Earlier functional recovery with an amniochorionic membrane allograft nerve wrap after in-continuity stretch injury in rat median nerves

Introduction We investigated the use of an amniochorionic membrane allograft wrap (ACMShield) for treating epineuroclasis stretch injuries in rat median nerves. Epineuroclasis refers to in-continuity injuries with a disrupted epineurium, identified via load-deformation-curves. Methods Twenty rats were randomized into three groups: untreated epineuroclasis (n=8), ACMShield-treated epineuroclasis (n=6), and sham-control surgery without injury (n=6). In untreated and ACMShield-treated rats, bilateral median nerves were stretched with a hook until epineuroclasis was observed on load-deformation curves. In treated rats, the ACMShield was wrapped around both the injured nerves. Forepaw grip strength was assessed via the grasping test pre-injury and at 1, 3, 6, and 9 weeks post-injury. Data were normalized to baseline and analyzed using mixed-effects models. Recovery was defined as reaching a statistically non-significant difference in strength compared to pre-injury baseline strength (p'0.05). Results Both injury groups lost grip strength at 1 week with 2.0±0.7% of baseline strength for the treated and 3.3±3.4% for untreated rats (p'0.001). The ACMShield group achieved strength with no statistically detectable difference to baseline at 6 weeks (100.8±34.6%, p'0.99) and this was sustained for 9 weeks (104.5±33.5%). Untreated rats achieved this at 9 weeks with 80.9±29.9% of baseline strength (p=0.34). No difference in percent-of-baseline grip strength was observed between the ACMShield and untreated groups at any postoperative time point. Conclusion In this pilot study, ACMShield-treated nerves returned to baseline-like grip strength by 6 weeks, whereas untreated nerves returned by 9 weeks. However, between-group comparisons at individual timepoints were not statistically significant; therefore, these findings should be interpreted as exploratory.