A radiograph of the hand in a patient with long-standing rheumatoid arthritis shows uniform joint space narrowing at the MCP and PIP joints, periarticular osteopenia, and bony erosions at the bare areas. The 'bare area' of a joint, where RA erosions preferentially occur, is located at:

• A The central portion of the articular surface
• B The intra-articular region not covered by articular cartilage, at the synovial reflection ✓
• C The subchondral bone deep to the cartilage
• D The metaphysis just proximal to the growth plate

Explanation

The 'bare area' is the intra-articular bone surface not covered by articular cartilage, at the marginal zone where synovium reflects onto bone. This area is directly exposed to proliferative pannus in rheumatoid arthritis, producing the characteristic marginal erosions seen earliest at the MCP and PIP joints. Subchondral erosions occur later; metaphyseal involvement is not a feature of RA erosions.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.