What is the course of the ulnar nerve upon entering the cubital tunnel?

Updated: Jun 08, 2018
  • Author: Charles F Guardia, III, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Upon entering the cubital tunnel, the ulnar nerve gives off an articular branch to the elbow. It then passes between the humeral and ulnar heads of the flexor carpi ulnaris and descends into the forearm between the flexor carpi ulnaris and the flexor digitorum profundus. About 5 cm distal to the medial epicondyle, the ulnar nerve pierces the flexor-pronator aponeurosis, the fibrous common origin of the flexor and pronator muscles.

The ligament of Spinner is an additional aponeurosis between the flexor digitorum superficialis of the ring finger and the humeral head of the flexor carpi ulnaris. This septum is independent of the other aponeuroses and attaches directly to the medial epicondyle and the medial surface of the coronoid process of the ulna. With anterior transposition of the ulnar nerve, it is important to recognize and to release this structure to prevent kinking.

In the forearm, the ulnar nerve extends motor branches to the flexor carpi ulnaris and the flexor digitorum profundus of the ring and small fingers. The ulnar nerve may extend as many as 4 branches to the flexor carpi ulnaris, ranging from 4 cm above to 10 cm below the medial epicondyle. Proximal dissection of the first motor branch to the flexor carpi ulnaris from the ulnar nerve may be performed up to 6.7 cm proximal to the medial epicondyle, facilitating anterior transposition of the nerve.

Posterior branches of the medial antebrachial cutaneous nerves cross the ulnar nerve anywhere from 6 cm proximal to 4 cm distal to the medial epicondyle. These branches are often cut in the course of making the skin incision for a cubital tunnel release, creating an area of dysesthesia or resulting in potential neuroma formation.

As the ulnar nerve courses down the forearm toward the wrist, the dorsal ulnar cutaneous nerve leaves the main branch. A little further down, the palmar cutaneous branch takes off. Thus, neither of these two branches goes through the canal of Guyon. [1] The remainder of the ulnar nerve enters the canal at the proximal portion of the wrist. This is bounded proximally and distally by the pisiform bone and the hook of the hamate bone. It is covered by the volar carpal ligament and the palmaris brevis.


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