Ulnar tendon pain can have a number of causes, including ECU tendonitis and ECU tendon subluxation.ECU stands for the extensor carpi ulnaris tendon, one of the major wrist tendons, located on the ulnar side of the wrist, which is the same side as the small finger. The ECU tendon starts on the back of the forearm and crosses the wrist joint directly on the side.
Source: Verywell Health
