The presence of a separately innervated muscle unit of the triceps may have possible surgical importance because it might be used for motor reconstructions. The ulnar nerve is very closely situated to the triceps muscle and rarely is examined above the elbow. In this cadaveric study, we dissected 18 limbs from axillae to midforearm to explore a possible contribution of the ulnar nerve to motor innervation of the medial head of the triceps. The ulnar nerve innervation of the medial head of the triceps was supported by this cadaveric study. The limitation of this study is that we did not measure the precise location of the branches. In a cadaver study, it is impossible to determine whether a branch is motor or sensory, but the location of each branch can be mapped. During this particular study, our main goal was to determine the presence or absence of nerve connection. Our attention was focused on defining the nature of each connection; ie, whether it was a nerve or whether it was connective tissue. Therefore, we did not measure the location of the branches.
Although the majority of the observed nerve branches originated from the main ulnar nerve, some also came from the ulnar collateral branch of the radial nerve. This branch of the radial nerve, although easily separated from the ulnar nerve by loupe magnification, is situated so close to the ulnar nerve as to be indistinguishable by the naked eye.
With the ulnar nerve branch innervation of the triceps, the dual nerve supply could allow separation of the triceps muscle. This could explain the clinical observation that radial nerve denervation does not result in complete lack of triceps function.
The triceps muscle and its main motor nerve, the radial nerve, have multiple connection modalities. New advances in peripheral nerve surgery such as neurotization of muscle by direct suture of nerve end to muscle, or transfer of healthy motor nerve branches to the motor nerve end of a denervated muscle have given the surgeon great capacity for motor reconstructions.
Witoonchart et al. [13
] described the concept of using the radial nerve branch to the long head of the triceps brachii for reinnervation of the anterior branch of the axillary nerve in upper brachial plexus injuries. In selected cases, the ulnar collateral branch of the radial nerve to the ulnar nerve or motor branch ramifying from the ulnar nerve could be used for reinnervation of a denervated muscle closely situated. Another possibility may be the transfer of the entire muscle unit for motor use. This independent motor unit may be helpful in restoring elbow flexion in selected cases or it may be used like a motor unit of forearm movement in the manner the brachialis muscle is used [1
]. If well described, this small selective donor site would have an easy anatomic approach and acceptable potential morbidities.
It is essential to change the current thought that no major ulnar nerve branches occur above the elbow. Dissections proximal to the epicondyles must be performed carefully so as to avoid destruction of these branches, preventing partial denervation and atrophy of the triceps muscle and additional fibrosis of the medial head and resultant postsurgical elbow stiffness. Finally, the importance of the ulnar collateral branch of the radial nerve must be emphasized. Our anatomic dissections showed this nerve to be a distinct entity with a diameter large enough to be appreciated easily on loupe magnification. With popularization of neurotization, this nerve would be a prime candidate for reinnervation of denervated muscle through nerve-to-nerve repair (for example, musculocutaneous nerve interruption with resultant denervation of the biceps brachii). The nerve also could be used for direct transfer to another muscle.
We conclude the ulnar nerve and the ulnar collateral branch of the radial nerve are previously unrecognized sources of triceps brachii innervation. Additional study will be directed toward exploitation of these branches as potential sources for reinnervation of denervated muscle by direct nerve transfer without nerve grafting for management of brachial plexus injuries and biceps brachii denervation and eventually for reinnervation of other muscles in the arm and forearm.