs, including the cardiovascular and genitourinary systems and upper respiratory tract.

GENERAL PATHOLOGIC FEATURES Abnormal pigmentation of the connective tissue may be observed in the sclera; cornea; laryngeal, tracheal, bronchial, and costal cartilage; tympanic membrane; aortic intima; heart valves; kidney; and prostate. Pigment may also involve articular cartilage, tendons, and ligaments. It appears coal black in some areas, and the chemical characteristics of the pigment resemble those of melanin. In the large diarthrodial joints, the pigment is located in the deeper layers of cartilage. Pigmented necrotic cartilage may become embedded within the marrow, and displaced pieces of cartilage and bone may become lodged in the synovial membrane, where they may stimulate metaplasia of synovial lining cells into chondrocytes. Foreign body reaction, synovial polyp formation, and osteochondral bodies are observed. Inflammatory changes in the synovial membrane are absent or minimal. In the spine, ochronotic disc deterioration is related to cartilage brittleness, similar to that observed in the cartilage of diseased peripheral joints, and such deterioration may lead to disc fragmentation.

GENERAL RADIOGRAPHIC FEATURES KEY CONCEPTS: Radiographic Features • S ee Box 17.1. • S pinal abnormalities are characterized by disc calcification or ossification and disc space narrowing. • Extraspinal findings are reminiscent of osteoarthrosis, although unusual locations, patterns, and severity are identified.

273

274

SECTION 2  Articular Disorders

Spinal Abnormalities Disc calcification is the most characteristic abnormality of the spine (Fig. 17.1). The calcium deposits are found predominantly in the inner fibers of the annulus fibrosus, although they may be distributed diffusely throughout the intervertebral disc in a wafer-like configuration. They consist of apatite crystals and are considered dystrophic in nature. Calcification may appear in any segment of the vertebral column but has a predilection for the intervertebral discs of the lumbar spine; cervical spine alterations are less frequent. Narrowing of the intervertebral disc space is also a characteristic manifestation of alkaptonuria. Vacuum phenomena, with linear or

BOX 17.1  Diagnostic Features of

Ochronotic Arthropathy

Spinal Abnormalities Osteoporosis of vertebral bodies Calcification and ossification of intervertebral discs Disc space narrowing with vacuum phenomena Small or absent osteophytes Loss of lumbar lordosis

Extraspinal Abnormalities At the symphysis pubis, articular space narrowing, calcification, bony eburnation, and fragmentation may be seen. Similarly, joint space narrowing, sclerosis, and osteophytosis may be apparent at the sacroiliac articulations (Fig. 17.4). The knee is the most common site of peripheral abnormality (Fig. 17.5). Findings in this location simulate those of uncomplicated degenerative joint disease and consist of effusion, articular space narrowing, and bony sclerosis. Differences between these two diseases may include isolated involvement of the lateral femorotibial compartment, relatively symmetric involvement of both the medial and lateral femorotibial compartments, bony collapse and fragmentation with multiple radiopaque intraarticular bodies, meager osteophytosis, and tendinous calcification in alkaptonuria.

Extraspinal Abnormalities Involvement of sacroiliac joints, symphysis pubis, and large peripheral joints Articular space narrowing Bone sclerosis Bone collapse and fragmentation with intra­articular osseous bodies Small or absent osteophytes Tendinous calcification, ossification, and rupture Unusual involvement of hand, wrist, foot, elbow, and ankle

A

circular radiolucent collections of gas overlying the intervertebral disc at multiple levels, is also suggestive of this diagnosis (Fig. 17.2). Progressive ossification of the discs may be seen, with the formation of marginal intervertebral bridges and obliteration of the intervertebral space (Fig. 17.3). These bridges resemble the syndesmophytes of ankylosing spondylitis. Severe changes in long-­standing disease include progressive kyphosis, osteoporosis, obliteration of intervertebral disc spaces, and bony bridging, with a bamboo spine that may lead to an erroneous diagnosis of ankylosing spondylitis. Further, spondylitis-­like changes in the sacroiliac and apophyseal joints, symphysis pubis, and hips have been ascribed to alkaptonuria. Magnetic resonance (MR) imaging reveals the extent of spinal disease and complications such as disc displacement, but the findings lack specificity, inasmuch as regions of disc calcification may be difficult to identify.

B

Fig. 17.1  Radiographic features of alkaptonuria: thoracic spine. (A) Alterations include disc calcification (arrow) and ossification (arrowhead), disc space loss, vertebral body osteoporosis with marginal sclerosis, and mild osteophytosis. (B) In another patient, the most obvious abnormalities are disc space loss, vertebral body marginal sclerosis, and anterior osteophytes.

CHAPTER 17  Alkaptonuria and Oxalosis

A

275

B

Fig. 17.2  Radiographic and magnetic resonance imaging features of alkaptonuria: disc space narrowing and vacuum phenomenon. (A) Observe the linear radiolucent areas (arrows) within multiple narrowed intervertebral discs. Disc calcification is not prominent. Apophyseal joint space narrowing is seen. Note the spondylolysis of a lower lumbar vertebra (arrowhead). (B) Sagittal intermediate-­weighted magnetic resonance image shows diffuse loss of intervertebral disc spaces. Low signal intensity in each of the discs is compatible with the presence of gas, calcification, or both. Posterior disc extensions are also observed. (B, Courtesy of P. Katzenstein, MD, Houston, TX.)

A

Fig. 17.3  Radiographic features of alkaptonuria: disc calcification and ossification. Frontal radiograph of the lumbar spine shows osteoporosis, disc calcification, and, at the periphery of the intervertebral disc, ossification simulating the syndesmophytes of ankylosing spondylitis. (Courtesy J. Loewy, MD, Saskatoon, Saskatchewan, Canada.)

B

Fig. 17.4  Radiographic features of alkaptonuria: abnormalities in the symphysis pubis and sacroiliac joint. (A) Symphysis pubis. The findings are extreme narrowing of the joint space and extensive bony sclerosis. Beaklike ­ osteophytes are seen. (B) Sacroiliac joint. Diffuse narrowing of the articular space is associated with irregularity of subchondral bone and sclerosis. The articular margins are more sharply defined than would be expected in ankylosing spondylitis.

276

SECTION 2  Articular Disorders

Radiographic findings in the hip may be identical to the changes of degenerative joint disease, with articular space narrowing and sclerosis (Fig. 17.6). In some patients with alkaptonuria, diffuse loss of joint space, severe destruction with fragmentation and formation of intraarticular cartilaginous and osseous bodies,

and tendinous calcification and ossification permit differentiation from typical degenerative alterations. Involvement of the glenohumeral joint, small joints of the hands and feet, elbow, and ankle is not common.

DIFFERENTIAL DIAGNOSIS Spinal Manifestations

Fig. 17.5  Radiographic features of alkaptonuria: abnormalities of the knee. In this patient, abnormalities include joint space narrowing in the lateral femorotibial and patellofemoral compartments associated with bony sclerosis, small osteophytes, and multiple intraarticular osseous bodies (arrows).

Disc calcification in alkaptonuria may be confused with that accompanying other disorders. Dystrophic calcification of the nucleus pulposus is generally globular and confined to the central portion of the intervertebral disc. This pattern of central disc calcification can be readily differentiated from the diffuse disc calcification at multiple levels of the spine in patients with alkaptonuria. Calcification of the intervertebral disc may be seen as a secondary phenomenon in patients with primary disorders that lead to spinal ankylosis. Thus disc calcification can be noted in patients with ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, juvenile-­onset rheumatoid arthritis, Klippel-­Feil deformities, and surgical fusion of the spine. Disc calcification is also observed in calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. In this disorder, the deposits predominate in the outer fibers of the annulus fibrosus, and waferlike collections are not seen. Disc space loss, vacuum phenomenon, and vertebral body marginal sclerosis accompany intervertebral osteochondrosis. The findings are generally not as pronounced or widespread as in alkaptonuria, and they frequently occur in elderly patients. Nonetheless, the possibility of alkaptonuria must be considered in any patient whose radiographs reveal loss of height of multiple intervertebral discs, particularly if the changes occur in a middle-­aged patient and are accompanied by multiple vacuum phenomena, disc calcification, vertebral fusion, and kyphosis. Disc ossification with fusion of the vertebral bodies, a finding in alkaptonuria, may resemble abnormalities in ankylosing spondylitis. In long-­standing alkaptonuria, a bamboo spine may again simulate that of ankylosing spondylitis.

Extraspinal Manifestations

Fig. 17.6  Radiographic features of alkaptonuria: abnormalities of the hip. Extensive resorption and flattening of the femoral head are associated with a bizarre radiographic appearance. Findings include joint space narrowing, mild acetabular protrusion, and bone fragmentation (arrow).

Involvement of extraspinal sites in patients with alkaptonuria may lead to a radiographic appearance reminiscent of osteoarthrosis, with some differentiating features (Table 17.1): 1. Involvement of unusual articular sites: Severe degenerative-­ like arthropathy of the glenohumeral joint should raise the possibility of alkaptonuria in addition to osteoarthrosis. Similarly, severe changes in the sacroiliac or symphyseal joints may be a clue to the presence of ochronotic arthropathy. 2. Unusual patterns of joint space loss: Ochronotic arthropathy of the knee may lead to isolated lateral femorotibial compartment changes or to diffuse loss of articular space in both the medial and lateral femorotibial compartments, patterns that are not typical of osteoarthrosis. 3. Severe articular abnormalities: Extreme bone sclerosis and fragmentation and intraarticular cartilaginous and osseous bodies may be seen. The severity of the changes accompanying ochronotic arthropathy may be greater than those usually seen in osteoarthrosis. The production of multiple intraarticular bodies is particularly characteristic. Ochronotic arthropathy may be simulated by other disorders, such as CPPD crystal deposition disease, calcium hydroxyapatite crystal deposition disease, acromegaly, and epiphyseal and spondyloepiphyseal dysplasias.

CHAPTER 17  Alkaptonuria and Oxalosis

TABLE 17.1  Ochronotic Arthropathy Versus

Degenerative Joint Disease Ochronotic Arthropathy

Degenerative Joint Disease

Involvement of hip, shoulder, knee, sacroiliac joint, and symphysis pubis

Involvement of hip, knee, and hand

Focal or diffuse joint space loss

Focal joint space loss

Absent or meager osteophytosis

Prominent osteophytosis

Small cystic lesions

Small or large cystic lesions

Collapse, fragmentation, and intraarticular osseous bodies

No collapse or fragmentation

Tendon abnormalities

No tendon abnormalities

OXALOSIS PRIMARY OXALOSIS (PRIMARY HYPEROXALURIA) Primary oxalosis is a group of autosomal recessive disorders that has been divided classically into two types and, more recently, into three types. The two classic types of this disorder are type 1, glycolic aciduria, the most common type, caused by a defect in the enzyme alanine glyoxylate aminotransferase; and type 2, 1-­glyceric aciduria, caused by a defect in the enzyme glyoxylate/hydroxypyruvate reductase. Primary hyperoxaluria type 3 is a recently described subgroup related to a genetic defect on chromosome 9. Overproduction of oxalate, primarily by the liver, related to these enzyme defects is accompanied by its accumulation in various tissues. Damage to the kidneys in the form of calcium oxalate nephrolithiasis and nephrocalcinosis produces progressive renal failure and uremia. Extrarenal accumulation of calcium oxalate occurs in the small arteries, eyes, soft tissues, and bones.

A

277

Both boys and girls are affected. Clinical manifestations generally become apparent before the age of 5 years and are mainly the result of renal accumulation of calcium oxalate crystals. Calculi and pyelonephritis are observed. Radiographic examination of the genitourinary system may reveal small, contracted kidneys with parenchymal calcification. Primary oxalosis accounts for 1% to 2% of cases of pediatric end-­stage renal disease. The skeletal abnormalities associated with primary oxalosis include irregular transverse sclerotic bands in the metaphyseal segments of tubular bones, including the femur, humerus, tibia, fibula, metacarpals, metatarsals, and phalanges. These bands, which usually are bilateral and symmetric, extend into the epiphyses. Narrow translucent zones, which may replace the radiodense lines, are seen at the level of the physis between the epiphyseal and metaphyseal components (Fig. 17.7A). Similar radiodense regions can appear in subchondral areas in the humeri and femora, and resemble the findings of ischemic necrosis. Alternating radiolucent and radiodense bands have been identified in the ilium and sternum, whereas in the spine, sclerotic zones at the top and bottom of the vertebral bodies simulate the rugger-­jersey appearance of renal osteodystrophy (see Fig. 17.7B). Diffuse osteosclerosis of the vertebrae may also occur, and oxalate crystal deposition in adjacent ligaments and soft tissues may contribute to spinal stenosis. Additional skeletal alterations include a drumstick configuration of the metacarpal bones and patchy sclerosis in the clavicles. Eventually, chronic renal failure can lead to the widespread skeletal abnormalities of renal osteodystrophy. Histologic investigation of the skeletal abnormalities in both primary and secondary oxalosis indicates that the sclerotic regions in the tubular bones represent, in large part, deposition of calcium oxalate crystals in the marrow. A foreign body giant cell reaction results and stimulates new bone formation. Massive deposits of calcium oxalate are associated with resorption and disappearance of trabeculae, cystic lesions, fracture, and deformities such as acetabular protrusion.

B Fig. 17.7  Primary oxalosis: radiographic abnormalities. In this 32-year-old ­ ­ man, diffuse skeletal abnormalities are present. (A) Findings include a drumstick configuration of the metacarpal bones, hypoplasia of the terminal phalanges, a coarsened trabecular pattern, and patchy metaphyseal sclerosis. (B) In the spine, abnormalities include irregularities in vertebral shape and a rugger-jersey ­ appearance in the vertebral bodies. Surgical clips are evidence of previous renal transplantation. (Courtesy R. Bluestone, MD, Los Angeles, CA.)

278

SECTION 2  Articular Disorders to blood urea nitrogen in end-­stage renal failure. Deposition of calcium oxalate subsequently occurs in the body’s tissues, primarily in the kidney itself; more than 75% of patients with end-­stage renal disease of longer than 2 months’ duration have significant accumulations of calcium oxalate in the kidney. Other organs that are involved include the myocardium, thyroid gland, spleen, liver, lymph nodes, brain, salivary glands, dentin, dental pulp, arteries and veins, and musculoskeletal tissues. Trabecular condensation or disarray, or both, accounts for the resulting radiodensity and cystic appearance on radiographs. Articular manifestations, which may include effusions, pain, and stiffness, have been reported in multiple locations, including the knee, wrist, and metacarpophalangeal and interphalangeal joints. Chondrocalcinosis, as well as calcification in the joint capsule and tendons, may be related to CPPD, calcium hydroxyapatite, or calcium oxalate crystal deposition (or any combination of the three) in patients with chronic renal disease (Fig 17.8). Additional skeletal and articular findings relate to secondary hyperparathyroidism, which itself is related to renal failure.

FURTHER READING

Fig. 17.8  Secondary oxalosis: radiographic abnormalities. Radiograph reveals periarticular and intraarticular calcification. The latter is within the capsule, the synovium, and, possibly, the cartilage. Minimal subperiosteal bone resorption is suggested.

SECONDARY OXALOSIS (SECONDARY HYPEROXALURIA) Oxalosis is a recognized complication of other diseases, especially renal disorders; secondary forms of oxalosis are also related to (1) ingestion of substances that either contain the oxalate ion or are metabolized to oxalate (rhubarb, spinach, ethylene glycol), (2) thiamine and pyridoxine deficiencies that inhibit glyoxylate metabolism and increase the production of oxalate, (3) alterations in intestinal microflora (e.g., loss of Oxalobacter formigenes through the use of antibiotics), and (4) bowel disorders that cause malabsorption and steatorrhea. One factor that may lead to secondary oxalosis relates to juicing, as some juices contain high amounts of oxalate, leading to increased intestinal absorption of oxalate that overwhelms the ability of the kidney to excrete this substance. Because oxalic acid is excreted by the kidneys, plasma oxalate levels generally rise in proportion

Bhasin B, Urekli HM, Atta MG. Primary and secondary hyperoxaluria: understanding the enigma. World J Nephrol. 2015;4:235. Brancaccio D, Poggi A, Ciccarelli C, et al. Bone changes in end-­stage oxalosis. AJR Am J Roentgenol. 1981;136:935. Cochat P, Rumsby G. Primary hyperoxaluria. N Engl J Med. 2013;369:649. Day DL, Scheinman JI, Mahan J. Radiological aspects of primary hyperoxaluria. AJR Am J Roentgenol. 1986;146:395. Hamada T, Yamamoto T, Shida J, et al. Subchondral insufficiency fracture of the femoral head in a patient with alkaptonuria. Skeletal Radiol. 2014;43:827. Justesen P, Andersen Jr PE. Radiologic manifestations in alcaptonuria. Skeletal Radiol. 1984;11:204. Lagier R, Sitaj S. Vertebral changes in ochronosis: anatomical and radiological study of one case. Ann Rheum Dis. 1974;33:86. Lasker RH, Sargison KD. Ochronotic arthropathy: a review with four case reports. J Bone Joint Surg Br. 1970;52:653. Millea TP, Segal LS, Liss RG, et al. Spine fracture in ochronosis: report of a case. Clin Orthop. 1992;281:208. Millucci L, Bernardini G, Spreafico A, et al. Histological and ultrastructural characterization of alkaptonuric tissues. Calcified Tissue Int. 2017;101:50. Selvi E, Manganelli S, Benucci M, et al. Chronic ochronotic arthritis: Clinical, arthroscopic, and pathologic findings. J Rheumatol. 2000;27:2272. Strauss SB, Waltuch T, Bivin W, et al. Primary hyperoxaluria: spectrum of clinical and imaging findings. Pediatr Radiol. 2017;47:96. Ventura-­Rios L, Hernandez-­Diaz C, Gutierrez-­Perez L, et al. Ochronotic arthropathy as a paradigm of metabolically induced degenerative joint disease. A case-­based review. Clin Rheumatol. 2016;35:1389. Zatkova A. An update on molecular genetics of alkaptonuria (AKU). J Inherited Metab Dis. 2011;34:1127.

18 Neuropathic Osteoarthropathy S U M M A R Y O F K E Y F E AT U R E S • D  eprivation of sensory feedback with continued stress causes progressive joint deterioration. • Articular changes include joint space narrowing, bony eburnation, osteophytosis, fragmentation, fracture, and subluxation.

• Th  ere are various causes of neuropathic osteoarthropathy, which can be predicted based on the distribution of imaging findings.

INTRODUCTION

No agreement exists on the pathogenesis of the articular changes. Two fundamental theories of pathogenesis are (1) the “French theory,” holding that joint changes are the result of damage to the CNS trophic centers, which control nutrition of the bones and joints, and (2) the “German theory,” which maintains that unusual mechanical stresses about a weight-­bearing joint in an ataxic person lead to recurrent subclinical trauma. Although other theories exist, there is considerable evidence that both mechanical and vascular factors contribute to subsequent disintegration of the joint (Fig. 18.1). What is clear is that loss of normal neurologic function renders a joint and adjacent bone susceptible to a sequence of pathologic and radiologic alterations that may ultimately produce their disintegration. Joint instability that precedes neurologic dysfunction may make this sequence more likely.

  

In 1868, Charcot described an apparent cause-­and-­effect relationship between primary lesions of the central nervous system (CNS) and certain arthropathies. Charcot continued to study and characterize the disorder for the next 15 years, and although his description was virtually confined to patients with tabes dorsalis, the name Charcot joint has become synonymous with all articular abnormalities related to neurologic deficits, regardless of the nature of the primary disease. Other terms applied to this disorder are neuroarthropathy and neurotrophic or neuropathic joint disease. None of these terms is ideal, however, because the initial event in some cases occurs not in the joint itself but in the adjacent bone or even some distance from the articulation. Therefore, the designations neuropathic osteoarthropathy and neuropathic bone and joint disease are more suitable. The effect of the deprivation of sensory feedback on the musculoskeletal system can be profound. An anesthetized joint or bone that is subject to continuing stress deteriorates progressively, with the appearance of specific radiographic abnormalities. These changes, which include articular space narrowing, bony eburnation, osteophytosis, fragmentation, fracture, and subluxation, can accompany a variety of disorders but are most common in diabetes mellitus, syringomyelia, and spinal cord injury. A mnemonic that has been used to describe the resulting radiographic abnormalities, particularly in the spine, relates to the “six Ds: distention (soft tissue mass), density (bone sclerosis), debris, disorganization, dislocation, and destruction. When severe, the resulting radiographic picture is diagnostic; in earlier stages, however, the findings may resemble those of osteoarthrosis, calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, calcium hydroxyapatite crystal deposition disease, or osteonecrosis.

CAUSE AND PATHOGENESIS Central (upper motor neuron) and peripheral (lower motor neuron) lesions can lead to neuropathic osteoarthropathy. Among the central lesions that may produce neuropathic osteoarthropathy are syphilis, syringomyelia, meningomyelocele, trauma, multiple sclerosis, Charcot-­Marie-­ Tooth disease, congenital vascular anomalies, and other causes of cord compression, injury, or degeneration; peripheral causes include diabetes mellitus, alcoholism, amyloidosis, infection (tuberculosis, yaws, leprosy), pernicious anemia, trauma, and intraarticular or systemic administration of steroids. Additionally, specific syndromes leading to congenital insensitivity to pain and dysautonomia produce similar alterations.

GENERAL RADIOGRAPHIC AND PATHOLOGIC ABNORMALITIES Although the pathologic and radiographic radiologic features of advanced neuropathic osteoarthropathy are characteristic, early features may simulate those of osteoarthrosis (Fig. 18.2). An enlarging and persistent effusion, minimal joint subluxation, fracture, and bone fragmentation should alert a radiologist to the possibility of neuropathic osteoarthropathy; similarly, the finding of considerable amounts of cartilaginous and osseous debris attached to and incorporated into the synovial membrane (detritic synovitis) should suggest to a pathologist that the changes may represent joint manifestations of neuropathic disease (Box 18.1). These early changes may show rapid progression, and the joint may appear to fall apart in a matter of days or weeks (Fig. 18.3). More advanced imaging abnormalities consist of depression, absorption, and shattering of subchondral bone; bone sclerosis and osteophytosis; intraarticular osseous fragments; joint subluxation; massive soft tissue enlargement and effusion; and fracture of neighboring bones (Fig. 18.4). Pathologically, capsular thickening, induration and villous proliferation of the synovial membrane, and fluid and adhesions within the joint are seen. In the synovial membrane, chondral metaplasia can lead to radiographically detectable calcific and ossific debris that may migrate far away from the joint itself (Fig. 18.5). In long-­standing neuropathic osteoarthropathy, joint disorganization becomes profound (Fig. 18.6). The degree of sclerosis, osteophytosis, and fragmentation in this disorder is greater than that in any other process. Yet the bone shards and irregular articular surfaces produced by the considerable osseous fragmentation and collapse accompanying this disease are generally well defined and sharp. Poorly marginated, fuzzy bone contours,

279

280

SECTION 2  Articular Disorders Neuropathic osteoarthropathy can accompany many disorders that lead to sensory disturbances. Although some motor function is fundamental in the pathogenesis of the lesions, neuropathic osteoarthropathy can develop in patients with both sensory and motor loss, presumably related to vigorous physical therapy. The imaging and pathologic features of this condition are generally similar in these various disorders, but certain subtle differences may be evident, and the distribution of abnormalities varies among the disorders (Table 18.1).

Loss of deep sensation and proprioception

Relaxation and hypotonia of supporting structures Recurrent injury

Diabetes Mellitus Loss of pain and loss of proprioceptive sensation appear to be of major importance in diabetic neuropathic osteoarthropathy and, in the presence of repetitive microtrauma or macrotrauma, promote the changes. Infectious processes are commonly superimposed on neuropathic changes in diabetic patients, especially in superficially located joints; however, lack of soft tissue ulceration, penetrating injury, or surgery makes superimposed osteomyelitis very unlikely regardless of imaging findings. Although the exact frequency of neuropathic bone and joint changes in diabetic persons is not clear, this disease is the leading cause of neuropathic osteoarthropathy and represents the underlying disorder in more than 98% of cases. Typically, diabetic neuropathic osteoarthropathy appears in a man or woman with long-­standing diabetes mellitus, generally in the fifth to seventh decades of life. One or more joints of the forefoot and midfoot are affected most commonly. Painless soft tissue swelling, skin ulceration, and joint deformity are encountered. Productive or resorptive bone abnormalities occur, depending on the location of the neuropathic changes. In the intertarsal or tarsometatarsal joints, osseous fragmentation and sclerosis and joint subluxation or dislocation may be prominent, and complete disintegration of one or more tarsal bones can occur rapidly (see Fig. 18.6). Calcaneal fragmentation is typical (Fig. 18.7). Talar disruption and dorsolateral displacement of the metatarsal bones in relation to the cuneiform and cuboid bones are also characteristic, and the resulting radiographic picture may resemble that occurring in an acute Lisfranc fracture-­dislocation (Fig. 18.8). At the metatarsophalangeal joints, osseous resorption is frequent and leads to partial or complete disappearance of the metatarsal heads and proximal phalanges, with tapering or pencil-­pointing of the

Malalignment Erosion of chondral surface, subchondral sclerosis, fracture, fragmentation Joint disorganization Fig. 18.1  Pathogenesis of neuropathic osteoarthropathy. Probable sequential steps in the development of the disease are indicated.

as occur in osteomyelitis and septic arthritis, are not usually evident unless infection has become superimposed on the neuropathic process.

SPECIFIC DISORDERS KEY CONCEPTS  • D  iabetes mellitus: the most frequent cause of neuropathic osteoarthropathy, most commonly involves the midfoot and forefoot. • Tabes dorsalis: most commonly involves the lower extremities. • Syringomyelia: most commonly involves the upper extremities, especially both glenohumeral joints. • Alcoholism and amyloidism: have a distribution similar to that of diabetes mellitus. • Congenital indifference to pain: most commonly involves the lower extremity with findings of chronic physeal and periphyseal trauma. • Meningomyelocele: has a distribution and findings similar to those of congenital indifference to pain.

A

B

C

D

Fig. 18.2  General radiologic and pathologic abnormalities of synovial joints in the various stages of neuropathic osteoarthropathy. (A) Normal synovial joint. (B) Initially, cartilaginous fibrillation and fragmentation can be observed. Some of the cartilaginous debris remains attached to the chondral surface, some is displaced into the articular cavity, and some becomes embedded in the synovial membrane. (C) Subsequently, osseous and cartilaginous destruction becomes more extensive, and the embedded pieces of cartilage and bone produce local synovial irritation. Bony eburnation and subluxation are also evident. (D) Eventually, large portions of the chondral coat are lost, bone sclerosis is extreme, capsular rupture can occur, and shards of bone can dissect along the soft tissue planes (arrow).

CHAPTER 18  Neuropathic Osteoarthropathy

BOX 18.1  Causes of Detritic Synovitis Neuropathic osteoarthropathy Osteonecrosis Calcium pyrophosphate dihydrate crystal deposition disease Psoriatic arthritis Osteoarthrosis Osteolysis with detritic synovitis

phalangeal and metatarsal shafts (Fig. 18.9). Flattening and fragmentation of the metatarsal heads are particularly characteristic and may resemble the changes of Freiberg disease, or infraction. (Fig. 18.10). Ankle involvement is uncommon, and knee abnormalities are rare. Diabetic neuropathic osteoarthropathy in the spine can be generalized or localized. The resulting radiographic changes, which include destruction of vertebral bodies, bone sclerosis, osteophytosis, bone fragmentation and ankylosis, altered spinal curvature, and spinal angulation, resemble those in tabes or syringomyelia (Fig. 18.11).

Tabes Dorsalis It is estimated that 5% to 10% of patients with tabes dorsalis from syphilis have neuropathic osteoarthropathy. The joints of the lower extremity are affected in 60% to 75% of cases. The knee, hip, ankle, shoulder, and elbow are altered, in descending order of frequency (see Figs. 18.3 to 18.5 and 18.12). Other involved sites include the joints of the forefoot, midfoot, vertebral column, and fingers, and the temporomandibular and sternoclavicular joints. Polyarticular alterations are not unusual. Typically, painless swelling, deformity, weakness, and instability are evident clinically. In as many as one third of patients, the affected joints may be painful. Axial neuropathic osteoarthropathy is not uncommon in tabes and is often painful. It is most frequent in the lumbar spine, where one or more vertebrae may be affected. Radiographically, intervertebral disc

A

281

space and apophyseal joint narrowing, sclerosis, and osteophytosis are generally more exaggerated than those of degenerative joint disease (Fig. 18.13). Fracture with osseous fragmentation in spinal and paraspinal locations, as well as malalignment, may also be evident. The resulting radiographic findings, when severe, are unique to this disorder and differ from the spinal manifestations of degenerative joint disease, infection, skeletal metastasis, and Paget disease (Table 18.2). Less commonly, osteolytic changes predominate in axial neuropathic osteoarthropathy, and these can appear acutely, progress rapidly, and lead to significant bony dissolution in a period of weeks or months. The appearance of this lytic variety of neuropathic disease can resemble that of infection or skeletal metastasis.

Syringomyelia It has been estimated that neuropathic osteoarthropathy develops in 20% to 25% of patients with syringomyelia. Neuropathic changes in syringomyelia are common in the joints of the upper extremity, especially the glenohumeral articulation (Fig. 18.14). In the lower extremity, the knee, ankle, and hip are affected with approximately equal frequency; in both the upper and lower limbs, bilateral symmetric changes are not as common as in tabes. Generally, neuropathic osteoarthropathy occurs during the later phases of syringomyelia, but occasionally, joint findings may be the initial or predominant manifestation of the disease. The clinical, radiographic, and pathologic alterations of neuropathic osteoarthropathy in syringomyelia are similar to those in tabes. The degree of fragmentation and sclerosis of the humeral head can be striking, and these changes may be associated with fractures of neighboring bones, including the scapula, clavicle, and ribs. Further, spontaneous dislocation of the glenohumeral joint may be the initial manifestation of neuropathic osteoarthropathy in syringomyelia.

Alcoholism and Amyloidosis Although peripheral neuropathy may be evident in as many as 30% of alcoholic patients, reports of neuropathic osteoarthropathy in these

B

Fig. 18.3  General radiographic and pathologic abnormalities of neuropathic osteoarthropathy: rapid disease progression. (A–B) The appearance and progression of articular destruction can occur rapidly. Initial foci of chondral and osseous destruction can lead to fragmentation and collapse in a matter of weeks. This patient has tabes dorsalis.

282

SECTION 2  Articular Disorders

A

B

Fig. 18.4  General radiographic and pathologic abnormalities of neuropathic osteoarthropathy: fractures and subluxations. (A) Gross disorganization of the joint in a tabetic patient is characterized by lateral subluxation of the tibia on the femur, lateral patellar dislocation, soft tissue swelling, osseous fragmentation and sclerosis, and periostitis. (B) In a different patient with the same disease, note the angular deformity of the ankle, with fragmentation, sclerosis, and fractures. Periostitis and soft tissue swelling are evident.

persons are infrequent. When present, neuropathic osteoarthropathy is evident in the feet and resembles the changes accompanying diabetic neuropathic disease. Occasionally, neuropathic bone and joint disease develops in patients with amyloidosis, with or without additional plasma cell dyscrasias. The knee and the ankle appear to be the predominant sites of involvement.

Congenital Indifference to Pain Indifference or insensitivity to pain is a feature common to several distinct hereditary sensory neuropathies that differ in their patterns of inheritance, precise clinical manifestations, and prognosis. In most of these syndromes, the neurologic deficit can be recognized in infancy or childhood. A decreased or absent reaction to pain, scars on the tongue or fingers related to burns or infections, corneal opacities resulting from unnoticed foreign bodies, and aggressive behavior may be found. Self-­mutilation with amputation of fingers and toes is also encountered. Skeletal lesions in the syndromes of congenital indifference to pain (and related disorders) demonstrate fractures of the metaphysis and diaphysis of long bones, epiphyseal separations, neuropathic osteoarthropathy, and soft tissue ulcerations (Fig. 18.15). These injuries, which are often unrecognized and untreated, can lead to severe disability and are generally more frequent in the lower extremity than the upper extremity. Epiphyseal separation is the result of chronic trauma or stress, because the growth plate represents the weak link in the child’s skeleton; widening and irregularity of the growth plate, lysis and sclerosis of the metaphysis, periostitis and callus, and variable degrees of epiphyseal displacement are recognized. Neuropathic osteoarthropathy is especially common in the knee, ankle, and tarsal areas. Overt neurologic symptoms and signs may be absent in children and adolescents with some types of congenital insensitivity to pain. Therefore,

the presence of unusual fractures and physeal abnormalities on radiographs should stimulate a search for a subtle neurologic deficit, especially if the clinical findings appear mild in comparison to the severity of the radiographic alterations. Virtually identical skeletal abnormalities are seen in all the syndromes of congenital insensitivity to pain.

Meningomyelocele (Spinal Dysraphism) Sensory impairment resulting from spina bifida and meningomyelocele is the most frequent underlying cause of neuropathic osteoarthropathy in childhood. It affects principally the ankle and the tarsal joints. In active children, radiographic changes may appear in the first 3 years of life. These changes are identical to those in the syndromes of congenital indifference to pain and include osteoporosis, diaphyseal and metaphyseal fractures, injuries to the growth plate, epiphyseal separations, persistent effusions, articular destruction, and soft tissue ulcerations (Fig. 18.16).

Other Diseases Numerous other causes of neuropathic skeletal alterations exist, including spinal cord or peripheral nerve injury, myelopathy of pernicious anemia, Charcot-­Marie-­Tooth disease, Arnold-­Chiari malformation, neurofibromatosis, arachnoiditis, intraspinal tumors, degenerative spinal disease, paraplegia, quadriplegia, familial interstitial hypertrophic polyneuropathy of Dejerine and Sottas, chronic inflammatory demyelinating polyradiculoneuropathy, limb replantation, leprosy, paraneoplastic sensory neuropathy, and yaws. An idiopathic variety of neuropathic osteoarthropathy of the elbow and shoulder has also been identified. Neuropathic-­like changes occur in patients with chronic paraplegia and quadriplegia. Neuropathic osteoarthropathy may be seen in

CHAPTER 18  Neuropathic Osteoarthropathy

283

A

B Fig. 18.5  General radiographic and pathologic abnormalities of neuropathic osteoarthropathy: migration of bony shards. In this patient with syphilis, numerous fragments of bone originating from the destroyed articular surfaces have moved into the far recesses of the joint or migrated along adjacent tissue planes (arrowheads).

paralyzed patients, initiated by physical therapy and by daily activities such as transferring from a bed to a wheelchair. Most reports of neuropathic osteoarthropathy occurring in paralyzed patients have indicated a predilection for the spine.

MAGNETIC RESONANCE IMAGING ABNORMALITIES The general magnetic resonance (MR) imaging findings of neuropathic osteoarthropathy parallel the known pathologic findings and include large joint effusions, capsular distention and rupture, synovial cysts, ligamentous disruption, and intraarticular bodies. Additionally, enhancing increased T2-­weighted marrow signal abnormality is common, replacing the normal T1-­weighted fatty marrow signal (Fig. 18.17). In the spine, findings are similar to those of infection (e.g., sclerosis and erosions of the vertebral endplates, decreased height of the intervertebral disc, soft tissue masses), although identification of gas in the affected intervertebral disc, spondylolisthesis, involvement of the facet joints, diffuse abnormalities of signal intensity in the vertebral bodies, and rim enhancement of signal intensity in the intervertebral discs on intravenous gadolinium-­enhanced MR images are more suggestive of neuropathic osteoarthropathy than of infection. Diagnostic problems are encountered in the differentiation of osteomyelitis and neuropathic osteoarthropathy in patients with diabetes mellitus. Ongoing neuropathic changes encountered in ambulatory diabetic patients may be associated with edema in both the adjacent bones and the soft tissues. The signal intensity patterns of such edema in neuropathic osteoarthropathy are similar, if not identical, to those

Fig. 18.6  Diabetes mellitus: midfoot. Radiograph (A) and sagittal reformatted computed tomography image (B) show subluxation, fragmentation, and sclerosis at the midfoot.

