Donor-To-Recipient Mean Axonal Count Ratios of Upper Limb Nerves Used in Nerve Transfer Surgery: A Systematic Review of Histomorphometric Cadaveric Studies.

Nerve transfer surgery may be performed to restore sensorimotor function following peripheral nerve trauma or dysfunction. There is biological plausibility and limited correlative evidence that donor-to-recipient axon count ratios may impact functional outcomes. Collating anatomical studies that report mean axonal count ratios could guide surgical practice. This systematic review aimed to collate anatomical studies reporting mean axonal counts (MAC) of nerve branches used in upper limb nerve transfer surgery, and calculate MAC ratios for donor-to-recipient nerves and pooled MAC ratios between studies. PubMed, OVID MEDLINE, Google Scholar, and Cochrane were screened for cadaveric studies. For included studies, the donor-to-recipient mean axon ratio was calculated for pairs of nerves suitable for transfer, and ratios were calculated between studies. Methodological heterogeneity precluded metaanalysis. The search yielded 299 results. These were screened to include 54 studies. Mean axonal counts were reported for a total of 225 nerves. Donor-to-recipient axonal ratios were calculated, and stratified into most clinically relevant recipient transfer options; that may be used to inform selection of successful donor nerve options. This is the first comprehensive review of mean axonal count ratios. The collated information regarding MAC ratios could support surgeons in selecting the appropriate donor nerves for upper limb nerve transfer surgery.