In human anatomy, the extensor carpi ulnaris is a skeletal muscle located on the ulnar side of the forearm.

It originates from the lateral epicondyle of the humerus and the posterior border of the ulna, and crosses the forearm to the ulnar (medial) side to insert at the base of the 5th metacarpal.

This injury occurs in people who participate in activities requiring repetitive arm, elbow, and wrist, especially when they are tightly gripping an object.

Some symptoms of an extensor carpi ulnaris injury include pain when shaking hands or when squeezing/gripping an object.

Conservative treatments include immobilization and stabilization of the affected wrist by placing it in a cast.