A lame 8 month old foal Because of the lameness and joint capsular swelling multiple radiographs were made of both stifle joints including lateral and lateral oblique studies. Oblique views - right affected and left normal joints Lateral views - right affected and left normal joints Radiographic diagnosis - osteochondrosis of the lateral trochlear ridge Osteochondrosis of the lateral trochlear ridge with soft tissue swelling suggesting intracapsular fluid accumulation (arrows). The lesion is best understood by finding the lateral trochlear shadow on the normal study (arrows) and then noting the flattening of the lateral trochlear ridge with failure to ossify on the affected limb. This is a continuation of the case from last month and demonstrates the marked variation that can be seen in patients with the same diagnosis. Last month, the OCD lesion was minimal with only small fragments of mineralized cartilage identified. The case shown this month is actually diagnosed by the flattening with absence of much of the trochlear ridge. The prognosis is obviously different in this month’s patient. Radiographic diagnosis - osteochondrosis of the lateral trochlear ridge Osteochondrosis is a failure of endochondral ossification, in this case, of the articular-epiphyseal cartilage complex resulting in cartilage fragmentation of the lateral trochlea of the femur or complete failure of the trochlar ridge to ossify. The lesion varies in size and area of articular cartilage involvement and often becomes dissecting with formation of chondral or osteochondral fragments that become detached and form joint mice. Blood vessels from the synovium often remain in communication with the cartilage flaps or detached flakes leading to calcification or ossification of the avulsed cartilage making some of the fragmented lesions visible radiographically. The mineralized fragments are easily recognized both because of their density and predictable location. Studies of the opposite limb should be included irrespective of clinical signs because of the frequency of occurrence bilaterally. Studies in the dog and pig have shown that the lesions of osteochondrosis are often seen in multiple anatomic locations suggesting a systemic disease. It then is a question of how complete the radiographic/clinical examination should be in a horse with knowledge of the presence of one OCD lesion.
