Mallet Finger

Mallet finger is a disruption of the terminal extensor tendon at the distal interphalangeal (DIP) joint, leaving the fingertip drooping in flexion with loss of active extension.

It usually follows forced flexion of a straight fingertip, such as a ball striking the end of the finger, but trivial injuries like tucking in bed sheets can cause it. The tendon may tear or pull off a fragment of bone (a bony mallet).

Most injuries are treated with continuous extension splinting for 6 to 8 weeks. Surgery is reserved for selected patterns, chiefly open injuries and bony mallets with volar subluxation of the distal phalanx.

The terminal extensor tendon, formed where the lateral bands join, inserts on the dorsal base of the distal phalanx. Without it, flexor digitorum profundus pulls the DIP joint into flexion unopposed.

Injuries are tendinous (the commonest pattern, no fracture) or bony (avulsion of the dorsal base of the distal phalanx). The Doyle classification:

• •Type I: closed, with or without a small avulsion fragment
• •Type II: open, with tendon laceration
• •Type III: open, with loss of skin and tendon
• •Type IV: bony; IVA physeal injury in children, IVB fragment of 20% to 50% of the articular surface, IVC more than 50%, often with volar subluxation

Left untreated, the lag does not correct, and extensor imbalance can produce a secondary swan-neck deformity with proximal interphalangeal (PIP) hyperextension.