Which finding suggests a rupture of the extensor tendon at the DIP joint in a mallet finger injury?

Which finding suggests a rupture of the extensor tendon at the DIP joint in a mallet finger injury?

• A. Inability to extend the distal phalanx
• B. Inability to flex the distal phalanx
• C. Pain with MCP joint movement
• D. Pain at the proximal phalanx

Answer: (A)

Extending the fingertip at the DIP relies on the extensor tendon attaching to the distal phalanx. When that extensor tendon is ruptured at the DIP, the distal phalanx can no longer be actively straightened, so the fingertip droops in flexion and an extensor lag is seen. Passive extension may still be possible, but active extension is lost, which is the hallmark of a mallet finger. This contrasts with injuries like jersey finger, where flexion at the DIP is impaired due to FDP disruption, or problems at the MCP or proximal phalanx which involve other joints.

Extending the fingertip at the DIP relies on the extensor tendon attaching to the distal phalanx. When that extensor tendon is ruptured at the DIP, the distal phalanx can no longer be actively straightened, so the fingertip droops in flexion and an extensor lag is seen. Passive extension may still be possible, but active extension is lost, which is the hallmark of a mallet finger. This contrasts with injuries like jersey finger, where flexion at the DIP is impaired due to FDP disruption, or problems at the MCP or proximal phalanx which involve other joints.