Dorsal defect of the patella.

Dorsal defect of the patella is a benign subchondral lesion of unknown etiology, located in the superolateral region of the patella. The lesion presents with a characteristic radiographic appearance consisting of a rounded focus of radiolucency surrounded by a sclerotic margin. Although often an incidental finding on knee radiographs, it occasionally may be symptomatic. It occurs in males and females with equal frequency, is bilateral in up to one third of individuals, and is most frequently found in adolescents. This report describes a series of eight such lesions in five patients.