What is the name of complete rupture of the extensor tendon at the distal phalanx causing DIP flexion?

• A. Jersey finger
• B. Mallet finger
• C. Boutonniere deformity
• D. Swan neck

Answer: (B)

Injury to the fingertip extensor mechanism that leaves the tip unable to straighten produces a mallet finger. When the extensor tendon is completely ruptured at the distal phalanx, it can no longer extend the distal joint, so the DIP sits in flexion and the fingertip droops. The flexor digitorum profundus can still flex the DIP, so you see a flexed fingertip that cannot be actively extended. This commonly follows a forceful impact to a finger that is bent, like catching a ball, sometimes with a small bony avulsion at the dorsal base of the distal phalanx.

Jersey finger is the opposite problem—rupture of the flexor digitorum profundus with an inability to flex the DIP. Boutonniere deformity comes from injury to the central slip leading to PIP flexion with DIP hyperextension, not just DIP flexion. Swan neck involves PIP hyperextension with DIP flexion due to different imbalance in the extensor mechanism.