After reconstructive nerve surgery, muscle force and function are often impaired because of incomplete reinnervation and altered motor unit properties. Surgical peripheral nerve transfers can overcome some of these dismal effects by specifically transferring a high-capacity donor nerve (i.e., peripheral nerves with large cognitive control such as the ulnar and median nerves) of a sufficiently large motor neuron pool to an alternate target muscle. 

In this study, researchers investigated the neurophysiological effects of rewiring motor axons originating from spinal motor neuron pools into target muscles with lower innervation ratio in a rat model. Following reinnervation, the target muscle’s force regenerated almost completely, with the motor unit population increasing to 116% in functional and 172% in histological assessments with subsequently smaller muscle units. Muscle fiber type populations transformed into the donor nerve’s original muscles. [Researchers] thus demonstrate that axons of alternative spinal origin can hyper-reinnervate target muscles without loss of muscle force regeneration, but with a donor-specific shift in muscle fiber type. These results explain the excellent clinical outcomes following nerve transfers in neuromuscular reconstruction. They indicate that reinnervated muscles can provide an accurate bioscreen to display neural information of lost body parts for high-fidelity prosthetic control.

 

Experimental nerve transfer model.
A high-capacity multifascicular donor nerve originating from a different spinal topography was surgically transferred to selectively reinnervate a single target muscle instead of its original motor branch. The contralateral untreated side was used as control.
The nerve transfer successfully reinnervated the target muscle, and no additional reinnervation was observed during dissection or electrophysiological testing. MCN, musculocutaneous nerve.

Credit: Science Advances, DOI: 10.1126/sciadv.aau2956

 

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