A 45-year-old woman with rheumatoid arthritis develops boutonnière deformity of the index finger. The primary pathological event leading to this deformity is:

• A Rupture of the terminal tendon at the distal phalanx causing mallet finger progression
• B Radial deviation of the MCP joint due to intrinsic muscle tightness
• C Dorsal subluxation of extensor tendons at the MCP joint
• D Attenuation and central slip disruption at the PIP joint with volar subluxation of lateral bands ✓

Explanation

Boutonnière deformity arises from disruption or attenuation of the central slip of the extensor tendon at the PIP joint, allowing the PIP to flex (buttonhole through the extensor hood). The lateral bands slip volarly, converting them from PIP extensors to flexors, and they tighten to hyperextend the DIP joint. The result is PIP flexion + DIP hyperextension. In rheumatoid arthritis, synovitis of the PIP joint stretches and attenuates the central slip. This is distinct from swan-neck deformity (PIP hyperextension + DIP flexion) caused by volar plate laxity or FDS weakness. Mallet finger involves only the terminal tendon at the DIP.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.