Corpus: Extensor carpi ulnaris muscle
Definition
The extensor carpi ulnaris muscle belongs to the superficial layer of the extensor muscles of the forearm. Some authors describe the muscle as having two heads because it attaches to both the ulna and the humerus. Others consider it a single-headed muscle.
Anatomy
Origin
The humeral head of the extensor carpi ulnaris muscle originates from the lateral epicondyle of the humerus between the anconeus muscle and the extensor digitorum muscle. The ulnar head has its origin surface on the dorsal edge of the ulna. Additionally, there are origin surfaces on the antebrachial fascia.
Insertion
The muscle runs along the ulna distally and ends in a long tendon that passes to the wrist in a groove between the head and the styloid process of the ulna. It continues under the extensor retinaculum distally and finally inserts – marked by a bony tubercle – at the base of the fifth metacarpal bone.
Innervation
The innervation of the extensor carpi ulnaris muscle is provided by the deep branch of the radial nerve with fibers from segments C7 and C8.
Function
The extensor carpi ulnaris causes ulnar abduction and extension (dorsiflexion) at the wrist. According to some authors, the dorsiflexion at the radiocarpal joint and the palmar flexion at the midcarpal joint cancel each other out, so the muscle essentially acts as a pure abductor.