This is a flexion deformity affecting the distal inter-phalangeal joint of the finger and is due to either distal extensor tendon rupture or avulsion with a bony fragment after traumatic forced flexion of the extended finger tip. The resultant weakness is often painless and presents with an inability to actively extend the fingertip.

Non traumatic mallet finger occurs more often in diabetics. Treatment is usually by splinting the distal inter-phalangeal joint in extension. Surgery is rarely required.