Ulnar Nerve Innervation to Triceps: A Cadaveric Study and a Technical Note on Partial Triceps to Biceps Transfer

Triceps and cutaneous radial nerve branches investigated via an axillary anterior arm approach: new findings in a fresh-cadaver anatomical study

OBJECTIVE

The authors sought to describe the anatomy of the radial nerve and its branches when exposed through an axillary anterior arm approach.

METHODS

Bilateral upper limbs of 10 fresh cadavers were dissected after dyed latex was injected into the axillary artery.

RESULTS

Via the anterior arm approach, all triceps muscle heads could be dissected and individualized. The radial nerve overlaid the latissimus dorsi tendon, bounded by the axillar artery on its superior surface, then passed around the humerus, together with the lower lateral arm and posterior antebrachial cutaneous nerve, between the lateral and medial heads of the triceps. No triceps motor branch accompanied the radial nerve's trajectory. Over the latissimus dorsi tendon, an antero-inferior bundle, containing all radial nerve branches to the triceps, was consistently observed. In the majority of the dissections, a single branch to the long head and dual innervations for the lateral and medial heads were observed. The triceps long and proximal lateral head branches entered the triceps muscle close to the latissimus dorsi tendon. The second branch to the lateral head stemmed from the triceps lower head motor branch. The triceps medial head was innervated by the upper medial head motor branch, which followed the ulnar nerve to enter the medial head on its anterior surface. The distal branch to the triceps medial head also originated near the distal border of the latissimus dorsi tendon. After a short trajectory, a branch went out that penetrated the medial head on its posterior surface. The triceps lower medial head motor branch ended in the anconeus muscle, after traveling inside the triceps medial head. The lower lateral arm and posterior antebrachial cutaneous nerve followed the radial nerve within the torsion canal. The lower lateral brachial cutaneous nerve innervated the skin over the biceps, while the posterior antebrachial cutaneous nerve innervated the skin over the lateral epicondyle and posterior surface of the forearm. The average numbers of myelinated fibers were 926 in the long and 439 in the upper lateral head and 658 in the upper and 1137 in the lower medial head motor branches.

CONCLUSIONS

The new understanding of radial nerve anatomy delineated in this study should aid surgeons during reconstructive surgery to treat upper-limb paralysis.

Anatomy of the ulnar nerve in the posterior compartment of the upper arm: Relationships with the triceps brachii muscle

The aim of our descriptive anatomical study was to clarify the relationships between the ulnar nerve and the triceps brachii muscle in the posterior compartment of the upper arm. This study involved 30 fresh adult upper limbs. In all specimens, the ulnar nerve crossed from the anterior to posterior compartment in a space formed by the medial intermuscular septum and muscle fibers of the triceps' medial head. This transition zone was located an average of 126mm (115-135mm) proximal to the start of the ulnar groove. In the posterior compartment, the nerve descended vertically, and its anterior side was attached to the posterior side of the septum. Its posterior and lateral sides were covered by muscle fibers from the medial head. Its medial side was always free meaning that the nerve did not penetrate through the medial head. The other heads of the triceps muscle had no direct interactions with the ulnar nerve within this compartment. During its posterior course, the nerve was accompanied by the superior ulnar collateral artery. The ulnar nerve did not give off any branches in the upper arm.