A 55-year-old woman with long-standing rheumatoid arthritis develops a deformity of the fingers characterized by hyperextension of the proximal interphalangeal joint and flexion of the distal interphalangeal joint. What is this deformity called?
- A Boutonnière deformity
- B Swan neck deformity ✓
- C Ulnar deviation
- D Hitchhiker's thumb
Correct answer: B. Swan neck deformity
Explanation
Swan neck deformity consists of PIP hyperextension with DIP flexion. It results from intrinsic muscle tightness, volar plate laxity, and terminal extensor tendon attenuation. Boutonnière deformity is the opposite: PIP flexion with DIP hyperextension, caused by central slip rupture. Ulnar deviation occurs at the MCP joints. Hitchhiker's thumb (Z-deformity) is seen in RA at the thumb IP joint.
Reference: Bailey and Love's Short Practice of Surgery, 28th ed.
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