Unusual osteochondral lesions of the talus in a horse

A 2-year-old Thoroughbred gelding was evaluated for a grade 3 out of 5 unil ateral hind limb lameness. Flexion of the right hock and stifle joints (spa vin test) exacerbated the lameness. Response to intra-articular and perineu ral anaesthesia isolated the source of lameness to the tarsocrural area, de spite an absence of tarsocrural joint effusion. Routine radiographic examin ation of the hock did not reveal any significant abnormalities. Skeletal nu clear scintigraphic evaluation revealed a focal region of increased bone ac tivity in the proximal medial trochlear ridge of the talus. Flexed laterome dial radiographic views identified three discrete semicircular lytic lesion s at the proximal articular margin of the medial trochlear ridge of the tal us. Conservative management of the lesions was associated with a successful return to racing. The location and appearance of the osteochondral lesions of this report have not been previously reported and may be a manifestatio n of developmental orthopaedic disease and abnormal endochondral ossificati on. Nuclear scintigraphy and flexed lateromedial radiographic views facilit ated identification of the lesions. This radiographic view is recommended w hen lameness is isolated to the tarsocrural joint and standard radio-graphi c projections fail to identify a cause.