A 78 year old woman was discovered to have acquired double patella syndrome after a suprapatellar tendo-periosteal avulsion was treated without immobilisation. Often these avulsions are misdiagnosed and therefore treated only with a cast or no immobilisation. Repeated injuries of the extensor mechanism of the knee and episodes of the knee giving way lead to extensive ossification. The peculiar shape of this ossification overriding the primary kneecap justifies the denomination of double patella. Congenital double patella syndrome is even rarer than the acquired syndrome and may be found in patients with multiple epiphyseal dysplasia.

H Sharma, senior house officer, F Denolf, consultant, R Burgul, consultant radiologist, department of trauma and orthopaedics, Falkirk and District Royal Infirmary, Falkirk FK1 5QE