Case report 789: Dorsal defect of the left patella.

Dorsal defect of the patella is an uncommon but well known abnormality. It is believed to be an incidental finding that should not merit further intervention. However, the association of patellofemoral symptoms and a dorsal defect of the patella suggests abnormality of the cartilage overlying the defect. Resection of this area of abnormal cartilage has resulted in relief of symptoms in some patients. A patient who had a dorsal defect of the patella and persistent symptoms had MR imaging. The MR scans showed signal inhomogeneity with streaks of high signal in the cartilage overlying the lesion on both T1-weighted and T2-weighted images. Drilling of the defect relieved his pain.