Epidemiologic study of dogs with the displacement or deformity of the medial and lateral fabellae in Japan.

: The prevalences of displacement and deformity of the medial and lateral fabellae in dogs were investigated. This was a retrospective epidemiologic study. Radiographs of canine stifle joints (1022 limbs, 534 dogs) were obtained. The images were taken at the Nihon University Animal Medical Center and three private animal hospitals from January 2003 to July 2012. The position and morphology of the medial or lateral fabella were evaluated on the radiographs. The prevalence of displacement of the medial and lateral fabellae was 1.7% and 0.3%, respectively. The prevalence of deformity of the medial and lateral fabellae was 6.9% and 4.6%, respectively. Aplasia or hypoplasia of the fabella was detected more frequently in the medial fabella. On the other hand, a bipartite or multipartite fabella was observed more frequently in the lateral fabella. Nearly all cases of displacement or deformity of the fabella occurred in dogs weighing less than 10 kg. Abnormalities of the fabella were observed in the medial and lateral fabella. We found that abnormal fabellae were closely associated with medial patellar luxation and to a lesser extent with cranial cruciate ligament rupture. No clinical signs were associated with an abnormality of the fabella, with the exception of two dogs with traumatic avulsion of the lateral head of the gastrocnemius muscle.