Which radiographic finding is most directly responsible for the 'bone-on-bone' appearance in OA?

• A. Joint space narrowing
• B. Osteophyte formation
• C. Subchondral sclerosis
• D. Eburnation

Answer: (A)

When osteoarthritis shows a bone-on-bone appearance on radiographs, the key factor is loss of articular cartilage that normally cushions the joint, leading to joint space narrowing. As cartilage wears away, the space between the two ends of the bone becomes smaller until the bones come into contact, producing the classic bone-on-bone look on the image. This narrowing is the direct cause of the contact between opposing bone surfaces.

Other radiographic features reflect the joint’s response to this process but don’t cause the bone-on-bone contact. Osteophyte formation are bone spurs at the margins that develop as the joint tries to stabilize itself. Subchondral sclerosis is thickening of the bone just beneath the cartilage from remodeling over time. Eburnation is the polishing of exposed subchondral bone that occurs after the cartilage is lost and the bone rubs against bone; it’s a consequence of bone-on-bone contact rather than its initiator.