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Osteochondritis Dissecans |  |
| For complete discussion of equine osteochondrosis, see
Osteochondrosis . |
| In osteochondritis dissecans (OCD), a focal area of the immature articular cartilage is retained, and the matrix in the basal area of this region becomes chondromalacic and acellular. The immature articular cartilage separates from the underlying trabecular bone. The chondral fracture extends horizontally and vertically until a flap is formed. Synovial fluid gains entrance to the underlying medullary space, and subchondral cysts may form (usually only in larger animals). The flap
of immature articular cartilage may break away completely (“joint mice”) or may reattach by endochondral ossification to the underlying bone, especially in pigs, and result in a wrinkled articular surface. The latter occurs only if the joint is rested or protected, which permits reestablishment of the circulation necessary for endochondral ossification. If the flap is torn free by joint motion, it may be ground into smaller pieces during locomotion and disappear, while the larger
plaques may become attached to the synovial membrane, become vascularized, and ossify. The resultant articular defect, in time, fills with fibrocartilage. |
| Etiology: |
| The exact cause is unknown but is assumed to be multifactorial. Factors include genetic predisposition, fast growth, high caloric intake, low copper and high zinc levels, and endocrine factors. |
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| Clinical Findings: |
| The most common sites of OCD, which usually is seen in young animals, are the femoropatellar joint, tibiotarsal (tarsocrural) joint, fetlock (metacarpophalangeal and metatarsophalangeal) joints, and the shoulder. |
| Animals with OCD of the shoulder usually present when <1 yr old with severe forelimb lameness and possibly some muscular atrophy. Animals with osteochondrosis in the other joints usually present with synovial effusion and varying degrees of lameness. Diagnosis is confirmed with radiographs. |
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| Diagnosis: |
| The history, age, breed, sex, and clinical signs provide useful information; however, radiographs are required to substantiate the diagnosis. |
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| Treatment: |
| The treatment of OCD depends on the location and degree of involvement. Femoropatellar joint lesions are associated with the lateral trochlear ridge of the femur, medial trochlear ridge of the femur, or distal patella. They are amenable to arthroscopic surgery, which is recommended in all cases except early lesions characterized by flattening (without fragmentation) <2 cm long on the lateral trochlear ridge. In the tarsocrural joint, OCD lesions are seen in decreasing
frequency on the intermediate (sagittal) ridge of the tibia, lateral trochlear ridge of the talus, medial malleolus of the tibia, and medial trochlear ridge of the talus. All lesions are amenable to arthroscopic surgery, and the prognosis is usually good. Surgery is recommended when synovial effusion is present. Lesions without fragmentation in the metacarpophalangeal or metatarsophalangeal joints can be treated conservatively, and most affected animals recover well. If a
fragment is present, arthroscopic surgery is recommended. In the shoulder, surgery is always recommended, but the prognosis is less favorable than in the other joints. |
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