Which hip X-ray findings are associated with rheumatoid arthritis?

• A. Osteophyte formation
• B. Joint space narrowing of the acetabulum
• C. Acetabular joint narrowing and acetabulo-protrusio
• D. Normal hip joints

Answer: (C)

Rheumatoid arthritis produces destructive, erosive changes in joints rather than the osteophyte formation seen in osteoarthritis. In the hip, this destruction leads to loss of cartilage and bone around the joint, so you see joint space narrowing. A distinctive and characteristic finding in RA of the hip is acetabular protrusio, where the femoral head pushes into the pelvis due to laxity and destruction of the acetabular rim from ongoing pannus and inflammatory erosion. So the combination of acetabular joint narrowing with acetabulo-protrusio best reflects rheumatoid involvement of the hip.

Osteophyte formation points to OA rather than RA, and normal hips wouldn’t show these destructive changes, so those options don’t fit RA patterns as well.