The effect of severing L6 nerve root of the sacral plexus on lower extremity function: an experimental study in rhesus monkeys.

Background: Nerve transfer is a valid surgical procedure for lower-extremity function restoration after lumbosacral plexus avulsion.
Objective: To evaluate the impact of severing the L6 nerve root on the functions of the healthy limb in rhesus monkeys and the feasibility of using the contralateral L6 nerve root as a donor nerve to repair lumbosacral plexus root avulsion.
Methods: Twenty-four rhesus monkeys were randomly assigned into 2 groups. In the experimental group, the right L6 nerve root was explored and severed, whereas in the control group animals underwent a sham operation. Electrophysiology, muscle mass, histology, and ultrastructure of the target muscles were examined.
Results: Three weeks after transection, reduced amplitude and prolonged latency of compound muscle action potential were observed in the medial gastrocnemius, extensor digitorum brevis, peroneus longus, and abductor hallucis muscles of the experimental group, as well as reduction in muscle mass and myofiber cross-sectional area of these muscles. The number of myelinated nerve fibers of the sciatic nerve in the experimental group was significantly less than that of the control group. Abnormal ultrastructure of motor end plates of these muscles was also observed in the experimental group. Eight weeks postoperatively, all of these parameters were similar between the experimental and control groups.
Conclusion: Severing the L6 nerve root does not damage the healthy limb as far as electrophysiology, muscle mass, histology, and ultrastructure of the target muscles are concerned. L6 (analogous to S1 in humans) nerve root may be used as a donor nerve to repair lumbosacral plexus root avulsion.