Synovial cell sarcoma presenting as spasmodic peroneal flatfoot

Abstract Commonest cause for spasmodic peroneal flatfoot is tarsal coalition with others being juvenile chronic arthritis, infections of the subtalar joint, trauma, osteoid osteoma and fibrosarcoma. We present a rare cause of synovial cell sarcoma of the sinus tarsi. This case report highlights the unusual clinical presentation, difficulties in its diagnosis and the resultant delay in diagnosis. We recommend MRI scan in addition to the usual imaging modalities and to consider this rare cause in the differential diagnosis of spasmodic peroneal flatfoot.