Lipoma arborescens of the knee

Abstract Lipoma arborescens (diffuse articular lipomatosis) is a rare, benign intra-articular lesion of unknown aetiology. It is characterised by villous proliferation of the synovium and diffuse replacement of the subsynovial tissue by mature fat cells. It forms part of the differential diagnosis for a slowly progressive chronically swollen knee. We present a very rare case of bilateral involvement of the knee and discuss the symptoms, diagnosis and treatment of this condition.