A 40-year-old woman with seropositive rheumatoid arthritis develops a finger deformity in which the proximal interphalangeal joint is held in flexion while the distal interphalangeal joint is hyperextended. Which structure, when ruptured, produces this deformity?
- A Transverse retinacular ligament of the extensor hood
- B Flexor digitorum profundus tendon
- C Central slip of the extensor tendon at its insertion into the base of the middle phalanx ✓
- D Ulnar collateral ligament of the metacarpophalangeal joint
Correct answer: C. Central slip of the extensor tendon at its insertion into the base of the middle phalanx
Explanation
Rupture of the central slip over the proximal interphalangeal (PIP) joint lets the head of the proximal phalanx buttonhole through the extensor hood, displacing the lateral bands volarly. The lateral bands now act as flexors of the PIP joint while extending the distal interphalangeal (DIP) joint, giving the boutonniere pattern of PIP flexion with DIP hyperextension. The distractor pattern of PIP hyperextension with DIP flexion defines swan neck deformity, caused instead by volar plate laxity or mallet-type weakness.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.