TABLE 18.1  Common Sites of Involvement

in Neuropathic Osteoarthropathy Disease

Site of Involvement

Tabes dorsalis

Knee, hip, ankle, spine

Syringomyelia

Glenohumeral joint, elbow, wrist, spine

Diabetes mellitus

Metatarsophalangeal, tarsometatarsal, intertarsal joints

Alcoholism

Metatarsophalangeal, interphalangeal joints

Amyloidosis

Knee, ankle

Meningomyelocele

Ankle, intertarsal joints

Congenital sensory neuropathy, Knee, ankle, intertarsal, hereditary sensory radicular metatarsophalangeal, interphalangeal neuropathy joints Spinal cord injury

Spine

encountered in infection. This edema is often prominent in cases of acute neuropathic osteoarthropathy, accompanied by fracture and fragmentation of bone. Additionally, sympathetic joint effusions are consistently observed in the feet of diabetic patients, and this may simulate findings of septic arthritis, although uncommon, given poor vascularity. To assist in the differentiation of neuropathic osteoarthropathy, it is important to remember that pedal osteomyelitis results almost exclusively from contiguous infection. Frequent sites of osteomyelitis occur where soft tissue ulcers are found, such as the first and fifth

284

SECTION 2  Articular Disorders

Fig. 18.7  Diabetes mellitus: calcaneus. Radiograph shows fractures of the posterior aspect of the calcaneus and subtalar region and collapse of the bone.

Fig. 18.8  Diabetes mellitus: tarsometatarsal joints. Note the lateral displacement of the bases of the metatarsals (arrows) with respect to the tarsals. This finding, combined with soft tissue swelling and fragmentation, represents a neuropathic Lisfranc fracture-­dislocation.

metatarsophalangeal joints, as well as at the calcaneus and distal phalanges. Therefore the location of soft tissue ulceration is critical when MR images are surveyed, as this is the site where osteomyelitis would be present. On the contrary, absence of a soft tissue ulcer in a diabetic foot would make osteomyelitis uncommon, regardless of the imaging findings (Fig. 18.18). Additional observations based on MR imaging may also help differentiate neuropathic abnormalities alone from those of neuropathic and infectious abnormalities together, especially in the diabetic foot. A “ghost sign” refers to obscuration of the cortical outline of involved bones on T1-weighted images that reappears on fluid-sensitive or contrast-enhanced sequences, generally indicating osteomyelitis, whereas the absence of this sign, that is the preservation of the cortical outline

Fig. 18.9  Diabetes mellitus: metatarsophalangeal and interphalangeal joints. Neuropathic osteoarthropathy and infection in the forefoot of a diabetic patient combine to produce bizarre abnormalities consisting of osteolysis of the distal metatarsals and proximal phalanges, with tapering of the osseous contours.

Fig. 18.10  Diabetes mellitus: metatarsophalangeal joints. Observe the collapse of the second and third metatarsal heads, similar to the findings in Freiberg disease (Freiberg infraction). Fractures in the bases of the proximal phalanges are also evident. (Courtesy A. D’Abreu, MD, Porto Alegre, Brazil.)

of involved bones, is suggestive of neuropathic osteoarthropathy alone. Also, sinus tracts leading directly from the skin surface to the affected bone(s) are strong evidence that infection is present.

DIFFERENTIAL DIAGNOSIS When severe, neuropathic osteoarthropathy is associated with imaging changes that are almost pathognomonic. Bony eburnation, fracture, subluxation, and joint disorganization are more profound in this disorder than in any other condition. In the joints of the appendicular skeleton, joint space loss and bone sclerosis and fragmentation in the early stages of neuropathic osteoarthropathy can resemble the

CHAPTER 18  Neuropathic Osteoarthropathy

A

B

285

C

Fig. 18.11  Diabetes mellitus: spine. Progressive deterioration of the lumbar spine is apparent during a 3-­year period of observation. Initially (A), the changes at the lower lumbar level resemble degenerative disc disease. Subsequently (B and C), this level deteriorates slowly; one level above, however, rapid destruction of the intervertebral disc and bone is evident. The vacuum phenomenon in the upper disc, as well as the well-­ defined and sclerotic bone in (B), makes infection unlikely. In (C), the pattern of disc destruction is identical to that of infection, although the latter was not apparent clinically. (Courtesy U.S. Naval Hospital, San Diego, CA.)

Fig. 18.12  Tabes dorsalis: neuropathic osteoarthropathy of the appendicular skeleton—hip. Sclerosis and fragmentation are prominent, and subluxation of the joint is evident.

changes in osteoarthrosis, although vascular calcifications in diabetes may be a clue to the diganosis of neuropathic osteoarthropathy. With progressive flattening and deformity of the articular surfaces, the production of numerous intraarticular bone fragments, and the appearance of increasing bone sclerosis and osteophytosis, the diagnosis of neuropathic osteoarthropathy becomes more obvious. In CPPD crystal deposition disease, a neuropathic-­like arthropathy characterized by joint space narrowing and bone eburnation and fragmentation can appear, especially in the knee, wrist, and metacarpophalangeal joints. Identification of articular and periarticular calcification, involvement of specific joints and parts of joints, and the variability in osteophyte formation are helpful clues to the accurate diagnosis of pyrophosphate arthropathy. Intraarticular deposition of calcium hydroxyapatite crystals may lead to progressive destruction of a joint, especially in the shoulder, with fracture and dissolution of bone. Bony fragmentation and collapse are also manifestations of subchondral insufficiency fractures, osteonecrosis, posttraumatic osteoarthritis, intraarticular steroid arthropathy, neglected infection, and alkaptonuria. Once the imaging findings are interpreted as those of neuropathic osteoarthropathy, identification of the underlying disorder usually depends on the location of the changes. Tabes typically produces changes in the hip, knee, ankle, and spine; diabetes mellitus leads to alterations in the midfoot and forefoot; syringomyelia affects the articulations of the upper extremity and cervical spine; spinal cord injury often leads to neuropathic changes in the vertebral column; and the syndromes of congenital indifference to pain and meningomyelocele commonly localize in the joints (including the physes) of the lower

286

SECTION 2  Articular Disorders

A

B

Fig. 18.13  Tabes dorsalis: neuropathic osteoarthropathy of the axial skeleton—spine. (A) Localized disease. Frontal and lateral radiographs of the lumbar spine reveal extensive disorganization involving two vertebral bodies (arrows) and the intervening intervertebral disc. Note the loss of intervertebral disc space, bone sclerosis, and osteophytosis. The resulting osseous contours are relatively well defined. (B) Generalized disease. Widespread abnormalities in the lumbar spine consist of loss of height of multiple intervertebral discs, extreme sclerosis, osteophytes, subluxation, and vertebral angulation.

TABLE 18.2  Axial Neuropathic Osteoarthropathy and Its Differential Diagnosis Neuropathic Osteoarthropathy

Intervertebral (Osteo)Chondrosis

Infection

CPPD Crystal Deposition Disease

Sites of involvement

Frequently widespread One or more levels Predominates in thoracolumbar Cervical, thoracic, or lumbar spine spinea

Frequently one level Widespread Predominates in thoracolumbar Cervical, thoracic, or lumbar spine spine

Intervertebral disc spaces

Narrowed or obliterated

Narrowed

Narrowed or obliterated

Calcification; narrowed Variablec

Bone sclerosis

May be extreme

Usually mild to moderate

Variableb

Osteophytosis

May be massive

Absent or moderate in size

Usually absent

Variable

Bone fragmentation

May be extreme

Absent or minimal

Usually absent

Variabled

Subluxation, angulation

Common

Rare

Variablee

Variable

Paravertebral mass

Usually absent

Absent

Common

Absent

aInfluenced

by the specific underlying disorder. sclerosis more typical in pyogenic spondylitis and in Black patients with tuberculous spondylitis. cDisc calcification may appear without sclerosis, or disc space loss may be combined with moderate or severe bone sclerosis. dIn some patients, bone fragmentation and deformity may be severe, especially in the cervical spine. eIn tuberculosis, kyphosis may become prominent. CPPD, Calcium pyrophosphate dihydrate. bBone

CHAPTER 18  Neuropathic Osteoarthropathy

Fig. 18.14  Syringomyelia. Radiograph of the right shoulder reveals dissolution of the humeral head, with extensive bone fragmentation.

A

B

Fig. 18.15  Syndromes of congenital indifference to pain. (A) In this 7-­year-­old boy, fragmentation of the lateral femoral condyle (arrow) and patella is associated with a joint effusion and intraarticular osseous bodies. The opposite side (not shown) was similarly affected. (B) In a 17-­year-­old patient, osteolysis and autoamputation of multiple phalanges are evident. The opposite hand was similarly involved. (Courtesy M. Mitchell, MD, Halifax, Nova Scotia, Canada.)

287

288

SECTION 2  Articular Disorders

A

B

Fig. 18.16  Meningomyelocele (spinal dysraphism). (A) In this child with a meningomyelocele, note the epiphyseal separation of the distal end of the tibia, along with a widened and irregular growth plate, bone sclerosis, and periostitis. (B) Lateral radiographs of the femora in this child with a meningomyelocele reveal irregular and widened distal femoral growth plates, fracture and fragmentation, and exuberant periostitis. (Courtesy J. E. L. Desautels, MD, Calgary, Alberta, Canada.)

A

B

C

D

Fig. 18.17  Neuropathic osteoarthropathy: diabetes mellitus. (A) Radiograph shows sclerosis, fragmentation, and subluxation at the midfoot (arrows). Long axis (B) T1-­weighted, (C) fluid-­sensitive, and (D) T1-­weighted fat-suppressed contrast-enhanced MR images show marrow replacement with low T1 and enhancing high T2 signal abnormalities (arrows). Note absence of soft tissue ulcer and characteristic midfoot location of imaging findings. The cortical surfaces of some of the involved bones are still visible in the T1-weighted image. Therefore the “ghost sign” indicative of infection is not present, further supporting the diagnosis of neuropathic osteoarthropathy alone.

CHAPTER 18  Neuropathic Osteoarthropathy

289

B

C

A

D

E

Fig. 18.18  Neuropathic osteoarthropathy: diabetes mellitus. (A–B) Radiographs show sclerosis, fragmentation, and subluxation at the midfoot (arrows). Long axis (C) T1-­weighted and (D) fluid-­sensitive MR images show significant marrow replacement with low T1 and high T2 signal signal abnormalities (arrows). In (C), observe that the cortical surfaces of the involved bones are preserved. That is, no ghost sign is present, favoring the diagnosis of neuropathic disease alone rather than both neuropathic and infectious disease together. (E) Axial T1-­weighted fat-suppressed, contrast-enhanced MR image shows peripheral enhancing joint effusion (curved arrow). Note absence of soft tissue ulcer and characteristic midfoot location of imaging findings.

extremity. The presence of metaphyseal and growth plate destruction in an immature skeleton is especially characteristic of congenital indifference to pain and meningomyelocele.

FURTHER READING Bjorkengren AG, Weisman M, Pathria MN, et al. Neuroarthropathy associated with chronic alcoholism. AJR Am J Roentgenol. 1988;151:743. Brower AC, Allman RM. Pathogenesis of the neurotrophic joint: neurotraumatic versus neurovascular. Radiology. 1981;139:349. Campbell WL, Feldman F. Bone and soft tissue abnormalities of the upper extremity in diabetes mellitus. AJR Am J Roentgenol. 1975; 124:7. Eichenholtz SN. Charcot Joints. Springfield, Ill: Charles C Thomas; 1966. El-­Khoury GY, Kathol MH. Neuropathic fractures in patients with diabetes mellitus. Radiology. 1980;134:313. Feldman F, Johnson AM, Walter JF. Acute axial neuroarthropathy. Radiology. 1974;111:1. Forrester DM, Magre G. Migrating bone shards in dissecting Charcot joints. AJR Am J Roentgenol. 1978;130:1133.

Giesecke SB, Dalinka MK, Kyle GC. Lisfranc’s fracture-­dislocation: a manifestation of peripheral neuropathy. AJR Am J Roentgenol. 1978;131:139. Gondos B. The pointed tubular bone: its significance and pathogenesis. Radiology. 1972;105:541. Hodgson J, Pugh D, Young H. Roentgenologic aspects of certain lesions of bone: neurotropic or infectious? Radiology. 1948;50:65. Jones EA, Manaster BJ, May DA, et al. Neuropathic osteoarthropathy: diagnostic dilemmas and differential diagnosis. Radiographics. 2000;20:279. Kathol MH, El-­Khoury GY, Moore TE, et al. Calcaneal insufficiency avulsion fractures in patients with diabetes mellitus. Radiology. 1991;180:725. Ledbetter LN, Salzman KL, Sanders RK, et al. Spinal neuroarthropathy: pathophysiology, clinical and imaging features, and differential diagnosis. RadioGraphics. 2016;36:783. Ledermann HP, Morrison WB, Schweitzer ME. MR image analysis of pedal osteomyelitis: distribution, patterns of spread, and frequency of associated ulceration and septic arthritis. Radiology. 2002;223:747. Morrison WB, Schweitzer ME, Batte WG, et al. Osteomyelitis of the foot: relative importance of primary and secondary MR imaging signs. Radiology. 1998;207:625.

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SECTION 2  Articular Disorders

Noguerol TM, Alcala AL, Beltran LS, et al. Advanced MR imaging techniques for differentiation of neuropathic arthropathy and osteomyelitis in the diabetic foot. RadioGraphics. 37: 2017 Norman A, Robbins H, Milgram JE. The acute neuropathic arthropathy—a rapid severely disorganizing form of arthritis. Radiology. 1968;90:1159. Rosskopf AB, Loupatatzis C, Pfirrmann CWA, et al. The Charcot foot: a pictorial review. Insights in Imaging. 2019;77:2019. Schneider R, Goldman AB, Bohne WH. Neuropathic injuries to the lower extremities in children. Radiology. 1978;128:713. Schweitzer ME, Daffner RH, Weissman BN, et al. ACR appropriateness criteria on suspected osteomyelitis in patients with diabetes mellitus. J Am Coll Radiol. 2008;5:881–886.

Siegelman S, Heimann WG, Manin MC. Congenital indifference to pain. AJR Am J Roentgenol. 1966;97:242. Wagner SC, Schweitzer ME, Morrison WB, et al. Can imaging findings help differentiate spinal neuropathic arthropathy from disk space infection? Initial experience. Radiology. 2000;214:693. Walker EA, Beaman FD, Wessell DE, et al. ACR Appropriateness Criteria Suspected Osteomyelitis of the foot in patients with diabetes mellitus. J American College Radiology. 2019;S440–S550. Westcott MA, Dynes MC, Remer EM, et al. Congenital and acquired orthopedic abnormalities in patients with myelomeningocele. Radiographics. 1992;12:1155.

SECTION 3  Infectious Disorders

19 Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations S U M M A R Y O F K E Y F E AT U R E S • O  steomyelitis can occur via four routes of contamination: hematogenous, spread from a contiguous source, direct implantation, and postoperative. • Imaging features of osteomyelitis are predicted by the route of contamination. • The radiographic and pathologic features of osteomyelitis differ in children, infants, and adults, related in large part to peculiarities of the vascular anatomy of the tubular bones in each age group. • The imaging features of acute osteomyelitis include osteolysis and bone destruction; periostitis is a prominent feature of acute osteomyelitis in children. • Chronic osteomyelitis is characterized by osteosclerosis and periostitis with possible sequestrum and cloaca formation.

• O  n magnetic resonance imaging, high T2 and low T1 marrow signal abnormality is consistent with osteomyelitis. • Infections of the joint and soft tissues can occur via four routes of contamination: hematogenous, spread from a contiguous source, direct implantation, and postoperative. • Uniform joint space narrowing with joint effusion and possible erosions in the correct clinical setting should raise concern for septic arthritis. • Septic arthritis from tuberculosis and fungal disease is characterized by synovial hypertrophy and relatively slower joint destruction. • Computed tomography, ultrasonography, and magnetic resonance imaging are used to diagnose soft tissue infections.

  

INFECTION TERMINOLOGY Osteomyelitis: An infection of bone and marrow. It most commonly results from bacterial infections, although fungi, parasites, and viruses can infect the bone and the marrow. Infective (suppurative) osteitis: Contamination of the bone cortex. Infective osteitis can occur as an isolated phenomenon or, more frequently, as a concomitant to osteomyelitis. Infective (suppurative) periostitis: Contamination of the periosteal cloak that surrounds the bone. In this situation, a subperiosteal accumulation of organisms frequently leads to infective osteitis and osteomyelitis. Sequestrum: A segment of necrotic bone that is separated from living bone by granulation tissue. Sequestra may reside in the marrow for protracted periods, harboring living organisms that have the capability of evoking an acute flareup of the infection. Involucrum: A layer of living bone that has formed about the dead bone. It can surround and eventually merge with the parent bone. Cloaca: An opening in the involucrum through which granulation tissue and sequestra can be discharged. Sinuses: Tracts leading to the skin surface from the bone. Brodie abscess: A bone abscess that is a sharply delineated focus of infection. It is of variable size, can occur at single or multiple locations, and represents a site of active infection. It is lined by granulation tissue and frequently is surrounded by eburnated bone. Garré sclerosing osteomyelitis: A sclerotic, nonpurulent form of osteomyelitis. Although this term is applied carelessly to any form of

osteomyelitis with severe osseous eburnation, it should be reserved for those cases in which intense proliferation of the periosteum leads to bony deposition and in which no necrosis or purulent exudate and little granulation tissue are present. Soft tissue infection: Contamination of cutaneous, subcutaneous, muscular, fascial, tendinous, ligamentous, or bursal structures. This may be seen as an isolated condition or as a complication of periosteal, osseous, marrow, or articular infection. Articular infection: A septic process of the joint itself. Septic arthritis can occur as an isolated condition that may quickly spread to the neighboring bone or as a complication of adjacent osteomyelitis or soft tissue infection.

OSTEOMYELITIS INTRODUCTION The clinical stages of osteomyelitis are frequently designated acute, subacute, and chronic. This does not imply that definitive divisions exist between one stage and another, nor does it signify that all cases of osteomyelitis progress through each of these phases. The relatively abrupt onset of clinical symptoms and signs during the initial stage of infection is a clear indication of the acute osteomyelitic phase; if this acute phase passes without complete elimination of infection, subacute or chronic osteomyelitis can become apparent. The transition from acute to subacute and chronic osteomyelitis may indicate that therapeutic measures have been inadequate.

291

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SECTION 3  Infectious Disorders

ROUTES OF CONTAMINATION Osseous (and articular) structures can be contaminated by four principal routes: 1. Hematogenous spread of infection. Infection can reach the bone (or joint) via the bloodstream. 2. Spread from a contiguous source of infection. Infection can extend into the bone (or joint) from an adjacent contaminated site. Cutaneous, sinus, and dental infections are three important sources of extraskeletal infective foci. 3. Direct implantation. Direct implantation of infectious material into the bone (or joint) may occur after puncture or penetrating injuries. 4. Postoperative infection. Postoperative infection may occur via direct implantation, spread from a contiguous septic focus, or hematogenous contamination of the bone (or joint).

HEMATOGENOUS INFECTION Bacteremia Bacteria usually enter the blood vessels (or the lymphatics and then the blood vessels) by direct extension from extravascular sites of infection, which include the genitourinary, gastrointestinal, biliary, and respiratory systems; the skin and soft tissues; and other structures. In some instances, no primary source of infection is identifiable. Bacteremia is often transient and totally asymptomatic; however, in some cases, prominent clinical manifestations may occur. A single pathogenic organism is usually responsible for hematogenous osteomyelitis. In neonates and infants, Staphylococcus aureus, group B streptococcus, and Escherichia coli are the bone isolates recovered most frequently. In children older than 1 year of age, S. aureus, Streptococcus pyogenes, and Haemophilus influenzae are responsible for most cases of hematogenous osteomyelitis. In those older than 4 years, staphylococci are the major pathogens in this disease as the prevalence of osteomyelitis related to H. influenzae decreases. Gram-­ negative organisms assume importance as pathogens in bone and joint infections in adults and in intravenous drug abusers. A recent surgical procedure or concurrent soft tissue infection is frequently associated with staphylococcal septicemia and osteomyelitis; disorders of the gastrointestinal or genitourinary tract may initiate a gram-­negative septicemia; and an acute or chronic respiratory infection is important in the pathogenesis of tuberculous, fungal, and pneumococcal osteomyelitis. Blood cultures are positive in approximately 50% of patients with acute hematogenous osteomyelitis.

General Clinical Features Childhood osteomyelitis can be associated with a sudden onset of high fever, a toxic state, and local signs of inflammation, although this presentation is not uniform. Indeed, as many as 50% of children have vague complaints, including local pain of 1 to 3 months’ duration, with minimal, if any, temperature elevation. In infants, hematogenous osteomyelitis often leads to less-­dramatic findings, including pain, swelling, and an unwillingness to move the affected bones. The adult form of hematogenous osteomyelitis may have a more insidious onset, with a relatively longer period between the appearance of symptoms and signs and accurate diagnosis. In all age groups, the prior administration of antibiotics for treatment of the febrile state can attenuate or alter the clinical (and imaging) manifestations of the bone infection. Single or multiple bones can be infected; involvement of multiple osseous sites appears to be particularly common in infants. In the younger age group, the long tubular bones of the extremities are especially vulnerable; in adults, hematogenous osteomyelitis is encountered more frequently in the axial skeleton (see Chapter 56).

9

8

5

10

3

4 6

11 12

2

1

7 Fig. 19.1  Normal osseous circulation to a growing tubular bone. Nutrient arteries (1) pierce the diaphyseal cortex and divide into descending and ascending (2) branches. These latter vessels continue to divide, becoming fine channels (3) as they approach the end of the bone. They are joined by metaphyseal vessels (4) and, in the subepiphyseal (growth) plate region, form a series of end-­arterial loops (5). The venous sinuses extend from the metaphyseal region toward the diaphysis, uniting with other venous structures (6) and eventually piercing the cortex as a large venous channel (7). At the ends of the bone, nutrient arteries of the epiphysis (8) branch into finer structures, passing into the subchondral region. At this site, arterial loops (9) are again evident, some of which pierce the subchondral bone plate before turning to enter the venous sinusoid and venous channels of the epiphysis (10). At the bony surface, cortical capillaries (11) form connections with overlying periosteal plexuses (12). Note that in the growing child, distinct epiphyseal and metaphyseal arteries can be distinguished on either side of the cartilaginous growth plate. Anastomoses between these vessels either do not occur or are infrequent.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

Vascular Anatomy The vascular supply of a tubular bone is derived from several points of arterial inflow, which become complicated sinusoidal networks within the bone (Fig. 19.1). One or two diaphyseal nutrient arteries pierce the cortex and divide into ascending and descending branches. As they extend to the ends of the bones, they branch repeatedly, becoming finer channels, and are joined by the terminals of metaphyseal and epiphyseal arteries. The metaphyseal arteries originate from neighboring systemic vessels, whereas the epiphyseal arteries arise from periarticular vascular arcades. The arteries within the bone marrow form a series of cortical branches that connect with the fenestrated capillaries of the haversian systems. At the bony surface, the cortical capillaries form connections with overlying periosteal plexuses, which themselves are derived from the arteries of the neighboring muscles and soft tissues. The cortices of the tubular bones derive nutrition from both the periosteal and the medullary circulatory systems. The central arterioles drain into a thin-­walled venous sinus, which subsequently unites with veins that retrace the course of the nutrient arteries, piercing the cortex at various points and joining larger and larger venous channels. Joints receive blood vessels from periarterial plexuses that pierce the capsule to form a vascular plexus in the deeper part of the synovial membrane. The blood vessels of the synovial membrane terminate at the articular margins as looped anastomoses (circulus articularis vasculosus). The epiphysis and the adjacent synovium share a common blood supply. The radiographic and pathologic features of osteomyelitis differ in children, infants, and adults, related in large part to peculiarities of the vascular anatomy of the tubular bones in each age group (Table 19.1).

Childhood Pattern Between the age of approximately 1 year and the time when the open cartilaginous growth plates fuse, a childhood vascular pattern can be

293

recognized in the ends of the tubular bones (Fig. 19.2A). In the metaphysis, the vessels turn in acute loops to join large sinusoidal veins, which occupy the intramedullary portion of the metaphysis; here, the blood flow is slow and turbulent. The epiphyseal blood supply is distinct from that on the metaphyseal aspect of the plate. This anatomic characteristic explains the peculiar predilection of hematogenous osteomyelitis to affect metaphyses and equivalent locations in children.

Infantile Pattern A fetal vascular arrangement may persist in some tubular bones up to the age of 1 year (see Fig. 19.2B). Some vessels at the surface of the metaphysis penetrate the preexisting growth plate, ramifying in the epiphysis. This arrangement affords a vascular connection between the metaphysis and epiphysis, and explains the frequency of epiphyseal and articular infection in infants.

Adult Pattern With narrowing and closing of the physeal growth plate, metaphyseal vessels progressively reestablish a vascular connection between the metaphysis and the epiphysis (see Fig. 19.2C). Blood within the nutrient vessels can then reach the surface of the epiphysis through large anastomosing channels.

Age-­Related Hematogenous Osteomyelitis Patterns KEY CONCEPTS: Hematogenous Osteomyelitis • S ee Fig. 19.3 and Table 19.2. • In childhood, metaphyseal location is characteristic as the growth plate inhibits spread to the epiphysis. • In infancy, epiphyseal location is characteristic. • In adults, involvement of the spine, pelvis, and small bones is more common than of long bones.

TABLE 19.1  Vascular Patterns of Tubular

Bones Pattern

Age (yr)

Characteristics

Infantile

0–1a

Diaphyseal and metaphyseal vessels may perforate open growth plate.

Childhood

1–16b

Diaphyseal and metaphyseal vessels do not penetrate open growth plate.

Adult

>16

Diaphyseal and metaphyseal vessels penetrate closed growth plate.

aUpper

age limit depends on specific local anatomic variation in the appearance and growth of the ossification center. bUpper age limit is related to the time at which the open growth plate closes.

2 1

B A

C A

B

C

Fig. 19.2  Normal vascular patterns of tubular bone, based on age. (A) In the child, the capillaries of the metaphysis turn sharply, without violating the open growth plate. (B) In the infant, some metaphyseal vessels may penetrate or extend around the open growth plate, ramifying in the epiphysis. (C) In the adult, with closure of the growth plate, a vascular connection between the metaphysis and epiphysis can be recognized.

Fig. 19.3  Sites of hematogenous osteomyelitis of tubular bone, based on age. (A) In the child, a metaphyseal focus is frequent. From this site, cortical penetration can result in a subperiosteal abscess in locations where the growth plate is extraarticular (1) or in a septic joint in locations where the growth plate is intraarticular (2). (B) In the infant, a metaphyseal focus may be complicated by epiphyseal extension, owing to the vascular anatomy in this age group. (C) In the adult, a subchondral focus in an epiphysis is not unusual, owing to the vascular anatomy in this age group.

294

SECTION 3  Infectious Disorders

Childhood In childhood hematogenous osteomyelitis, the metaphyseal location is related to (1) the peculiar anatomy of the vascular tree, (2) the inability of vessels to penetrate the open physeal plate, (3) the slow rate of blood flow in this region, (4) a decrease in phagocytic ability of neighboring macrophages, or (5) secondary thrombosis of the nutrient artery. Primary involvement of an epiphysis or secondary extension across the physis to an epiphysis is encountered rarely. Inflammation in the adjacent bone of the metaphysis is characterized by vascular engorgement, edema, cellular response, and abscess formation. Transudates extend from the marrow to the adjacent cortex. A rise in intramedullary pressure, caused by the presence of inflammatory and edematous tissue confined by the rigid cortical columns of bone,

TABLE 19.2  Hematogenous Osteomyelitis

of Tubular Bones Aspect

Infant

Child

Adult

Localization

Metaphyseal with epiphyseal extension

Metaphyseal

Epiphyseal

Involucrum

Common

Common

Not common

Sequestrum

Common

Common

Not common

Joint involvement

Common

Not common

Common

Soft tissue abscess

Common

Common

Not common

Pathologic fracture

Not common

Not common

Commona

Sinus tracts

Not common

Variable

Common

aIn

neglected cases.

1

A

encourages the extension of infected fluid by way of haversian and Volkmann canals. The inflammatory process soon reaches the outer surface of the cortex and abscesses develop, lifting the periosteum and disrupting the periosteal blood supply to the external cortical surface. Elevation of the periosteum is prominent in the immature skeleton because of its relatively loose attachment to the subjacent bone. The elevated periosteum produces single or multiple layers of bone (i.e., periostitis) and eventually lays down bone in the form of an involucrum. Infection may penetrate the periosteal membrane, producing cloacae (Fig. 19.4). Childhood hematogenous osteomyelitis is not confined to tubular bones. In flat or irregular bones such as the calcaneus, clavicle, and bones of the pelvis, childhood osteomyelitis may show a predilection for metaphyseal-­equivalent osseous locations adjacent to an apophyseal cartilaginous plate and epiphyseal-­equivalent locations adjacent to articular cartilage.

Infancy In infants, because some of the vessels in the metaphysis penetrate the growth plate, a suppurative process of the metaphysis may extend into the epiphysis (Fig. 19.5). Epiphyseal infection can then result in articular contamination and damage to the cells on the epiphyseal side of the growth cartilage, leading to arrest or disorganization of growth and maturation. Articular involvement is also facilitated by the frequent localization of infantile osteomyelitis to the ends of bones in which the growth plate is intraarticular (e.g., hip).

Adulthood Unique manifestations of hematogenous osteomyelitis are seen in adults (see Table 19.2). The disease in the mature skeleton does not

3

B 4

5

Fig. 19.4  Hematogenous osteomyelitis of tubular bone in a child. Sequential steps in the initiation and progression of infection are: 1, a metaphyseal focus is common; 2, the infection spreads laterally, reaching and invading the cortical bone; 3, cortical penetration is associated with subperiosteal extension and elevation of the periosteal membrane; 4, subperiosteal bone formation leads to an involucrum or shell of new bone; 5, the involucrum may become massive, with continued infection. (B) Lytic metaphyseal focus in the femur is readily apparent. It extends to the growth cartilage (causative organism is Staphylococcus).

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

Fig. 19.5  Hematogenous osteomyelitis of tubular bone in an infant. In this infant with acute staphylococcal osteomyelitis, metaphyseal and epiphyseal involvement of the distal end of the femur is associated with periostitis and articular involvement.

commonly localize in the tubular bones; hematogenous osteomyelitis of the spine, pelvis, and small bones is more common in adult patients. In cases in which involvement of tubular bones is evident, the free communication of the metaphyseal and epiphyseal vessels through the closed growth plate allows infection to localize in the subchondral (beneath the articular cartilage) regions of the bone (Fig. 19.6). Joint contamination can complicate this epiphyseal location. The firm attachment of the periosteum to the cortex in adults resists displacement; therefore, subperiosteal abscess formation, extensive periostitis, and involucrum formation are relatively unusual in this age group. Extensive sequestration is not a common feature. In adults, infection violates and disrupts the cortex itself, producing atrophy and osseous weakening, and predisposes the bone to pathologic fracture.

Radiographic and Pathologic Abnormalities Acute Hematogenous Osteomyelitis (Table 19.3)

Radiographic evidence of significant osseous destruction is delayed for a period of days to weeks. Nevertheless, initial and subtle radiographic changes in the soft tissues may appear within 3 days after bacterial contamination of bone, although radiographically evident bone destruction and periostitis can be delayed for 1 to 2 weeks. Eventually, large destructive lesions become evident on the radiograph. In children, these lesions appear as enlarging, poorly defined lucent shadows of the metaphysis, surrounded by varying amounts of eburnation; the lucent lesions extend to the growth plate and, on rare occasions, may violate it. In addition, destruction progresses horizontally, reaching the cortex, and periostitis follows. In infants, the epiphyses are unossified or only partially ossified, making radiographic recognition of epiphyseal destruction extremely difficult. Metaphyseal lucent lesions, periostitis, and joint effusion are helpful radiographic clues. In adults, soft tissue alterations are more difficult to detect on radiographic examination. Epiphyseal

295

Fig. 19.6  Hematogenous osteomyelitis of tubular bone in an adult. Epiphyseal localization is not infrequent in this age group. Observe the lytic lesion (abscess), with surrounding sclerosis extending to the subchondral bone plate (arrows). Metaphyseal and diaphyseal sclerosis is evident. The elongated shape of the lesion is typical of infection (causative organism is Staphylococcus).

(Fig. 19.7), metaphyseal, and diaphyseal osseous destruction creates radiolucent areas of varying size, which are associated with mild periostitis. Cortical resorption can be identified as endosteal scalloping, intracortical lucent regions or tunneling, and poorly defined subperiosteal bony defects. Magnetic resonance (MR) imaging is an excellent method to identify acute osteomyelitis, showing low T1 and high T2 marrow signal abnormality with enhancement, and for the demonstration of soft tissue extension from the affected bone (Fig. 19.8).

Subacute and Chronic Hematogenous Osteomyelitis Brodie abscess. Single or multiple radiolucent abscesses may be evident during subacute or chronic stages of osteomyelitis. These abscesses are now defined as circumscribed lesions showing a predilection for (but not confined to) the ends of tubular bones; they are found characteristically in subacute pyogenic osteomyelitis and are usually of staphylococcal origin. It has been suggested that bone abscesses develop when an infective organism has a reduced virulence or when the host demonstrates increased resistance to infection. Brodie abscesses are especially common in children, more typically in boys. In this age group, they appear in the metaphysis, particularly that of the distal or proximal portion of the tibia. In young children and infants, Brodie abscesses may occur in epiphyses. Radiographs outline radiolucent areas with adjacent sclerosis (Fig. 19.9). This lucent region is commonly located in the metaphysis, where it may connect with the growth plate by a tortuous channel. Radiographic detection of this channel is important; identification of a metaphyseal defect connected to the growth plate by such a tract ensures the diagnosis of osteomyelitis. In the diaphysis, the radiolucent abscess

296

SECTION 3  Infectious Disorders

TABLE 19.3  Hematogenous Osteomyelitis Radiographic-­Pathologic Correlation Pathologic Abnormality

Radiographic Abnormality

Vascular changes and edema of soft tissues

Soft tissue swelling with obliteration of tissue planes

Infection in medullary space with hyperemia, edema, abscess formation, and trabecular destruction

Osteoporosis, bone lysis

Infection in haversian and Volkmann canals of cortex

Increasing lysis, cortical lucency

Subperiosteal abscess formation with lifting of the periosteum and bone formation

Periostitis, involucrum formation

Infectious penetration of periosteum with soft tissue abscess formation

Soft tissue swelling, mass formation, obliteration of tissue planes

Localized cortical and medullary abscesses

Single or multiple radiolucent cortical or medullary lesions with surrounding sclerosis

Deprivation of blood supply to cortex as a result of thrombosis of metaphyseal vessels and interruption of periosteal vessels, cortical necrosis

Sequestration

External migration of dead pieces of cortex, with breakdown of skin and subcutaneous tissue

Sinus tracts

A

FL

B

C

Fig. 19.7  Hematogenous osteomyelitis. In this patient with coccidiodomycosis, an oblique radiograph of the ankle (A) shows osteolysis (arrow) of the talus. Sagittal T1-­weighted (B) and fluid-­sensitive (C) magnetic resonance images reveal involvement of the proximal half of the talus, with the lesion (arrow) involving the subchondral bone. There is a moderate-­sized effusion of the ankle, with synovial proliferation, suggesting that infection, which originated in the bone, has now contaminated the joint.

cavity may be located in central or subcortical areas of the spongiosa or in the cortex itself and may contain a central sequestrum. In an epiphysis, a circular, well-­defined osteolytic lesion is seen, which, in the immature skeleton, may border on the chondro-­osseous junction or on the physis, where it may extend into the metaphysis. When an abscess is located in the cortex, its radiographic appearance, consisting of a lucent lesion with surrounding sclerosis and periostitis, simulates that of an osteoid osteoma or stress fracture. A rounded radiolucent lesion without calcification is characteristic of a cortical abscess; a circular lucent area with or without calcification that is smaller than 2 cm is more typical of an osteoid osteoma; and a linear lucent shadow without calcification is characteristic of a stress fracture. In any skeletal location, computed tomography (CT) scanning or MR imaging can be used to better assess the extent of the abscess and any signs of its reactivation. Sequestration. During the course of hematogenous osteomyelitis, cortical sequestration may become evident (Fig. 19.10). One or more areas of osseous necrosis are commonly situated in the medullary aspect of a tubular bone (sequestration is less prominent in flat bones), where they create radiodense bony spicules. The sequestrum frequently is marginated sharply, surrounded by granulation tissue. Sequestra may extrude through cortical breaks, extending into the adjacent soft

tissues, where they eventually may be discharged through draining sinuses. CT imaging is an ideal method to identify sequestration, especially in the presence of diffuse sclerosis, periostitis, and bone remodeling that are characteristic of chronic osteomyelitis (Fig. 19.11) Sclerosing osteomyelitis. In the subacute and chronic stages of osteomyelitis, considerable periosteal bone formation can surround the altered cortex, and an increased number and size of spongy trabeculae can reappear in the affected marrow, leading to considerable radiodensity and contour irregularity of the affected bone (Fig. 19.12). Cystic changes may occur within the sclerotic area, but sequestra are uncommon. At any site, the radiographic findings of sclerosing osteomyelitis resemble those of osteoid osteoma, fibrous dysplasia, and Ewing sarcoma.

