The terminal extensor tendon is the final part of the finger's extensor mechanism, formed where the two lateral bands join together over the middle phalanx. It runs across the back of the distal interphalangeal (DIP) joint to insert on the dorsal base of the distal phalanx, and it is the only tendon that straightens the fingertip. The triangular ligament holds the lateral bands together just before they merge into it.
| Muscle |
|
|---|---|
| Attachment | Dorsal base of the distal phalanx of each finger |
Extends the distal interphalangeal joint of the finger, straightening the fingertip
The terminal extensor tendon is thin and lies directly on bone, so it is easily torn or cut. Forced bending of a straightened fingertip, for example when a ball strikes the end of the finger, ruptures the tendon or pulls off a fragment of bone, producing a mallet finger with a drooping fingertip. Most mallet injuries are treated with continuous splinting of the DIP joint in extension for about 6-8 weeks, and any bending during this period restarts healing. Untreated mallet finger can lead to a swan-neck deformity as the extensor force is redirected to the PIP joint.
Rupture of the terminal extensor tendon or avulsion of its bony insertion, leaving the fingertip unable to straighten actively; usually treated by full-time extension splinting of the DIP joint.
Hyperextension of the PIP joint with flexion of the DIP joint that can develop after an untreated mallet finger, as extensor force is concentrated at the PIP joint.
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