Extensor carpi ulnaris
The wrist extensor on the little-finger side, running in its own groove in the ulna.
- Type
- Muscle
- Region
- Forearm
- Standard name
- m. extensor carpi ulnaris
- Origin
- Lateral epicondyle of the humerus via the common extensor tendon, and the posterior border of the ulna
- Insertion
- Base of the fifth metacarpal
- Actions
- wrist extensionwrist ulnar deviation
- Verify
- TA2 2507 TA98 A04.6.02.045
What it is
The most medial of the wrist extensors, running down the back of the forearm on the little-finger side, from the outer elbow and the ulna to the base of the fifth metacarpal.
Its tendon runs in a distinct groove in the head of the ulna, held there by its own sheath. That arrangement is unique among the forearm extensors and it matters: the tendon has to stay in its groove as the forearm rotates, and it can subluxate out of it, which is a recognised cause of a snapping sensation at the wrist.
What it does
Extends the wrist and deviates it towards the little finger. Working with flexor carpi ulnaris it produces pure ulnar deviation; working with the radial extensors it produces pure extension.
It stabilises the wrist during gripping.
It is under particular demand during forearm rotation, because its tendon's path changes as the ulna's relationship to the radius changes.
What loads it
Gripping, and racquet or club sports where the wrist deviates under load and the forearm rotates.
What is commonly got wrong about it
Ulnar-sided wrist pain as a simple strain. The little-finger side of the wrist contains this tendon, the triangular fibrocartilage complex, and several small joints. It has a reputation among clinicians as the difficult side of the wrist to diagnose. Persistent pain there warrants assessment.
That wrist extensors only work when you extend your wrist. They work isometrically every time you grip.