Giant Extra-articular Synovial Osteochondromatosis of the Sinus Tarsi: A Case Report

A 32-year-old male presented with painful swelling of the sinus tarsi that occurred during daily activities. Diagnostic imaging suggested the presence of a large synovial osteochondromatosis that blocked subtalar motion with deformity of the adjacent bone. The large bony mass was excised, and normal subtalar motion was achieved.