INFECTION FROM A CONTIGUOUS SOURCE General Clinical Features In most cases of osteomyelitis and septic arthritis arising from such a contiguous source, soft tissue infections are implicated. The importance of osteomyelitis of the mandible and maxilla in persons with poor dental hygiene and of the frontal portion of the skull and face in persons with chronic sinusitis is undeniable. Soft tissue infections that

B

A

T

C

D

Fig. 19.8  Hematogenous osteomyelitis. (A) Axial T1-­weighted and (B) fluid-­sensitive MR images show low T1 and high T2 marrow signal intensity within the tibia representing osteomyelitis (arrowhead) with extension into the adjacent soft tissues (arrow). (C) Note corresponding peripheral enhancement on a T1-­weighted fat-­suppressed contrast-­enhanced MR image, indicating an abscess (arrow). (D) Ultrasonography shows a hypoechoic abscess (arrows) extending from the tibia (T) with cortical irregularity (arrowhead).

A

B

Fig. 19.9  Chronic osteomyelitis: Brodie abscess. (A) Lateral radiograph outlines a typical appearance of an abscess of the distal end of the tibia caused by staphylococci. Observe the elongated radiolucent lesion, with surrounding sclerosis extending to the closing growth plate (arrows). The channel-like ­ shape of the lesion is important in the accurate diagnosis of this condition. (B) In a second patient, a 19-year-old ­ ­ woman, a routine radiograph shows a metaphyseal radiolucent lesion (arrow) with a medial channel (arrowheads). (B, Courtesy M. Mitchell, MD, Halifax, Nova Scotia, Canada.)

298

SECTION 3  Infectious Disorders

B

C

A

D

Fig. 19.10  Chronic osteomyelitis: sequestration. (A) Frontal radiograph of the femoral shaft shows sclerosis and diffuse periostitis (arrows). (B)–(C), Axial CT images allow identification of sequestered bone (arrowhead), also showing periostitis (straight arrows) and soft tissue gas (curved arrow). (D) Delayed bone scan image shows diffuse femoral uptake (arrow).

A

B

C

D

E

F

Fig. 19.11  Chronic osteomyelitis: sequestration. (A) Lateral radiograph of the femur shows linear sclerotic sequestration (arrowheads). (B) Sagittal short-tau ­ inversion recovery and axial (C) T1-weighted, ­ (D) fluid-­ sensitive, and (E) T1-weighted ­ fat-suppressed ­ contrast-enhanced ­ MR images show low signal sequestration (arrowhead) surrounded by abnormal marrow signal. Note periostitis (arrow) with surrounding soft tissue edema. (F) Axial CT image shows several foci of sequestered bone (arrowhead) and periostitis (arrow).

299

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

A

C

B

Fig. 19.12  Chronic sclerosing osteomyelitis. (A) Chronic osteomyelitis can be associated with considerable new bone formation. Axial (B) T1-­weighted and C, fluid-sensitive MR images show sequestered bone (arrowheads) and a soft tissue abscess (arrow).

lead to bone and joint contamination are frequent after trauma, animal and human bites, puncture wounds, irradiation, burns, and decubitus or pressure ulcers in paralyzed or immobilized patients.

General Radiographic and Pathologic Features Whereas the direction of contamination in hematogenous osteomyelitis is from the bone outward into the soft tissue, the direction of contamination in osteomyelitis resulting from adjacent sepsis is from the soft tissues inward into the bone (or joint) (Table 19.4 and Fig. 19.13). Periosteal bone formation is commonly the initial radiographic manifestation of osteomyelitis in skeletally immature patients in whom the periosteum is loosely adherent to the bone cortex. After traumatic initiation of soft tissue infection, periostitis may appear early in response to injury and may not reflect actual bone infection. With further accumulation of pus, subperiosteal resorption of bone and cortical disruption ensue. As infection gains access to the spongiosa, it may spread in the marrow, producing lytic osseous defects on the radiograph.

TABLE 19.4  Osteomyelitis Resulting From

Spread From a Contiguous Source of Infection Radiographic-­Pathologic Correlation Pathologic Abnormality

Radiographic Abnormality

Soft tissue contamination and abscess formation

Soft tissue swelling, mass formation, obliteration of tissue planes

Infectious invasion of the periosteum Periostitis with lifting of the membrane and bone formation Subperiosteal abscess formation and Cortical erosion cortical invasion Infection in haversian and Volkmann canals of cortex

Cortical lucency and destruction

Contamination and spread in marrow Bone lysis

Specific Locations Hand. Three distinct routes are available to organisms that become lodged in the soft tissues of the hand; infection may disseminate via tendon sheaths, fascial planes, or lymphatics (Fig. 19.14). Infective digital tenosynovitis can result from a puncture wound, particularly in a flexor crease of the finger, where skin and sheath are intimately related. A sheath infection may perforate into an adjacent bone or joint in the finger; the most characteristic site of such extension is the proximal interphalangeal articulation and adjacent middle phalanx (Fig. 19.15). The metacarpophalangeal joints are altered less commonly. Such tenosynovitis causes exquisite tenderness over the course of the sheath, a semiflexed position of the finger, severe pain on extension of the finger, and fusiform swelling of the digit. Infections in the fascial planes of the hand are numerous but result in joint or bone alterations less frequently than do those in the synovial sheaths. Lymphangitis may result from superficial injuries. In intense cases, complications may include tenosynovitis, septicemia, osteomyelitis, and septic arthritis. A felon results from infection in the terminal pulp space. Bone involvement is not infrequent in neglected cases because of the close proximity of the terminal phalanx (Fig. 19.16). Subcuticular abscesses of the nail fold are termed paronychia. Foot. The plantar aspect of the foot is especially vulnerable to soft tissue infection. Foreign bodies, puncture wounds, or skin ulceration from weight bearing can represent the portal of entry for various organisms. In a diabetic patient, soft tissue breakdown over certain

1

2

3

Fig. 19.13  Diagrammatic representation of the sequential steps of osteomyelitis resulting from a contiguous contaminated source. 1, Initially, a soft tissue focus of infection is apparent. Occasionally, such a focus can irritate the underlying bone, producing periostitis without definite invasion of the cortex. 2, The infection subsequently invades the cortex, spreading via haversian and Volkmann canals. 3, Finally, the medullary bone and marrow spaces are affected.

pressure points (e.g., metatarsal heads, calcaneus) leads to infection that is combined with vascular and neurologic abnormalities. The clinical, radiographic, and pathologic characteristics of osteomyelitis (and septic arthritis) complicating foot infections in diabetic patients are modified by the associated problems of these persons, including vascular insufficiency and neurologic deficit. An early radiographic finding, characteristically adjacent to a soft tissue ulceration, is focal osteopenia with thinning or discontinuity of the bone cortex

300

SECTION 3  Infectious Disorders Intermediate bursa Radial bursa

Ulna bursa

Midpalmar space Thenar space

Midpalmar space Sheath

Tendons

Thenar space

B

Tendon sheath Fig. 19.14  Spread of infection in the hand: available anatomic pathways. (A) Drawing demonstrates the relationships of the tendon sheaths, bursae, and fascial planes (thenar space, midpalmar space). (B) Drawing of a section through the metacarpal bones outlines two spaces—the midpalmar and thenar spaces—separated by a septum and located above the digital flexor tendon sheaths. Note the close relationship between the sheath of the index finger and the thenar space and between the sheaths of the third, fourth, and fifth fingers and the midpalmar space. (From Resnick D. Osteomyelitis and septic arthritis complicating hand injuries and infections: pathogenesis of roentgenographic abnormalities. J Can Assoc Radiol. 27:21, 1976.)

A

Fig. 19.15  Spread of infection in the hand: digital flexor tenosynovitis. After a neglected puncture wound, a 45-­year-­old woman developed tenosynovitis and osteomyelitis. Note the soft tissue swelling, particularly along the volar surface of the proximal phalanx (open arrow); the semiflexed position of the finger; and extensive permeative osseous destruction, with a pathologic fracture (solid arrow) of the proximal phalanx. (From Resnick D. Osteomyelitis and septic arthritis complicating hand injuries and infections: pathogenesis of roentgenographic abnormalities. J Can Assoc Radiol. 27:21, 1976.)

(Fig. 19.17). Gas within the ulcer also may be evident. The radiographic picture subsequently reveals mottled osteolysis (Fig. 19.18). Septic arthritis may coexist, with later stages of osteomyelitis showing sclerosis and periostitis (Fig. 19.19). MR imaging is a useful imaging method to allow diagnosis of acute osteomyelitis before radiographic findings are apparent. Characteristic features of acute osteomyelitis with MR imaging include low T1-­weighted signal and high T2-­weighted signal within the marrow adjacent to the soft tissue ulcer with enhancement after intravenous gadolinium adminstration (see Figs. 19.17 and

Fig. 19.16  Spread of infection in the hand: felon. An infection in the pulp space has produced considerable soft tissue swelling (open arrows). Extension into the tuft and diaphysis of the terminal phalanx is apparent (solid arrows). Shrapnel from a previous injury can be seen. (From Resnick D. Osteomyelitis and septic arthritis complicating hand injuries and infections: pathogenesis of roentgenographic abnormalities. J Can Assoc Radiol. 27:21, 1976.)

19.18). Cortical destruction also may be seen, although such findings are often best displayed with radiography and CT imaging. In some diabetic patients, the imaging findings of osteomyelitis can simulate those of diabetic neuropathic osteoarthropathy, with both showing low T1-­weighted and high T2-­weighted marrow signal and enhancement. The key features that allow differentiation between neurologic and infectious processes on MR imaging include the characteristic midfoot location of neuropathic osteoarthropathy and lack of soft tissue ulceration (Fig. 19.20). A finding that suggests osteomyelitis superimposed on neuropathic osteoarthropathy is a positive ghost sign, when the non-­visible bone cortex on T1-­weighted images

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

301

C

B

A

D

Fig. 19.17  Osteomyelitis from contiguous source: foot. (A) Radiograph shows thinning of the subchondral bone plate along the plantar surface of the fifth metatarsal head (arrowhead) when compared with the prior radiograph (B). Note gas within a soft tissue ulcer (arrow) that can simulate a gas-­filled abscess. (C) T1-­ weighted and (D) fluid-­sensitive short axis MR images show concordant low T1 and high T2 marrow signal abnormality in the metatarsal head (arrowhead) immediately dorsal to the gas-­filled soft tissue ulcer (arrow) with surrounding soft tissue inflammation.

A

B

C

D

Fig. 19.18  Osteomyelitis from contiguous source: foot. (A) Radiograph shows bone erosion and mottled osteolysis of the fifth metatarsal head and neck (arrowheads) adjacent to a granulation-­filled soft tissue ulcer (arrow). (B) T1-­weighted, (C) fluid-­sensitive, and (D) T1-­weighted fat-­suppressed contrast-­enhanced long axis MR images show concordant low T1 and high T2 marrow signal abnormality and enhancement of the metatarsal and proximal phalanx (arrowheads) consistent with osteomyelitis and septic arthritis with surrounding soft tissue inflammation.

becomes visible or reappears after the administration of intravenous gadolinium or on fluid-­sensitive MR sequences. Pelvis. Soft tissue breakdown that occurs in debilitated persons who maintain a single position for long periods is referred to as a pressure sore, decubitus ulcer, or bedsore. Although other sites (e.g., heels) may be affected, most pressure sores develop about the pelvis, especially near the sacrum, ischial tuberosities, trochanteric regions, and buttocks. Local soft tissue infection and bacteremia are commonly associated with decubitus ulcers. Osteomyelitis is observed most

commonly in the innominate bones and proximal portions of the femora, areas subjacent to sites of skin breakdown, related to spread from a contiguous contaminated source (Fig. 19.21). The accurate diagnosis of osteomyelitis complicating pressure sores is difficult, owing to a number of other conditions that may become evident in immobilized or paralyzed patients. Pressure-­related changes in bone are not infrequent, leading to flattening and sclerosis of bony prominences such as the femoral trochanters and ischial tuberosities. Heterotopic ossification, a well-­recognized accompaniment of neurologic

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SECTION 3  Infectious Disorders

A

B

Fig. 19.19  Osteomyelitis and septic arthritis from contiguous source: foot. (A) Initial radiograph shows gas within a soft tissue ulcer (arrow) simulating an abscess. (B) Subsequent radiograph several weeks later shows cortical erosion and osteolysis (arrowheads) about the fourth metatarsophalangeal joint representing osteomyelitis and septic arthritis with extensive periostitis (curved arrow).

injury, further complicates the early diagnosis of osteomyelitis. Routine radiography is reported to be insensitive and nonspecific in the diagnosis of bone infection in patients with pressure sores, related in part to the difficulty of differentiating changes caused by abnormal pressure from those of osteomyelitis. CT image interpretation proves difficult because bone sclerosis and remodeling may simulate chronic osteomyelitis. MR imaging can be useful to show marrow signal abnormality consistent with osteomyelitis, although identification of the sinus tract extending to the abnormal bone (see Fig. 19.21C), best visualized after intravenous gadolinium administration, adds specificity to the diagnosis.

DIRECT IMPLANTATION OF INFECTION General Clinical Features Puncture wounds of the hand and foot can lead to osteomyelitis (and septic arthritis) by contamination of adjacent soft tissues or direct inoculation of the bone or joint. This latter complication is especially prevalent in the foot, where nails, splinters, or glass can lead to deep puncture wounds; in the hand, where a human bite received during a fistfight can directly injure osseous and articular structures; and in any site after an animal bite.

General Radiographic Features The features of bone (and joint) involvement after direct implantation of an infectious process are virtually identical to those occurring after spread of infection from a contiguous contaminated source. Commonly, osseous destruction and proliferation lead to focal areas of lysis, sclerosis, and periostitis. Soft tissue swelling is common, related not to infection but to edema resulting from the injury itself.

Human Bites The most common cause of human bite injury is a fist blow to the mouth that results in laceration of the dorsum of the metacarpophalangeal joint. Joint infection is more common than bone infection in these cases. S. aureus or Streptococcus species are the usual implicated organisms. The radiographic findings, which are particularly well shown on steep oblique and lateral radiographs, include peculiar bony defects and fractures, tooth fragments, and osseous and articular destruction (Fig. 19.22).

Animal Bites Superficial animal bites or scratches can inoculate local soft tissues, leading to infection of underlying bones and joints. Deep animal bites can introduce organisms directly into osseous and articular structures. Dog bites account for approximately 90% of these injuries and cat bites for about 10%. Approximately 5% of dog bites and 20% to 50% of cat bites become infected significantly. The infecting organisms vary, but Pasteurella multocida is commonly implicated, especially in cat bites. Any anatomic site can be affected, although animal bites are seen predominantly in the hand, arm, and leg (Fig. 19.23).

Open Fractures and Dislocations Whenever a fracture or dislocation is complicated by disruption of the overlying skin, direct inoculation of bones and joints can occur. This problem is especially relevant to injuries of the tibia. Despite the early administration of antibiotics, chronic osteomyelitis is frequent in this setting.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

A

B

C

D

303

E

Fig. 19.20  Neuropathic osteoarthropathy: diabetes mellitus. (A) and (B) Radiographs show sclerosis, fragmentation, and subluxation at the midfoot (arrows). Long axis (C) T1-­weighted and (D) fluid-­sensitive MR images show significant marrow replacement, with low T1 and high T2 signal abnormalities (arrows). (E) Long axis T1-­weighted fat-­supressed contrast-­enhanced MR image shows a peripheral enhancing joint effusion (curved arrow). The absence of a soft tissue ulcer and the characteristic midfoot location favor the diagnosis of neuropathic osteoarthropathy over infection. Furthermore, in (C), the outline, or surface, of the involved tarsal bones is still visible; in cases of osteomyelitis, this outline is often lost, a finding known as the “ghost sign.”

POSTOPERATIVE INFECTION Postoperative infections occur as a result of contamination of bones and joints from adjacent infected soft tissues, direct inoculation of osseous and articular tissue at the time of surgery, or, less frequently, hematogenous spread to an operative site from a distant location. Particularly troublesome are instances of infection that occur after internal fixation of fractures, intervertebral disc surgery, median sternotomy, and various types of reconstructive procedures and arthroplasty. One

or more organisms may be implicated; S. aureus is the most common pathogen. One special type of postoperative infection relates to the transcutaneous insertion of pins into bone. The causative organisms vary, but infections caused by gram-­n egative bacteria are common. The mechanisms of contamination are also variable; in some cases, the pins are inserted into bones that are already the site of osteomyelitis, whereas in others, osseous infection occurs at the time of or after pin insertion. Radiographs reveal progressive osteolysis

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SECTION 3  Infectious Disorders

A

B Fig. 19.22  Infection due to direct implantation: human bites. Destruction of the third metacarpal head (solid arrow) and a narrowed metacarpophalangeal joint (open arrow) resulted from infection after a fistfight in which the patient’s fist struck the opponent’s teeth. (From Resnick D. Osteomyelitis and septic arthritis complicating hand injuries and infections: pathogenesis of roentgenographic abnormalities. J Can Assoc Radiol. 27:21, 1976.)

Epiphyseal Growth Disturbance

C Fig. 19.21  Osteomyelitis from contiguous source: pelvis. (A) T1-­ weighted, (B) fluid-­ sensitive, and (C) T1-­ weighted fat-­ suppressed contrast-­enhanced axial MR images show concordant low T1 and high T2 marrow signal abnormality and enhancement of the proximal femur, indicative of osteomyelitis (arrowhead). Note the sinus tract extending from the soft tissue ulcer to the femur demonstrated on the postcontrast image (arrows).

about the metal or, after removal of the pin, a ring sequestrum (Fig. 19.24). In the latter instance, the central circular radiolucent area created by the pin itself is surrounded by a ring of bone which, in turn, is surrounded by an area of osteolysis.

COMPLICATIONS Severe Osteolysis If osteomyelitis is not treated adequately or early enough, severe osteolysis may ensue. Large foci of destruction eventually can lead to disappearance of long segments of tubular or flat bones.

Injury to the cartilage cells on the epiphyseal side of the growth plate is irreparable, and subsequent growth disturbances are to be expected. Even with severe epiphyseal disintegration, however, some regeneration of the epiphysis can occur after eradication of the infection, although it is difficult to predict the occurrence and extent of epiphyseal recovery after injury.

Neoplasm Epidermoid carcinoma arising in a focus of chronic osteomyelitis is not uncommon. The latent period between the onset of osteomyelitis and the appearance of neoplasm is variable, although a time span of 20 to 30 years is typical. Neoplasm most frequently arises adjacent to the femur and the tibia and is clinically evident as pain, increasing drainage, hemorrhage, onset of a foul odor from the sinus tract, a mass, and lymphadenopathy. Radiographically, there is progressive destruction of bone (Fig. 19.25). The prognosis is guarded.

Amyloidosis Secondary amyloidosis can complicate chronic osteomyelitis. This complication has become less frequent, however, owing to improvement in the chemotherapy of infection. It is seen in less than 5% of cases of chronic osteomyelitis.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

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DIFFERENTIAL DIAGNOSIS The combination of clinical and imaging characteristics in osteomyelitis usually ensures the correct diagnosis. Occasionally, aggressive bone destruction combined with periostitis and soft tissue swelling simulates the changes in malignant neoplasms, especially Ewing sarcoma or osteosarcoma in children, histiocytic lymphoma in young adults, and skeletal metastasis in older persons. The imaging features of osteomyelitis may resemble those of bone infarction, especially in the diaphysis of a long bone. Further, patients who have sickle cell anemia or Gaucher disease, and those who have lymphoproliferative disorders or are receiving steroid medications, are predisposed to the development of osteomyelitis, osteonecrosis, or both, compounding the diagnostic difficulty.

SPECIFIC SITUATIONS Chronic Granulomatous Disease This heterogeneous disorder is a hereditary condition, usually transmitted as an X-­linked recessive trait that occurs in male children, although a similar syndrome has been identified in female and male children without a family history of disease. The syndrome is characterized by purulent granulomatous and eczematoid skin lesions, granulomatous

A

B

Fig. 19.23  Infection due to direct implantation: animal bites. (A) After a cat bite, this patient developed Pasteurella osteomyelitis and septic arthritis. Observe soft tissue swelling, osseous destruction of the proximal and middle phalanges, and joint space narrowing and flexion at the proximal interphalangeal joint. (B) In a different patient who developed Pasteurella osteomyelitis and septic arthritis after a cat bite, a coronal T1-­weighted MR image obtained with fat suppression and intravenous gadolinium enhancement shows high signal intensity in the third metacarpophalangeal joint and adjacent bone and soft tissue.

A

Fig. 19.24  Postoperative infection: pinhole ring sequestrum. Percutaneous pins were used to treat a fracture about the wrist in this 27-­year-­old man. Purulent drainage occurred, requiring removal of the pins. Note the classic radiographic findings of a ring sequestrum (arrow).

B

Fig. 19.25  Complications of osteomyelitis: neoplasm. This 69-­year-­old man developed a squamous cell carcinoma of a sinus tract after years of osteomyelitis of the tibia with drainage. (A) Lateral radiograph shows osteolysis of the tibia, which was related to tumorous involvement of the bone. A soft tissue mass at this site cannot be seen in this image. The soft tissue mass and involved bone were excised. (B) In the immediate postoperative period, a sagittal fat-­suppressed, T1-­weighted MR image obtained after intravenous gadolinium contrast agent administration shows edema of high signal intensity in the tibia, presumably related to the surgery, although the presence of residual intraosseous tumor could not be excluded.

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SECTION 3  Infectious Disorders

lymphadenitis with suppuration, hepatosplenomegaly, recurrent and persistent pneumonias, and chronic osteomyelitis (25% to 35%). It is frequently fatal (40%), and death before adolescence is common. Virtually every organ or tissue is vulnerable to infection in this disorder. Histologically, granulomas composed primarily of plasma cells, lymphocytes, macrophages, and multinucleated giant cells, with or without central caseation, are seen. A defect has been noted in the ability of the polymorphonuclear leukocytes and monocytes to destroy certain pathogenetic organisms adequately. Certain clinical and radiographic peculiarities characterize the osteomyelitis of chronic granulomatous disease of childhood: 1. The disease lacks the usual early clinical signs and symptoms of osteomyelitis, so that initial radiographs frequently reveal considerable bony involvement. 2. The causative organisms are usually of low virulence. 3. The most frequent site of involvement is the small bones of the hands and feet. 4. Osteomyelitis may result from contamination related to an adjacent focus of infection, especially in the thoracic region, or from hematogenous dissemination. 5. The radiographic abnormalities are characterized by extensive osseous destruction with minimal reactive sclerosis. 6. Osteomyelitis may develop in new areas despite continuous therapy. 7. Osteomyelitis eventually responds to long-­term antibiotic therapy, so operative intervention is seldom necessary.

Chronic Recurrent Multifocal Osteomyelitis Chronic recurrent multifocal osteomyelitis (CRMO), which is also discussed as part of the SAPHO (synovitis, acne, pustulosis, hyperostosis,

osteitis) syndrome in Chapter 44, is a variety of subacute and chronic osteomyelitis of unknown cause that occurs in childhood and frequently causes multiple and symmetric alterations (Fig. 19.26). It also has been referred to as condensing osteitis of the clavicle in childhood, chronic symmetric plasma cell osteomyelitis, chronic sclerosing osteomyelitis, and multifocal chronic osteomyelitis. The usual age of onset of the disease is 5 to 10 years, although infants and adults may be affected. Skin lesions, including pustulosis palmaris et plantaris, acne fulminans, and psoriasis, are observed in some patients. CRMO also has been associated with Wegener granulomatosis, inflammatory bowel disease, and leukemia. The metaphyses of the bones of the lower extremity and the medial ends of the clavicles are particularly vulnerable. Osteolysis with intense sclerosis may be noted. In certain locations, such as the clavicle, the bone may become massive (Fig. 19.27). The dominant radiographic feature at any skeletal site is bone sclerosis. This feature is similar or identical to that described in cases of Garré sclerosing osteomyelitis. Both bone scintigraphy and MR imaging can be used to detect skeletal lesions in CRMO. With the former method, diagnostic difficulty is sometimes encountered owing to the normal uptake of radionuclide in the metaphyseal region of tubular bones. With MR imaging, low signal intensity in affected regions is seen on T1-­weighted images, and variable signal intensity is noted on T2-­weighted images. Laboratory analysis is usually nonspecific, and cultures of blood or bone after biopsy may be nonrewarding. Although the long-­term prognosis is good, the condition may run a protracted course with resultant skeletal deformities. Of considerable interest, the selective hyperostosis of the clavicle in this condition also may be seen in two other disorders. Osteitis condensans (condensing osteitis) of the medial end of the bone has been reported, especially in young women (see Chapter 34).

D

A

B

C

E

F

Fig. 19.26  Chronic recurrent multifocal osteomyelitis. (A) Radiograph of the tibia shows a lytic region with periostitis (arrow). Coronal (B) T1-weighted ­ and (C) fluid-sensitive ­ MR images show low T1 and high T2 marrow signal abnormality with periostitis and surrounding soft tissue changes (arrow). (D) Sagittal reformatted CT image redemonstrates the radiographic findings (arrow) with similar findings of the involved rib (arrowhead) on the axial CT image (E), associated with uptake in both the rib and tibia on bone scan imaging (arrow, arrowhead) (F).

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

Fig. 19.27  Chronic recurrent multifocal osteomyelitis: clavicle. Note massive enlargement of the clavicle. Biopsy and histologic evaluation indicated only chronic osteitis. Cultures were negative. (Courtesy G. Greenway, MD, Dallas, TX.)

Sternocostoclavicular hyperostosis of unknown cause, with painful swelling of the sternum, clavicles, and upper ribs, also has been described. Men and women are both affected, and the usual age at onset is in the fifth or sixth decade of life. Sternocostoclavicular hyperostosis is discussed further in Chapter 44. The relationship of CRMO to these other conditions is not clear, although the common involvement of the clavicle, as well as several other features, suggests an association.

OTHER DIAGNOSTIC TECHNIQUES CT The primary applications of CT to the evaluation of musculoskeletal infections are the delineation of the osseous and soft tissue extent of the disease process, especially in areas of complex anatomy such as the vertebral column, and the monitoring of percutaneous aspiration and biopsy procedures, particularly of the spine, retroperitoneal tissues, and sacroiliac joints. CT imaging is an ideal method in the setting of subacute or chronic osteomyelitis to evaluate for cortical sequestration, cloacae, and bone and soft tissue abscesses (see Figs. 19.10 and 19.11).

Sinography Retrograde injection of contrast material defines the course and extent of the sinus tract and its possible communication with an underlying bone or joint. Sinography may be combined with CT scanning or MR imaging for better delineation of the sinus tracts.

Ultrasonography Although evaluation for osteomyelitis with ultrasonography (US) is somewhat limited given the inability to image tissues inside an intact bone cortex and incomplete evaluation of cortical surfaces, a number of findings may suggest osteomyelitis. For example, cortical irregularity, although not specific for one diagnosis, could indicate infection in the correct clinical setting, especially if an adjacent infectious process is applied to the surface of the bone. Soft tissue infection may be identified with US as a complication of osteomyelitis (see Fig. 19.8D). In children in whom the periosteum is loosely adherent to the bone cortex, periostitis and subperiosteal abscess can be visualized with US. Radiographic and often CT or MR imaging correlation is typically required.

Radionuclide Examination Technetium phosphate bone scans become abnormal within hours to days after the onset of bone infection and days to weeks before the disease becomes manifest on conventional radiographs. The scintigraphic abnormality initially may be evident as a photodeficient area (cold spot), a finding that is related to fulminant infection with thrombosis or vascular compression; within a few days, however, increased accumulation of the radioisotope (hot spot) is typical (see Fig. 19.10D). The

307

addition of CT to routine single-­photon emission computed tomography (SPECT), or SPECT/CT, further assists in localizing the radionuclide uptake to bone to improve accuracy (Fig. 19.28). The bone scan also can be used to monitor the disease course and response to treatment, although several weeks may be required before the scan returns to normal, and the correlation between clinical and scintigraphic improvement is not uniformly good. Occasional difficulty in interpreting the bone scan in younger patients arises from an inability to differentiate between normal and abnormal activity in the metaphyseal region. A gallium scan can be performed in conjunction with a technetium scan in the same patient, and the resulting information may be more useful than that obtained by either examination alone (Table 19.5). Gallium scans may reveal abnormal accumulation in patients with active osteomyelitis when technetium scans reveal decreased activity (cold lesions) or perhaps normal activity (transition period between cold and hot lesions). It should be remembered that gallium is a bone-­scanning agent that accumulates in regions of increased bone remodeling, such as occurs in osteomyelitis. Therefore, its accumulation in osseous sites that are also positive on technetium phosphate scans is not unexpected, and such accumulation by itself does not increase the specificity of the radionuclide examination. Rather, when both technetium phosphate and gallium scanning are used, it is important to compare the degree and extent of radionuclide uptake on the two examinations. Disparate distribution of uptake or increased intensity of uptake on the gallium study is an important sign of osteomyelitis. Such infection is unlikely when both technetium phosphate and gallium scanning are negative, or when the distribution of both tracers is spatially congruent and the relative intensity of gallium uptake is less than that of the bone tracer. Although a negative delayed bone image appears to be specific in excluding infection, a positive finding during the delayed static phase of the examination lacks specificity for infection and has stimulated considerable interest in three-­phase examinations in patients with musculoskeletal infection. This encompasses serial images obtained during the first minute after a bolus injection of a technetium compound (angiographic phase), a postinjection image obtained at the end of the first minute or after several minutes (blood pool phase), and additional images obtained 2 or 3 hours later (delayed phase). If increased accumulation of radionuclide within bone is observed in all three phases, the diagnosis of osteomyelitis is highly likely. Conversely, if such an increase is present only on the delayed image, an alternative diagnosis should be considered. The addition of a fourth phase to the scintigraphic examination, representing a static image obtained 24 hours after injection of the bone-­seeking radiopharmaceutical agent, shows continued accumulation of the technetium phosphate radionuclide in the abnormal woven bone about foci of infection. The accumulation of leukocytes at sites of abscess formation has led to the use of indium-­labeled autologous leukocytes for the evaluation of inflammatory processes. In general, indium-­111–labeled leukocyte scintigraphy is less sensitive in detecting bone infections than soft tissue infections and leads to difficulty in differentiating osteomyelitis and septic arthritis. It can demonstrate soft tissue extension from an area of bone infection. Positive leukocyte images are encountered in musculoskeletal conditions other than infection. Rheumatoid arthritis and other synovial inflammatory disorders can lead to findings simulating those of septic arthritis, and primary or secondary tumors in the soft tissue or bone can produce positive leukocyte images similar to those accompanying infection. Compared with bone imaging with technetium-­99m compounds, 111In scintigraphy has increased sensitivity in the detection of early osteomyelitis. The routine use of fluorodeoxyglucose positron emission tomography (FDG-­PET) in evaluation for osteomyelitis is limited due to cost; however, its use has been shown to be effective in evaluating fever of

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SECTION 3  Infectious Disorders

RMED LLAT

A

B

Fig. 19.28  Osteomyelitis: bone scan and SPECT/CT. Note the uptake in the second metatarsal on the delayed bone scan (A) and SPECT/CT image (B) (arrow). LLAT, Left lateral; RMED, right medial.

TABLE 19.5  Radionuclide Evaluation of Osseous and Soft Tissue Infection Agent

Cellulitis

Acute Osteomyelitis

Chronic Osteomyelitis

Technetium phosphates

Early scans show increased uptake; later scans are normal.

Early and late scans show increased uptake (scans in early acute osteomyelitis may reveal cold spots).

Scans may remain positive, even in inactive disease.

Gallium

Increased uptake

Increased uptake

Increased uptake in areas of active disease

unknown orgin. When combined with CT scanning, FDG-­PET integrates anatomic and functional imaging, with results showing higher sensitivity and equal specificity when compared with to labeled white blood cell imaging in the diagnosis of osteomyelitis.

MR Imaging KEY CONCEPTS  • M  R imaging findings of confluent low T1-­weighted marrow signal abnormality concordant with high T2-­weighted fat saturation or short-­tau inversion recovery signal and enhancement are consistent with osteomyelitis. • In the diabetic foot, the absence of a soft tissue ulcer makes osteomyelitis unlikely in the absence of penetrating injury or surgery. • Although marrow signal abnormality in neuropathic osteoarthropathy can appear similar to that in osteomyelitis, midfoot location and lack of soft tissue ulceration make osteomyelitis unlikely. • Intravenous gadolinium is used to document an abscess and assist in identifying a sinus tract.

MR imaging has been advocated as an ideal imaging method to evaluate for osteomyelitis with good sensitivity (80% to 90%) and fair specificity (70% to 80%), typically outperforming tagged white blood cell scan (fair sensitivity and specificity) and bone scan (good sensitivity but poor specificity). The diagnosis of acute osteomyelitis relies on abnormal marrow signal on MR imaging, typically appearing as an area of low signal intensity on T1-­weighted MR images and high signal intensity on fluid-­sensitive images (Fig. 19.29). Increased marrow signal on short tau inversion recovery (STIR) imaging is typically present with osteomyelitis, with a high sensitivity and high negative predictive value; the absence of this finding makes osteomyelitis unlikely. If increased signal is present on fluid-­sensitive

sequences, low signal on T1-­weighted MR images adds specificity; mild increased T2-­weighted marrow signal with normal T1-­weighted signal could represent reactive edema and is not diagnostic for acute osteomyelitis. The presence of decreased T1-­weighted marrow signal in a geographic and confluent medullary distribution with concordant signal abnormality on fat-­suppressed T2-­weighted and postcontrast MR imaging is indicative of osteomyelitis. Other MR imaging abnormalities in either acute or chronic osteomyelitis include cortical erosion or perforation; periosteal bone formation; soft tissue involvement; and, in chronic osteomyelitis, abscesses, bone sequestration, and sinus tracts. The use of intravenous gadolinium is not required for the diagnosis of osteomyelitis, but, indeed, its use adds value in the delineation of abscesses and sinus tracts (see Fig. 19.21) After intravenous administration of a gadolinium contrast agent, areas of vascularized inflammatory tissue reveal enhancement of signal intensity, but nonvascularized abscess collections show either no enhancement or enhancement at the margin of the lesion. Brodie abscesses (Fig. 19.30) typically appear as well-­defined intraosseous regions of low signal intensity on T1-­weighted spin echo MR images (with a rim of intermediate signal intensity related to a layer of highly vascularized granulation tissue, termed the penumbra sign, surrounded by a variable amount of low signal intensity related to marrow edema) and as areas of high signal intensity on fluid-sensitive MR images (with a rim of low signal intensity due to sclerotic bone surrounded by a variable amount of high signal intensity related to marrow edema); they may be better delineated with gadolinium-­enhanced MR imaging. Sequestra, although better seen on CT scans, appear as regions of low to intermediate signal intensity on both T1-­and T2-­weighted images, and do not show enhancement of signal intensity after intravenous administration of a gadolinium-­based contrast agent.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

A

B

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C

Fig. 19.29  Diabetic foot infection: MR imaging. This 63-­year-­old man required amputation of the third toe at the level of the metatarsophalangeal joint for control of infection. He later developed clinical manifestations of recurrent infection. (A) Long axis T1-­weighted MR image shows abnormally low signal intensity in the third and fourth metatarsal bones (arrows) and in the adjacent soft tissues. The head of the second metatarsal bone also appears to be involved. (B) Long axis STIR MR image reveals high signal intensity in these metatarsal bones (arrows) and soft tissues. (C) Long axis T1-­weighted fat-­suppressed image obtained in conjunction with intravenous administration of a gadolinium contrast agent provides information similar to that in (B). A third and fourth ray resection confirmed the presence of osteomyelitis.

