Mallet finger involves injury to which joint?

• A. Proximal interphalangeal joint
• B. Distal interphalangeal joint
• C. Metacarpophalangeal joint
• D. Carpometacarpal joint

Answer: (B)

Mallet finger is a problem with the distal interphalangeal joint—the joint at the tip of the finger. It happens when the terminal extensor tendon, which straightens the fingertip, is torn away from the distal phalanx (often with a small bone fragment) after the fingertip is forcefully jammed or struck. Because the extensor mechanism is disrupted at the DIP, the patient cannot actively extend the fingertip, so the tip droops into flexion.

The other finger joints (proximal interphalangeal, metacarpophalangeal, and carpometacarpal) aren’t the primary sites of this injury, and involvement of a different joint would point to a different condition (for example, a boutonnière deformity involves the PIP).