A 50-year-old woman with rheumatoid arthritis develops hyperextension of the ring finger proximal interphalangeal joint with flexion of the distal interphalangeal joint. The primary pathological change permitting proximal interphalangeal hyperextension is:

• A Rupture of the terminal extensor tendon
• B Rupture of the central slip of the extensor tendon
• C Attenuation of the volar plate and collateral ligaments by synovitis ✓
• D Contracture of the oblique retinacular ligament

Explanation

Swan neck deformity results from failure of the structures restraining proximal interphalangeal hyperextension. In rheumatoid arthritis, proliferative synovitis stretches the volar plate and collateral ligaments, allowing the joint to hyperextend, and the distal interphalangeal joint then flexes. Central slip rupture produces a boutonniere pattern, the opposite deformity. Terminal tendon rupture produces a mallet finger, which can secondarily cause swan neck, but the primary restraint lost here is the volar plate complex.

Reference: Green's Operative Hand Surgery, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.