Although numerous reviews have emphasized the sensitivity of MR imaging in the diagnosis of musculoskeletal infections, it is this very sensitivity that can lead to diagnostic problems, particularly in defining the extent of the process. Several specific problem areas can be defined: 1. In acute osteomyelitis, differentiating soft tissue extension of infection from soft tissue edema or differentiating osteomyelitis from surrounding intraosseous reactive edema. 2. In septic arthritis, differentiating secondary osteomyelitis from bone marrow edema or in acute osteomyelitis affecting epiphyses, differentiating secondary septic arthritis from sympathetic effusions. 3. In chronic osteomyelitis, differentiating active and inactive disease. 4. In soft tissue infections, differentiating infective periostitis, osteitis, or osteomyelitis from bone marrow edema.

DIABETIC FOOT ASSESSMENT

Fig. 19.30  Brodie abscess: MR imaging. In a sagittal T1-­weighted MR image, the wall of the abscess in the distal metaphysis of the tibia has intermediate signal intensity (arrow), the penumbra sign. Note surrounding marrow edema of low signal intensity. (Courtesy D. Goodwin, MD, Hanover, NH.)

The assessment of infection in the feet of diabetic patients provides unique challenges. On MR images, features of osteomyelitis and neuropathic osteoarthropathy may appear similar. Both may show high T2-­weighted and low T1-­weighted signal with enhancement after the intravenous administration of a gadolinium-­containing contrast agent (see Fig. 19.20). Two helpful features that allows differentation are location of MR imaging findings and the presence or absence of a soft tissue ulcer. If such MR imaging findings involve the midfoot and there is absence of a soft tissue ulcer (or penetrating injury) in the diabetic foot, osteomyelitis is unlikely, and imaging findings are usually attributed to neuropathic osteoarthropathy (Fig. 19.31). Although reported data indicate the value of scintigraphic methods, particularly 111In-­ labeled leukocyte imaging with or without

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SECTION 3  Infectious Disorders

Osteomyelitis: Diabetic foot Soft tissue ulcer? Yes T2W fat sat or STIR High T1W signal Low

No Normal (probably)

Normal No osteomyelitis

Normal

2. Spread from a contiguous source of infection: A joint may become contaminated by intraarticular extension of osteomyelitis from an epiphyseal or metaphyseal focus or of neighboring suppurative soft tissue processes. 3. Direct implantation: Inoculation of a joint can occur during aspiration or arthrography or after a penetrating wound. 4. Post operative infection: An intraarticular suppurative process can occur after arthroscopy or any other type of joint surgery.

HEMATOGENOUS INFECTION Pathogenesis

Osteomyelitis

Reactive edema

Supporting evidence: Enhancement, cortical destruction Fig. 19.31  Diabetic foot MR imaging: algorithm.

bone scintigraphy, the day-­to-­day clinical experience of many physicians suggests otherwise. A normal bone scan virtually excludes the presence of osteomyelitis, neuropathic osteoarthropathy, or both. The hyperemia associated with either process can lead to positive results with three-­phase bone scintigraphy. Decreased blood flow and possible impaired leukocyte responsiveness limit the sensitivity achievable with 111In-­labeled leukocyte scintigraphy in diabetic foot infections; however, reports indicate that the finding of definite increased uptake on leukocyte scans has a high positive predictive value, and the absence of increased leukocyte uptake in or near bone makes the diagnosis of osteomyelitis very unlikely.

SEPTIC ARTHRITIS ARTICULAR MANIFESTATIONS OF INFECTION Septic arthritis is but one of several processes that can cause or perpetuate articular disease in patients with infection. An infectious agent may trigger a sterile synovitis at a site distant from the primary infective focus. A classic example is the reactive arthritis of acute rheumatic fever occurring as a complication of streptococcal throat infection. Clinical characteristics common to reactive arthritides include a symptom-­free interval, a self-­limited course in which cartilage or bone destruction is rare, a characteristic clinical presentation that includes acute migratory polyarthritis, a tendency in some patients toward involvement of the heart, and a negative serologic test for rheumatoid factor. Inciting infections commonly reach the body through one of three portals of entry: the oronasopharynx and respiratory tract, the urogenital tract, and the intestinal tract. The existence of reactive arthritis in patients with infection underscores the importance of performing joint aspiration and attempting to isolate the causative organisms in all cases of suspected septic arthritis.

ROUTES OF CONTAMINATION The potential routes of contamination of joints can be divided into the same categories used in the previous discussion of osteomyelitis (Fig. 19.32). 1. Hematogenous spread of infection: Hematogenous seeding of the synovial membrane results from either direct transport of organisms within the synovial vessels or spread from an adjacent epiphyseal focus of osteomyelitis by means of vascular continuity between the epiphysis and the synovial membrane.

Hematogenous spread of infection to a joint indicates that organisms are transported within the vasculature of the synovial membrane directly from a distant infected source or indirectly from an adjacent bone infection. In either case, infection of the synovial membrane precedes contamination of the synovial fluid. Therefore, initial arthrocentesis may suggest bland inflammation of the joint. The reaction of the synovial tissue to the contained organisms varies according to the local and general resistance of the patient and the number, type, and virulence of the infecting agents.

General Clinical Features Monoarticular involvement is the major pattern of presentation, especially in younger age groups. The specific site or sites of infection depend on the age of the patient, the organism, and the existence of an underlying disease or problem. The knee, particularly in children, infants, and adults, and the hip, especially in children and infants, are frequently affected. With pyogenic infection, an acute onset with fever and chills is typical, although a prodromal phase of several days’ duration, with malaise, arthralgia, and low-­grade fever, can be encountered. Pain, tenderness, redness, heat, and soft tissue swelling of the involved joint are common. Leukocytosis and positive blood and joint cultures are important laboratory parameters of pyogenic arthritis. Elevated erythrocyte sedimentation rates and C-­reactive protein levels are also encountered. The organism most commonly implicated is Staphylococcus aureus. Haemophilus influenzae represents an important and common cause of septic arthritis in children younger than 5 years.

Imaging-­Pathologic Correlation In response to bacterial infection, the synovial membrane becomes edematous, swollen, and hypertrophied. Increased amounts of synovial fluid are produced; the fluid may be thin and cloudy, contain large numbers of leukocytes, and reveal a lowered sugar level and an elevated protein count. After a few days, frank pus accumulates in the articular cavity, and destruction of cartilage begins (Table 19.6 and Fig. 19.33). Prominent abnormality may appear at the margins or in central portions of joints, accompanied by growth of the inflamed synovium across the surface of the cartilage or between cartilage and bone. Cartilaginous erosion (from superficially located pannus) and disruption of the chondral surface (from subchondral pannus) can develop. With further accumulation of joint fluid, the capsule becomes distended, surrounding soft tissue edema is evident, and osseous abnormalities ensue. Superficial marginal and central bony erosions may progress to extensive destruction of large segments of the articular surface. Fibrous or bony ankylosis can eventually occur. Imaging abnormalities parallel the pathologic changes in pyogenic arthritis. Interosseous space narrowing, which is frequently diffuse or uniform, reflects damage and disruption of the chondral surface (Fig. 19.34). Periarticular osteopenia and soft tissue swelling are also

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CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

2

5

2

4 3

1 3

1 6 4

B

A

5

1

2

C

D

Fig. 19.32  Septic arthritis: potential routes of contamination. (A) Hematogenous spread of infection to a joint can result from direct lodgement of organisms in the synovial membrane (1). Spread into the joint from a contiguous source can occur from a metaphyseal focus that extends into the epiphysis and from there, into the joint (2), from a metaphyseal focus with extension into the joint when the growth plate is intraarticular (3), or from a contiguous soft tissue infection (4). Direct implantation after a penetrating wound (5) can also lead to septic arthritis. (B) Hematogenous spread of infection to a joint can occur owing to vascular continuity between the epiphysis and the synovial membrane. The vessels shown include arterioles (1), venules (2), and capillaries (3) of the capsule; periosteal vessels (4); the nutrient artery (5); and metaphyseal-­epiphyseal anastomoses (6). (C) Sequence of events by which the synovial membrane can become infected from an osseous focus before the joint fluid is contaminated. (D) Spread from a contiguous osseous surface can result from penetration of the cartilage (1) or pathologic fracture with articular contamination (2). In this situation, synovial fluid may become infected before the synovial membrane.

often present. Osseous erosions at the edges of the joint, related to the effects of diseased synovium on bone, lead to marginal defects (Fig. 19.35). Subchondral extension of pannus destroys the bone plate and adjacent trabeculae, leading to thinning or poorly defined gaps in the

subchondral white line on the radiograph (Fig. 19.36). US may be used to evaluate for joint effusion; however, the US appearance of joint recess distention may range from anechoic (Fig. 19.37) to hypoechoic fluid (Fig. 19.38), and US findings cannot predict if the fluid is infected.

312

SECTION 3  Infectious Disorders

1

TABLE 19.6  Septic Arthritis

2

Imaging-­Pathologic Correlation Pathologic Abnormality

Imaging Abnormality

Edema and hypertrophy of synovial membrane with fluid production

Joint effusion, soft tissue swelling

Hyperemia

Osteoporosis

Inflammatory pannus with chondral destruction

Joint space loss

Pannus destruction of bone

Marginal and central osseous erosion

Fibrous or bony ankylosis

Bony ankylosis

On MR imaging, although a joint effusion alone is not specific for infection, a large effusion with periarticular bone marrow edema, and enhancing synovial hypertrophy should raise concern for septic arthritis. Irregularity or discontinuity of the subchondral bone plate would suggest that the subjacent high T2 marrow signal abnormality represents secondary osteomyelitis. Rapid destruction of bone and cartilage is characteristic of bacterial arthritis, whereas in tuberculosis and fungal diseases, articular changes occur more slowly. In tuberculosis, marginal osseous erosions with preservation of joint space may be seen and periarticular osteoporosis may be prominent. Infrequently, gas formation within a joint complicates septic arthritis. Much more frequently, the appearance of radiolucent collections in an infected joint representing air bubbles indicates that a prior arthrocentesis has been performed.

INFECTION FROM A CONTIGUOUS SOURCE Pathogenesis In certain age groups, osteomyelitis can be complicated by contamination of the adjacent articulation. Septic arthritis complicating osteomyelitis occurs in as many as one-­third of patients and is seen most commonly in the hip and knee. In infants, the presence of vascular communication

A

3

4

5

Fig. 19.33  Septic arthritis: pathologic abnormalities. 1, Normal synovial joint. 2, An edematous, swollen, and hypertrophic synovial membrane becomes evident. 3 and 4, Accumulating inflammatory pannus leads to chondral destruction and to marginal and central osseous erosions. 5, Bony ankylosis may eventually result.

between metaphyseal and epiphyseal segments of tubular bones allows organisms within nutrient vessels to localize in the epiphysis and subsequently extend into the joint. In adults, vascular connections between the epiphysis and metaphysis are reestablished as the growth plate closes. Hematogenous osteomyelitis thus can affect the epiphysis in this age group. A second situation in which septic arthritis can occur as a result of contamination from a contiguous source is related to adjacent soft tissue infection or, more infrequently, nearby visceral infection (e.g.,

B

Fig. 19.34  Septic arthritis: hematogenous spread of infection. Radiographs reveal uniform joint space narrowing (A, arrow) and osseous erosion (B, arrowhead) with periarticular osteopenia and soft tissue swelling.

A

B Fig. 19.35  Septic arthritis: hematogenous spread of infection. (A) Radiograph reveals joint space narrowing and osseous erosions, which predominate at the margins of the talus (arrows). (B) In this patient with acquired immunodeficiency syndrome, a sagittal STIR MR image shows classic features of septic arthritis of the ankle, with cartilage and bone erosion and marrow alterations in the tibia and talus that reflect osteomyelitis.

A

D

B

C

E

F

Fig. 19.36  Septic arthritis: hematogenous spread of fungal infection. (A) Radiograph shows interval development of joint space narrowing and thinning of the subchondral bone plate (arrow) with periarticular osteopenia when compared to (B) an earlier radiograph. (C) Axial CT shows similar findings (arrow). (D) Coronal T1-weighted ­ and (E), fluid-sensitive MR images and (F) an axial T1-weighted ­ fat-saturated ­ contrast-enhanced ­ MR image show enhancing synovial hypertrophy distending the hip joint recesses (arrows). Note in (F) nonenhancing joint fluid (arrowhead) and adjacent infammatory changes (arrows) extending throughout the proximal thigh.

314

SECTION 3  Infectious Disorders

Tibia Talus

B

A

Fig. 19.37  Septic arthritis: US. (A) Radiograph shows distention of the anterior ankle joint recess (arrow) corresponding to an (B) anechoic joint effusion (arrows).

Talus

Navicular

A

B

C

Fig. 19.38  Septic arthritis: MR imaging and US. (A) US shows a hypoechoic joint effusion (arrows) corresponding to findings on sagittal (B) T1-­weighted and (C) fluid-­sensitive MR images (arrow). Note high T2-­ weighted signal of the adjacent bone marrow, which could represent reactive edema but is suspicious for secondary osteomyelitis, given the subchondral bone plate irregularity.

vesicoacetabular or enteroacetabular fistulas). Predisposing factors include pelvic trauma, surgical manipulation, and diverticulitis. Joint infection may also develop as a result of extension from a surrounding suppurative process in sites where the growth plate has an intraarticular location; the most important such sites are the hip and the glenohumeral joint. Because of this anatomic arrangement, osteomyelitis localized to the metaphysis can enter the joint by extending laterally without violating the growth plate.

Imaging-­Pathologic Correlation Usually, imaging evidence exists that the infective process originates outside the articulation. This evidence may include a soft tissue deficit, swelling, or gas formation; osteomyelitis with typical epiphyseal or metaphyseal destruction; and diverticulitis or cystitis with fistulization. In certain situations, however, a joint effusion and cartilaginous and subchondral osseous destruction are the first imaging clues to infection. Once the articulation has been violated, the imaging and pathologic abnormalities of the infection are virtually identical to those associated with hematogenously derived suppurative joint disease. If untreated, further destruction of bone becomes evident, and in late stages, bony ankylosis of the joint may result (Fig. 19.39).

Specific Entities

Fig. 19.39  Septic arthritis: intra-­ articular bone fusion. (A–B) Radiographs show mature osseous fusion across the interphalangeal joint of the great toe at the site of prior osteomyelitis (arrow) and septic arthritis as a result of direct extention of infection from an adjacent soft tissue ulceration.

Neonatal septic arthritis affects the hip joint most frequently, and S. aureus is the organism most commonly implicated. In this age group, infection can reach the hip via spread from a metaphyseal focus of osteomyelitis either directly into the joint (the growth plate is intraarticular) or via the epiphysis by way of vascular channels that cross the growth plate. Clinically, infants with septic arthritis of the hip may manifest irritability, loss of appetite, and fever. Initial radiographs of the hip are frequently

unremarkable. With accumulation of intraarticular fluid, pathologic subluxation or dislocation of the femoral head can occur, although the lack of ossification in most of the proximal capital femoral epiphysis makes this sign difficult to apply (Fig. 19.40). A helpful finding, however, is radiographically detectable osteomyelitis of the femoral metaphysis manifested as osteolysis, osteosclerosis, or periostitis.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations The radiographic findings of hip infection in infants can simulate those of other conditions; therefore aspiration of the joint is mandatory to firmly establish the diagnosis of septic arthritis and provide guidelines for adequate therapy. Only as the child develops and ossification of the immature skeleton proceeds will the degree of residual deformity from destruction of the cartilaginous femoral head and acetabulum become apparent (Fig. 19.41).

315

Septic arthritis of the hip is also frequent in children, although the overall frequency of this problem and the extent of its devastating effects on local cartilage and bone are less than in infants. It may be associated with the acute onset of fever, pain, swelling, and limping, as well as a dramatic leukocytosis. On radiographs, accumulation of intraarticular fluid may produce soft tissue swelling, capsular distention, and subtle lateral displacement of the ossified epiphysis. The prognosis of septic arthritis of the hip for a child is far better than that for an infant. Osteonecrosis of the femoral head occurring after metaphyseal or epiphyseal infection in a child (or infant) is an important complication of the disease (Fig. 19.42). Osteonecrosis of the epiphysis is usually not recognized until 6 to 8 weeks after the onset of infection. The epiphysis can reveal a generalized increase in radiodensity, followed by fragmentation and, less commonly, collapse.

DIRECT IMPLANTATION OF INFECTION Arthrocentesis for the evaluation of synovial contents or for arthrography can introduce gram-­positive or gram-­negative bacteria. Similarly, penetrating injuries, such as those that occur in a fistfight or from a bullet, knife, nail, or other sharp object, can lead to septic arthritis.

POSTOPERATIVE INFECTION Fig. 19.40  Septic arthritis of the hip: infancy. This infant developed septic arthritis of the right hip and osteomyelitis. Note displacement of the capsular and obturator fat planes (solid arrows), obliteration of the iliopsoas fat plane (arrowhead), and a metaphyseal focus of infection (open arrow). The femoral head is displaced laterally and is slightly enlarged. The soft tissue findings indicative of intraarticular fluid may be of more diagnostic help in this age group than in adults. (Courtesy J. Weston, MD, Lower Hutt, New Zealand.)

A

Articular surgery in the form of arthroscopy, arthrotomy, arthrodesis, arthroplasty, or another procedure can be complicated by joint infection in the postoperative period. Infections occurring soon after such procedures are usually related to direct inoculation of the joint during the operation or to intraarticular spread from an adjacent contaminated focus (e.g., soft tissue abscess). Joint infection occurring long after surgery is frequently associated with obvious preceding sepsis elsewhere in the body and may relate to hematogenous spread to the joint from this distant process.

B Fig. 19.41  Septic arthritis of the hip: infancy. (A) This neonate developed septic arthritis of the right hip. The initial radiograph reveals soft tissue swelling and periosteal reaction along the femur (arrowhead). (B) At age 13 years, the ossification centers of the greater and lesser trochanters are apparent. Femoral dislocation, acetabular shallowness, and absence of epiphyseal ossification are evident. (From Freiberger RH, Ghelman B, Kaye JJ, Spragge JW. Hip disease of infancy and childhood. In: Moseley RD Jr, et al. [eds]: Current Problems in Radiology. Chicago: Year Book Medical Publishers; 1973.)

316

SECTION 3  Infectious Disorders of the causative organisms from blood culture or joint aspiration can be difficult. Gram-­negative bacterial agents are especially common in pyogenic arthritis of the sacroiliac joint in intravenous drug abusers.

Radiographic-­Pathologic Correlation In almost all cases of sacroiliac joint infection, a unilateral distribution is encountered. In pyogenic arthritis, radiographic findings generally occur in 2 or 3 weeks and are characterized by blurring and indistinctness of the subchondral osseous line and narrowing or widening of the interosseous space (Fig. 19.43). Although these two alterations frequently coexist, their time of appearance is dictated by the initial site of contamination: if osteomyelitis precedes septic arthritis, bony abnormalities may antedate the articular changes; if the joint is affected initially, cartilaginous and osseous alterations may coexist. In both situations, the most extensive findings are commonly evident about the inferoanterior aspect of the joint (Fig. 19.44). Surrounding condensation of bone is variable in frequency and degree, and it is influenced by the type and virulence of the infecting microorganism.

Other Diagnostic Techniques Fig. 19.42  Septic arthritis of the hip: childhood. The complication of osteonecrosis in a child with septic arthritis of the hip is well demonstrated in this patient. Subsequently, progressive osteomyelitis and septic arthritis produced increased intraarticular fluid and osteonecrosis of the femoral head, manifested as increased radiodensity. Eventually, disintegration of the femoral head occurred.

SPECIFIC LOCATIONS Sacroiliac Joint KEY CONCEPTS  • U  nilateral uniform joint space involvement, erosions, and effusion should raise concern for septic arthritis. • Periarticular muscle edema is a secondary feature of septic arthritis and is not typically present with systemic arthritis, such as ankylosing spondylitis.

Routes of Contamination The sacroiliac joint may become infected by the hematogenous route, by contamination from a contiguous suppurative focus, by direct implantation, or after surgery. Hematogenous involvement of this joint likely begins in the subchondral bone of the ilium. Contamination of the sacroiliac joint or neighboring bone can result from an adjacent infection. Pelvic abscesses can disrupt the anterior articular capsule or the periosteum and cortex of the ilium or sacrum. Thus vaginal, uterine, ovarian, bladder, and intestinal processes can lead to iliac or sacral osteomyelitis and sacroiliac joint suppuration by contiguous contamination (as well as by hematogenous spread via Batson plexus). Pressure sores related to prolonged immobilization are not infrequent in the sacral region and can lead to subsequent articular and osseous infection. Direct implantation of organisms after diagnostic, therapeutic, or surgical procedures represents another, though uncommon, source of sacroiliac joint infection.

Clinical Abnormalities Pyogenic infection of the sacroiliac joint may develop in patients of all ages. Unilateral alterations predominate. Fever, local pain and tenderness, and a limp may be evident. Accurate diagnosis is often delayed in cases of septic sacroiliitis, which increases the frequency of such extraarticular contamination. Elevation of the erythrocyte sedimentation rate and leukocytosis are common but variable laboratory findings. Identification

Scintigraphy, with the use of technetium phosphate, gallium, or both, may outline increased accumulation of radionuclide when findings on routine radiographs are unimpressive Abnormal unilateral uptake of isotope in the sacroiliac joint indicates infection until proved otherwise. US may be used to assess for sacroilitis; however, the finding of a joint effusion is not specific for one diagnosis. In addition, the sacroiliac joint recess may be difficult to identify, given its small size, especially in a patient with a large body habitus. Hyperemia on color Doppler imaging may be an associated finding, and US can be used to guide percutaneous joint aspiration. CT scanning is valuable in the early diagnosis of septic sacroiliitis, because it reveals cartilaginous and osseous destruction and intraosseous gas (see Figs. 19.43 and 19.45), and as an aid to aspiration and biopsy techniques. The latter procedures can be difficult without CT guidance. MR imaging shows marrow edema in the sacrum and ilium, irregularity of the subchondral bone on either side of the joint space, joint fluid, muscle edema and abscess, fluid-­filled channels, sinus tracts, and fistulas. Intravenous administration of a gadolinium contrast agent can be used to accentuate the MR imaging abnormalities and to delineate adjacent soft tissue involvement (Figs. 19.43 and 19.46).

Differential Diagnosis The unilateral nature of infective sacroiliac joint disease is its most useful diagnostic feature. Bilateral symmetric or asymmetric articular changes are characteristic of ankylosing spondylitis, psoriasis, reactive arthritis, osteitis condensans ilii, and hyperparathyroidism. Unilateral changes can be encountered in rheumatoid arthritis, gout, reactive arthritis, psoriasis, and paralysis (because of chondral atrophy). In these latter conditions, adjacent periarticular muscle edema is absent; the presence of this finding on MR imaging, in addition to the previously described abnormalities of the sacroiliac joint, is a characteristic finding that would suggest septic arthritis.

Sternoclavicular and Acromioclavicular Joints and Other Sites

In intravenous drug users, osteomyelitis and septic arthritis of the sternoclavicular and acromioclavicular joints, in addition to the spine and sacroiliac joint, may be evident. After urologic procedures or athletic endeavors, osteomyelitis of the symphysis pubis may be difficult to differentiate from osteitis pubis. Infection of the sternum and the manubriosternal and sternoclavicular joints can result from direct hematogenous inoculation (Fig. 19.47) or secondary contamination

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

A

B

C

D

317

F

E Fig. 19.43  Sacroiliac joint infection: hematogenous spread of infection. (A) Radiograph and (B) axial CT image show right sacroiliac joint space widening and erosions of the subchondral bone plate (arrow). (C) T1-­ weighted, (D) fluid-­sensitive, and (E) T1-­weighted fat-­saturated contrast-­enhanced MR images show a joint effusion, erosions, and subjacent marrow signal abnormalities (arrow). Note the periarticular abnormalities characterstic of an infected sacroiliac joint (arrowhead). (F) FDG-­PET scan shows corresponding sacroiliac joint uptake (arrow).

resulting from local injury, surgery, or diagnostic or therapeutic procedures. In some sites, such as the sternoclavicular joint, abscess formation and inflammation in nearby tissues are common, and these complications are well studied by CT scanning or MR imaging.

COMPLICATIONS Several potential complications of septic arthritis deserve emphasis. The frequency of synovial cyst formation in septic arthritis appears to be low. Infrequently, synovial rupture of the cyst, with or without sinus tract formation, is observed. Septic arthritis can lead to disruption of adjacent capsular, tendinous, and soft tissue structures. This complication has been well documented in the glenohumeral joint. Imaging and pathologic evidence of osteomyelitis is associated with septic arthritis. Bony abnormalities can antedate and be the source of the suppurative joint process, or they can indicate the contamination

of adjacent bony surfaces from a primary joint infection. Partial or complete osseous fusion may represent the residual findings of septic arthritis (see Fig. 19.39). This complication is not frequent; however, bone ankylosis is occasionally encountered after pyogenic processes. Significant destruction of articular cartilage from joint sepsis can lead to incongruity of apposing articular surfaces and, later, to changes of secondary osteoarthrosis. The resulting radiographic findings, consisting of joint space narrowing, sclerosis, and osteophytosis, may be difficult to differentiate from primary osteoarthrosis.

OTHER DIAGNOSTIC TECHNIQUES Arthrography The principal reason for performing a joint puncture in the clinical setting of infection is to obtain fluid for bacteriologic examination, typically using US or fluoroscopy. If using fluoroscopy, cross-­sectional

318

SECTION 3  Infectious Disorders

A

Fig. 19.44  Sacroiliac joint infection: early abnormalities. Pseudomonas osteomyelitis and septic arthritis developed in a 35-­year-­old male heroin addict. Radiograph reveals changes in the right sacroiliac joint consisting of subchondral osseous erosion, poorly defined articular margins, and widening of the joint space (arrows).

B

A

C

Fig. 19.46  Sacroiliac joint infection: MR imaging. Staphylococcal infection of the left sacroiliac joint developed in this 48-­year-­old woman. (A) The infectious process in the sacrum and ilium is not well visualized on this axial T1-­weighted MR image because of the similar signal intensity of the inflammatory response and the hematopoietic bone marrow. The soft tissue extension of infection is also not well seen. (B) Axial fluid-­sensitive MR image reveals high signal intensity in the sacrum and ilium, as well as in the anterior and posterior soft tissues and musculature (arrows). (C) Axial T1-­weighted MR image obtained with fat suppression after the intravenous injection of a gadolinium contrast agent reveals the inflammatory reaction, with high signal intensity in the bone and about the anterior and posterior abscesses. Note the low signal intensity of the fluid in the joint and in the soft tissues and musculature. (Courtesy M. Schweitzer, MD, Detroit, MI.)

joint can be used to outline the extent of the synovial inflammation and the presence of capsular, tendinous, and soft tissue injury.

Sinography

B Fig. 19.45  Sacroiliac joint infection: CT scanning. In this 20-­year-­old intravenous drug user, CT scans with bone (A) and soft tissue (B) windows show involvement of the left sacroiliac joint (arrow) and an abscess (arrowheads) in the iliac muscle. (Courtesy J. Hodler, MD, Zurich, Switzerland.)

imaging should be considered to evaluate for soft tissue infection that may unknowingly seed a sterile joint during the aspiration. After removal of the joint contents, however, contrast opacification of the

Retrograde injection of contrast material defines the course and extent of the sinus tract and its possible communication with an underlying bone or joint. Sinography may be combined with CT scanning or MR imaging for better delineation of the sinus tracts.

US US is a useful technique for detecting effusions (see Figs. 19.37B, 19.38A, and 19.47A), especially in the hip in children with transient synovitis, septic arthritis, or Legg-­Calvé-­Perthes disease. The absence of fluid in this joint with US excludes the diagnosis of septic arthritis, though it does not eliminate the possibility of osteomyelitis. Further, US can be used to guide aspiration of the effusion. US also can be employed in the detection of joint fluid in adults with septic arthritis, although small effusions in deep joints may be difficult to identify.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

319

Sternum

Clavicle

A

B

C

E

F

C

C S

D

Fig. 19.47  Sternoclavicular joint infection: hematogenous spread of infection. (A) Conventional and (B) color Doppler US show marked hypoechoic distention of the sternoclavicular joint recess (arrows) with hyperemia. Subchondral erosion (arrowheads) is better delineated on an (C) axial CT image, which also shows marked joint recess distention (arrows). Coronal (D) T1-­weighted, (E) fluid-­sensitive, and (F) T1-­weighted fat-­ saturated contrast-­enhanced MR images show joint capsule distention (arrow), a nonenhancing joint effusion (arrowhead), and adjacent enhancing bone marrow and soft tissue abnormalities. C, Clavicle; S, sternum.

Radionuclide Examination With bone scintigraphy, septic arthritis is usually accompanied by increased uptake of the radiopharmaceutical agent in juxtaarticular bone in the delayed images, moderate and diffuse blood pool hyperemia, and, on the radionuclide angiogram, increased flow to the joint space (Fig. 19.48). Similarly, gallium scans, labeled leukocyte imaging, and PET scans can show periarticular uptake with septic arthritis. The use of SPECT and, more importantly, CT in conjunction with radionuclide scanning more accurately allows the identification of the anatomic location of radiotracer uptake.

A

C

B

D

CT The features of septic arthritis on CT parallel what is seen on radiography, namely joint space narrowing, periarticular osteopenia, erosions, and a joint effusion and/or synovial hypertrophy (see Fig. 19.36C).

MR Imaging The common feature of septic arthritis is a joint effusion. Although nonspecific, the presence of a large joint effusion with periarticular bone marrow and soft tissue edema should raise suspicion for the diagnosis of infection (see Figs. 19.36, 19.38, 19.43, and 19.47). Intravenous gadolinium contrast is used to delineate the degree of synovial hypertrophy, which is more common with chronic or atypical infections, such as fungal causes. MR imaging may be problematic in septic arthritis, differentiating secondary osteomyelitis from bone marrow edema, or in acute osteomyelitis affecting epiphyses, differentiating secondary septic arthritis from sympathetic effusions.

Fig. 19.48  Septic arthritis: bone scanning. (A–C) Three-­phase technetium phosphate study documents increased flow (arrow) in the angiographic phase (A), diffuse hyperemia about the hip (arrow) in the blood pool stage (B), and increased uptake of the radiopharmaceutical agent (arrow) in the delayed image (C). These findings indicate septic arthritis. (D) Gallium scan is also abnormal, with increased scintigraphic activity about the hip (arrow). (Courtesy G. Greenway, MD, Dallas, TX.)

320

SECTION 3  Infectious Disorders

DIFFERENTIAL DIAGNOSIS Although numerous disorders such as pigmented villonodular synovitis (intra-­articular, diffuse-­type tenosynovial giant cell tumor), idiopathic synovial osteochondromatosis, juvenile idiopathic arthritis, and even adult-­onset rheumatoid arthritis can be associated with monoarticular changes (Fig. 19.49), infection must be considered the prime diagnostic possibility until proved otherwise. This is particularly true when the joint process is associated with loss of interosseous space, poorly defined or fuzzy osseous margins, and a sizable effusion. In patients with pyogenic infection, the articular destruction can be rapid. Diagnostic difficulty arises when the septic process involves more than one joint or when septic arthritis appears during the course of another articular disorder. Of all the radiographic features of infection, it is the poorly defined nature of the bony destruction that is most characteristic. Osseous erosions or cysts in gout, rheumatoid arthritis, spondyloarthropathies, osteoarthrosis, pigmented villonodular synovitis, synovial chondromatosis, hemophilia, and calcium pyrophosphate dihydrate crystal deposition disease are more sharply marginated. Further, concentric loss of interosseous space is typical in infection, but focal diminution of the articular space (as noted in osteoarthrosis) and relative preservation of articular space (as seen in gout, pigmented villonodular synovitis, idiopathic synovial chondromatosis, and hemophilia) are rare in pyogenic infection. Marginal erosions are frequent in processes associated with significant synovial inflammation, such as sepsis, rheumatoid arthritis, and the spondyloarthropathies. They may also be observed in gout and, less commonly, in pigmented villonodular synovitis and synovial chondromatosis. Similarly, periarticular osteoporosis can be encountered in

A

C

rheumatoid arthritis, reactive arthritis, juvenile idiopathic arthritis, hemophilia, and nonpyogenic suppurative processes, such as tuberculosis or fungal disease. Intraarticular bony ankylosis can represent the end stage of septic arthritis, the spondyloarthropathies, and, in some locations, rheumatoid arthritis and juvenile idiopathic arthritis.

SOFT TISSUE INFECTION ROUTES OF CONTAMINATION Infection of soft tissue structures commonly results from direct contamination after trauma. Any process that disrupts the skin surface can lead to secondary infection. Hematogenous spread is less important as a mechanism in soft tissue contamination than it is in osteomyelitis and septic arthritis.

IMAGING-­PATHOLOGIC CORRELATION Swelling with obliteration of adjacent tissue planes is characteristic of soft tissue infection. Radiolucent streaks within the contaminated area can relate to collections of air derived from the adjacent skin surface or to gas formation by various bacteria (Fig. 19.50). Erosion of bone due to pressure from an adjacent soft tissue mass is much more frequent when the mass is neoplastic rather than infectious in origin. When osseous abnormalities appear after soft tissue contamination, infective periostitis, osteitis, or osteomyelitis is usually present (Fig. 19.51). A well-­defined soft tissue mass is less typical of infection than of neoplasm. The edema of an infectious process usually leads to infiltration of surrounding soft tissues rather than displacement.

B

D

E

Fig. 19.49  Rheumatoid arthritis. (A) Anteroposterior and (B) lateral elbow radiographs show joint recess distention with abnormally elevated fat pads (arrowheads) and diffuse subchondral erosions. (C) Axial T1-­ weighted and (D) fluid-sensitive, ­ and (E) sagittal T1-weighted ­ fat-saturated ­ contrast-enhanced ­ MR images show enhancing synovial hypertrophy (arrows) and extensive erosions. A chronic atypical infection, such as fungal-related, ­ can appear similar at imaging.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

A

321

B

Fig. 19.50  Soft tissue infection: gas formation. Note the bubbly radiolucent collections in the foot (arrows).

Fig. 19.51  Soft tissue infection: osteomyelitis. This 30-­year-­old man developed a soft tissue infection after an injury. (A) Radiograph shows soft tissue swelling and bone erosion in the middle phalanx (arrow). (B) Coronal fat-­suppressed fluid-­sensitive MR image confirms the presence of osteomyelitis with bone erosion and edema, and a soft tissue infective focus manifested as a region of high signal intensity.

