A patient with chronic rheumatoid arthritis develops progressive 'swan-neck' deformity of the finger. The primary anatomical disruption causing this deformity is:

• A Rupture of the central slip of the extensor tendon at the PIP joint
• B Volar plate laxity at the PIP joint with dorsal subluxation and DIP flexion due to extensor lag ✓
• C Intrinsic tightness causing DIP hyperextension and MCP flexion
• D FDP tendon adhesion causing DIP fixed flexion

Explanation

Swan-neck deformity (PIP hyperextension + DIP flexion) in RA results from volar plate attenuation at the PIP joint, allowing the dorsal apparatus to hyperextend the PIP joint. Terminal extensor mechanism weakness then produces DIP flexion (extensor lag at DIP). In contrast, boutonniere deformity (PIP flexion + DIP hyperextension) results from central slip rupture. Intrinsic tightness also contributes by pulling the lateral bands dorsally.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.