Applied Surgical Anatomy of the Approach to the Ulna

Anatomy of the Surgical Dissection and Its Dangers

Two muscles are separated in the approach to the ulna: The flexor carpi ulnaris (which is supplied by the ulnar nerve) and the extensor carpi ulnaris (which is supplied by the posterior interosseous nerve; see Fig. 422).

The muscular branch of the ulnar nerve, which innervates the flexor carpi ulnaris, effectively tethers the nerve, preventing further distal mobilization during decompression at the elbow. Compression lesions of

the nerve have been described (see Fig. 3-49).21,22

The extensor carpi ulnaris is the most medial of the muscles that are innervated by the posterior interosseous nerve. Thus, it forms one border of the internervous plane between the muscles that are innervated by the posterior interosseous nerve and those that are innervated by the ulnar nerve, the most medial of which is the flexor carpi ulnaris (see Fig. 4-19).

The ulnar nerve runs down the medial side of the forearm between the flexor digitorum profundus and the flexor digitorum superficialis, and under the flexor carpi ulnaris. In the forearm, it supplies the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus (see Fig. 4-14).

The ulnar artery is a terminal branch of the brachial artery. It usually enters the forearm deep to the deep head of the pronator teres before angling medially across the forearm and passing under the fibrous arch of the flexor digitorum superficialis, where it runs just deep to the median nerve (see Figs. 4-12 to 4-14). In the distal two-thirds of the forearm, the artery runs on the lateral side of the ulnar nerve, lying on the flexor digitorum profundus and under the flexor carpi ulnaris. The artery has one major branch in the forearm, the common interosseous artery, which divides almost immediately into two tributaries, the anterior interosseous artery (which runs down the forearm in the midline, lying on the interosseous membrane) and the posterior interosseous artery (which pierces the interosseous membrane, running down the forearm in its posterior compartment; see Fig. 4-14).

The ulnar nerve and ulnar artery may be endangered during superficial dissection if the dissection strays to the flexor side of the bone.