Solitary synovial chondromatosis as a cause of Hoffa's fat pad impingement

Synovial chondromatosis is a benign disease of synovial membrane usually affecting knee, elbow and shoulder joints. It rarely appears as a solitary formation and exceptionally within Hoffa's fat pad.

We report a case of solitary synovial chondromatosis within Hoffa's fat pad as a cause of its impingement in a female patient aged 63. At first, the patient had anterior knee pain with limited extension of the knee. Standard radiogram showed only mild patellofemoral osteoarthritic changes. Magnetic resonance of the knee showed ovoid solitary formation within Hoffa's fat pad repressing its superior part between the kneecap and distal femur. Histopathological examination confirmed a case of extra-articular synovial chondromatosis. The tumorous mass was extracted surgically en bloc.

Solitary synovial chondromatosis is an uncommon cause of Hoffa's fat pad impingement and anterior knee pain in elderly female patients and can easily be misinterpreted as a different diagnosis.