Clinical Sciences/Health Conditions
Mathew IB Debenham, PhD
Postdoctoral Researcher
University of British Columbia
Port Coquitlam, British Columbia, Canada
Kyle IB Missen, PhD
Postdoctoral Researcher
The University of British Columbia (ICORD)
Vancouver, British Columbia, Canada
Harvey IB Wu, MD
Research Manager
The University of British Columbia (ICORD)
Vancouver, British Columbia, Canada
Christopher Doherty, MD
Clinical Associate Professor
The University of British Columbia
Vancouver, British Columbia, Canada
Sean Bristol, MD
Clinical Associate Professor
The University of British Columbia
Vancouver, British Columbia, Canada
Russell O'Connor, MD
Clinical Assistant Professor
The University of British Columbia
Vancouver, British Columbia, Canada
Amy Hanlan, MD
Physical Medicine and Rehabilitation Residency Program Director
The University of British Columbia
Vancouver, British Columbia, Canada
Michael Berger, MD
Clinical Associate Professor
ICORD
Vancouver, British Columbia, Canada
Nerve transfer surgery (NTS) can restore movement to paralyzed muscles after cervical spinal cord injury (SCI). It has been postulated that successful NTS is conditional on cortical plasticity to repurpose the donor nerve action to control the recipient muscle. However, voluntary activation (VA), a measure of neural drive to the motor neuron pool of a contracting muscle, has not been measured following NTS, nor compared between an isolated recipient vs. donor–recipient co-contraction. Thus, our objective was to assess neural drive as an index of cortical plasticity after NTS.
Design:
Eleven participants with motor-complete cervical SCI (9 males; 44.9±14.3years; 3C6, 4C5, 4C4) who underwent musculocutaneous-to-anterior interosseous nerve (AIN) transfer to restore thumb/finger flexion, were evaluated 3.5±1.6years post-NTS. Participants performed maximal voluntary contractions (MVCs) of their flexor pollicis longus (FPL), either with or without co-contraction of the elbow flexor donor. An electrical stimulus was delivered to the musculocutaneous nerve during MVCs to quantify VA. Surface electromyography (EMG) was recorded from the FPL and quantified as root-mean-square (RMS) amplitude.
Results: MVC torque (12.4±9.4N vs. 3.1±2.2, p≤0.002; d=8.0), VA (61.9±33.1% vs. 26.3±25.1; p≤0.001; d=28.9) and RMS-EMG (0.21±0.23mV vs. 0.11±0.13; p=0.004; d=0.12), were all significant increased when recruiting the donor together with the recipient, compared to recipient recruitment alone.
Conclusion:
Despite the increase in VA with donor activation, neural drive was still substantially impaired to the FPL. These data indicate that even long after NTS, there is minimal decoupling between donor and recipient actions and significant deficits in neural drive, even when co-contracting the donor and recipient muscles. Accordingly, limited cortical plasticity after NTS likely remains a critical factor influencing functional recovery.
