Symptomatic dorsal defect of the patella in a runner.

The dorsal defect of the patella is a benign lesion characteristically located in the superolateral corner of the patella. The microscopic pathology shows fibrous tissue, reactive woven bone, and stringy, eosinophilic, extracellular debris. Although the lesion is usually asymptomatic, the juxtaarticular location in the patella can provoke symptoms in the athlete. Excision of the lesion and cancellous bone graft of the defect resolved the problem in a competitive adolescent runner.