Giant intra-articular extrasynovial osteochondroma of the Hoffa's fat pad

Abstract

The commonly encountered osteochondroma is a benign tumour that usually arises from the metaphyseal region of long bones, demonstrates mature bone with a cartilaginous cap, a continuation of the medullary cavity with that of the long bone and grows away from the joint till achievement of skeletal maturity. Extraskeletal para-articular osteochondroma, also known as intracapsular chondroma, arises from the capsule and/or connective tissue adjacent to the capsule due to osteocartilaginous metaplasia and occurs most frequently around the knee, particularly the infrapatellar fat pad of Hoffa.1 Extraskeletal para-articular osteochondroma is a rare entity with only 23 cases reported till 19972 and about 40 cases by 2006.3 This article reports another giant intra-articular extrasynovial osteochondroma of the knee which was surgically excised and discusses the clinical and imaging features, the histology and purported pathogenesis, and the differential diagnosis.