Location: >50 % knee, then elbow, shoulder, wrist, hip, and ankle. Extra-articular form in the fingers.

Clinical: Pain, limited joint motion, and sensation of joint crackling. Rare blocking and joint effusion. Palpated loose bodies. Recurring and slowly progressive symptoms. Plurilobulated hard-elastic mass expanding around a joint in aggressive type.

Imaging: On X-ray—negative if not calcified or small-sized calcified nodules into the joint, typical rice grain-like. The joint is normal. Arthrosis is frequent in inveterate cases and bone erosion or cortical scalloping in the aggressive ones. On CT—more evident pseudotumoral mass, calcifications, bone lesions, and invasion of the surrounding tissues. On MRI—increased joint fluid, lobular intra-articular mass, intermediate intensity if uncalcified or with white punctuated appearance if ossified on T1, round, ringlike, dark signal voids in strong enhancement of the synovial tissue on contrast T1 and in bright signal of the joint fluid on T2.

Histopathology: White, smooth, lucent, translucid soft or firm, loose bodies of different size. Thickened and seeded with cartilaginous nodule synovial membrane; hard, granular, yellowish ossified areas in the nodules. Minute nests of cartilage enmeshed in primitive mesenchymal tissue in all stages of maturation. Well-differentiated rather cellular hyaline cartilage. Cells in small bunches, divided by bands of ground substance. Well-defined boundaries of the lobuli; large, numerous cells with a plump, double nucleus, with nuclear pleomorphism and abnormalities like in chondrosarcoma grade 1 or 2. Endochondral ossification areas.

Course and Staging: Slow growth and rare recurrence even if surgery is inadequate. Usually, stage 2 or 3. Sometimes it may spontaneously regress. Very rare cases can transform into chondrosarcoma.