Which condition is marked by the rupture of the central extensor tendon at the dorsal side of the middle phalanx?

• A. Mallet finger
• B. Boutonnière deformity
• C. Swan neck deformity
• D. Dupuytren's contracture

Answer: (B)

The condition characterized by the rupture of the central extensor tendon at the dorsal side of the middle phalanx is indeed Boutonnière deformity. In this condition, the central slip—the part of the extensor tendon that inserts into the middle phalanx—ruptures, leading to a specific clinical presentation where the proximal interphalangeal joint becomes flexed, and the distal interphalangeal joint is hyperextended.

This deformity occurs commonly due to trauma to the finger, such as a laceration or an avulsion injury. In addition to the tendon rupture, the extensor mechanism is compromised, affecting the overall function of the finger. The hallmark signs include swelling and pain at the PIP joint, deformation of the finger appearance, and difficulty in straightening the affected joint.

Mallet finger, on the other hand, is associated with a rupture at the distal phalanx, while Swan neck deformity involves a different mechanism of instability and joint positioning. Dupuytren's contracture involves the thickening and shortening of the palmar fascia rather than any tensile rupture of the extensor tendons. Thus, the specific involvement of the central extensor tendon at the middle phalanx uniquely identifies Boutonnière deformity