Aneurysmal bone cyst of the patella.

Aneurysmal bone cysts are uncommon lesions accounting for less than 1% of reported primary bone tumors. This case study reports the ninth primary aneurysmal bone cyst of the patella, and the second to be reported in a white male patient. The scarcity of reports in this vulnerable site may refute trauma as the cause. If the articular surface is spared, this lesion can be treated successfully by curettage and bone grafting, once a definitive diagnosis is made.