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.