UCSD Musculoskeletal Radiology bonepit.com MSK Classifications

Class I has islands of bone within the soft tissues.

Class II has bone spurs from the pelvis or proximal end of the femur, leaving at least 1 cm between opposing surfaces.

Class III has bone spurs from the pelvis and/or proximal end of the femur, reducing the space between opposing bone surfaces to less than 1 cm.

Class IV shows apparent bone ankylosis of the hip.