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American Association for Hand Surgery

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Surgical Anatomy of the Proximal Musculocutaneous Nerve and Application for Nerve Transfers
Zachary C. Hanson, M.D.1, Mikhail Alexeev, M.D.1, Donald D. Davis, M.D.1 and Allan E Peljovich, M.D.2, (1)Wellstar Atlanta Medical Center, Atlanta, GA, (2)Hand and Upper Extremity Center of Georgia, Atlanta, GA

ABSTRACT
BACKGROUND: Intercostal nerve transfer to the musculocutaneous nerve (MCN) is a commonly utilized procedure for patients with brachial plexus injuries in which multiple nerves are harvested from intercostal spaces 3-6 and passed through the axilla to the recipient MCN to restore elbow flexion. Direct neurotization of donor to recipient is the goal, as it has been shown to lead to superior motor strength outcomes; but, there are circumstances where the length of the intercostal nerves fall short of the recipient nerve(s). Steps to close a gap include maximal mobilization of the recipient nerve, anastomosis into a more proximal recipient that will eventually branch into the desired recipient, neurotization in relative shoulder adduction, and use of interpositional nerve grafts.
The purpose of this study is to evaluate a technique of MCN recipient mobilization involving internal neurolysis at its origin from the lateral cord of the brachial plexus to gain length and close the potential distance to the donor intercostal nerves. We hypothesize that the "true origin" of the MCN, where its fascicles become distinct, is further proximal than its apparent origin of the epineural sheath.
MATERIALS & METHODS: The proximal origin of the MCN at the lateral cord was identified in 6 cadaveric specimens. Magnified loupe dissection of common epineurium at the apparent origin from the lateral cord was performed and extended until the perineurium of the MCN fascicles became confluent with that of the lateral cord. Distance from bony landmarks to various points along the MCN and its major branches were recorded.
RESULTS: The fascicles of the MCN nerve were clearly distinguishable and extended proximally an average of 1.7 +/- 0.5 cm in length. The coracoid process was closest in proximity to the MCN at its origin from the lateral cord of the brachial plexus (3.0 +/- 0.5 cm). The distance from bony landmarks to the course of the MCN was significantly shorter in 45 degrees adduction versus 90 degrees abduction.
CONCLUSIONS: Internal neurolysis of the lateral cord adds an additional 1.7 cm of MCN length that can be utilized in closing any potential gap during neurotization to allow for direct coaptation to the donor intercostal nerves. This information is useful for surgeons who find themselves in situations where there is insufficient length for direct coaptation, and in clinical practice, has eliminated the need for interposition nerve grafting and allowed for tension free repairs.


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