|Extensor carpi ulnaris|
Posterior surface of the forearm. Extensor carpi ulnaris labeled in purple at center right.
|Origin||Humeral head: Lateral epicondyle of the Humerus.Ulnar head: Olecranon, Posterior surface of ulna, antebrachial fascia|
|Nerve||Deep branch of the radial nerve (C7, C8)|
|Actions||extends and adducts the wrist|
|Antagonist||Flexor carpi radialis|
|Latin||musculus extensor carpi ulnaris|
|Anatomical terms of muscle|
Being an extensor muscle, extensor carpi ulnaris is on the posterior side of the forearm.
The muscle is a minor extensor of the carpus in carnivores, but has become a flexor in ungulates. In this case it is described as ulnaris lateralis.
Despite its name, the extensor carpi ulnaris is innervated by the posterior interosseous nerve (C7 and C8), the continuation of the deep branch of the radial nerve. It would therefore be paralyzed in an injury to the posterior cord of the brachial plexus.
A common injury to the extensor carpi ulnaris is tennis elbow. This injury occurs in people that participate in activities requiring repetitive arm, elbow, and wrist, especially when they are tightly gripping an object. Some symptoms include pain when shaking hands or when squeezing/gripping an object. The pain worsens when a person moves their wrist with force. The pain intensifies because the extensor carpi ulnaris has an injury near the elbow area and as a person moves their arm, the muscle contracts, thus causing it to move over the medial epicondyle of the humerus. This causes irritation to the already existing injury. Some treatments for tennis elbow include occupational therapy, physical therapy, anti-inflammatory medication, and rest from the activity that caused the injury. A similar injury involving the medial elbow is known as golfer's elbow. 
An ECU injury most often requires imaging (CT, MRI, ultrasound) for diagnosis. After the ECU injury is diagnosed, a physician will choose a course of treatment, which depends upon the severity of the injury. Conservative treatments include immobilization and stabilization of the affected wrist by placing it in a cast. A long arm cast may be required in order to ensure that all wrist movement has been stopped. The duration of the immobilization is at the treating physician's discretion. After the immobilization period has ended, the cast will be removed and further analysis of the injury will be required. If the injury did not improve with the conservative courses of treatment, or if the injury was initially too severe for conservative treatment, invasive procedures may become necessary. Steroid injections and surgical procedures are the most prominent invasive procedures. Surgical repair or reconstruction of the ECU is not often required, yet a severe ECU injury may cause these approaches to be necessary.