Extraskeletal paraarticular osteochondroma of the knee—a case report and tumor overview

Extraskeletal paraarticular osteochondromas are rather unusual osteocartilaginous lesions that arise in the soft tissues adjacent to the joint with no bony or joint continuity. This diagnosis should be considered with the demonstration of a well-circumscribed extraskeletal mineralized mass without any direct continuity with adjacent bone or joint. However, as with other lesions, clinicoradiographic features with histological correlation clinch the diagnosis. Differentiation from other lesions, particularly synovial osteochondromatosis and chondrosarcoma is essential to avoid unnecessary aggressive surgical procedures as marginal excision is adequate for these lesions. We present here such an infrapatellar lesion and discuss criteria helpful in distinguishing these benign lesions from other morphological similar lesions.