The double patella syndrome.

First described by A. Trillat, the double patella is an uncommon clinical feature following repetitive injuries of the extensor mechanism of the knee. The first injury is a tendo-periosteal avulsion of the suprapatellar or, less frequently, infrapatellar tendon from the corresponding patellar pole. Often these avulsions are misdiagnosed and therefore treated only with a cast or no immobilization at all. Subsequent giving-way episodes lead to extensive ossification which is adjacent to or separated from the patella. The peculiar shape of this ossification overriding or underlying the primary kneecap justifies the denomination of double patella. Surgical treatment consists of removal of the calcification and reattachment of the tendon to the patella by transosseous sutures.