A Comprehensive Review of Topography and Axon Counts in Upper-Extremity Peripheral Nerves: A Guide for Neurotization.

Purpose: Currently, no comprehensive database detailing topography and axon counts exists. This study aims to review the axon counts and topography of the major peripheral motor nerves of the upper extremity to allow for optimal surgical planning for peripheral nerve reconstruction via neurotization. Methods: Peer-reviewed journal articles were identified through PubMed, ScienceDirect, Google Scholar, and CENTRAL. Studies were included for review based upon the identification of the described topography or axon count of any upper-extremity peripheral motor nerve. Animal research, laboratory studies, and unpublished studies were excluded from our review. A total of 43 studies were identified, and 38 of these met the inclusion criteria. Statistical analysis was performed to determine axon count averages for all upper extremity motor nerves identified in the included studies. Results: Thirty-eight studies were reviewed, giving insights into the topography and axon counts of the major peripheral nerves of the upper extremity, including the brachial plexus and its terminal branches as well as common donor nerves such as the spinal accessory nerve and intercostal nerves. Studies showed considerable variability in reported axon counts. Conclusions: Existing data were relatively weak and included several case reports and series. Taking this into consideration, we posit that there is a need for further studies of upper-extremity nerve axon counts that include large study populations and more consistent methods of nerve specimen analysis. Clinical relevance: Understanding the topographical anatomy of donor and recipient nerves, as well as appropriately matching the motor axon counts for each donor and recipient, is helpful in upper-extremity nerve reconstruction.