gms | German Medical Science

Objectives/Interrogation: Surgical nerve transfers provide the nerve surgeon with the ability to convert proximal into distal nerve lesions and thereby bypass slow nerve regeneration. Many nerve transfer procedures have been described and are successfully used in the reconstruction of brachial plexus and peripheral nerve injury. Despite their success, little is known about the neurophysiological effects of peripheral nerve transfers, especially regarding the motor unit rewiring that results thereby. In this work, we review the neurophysiological effects of nerve transfers in regard to refining surgical procedures and external aspects such as age on outcomes.

Methods: We review the literature investigating peripheral nerve transfers and their effects on the motor unit. Additional information is drawn from classic cross-innervation studies that present a similar surgical nerve transfer procedure and have been well-investigated. Specifically highlighted are the effects of donor nerve quality (agonist or antagonist) and axon quantity (donor-to-recipient ratio) on functional outcomes. Additionally, the poor results of nerve transfers in the lower extremity compared to their success in the upper extremity are discussed.

Results and Conclusions: Few publications, yet with growing tendency, specifically investigate the neurophysiological effects of nerve transfers, as applied in modern nerve surgery. Many conclusions can be drawn from cross-innervation studies. In general, agonist donor nerves provide a higher success rate and less-complicated motor re-education. Donor nerves with similar motor axon numbers as their recipient nerve provide better functional outcomes, likely the result of more functional motor units. This has been specifically shown for brachial plexus reconstruction. Experimentally, hyper-reinnervation, e.g. providing a surplus of axons, provides the best functional outcomes regarding muscle force. High patient age, the need for nerve grafts between donor and recipient, or the use of antagonist donor nerves have been reported to result in inferior results but are no contradiction for the use of nerve transfers in the upper extremity. Understanding the neurophysiological effects of nerve transfers has helped to refine surgical techniques. Future studies will provide additional information on motor unit effects and functional outcomes (muscle force).