The following changes are seen in the affected joints on X-ray depending on the severity of the disease: (1) narrowing of the joint space; (2) sclerosis of the subchondral bone; (3) formation of perichondral bone fragments or free bodies; (4) cystic changes in the subchondral bone and, in rare cases, chisel-like bone changes; (5) inversion or valgus deformity of the joint, or subluxation changes. It should be noted that the x-ray presentation of osteoarthritis is not parallel to the clinical symptoms, i.e., the symptoms of a knee with a severe x-ray presentation are not necessarily more severe than those of a joint with a mild x-ray presentation.