Muscle Preservation by Prolonged Sensory Protection

Abstract

The functional recovery of a muscle target following nerve repair is inversely related to the denervation time: i.e., the longer the muscle denervation, the poorer the functional outcome following nerve reconstruction. The trophic and protective effects of sensory innervation to a motor nerve, following prolonged denervation (greater than 6 months), have been studied. Following proximal transection of the musculocutaneous nerve (MC) close to its C6 origin in 10 adult male Sprague-Dawley rats, the severed nerve was coapted to supraclavicular purely sensory nerves originating from C3 and C4 (sensory protection [SP] group). In another 10 Sprague-Dawley rats, the transected MC nerve was not protected by coaptation to sensory nerves (control group). After prolonged denervation or "sensory protection" (6 months), the MC nerve was then coapted in both groups to the purely motor medial pectoral nerve. Behavioral testing (grooming test) was performed on a weekly basis during the reinnervation time, which lasted 4 weeks. Statistically significant differences (p<0.05) favoring the SP group, were found at the second week of the reinnervation period, but not at the end of the experiment. Evaluation also included intraoperative electrical stimulation of the MC nerve, biceps muscle dry weights, motor endplate counts, and nerve axon counts of the MC nerve. The biceps muscle dry weights were statistically higher in the SP group, along with a trend for a higher number of motor endplates. No statistically significant difference was found in the nerve axon counts of the MC nerve between the two groups. Statistically better intraoperative electrical stimulation results were also encountered in the sensory protection group. An interpretation of the results favors the hypothesis that sensory reinnervation of a motor target may provide the necessary trophic environment to minimize muscle atrophy, until a motor donor nerve becomes available.

Sensory Protection of Rat Muscle Spindles following Peripheral Nerve Injury and Reinnervation

“…4,12 Patients have reported a perception of muscle tension (stretch) with muscle activity during sensory protection and improved function (walking) resulting from improvement in ankle position even before significant changes in motor recovery of the targets. 24 The molecular and cellular mechanisms responsible for the functional extrafusal fiber recovery are under investigation.…”

“…2,4,5,11,12 This strategy, called "sensory protection," uses a readily available sensory nerve to temporarily innervate a denervated muscle until the injured motor nerves regenerate and become available for surgical reconstruction. We have shown that temporary sensory innervation improves functional recovery of denervated skeletal muscle following reinnervation.…”

NGF, BDNF, NT-3, and GDNF mRNA Expression in Rat Skeletal Muscle following Denervation and Sensory Protection

“…Sensory nerve cross-anastomosis to the distal motor nerve (sensory protection) significantly improves muscle weight, with larger compound muscle action potentials, less fiber atrophy and connective tissue hyperplasia than in denervated muscle (Hynes et al, 1997;Bain et al, 2001). An increased number of motor endplates is also found in muscles that receive sensory protection (Papakonstantinou et al, 2002).…”

A gastrocnemius heterotopical transplant model with end-to-side neurorraphy

“…When the motor nerve was connected end-to-end to the sensory nerve ("Sensory protection"), it seemed to provide trophic environment to minimize muscle atrophy until a motor donor nerve became available. Although incapable of forming excitable neuromuscular junctions, sensory nerves were found to exert powerful trophic effects on denervated muscle fibers [12][13][14] .…”