An artificial myotatic reflex: a potential avenue to fine motor control

When a striated muscle becomes paralyzed, not only its motor function, but its sensory innervation may be impaired. Methods of rehabilitation have previously focused only on motor innervation, although striated muscles are submitted to self-regulation of length and tension. Indeed, reinnervated muscle may not contract appropriately unless sensory information is available, nor is it known whether sensory receptors are included in the reinnervation process. We hypothesized that the myotatic reflex (MR) would be absent in the event these sensory organs are not reinnervated, and that an artificial myotatic reflex (AMR) would be useful in reestablishing fine motor control. The strap muscles were exposed in six anesthetized rabbits. The MR was verified by stretching an intact sternohyoid muscle. Next, loss of the reflex was documented after the ipsilateral ansa hypoglossi was divided, and a crossover nerve-muscle pedicle (NMP) was brought in from the opposite sternothyroid. After 3 months, the MR was still absent; however, stretch of the contralateral sternohyoid produced a reflex response on the reinnervated side. A strain gauge sutured to the reinnervated muscle was linked to an electronic modulator so that stretch induced electric stimulation of the NMP and contraction (the AMR). We conclude that (1) proprioception is not reestablished in the reinnervated muscle; (2) by contrast, sensory information from the muscle of origin of the NMP is conveyed to the reinnervated side; and (3) the AMR offers promise toward more sophisticated control of paralyzed (i.e., facial, laryngeal) musculature.