SPECIFIC ENTITIES

Cellulitis

Septic Subcutaneous Bursitis

Cellulitis represents an acute inflammatory process of the deeper subcutaneous tissue; involvement of deep fasciae and muscles is unusual in cases of uncomplicated cellulitis. Clinical findings include pain or tenderness, redness, swelling, warmth, and mild to moderate fever. Cellulitis generally results from a streptococcal or, less commonly, a staphylococcal infection. Radiographic findings are nonspecific and are usually confined to the soft tissues. With fluid-­sensitive MR imaging, cellulitis is characterized by subcutaneous thickening and hyperintense streaks or fluid collections in the subcutaneous fat and superficial fascial tissues (Fig. 19.55). Enhancement of signal intensity in these regions is evident when gadolinium contrast agents are administered intravenously. At US (Fig. 19.56), acute cellulitis will appear as abnormal hyperechoic thickening of the subcutaneous tissues with sound beam attenuation, while chronic cellulitis will appear as branching anechoic channels.

Septic bursitis most frequently localizes to the olecranon, the prepatellar, and, less frequently, the subdeltoid regions. A history of recent injury, occupational trauma, or puncture is frequently, though not invariably, present. Clinical manifestations include painful swelling localized to the involved bursa, subcutaneous edema, a normal range of joint motion, and fever. Routine radiography, US, or MR imaging (Fig. 19.52) may be used to define the extent of the soft tissue infection. Septic bursitis is usually not associated with infectious arthritis.

Septic Tenosynovitis Septic processes originating from a distant or local focus or occurring after trauma can also lead to tenosynovitis. Soft tissue swelling and surface resorption and erosion of underlying bony structures may be evident. MR imaging and US (Fig. 19.53) are appropriate diagnostic methods applied to the assessment of suppurative tenosynovitis.

Lymphadenitis Lymphadenitis, usually with an accompanying cellulitis, can complicate streptococcal or staphylococcal infections. Nodular or diffuse soft tissue swelling and underlying periostitis may be encountered. Cat scratch disease often manifests in this fashion, most commonly with involvement of the epitrochlear lymph node at the medial elbow (Fig. 19.54) and possibly the axillary region from Bartonella henselae infection.

Necrotizing Fasciitis Necrotizing fasciitis represents a rare type of soft tissue infection that is accompanied by widespread fascial necrosis in the absence of muscular or cutaneous infection. It is a serious condition associated with systemic toxicity and, if untreated, death. Routine radiography may reveal evidence of soft tissue gas, although the clinical findings of fever, pain, swelling, and bullae usually allow an accurate diagnosis. CT may be needed to ideally demonstrate the soft tissue gas. MR imaging shows involvement of both superficial and deep soft tissue structures; the demonstration of deep fasciae with fluid collections, thickening, and

322

SECTION 3  Infectious Disorders

A

Olecranon

B

Fig. 19.52  Septic olecranon bursitis. (A) Note soft tissue swelling (arrows) and soft tissue edema as a result of Staphylococcus aureus infection. Previous surgery and trauma are the causes of the adjacent bony abnormalities. (B) US image from a different patient shows hypoechoic distention of the olecranon bursa (arrows).

T

B

A

C

Fig. 19.53  Infective tenosynovitis. (A) Axial fluid-­sensitive and (B) T1-­weighted fat-­saturated post-­contrast MR images show peripheral enhancing fluid distending the extensor tendon sheath (arrow). (C) US long axis to an extensor tendon (T) shows hypoechoic tendon sheath distention (arrows).

A

B

C

Fig. 19.54  Cat scratch disease. (A) Axial fluid-­sensitive and (B) T1-­weighted fat-­saturated contrast-­enhanced MR images show an enhancing epitrochlear lymph node (arrowhead) and a peripheral enhancing fluid collection (arrow). (C) US shows a hypoechoic lymph node with echogenic hilum (arrowhead) and an adjacent hypoechoic fluid collection (arrow). Note the characteristic location of the imaging findings. (From Melville D,M, Jacobson JA, Downie B, et al. Sonography of cat scratch disease. J Ultrasound Med. 2015; 34:387-­394.)

A

B

C

Fig. 19.55  Cellulitis. (A) Radiograph shows increased soft tissue density and soft tissue swelling (arrow). (B) Short axis T1-­weighted and (C) fluid-­sensitive MR images show increased T2 signal within the subcutaneous fat (arrow).

A

B Fig. 19.56  Cellulitis: US. (A) US shows acute cellulitis (arrows) appearing as increased echogenicity of the subcutaneous tissues with sound beam attenuation. Note normal adjacent hypoechoic subcutanteous fat. (B) US in a different patient shows chronic cellulitis appearing as branching anechoic channels (arrows).

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SECTION 3  Infectious Disorders

enhancement of signal intensity with intravenous gadolinium contrast agents generally distinguishes this condition from cellulitis (Fig. 19.57).

Infectious Myositis Inflammation of muscle may occur in a variety of infectious disorders caused by viruses, bacteria, protozoa, and parasites. Pyogenic myositis (pyomyositis) is a well-­recognized and serious infection affecting children and young adults in tropical regions (tropical pyomyositis) and, less frequently, in other locations. Although the disease, as described classically, occurs in otherwise healthy persons, it is being recognized with increasing frequency in malnourished and immunodeficient patients. Pyomyositis is related to S. aureus infection in about 90% of cases (streptococci account for most of the remaining cases). CT imaging after intravenous contrast administration will show peripheral enhancement; gas may be evident on radiography and CT (Fig. 19.58). At US, abscess echogenicity ranges from hypoechoic (Fig. 19.59) to hyperechoic (Fig. 19.60); therefore, identification of a deep abscess may prove difficult. MR imaging findings (Fig. 19.60) include muscle enlargement; abscesses characterized by a peripheral rim of increased signal intensity on T1-­weighted MR images, a central region (representing fluid) of intense signal on fluid-­sensitive images, and peripheral enhancement after intravenous administration of gadolinium contrast; and associated abnormalities of subcutaneous edema in some cases. The differential diagnosis for peripheral enhancement of muscle includes diabetic muscle infarction (see Fig. 26.33).

Foreign Bodies Fig. 19.57  Necrotizing fasciitis and myositis with abscess formation and fistula: MR imaging. After the intravenous administration of a gadolinium contrast agent, a transverse T1-­weighted MR image of the thigh reveals peripheral enhancement (arrows), consistent with an abscess. Note the presence of the fistula. (From Rahmouni A, Chosidow O, Mathieu D, et al. MR imaging in acute infectious cellulitis. Radiology. 192:493, 1994.)

A

KEY CONCEPTS  • G  lass foreign bodies are radiopaque regardless of color or tint. • Wood and plant matter are not radiopaque and are further localized with US, CT, and MR imaging.

B

Fig. 19.58  Abscess: radiography and CT. (A) Radiograph and (B) axial postcontrast CT image show a focus of soft tissue gas (arrowhead) within the peripheral enhancing abscess (arrows).

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

Ulna

Fig. 19.59  Abscess: US. US of the forearm shows a hypoechoic abscess (arrows) with increased posterior through-­transmission.

A

B

C

D

Fig. 19.60  Abscess: US and MR imaging. (A) US shows a hyperechoic abscess (arrow) with increased posterior through-­transmission. (B) Axial T1-­weighted, (C) fluid-­sensitive, and (D) T1-­weighted fat-­saturated contrast-­enhanced MR images show a high T2 signal abscess with peripheral enhancement (arrow).

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SECTION 3  Infectious Disorders

Evaluation for soft tissue foreign bodies typically begins with radiography (Fig. 19.61); however, there are a number of foreign bodies that are not radiopaque, such as wood and plant matter. All glass is opaque on radiographs, regardless of tint, although their density is equal to trabecular bone and can be easily overlooked (Fig. 19.62). A negative radiograph may be followed by US, in which all foreign

bodies are initially hyperechoic (Fig. 19.63). Often, a hypoechoic halo of inflammation is found and shadowing and/or posterior reverberation artifact may occur. CT scanning and MR imaging are also used to identify foreign bodies. A retained sponge foreign body, termed gossypiboma or textiloma, creates a heterogeneous appearance and may present as a soft tissue mass (Fig. 19.64).

Fig. 19.61  Foreign body: cat tooth. Radiograph after an animal bite shows a retained cat tooth (arrow).

Olecranon

A

B Fig. 19.62  Foreign body: glass. (A) Radiograph shows several radiopaque glass foreign bodies (arrows). (B) US shows a glass foreign body as a hyperechoic focus (arrow), with posterior reverberation artifact.

CHAPTER 19  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations

Fig. 19.63  Foreign body: wood. US shows a wood foreign body as a hyperechoic focus (arrows) with partial posterior shadowing and reverberation artifact and a surrounding hypoechoic halo of inflammation. (From Jacobson JA: Fundamentals of Musculoskeletal Ultrasound. 3rd ed. Philadelphia: Elsevier; 2018.)

A

B

C

D

Fig. 19.64  Foreign body: gossypiboma. (A) US shows a heterogeneous hyperechoic area with a surrounding hypoechoic halo (arrow). (B) Axial T1-­weighted, (C) fluid-­sensitive, and (D) T1-­weighted fat-­saturated contrast-­enhanced MR images show a heterogeneous mixed signal abnormality with scattered internal low signal foci and peripheral enhancement (arrow).

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FURTHER READING Azouz EM. Computed tomography in bone and joint infections. J Can Assoc Radiol. 1981;32:102. Bonakdar-­pour A, Gaines VD. The radiology of osteomyelitis. Orthop Clin North Am. 1983;14:21. Boutin RD, Resnick D. The SAPHO syndrome: an evolving concept for unifying several idiopathic disorders of bone and skin. AJR Am J Roentgenol. 1998;170:585. Bressler EL, Conway JJ, Weiss SC. Neonatal osteomyelitis examined by bone scintigraphy. Radiology. 1984;152:685. Butt WP. Radiology of the infected joint. Clin Orthop. 1973;96:136. Butt WP. The radiology of infection. Clin Orthop. 1973;96:20. Capitanio MA, Kirkpatrick JA. Early roentgen observations in acute osteomyelitis. AJR Am J Roentgenol. 1970;108:488. Capriotti G, Chianelli M, Signore A. Nuclear medicine imaging of diabetic foot infection: results of meta-­analysis. Nucl Med Commun. 2006;27(10):757–764. Collins MS, Schaar MM, Wenger DE, Mandrekar JN. T1-­weighted MRI characteristics of pedal osteomyelitis. Am J Roentgenol. 2005;185:386–393. Curtiss Jr PH. The pathophysiology of joint infections. Clin Orthop. 1973;96:129. Davis LA. Antibiotic modified osteomyelitis. AJR Am J Roentgenol. 1968;103:608. Dibble EH, Yoo DC, Baird GL, Noto RB. FDG/PET CT of infection: should it replace leukocyte scintigraphy of inpatients? Am J Roentgenol. 2019;213:1358–1365. Erdman WA, Tamburro F, Jayson HT, et al. Osteomyelitis: characteristics and pitfalls of diagnosis with MR imaging. Radiology. 1991;180:533. Fitzgerald RH, Brewer NS, Dahlin DC. Squamous-­cell carcinoma complicating chronic osteomyelitis. J Bone Joint Surg Am. 1976;58:1146. Fletcher BD, Scoles PV, Nelson AD. Osteomyelitis in children: detection by magnetic resonance. Work in progress. Radiology. 1984;150:57. Gilday DL, Paul DJ, Paterson J. Diagnosis of osteomyelitis in children by combined blood pool and bone imaging. Radiology. 1975;117:331. Goldberg JS, London WL, Nagel DM. Tropical pyomyositis: A case report and review. Pediatrics. 1979;63:298. Graif M, Schweitzer ME, Deely D, et al. The septic versus nonseptic inflamed joint: MRI characteristics. Skeletal Radiol. 1999;28:616. Green NE, Beauchamp RD, Griffin PP. Primary subacute epiphyseal osteomyelitis. J Bone Joint Surg Am. 1981;63:107. Grey AC, Davies AM, Mangham DC, et al. The “penumbra sign” on T1-­ weighted MR imaging in subacute osteomyelitis: frequency, cause and significance. Clin Radiol. 1998;53:587. Handmaker H, Leonards R. The bone scan in inflammatory osseous disease. Semin Nucl Med. 1976;6:95. Hofer P. Gallium and infection. J Nucl Med. 1980;21:484. Horton LK, Jacobson JA, Powell A, Fessell DP, Hayes CW. Sonography and radiography of soft tissue foreign bodies. Am J Roentgenol. 2001;176:1155– 1159. Kahn M-­F, Chamot A-­M. SAPHO syndrome. Rheum Dis Clin North Am. 1992;18:225. Kang Y, Hong SH, Kim JY, et al. Unilateral sacroiliitis: Differential diagnosis between infectious sacroiliitis and spondyloarthritis based on MRI findings. Am J Roentgenol. 2015;205:1048–1055.

Kaye JJ. Bacterial infections of the hips in infancy and childhood. Curr Probl Radiol. 1973;3(17). Kemp HBS, Lloyd-­Roberts GC. Avascular necrosis of the capital epiphysis following osteomyelitis of the proximal femoral metaphysis. J Bone Joint Surg Br. 1974;56:688. Kido D, Bryan D, Halpern M. Hematogenous osteomyelitis in drug addicts. AJR Am J Roentgenol. 1973;118:356. McAfee JG, Subramanian G, Gagne G. Technique of leukocyte harvesting and labeling: problems and perspective. Semin Nucl Med. 1984;14:83. Mendelson EB, Fisher MR, Deschler TW, et al. Osteomyelitis in the diabetic foot: a difficult diagnostic challenge. Radiographics. 1983;3:248. Miller WB, Murphy WA, Gilula LA. Brodie abscess: Reappraisal. Radiology. 1979;132:15. Miller TT, Randolph Jr DA, Staron RB, et al. Fat-­suppressed MRI of musculoskeletal infection: fast T2-­weighted techniques versus gadolinium-­ enhanced T1-­weighted images. Skeletal Radiol. 1997;26:654. Mok PM, Reilly BJ, Ash JM. Osteomyelitis in the neonate: clinical aspects and the role of radiography and scintigraphy in diagnosis and management. Radiology. 1982;145:677. Murray SD, Kehl DK. Chronic recurrent multifocal osteomyelitis: a case report. J Bone Joint Surg Am. 1984;66:1110. Pennington WT, Mott MP, Thometz JG, et al. Photopenic bone scan osteomyelitis: a clinical perspective. J Pediatr Orthop. 1999;19:695. Rasool MN. Primary subacute haematogenous osteomyelitis in children. J Bone Joint Surg Br. 2001;83:93. Resnick D, Pineda CJ, Weisman MH, et al. Osteomyelitis and septic arthritis of the hand following human bites. Skeletal Radiol. 1985;14:263. Resnick D. Osteomyelitis and septic arthritis complicating hand injuries and infections: pathogenesis of roentgenographic abnormalities. J Can Assoc Radiol. 1976;27:21. Rosenbaum DM, Blumhagen JD. Acute epiphyseal osteomyelitis in children. Radiology. 1985;156:89. Rosskopf AB, Loupatatzis C, Pfirrmann CWA, et al. The charcot foot: a pictorial review. Insights into imaging. 2019;10:77. Schweitzer ME, Daffner RH, Weissman BN, et al. ACR appropriateness criteria on suspected osteomyelitis in patients with diabetes mellitus. J Am Coll Radiol. 2008;5:881–886. Solheim LF, Paus B, Liverud K, et al. Chronic recurrent multifocal osteomyelitis. Acta Orthop Scand. 1980;51:37. Tehranzadeh J, Wang F, Mesqarzadeh M. Magnetic resonance imaging of osteomyelitis. CRC Crit Rev Diagn Imaging. 1992;33:495. Trueta J. Studies of the Development and Decay of the Human Frame. Philadelphia: WB Saunders; 1968:254. Turecki MB, Tajlanovic MS, Stubbs AY, et al. Imaging of musculoskeletal soft tissue infections. Skeletal Radiol. 2010;39:957–971. Unger E, Moldofsky P, Gatenby R, et al. Diagnosis of osteomyelitis by MR imaging. AJR Am J Roentgenol. 1988;150:605. Waldvogel FA, Vasey H. Osteomyelitis: the past decade. N Engl J Med. 1980;303:360. Wolfson JJ, Kane WJ, Laxdal SD, et al. Bone findings in chronic granulomatous disease of childhood: a genetic abnormality of leukocyte function. J Bone Joint Surg Am. 1969;51:1573. Wood BP. The vanishing epiphyseal ossification center: A sequel to septic arthritis of childhood. Radiology. 1980;134:387.

20 Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms S U M M A R Y O F K E Y F E AT U R E S • O  sseous, articular, and soft tissue structures may become involved in many infectious disorders. • Bacteria, mycobacteria, spirochetes, fungi, viruses, rickettsiae, protozoa, and worms are all capable of affecting the musculo­ skeletal system.

  

INTRODUCTION Although the skeleton can react in only a limited number of ways, certain characteristics of its response to a particular infectious agent may differ, at least subtly, from the changes encountered in the presence of another agent. Thus certain organisms produce rapid and destructive osseous or articular disease, whereas others are associated with a more indolent process. Further, some agents show a predilection for certain anatomic regions of the skeleton.

BACTERIAL INFECTION Gram-­Positive Cocci

Staphylococcal Infection

Staphylococci are responsible for most cases of acute osteomyelitis and nongonococcal infectious arthritis. The two major pathogens are Staphylococcus aureus (coagulase positive) and Staphylococcus epidermidis (coagulase negative). S. aureus is most typical in pyogenic osteomyelitis. Localization of the infection to the metaphysis of the tubular bones in children is typical, and Brodie abscesses may be seen (Figs. 20.1 and 20.2). Staphylococci are also responsible for many of the deep infections that occur after bone or joint surgery; the foot infections in diabetic patients; cases of osteomyelitis and septic arthritis in hemodialysis patients with infected shunts, intravenous drug users, and patients with rheumatoid arthritis; and the osseous, articular, and soft tissue suppurative processes that follow penetrating or open wounds. S. aureus is implicated in most cases of pyomyositis.

Streptococcal Infection Streptococci are gram-­positive cocci. In infants, hemolytic streptococcal agents are an important causative factor in neonatal or infantile osteomyelitis. The clinical manifestations of streptococcal bone infection may be mild, even in the presence of significant radiographic alterations. Infection of a single bone is most frequent, and a predilection for the humerus has been noted (Fig. 20.3).

Pneumococcal Infection Pneumococcus is now referred to as Streptococcus pneumoniae. Pulmonary and upper respiratory tract infections predominate. Pneumococcal arthritis and osteomyelitis are infrequent. Sickle cell anemia may be an underlying problem.

• I n some cases, the distribution and morphology of imaging features are sufficiently characteristic to suggest a single infectious process. • Imaging studies must be interpreted in conjunction with the clinical and pathologic manifestations.

Gram-­Negative Cocci

Meningococcal Infection

Meningococcal infection caused by Neisseria meningitidis occurs almost exclusively in persons who have no measurable antimeningococcal antibody. It varies remarkably in severity, from benign and asymptomatic to a fulminant and fatal disorder. Septicemia may lead to contamination of many sites, but the microorganisms commonly lodge in the central nervous system, skin, adrenal glands, and serosal surfaces. Meningococcemia leads to the rapid development of fever, shaking chills, skin eruption, petechiae, myalgias, and a variety of neurologic manifestations. In fulminant cases (Waterhouse-­ Friderichsen syndrome), hypotension, confusion, tachypnea, peripheral cyanosis, and consumptive coagulopathy develop. In children, characteristic skeletal abnormalities have been described in which localized premature fusion of part of several physes is seen, usually in a bilateral and relatively symmetric distribution (Fig. 20.4). Commonly, the central aspect of the physis is affected, and a cupped or cone-­shaped metaphysis results. Subsequently, epiphyseal disintegration and bowing and angular deformities appear, especially in the legs, and lead to limb shortening.

Gonococcal Infection Gonorrhea is produced by the microorganism Neisseria gonorrhoeae, which infects the mucous membranes of the urethra, cervix, rectum, and pharynx. The frequency of gonococcal arthritis is rising, possibly owing to an increasing resistance to antibiotics. The disease is transmitted almost exclusively through sexual contact with persons who have asymptomatic or ignored symptomatic infection. It is also encountered during pregnancy and after gonococcal vulvovaginitis in children and neonates. Only a minority of gonococcal infections eventually disseminate. Gonococcemia leads to skin rash, fever, and arthritis, the last occurring in approximately 75% of disseminated cases. The articular disease may have an insidious onset with fleeting arthralgias or a sudden onset with fever and red, hot, swollen, and tender joints. Polyarticular findings are frequent, but the infection tends to localize in one or two joints. The affected articulations, in decreasing order of frequency, are the knee, ankle, wrist, and joints of the shoulder, foot, and spine. In approximately 50% to 70% of cases, acute asymmetric tenosynovitis or periarthritis is evident, particularly in the dorsal aspect of the fingers, hand, or wrist or in the ankle. If appropriate treatment is delayed, more prominent radiographic findings are encountered, including joint space narrowing, marginal

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and central osseous erosions, lytic destruction of adjacent metaphyses and epiphyses, and periostitis (Fig. 20.5). Differentiating the radiographic features of gonococcal pyarthrosis and reactive arthritis can be extremely difficult.

Escherichia coli and Enterobacter (Aerobacter) aerogenes. Articular and osseous infections with these agents are rare except in intravenous drug abusers, those with preexisting joint disease, and patients with chronic debilitating disorders.

Enteric Gram-­Negative Bacilli

Proteus Infection

Although the terminology related to this group of bacteria is not constant, two major families of microorganisms are identified: Enterobacteriaceae and Pseudomonadaceae. In general, these gram-­negative bacilli are responsible for as many as 25% of skeletal infections.

Proteus mirabilis infection of a joint or bone is rarely observed. Monoarticular involvement of the knee or another joint is typical.

Coliform Bacterial Infection The coliform bacteria are gram-­negative bacilli that normally inhabit the human intestinal tract. The best-­known organisms in this group are

A

Premature infants, children with congenital anomalies, intravenous drug abusers, patients with myeloproliferative disorders or those receiving immunosuppressive agents, and geriatric patients with

B

Fig. 20.1  Staphylococcal osteomyelitis. (A) Radiograph and (B) coronal reformatted CT show a well-­defined lucent lesion surrounded by a sclerotic margin in the metaphysis of a long tubular bone (arrow), findings typical of a Brodie abscess.

A

Pseudomonas Infection

B

Fig. 20.3  Streptococcal osteomyelitis and septic arthritis. In this infant, radiography shows an osteolytic lesion of the metaphysis of the humerus. The proximal epiphysis is not ossified. (Courtesy J. Tomanek, MD, Johnson City, TN.)

C

Fig. 20.2  Brodie abscess. In this young child with knee pain, sagittal T1-weighted ­ (A) and fluid-sensitive ­ (B) and axial fluid-sensitive ­ (C) magnetic resonance imaging shows a well-defined ­ lesion (arrow) involving the posterior aspect of the chondroepiphysis, with equal involvement of the bone and the cartilage. The moderate-sized ­ effusion is a reaction to the lesion rather than evidence of septic arthritis. (Courtesy R. Cheng, MD, Honolulu, HI.)

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331

A

Fig. 20.5  Gonococcal arthritis: knee. Observe the joint space loss, poorly defined marginal and central osseous erosions, and soft tissue swelling. The lack of osteoporosis is impressive. Bone proliferation is evident along the distal medial portion of the femur.

B Fig. 20.4  Meningococcemia with skeletal deformities. This 5-year-­ old-­boy demonstrates the skeletal deformities that can follow meningococcemia with intravascular coagulation. (A) Findings in the knee include metaphyseal sclerosis, epiphyseal irregularity and deformity, subluxation and, in the tibia, a previous fracture. (B) Observe the metaphyseal cupping and irregularity in the phalanges, metacarpal bones, and radii, with amputation of some of the digits. (Courtesy M. Dalinka, MD, Philadelphia, PA.)

debilitating diseases are susceptible to osteomyelitis or septic arthritis from Pseudomonas aeruginosa. Pseudomonas infection commonly localizes in the axial skeleton and affects the spine and the sacroiliac, sternoclavicular, and acromioclavicular joints. Pseudomonas osteomyelitis is a recognized complication of puncture wounds.

and other hemoglobinopathies, as well as leukemia, lymphoma, bartonellosis, cirrhosis of the liver, and systemic lupus erythematosus. It has been postulated that multiple bowel infarcts allow the organisms to leave the colon and enter the bloodstream, and that Salmonella organisms are well suited for survival in areas of medullary bone infarction. In fact, Salmonella osteomyelitis frequently originates in the medullary cavity of a tubular bone. Salmonella infection may be characterized by a symmetric distribution, a combination of lysis and sclerosis, and periostitis, findings that are difficult to differentiate from those of infarction alone.

Shigella Infection At 2 to 3 weeks after an episode of acute bacillary dysentery, a noninfectious polyarthritis showing a predilection for the knees, elbows, wrists, or fingers may be evident.

Yersinia Infection

Rarely, Klebsiella pneumoniae results in osteomyelitis and septic arthritis in a host with diminished resistance. Emphysematous septic arthritis also may be seen.

Two types of bone or joint affliction can occur in association with infection caused by Yersinia enterocolitica. A nonsuppurative, self-­limited polyarthritis, especially of the knees and ankles, can appear approximately 3 weeks after the onset of illness. This articular manifestation may be complicated by sacroiliitis and presence of the human leukocyte antigen (HLA)-­B27. The second type of affliction relates to the presence of Y. enterocolitica septicemia, particularly in patients with underlying abnormalities.

Salmonella Infection

Serratia Infection

Salmonella typhi produces a systemic infection, typhoid fever. Bone infection in such cases is rare. Involvement can occur in spinal locations, with a radiographic picture resembling that of tuberculosis. An association exists between Salmonella infection and sickle cell anemia

Serratia marcescens can cause infection of the musculoskeletal system, especially in persons with underlying disorders such as diabetes mellitus, systemic lupus erythematosus, neutrophil dysfunction syndromes, and rheumatoid arthritis. It can also occur after trauma; placement of

Klebsiella Infection

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intravenous, arterial, or urinary catheters; ischemic necrosis of bone; or intravenous drug abuse.

Other Gram-­Negative Bacilli Haemophilus Infection

Acute septic arthritis caused by Haemophilus influenzae is more frequent in children, particularly those between the ages of 7 months and 4 years, than in adults (Fig. 20.6). In fact, this microorganism appears to be the leading cause of pyarthrosis in the first 2 years of life. Hematogenous spread is the usual mechanism of joint infection. Single or, less commonly, multiple joints may be affected, with the knee and ankle being the most frequent sites of involvement.

Brucella Infection Brucellosis (undulant fever) is endemic in Saudi Arabia, South America, Spain, Italy, and the midwestern United States. Brucella is transmitted to humans from animals such as goats, cows, and hogs through the ingestion of milk or milk products containing viable bacteria, or through skin contact with infected tissues or secretions. The disease is rarely transmitted from one human to another. The invading organisms localize in tissues of the reticuloendothelial system, such as the liver, spleen, lymph nodes, and bone marrow. Involvement of joints, bones, and bursae is relatively uncommon, although an inflammatory process in any one of these sites in a farmer or meat handler should arouse suspicion of brucellosis. The arthritis is usually monoarticular or pauciarticular, with the hip and knee being involved most frequently. Alterations in bursae may be especially characteristic. Osteomyelitis of long, short, or flat bones may be encountered. Brucellar spondylitis, which appears to be the most common form of musculoskeletal disease, typically affects the lumbar spine, and is associated with an acute clinical onset and rapid progression of radiographic findings (Fig. 20.7). Abnormalities include destruction of vertebrae and intervertebral discs, sclerosis, paravertebral abscess formation, and healing with intraosseous fusion and osteophytosis. A large, parrot beak–like osteophyte has been reported as a characteristic feature of spinal brucellosis.

Aeromonas Infection Aeromonas hydrophila is an aerobic gram-­negative rod found in fresh water, tap water, swimming pools, and soil, as well as in the stools of some persons. Although rarely a pathogen, it can cause infection in patients with neoplasm or chronic liver disease. A history of exposure to water in a pool or lake, especially when combined with trauma, is characteristic. Necrotizing lesions can lead to gas formation.

Pasteurella Infection Typical pathogens in animals, Pasteurella organisms can also produce human infection. Cutaneous and subcutaneous abscesses, cellulitis, and lymphangitis are local and regional manifestations of Pasteurella infection and can be followed by septicemia and involvement of distant sites. Localization of infection in the knee is common. Bone and joint contamination in the hand or foot is commonly related to direct inoculation of organisms or spread of infection from involved soft tissues as a result of injury (animal bite or scratch).

Other Bacteria

Clostridial Infection

Wounds that are contaminated by gas gangrene may contain a mixture of clostridial organisms. These organisms are anaerobic and are capable of producing extensive tissue destruction, with gas formation at the site of invasion. Soft tissue contamination with gas gangrene develops in

Fig. 20.6  Haemophilus osteomyelitis and septic arthritis. Osteomyelitis of the proximal metaphysis and diaphysis of the humerus, with glenohumeral joint involvement, developed in this infant secondary to Haemophilus infection. Observe the metaphyseal erosion (arrow), permeative bone destruction, and periostitis (arrowhead).

devitalized tissues in which the arterial blood supply has been compromised. War wounds, vehicular trauma, surgery, burns, and decubitus ulcers are some predisposing factors. Clinical manifestations of clostridial myonecrosis may become evident within 6 to 8 hours of injury and include severe pain and an edematous, pulseless, and gangrenous limb. Crepitation with detection of gas in the soft tissues is apparent in later stages. On radiographs, radiolucent collections may appear within subcutaneous or muscular tissue (Fig. 20.8). In the former location, they produce linear or netlike lucent areas. Gas in muscular tissue may produce circular collections of varying size. It should be emphasized, however, that soft tissue gas is not specific for clostridial infection because it is evident in some cases of infection with E. coli, other coliform bacteria, streptococci, and Bacteroides species. Septic arthritis related to clostridia also occurs. Monoarticular disease, particularly of the knee, is typical. Synovial edema and inflammation and cartilaginous destruction may be evident, perhaps related to the effect of the highly toxic enzymes produced by these bacteria. In addition to joint space narrowing and osseous defects, radiographs may delineate gas in the joint or adjacent tissues.

Bacteroides and Related Anaerobic Infection In comparison to clostridia, which are spore-­forming obligate anaerobic bacteria, Bacteroides and several other anaerobic bacteria are nonspore-­forming obligate anaerobes. Many of these organisms exist as part of the normal microflora on the skin and adjacent mucous membranes, and clinically evident infections result when breaks in the mucosa or skin allow the microflora to become displaced into

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333

A

Fig. 20.8  Clostridial soft tissue infection. Linear collections of gas in subcutaneous and muscular tissue reflect the presence of clostridial myositis and cellulitis.

Mycobacteria

Tuberculous Infection

B Fig. 20.7  Brucellar spondylitis: lumbar spine. (A) Involvement in this case is characterized by irregular destruction of the osseous surfaces of two adjacent vertebrae with reactive sclerosis. Note the parrot beaklike osteophytes. (B) In another patient, findings include disc space loss at two levels (T12–L1, L1–L2) with osteophyte formation. A sagittal T1-­ weighted fat-­ suppressed contrast-­ enhanced magnetic resonance image reveals high signal intensity in the affected vertebral bodies and intervertebral discs, as well as in the anterior soft tissues and intraspinal regions. The spinal cord is displaced and encased by the infection.

deeper tissues and reach the bloodstream. Characteristics of such infections include localization to a site normally inhabited by anaerobic bacteria, traumatic disruption of the skin or mucous membranes, and a history of diabetes mellitus or other chronic debilitating disease. In the musculoskeletal system, crepitant cellulitis, necrotizing fasciitis, and myonecrosis are typical expressions. Septic arthritis, infective spondylitis, and osteomyelitis are rare and may be manifestations of hematogenous dissemination. Gas formation in the soft tissues or, rarely, the articular cavity or intervertebral discs aids in the precise radiographic diagnosis.

The frequency of tuberculosis has changed dramatically since the advent of appropriate chemotherapy for this disease; however, even when pulmonary tuberculosis was common, musculoskeletal involvement was not frequent. Currently, the rate of pulmonary tuberculosis is on the rise, and the frequency of musculoskeletal tuberculosis has also increased. Contributing factors to this increase in tuberculosis cases include a greater number of people who have suppressed immune systems, the development of drug-­ resistant strains of mycobacteria, an aging population, and an increase in the number of healthcare workers exposed to the disease. Further, the use of modern therapeutic techniques, including bacille Calmette-­Guérin (BCG) vaccination, has produced examples of iatrogenic infection (see the discussion later in this chapter). Additionally, the pattern of osteoarticular tuberculosis has changed over the years. Initially, the disease was usually encountered in children and young adults; currently, patients of all ages are affected. Persons with underlying disorders, those receiving corticosteroid medication, alcoholic patients, intravenous drug abusers, persons who harbor human immunodeficiency virus (HIV), and immigrants may be hosts for this disease. Tuberculous spondylitis is the most typical form of the disease, with the spine being involved in 25% to 50% of cases of skeletal tuberculosis. In recent years, however, articular changes in extraspinal sites, such as the hip, knee, wrist, and elbow, have become more prominent. Tuberculous dactylitis, multiple sites of involvement, and tendon sheath abnormalities are also commonly encountered. Clinical abnormalities. Skeletal tuberculosis can affect persons of all ages. Extrapulmonary tuberculosis is more common in children than in adults. The vertebral column, pelvis and hip, and knee are the most frequent sites of involvement. Tuberculous arthritis can lead to pain, swelling, weakness, muscle wasting, a draining sinus, and other manifestations. Tuberculous spondylitis first manifests clinically as an insidious onset of back pain, stiffness, local tenderness, and possibly fever. Tuberculous dactylitis usually appears as painless swelling of the hand or foot. Tuberculous tenosynovitis and bursitis can produce soft

334

SECTION 3  Infectious Disorders

tissue swelling and tenderness in the ulnar or radial bursa, fingers, and toes. A positive skin test for tuberculosis is of little help in diagnosing this disease (older patients who have never exhibited any clinical manifestations of tuberculosis have a high frequency of positive skin tests), although a negative skin test usually (but not invariably) excludes the diagnosis. A negative chest radiograph in an adult patient does not exclude the possibility of skeletal tuberculosis. In a child, such a radiograph makes tuberculosis an unlikely cause of bony abnormalities. Pathogenesis. It is generally accepted that skeletal involvement in tuberculosis occurs mainly by the hematogenous route. Hematogenous seeding of the skeleton may arise from a primary infection of the lung, particularly in children, or, at a later date, from a quiescent primary site or an extraosseous focus. Pulmonary involvement may be evident in 50% of cases, is more frequent in children, and on radiographs, may appear either active or inactive. Urogenital lesions may coexist with skeletal involvement in 20% to 45% of cases. General pathologic considerations. The typical response of tissue is the formation of tubercles that are sharply demarcated from surrounding tissue. Around a central zone are clusters of epithelioid cells. In the central part of the tubercle are multinucleated giant cells, whereas at the periphery of the tubercle is a mantle of lymphocytes. Central caseating necrosis is characteristic of these tubercles. It should be emphasized that granulomatous disease, including that of the bone marrow, is a nonspecific response to a persistent antigenic stimulus and has been identified in a wide range of illnesses (Table 20.1). Tuberculous spondylitis. The vertebral column is affected in 25% to 60% of cases of skeletal tuberculosis. The first lumbar vertebra is most commonly affected, and the frequency of involvement decreases equally as one proceeds in either direction from this level. Tuberculous infection of the upper cervical and sacroiliac joint is not rare. More than one vertebra is typically affected, and the vertebral body is involved more commonly than the posterior elements (Fig. 20.9). In the vertebral body, an anterior predilection is striking. Tuberculous spondylitis is generally thought to result from hematogenous spread of infection, related to either the arterial route or the paravertebral venous plexus of Batson. Radiographic-­pathologic correlation. In most cases, tuberculous spondylitis begins as an infectious focus in the anterior aspect of the vertebral body adjacent to the subchondral bone plate (Fig. 20.10). Infection may spread to the adjacent intervertebral discs. Such spread may occur if the bacilli extend beneath the anterior or posterior longitudinal ligament to violate the peripheral disc tissue; if the organisms penetrate the subchondral bone plate and overlying cartilaginous endplate to enter the intervertebral disc; or if an intraosseous lesion weakens the vertebral body to such a degree that it produces disc displacement (cartilaginous node), contamination of invading disc tissue, and subsequent spread through the defect into the intervertebral disc. The combination of vertebral body and disc destruction in tuberculosis is similar to that occurring in pyogenic spondylitis, although the tuberculous process is not usually rapidly progressive (Fig. 20.11). Only rarely does vertebral body tuberculosis extend into the pedicles, laminae, or transverse or spinous processes. Paraspinal extension. Extension of tuberculosis from vertebral and disc sites to the adjacent ligaments and soft tissue is frequent. Subligamentous extension of a tuberculous abscess can allow osseous and disc invasion at distant sites (Fig. 20.12). Burrowing abscesses can extend for extraordinary distances before perforating an internal viscus or the body surface. Abscess formation in tuberculosis can produce soft tissue swelling on radiographs that appears out of proportion to the degree of osseous and disc destruction. Psoas abscesses are usually easy

TABLE 20.1  Diseases Associated With Bone

Marrow Granuloma Infectious Diseases

Bacterial infection and exposures Mycobacterial disease Tuberculosis Bacille Calmette-Guérin vaccination Leprosy Brucellosis Tularemia Glanders Fungal infection (disseminated) Histoplasmosis Cryptococcosis Paracoccidioidomycosis Saccharomyces cerevisiae infection Viral infection Infectious mononuclesosis Cytomegalovirus infection Viral hepatitis Parasitic infection Toxoplasmosis Leishmaniasis Other Rocky Mountain spotted fever Q fever Mycoplasma pneumoniae infection Malignant Diseases Hodgkin disease Non-­Hodgkin lymphoma Metastatic carcinoma Acute lymphocytic leukemia Drugs Chlorpropamide Phenylbutazone (oxyphenbutazone) Allopurinol Procainamide Ibuprofen Phenytoin Autoimmune or Allergic Diseases Rheumatoid arthritis (Felty syndrome) Systemic lupus erythematosus Primary biliary cirrhosis Farmer’s lung Miscellaneous Syndrome of marrow and lymph node granuloma, uveitis, and reversible renal failure Berylliosis Sarcoidosis From Bodem CR, Hamory BH, Taylor HM, et al: Granulomatous bone marrow disease: A review of the literature and clinicopathologic analysis of 58 cases. Medicine (Baltimore). 1983;62:372.

to identify and may contain calcification (Fig. 20.13); nontuberculous psoas abscesses rarely calcify. Psoas abscess formation can complicate 5% of cases of tuberculous spondylitis. Magnetic resonance (MR) imaging of tuberculous spondylitis, in common with computed

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

4

1

5

2

3

Fig. 20.9  Tuberculous spondylitis: sites of involvement. Tuberculous lesions can localize in the vertebral body (1) or, more rarely, the posterior osseous or ligamentous structures (2). Extension to the intervertebral disc (3) or prevertebral tissues (4) is not infrequent. Subligamentous spread (5) can lead to erosion of the anterior vertebral surface.

