The incidence of fabellae in osteoarthrosis of the knee.

I examined radiographs of the knees of 600 men to determine the incidence of fabellae in radiographically normal knees as compared with knees with primary osteoarthrosis. At least a unilateral fabella was present in 106 (35 per cent) of 300 patients with primary osteoarthrosis of the knee. In an age-matched group of 300 patients with radiographically normal knees, only forty-four (15 per cent) had a fabella. The presence of a fabella may represent an atavistic pattern, and the fact that knees with primary osteoarthrosis are more likely to contain a fabella raises the question of whether an atavistic pattern predisposes a knee to osteoarthrosis.