EXERCISE 7-5. MISCELLANEOUS JOINT DISORDERS
7-18. The most likely diagnosis for Case 7-18 (Figure 7-46) is
A. synovial osteochondromatosis.
B. pigmented villonodular synovitis.
C. avascular necrosis of the femoral condyle.
D. osteochondritis dissecans (OCD) of the femoral condyle.
7-19. The most likely diagnosis for Case 7-19 (Figure 7-47) is
B. synovial osteochondromatosis.
C. pigmented villonodular synovitis.
D. calcified Heberden’s nodes.
7-20. The most likely diagnosis for Case 7-20 (Figure7-48) is
A. chronic changes of transient synovitis of the right hip.
B. chronic changes of slipped capital femoral epiph-ysis (epiphysiolysis).
C. chronic changes of Legg-Calvé-Perthes disease of the right hip.
7-21. Concerning Case 7-21 (Figure 7-49), the observa-tions include all of the following except
A. osteophyte in both femoral heads.
B. irregularity and loss of spherocity of the right femoral head.
C. depression/subchondral fracture of right femoral head.
D. bilateral acetabular sclerosis.
7-18. The AP view of the right knee (Figure 7-46) shows an ovoid bony fragment on the inner aspect of the me-dial femoral condyle (arrow) separated from the femur by a lucency (arrowheads). This appearance is diagnostic of osteochondritis dissecans (OCD) of the knee (D is the correct answer to Question 7-18).
7-19. The radiograph of the right shoulder in Figure 7-47 shows multiple rounded calcific bodies overlying the proximal humerus and glenoid process of the scapula. The distribution of these is within the joint and axillary recess (arrows). This appearance is classic for synovial osteochondromatosis (SOC) (B is the correct answer to Question 7-19).
7-20. The radiograph of the pelvis in Figure 7-48 shows collapse of the right capital femoral epiphysis, which is broad and short and forms an acute angle with the shaft of the femur. The femoral head is displaced lat-erally and is not completely covered by the mildly re-modeled acetabulum. The left hip is normal. The findings are characteristic of the late changes in Legg-Calvé-Perthes disease (C is the correct answer to Question 7-20).
7-21. The radiograph of both hips in Figure 7-49 demon-strates that the right femoral head is no longer smooth and spherical (loss of spherocity), and this is due to the presence of subchondral collapse in the superiolateral aspect (arrow). The left femoral head is still spherical but shows sclerosis. Also note the marginal osteo-phytes arising from the inferior and medial aspect of the left femoral head (arrowhead). The acetabuli are normal, and these radiographic features are typical of avascular necrosis (osteonecrosis) of the femoral head (D is the correct answer to Question 7-21).
Osteochondritis dissecans is a bone disorder that produces joint symptoms because of the intraarticular location of the abnormality. OCD, as classically demonstrated in Figure 7-46, is seen on the radiograph as a semicircular focus of bone and overlying cartilage separated from the convex articular sur-face of the native bone by a lucency. The etiology is uncertain, but current opinion favors repetitive microtrauma and vascu-lar insult to the subchondral bone. Almost any joint may be af-fected, but the knee (distal femur), ankle (dome of the talus), and elbow (capitellum) joints are the most commonly involved sites. The disease is slightly more common in active young men but is increasingly being encountered in young women because they are more actively involved in athletics today. In the knee, OCD most commonly involves the non-weight-bearing aspect of the medial femoral condyle (ie, the inner aspect and area shown in Figure 7-46) and the lateral femoral condyle. MR im-aging is the most appropriate modality to stage the lesion, as-sess the stability of the fragment, and plan definitive treatment. CT or CT arthrography is an alternate modality to use in pa-tients who cannot undergo MR imaging.
Synovial osteochondromatosis is a joint abnormality char-acterized by the presence of cartilaginous and osseous loose bodies within the synovial cavity in the joint. The exact cause is not known, but “primary” SOC is thought to be caused by synovial metaplasia. “Secondary” OCD is assumed to be due to fractures of osteophytes or articular cartilage that shed into the joint cavity. If calcified, these intraarticular fragments can be visualized on conventional radiographs (Figure 7-47, ar-rows). MR imaging is the best modality to use to show both ossified and nonossified intraarticular fragments and to eval-uate the other soft-tissue structures around the joint.
Pigmented villonodular synovitis (PVNS) is a condition of unknown etiology characterized by hyperplasia or excessive villous proliferation of the synovium. This condition may occur in a single joint (localized form) or involve multiple joints (diffuse form). Thought to be caused by hemorrhage, PVNS shows hemosiderin-laden macrophages within the syn-ovium best appreciated by gross examination. Radiographs often show a joint effusion with preservation of the articular space and normal bone mineral density. The later stages of the disease result in erosions on both sides of the joint. Joint aspiration yields dark brown fluid (“chocolate” effusion) due to the presence of the hemosiderin-laden macrophages. MR imaging is an excellent preoperative test to evaluate PVNS because the pigmented material (hemosiderin) shows low signal intensity on both the short TE (T1-weighted) and the long TE (T2-weighted) MR sequences. The gradient echo se-quence is particularly sensitive for the detection of hemo-siderin. In fact, this finding is a very specific appearance for this disease.
Heberden’s node is a disfigurement of the interphalangeal joints as a result of severe osteoarthritis. Initially, it is due to soft-tissue inflammatory changes and is subsequently due to bony changes at the distal interphalangeal joints. It is more commonly seen in female patients.
Osteonecrosis can occur in any bone and is associated with a variety of disorders, including sickle cell hemoglo-binopathy, Gaucher’s disease, SLE, pancreatitis, alcoholism, steroid treatment, and barotrauma. When the process occurs at an articular surface, it is known as avascular necrosis or os-teonecrosis; when it occurs in the metaphysis of the bone, it is commonly referred to as a bone infarct. Eponyms have been used to designate osteonecrosis in certain sites. For example, Perthes’ disease (Legg-Calvé-Perthes disease) is the eponym used to refer to idiopathic osteonecrosis of the femoral head occurring in a child as shown in Case 7-20 (Figure 7-48).
Other common eponyms include Freiberg’s infarction, (avas-cular necrosis of the head of the second or third metatarsal), Kohler’s disease (tarsal navicular), Panner’s disease (capitel-lum of the humerus), and Kienbock’s disease (carpal lunate). The exact mechanism of the development of osteonecrosis is unknown, although bone-marrow edema after thrombosis and occlusion of the osseous capillaries and end arterioles are believed to be primarily responsible.
Conventional radiographs are much less sensitive compared to MR regarding the detection of early osteonecrosis. Increased areas of serpiginous sclerosis and osteolysis can be noted on conventional radiographs; however, these abnormalities found relatively late compared to MR imaging, and therefore treat-ment outcome of the disease may be delayed or adversely af-fected (Figure 7-49). Importantly, if the disease is not diagnosed and treated early, the affected bone may go through a phase of subchondral collapse and become deformed. Subsequently, complications of secondary osteoarthrosis will develop in the affected joint. Traditionally, nuclear medicine bone scanning has been used in this setting, but today MR imaging is the most sensitive available modality for the early diagnosis of this dis-ease (Figure 7-50).
Hemochromatosis is a rare disorder of iron metabolism, in which iron is deposited in the skin, parenchymal organs, and articular cartilage. This predisposes the joint to degenerative disease. Arthritis due to hemochromatosis is characterized by loss of joint space and formation of peculiar hooked osteo-phytes, especially at metacarpal heads.
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