Fig. 20.10  Tuberculous spondylitis: discovertebral lesion. Radiograph reveals subchondral destruction of two vertebral bodies, with mild surrounding eburnation and loss of intervertebral disc height. The appearance is identical to that in pyogenic spondylitis.

tomography (CT), provides an accurate display of paraspinal and intraspinal extension of disease, as well as the extent of bone and disc involvement. Posterior element lesions. Occasionally, the posterior elements may be the initial spinal site of tuberculosis. In these instances, radiographic findings include pediculate or laminal destruction,

335

erosion of the posterior cortex of the vertebral body and adjacent ribs, a large paraspinal mass, and relative sparing of the intervertebral discs. Solitary vertebral involvement. Rarely, tuberculosis leads to isolated involvement of a single vertebral body. In children or adults, vertebra plana can appear and simulate eosinophilic granuloma. Kyphosis, scoliosis, and ankylosis. Collapse of partially destroyed vertebral bodies during the course of tuberculous spondylitis can lead to severe tuberculous kyphosis or a gibbus deformity. Despite the striking nature of the deformity, the diameter of the spinal canal may not be significantly altered (Fig. 20.14). Healing in tuberculous spondylitis can be associated with osseous fusion of the vertebral bodies. Atlantoaxial destruction. Involvement of the upper cervical spine is rare, occurring in less than 2% of cases of tuberculous spondylitis. Quadriparesis may be observed in as many as 40% of patients with cervical tuberculosis. Radiographic abnormalities include occipitoatlantoaxial subluxation, bone erosion, and a prevertebral soft tissue mass. Tuberculous osteomyelitis. Tuberculous osteomyelitis is relatively infrequent and is almost uniformly related to hematogenous dissemination. Most often, it arises from septic arthritis. Virtually any bone can be affected, including the pelvis, phalanges and metacarpals (tuberculous dactylitis), and long bones. In the long tubular bones, tuberculosis usually originates in one of the epiphyses and soon spreads into the neighboring joint (Fig. 20.15). This feature deserves emphasis because pyogenic infections arising in the metaphyseal segment of a child’s tubular bone generally do not extend across the physis, and detection of a transphyseal spread of infection favors the diagnosis of a granulomatous infectious process. Cystic tuberculosis. A rare variety of tuberculosis is associated with disseminated lesions. Cystic lesions of one or multiple bones are encountered much more frequently in children than in adults (Fig. 20.16). In children, these lesions usually but not invariably affect the peripheral skeleton, favor the metaphyseal regions of tubular bones, may be symmetric, are of variable size, and are generally unaccompanied by sclerosis. The prognosis in this variety of tuberculosis is good. The radiographic characteristics of cystic tuberculosis resemble those of eosinophilic granuloma, sarcoidosis, cystic angiomatosis, plasma cell myeloma, fungal infection, metastasis, and other conditions. Tuberculous dactylitis. Tuberculous involvement of the short tubular bones of the hands and feet is termed tuberculous dactylitis. It is especially frequent in young children, uncommon after the age of 5 years, and rare after the age of 10 years. Although involvement of one bone of the hand or foot is common, multiple osseous foci can be identified in 25% to 35% of cases and are especially characteristic of childhood dactylitis. Soft tissue swelling is usually the initial manifestation. Mild or exuberant periostitis of the phalanges, metacarpals, or metatarsals may be evident (Fig. 20.17). Cystlike expansion of the bone is termed spina ventosa. Tuberculous arthritis. Tuberculous arthritis typically affects large joints such as the knee and hip, although any articular site can be involved. Monoarticular disease is the rule. Most joint lesions occur secondary to adjacent osteomyelitis. Most patients are middle-­aged or elderly, and many have underlying disorders or have received intraarticular injections of steroids. Tuberculous joint disease may persist and cause chronic pain and only minimal signs of inflammation. Delay in diagnosis is frequent, and correct diagnosis requires the use of synovial fluid and tissue for culture and histologic studies. A triad of radiographic findings (Phemister triad) is characteristic of tuberculous arthritis: juxtaarticular osteoporosis, peripherally located osseous erosions, and gradual narrowing of the interosseous

336

SECTION 3  Infectious Disorders

A

B

Fig. 20.11  Tuberculous spondylitis: discovertebral lesion. (A) Sagittal fluid-­sensitive magnetic resonance image shows disc space narrowing with fluid signal extending into the adjacent vertebral body (arrow). (B) In a different patient, sagittal fluid-­sensitive magnetic resonance image shows disc destruction and involvement of the adjacent vertebral bodies with focal kyphosis (arrow).

Fig. 20.12  Tuberculous spondylitis: subligamentous extension. The findings, though subtle, include erosion of the anterior surface of the vertebral bodies (arrows). (Courtesy C. Resnik, MD, Baltimore, MD.)

space (Fig. 20.18). Marginal erosions are especially characteristic of tuberculosis in “tight” or weight-­bearing articulations such as the hip, knee, and ankle. They produce corner defects simulating the erosions

of other synovial processes, such as rheumatoid arthritis. The combination of regional osteoporosis, marginal erosions, and relative preservation of joint space is highly suggestive of tuberculous arthritis. In rheumatoid arthritis, early loss of articular space is more typical. The eventual result in tuberculous arthritis is usually fibrous ankylosis of the joint. Bony ankylosis is occasionally seen, but this sequela is more frequent in pyogenic arthritis. The diagnosis of tuberculous arthritis is not difficult when classic radiographic features appear in typical locations, such as the knee, hip, wrist, or elbow. The appearance of periarticular osteoporosis, marginal erosions, and absent or mild joint space narrowing is most helpful in the accurate diagnosis of this disease (Table 20.2). In rheumatoid arthritis, osteoporosis and marginal erosions are accompanied by early and significant loss of articular space. In gout, osteoporosis is mild or absent, although marginal erosions and preservation of interosseous space can be observed. Tuberculous bursitis and tenosynovitis. The synovial membrane of bursae and tendon sheaths and the tendons themselves may be involved in tuberculosis. Typical sites include the radial and ulnar bursae of the hand (Fig. 20.19), the flexor tendon sheaths of the fingers, the bursae about the ischial tuberosities, and the subacromial-subdeltoid and subgluteal bursae. Rarely, other tendon sheaths are affected. Osseous destruction can be encountered in the region of the greater trochanter, and the hip joint may become infected secondarily. In any bursal location, dystrophic calcification may appear, a finding that is especially characteristic about the hip and elbow. BCG vaccination–induced infection. BCG is a vaccine of an attenuated bovine tubercle bacillus that has been used for immunization against tuberculosis. Although complications are unusual, generalized

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

337

B

A Fig. 20.13  Tuberculous spondylitis: psoas abscess. (A) Large, noncalcified left psoas abscess is seen (arrows). (B) Diffusely calcified psoas abscesses are noted in association with spinal abnormalities.

Fig. 20.14  Tuberculous spondylitis: kyphosis. Severe thoracolumbar kyphosis, associated with calcification and an increased superoinferior dimension of a lumbar vertebral body, is evident. (Courtesy T. Yochum, DC, Denver, CO.)

BCG infection and bone and joint infection have been identified after vaccination. The former complication is almost invariably fatal and is especially common in patients with immunologic deficiency. The latter complication results from hematogenous spread of BCG infection to the skeleton, is not usually associated with immunologic disorders, and has a favorable prognosis. The interval between the time of vaccination and the diagnosis of osteomyelitis is widely variable but is commonly within 6 to 12 months after vaccination. BCG osteomyelitis involves boys and girls between the ages of 5 months and 6 years. It usually affects the metaphyses and the epiphyses of the tubular bones. Lesions in tubular bones are more frequent on the side of the body where the vaccine was given. Solitary lesions

Fig. 20.15  Tuberculous osteomyelitis: tubular bones. Transphyseal spread of a metaphyseal lesion into the epiphysis is evident.

predominate and are characterized by well-­defined lytic foci, with only minor degrees of sclerosis or periostitis.

Atypical Mycobacterial Infection Acid-­fast bacteria that are morphologically similar to tubercle bacilli are commonly associated with skin and pulmonary disease, although they can be associated with bone and joint alterations as well. Mycobacterial osteomyelitis and arthritis can complicate connective tissue disorders and may be evident in patients with impaired resistance,

338

SECTION 3  Infectious Disorders

A

B

Fig. 20.16  Cystic tuberculosis. (A) Note the well-­defined lytic lesions of the medullary and cortical areas of the metaphysis and diaphysis of the humerus. The proximal epiphysis is also affected. Sclerosis is absent, although periostitis can be seen. (B) Similar lesions are present in the tibia and fibula. Some of these lesions are central, whereas others are eccentric or peripheral.

those who have received renal transplants, patients with acquired immunodeficiency syndrome (AIDS), or those receiving corticosteroids. They may also occur in an otherwise normal host. Mechanisms of the musculoskeletal alterations include hematogenous spread and contamination after injury or surgery. Radiographic characteristics include the following: multiple lesions predominate over solitary lesions, the metaphyses and diaphyses of long bones are commonly affected, discrete lytic areas may contain sclerotic margins, osteoporosis may not be as striking as in tuberculous infection, a tendency for the development of abscesses and sinus tracts is present, and articular disease can simulate tuberculosis or rheumatoid arthritis (Fig. 20.20). Accurate diagnosis remains difficult, although clinical findings such as tenosynovitis and carpal tunnel syndrome are characteristic. Information regarding a specific occupational history or recreational activities is important. For example, gardening may allow the introduction of Mycobacterium terrae organisms, which can be found in soil and vegetables. People working in the fishing industry or aquarium workers may acquire infections from Mycobacterium marinum, because these organisms grow in fresh or salt water.

Leprosy (Hansen Disease) Leprosy is an infectious disease caused by Mycobacterium leprae. Despite its infrequent occurrence in the United States, it is not uncommon in areas of Africa, South America, and Asia. Leprosy is characterized by a lengthy incubation period and a chronic course, with involvement of the skin, mucous membranes, and peripheral nervous system. Involvement of peripheral nerves is especially characteristic. The lesions of leprosy have been divided into four principal types,

according to their microscopic appearance: lepromatous, tuberculoid, dimorphous, and indeterminate. The clinical manifestations vary among these types. Clinical abnormalities. Organisms enter the body through the skin or mucous membranes, especially the nasal mucosa, and are disseminated by the bloodstream and the lymphatics and localize in the skin, the nerves, and, in advanced cases, many of the viscera. The incubation period has been estimated to be 3 to 6 years. The disease may begin at any age, although leprosy commonly manifests before 20 years of age. Prodromal symptoms and signs include malaise, fever, drowsiness, rhinitis, and profuse sweating. Lymphadenopathy is seen in all types of leprosy, although it is most striking in the lepromatous variety. Laboratory abnormalities may include a positive lepromin skin test (in tuberculoid leprosy), an elevated erythrocyte sedimentation rate, and a positive serologic test for syphilis (20% to 40% of cases). The diagnosis is established by demonstration of the bacilli in typical histologic lesions. Musculoskeletal abnormalities. Musculoskeletal abnormalities include (1) those directly related to the presence of the bacilli, in which granulomatous lesions appear in the osseous tissue, and (2) those that involve the skeleton indirectly as a result of neural abnormalities. Leprous periostitis, osteitis, and osteomyelitis. The frequency of direct involvement of the skeleton in leprosy is low and varies from 3% to 5% in hospitalized patients. The changes are usually confined to the small bones of the face, the hands, and the feet. In these cases, osseous involvement is usually due to extension of the infection from overlying dermal or mucosal areas; initially, the periosteum is contaminated (leprous periostitis) and subsequently, the subjacent cortex, spongiosa, and marrow (leprous osteitis and osteomyelitis) become involved (Fig. 20.21). Less commonly, hematogenous spread of infection to bone can occur. In the face, nasal destruction is most characteristic. Destruction of the alveolar process and anterior nasal spine of the maxilla appears to be related to direct lepromatous contamination of the bone, as well as secondary infection. In the tubular bones, symmetric periostitis of the tibia, fibula, and distal portion of the ulna may be noted. Intractable pain and tenderness may develop. The constellation of erythematous skin lesions, pain, and periostitis involving the lower extremity has been called “red leg.” Neuropathic musculoskeletal lesions. The skeletal abnormalities occurring on a neurologic basis are much more frequent and severe than those produced by direct leprous infiltration of bone. These changes may be evident in 20% to 70% of hospitalized patients. They result from denervation and produce sensory or motor impairment, or both. Repeated injuries and secondary infections subsequently lead to considerable osseous and articular destruction. The bones of the hands, wrists, ankles, and feet are especially susceptible. Denervation can be associated with the absorption of cancellous bone and the development of concentric bone atrophy. The result is a tapered appearance of the end of the bone, termed the “licked candy stick” (Fig. 20.22). In the foot, progressive resorption of the metatarsals and proximal phalanges occurs. In the hand and the foot, distal phalangeal resorption is also encountered. Although all insensitive digits can be altered, the index and long fingers are usually the first affected. Tarsal disintegration alone or in combination with ankle involvement is not infrequent and is attributable to sensory and motor dysfunction, trauma, and secondary infection. The radiographic appearance of neuropathic osteoarthropathy in leprosy resembles that in syphilis, diabetes mellitus, congenital insensitivity to pain, and syringomyelia. Secondary infection. Ulceration followed by secondary infection and pyogenic osteomyelitis is common in anesthetic feet. Differentiating the effects of pyogenic osteomyelitis and arthritis from

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

A

B

Fig. 20.17  Tuberculous dactylitis. In this young man with finger swelling, frontal (A) and lateral (B) radiographs show centrally located and trabeculated osteolytic lesions in the proximal phalanges of the second and fourth digits, with endosteal erosion, cortical penetration, especially along the volar and medial aspects in the fourth finger (arrow), and soft tissue swelling. Biopsy confirmed tuberculous infection.

A

B Fig. 20.18  Tuberculous arthritis. (A) Knee. On a conventional tomogram, typical marginal and central osseous erosions (arrows) accompany tuberculous arthritis. Osteoporosis is not prominent. (B) Hip. In a different patient, osseous erosions on both sides of the joint, diffuse loss of interosseous space, and osteoporosis are evident. (B, Courtesy J. Kaye, MD, Nashville, TN.)

339

340

SECTION 3  Infectious Disorders

TABLE 20.2  Comparison of Tuberculous

and Pyogenic Arthritis

Tuberculous Arthritis

Pyogenic Arthritis

Soft tissue swelling

+

+

Osteoporosis

+

±

Joint space loss

Late

Early

Marginal erosions

+

+

Bony proliferation ± (sclerosis, periostitis)

+

Bony ankylosis

±

+

Slow progression

+

–

+, Common; ±, infrequent; –, rare or absent.

Fig. 20.20  Atypical mycobacterial infection: septic arthritis caused by Mycobacterium avium. Radiograph shows cystic areas in the ulna, radius, scaphoid, triquetrum, and pisiform bones. The joint spaces are preserved. Synovial biopsy indicated hypertrophy of the synovial membrane with chronic granulomatous inflammation. M. avium was recovered from the tissue. (Courtesy J. Scavulli, MD, San Diego, CA.)

Fig. 20.19  Tuberculous bursitis: ulnar bursa. Fluid-­sensitive coronal MR image shows a distended ulnar bursa containing fluid and foci of low signal (arrows), the latter representing early rice body formation. (Courtesy of V. Vaghela, Gujarat, India)

leprous osteomyelitis or neuropathic osteoarthropathy is extremely difficult. Soft tissue calcification and neoplasm. Rarely, linear calcification of involved nerves can be seen on radiographs (Fig. 20.23). Similarly, abscess formation within the nerve, especially the ulnar nerve, can be associated with calcification. Leprosy with cutaneous ulcerations may be complicated by the development of secondary neoplasia, specifically, squamous cell carcinoma of the skin.

Spirochetes and Related Organisms Syphilis

Syphilis is a chronic systemic infectious disease caused by Treponema pallidum, a slender spirochete. Syphilis is transmitted by direct and intimate contact with moist infectious lesions of the skin and mucous membranes. Infection is usually spread during sexual contact.

Fig. 20.21  Leprous tenosynovitis, periostitis, osteitis, and osteomyelitis. Contamination of the soft tissues, tendon sheath, tendon, and phalanges occurred secondary to skin involvement.

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

A

341

B Fig. 20.22  Leprosy: neuropathic lesions. (A) Examples of concentric bone atrophy in the foot illustrate the tapered osseous surfaces (arrows) and phalangeal osteolysis. (B) Fragmentation and collapse of the talar, tibial, and calcaneal surfaces can be seen. The appearance is similar to that in tabes dorsalis. (A, Courtesy W. Coleman, MD, Carville, LA.)

Fig. 20.23  Leprosy: calcification of nerves. The linear radiodense regions (arrows) represent calcification of nerves. This finding, though rare, suggests the diagnosis of leprosy but must be distinguished from vascular calcification. (Courtesy M. Dalinka, MD, Philadelphia, PA.)

Children may acquire the disease by sharing a bed with an infected person. Such cases are termed acquired syphilis. In addition, the fetus may be infected by transmission of the organism through the placenta, termed congenital syphilis.

Approximately 3 to 6 weeks after the organism has entered the body, a primary lesion, called a chancre, develops at the site of inoculation. This skin ulceration heals spontaneously. About 6 weeks later, a generalized skin eruption known as secondary syphilis develops. After healing of both primary and secondary manifestations, the patient may be without symptoms and signs for a protracted period—a stage termed latent syphilis—although progressive inflammatory alterations may be slowly occurring in many of the organ systems. Cardiovascular syphilis or neurosyphilis may manifest 10 to 30 years later; however, tertiary manifestations of syphilis never develop in approximately 50% of cases. In patients with significant later alterations, large destructive lesions, or gummas, may be evident in almost any organ of the body, particularly the skin and the bones. Congenital Syphilis. The disorder originates from transplacental migration of the treponema and invasion of the perichondrium, periosteum, cartilage, bone marrow, and sites of active endochondral ossification, especially in the metaphyseal regions of tubular bones. The spirochetes inhibit osteogenesis. A fetus that is heavily infiltrated with spirochetes may be aborted or die shortly after birth. Others survive and develop the stigmata of congenital syphilis. Approximately 75% of cases of congenital syphilis are diagnosed in children older than 10 years. Such children may have the hutchinsonian triad, which consists of Hutchinson teeth, interstitial keratitis, and nerve deafness. Additional manifestations include fissuring about the mouth and anus (rhagades), anterior bowing of the lower part of the leg (saber shin), collapse of the nasal bones (saddle nose), and perforation of the palate. Early osseous lesions. In fetuses, neonates, and very young infants, bony abnormalities include osteochondritis, diaphyseal osteomyelitis (osteitis), periostitis, and miscellaneous changes. Syphilitic osteochondritis usually results in symmetric involvement of sites of endochondral ossification. The epiphyseal-­ metaphyseal junction of tubular bones, the costochondral regions, and, in severe

342

SECTION 3  Infectious Disorders

cases, the flat and short tubular bones and the centers of ossification of the sternum and vertebrae are affected. In the growing metaphyses of the long bones, particularly about the knee, widening of the provisional calcification zone, serrations, and adjacent osseous irregularity are seen, which on histologic evaluation are found to result from a disturbance in endochondral ossification. Radiographs outline broad, horizontal radiolucent bands reminiscent of those identified in leukemia or metastasis from neuroblastoma. If the process continues, metaphyseal irregularities appear (Fig. 20.24). Epiphyseal separation may result. The medial surface of the proximal tibial shaft is a particularly characteristic site of erosion, a finding termed the Wimberger sign. The lesions of osteochondritis generally heal within 2 weeks, a process that is often complete within 2 months. Diaphyseal osteomyelitis (osteitis) can appear in infants with congenital syphilis who have not received therapy or in whom treatment has been inadequate. Granulation tissue in the metaphysis may extend into the diaphysis and induce infective foci of variable size (Fig. 20.25). Osteolytic lesions with surrounding bony eburnation and overlying periostitis may be seen on radiographs of involved tubular bones. Late osseous lesions. The early manifestations of congenital syphilis generally regress or disappear in the first few years of life, even in the absence of adequate therapy. Exacerbation of disease may appear in a young child or adolescent (5 to 20 years of age), however. Although the evolving skeletal lesions that occur late in the course of congenital syphilis may rarely resemble those of early congenital syphilis (osteochondritis, osteomyelitis, periostitis), they more typically resemble the changes observed in acquired syphilis (see later discussion). Osteomyelitis and periostitis can involve the tubular bones, the flat bones, and even the cranium.

A

Gummatous or nongummatous osteomyelitis or periostitis results in diffuse hyperostosis of the involved bone. Endosteal bony proliferation produces encroachment on the medullary cavity, whereas periosteal bony proliferation creates an enlarged, undulating, and dense osseous contour. In the tibia, a typical saber shin may be encountered, with anterior bending of the bone. Its radiographic appearance may resemble that of Paget disease, although the syphilitic hyperostosis may not extend to the epiphysis (Fig. 20.26). Lucent defects within areas of hyperostosis may represent gummas. Abnormalities of the skull and mandible include destruction of the nasal bones, calvarial gumma, and Hutchinson teeth (characterized by peg-­shaped, notched, and hypoplastic dental structures). Bilateral painless effusions, especially of the knee, have been termed Clutton joints. Acquired syphilis. The osseus and articular manifestations of acquired syphilis usually appear in the latent or tertiary phase of the disease. The frequency of osseous lesions varies from rare to as high as 8% to 20%. Early acquired syphilis. Spirochetemia appearing 1 to 3 months after documentation of a primary lesion can lead to dissemination of organisms throughout the body. The spirochetes can reach the bone, with development of osteochondritis, periostitis, osteitis, or osteomyelitis. Proliferative periostitis is the most common osseous lesion in early acquired syphilis. It may be especially prominent in the tibia, skull, ribs, and sternum, although other bones, such as the clavicle, femur, fibula, and osseous structures of the hand and foot, also can be affected. Destructive bone lesions occur much less commonly than periostitis in early syphilis. These lesions are attributable to osteomyelitis and infective osteitis (as well as septic arthritis) (Fig. 20.27). Involvement of the skull is particularly characteristic.

B Fig. 20.24  Congenital syphilis: osteochondritis. (A) In this 3-week-old ­ ­ infant, the lucent band in the metaphysis (arrow) is caused by a disturbance in endochondral ossification. The appearance is similar to that in leukemia or neuroblastoma. (B) In another infant with syphilis, a “celery stalk” appearance, with alternating longitudinal lucent and sclerotic bands caused by an abnormality in endochondral ossification, resembles the changes seen in rubella. (B, Courtesy of D. Edwards, MD, San Diego, Calif.)

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343

Late acquired syphilis. Osseous lesions occurring during the later stages of acquired syphilis can be related to gummatous or nongummatous inflammation. A gumma is a discrete or confluent area of variable size that contains caseous necrotic material, although the organisms themselves are not usually demonstrable within the lesions. The radiographic features are characterized by lytic and sclerotic areas of bone. Involvement of the cranial vault, nasal bones, maxilla, mandible, tubular bones of the appendicular skeleton, spine, and pelvis has been noted (Fig. 20.28). The degree of periosteal proliferation can become extreme and, in tubular bones, can lead to gross enlargement of osseous tissue. The resultant radiographic and pathologic features resemble those in the late stages of congenital syphilis, including the saber shin deformity. Articular involvement. The frequency of articular involvement in syphilis is low. In congenital syphilis, articular changes predominate in the late phases of the disorder; in acquired syphilis, joint manifestations appear in the tertiary or, less frequently, the secondary stage. Joint effusions associated with pain and tenderness, which may be infectious or noninfectious in origin, are commonly bilateral and most typically affect the knee. Infectious syphilitic arthritis can occur in any axial or extraaxial site. On radiographs, osteoporosis, joint space narrowing, bony destruction, sclerosis, and intraarticular osseous fusion may be seen, findings similar to those occurring in other infectious arthritides. Fig. 20.25  Congenital syphilis: osteochondritis and osteomyelitis. Note tibial erosion with periostitis (arrows). The predilection for the medial tibial metaphysis is noteworthy.

A

B

Yaws Yaws is an infectious disorder caused by Treponema pertenue. Yaws occurs in tropical climates and is prevalent in Africa, South America,

C

Fig. 20.26  Congenital syphilis: late osseous changes. (A) Observe the radiolucent foci within the anterior cortex of the tibia (arrows), along with periostitis and endosteal proliferation. (B) In a different patient, more exuberant hyperostosis of both the tibia and the fibula has resulted in bowed and prominent osseous surfaces. The changes are somewhat reminiscent of those in Paget disease. (C) A typical saber shin deformity of the tibia is associated with anterior bowing of the bone. The fibula is also involved.

344

SECTION 3  Infectious Disorders

B

A

Fig. 20.27  Acquired syphilis: osteitis, osteomyelitis, and periostitis. (A) Lytic lesions of the frontal region of the skull (arrows) are accompanied by reactive sclerosis. (B) Note the osteolysis of the metatarsal bone and proximal phalanx, associated with soft tissue swelling, periostitis, pathologic fracture, and articular involvement.

A

B

C

Fig. 20.28  Acquired syphilis: osteitis, osteomyelitis, and periostitis. In this 32-­year-­old man with hand pain and a rash, a posteroanterior radiograph (A) reveals osteolysis of the distal aspect of the second metacarpal bone with periostitis (arrow). Coronal T1-­weighted (B) and fluid-­sensitive (C) MR images reveal features indicative of osteomyelitis, infective periostitis and osteitis, and soft tissue edema (arrow). The changes in the second metacarpophalangeal joint are consistent with septic arthritis as well. A skin biopsy and laboratory tests confirmed the diagnosis of syphilis.

the South Pacific islands, and the West Indies. It is generally acquired before puberty during contact with open lesions containing the spirochetes. Transmission of the disease is rarely associated with sexual contact. Within a period of weeks after inoculation, a granulomatous primary lesion appears, referred to as the mother yaw. Approximately 1 to 3 months later, a generalized papular skin eruption occurs on the extremities, buttocks, neck, and face. Involvement of the soles, called

crab yaws, may make walking painful. After several years, destructive lesions may become evident in cutaneous and osseous tissue. The tubular bones of the extremities, including those of the hands and feet, the pelvis, the skull, and the facial bones, may become the sites of periostitis or osteitis. Lucent lesions in the cortex or spongiosa are accompanied by florid periosteal bone formation (Fig. 20.29). Saber shin deformities (as in syphilis), dactylitis, and nasal destruction may

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

Fig. 20.29  Yaws. Dactylitis is characterized by lytic lesions surrounded by florid periosteal proliferation. Note the enlarged and sclerotic osseous contours. (Courtesy W. P. Cockshott, MD, Hamilton, Ontario, Canada.)

be encountered. Destructive changes in the fingers and toes can resemble leprosy or psoriatic arthritis. In yaws, however, the distal phalanges are usually spared. The radiographic changes in the skeleton in patients with yaws are similar to those of syphilis.

Tropical Ulcer Tropical ulcers are seen in patients of all ages from Central and East Africa. The initial lesions are painful, tense swellings with a serosanguineous discharge that appear on the anterolateral aspect of the distal portions of the lower limbs and spread rapidly. Because the ulcer erodes muscles and tendons, it may reach the underlying bone. The favorite target area is the middle third of the tibia; fibular involvement is less frequent and, when present, is most common in the distal third of the shaft. Periostitis leads to broad-­based excrescences resembling osteomas (Fig. 20.30). Approximately 25% of cases show malignant degeneration leading to epidermoid carcinomas. The cause of tropical ulcer appears to be multifactorial. Trauma is common, and cultures of the lesion frequently isolate Vincent types of fusiform bacilli and spirochetes.

Lyme Disease First observed in 1975, Lyme disease is an inflammatory articular condition named for the Connecticut town where it was initially encountered. In the United States, most cases of Lyme disease have occurred in the Northeast, upper Midwest, and far West. Both children and adults are affected. Clinical manifestations generally appear within 7 days of a tick bite. The illness characteristically begins in the summer in the form of a distinctive skin lesion, erythema chronicum migrans, in the area of a previous tick bite. Approximately 2 to 6 months later, joint manifestations appear and are characterized by a monoarticular, oligoarticular, or polyarticular process that is sudden in onset, short in duration, and

A

345

B

Fig. 20.30  Tropical ulcer. (A) The anterior surface of the tibia reveals a broad-­based excrescence and an ivory osteoma. The bone is bowed, and the thickened trabeculae in the medullary bone indicate a response to altered stress. (B) In a different patient, malignant degeneration at the site of skin ulceration has led to destruction of the underlying bone. Note the irregularity of the involved soft tissues. (Courtesy S. Bohrer, MD, Winston-­Salem, NC.)

associated with recurrence and, sometimes, migration from one location to another. Sites of involvement, in order of decreasing frequency, are the knee, shoulder, and elbow. The radiographic characteristics of joint involvement are soft tissue swelling and effusions. Juxtaarticular osteoporosis, cartilage loss, and marginal bone erosions may appear (Fig. 20.31). MR imaging will demonstrate a joint effusion, synovitis, and periarticular soft tissue edema (Fig. 20.32). Lyme disease is transmitted by Ixodes dammini or related ixodid ticks and is caused by a spirochete. The clinical and radiographic features of Lyme disease resemble those of juvenile idiopathic arthritis.

FUNGAL AND HIGHER BACTERIAL INFECTION A variety of pathogenic fungi can produce human disease. Although healthy persons may become hosts for fungal diseases, these pathogens become more virulent in persons with depressed immunologic function in whom widespread and sometimes fatal abnormalities may occur.

Actinomycosis Actinomycosis is a noncontagious, suppurative infection caused by anaerobic organisms that are normally found in the mouth. These organisms are higher bacteria that resemble mycobacteria and are frequently misclassified as fungi. The infections are especially frequent in the face and neck, which is probably explained by the prevalence of these organisms within the oral and nasal cavities. Trauma is important

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SECTION 3  Infectious Disorders

in the introduction of organisms into tissues. From infective foci in the face, lung, or bowel, hematogenous dissemination of organisms can lead to contamination of subcutaneous tissue, liver, spleen, kidneys, brain, bones, and joints. Typically, the skeleton becomes contaminated from an adjacent infected soft tissue focus; less commonly, hematogenous seeding of osseous or articular tissue occurs. The mandible, the flat bones of the axial skeleton (pelvis, ribs, spine), and the major joints of the appendicular skeleton are most commonly affected. Mandibular and maxillary bone involvement may follow trauma or extraction of a tooth. Osseous involvement is characterized by a combination of lysis and sclerosis (Fig. 20.33). In the ribs, the degree of bony proliferation may be extensive, and the combination of severe osseous eburnation, cutaneous sinus tracts, and pleuritis is suggestive of actinomycosis. In the vertebral column, infection can originate from adjacent mediastinal or

retroperitoneal foci. Several vertebrae are commonly affected, and the intervening intervertebral discs may be spared. Paravertebral abscesses may appear, but they are usually smaller than the abscesses in tuberculosis and do not calcify.

Cryptococcosis (Torulosis) Cryptococcosis, a serious disease of worldwide distribution, is caused by Cryptococcus neoformans, an organism that demonstrates an unusual predilection for the central nervous system. The disease is generally acquired by the respiratory route through the inhalation of aerosolized spores. Once they reach the body and proliferate, cryptococci can be detected in the brain, meninges, lungs, other viscera, and bones and joints. Neurologic manifestations predominate, and many patients die within a few months. Cryptococcus infection may be seen in association with leukemia, lymphoma, Hodgkin disease, sarcoidosis, tuberculosis, and diabetes mellitus, as well as in persons with AIDS, those receiving steroid medications, and those who have undergone renal transplantation. Osseous involvement is a manifestation of disseminated cryptococcosis and appears in 5% to 10% of such cases. Adults are affected far more frequently than children. The most commonly involved skeletal sites are the spine, pelvis, ribs, skull, tibia, and bones about the knees, in descending order of frequency. Bony prominences may be affected, a peculiarity that is also evident in coccidioidomycosis. The radiographic features of bony involvement are not specific. Osteolytic lesions show discrete margins, mild surrounding sclerosis, and little or no periosteal reaction (Fig. 20.34). Arthritis related to cryptococcosis is very uncommon.

North American Blastomycosis

Fig. 20.31  Lyme disease. The glenohumeral joint space is narrowed, and erosions and osteophytes in the humeral head are seen. (Courtesy J. Lawson, MD, New Haven, CT.)

A

B

This fungal disease is produced by Blastomyces dermatitidis. In the United States, its frequency is highest in the Ohio and Mississippi River valleys and in the Middle Atlantic states. The skin appears to be the portal of entry in some cases, with infection commonly following cutaneous injuries. The respiratory tract may be a second site of entry. In the skin, cutaneous abscesses develop beneath the epidermis and are surrounded by a granulomatous reaction. Similar lesions may be encountered in the lungs. The bones may be altered in as many as 50% of patients with disseminated disease. Skeletal changes can occur from hematogenous seeding

C

Fig. 20.32  Lyme disease. Axial T1-weighted ­ (A), axial fluid-sensitive ­ (B), and sagittal fluid-sensitive ­ (C) MR images reveal a moderate-sized ­ joint effusion with a thickened edematous synovium (arrow), without evidence of cartilage loss or bone erosions. Note edema within the prefemoral and suprapatellar fat, as well as considerable soft tissue and muscular edema.

