Excitation thresholds for nerve pedicles: A preliminary report

Ongoing interest in the rehabilitation of paralyzed musculature in the head and neck has focused on the electronic stimulation of nerve-muscle pedicles that have been reimplanted into the incapacitated effector(s). Despite visual and histochemical evidence of reinnervation, it is still not known whether the excitability of a nerve-muscle pedicle (or for that matter a direct nerve implant) is equivalent to or better than that of reinnervated or normal muscle. Such information is necessary for the eventual construction of an implantable stimulator. Eighteen rabbits were anesthetized with intramuscular xylazine and ketamine and the ansa hypoglossi nerve was cut on one side. A crossover nerve-muscle pedicle was brought in from the opposite sternothyroid muscle to the sternohyoid in nine animals; the other nine received a direct nerve implant. After a minimum neurotization period of 3 months and reexploration, an electrical stimulator capable of delivering square wave pulses of variable amplitude and width was used to determine the thresholds of contraction of the nerve pedicles, an intact motor nerve of similar size, a normal muscle, and the reinnervated strap in 16 evaluable rabbits. Strength duration curves were established. The data indicate that thresholds for nerve pedicles are equivalent to those of normal nerves and are significantly lower than those of muscle.