Peripheral Nerve Basic Science Research-What Is Important for Hand Surgeons to Know?

Does short-term intraoperative electrical stimulation enhance nerve regeneration following peripheral nerve repair? A systematic review and meta-analysis

BACKGROUND

Although intraoperative electrical nerve stimulation appears to be a promising neuroenhancing adjunct to peripheral nerve repair, insight into its effects on nerve regeneration is essential to advocate its application in clinical settings.

OBJECTIVE

This study examined whether electrical stimulation during microsurgical repair of peripheral nerve injury results in enhanced nerve regeneration compared to suture repair alone in experimental animals.

METHODS

A systematic search in Embase, MEDLINE, Web of Science, and Google Scholar databases was performed from inception to March 22, 2024. The search included animal studies assessing outcomes following peripheral nerve repair with and without intraoperative electrical stimulation. Outcomes were subdivided into 4 categories: motor function, sensory function, electrophysiology, and histology. We calculated standardized mean differences and combined these using random effects models to estimate the overall effect. The risk of bias was assessed using the SYRCLE tool.

RESULTS

From 3615 references, 21 articles were included. Thirteen studies evaluated motor functional outcomes and showed that electrical stimulation improved functional index, muscle mass, muscle force, footstep accuracy, footprint, and joint angle measures. Six studies examined sensory function and found that electrical stimulation improved mechanical algesimetry. Nine studies assessed electrophysiology outcomes. Although conduction velocity did not differ between the groups, electrical stimulation resulted in a higher amplitude and lower latency. Twenty studies evaluated the histological outcomes and demonstrated increased axon count and myelin thickness, whereas axon diameter and G-ratio did not differ.

DISCUSSION

The results suggest that intraoperative electrical stimulation following peripheral nerve repair accelerates and improves nerve regeneration compared with nerve repair alone.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42023455066.

Nerve Autografts Versus Allografts for Mixed Motor/Sensory Nerve Reconstruction

Reconstruction of peripheral mixed motor/sensory nerves using autografts has remained the gold standard. Inconsistent and nonphysiologic results across nerve allograft studies, including successful and failed motor reinnervation, have limited the current clinical application of nerve allografts to noncritical small-diameter sensory nerve defects less than 3 cm. This scoping review aimed to compare outcomes in both basic science and clinical applications of autograft and allograft nerve reconstruction for mixed motor/sensory nerves.

Promoting Nerve Regeneration: Electrical Stimulation, Gene Therapy, and Beyond

Peripheral nerve injuries often result in life-altering functional deficits even with optimal management. Unlike the central nervous system, peripheral nerves have the ability to regenerate lost axons after injury; however, axonal regeneration does not equate to full restoration of function. To overcome this physiological shortcoming, advances in nerve regeneration and repair are paramount, including electrical stimulation, gene therapy, and surgical technique advancements.

Beyond the Knife-Reviewing the Interplay of Psychosocial Factors and Peripheral Nerve Lesions

Peripheral nerve injuries are a common clinical problem. They not only affect the physical capabilities of the injured person due to loss of motor or sensory function but also have a significant impact on psychosocial aspects of life. The aim of this work is to review the interplay of psychosocial factors and peripheral nerve lesions. By reviewing the published literature, we identified several factors to be heavily influenced by peripheral nerve lesions. In addition to psychological factors like pain, depression, catastrophizing and stress, social factors like employment status and worker's compensation status could be identified to be influenced by peripheral nerve lesions as well as serving as predictors of functional outcome themselves, respectively. This work sheds a light not only on the impact of peripheral nerve lesions on psychosocial aspects of life, but also on the prognostic values of these factors of functional outcome. Interdisciplinary, individualized treatment of patients is required to identify patient at risk for adverse outcomes and provide them with emotional support when adapting to their new life situation.

Functional Outcomes of Nerve Allografts Seeded with Undifferentiated and Differentiated Mesenchymal Stem Cells in a Rat Sciatic Nerve Defect Model

BACKGROUND

Mesenchymal stem cells have the potential to produce neurotrophic growth factors and establish a supportive microenvironment for neural regeneration. The purpose of this study was to determine the effect of undifferentiated and differentiated mesenchymal stem cells dynamically seeded onto decellularized nerve allografts on functional outcomes when used in peripheral nerve repair.

METHODS

In 80 Lewis rats, a 10-mm sciatic nerve defect was reconstructed with (1) autograft, (2) decellularized allograft, (3) decellularized allograft seeded with undifferentiated mesenchymal stem cells, or (4) decellularized allograft seeded with mesenchymal stem cells differentiated into Schwann cell-like cells. Nerve regeneration was evaluated over time by cross-sectional tibial muscle ultrasound measurements, and at 12 and 16 weeks by isometric tetanic force measurements, compound muscle action potentials, muscle mass, histology, and immunofluorescence analyses.

RESULTS

At 12 weeks, undifferentiated mesenchymal stem cells significantly improved isometric tetanic force measurement and compound muscle action potential outcomes compared to decellularized allograft alone, whereas differentiated mesenchymal stem cells significantly improved compound muscle action potential outcomes. The autografts outperformed both stem cell groups histologically at 12 weeks. At 16 weeks, functional outcomes normalized between groups. At both time points, the effect of undifferentiated versus differentiated mesenchymal stem cells was not significantly different.

CONCLUSIONS

Undifferentiated and differentiated mesenchymal stem cells significantly improved functional outcomes of decellularized allografts at 12 weeks and were similar to autograft results in the majority of measurements. At 16 weeks, outcomes normalized as expected. Although differences between both cell types were not statistically significant, undifferentiated mesenchymal stem cells improved functional outcomes of decellularized nerve allografts to a greater extent and had practical benefits for clinical translation by limiting preparation time and costs.

Surgical Angiogenesis of Decellularized Nerve Allografts Improves Early Functional Recovery in a Rat Sciatic Nerve Defect Model

BACKGROUND

Surgical angiogenesis applied to nerve grafts has been suggested to enhance nerve regeneration after nerve injury. The authors hypothesized that surgical angiogenesis to decellularized nerve allografts would improve functional recovery in a rat sciatic nerve defect model.

METHODS

Sixty Lewis rats were divided in three groups of 20 animals each. Unilateral sciatic nerve defects were repaired with (1) autografts, (2) decellularized allografts, and (3) decellularized allografts wrapped with a superficial inferior epigastric artery fascial flap to add surgical angiogenesis. Twelve and 16 weeks after surgery, nerve regeneration was assessed using functional, electrophysiologic, histologic, and immunofluorescence analyses. Ultrasonography was used during the survival period to noninvasively evaluate muscle atrophy and reinnervation by measuring cross-sectional muscle area.

RESULTS

Surgical angiogenesis of allografts demonstrated significantly improved isometric tetanic force recovery at 12 weeks, compared to allograft alone, which normalized between groups at 16 weeks. Cross-sectional muscle areas showed no differences between groups. Electrophysiology showed superiority of autografts at both time points. No differences were found in histologic analysis, besides a significantly inferior N ratio in allografts at 12 weeks. Immunofluorescent expression of CD34, indicating vascularity, was significantly enhanced in the superficial inferior epigastric artery fascial group compared to allografts at 12 weeks, with highest expression at 16 weeks compared to all groups.

CONCLUSION

Surgical angiogenesis with an adipofascial flap to the nerve allograft increases vascularity in the nerve graft, with subsequent improvement of early muscle force recovery, comparable to autografts.