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Fig. 20.33  Actinomycosis. Mandible radiograph reveals erosion and sclerosis (arrows). (Courtesy R. Taketa, MD, Long Beach, CA.)

Fig. 20.35  North American blastomycosis. In this patient, blastomycosis involves the lung and bones. Note vertebral body and intervertebral disc destruction (arrowheads), accompanied by a paravertebral mass (open arrows). (Courtesy A. Brower, MD, Norfolk, VA.)

not unusual. Draining sinuses and cortical sequestration may appear in neglected cases. In the spine, blastomycosis resembles tuberculosis.

South American Blastomycosis (Paracoccidioidomycosis)

The fungal disorder called South American blastomycosis, caused by the organism Blastomyces (Paracoccidioides) brasiliensis, occurs only in South America and in areas of Mexico and Central America. The infective agents invade the pharynx, presumably after inhalation, and from there, spread locally or are disseminated throughout the body. Nasopharyngeal ulceration and local lymphadenopathy may antedate the clinical findings in other locations. Hematogenous spread of infection to the lungs, spleen, other abdominal viscera, and bones can occur. Musculoskeletal involvement is similar to that in North American blastomycosis, with findings of well-­defined bone destruction, marginal sclerosis, and periostitis. Fig. 20.34  Cryptococcosis (torulosis). Discrete osteolytic foci with surrounding sclerosis and, in some places, periosteal reaction are seen (arrows).

or by direct extension from overlying cutaneous lesions. One or several osseous sites can be affected, especially the vertebra, rib, tibia, and carpus and tarsus (Fig. 20.35). The radiographic features of blastomycotic osteomyelitis are not specific. In the tubular bones of the extremities, eccentric, saucer-­shaped erosions may be detected beneath cutaneous abscesses, or areas of focal or diffuse osteomyelitis may be encountered. The lesions frequently possess sclerotic margins and are surrounded by periostitis. Extension from the infected foci to soft tissues or joints is

Coccidioidomycosis Coccidioidomycosis results from inhalation of the fungus Coccidioides immitis in endemic areas in the southwestern United States, Mexico, and some regions of South America. After inhalation, the organisms lodge in the lungs, where an inflammatory reaction may ensue. Disseminated disease may develop, with spread of infection to the liver, spleen, lymph nodes, skin, kidneys, meninges, pericardium, and bones. In cases of wide dissemination, the mortality rate is high. Although an acute, self-­limited arthritis (desert rheumatism) may develop in approximately 33% of cases of coccidioidomycosis, granulomatous lesions in the bones and joints develop in only 10% to 20% of patients. Bone alterations relate to hematogenous spread, although

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SECTION 3  Infectious Disorders

A

B

Fig. 20.36  Coccidioidomycosis: osteomyelitis (appendicular skeleton). (A) Note the involvement of bony protuberances such as the ulnar olecranon (arrow). Discrete lesions with surrounding sclerosis are evident. (B) In another patient, the radiograph shows an osteolytic lesion with moth-­eaten bone destruction and periostitis of the radius.

cutaneous infection can lead to contamination of subjacent bones (and joints). Osseous involvement can be confined to a single bone, but multiple, symmetric osseous lesions may be seen. Radiographs frequently reveal multiple osseous lesions in the metaphyses of long tubular bones and in bony prominences (patella, tibial tuberosity, calcaneus, ulnar olecranon) (Fig. 20.36). Lesions involving the ribs can be associated with prominent extrapleural masses (Fig. 20.37). In the spine, abnormalities of one or more vertebral bodies, with paraspinal masses and contiguous rib changes, are typical. Joint involvement is most common in the ankle and knee (Fig. 20.38).

Histoplasmosis Histoplasmosis is caused by the dimorphic fungus Histoplasma capsulatum, which is present in many areas of the United States, particularly the Mississippi River valley. Histoplasmosis, which is the most common systemic fungal infection in the United States, results from exposure to soil containing the spores of this fungus. The portal of entry is usually the respiratory tract, although the gastrointestinal system may be an additional portal. The fungus proliferates most extensively in cells of the reticuloendothelial system. Involvement of the brain, lymph nodes, spleen, adrenal gland, lungs, bowel, and bone marrow is most typical. Skeletal sites of involvement include the pelvis, skull, ribs, and small tubular bones; children are affected more commonly than adults. Joint alterations, especially in the knees, ankles, wrists, and hands, lead to clinical (pain, swelling), radiographic (osteoporosis, joint space narrowing, erosion), and pathologic (granulation tissue with phagocytic cells) findings that are similar to those of sarcoidosis and tuberculosis. In histoplasmosis caused by Histoplasma duboisii, granulomatous lesions of the skin can be associated with osseous and articular changes in as many as 80% of patients (Fig. 20.39).

Fig. 20.37  Coccidioidomycosis: osteomyelitis (axial skeleton). The diagnosis of disseminated coccidioidomycosis was established by skin biopsy, bone marrow and cerebrospinal fluid examination, and positive serologic test results. Radiography outlines lytic lesions with surrounding sclerosis (arrows) involving the ribs.

Sporotrichosis Sporotrichosis, a chronic fungal disease caused by Sporothrix schenckii, is characterized by suppurating nodular lesions of the skin and subcutaneous tissue. The fungus resides as a saprophyte on vegetation and can invade the human body through a skin wound; the disease is not uncommon after cutaneous puncture with thorns. After inoculation, a painless, ulcerating cutaneous lesion develops, and the organisms spread locally and produce nodular lesions of the lymphatic channels. Rarely, disseminated disease can evolve. In the disseminated form of

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

A

B Fig. 20.38  Coccidioidomycosis: septic arthritis. (A) Radiograph reveals soft tissue swelling, marginal osseous erosions (arrows), and flattening, with sclerosis of the medial femoral condyle (arrowhead). The last-­mentioned findings resemble those in spontaneous osteonecrosis of the knee. (B) In a different patient, a coronal T1-­ weighted MR image shows similar marginal erosions, especially in the tibia, along with marrow edema and a joint effusion.

A

B Fig. 20.39  Histoplasma capsulatum var. duboisii osteomyelitis. (A) Radiograph of the hand reveals cystic lesions of the metacarpal bones and phalanges. In many areas, they are well marginated and surrounded by reactive bone formation and mature periostitis. (B) Extensive lesions of the tibial epiphysis and metaphysis have produced collapse of the articular surface, with sclerosis and mild periostitis. Extension across the growth cartilage is not unusual in fungal infections. (A, From Cockshott WP, Lucas AO: Histoplasmosis duboisii. Q J Med. 1964;33:223.)

349

350

SECTION 3  Infectious Disorders

Fig. 20.40  Sporotrichosis: septic arthritis. Note soft tissue swelling, joint space loss, and irregularity and poor definition of subchondral bone, with marginal and central osseous erosions. The changes are identical to those in other forms of septic arthritis. Joint involvement is not infrequent in this disorder, and osteoporosis may or may not be present. (Courtesy A. Brower, MD, Norfolk, VA.)

sporotrichosis, bone and joint changes may appear in 80% of cases, and death can occur rapidly. Localization in one or more joints is especially characteristic, with a predilection for the knee, wrist and hand, ankle, elbow, and metacarpophalangeal joints. Soft tissue swelling, effusion, and joint space loss are seen, as well as irregularity of subchondral bony margins (Fig. 20.40). Bone changes may take several forms. Eccentric erosions beneath subcutaneous lesions (especially in the tibia) may be encountered but are more typical of blastomycosis. Single or multiple lytic areas in bone can appear as a result of hematogenous spread. The tibia, fibula, femur, humerus, and short tubular bones of the hand (Fig. 20.41) and foot are involved most commonly. Osteolysis predominates, whereas periostitis is usually absent. These radiographic features simulate those of tuberculosis or other fungal disorders. Involvement of the small joints of the hands and feet appears to be more characteristic of this fungal disease than the others.

Candidiasis (Moniliasis) Of the various Candida species, Candida albicans is most commonly associated with human disease. Candida organisms normally reside on the mucous membranes. Abnormal proliferation on these membranes may occur in otherwise normal persons but is especially characteristic in debilitated children or adults, in patients receiving broad-­spectrum antibiotics, in those with diabetes mellitus, and in patients with intravenous or Foley catheters. In the mouth, a mucocutaneous infection can be found, consisting of white patches (thrush). Rarely, widespread infection may develop. Candida infection of the musculoskeletal system occurs when host resistance is depressed. Intravenous drug addicts may be affected, and a distinctive syndrome leading to systemic candidiasis with costochondral involvement has been recognized in approximately one-­third of heroin addicts. Bone involvement in cases of disseminated candidiasis

Fig. 20.41  Sporotrichosis: osteomyelitis. Note osteolysis of the fifth metacarpal bone, along with a pathologic fracture. (Courtesy A. G. Bergman, MD, Stanford, CA.)

is relatively rare, evident in less than 1% to 2% of cases. When present, such osseous involvement can result from direct hematogenous seeding or extension from an overlying soft tissue abscess. Osteomyelitis can occur in one or more sites, including the tubular bones of the extremities, flat bones, and spine. Common patterns of distribution are involvement of a single long bone, involvement of the sternum, and involvement of two consecutive vertebral bodies. Septic arthritis is also observed. Infection predominates in large weight-­bearing joints such as the knee. The pathogenesis of the articular infection can relate to hematogenous contamination or extension from an adjacent infected osseous or soft tissue structure. Radiographic findings include soft tissue swelling, joint space narrowing, irregularity of subchondral bone, and osteomyelitis (Fig. 20.42).

Aspergillosis Asperigillus is normally a harmless inhabitant of the upper respiratory tract. Uncommonly, in patients with low resistance or in those who have received an overwhelming inoculum, a chronic, localized pulmonary infection may result. The usual organism is Aspergillus fumigatus. The musculoskeletal system is rarely involved in aspergillosis. Two potential mechanisms of infection have been emphasized: hematogenous infection, which reportedly predominates in adults, and spread from a pulmonary or cutaneous infective site, a mechanism that may predominate in children. Pulmonary aspergillosis leading to chest wall involvement has been emphasized as a finding of chronic granulomatous disease in children (Fig. 20.43).

Maduromycosis (Mycetoma) Maduromycosis, a chronic granulomatous fungal disease, usually affects the feet (Madura foot). It can be observed throughout the world but is especially prevalent in India; the town of Madura in India is the source of its name. In the United States, a variety of organisms may cause Madura foot.

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351

with associated periostitis and sclerosis. Intraarticular osseous fusion may occur and lead to an appearance that is termed “melting snow.” A fairly specific MR imaging finding, a dot-­in-­circle appearance, has been emphasized (Fig. 20.45).

VIRAL INFECTION Rubella (German Measles) Rubella is a contagious viral disease. Although it is generally a benign disorder in adults, maternal infection in the first half of pregnancy can lead to serious skeletal and nonskeletal alterations in the fetus.

Postnatal Rubella

Fig. 20.42  Candidiasis: septic arthritis. Observe the massive soft tissue swelling, marginal osseous erosions (arrow), bone collapse and fragmentation, and joint space narrowing.

In adult patients (especially women), rubella arthritis may occur within a few days to 1 week of the skin rash. Persistent or migratory articular findings are most common in the small joints of the hands and wrists. After live attenuated rubella virus became available for active immunization, episodes of acute arthritis were noted in children injected with the virus. A chronic arthropathy in children and adults also has been associated with rubella vaccination. In this arthropathy, recurrent episodes of knee stiffness (catcher’s crouch syndrome) are evident. Oligoarthritis and polyarthritis are the clinical patterns observed. Radiographic findings are variable but include intraarticular bone erosions. The arthropathy resembles juvenile idiopathic arthritis, and reports indicate that rubella antibody levels are elevated not only in rubella vaccine–induced arthritis but also in a significant proportion of children (∼33%) with juvenile idiopathic arthritis, suggesting a possible role of rubella infection in this disease.

Intrauterine Rubella The radiographic features consist of metaphyseal lesions in long bones characterized by symmetry, linear areas of radiolucency, and increased bone density producing a longitudinally oriented, striated pattern (“celery stalk” appearance), as well as the absence of periostitis. These features can either disappear completely if the child recovers from the intrauterine viral infection or persist with increasing density of the juxtaepiphyseal region if the infection continues (Fig. 20.46). With healing, beaklike exostoses can be noted at the metaphyses.

Cytomegalic Inclusion Disease

Fig. 20.43  Aspergillosis: osteomyelitis. Axial CT scan of the thorax in a 5-­year-­old boy with X-­linked chronic granulomatous disease shows consolidation in the right apical portion of the lung, soft tissue swelling, loss of fat planes, and osteolytic lesions (arrow) in the posteromedial aspect of the right third rib. (From Kawashima A, Kuhlman JE, Fishman EK, et al: Pulmonary Aspergillus chest wall involvement in chronic granulomatous disease: CT and MRI findings. Skeletal Radiol. 1991;20:487.)

Infection of the foot (and, less commonly, other sites) results from posttraumatic soft tissue invasion by organisms that are normal inhabitants of soil. After soft tissue contamination, the organisms may penetrate the underlying structures (Fig. 20.44). Sinus tracts are common. The course of maduromycosis is usually progressive. Over a period of months to years, the foot becomes swollen, deformed, and necrotic. The radiographic findings vary with the virulence of the invading organism. In some cases, single or multiple localized osseous defects are evident; in others, extensive soft tissue and bony disruption occurs,

Intrauterine infection related to cytomegalic inclusion disease can lead to intracranial calcifications and rubella-­like abnormalities of the skeleton (Fig. 20.47). Metaphyseal osteopenia, irregularity of the growth plate, and a striated pattern parallel to the long axis of the bone characterized by alternating lucent and sclerotic bands are noted. The metaphyseal changes, which are related to alterations in endochondral ossification, are usually evident in the first few days of life and then disappear completely within a period of days to weeks.

Variola (Smallpox) Osteomyelitis and septic arthritis are well-­known complications of smallpox. No apparent relationship has been found between the severity of the infection and the frequency or severity of osteomyelitis or septic arthritis. Most typically, osseous and articular changes occur together. Symmetric involvement is frequent, and articular infection reveals an unusual affinity for the elbow (80% of patients). Three types of bone and joint lesions have been described: (1) a necrotic, nonsuppurative osteomyelitis, probably caused by the smallpox virus itself; (2) a suppurative arthritis related to contamination of the joint, probably as a result of secondary infection of a pustule; and (3) a nonsuppurative arthritis that appears 1 to 4 weeks after the initial

352

SECTION 3  Infectious Disorders

B

A

Fig. 20.44  Maduromycosis: Madura knee. Sagittal T1-­weighted (A) and fluid-­sensitive (B) MR images show prominent soft tissue involvement, especially anteromedially. Observe the circle-­in-­dot appearance (arrows). (Courtesy Abdalla Skaf, MD, Sao Paulo, Brazil.)

A

B Fig. 20.45  Maduromycosis: Madura foot. Sagittal T1-­weighted (A) and fluid-­sensitive (B) MR images of the ankle and foot show extensive involvement of multiple bones in the hindfoot and midfoot, particularly the talus, calcaneus, and navicular bone. A classic dot-­in-­circle sign (arrow) is evident in many of the lesions, (Courtesy Abdalla Skaf, MD, Sao Paulo, Brazil.)

infection. During the acute stage of osteomyelitis variolosa, findings simulate those of pyogenic osteomyelitis. Juxtametaphyseal osteoporosis and destruction, epiphyseal extension, periostitis, involucrum formation, and articular contamination, most commonly of the elbow, are seen (Fig. 20.48).

Human Immunodeficiency Virus Infection HIV infection leads to compromise of the body’s defense mechanisms, which in turn predisposes infected persons to a variety of opportunistic infections, anemia, arthritis, myositis (Fig. 20.49), and immune-­ related neoplasms. Musculoskeletal alterations in such persons are not infrequent. Many of the rheumatologic manifestations of HIV infection fall within the spectrum of differentiated and undifferentiated forms of spondyloarthropathy. Fasciitis and enthesopathy occur, especially in

the feet (Fig. 20.50), and are accompanied by marked muscle wasting. These characteristics have been referred to as the AIDS foot. Osteomyelitis, septic arthritis, pyomyositis, and septic bursitis are among the most frequent complications associated with HIV infection. Although the knee is the most common site of involvement, joints of the upper extremity and the acromioclavicular, sternoclavicular, and sacroiliac joints may also be affected. S. aureus or S. pneumoniae is implicated most often. Pyomyositis is a bacterial infection of muscle that is generally but not exclusively caused by S. aureus and is endemic in tropical regions of Africa, Southeast Asia, and South America. It commonly affects patients who are immunologically compromised or who have underlying chronic disorders such as HIV infection. Almost 95% of reported cases of pyomyositis associated with HIV infection involve locations in the lower extremity. Multiple abscesses are identified in about 50% of

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353

A

Fig. 20.47  Cytomegalic inclusion disease. Metaphyseal changes consist of irregularity of the growth plate and osseous fragmentation, most evident in the distal ends of the femora. (Courtesy F. N. Silverman, MD, Palo Alto, CA.)

B Fig. 20.46  Intrauterine rubella infection. (A) Radiolucent metaphyseal bands (arrow) in the distal end of the femur of this infant are associated with relative sclerosis of the diaphyses. (B) In a different infant, longitudinal striations have produced the characteristic “celery stalk” appearance. Periostitis is absent.

cases. The most typical pattern of disease, however, appears to be a solitary abscess in the quadriceps musculature. Clinical findings include fever and local muscle pain, redness, and swelling; if untreated, this may be accompanied by marked edema and septicemia.

Among the malignant tumors encountered with increased frequency in patients with HIV infection are lymphomas, Hodgkin disease, and Kaposi sarcoma. The last of these tumors arises from lymphatic endothelial cells, and it has been reported to be present in 15% to 20% of patients with HIV infection. In these patients, Kaposi sarcoma is aggressive in behavior, with multiorgan involvement. Bacillary angiomatosis is a disorder characterized by histologic evidence of vascular proliferation in affected tissues such as the skin, bone, lymph nodes, and brain and by the presence of numerous bacillary organisms. Recent biologic and microbiologic investigations have confirmed that at least two organisms, Rochalimaea henselae and Rochalimaea quintana, can cause this disease. Bacillary angiomatosis can occur in patients infected with HIV, but it is not restricted to such patients; it has also been observed in immunocompetent patients and in recipients of organ transplants. The typical clinical manifestation is that of a cutaneous disorder with multiple friable angiomatous papules closely resembling pyogenic granulomas, as well as the skin lesions of Kaposi sarcoma. Fever, chills, weight loss, night sweats, cellulitis, and subcutaneous nodules are additional clinical features. Bone lesions also may be seen, sometimes as an initial manifestation of the disease. Tubular bones of the extremities are typically affected, with the flat and irregular bones affected less commonly. Cortical or medullary destruction, or both, is seen, and an adjacent soft tissue mass is an associated feature. Periostitis is often identified, and this finding, combined with skin lesions in a patient with AIDS, is considered strong evidence of bacillary angiomatosis.

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SECTION 3  Infectious Disorders

A

B

Fig. 20.48  Variola osteomyelitis and septic arthritis: elbow involvement. Stages in the process of bone and joint disease are illustrated in two different patients. (A) Initial findings include destructive foci with periostitis (arrow). (B) Subsequently, irregularity of the articular surfaces can be seen (arrow). (Courtesy W. P. Cockshott, MD, Hamilton, Ontario, Canada.)

Fig. 20.50  Human immunodeficiency virus infection: reactive arthritis with enthesopathy and bursitis. Note enthesitis, with bone proliferation in the plantar aspect of the calcaneus, and retrocalcaneal bursitis, with erosion of the posterosuperior portion of the calcaneus. Fig. 20.49  Human immunodeficiency virus infection: myositis. In this young man with a history of HIV infection, a coronal short-­tau inversion recovery MR image shows bilateral muscle edema (arrows) with associated subcutaneous edema, findings consistent with myositis.

RICKETTSIAL INFECTION Cat-­Scratch Disease Cat-­scratch disease (CSD) has been linked to two soil-­borne proteobacteria, Bartonella henselae and, occasionally, Afipia felis. CSD is often

manifested as a local lymphadenitis with lymphadenopathy occurring within 1 or 2 weeks after being scratched by a cat. Such lymphadenopathy is generally preceded by an erythematous pustule or papule at the site of inoculation that resolves spontaneously within several weeks to months. Involvement of the central nervous system, lung, liver, spleen, bone, and skin may complicate CSD in as many as 2% of cases. A serologic test (indirect fluorescent antibody) for R. henselae is currently considered a useful adjunct for obtaining the correct diagnosis. Affected persons are between the ages of 5 and 21 years, and CSD is

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355

TABLE 20.3  Major Helminthic Infections of Humans NEMATODES (ROUNDWORMS)

TREMATODES (FLATWORMS)

CESTODES (TAPEWORMS)

Tissue

Intravascular

Pathogenic Form: Adult

Pathogenic Form: Larva

Ancylostoma duodenale Wuchereria bancrofti

Clonorchis sinensis

Schistosoma mansoni

Diphyllobothrium latum

Echinococcus granulosus

Necator americanus

Brugia malayi

Fasciola hepatica

Schistosoma japonicum

Taenia saginata

Echinococcus multilocularis

Ascaris lumbricoides

Onchocerca volvulus

Fasciolopsis buski

Schistosoma haematobium

Taenia solium

Taenia solium

Enterobius vermicularis

Loa loa

Paragonimus westermani

Hymenolepsis nana

Hymenolepsis nana

Hymenolepsis nana

Trichuris trichiura

Trichinella spiralis Toxocara canis Dracunculus medinensis

Intestinal

Tissue

From Korzeniowdki OM: Diseases due to helminths. In Stein JH, ed. Internal Medicine. Boston, Little, Brown; 1983:1455.

probably the leading cause of chronic benign lymphadenopathy. More than 90% of patients with CSD have a history of exposure to cats. The initial clinical manifestations are cutaneous and consist of skin eruptions at the site of inoculation. Because the hands and forearms are the most frequent sites of inoculation, adenopathy often develops around the elbow, axilla, and head and neck; specific areas of adenopathy, in decreasing order of frequency, are the axillary and epitrochlear nodes, the cervical and submandibular nodes, the groin, and the preauricular, postauricular, and supraclavicular chains. Conventional radiographs reveal soft tissue edema, masses, or both. Although ultrasonography also can be used to study the soft tissue and systemic manifestations of CSD, MR imaging may be more sensitive and is often diagnostic. An ill-­defined mass with heterogeneous low signal intensity on T1-­weighted MR images and intermediate to high signal intensity on fluid-­sensitive MR images in the region of the epitrochlear nodes about the elbow should suggest the diagnosis of CSD (see Fig. 19.54). Surrounding edema is common, and enhancement of signal intensity in the peripheral portion of the mass may be noted after contrast administration. Osseous lesions, probably related to hematogenous dissemination and spread from a contiguous contaminated lymph node, are encountered uncommonly.

PROTOZOAN INFECTION Toxoplasmosis Toxoplasmosis is an infectious disorder caused by an intracellular protozoan parasite, Toxoplasma gondii. Human infections with Toxoplasma may be either congenital or acquired. The congenital variety of toxoplasmosis can be severe. An infant may be stillborn at term or born prematurely, with active infection characterized by fever, rash, hepatosplenomegaly, intellectual disability, chorioretinitis, and convulsions, which may lead to death in 10% to 20% of cases. Osseous lesions are unusual, although metaphyseal alterations in tubular bones may simulate those of rubella, cytomegalic inclusion disease, or syphilis. Cerebral calcification may be evident. The acquired variety of the disease can occur at any age and may display variable manifestations, including rash, lymphadenopathy, ocular changes, widespread vascular alterations, and myositis. Osteoporosis, soft tissue swelling, and osseous cystic lesions have been described.

HELMINTHIC INFECTION A variety of helminths (worms) can cause infection (Table 20.3).

Hookworm Disease Hookworm disease is produced by Ancylostoma duodenale or Necator americanus. Anemia and its complications are the major clinical manifestations of this disorder.

Loiasis Loiasis is prevalent in West and Central Africa and is produced by the filaria Loa loa (African eyeworm). Infective larvae are deposited in the victim’s skin after a bite of the mango fly. The larvae burrow into the deeper subcutaneous tissue, where they mature to adult worms over a period of 6 months or longer. The dead worms cause abscesses, undergo calcification, or both. Calcific deposits in subcutaneous tissue may be fine, coiled, lacelike, and filamentous (calcification of the worm), or they may be thicker, beadlike, and lobulated (calcification of the fibrous capsule surrounding the worm) (Fig. 20.51 and Table 20.4).

Onchocerciasis Onchocerciasis is a form of filariasis produced by Onchocerca volvulus and transmitted by flies. It is prevalent in Africa and Central and South America. Soft tissue calcifications, similar to those in loiasis, may be detected.

Filariasis Filariasis is produced by adult worms of the species Wuchereria bancrofti or Brugia malayi, which localize in the lymphatic and soft tissues of the human body. The disease is predominant in tropical areas of Asia, Africa, South America, Australia, and the South Pacific islands. After prolonged and repeated attacks, filariasis can lead to massive lymphedema or elephantiasis, especially of the legs and scrotum. Radiographs show an affected limb to be greatly enlarged, with soft tissue thickening, blurring of subcutaneous fat planes, and a linear, striated pattern. Soft tissue calcification has been noted in W. bancrofti infestation, related to calcified, dead, encysted filariae. The calcifications are smaller than those in loiasis and occur predominantly in the lymphatic channels of the scrotum, thighs, and legs.

Dracunculiasis (Guinea Worm Disease) The guinea worm, Dracunculus medinensis, can cause human disease, particularly in parts of Africa, the Middle East, South America, India, and Pakistan. The disorder is contracted when larvae in contaminated water are ingested by a water flea (Cyclops), which in turn is swallowed in the drinking water by humans. The larvae eventually enter

356

SECTION 3  Infectious Disorders

the circulation and mature within human subcutaneous tissue. When the female parasites die, they may calcify and produce long, curled radiodense shadows in the lower extremities (Fig. 20.52) and hands or, less commonly, in the perineum and abdominal and chest walls. The

deposits are usually multiple and may become fragmented because of the action of adjacent musculature.

Fig. 20.51  Loiasis (African eyeworm disease). Soft tissue calcifications (arrowheads) are evident in the hand of this 29-­year-­old man. (Courtesy M. Dalinka, MD, Philadelphia, PA.)

Fig. 20.52  Dracunculiasis (guinea worm disease). Observe the long linear calcification (arrows) adjacent to the lower part of the tibia caused by the presence of a dying female worm.

Trichinosis After ingestion of infected pork, humans may contract trichinosis from the intestinal nematode Trichinella spiralis. Calcification of the cysts of

TABLE 20.4  Helminths (Worms) Associated With Calcification Helminth (Disease)

Frequency of Radiographic Calcification

Typical Location of Calcification

Typical Appearance of Calcification

Loa loa (loiasis)

Common

Widespread; subcutaneous tissues

Extended or coiled, linear or beaded, variable in size

Onchocerca volvulus (river blindness)

Rare

Legs, trunk, head; subcutaneous nodules

Extended or coiled, linear or beaded, small

Wuchereria bancrofti, Brugia malayi (filariasis)

Rare

Thighs, legs, scrotum; subcutaneous tissues

Straight or coiled, small

Dracunculus medinensis (guinea worm disease)

Common

Extremities

Extended or coiled, long

Taenia solium (cysticercosis)

Common

Widespread; muscular tissues

Numerous, linear or oval, variable in size, lie in plane of muscle

Echinococcus granulosus (echinococcosis)

Common

Liver, lungs, other organs

Curvilinear, cystic, eggshell

Sarcocystis lindemanni (sarcosporidiosis)

Common

Extremities; muscular and subcutaneous Numerous, linear or oval, variable in tissues size and orientation

Armillifer armillatus, Porocephalida, Pentastomida (porocephaliasis)

Variable

Abdomen, thorax

Multiple, crescent shaped or oval

Schistosoma haematobium (schistosomiasis)

Variable

Bladder, urinary tract

Linear, nodular

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

A

B

357

C

Fig. 20.53  Cysticercosis. Coronal MR images of the posterior subcutaneous and muscular tissues of the back, buttocks, and shoulder regions (A, B) and an axial MR image of the brain (C) show the innumerable calcified larvae (arrow) of this tapeworm. Note that the foci are similar in size and, in the muscles, the long axis of the calcified cysts lie in the plane of the muscle bundles. (Courtesy M. Pathria, MD, San Diego, CA.)

the parasite is commonly detected on microscopic examination but is rarely, if ever, noted on radiographic evaluation.

Cysticercosis The relationship between humans and the pork tapeworm Taenia solium is twofold: humans are the only definitive host of the adult tapeworm (the parasite inhabits the intestine), and humans may serve as an intermediate host (the usual intermediate host is the hog) and harbor the larval stage, cysticercus cellulosae. In the latter case, deposits of the larval form of the tapeworm may appear in subcutaneous and muscular tissue and in a variety of viscera, including the heart, brain, lung, liver, and eye (Fig. 20.53). When the larvae die, a foreign body reaction may ensue, followed over a period of years by caseation and calcification. Linear or oval elongated calcifications appear in the soft tissues and musculature and may reach 23 mm in length. The long axis of the calcified cysts lies in the plane of the surrounding muscle bundles (Fig. 20.54).

Echinococcosis Echinococcosis is produced principally by the larval stage of Echinococcus granulosus and is most prevalent in sheep-­and cattle-­raising areas of North and South Africa, South America, Central Europe, Australia, and Canada; less commonly, Echinococcus multilocularis is the causative agent, especially in Alaska and Eurasia. In humans, E. granulosus is contracted by ingestion of the eggs, which are contained in the feces of dogs (sheep or cattle dogs). After ingestion, the embryos escape from the eggs, traverse the intestinal mucosa, and are disseminated by venous and lymphatic channels. Cysts may develop in various viscera, particularly the liver and the lungs. They may calcify and produce irregular, curvilinear radiodense areas. Bone lesions are reported in 1% to 2% of cases of echinococcosis. Osseous involvement is almost invariably related to primary infection and is not the result of extension from a neighboring soft tissue lesion. Although hematogenous seeding of the skeleton can conceivably occur at any site, one bone, a few adjacent bones, or one skeletal region is usually affected. The vertebral column, pelvis, long bones, and skull are most commonly involved. The spine is involved in about 50% of cases. Radiographs can reveal single or multiple expansile, cystic, osteolytic lesions containing trabeculae (Fig. 20.55). These lesions may be associated with cortical violation and soft tissue mass formation, with

Fig. 20.54  Cysticercosis. The typical appearance of soft tissue calcification in this disorder consists of dense, elongated, linear or oval lesions oriented in the plane of the surrounding muscle bundles. (Courtesy B. Howard, MD, Charlotte, NC.)

subsequent calcification. The radiographic characteristics are similar to those of fibrous dysplasia, plasmacytoma, giant cell tumor, cartilaginous neoplasm, skeletal metastasis (especially from a tumor of the kidney or thyroid), brown tumor of hyperparathyroidism, angiosarcoma, or hemophilic pseudotumor. CT features of echinococcosis include a soft tissue mass adjacent to sites of bone involvement; the center of the mass contains fluid with water attenuation values. Cystic lesions within the bone and adjacent soft tissue are also identified with MR imaging; the signal characteristics of the cyst are variable (dependent on the type of cyst present and whether it is intact, ruptured, infected,

358

SECTION 3  Infectious Disorders

ADDITIONAL DISORDERS WITH A POSSIBLE INFECTIOUS CAUSE

or dead) (Fig. 20.56). The presence of numerous cystic lesions of high signal intensity on fluid-­sensitive MRI appears to be characteristic.

Ainhum Ainhum (dactylolysis spontanea) is a self-­limited dermatologic disorder that is characteristically found in African Blacks or their descendants. Most typically, the fifth toe on one or both feet is affected, although other toes (especially the fourth) and even the fingers can be involved. A deep soft tissue groove corresponding to a hyperkeratotic band within the epidermis appears and is associated with dermal fibrosis. The groove is initially evident along the medial aspect of the fifth toe and progressively deepens and encircles the toe. Bony resorption begins on the medial aspect of the distal portion of the proximal phalanx or the middle phalanx of the fifth toe (Fig. 20.57). The cause of ainhum is not clear. Traumatic and infectious factors appear most likely.

Tietze Syndrome Tietze syndrome and costochondritis are terms used to describe pain, tenderness, and swelling at the costosternal joints. This condition is common, of unknown cause, and may occur in as many as 10% of patients with chest pain. Tietze syndrome is benign and self-­limited. Typically, painful swelling and tenderness to local palpation of one or more costosternal junctions are observed. Radiographs are seldom revealing, although rarely, soft tissue swelling, calcification, osteophytosis, and periostitis are encountered. Increased activity may be demonstrated on bone scans. CT scanning and MR imaging may be helpful in some cases.

Fig. 20.55  Echinococcosis. An osteolytic lesion in the ilium is accompanied by sclerosis extending to the sacroiliac joint. (Courtesy A. D’Abreu, MD, Porto Alegre, Brazil.)

A

T1 FS FSE

B

T2 FSE

Fig. 20.56  Echinococcosis. In this elderly man, coronal T1-­weighted (A) and fluid-­sensitive (B) MR images show a mass within the musculature of the thigh containing cysts of variable size, virtually diagnostic of echinococcosis. (Courtesy S. Riad, MD.)

CHAPTER 20  Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Organisms

Fig. 20.57  Ainhum. Note the soft tissue groove (arrow) and osseous resorption, especially on the medial aspect of the proximal and middle phalanges of the fifth toe. Periostitis is absent.

FURTHER READING Alexander GH, Mansuy MM. Disseminated bone tuberculosis (so-­called multiple cystic tuberculosis). Radiology. 1950;55:839. Allen Jr JH. Bone involvement with disseminated histoplasmosis. AJR Am J Roentgenol. 1959;82:250. Baron AL, Steinbach LS, LeBoit PE, et al. Osteolytic lesions and bacillary angiomatosis in HIV infection: radiographic differentiation from AIDS-­ related Kaposi sarcoma. Radiology. 1990;177:77. Barre PS, Thompson GH, Morrison SC. Late skeletal deformities following meningococcal sepsis and disseminated intravascular coagulation. J Pediatr Orthop. 1985;5:584. Beggs I. The radiology of hydatid disease. AJR Am J Roentgenol. 1985;145:639. Bonakdarpour A, Zadeh YFA, Maghssoudi H, et al. Costal echinococcosis: report of six cases and review of the literature. AJR Am J Roentgenol. 1973;118:371. Braithwaite PA, Lees RF. Vertebral hydatid disease: Radiological assessment. Radiology. 1981;140:763. Casado E, Olivé A, Holgado S, et al. Musculoskeletal manifestations in patients positive for human immunodeficiency virus: correlation with CD4 count. J Rheumatol. 2001;28:802. Chang AC, Destouet JM, Murphy WA. Musculoskeletal sporotrichosis. Skeletal Radiol. 1984;12:23. Chapman M, Murray RO, Stoker DJ. Tuberculosis of the bones and joints. Semin Roentgenol. 1979;14:266.

