Fabellae and popliteal sesamoid bones in cats

Radiographs of the stifle joints of cats revealed a lack of mineralisation in the medial os fabella in a high percentage of domestic cats and also some exotic species of cat. In all the post mortem examinations undertaken the medial sesamoid bones were smaller. In the non-radiopaque sesamoid bones there was a solid mass which on histological examination consisted of fibrocartilage, whereas the radiodense sesamoid bones consisted of lamellar osseous tissue. The lack of mineralisation of the medial fabellae seems to be more prevalent in domestic than in pedigree cats. None of the exotic cats had mineralised tissue in the medial fabellae. Lack of mineralisation of the sesamoid bones is not significant clinically.