Can an injured nerve be used as a donor nerve for distal nerve transfer?—An experimental study in rats

Background: Distal nerve transfer has proven efficacy. The purpose of this study was to investigate if an injured nerve can be used as a donor nerve for transfer, and to determine the threshold of injury. Materials and Methods: Rat's left ulnar-nerves in the axilla with different degrees of injury were selected as the donor nerves for transfer, and the musculocutaneous-nerves the target nerves for being re-innervated. Six rats each served as positive and negative controls: Group A, intact ulnar-nerve transfer; and Group E, the ulnar-nerve was cut but no transfer. Ten rats each were assigned to Group B to Group D with 25%, 50%, and 75% transected ulnar-nerve, respectively and all were transferred to the musculocutaneous-nerve. After a 12-week recovery period, outcomes were evaluated. Results: Biceps muscle weight measurements showed all experimental groups—D 0.28 ± 0.02 g/72%, C 0.28 ± 0.03 g/73%, B 0.29 ± 0.04 g/74%, and A 0.29 ± 0.04 g/80%—were lighter than group H 0.36 ± 0.04 g, which were all statistically significant (P < 0.001). Muscle tetanus contraction force measurements were the lowest in group D35 ± 8.6 g/69%. Groups C and B measured 41 ± 8.5 g/75% and 40 ± 2.2 g/77% and group A 41 ± 9.4 g/95%, respectively. Group H showed muscle contraction force of 52 ± 7.2 g, which was statistically significant when compared to experimental groups (P < 0.05–0.001). EMG measurements of the biceps muscles showed: group D was 3.6 ± 0.7 mV/69%, group C was 3.6 ± 0.6 mV/75%, and group B was 4.2 mV ± 0.7/81%. Group H was5.1 ± 0.7 mV and statistically significant different when compared with experimental groups (P < 0.05–0.001).Axon counts of healthy ulnar-nerve (Group H) were 1849 ± 362. Axon counts of the injured ulnar-nerve were in group B 1447 ± 579/78%, group C 1051 ± 367/57% and group D 567 ± 230/31%. Conclusion: The donor nerve should be healthy in order to provide optimal result. A big nerve (e.g., ulnar nerve) but injured with at least 75% axon spared is still potentially effective for transfer. In contrast, a small nerve (e.g., intercostal nerve) once injured with 75%axon spared would be considered a suboptimal donor nerve.