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Cherian RS, Betty M, Manipadam MT, et al. The “dot-­in-­circle” sign—a characteristic MRI finding in mycetoma foot: a report of three cases. British J Radiol (online). 2009;82(980). Comstock C, Wolson AH. Roentgenology of sporotrichosis. AJR Am J Roentgenol. 1975;125:651. Cremin BJ, Fisher RM. The lesions of congenital syphilis. Br J Radiol. 1970;43:333. Dalinka MK, Dinnenberg S, Greendyke WH, et al. Roentgenographic features of osseous coccidioidomycosis and differential diagnosis. J Bone Joint Surg Am. 1971;53:1157. de Roos A, van Meerten ELVP, Bloem JL, et al. MRI of tuberculous spondylitis. AJR Am J Roentgenol. 1986;146:79. Dong PR, Seeger LL, Yao L, et al. Uncomplicated cat-­scratch disease: findings at CT, MR imaging, and radiography. Radiology. 1995;195:837. Ehrlich I, Kricun ME. Radiographic findings in early acquired syphilis: case report and critical review. AJR Am J Roentgenol. 1976;127:789. Enna CD, Jacobson RR, Rausch RO. Bone changes in leprosy: a correlation of clinical and radiographic features. Radiology. 1971;100:295. Fang D, Leong JCY, Fang HSY. Tuberculosis of the upper cervical spine. J Bone Joint Surg Br. 1983;65:47. Feldman F, Auerbach R, Johnston A. Tuberculous dactylitis in the adult. AJR Am J Roentgenol. 1971;112:460. Fetterman LE, Hardy R, Lehrer H. The clinico-­roentgenologic features of ainhum. AJR Am J Roentgenol. 1967;100:512. Goldblatt M, Cremin BJ. Osteo-­articular tuberculosis: its presentation in coloured races. Clin Radiol. 1978;29:669. Harisinghani MG, McLoud TG, Shepard JO, et al. Tuberculosis from head to toe. Radiographics. 2000;20:449. Harverson G, Warren AG. Tarsal bone disintegration in leprosy. Clin Radiol. 1979;30:317. Haygood TM, Williamson SL. Radiographic findings of extremity tuberculosis in childhood: back to the future? Radiographics. 1994;14:561. Hong SH, Kim SM, Ahn JM, et al. Tuberculous versus pyogenic arthritis: MR imaging evaluation. Radiology. 2001;218:848. Jaffe HL. Metabolic, Degenerative and Inflammatory Diseases of Bones and Joints. Philadelphia: Lea & Febiger; 1972. Kubihal V, Sharma R, Kumar RG. Imaging update in spinal tuberculosis. J Clin Orthop Trauma. 2022;25:101742. Lawson JP, Rahn DW. Lyme disease and radiographic findings in Lyme arthritis. AJR Am J Roentgenol. 1992;158:1065. Lifeso RM, Harder E, McCorkell SJ. Spinal brucellosis. J Bone Joint Surg Br. 1985;67:345. Martinoli C, Derchi LE, Bertolotto M, et al. US and MR imaging of peripheral nerves in leprosy. Skeletal Radiol. 2000;29:142. Merten DF, Gooding CA. Skeletal manifestations of congenital cytomegalic inclusion disease. Radiology. 1970;95:333. Mortensson W, Eklöf O, Jorulf H. Radiologic aspects of BCG-­osteomyelitis in infants and children. Acta Radiol (Diagn). 1976;17:845. Patriquin HB, Trias A, Jeoquier S, et al. Late sequelae of infantile meningococcemia in growing bones of children. Radiology. 1981;141:77. Sengupta S. Musculoskeletal lesions in yaws. Clin Orthop. 1985;192:193. Sharif HS, Aideyan OA, Clark DC, et al. Brucellar and tuberculous spondylitis: Comparative imaging features. Radiology. 1989;171:419. Silverman FN. Virus diseases of bone: do they exist? AJR Am J Roentgenol. 1976;126:677. Simeone FJ, Husseini JS, Yeh KJ, et al. MRI and clinical features of acute fungal discitis/osteomyelitis. Eur Radiol. 2020;30:2253. Steinbach LS, Tehranzadeh J, Fleckenstein JL, et al. Human immunodeficiency virus infection: musculoskeletal manifestations. Radiology. 1993;186:833.

SECTION 4  Tumors and Tumor-like Lesions

21 15 Tumors and Tumor-like Lesions of Bone S U M M A R Y O F K E Y F E AT U R E S • C  onventional radiographs are an essential first step in the evaluation of a bone tumor or tumor-like lesion. • Analysis of the lesion margin and periosteal reaction provides an assessment of biologic activity (aggressiveness) of a lesion, whereas matrix analysis may identify underlying pathology.

   The current World Health Organization (WHO) classification of bone tumors lists over 60 specific primary tumor diagnoses, with a wide spectrum of clinical presentations and an equally expansive spectrum of imaging features. As a result, this chapter is divided into four parts. The first part addresses the fundamental principles essential for the analysis of osseous lesions. The second section is a review of the imaging features of the most commonly encountered lesions in which a diagnosis can be made or strongly suggested on the basis of the imaging features. The third section addresses a new tumor category adopted in the 2020 revision of the WHO classification in which tumors common to bone and soft tissue are grouped together. The fourth and final section will address skeletal metastases.

FUNDAMENTAL CONCEPTS IN THE EVALUATION OF OSSEOUS LESIONS The initial assessment of a patient with a suspected osseous lesion begins with a thorough clinical history. As is true for soft tissue lesions, a patient’s history can provide essential information that may allow a specific diagnosis when imaging is not definitive. In contrast to a lesion arising in soft tissue, the biological activity of an osseous lesion is generally well correlated to its rate of growth. This relationship was initially recognized by Lodwick in 1964 when analyzing cases of fibrosarcoma of bone at the Armed Forces Institute of Pathology (AFIP). He correlated the patient 5-­year survival with the pattern of bone destruction, defining three specific patterns of osteolysis: geographic, moth-­eaten, and permeative. He correlated the pattern of tumor bone destruction with survival rates, identifying that the group demonstrating a “permeative destruction had few survivors,” those “with geographic destruction had many,” and the “set with moth-­eaten destruction had an intermediate number.” Lodwick recognized that the tumor growth rate reflected biological activity and “degree of malignancy” and that this was readily identified on radiographs. Lodwick and colleagues subsequently proposed five patterns of bone destruction, with this system further modified by Madewell in 1981, and again modified in 2016. This latest version is preferred and is designated the Modified Lodwick-­Madewell grading system (Fig. 21.1, Table 21.1).

• W  hen combined, patient age, lesion location (in the skeleton and the affected bone), and clinical history/presentation can allow one diagnosis or a limited differential. • Advanced imaging techniques such as magnetic resonance imaging may also be exceedingly helpful in establishing a specific diagnosis.

Pattern of Bone Destruction Radiographs are not extremely sensitive in the detection of small amounts of cancellous bone loss, and it is estimated that 30% to 50% of bone loss is required to recognize an area of osteolysis. Cortical bone loss is more readily identified, but this still can be difficult when the transition from involved to uninvolved cortex is gradual. The detection of a sharply marginated, radiolucent area overlying the medullary portion of a tubular bone (especially a large bone) in a single radiographic image implies cortical involvement. As noted earlier, three radiographic patterns of bone destruction were described initially: geographic, moth-­eaten, and permeative. This was subsequently expanded to five by Lodwick and colleagues and more recently expanded to seven. These are best addressed by dividing them into two groups: geographic and nongeographic bone destruction.

Geographic Bone Destruction KEY CONCEPTS  • A  geographic bone destruction designation is applied to those lesions in which the observer can outline the area of involvement. Such margins may be smooth, lobulated, or irregularly shaped. • Geographic lesions are further described by the definition of the interface between the lesion and the adjacent uninvolved bone as (1) well defined with sclerosis, (2) well defined without sclerosis, or (3) ill defined. • The most aggressive portion of the lesion should be evaluated. • Geographic lesions with sclerotic margins are benign in the overwhelming majority of cases. • Geographic lesions with well-­defined, nonsclerotic margins are usually benign, but caution is required in that they can be seen in processes such as myeloma and metastases. • Geographic ill-­defined lesions are always concerning—about half are malignant.

The geographic pattern is applied to those lesions in which the observer can discreetly outline the area of involvement. Such margins may be smooth, lobulated, or irregularly shaped. They are further

361

362

SECTION 4  Tumors and Tumor-like Lesions

IA

IB

II

IIIA

IIIB

IIIC

Fig. 21.1  Schematic of the bone lesions categorized by the Modified Lodwick-­Madewell grading system.

TABLE 21.1  Modified Lodwick-­Madewell Grading System Gradea Description

Comment

IA

Well-­defined geographic lytic lesion with a sclerotic rim

Slow-­growing or indolent lesion and almost always benign, with few exceptions

IB

Well-­defined geographic lytic lesion with a sharply defined (cookie cutter) margin without a sclerotic rim

Most lesions are benign, although differential diagnosis may include metastatic disease and myeloma in the appropriate clinical setting

II

Geographic lytic lesion with partial or circumferential ill-­defined margin

Should be considered indeterminate, but differential diagnosis should include malignancy

IIIA

Focal change in margination or change in margin over time on serial Focal changes in margin or changes over time indicate increased biological activity radiographs and should raise suspicion for malignancy/malignant transformationb

IIIB

Moth-­eaten or permeative patterns of osteolysis

Scattered and confluent holes in bone, giving the impression of arising from multiple foci or innumerable tiny areas of bone destruction that fade imperceptibly from normal bone to markedly abnormal bone.

IIIC

Radiographically occult lesion

Normal or near-­normal radiographic findings; lesion is seen on advanced imaging, such as MRI or PETc

aMargins

are often not pure, and combined patterns of osteolysis occur. Lesions should be evaluated by the most aggressive pattern of osteolysis. combined patterns of marginal osteolysis are not uncommon, a changing margin is uncommon and is more clinically significant and may indicate malignant transformation. This designation is best applied to areas of definitive change: for example, a lesion with a geographic sclerotic margin transitioning to an ill-defined ­ margin. cInfrequently encountered before MR and CT tumor imaging, such lesions are now seen with increased frequency. To assess these occult lesions in a meaningful way, one must consider truly incidental lesions, such as an incidental cartilaginous lesion identified on an MR image for a patient being evaluated for a meniscal tear, separately from clinically relevant lesions, a distinction that can be difficult. CT, Computed tomography; MR, magnetic resonance; PET, positron emission tomography. bAlthough

CHAPTER 21  Tumors and Tumor-like Lesions of Bone described by the definition of the interface between the lesion and the adjacent uninvolved bone. This interface is characterized by its most aggressive area as (1) well defined with sclerosis, (2) well defined without sclerosis, or (3) ill defined (Fig. 21.2). Recent studies have noted that the vast majority of geographic lesions with a sclerotic margin are benign (Fig. 21.2A), as are

A

90% of those with a well-­d efined, nonsclerotic (cookie cutter) margin (Fig. 21.2B). Malignancies rarely have a sclerotic margin, with the prime exception being the clear cell chondrosarcoma, although this lesion typically has a characteristic skeletal distribution (proximal femur and humerus) and intraosseous location (epiphysis) that usually allow an accurate presumptive

B

*

*

C

363

D

Fig. 21.2  Three main patterns of geographic bone destruction. (A) Geographic lesions with a sclerotic margin (arrows) represent the most indolent pattern of growth, as seen in this nonossifying fibroma. (B) Geographic lesions with well-defined ­ nonsclerotic margins are seen with more rapid growth, in which tumor growth and osteoclastic bone loss are matched (arrows), as seen in this epiphyseal chondroblastoma with metaphyseal extension. (C) Geographic lesions with ill-defined ­ margins are seen with greater biological activity, in which the lesion-stimulated ­ osteoclastic activity cannot match the more rapidly expanding lesion (asterisk), as seen in this case of metaphyseal osteomyelitis. (D) The term combination margin is sometimes used when more than one pattern of osteolysis is seen. This is not uncommon; however, assessment of lesion margins should be classified based on the most aggressive pattern of osteolysis. This fibrosarcoma shows areas in which the margin is well defined and nonsclerotic (arrows) and areas in which the margin is poorly defined (asterisk).

364

SECTION 4  Tumors and Tumor-like Lesions

radiographic diagnosis. Similarly, well-­ d efined, nonsclerotic margins are also classically seen in benign lesions, including bone cyst, enchondroma, and many others. The caveat is that well-­ d efined, nonsclerotic margins can be seen in multiple myeloma and metastatic disease. Although both of these malignant processes are typically multifocal, they can manifest as a solitary focus. Accordingly, it is appropriate to treat solitary geographic lytic lesions with greater scrutiny in older patients, considering them as indeterminate lesions in mature adults. With these limitations in mind, one can certainly state that, overall, a geographic intraosseous lesion with a sclerotic or well-­d efined nonsclerotic margin will be benign in more than 90% of cases. Geographic lesions with ill-­defined margins are far more problematic. Such lesions have a moderate risk of malignancy—it is reasonable to suggest that approximately half will be malignant (see Fig. 21.2C). Such statistics mandate biopsy or close clinical follow-­up depending on the clinical circumstances. Close follow-­up would be more appropriate for an asymptomatic, suspected cartilage tumor, and biopsy would be recommended for a possible giant cell tumor, although there are no established rules. Such patients should be referred to an orthopedic oncologist for management. When biopsy is required, contrast-­enhanced magnetic resonance (MR) imaging before biopsy is suggested. This allows for accurate local staging and for the identification of enhancing areas to target during biopsy in order to optimize tissue sampling. The term combination margin can be used when more than one pattern of bone loss is present; it reflects differences of growth rate and biological activity within the lesion. Lesions should be evaluated on the basis of their most aggressive margin (see Fig. 21.2D). Combination margins are not uncommon and are frequently present in lesions such as giant cell tumors. They need to be distinguished from a changing margin, as discussed in the section on nongeographic lesions that follows.

Nongeographic Bone Destruction KEY CONCEPTS  • T he nongeographic patterns (moth-­eaten, permeative, changing, and invisible) are always concerning for malignancy. • Although the moth-­eaten and permeative patterns were described separately, they often coexist and are now considered together, and are indicative of aggressive biological activity. • A changing margin reflects a change in biological activity and can be a marker of malignant transformations. This may be identified as a focal change at one point of time or a change over time. • An invisible margin may be seen with a highly aggressive pattern with a rapidly growing intramedullary tumor, growing so quickly that the host cannot respond. Caution is required in using this term when evaluating lesions that may be invisible on radiography because of their size or location.

A lesion with a more aggressive radiographic margin (moth-­e aten, permeative, invisible, and changing) must be assumed to be at high risk for malignancy. The moth-­e aten and permeative patterns of bone destruction were initially described by Lodwick. The former was described as “scattered and confluent holes in bone giving the impression of arising from multiple foci”; the latter was described as “multiple tiny holes in cortical bone, which fade imperceptibly in size and frequency from a zone of maximal involvement to cortex that is quite intact.” Lodwick recognized that these patterns could coexist; these are now considered together and indicative of an aggressive lesion that is malignant until proven otherwise (Fig. 21.3). The most aggressive pattern of nongeographic bone destruction is the invisible margin. The most rapidly growing intramedullary tumors may infiltrate through cancellous bone, with radiographs showing little or no change, resulting in the host bone appearing to be encased

*

*

* *

* A

B

C

Fig. 21.3  Original patterns of nongeographic bone destruction are moth-eaten ­ and permeative. (A) Moth-eaten ­ bone destruction (asterisks) as demonstrated in this patient with osseous lymphoma. (B) Permeative bone destruction is seen in this child with osteosarcoma as tumor blends imperceptibly with the normal-appearing ­ humerus distally. Note area of focal bone destruction proximally (white asterisk) and focus of osseous matrix (black asterisk). (C) These patterns of bone destruction may coexist, as in this child having Ewing sarcoma showing moth-eaten ­ changes distally (white arrow) and permeative involvement proximally (black arrow). Note remodeling of the adjacent metatarsals secondary to the tumor mass.

CHAPTER 21  Tumors and Tumor-like Lesions of Bone in tumor on cross-­sectional imaging. Recent experience with MRI and positron emission tomography (PET) has shown that this pattern of disease is not as uncommon as previously suspected and reinforces the observation that 30% to 50% of cancellous bone must be removed before radiolucency can be identified (Fig. 21.4). However, some caution is required using this term when evaluating lesions such as metaphyseal or diaphyseal enchondromas, although they may be invisible on radiography because of their size or location. As the name

A

would suggest, a changing margin reflects a change in biological activity and can be a marker of malignant transformations. This may be identified as a focal change at one point of time or a change over time, with these changes typically nongeographic (Fig. 21.5). Generally, nongeographic margins suggest aggressive biological behavior. Although other processes such as Langerhans cell histiocytosis and osteomyelitis may fall into this group, orthopedic oncology management referral is needed.

B

Fig. 21.4  Nongeographic invisible margin bone destruction. Radiograph of the ankle in a patient presenting with unexplained pain subsequently diagnosed with lymphoma was interpreted as normal (A), with follow-­up MR imaging showing an infiltrating mass encasing cancellous bone (B).

A

365

B

Fig. 21.5  Nongeographic changing margin bone destruction. Anteroposterior radiograph of the distal femur shows a well-­defined geographic lesion with a sclerotic margin (A, black arrows) and a focal area of nongeographic destruction (white arrow). (B) Axial CT image shows these areas to better advantage (arrows). Biopsy of the area of increased biological activity confirmed a high-­grade sarcoma consistent with malignant transformation in a preexisting benign lesion.

366

SECTION 4  Tumors and Tumor-like Lesions

Periosteal Reaction

Matrix

KEY CONCEPTS 

KEY CONCEPTS 

• T he periosteum covers the surface of bone and is composed of two layers: an outer fibrous layer and an inner, more cellular cambium layer. • Tumor-­related change to the contour of cortical bone is the result of periosteal reaction and is termed expansile remodeling; it is usually seen with slowly growing benign lesions. • Continuous periosteal reaction may manifest as cortical thickening or solid continuous periosteal new bone, which is classically associated with indolent, benign processes. • A more biologically active continuous periosteal new bone formation is a single lamella of new bone formation, also typically benign. • More aggressive periosteal reactions include multilamellated new bone formation, termed onion skin periosteal reaction, resulting from repeated phases of periosteal growth, and aggressive spiculated new bone formation, also known as hair on end periostitis, both of which are worrisome for malignancy. • Interrupted and complex periosteal reactions are also concerning for malignancy.

• T he pattern of osseous matrix mineralization is generally characterized as relatively well-­defined areas of increased opacity, classically described as ivorylike or cloudlike. • Although tumor bone is generally produced by osteoblasts, it can be produced by altered fibroblasts. The pattern produced in such cases is metaplastic, woven, or fibrous bone. • Low-­grade cartilage tumors show a disordered pattern of endochondral ossification, leading to the classic arc-­and-­ring pattern of mineralization with disorganized areas of provisional calcification; these findings are termed stipples. Similar, larger coalescent areas are termed floccules. • Dystrophic mineralization is the result of deposition of mineralization within degenerated or necrotic tissue, which may appear as patchy areas of increased opacity.

The periosteum covers the surface of bone and is composed of two layers: an outer fibrous layer and an inner, more cellular cambium layer. The periosteum is active during growth and development as well as during times of injury and repair; however, it is relatively inactive and more firmly adherent to the underlying cortex in adults. The configuration of tumor-­related periosteal reaction is a function of the manner and time course of its production and, as such, is a measure of the aggressiveness and duration of the underlying pathologic process. Although lesion margin is the most accurate indicator of biological activity, this activity is also reflected by periosteal reaction. Although more difficult to evaluate and more variable than margins, increased biological activity correlates with the aggressiveness of the periosteal reaction. These were well described by Ragsdale and colleagues and can be subdivided as continuous, interrupted, and complex (Fig. 21.6). Tumor-­related change to the contour of cortical bone is the result of periosteal reaction. Bone is quite rigid and cannot expand, but it can remodel to an expanded contour. To the pathologist, this is considered to be a continuous periosteal reaction with loss of the normal cortex, while often termed expansile remodeling by radiologists. This type of periosteal reaction is usually seen with slowly growing benign lesions such as nonossifying fibroma or a bone cyst but also can be seen in more active lesions such as aneurysmal bone cyst and intermediate lesions such as giant cell tumor or osteoblastoma (Fig. 21.7). Continuous periosteal reaction can be added to the existing cortex. This may manifest as cortical thickening or solid continuous periosteal new bone, which is classically associated with indolent, benign processes. A more biologically active continuous periosteal new bone formation is a single lamella of new bone formation, also typically benign. This type of periosteal reaction can be seen with processes such as osteomyelitis or Langerhans cell histiocytoma (Fig. 21.8). More aggressive periosteal reactions include multilamellated new bone formation, also termed onion skin periosteal reaction, resulting from repeated phases of periosteal growth, and aggressive spiculated new bone formation, also known as hair on end periostitis, both of which are concerning for malignant disease (Fig. 21.9). The same concern must be applied for all interrupted or complex periosteal reactions. One form of interrupted periosteal reaction that deserves special mention is the Codman angle. Ernest Codman originally described it in 1926 as follows: “Little cuff of reactive bone of trumpet shape which surrounds the upper limit of the tumor appears in the X-­ray as a triangular space on each side of the shaft under the uplifted periosteal edge,” a feature that he recognized as a harbinger of an aggressive, malignant process (Fig. 21.10).

The identification of matrix is important in that it can be a key to identifying the underlying histology. Matrix can be defined as the acellular, intercellular substance produced by mesenchymal cells, which is named for the cells synthesizing the matrix (e.g., osteoblasts produce osteoid). In contrast to non–matrix-­producing tumors, which may be named by gross or histologic features, or even after the author of the initial description, matrix-­producing tumors are named by the matrix that they produce (e.g., osteosarcoma). Although the reality today is much more complex, this concept provides some insight into the pathologic importance of matrix. Radiographically, matrix is useful only when sufficiently mineralized to allow the viewer to identify the characteristic pattern of mineralization. Highly aggressive tumors are often not associated with matrix mineralization.

Osseous Matrix The pattern of osseous matrix mineralization is generally characterized as relatively well-­defined areas of increased opacity, classically described as ivorylike or cloudlike. This is usually best seen in conventional osteosarcoma (Fig. 21.11) but can also be seen in other osseous lesions, such as osteoblastoma or osteoma. Although tumor bone is generally produced by osteoblasts, in certain situations, it can be produced by altered fibroblasts in fibrous tumors. The pattern produced in such situations may be termed metaplastic, woven, or fibrous bone and is generally less densely mineralized than bone produced by osteoblasts. This is the type of bone classically seen associated with fibrous dysplasia and demonstrates a more variable, hazy appearance, radiographically characterized as ground glass (Fig. 21.12).

Cartilaginous Matrix During normal bone formation, the cartilaginous physis undergoes endochondral ossification. The cartilage that is seen in benign and low-­ grade cartilage tumors may also undergo endochondral ossification. When this occurs within the inherently disorganized lobular architecture of cartilage tumors, without uniformity of growth, it results in a disordered pattern of endochondral ossification, leading to the classic arc-­and-­ring pattern of mineralization. The associated disorganized areas of provisional calcification are termed stipples. Similar larger, coalescent areas are termed floccules (Fig. 21.13).

Dystrophic Matrix Dystrophic mineralization is the result of deposition of mineralization within degenerated or necrotic tissue. This occurs most commonly in injured and necrotic fat and degenerating connective tissue. When this occurs within an intraosseous lipoma, it may appear as patchy areas of increased opacity (Fig. 21.14). A similar process occurs at the periphery of osteonecrotic areas.

CHAPTER 21  Tumors and Tumor-like Lesions of Bone

Periosteal Reactions CONTINUOUS Expansile Remodeling

Shell

INTERRUPTED

COMPLEX

Cortex Present

Solid

Codman Angle

Divergent Spiculated “Sunburst”

Lobulated Shell

Single Lamella

Lamellated “Onion Skin”

Lamellated

Combined

Parallel Spiculated Spiculated Rigid Shell “Trabeculated” or “Soap Bubble” “Hair on End” Fig. 21.6  Schematic of the most common periosteal reactions. (Modified from Ragsdale BD, Madewell JE, Sweet DE. Analysis of solitary bone lesions: Part II: Periosteal reactions. Radiol Clin North Am. 1981;19:749– 783.)

367

368

SECTION 4  Tumors and Tumor-like Lesions

A

B

Fig. 21.7  Expansile remodeling (shell-­like continuous periosteral reaction). (A) Smooth shell-­like expansile remodeling (arrows) in a patient with a nonossifying fibroma. (B) Ridged shell-­like trabeculated expansile remodeling, sometimes termed a “soap bubble” appearance (arrows) in a more biologically active aneurysmal bone cyst.

*

A

B

Fig. 21.8  Continuous periosteal reaction added to the existing cortex. (A) Solid continuous periosteal new bone formation (arrows) in a patient with multifocal Langerhans cell histiocytosis. (B) Single lamella of periosteal new bone formation (arrows) in a child with hematogenous osteomyelitis in the distal tibial metaphysis (asterisk).

CHAPTER 21  Tumors and Tumor-like Lesions of Bone

A

B

Fig. 21.9  More aggressive continuous periosteal reactions added to the existing cortex. (A) Multilamellated new bone formation, also termed “onion skin” periosteal reaction, showing the multiple periosteal layers (arrows) in a patient with Ewing sarcoma. (B) Aggressive spiculated new bone formation, also known as “hair on end” periostitis (arrows), also in a patient with Ewing sarcoma.

* A

B

Fig. 21.10  Aggressive complex periosteal reactions and Codman angle. (A) Lateral radiograph of the fibula demonstrating a complex combined periosteal reaction showing a multilamellated and spiculated pattern (arrows) in a patient with Ewing sarcoma. (B) Osteosarcoma of the distal femoral metaphysis (asterisk) with a Codman angle (arrow) identifying the upper margin of the lesion.

369

370

SECTION 4  Tumors and Tumor-like Lesions

* *

*

* A

*

B

Fig. 21.11  Osseous matrix. (A) Anteroposterior radiograph of the shoulder showing a large mass (asterisk) involving the metaphysis and epiphysis of the proximal humerus demonstrating an ivorylike opacity consistent with an osseous matrix in a high-­grade osteosarcoma. (B) Similar lesion in the distal femur, with a more cloudlike appearance (asterisks).

relatively narrow or quite broad depending on the tumor type (Tables 21.2 and 21.3). Similarly, many lesions will demonstrate a relatively characteristic skeletal distribution, most reliably identified in long bones (Fig. 21.15).

COMMONLY ENCOUNTERED PRIMARY BONE TUMORS

* *

Fig. 21.12  Woven or fibrous osseous matrix. The pattern of bone produced in fibrous dysplasia (arrows) demonstrates a less dense, more variable, hazy appearance (asterisks), radiographically characterized as ground glass.

Patient Age and Lesion Location Analysis of lesion margin and periosteal reaction allows an assessment of biological activity. Matrix, when present, can identify specific histologic groups. Patient age and lesion location are also important factors in establishing a diagnosis or a limited differential diagnosis. Specific tumor types have a propensity for specific age groups, which can be

KEY CONCEPTS  • T he WHO classification utilizes four distinct categories for the classification of both bone and soft tissue tumors: (1) benign, (2) intermediate (locally aggressive), (3) intermediate (rarely metastasizing), and (4) malignant. • The designation of locally aggressive is used for lesions that are frequently associated with an infiltrative growth and local recurrence. • The designation of rarely metastasizing is used for those lesions for which there is documentation of the potential to metastasize but when “such metastases occur in less than 2% of cases and are not predictable morphologically.” • The 2020 WHO classification divides bone tumors into eight families (classes), the vast majority of which involve the musculoskeletal system: (1) chondrogenic, (2) osteogenic, (3) fibrogenic, (4) vascular, (5) osteoclastic giant cell–rich, (6) notocordal, (7) other mesenchymal, and (8) hematopoietic tumors/ neoplasms of bone. These are further classified into more than 70 tumor types and subtypes. • The following section highlights the imaging features of the most commonly encountered lesions and/or those for which a diagnosis can be made or strongly suggested on the basis of the imaging features.

As is true for soft tissue tumors, benign tumors and tumor-like processes of bone are far more commonly encountered than are malignancies. To put this in perspective, the 2020 report Cancer Facts and Figures by the American Cancer Society estimates 3600 new malignant

CHAPTER 21  Tumors and Tumor-like Lesions of Bone

A

B

371

C

Fig. 21.13  Cartilaginous matrix. Atypical cartilaginous tumor of the proximal femoral shaft. (A) Anteroposterior radiograph shows the pattern of matrix mineralization well with areas of arc-­and-­ring mineralization (black arrow). Due to the superimposition of the mineralized components, it is difficult to identify the individual matrix components. Note moderate cortical scalloping (white arrow). (B) Corresponding coronal CT reformatted image shows the cartilaginous components to better advantage with arcs (long arrow), rings (short arrow), and multiple stipples (dashed arrow) and floccules (arrowhead). (C) Macroscopic histologic section of an enchondroma in a different patient shows the multilobulated pattern of cartilage growth (arrows), having a similar pattern of mineralization as noted in part B.

* *

Fig. 21.14  Dystrophic matrix. Intraosseous lipoma within the femoral neck with patchy areas of increased opacity (asterisks) representing ischemic bone formation.

prevalence of incidental benign osseous lesions; however, they are certainly not uncommon. The assessment criteria presented in the initial section of this chapter will allow the appropriate assessment of lesion biological potential. Although this chapter will address mainly primary tumors of bone, it is important to remember that metastatic bone disease is much more common. The WHO classifies bone tumors by their biological potential. Although it is convenient to simply divide lesions into benign and malignant, the current WHO classification utilizes four distinct categories for the classification of both bone and soft tissue tumors: benign, intermediate (locally aggressive), intermediate (rarely metastasizing), and malignant. The designation of locally aggressive is used for lesions that are frequently associated with an infiltrative growth and local recurrence, but “do not appear to have the potential to metastasize.” The designation of rarely metastasizing is used for those lesions for which there is documentation of the potential to metastasize, but when “such metastases occur in less than 2% of cases and are not predictable morphologically.” Tumors are grouped by their biological potential; however, the progression of aggressiveness in this classification should not be taken to suggest that there is a continuum of individual lesion to demonstrate increasing aggressive behavior over time. In the following discussions, we will highlight those bone tumors and tumor-like lesions for which the diagnosis can be made or suggested by imaging or are sufficiently common that knowledge of them is important.

Chondrogenic Tumors tumors of bone and joint for the calendar year. Although this is not an insignificant number, it pales in comparison to the 279,100 cases of newly diagnosed breast cancer or 228,800 cases of lung cancer for the same time period. It is impossible to accurately estimate the true

The current WHO classification of chondrogenic tumors includes 17 entities: 8 benign, 2 intermediate (locally aggressive), and 7 malignant. The following highlights the most common and/or characteristic lesions.

372

SECTION 4  Tumors and Tumor-like Lesions

TABLE 21.2  Common Tumor and Tumor-like Lesions by Age CAĠUA=NO

1QIKN



















Benign Enchondroma Osteochondroma Chondroblastoma Chondromyxoid fibroma Osteoma Osteoid Osteoma Aneurysmal bone cyst Non-ossifying fibroma Simple bone cyst Lipoma Hemangioma Intermediate (locally aggressive) Osteoblastoma Desmoplastic fibroma Intermediate (locally aggressive, rarely metastasizing) Giant cell tumor Malignant Chondrosarcoma Osteosarcoma Fibrosarcoma Angiosarcoma Malignant giant cell tumor Chordoma Adamantinoma Plasmacytoma Lymphoma Ewing sarcoma Skeletal metastasis

Benign Chondrogenic Tumors Enchondroma. KEY CONCEPTS  • E nchondroma is likely the most common benign cartilage neoplasm and has been identified as an incidental finding on 3% of routine knee MR scans. • Enchondromas are most frequent in the short tubular bones of the hands (40%–65%) and long tubular bones (25%). • In small bones, they appear radiographically as a well-­defined, intramedullary lesion with some degree of a lobulated contour, endosteal scalloping, and variable mineralization. • In the long tubular bones, radiographs are relatively similar, demonstrating osteolytic lesions of variable size but usually less than 5 cm. • MR images usually show a well-­circumscribed, lobulated lesion of low signal on T1-­weighted and increased signal on fluid-­sensitive sequences, characteristically with areas of fatty marrow between the cartilaginous nodules. • As would be expected, mineralization within the lesion will demonstrate decreased signal on all sequences.

Enchondroma is likely the most common benign cartilage neoplasm. Usually solitary, it represents as many as 17% of benign tumors in surgical series. The caveat “likely” is used in that it is often identified as an incidental finding and has been identified in 3% of knee MR examinations. Enchondromas are found with relatively similar prevalence in both males and females and are most frequently in the short tubular bones of the hands; this location accounts for 40% to 65% of cases. The long tubular bones account for about 25% of cases, with the upper extremity involved more frequently than the lower extremity. Enchondromas are very uncommon in the flat bones and a cartilage lesion in the ilium or sternum should be assumed to be a chondrosarcoma until proven otherwise. Lesions are typically small, less than 5 cm, and are seen across a wide age spectrum—most commonly found in the third to fifth decades. Lesions are typically asymptomatic; thus, symptoms should raise suspicion for a more biologically active lesion. The radiographic appearance of lesions in the small tubular bones of the hand and foot is usually characteristic. A well-­defined, intramedullary lesion with some degree of a lobulated contour, endosteal scalloping, and mineralization, classically with an arc-­and-­ring pattern,

CHAPTER 21  Tumors and Tumor-like Lesions of Bone

373

1

2

3

4

6 5

9

7 8

Fig. 21.16  Enchondroma, small tubular bone. Anteroposterior radiograph of the proximal phalanx of the long finger shows a small lytic lesion (arrows), with lobulated endosteal scalloping and mineralization, demonstrating an arc-­and-­ring pattern with stipples and floccules.

10 11

Fig. 21.15  Schematic of the most common lesions with characteristic long bone locations based on the field theory of bone tumors presented by Johnson in 1953. 1, Ewing sarcoma and round cell sarcoma; 2, osteoid osteoma; 3, fibrous dysplasia; 4, nonossifying fibroma; 5, bone cyst, osteoblastoma; 6, osteochondroma; 7, osteosarcoma; 8, enchondroma; 9, giant cell tumor (originating in the metaphysis with growth toward the end of the bone); 10, chondroblastoma; 11, dysplasia epiphysealis hemimelica (articular osteochondroma). (Modified from Madewell JE, Ragsdale BD, Sweet DE. Analysis of solitary bone lesions: Part I: Internal margins. Radiol Clin North Am. 1981;19:715–748.)

allows a confident diagnosis in most cases (Fig. 21.16). Cortical expansile remodeling or thickening and pathologic fracture are other potential radiographic characteristics (Fig. 21.17). Enchondromas in the long tubular bones often show a similar appearance, demonstrating centrally or eccentrically placed medullary, osteolytic lesions of variable size but usually less than 5 cm. Matrix mineralization is also variable. It has been postulated that enchondromas are the result of displaced physeal cartilage. As such, it is not surprising that they are often identified in the metaphyseal regions. It would follow that those that form earlier in life would be located further from the physis. It is important to recognize that long bones are predominantly filled with fatty marrow and as the amount of cancellous bone decreases from its prominence in the metaphysis to the diaphysis, it can be difficult to recognize unmineralized lesions (Fig. 21.18). The MR image of enchondroma is usually characteristic, showing a well-­circumscribed, lobulated lesion of low signal intensity on T1-­weighted MR images and high signal intensity on fluid-­sensitive sequences. Areas of fatty marrow are often seen between the cartilaginous nodules within the lesion; however, this is variable. As would be expected, mineralization within the lesion will demonstrate decreased

Fig. 21.17  Enchondroma in a small tubular bone. Anteroposterior radiograph of the proximal phalanx of the ring finger with pathologic fracture (arrows). Note mild contour changes of the proximal phalanx consistent with expansile remodeling as well as mineralized matrix.

signal on all sequences (Fig. 21.19). Following the administration of contrast, cartilage will demonstrate a characteristic peripheral and septal pattern of enhancement. This MR appearance allows incidental enchondromas to be diagnosed with confidence (Fig. 21.20). The distinction between enchondroma and low-­grade chondrosarcoma can be quite challenging. This has been addressed by the WHO and is discussed in detail later in the section on intermediate and malignant chondrogenic tumors.

374

SECTION 4  Tumors and Tumor-like Lesions

TABLE 21.3  Tumors and Tumor-­Like Lesions: Typical Sites of Skeletal Localization SITEa Tumor or Tumor-­Like Lesion (Number of Cases Evaluated) Femur

Tibia

Fibula

Foot

Patella

Humerus

Radius

Ulna

Hand, Wrist

Enostosis (371)

25

7

1

5