ABSTRACT
Objective:To confirm the reuse of mismatched regenerated motor axons of brachial plexus and explore the effect of target organs on their regeneration in a rat model.Methods:This study was carried out between January 2021 and December 2021 at the research laboratory of the Department of Microsurgery, Orthopaedic Trauma and Hand Surgery, the First Affiliated Hospital of Sun Yat-sen University. Animals were randomly assigned into 2 groups, as a regeneration group (RGen) with 5 subgroups and a reuse group (RUs) with 3 subgroups. There were 6 rats per subgroup with 42 rats in total. It was observed that in the groups of RGen1-4, after the transection and suture of the musculocutaneous nerve, the motor axons of the proximal end could accurately grow into the distal corresponding endoneural tube. It was also observed that in the mismatched regenerated group, motor axons were the axons that grew into the endoneurial tube of the lateral forearm cutaneous nerve (LFCN), and other non-target organ contacts were made to the regenerated nerves after mismatch. It was specifically further divided into RGen1, the group without an organ for nerve to make contact with; RGen2, the group with skin as the target organ with nerves contact by neurorrhaphy; RGen3, the group with skin as the target organ with originally reserved natural nerve contact; RGen4, the group with muscle as the target organ with nerves contact by neurorrhaphy and RGen5, a control group. After 8 weeks, the positive area (PA), mean density (MD) and integral optical density (IOD) were measured, with AChE and ChAT fluorescence staining of the medial branch of LFCN, to evaluate the regenerated nerves after mismatch. Of the RUs group, firstly, the innervating branches of the flexor carpi radialis (FCR) were dissected and exposed, then further assigned according to initially innervated FCR (RUs1), contacted with regenerated nerves after mismatch (RUs2) and denervated (RUs3), respectively. After 8 weeks, compound muscle action potential (CMAP) and wet weight ratio of FCR were taken. Masson staining of FCR was also performed to evaluate muscle reinnervation by the regenerated nerves after mismatch. Data analysis with One-Way ANOVA and Bonferroni 0.05 indicated a statistically significant difference.Results:In the RGen groups, after AChE staining, the PA, MD and IOD of RGen3 and RGen4 were higher than that of RGen1 and RGen5, and PA of RGen4 were higher than that of RGen2, with a statistically significant difference ( P<0.05). After ChAT staining, the values of PA and IOD of RGen3 and RGen4 were higher than that of RGen1 and RGen5, and PA of RGen4 were higher than that of RGen2, with a statistically significant difference ( P<0.05). In the RUs, electrophysiological assessment showed that no CMAP was observed in RUs3, there was no significant difference in Latency of RUs1 and RUs2. The difference was statistically significant ( P<0.05). Wet weight rate of muscle of RUs1 (98.91%±3.86%) was higher than that of RUs3 (86.67%±4.68%) with a statistically significant difference ( P<0.01), but no significant difference when compared with RU2 (92.74%±3.88%). Masson staining showed that the CVF value of RUs2 (8.61%±1.16%) was significantly higher than that of RUs1 (3.17%±0.76%), and statistic significantly lower than that of RUs3 (16.44%±2.26%)( P<0.01). Conclusion:Target organ contact can promote the regenerated nerves after mismatched regeneration, and the muscle target organs exhibit greater facilitation than the cutaneous target organs. Besides, regenerated nerves after mismatch can establish effective innervation with muscle target organs, comfirming their effective reuse.