Using Transcranial Magnetic Nerve Stimulation to Differentiate Motor and Sensory Fascicles in a Mixed Nerve: Experimental Rat Study

Abstract

Background

Accurately matching the correct fascicles in a ruptured mixed nerve is critical for functional recovery. This study investigates the use of transcranial magnetic stimulation (TMS) to differentiate motor and sensory fascicles in a mixed nerve.

Methods

In all 40 rats, the median nerve in the left upper arm was evenly split into three segments. The rats were separated into two groups. In Group A (20 rats), the segment with the highest amplitude during TMS was selected as the motor neurotizer and transferred to the musculocutaneous nerve. In Group B (20 rats), only the medial one-third segment was selected and transferred without using TMS. The results were compared using grooming tests, nerve electrophysiological studies, muscle tetanus contraction force measurements, muscle weight, and axon counts at 16 weeks.

Results

The grooming test showed that Group A performed significantly better than Group B at 12 and 16 weeks postoperatively. Tetanic muscle contraction force measurements also revealed that Group A had significantly better outcomes than Group B. However, electrophysiological testing, muscle weight, and axon counts showed no significant differences between the two groups.

Conclusion

This study suggests that TMS can be used to distinguish motor fascicles from sensory fascicles in a mixed nerve. It is desirable to apply this technique intraoperatively to differentiate motor and sensory fascicles for appropriate nerve matching and to select the motor fascicles as a motor neurotizer for functioning free muscle innervation in human mixed nerve injury.

Keywords

transcranial magnetic stimulation - mixed nerve injury - motor fascicle identification

Ethical Approval

Ethical approval for this study was obtained from the Chang Gung Memorial Hospital Institutional Review Board.

Publication History

Received: 17 July 2024

Accepted: 10 November 2024

Article published online:
07 January 2025

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