Dorsal effect of the patella: incidence and distribution.

To determine the incidence and distribution of dorsal defect of the patella, the radiographs of 2,349 knees in 1,192 consecutive patients were evaluated. The defect was present in about 1% of the population. It may be found at any age from the preadolescent to the mature adult. Females were more commonly affected than males. The test population group was validated by concurrent tabulation and comparison with other series of two other bening lesions occurring at the knee: fabella and multipartite patella.