The Effects of Intraoperative Electrical Stimulation on Regeneration and Recovery After Nerve Isograft Repair in a Rat Model

Abstract

Background: Therapeutic electrical stimulation (ES) applied to repaired nerve is a promising treatment option to improve regeneration. However, few studies address the impact of ES following nerve graft reconstruction. The purpose of this study was to determine if ES applied to a nerve repair using nerve isograft in a rodent model could improve nerve regeneration and functional recovery. Methods: Adult rats were randomized to 2 groups: "ES" and "Control." Rats received a tibial nerve transection that was repaired using a tibial nerve isograft (1.0 cm length), where ES was applied immediately after repair in the applicable group. Nerve was harvested 2 weeks postrepair for immunohistochemical analysis of axon growth and macrophage accumulation. Independently, rats were assessed using walking track and grid-walk analysis for up to 21 weeks. Results: At 2 weeks, more robust axon regeneration and greater macrophage accumulation was observed within the isografts for the ES compared to Control groups. Both walking track and grid-walk analysis revealed that return of functional recovery was accelerated by ES. The ES group demonstrated improved functional recovery over time, as well as improved recovery compared to the Control group at 21 weeks. Conclusions: ES improved early axon regeneration into a nerve isograft and was associated with increased macrophage and beneficial M2 macrophage accumulation within the isograft. ES ultimately improved functional recovery compared to isograft repair alone. This study supports the clinical potential of ES to improve the management of nerve injuries requiring a nerve graft repair.

Keywords: autograft; basic science; diagnosis; microsurgery; muscle; nerve; nerve regeneration; specialty.

Conflict of interest statement

Declaration of Conflicting Interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: M.D.W has been the recipient of sponsored research agreements from Checkpoint Surgical, Inc. and has consulted for Foundry Therapeutics, LLC and The Foundry, LLC. No personal compensation was provided. Checkpoint Surgical, Inc. did not influence or affect the experimental design or outcome of the studies. None of the other authors have any conflicts of interest to disclose.

Figures

Figure 1.

Schematic of electrical stimulation (ES) applied after nerve grafting. Experimental groups receiving ES therapy had a mono-polar electrode hooked around the tibial nerve proximal to the cut and repair site. A return electrode was placed securely in musculocutaneous facia. Note. ES was delivered immediately after nerve graft repair for 60 minutes using intraoperative constant current at 0.5 mA, a pulse width of 100 µs, and a frequency of 16 Hz.

Figure 2.

ES improved early axon regeneration within isografts. Representative immunofluorescence images and quantification of axons (βIII-tubulin) within nerve isografts 2 weeks postrepair. Inset boxes represent magnified fields presented within the graft and distal nerve. Note. Scale bars represent 20 µm. Mean ± SD, n = 4/group; * indicates P < .05. ES = electrical stimulation.

Figure 3.

ES increased macrophage accumulation within isografts. Representative immunofluorescence images and quantification of macrophages (pan: CD68; M2: CD206) within nerve isografts 2 weeks postrepair. Scale bars represent 20 µm. Mean ± SD, n = 4/group; * indicates P < .05. ES = electrical stimulation.

Figure 4.

ES improved functional recovery across isografts. Quantification of walking track using tibial functional index (a) and grid-walk analysis (b) at 21 weeks postrepair. Mean ± SD, n = 9/group; * indicates P < .05 vs Control and ^ indicates P < .05 vs postinjury (1 week). Note. ES = electrical stimulation.

Figure 5.

Final nerve regeneration quality within and across isografts. Representative histological images of repaired nerve within the isograft (graft-mid) and distal nerve at 21 weeks postrepair. Scale bars represent 20 µm. ES = electrical stimulation.