A 40-year-old woman with seropositive rheumatoid arthritis has a finger deformity with flexion at the proximal interphalangeal joint and hyperextension at the distal interphalangeal joint. The primary lesion responsible for this boutonniere deformity is:

• A Volar subluxation of the lateral bands of the extensor mechanism
• B Rupture of the terminal extensor tendon at the distal interphalangeal joint
• C Rupture of the central slip of the extensor tendon at the proximal interphalangeal joint ✓
• D Contracture of the intrinsic muscles with intact extensor hood

Explanation

In rheumatoid arthritis, synovitis of the proximal interphalangeal joint stretches or ruptures the central slip, allowing the lateral bands to migrate volarly. The lateral bands then act as flexors of the PIP joint while extending the DIP joint, producing the classic flexion-hyperextension posture. Terminal tendon rupture instead produces a mallet finger, which is the defining lesion of the distractor in option B.

Reference: Miller's Review of Orthopaedics, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.