Review of para-articular soft tissue osteochondromas of the knee

Para-articular osteochondromas (PAOCs) are a rare benign subtype of chondroma that occur in the soft tissues around the joints. Initially hypothesized to be derived from cartilaginous metaplasia, its aetiology and pathogenesis are still not fully understood. This tumour often causes a diagnostic and management dilemma due to similar clinical and histopathological features compared with other pathology. We report the fourth case of PAOC arising from the suprapatella region of the knee joint and review the literature to update our understanding of this tumour. From the data analysed, a distinctive pattern of tumour formation within or adjacent to a fat pad structure was evident, while trauma appears to play a role in its pathogenesis. Histologically, the tumour consists of a cartilage cap, with varying degrees of trabecular bone and endochondral ossification. Importantly, there are no features of nuclear pleomorphism or increased mitotic activity suggestive of a malignant process. All tumours were surgically removed and behaved in a benign fashion without evidence of recurrence. PAOC may often be suspected for more malignant processes; thus, recognition of this entity is important as simple excision is curative.