Comparative study of single-, double-, and triple-nerve transfer to a common target: Experimental study of rat brachial plexus

Background: The purpose of this study was to investigate the recovery of a common target motor function after different single and combined motor nerve transfers in rat brachial plexus model. Methods: The musculocutaneous nerve and biceps muscle were chosen as the target for neurotization. The phrenic, pectoral, and suprascapular nerves were selected as the neurotizers. Forty-two Sprague-Dawley rats were randomly assigned to seven groups (six rats in each group): single-neurotizer transfer (three groups), double-neurotizer transfer (three groups), and triple-neurotizer transfer (one group). The contralateral intact forelimb was used as a control. Functional outcomes were measured by grooming test, electrophysiological study, muscle contraction strength, muscle weight, and axon counts. Results: At 12 weeks, 40 operative rats were studied (two had died). In the single-neurotizer transfer, all three transfers showed no significant difference in motor recovery of the biceps. In the double-neurotizer transfer groups, the worst results were seen in group 6 (combined pectoral and suprascapular nerve transfer) despite increasing axon counts. Conclusions: This study may potentially suggest: (1) single-neurotizer transfer will not have synergistic or antagonistic effects; (2) two neurotizers with functional antagonism will significantly downgrade motor recovery of the neurotized muscle despite increasing axon counts; (3) multiple motor neurotizer transfers may not always provide a better outcome, although increasing axons may outweigh antagonistic effects; and (4) phrenic nerve transfer alone did not upgrade the functional outcome despite its automatic discharge. Any nerve transfer combined with phrenic nerve transfer, however, showed improved functional results.