Abstract
Several studies have investigated the use of invasive and non-invasive stimulation methods to enhance nerve regeneration, and varying degrees of effectiveness have been reported. However, due to the use of different parameters in these studies, a fair comparison between the effectiveness of invasive and non-invasive stimulation methods is not possible. The present study compared the effectiveness of invasive and non-invasive stimulation using similar parameters. Eighteen Sprague Dawley rats were classified into three groups: the iES group stimulated with fully implantable device, the tES group stimulated with transcutaneous electrical nerve stimulation (TENS), and the injury group (no stimulation). The iES and tES groups received stimulation for 6 weeks starting immediately after the injury. Motor function was evaluated using the sciatic functional index (SFI) every week. The SFI values increased over time in all groups; faster and superior functional recovery was observed in the iES group than in the tES group. Histological evaluation of the nerve sections and gastrocnemius muscle sections were performed every other week. The axon diameter and muscle fiber area in the iES group were larger, and the g-ratio in the iES group was closer to 0.6 than those in the tES group. To assess the cause of the difference in efficiency, a 3D rat anatomical model was used to simulate the induced electric fields in each group. A significantly higher concentration and intensity around the sciatic nerve was observed in the iES group than in the tES group. Vector field distribution showed that the field was orthogonal to the sciatic nerve spread in the tES group, whereas it was parallel in the iES group; this suggested that the tES group was less effective in nerve stimulation. The results indicated that even though rats in the TENS group showed better recovery than those in the injury group, it cannot replace direct stimulation yet because rats stimulated with the invasive method showed faster recovery and superior outcomes. This was likely attributable to the greater concentration and parallel distribution of electric field with respect to target nerve.
Highlights
Peripheral nerve injury typically occurs during road traffic accidents, industrial accidents, or injuries sustained at home
Various methods and parameters have been proposed for non-invasive stimulation to enhance peripheral nerve regeneration; its effectiveness compared with that of invasive stimulation is not well characterized
Previous studies that compared invasive vs. noninvasive stimulation employed different parameters, such as frequency, stimulation time, and stimulation period; this prevented any meaningful comparisons between the two modalities
Summary
Peripheral nerve injury typically occurs during road traffic accidents, industrial accidents, or injuries sustained at home. Despite recent advances in medical science, complete recovery after peripheral nerve injury is rare and injuries usually result in permanent partial loss of motor function, sensory function, or both [1]. Development of methods to enhance axonal regeneration is a key imperative to facilitate complete recovery after peripheral nerve injuries. Several studies have shown that direct electrical stimulation of the injured nerves can enhance sensory and motor axon regeneration, hasten functional recovery, and facilitate reinnervation [2, 5,6,7,8,9,10,11]. In a study by Mendonca et al, stimulation of injured peripheral nerves with continuous 1 μA electric current improved functional recovery significantly compared to control groups [5]. Koo et al demonstrated that animals that received electrical stimulation for six days (1h per day) showed superior motor function as compared to those that received stimulation for shorter periods [7]
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