Electrical Stimulation in Denervated Muscles of the Upper Limbs

Overview

In the last decade the stimulation of denervated muscles got more attention. Not at least because of the promising results of the RISE project (Use of electrical stimulation to restore standing in paraplegics with long-term denervated degenerated muscles). In this European project it was shown that electrical stimulation of denervated muscles in spinal cord injuries (SCI) increased muscle mass and improved the trophic situation of the lower extremities. Furthermore, structural altered muscle into fat- and connective tissue could be restored into contractile muscle tissue by stimulation. However, only a few studies investigated the effect of direct muscle stimulation in case of peripheral nerve damage in the upper extremities. None investigated the stimulation effect in denervated or partially denervated muscles in the upper extremities in tetraplegic patients.

In the last decade the stimulation of denervated muscles became part of the rehabilitation of spinal cord injuries (SCI). Not at least because of the promising results of the RISE project (Use of electrical stimulation to restore standing in paraplegics with long-term denervated degenerated muscles). In this European project it was shown that electrical stimulation of denervated muscles in SCI increased muscle mass and improved the trophic situation of the lower extremities. Furthermore, structural altered muscle into fat- and connective tissue could be restored into contractile muscle tissue by stimulation. However it has been shown that an extended time after SCI hinders the stimulation impact. The denervation process can be divided in four chronologically running steps. Muscle fibrillations are present some days after lesion followed by a loss of tension during electrical evoked tetanic contraction. After months a severe disorganization of the contractile structure in the muscle occurs and finally ends after years in a replacement of muscle fibers into fat tissue and collagen. The best results have been seen within three years after SCI. A stimulation protocol should be set up to start with single twitches combined with tetanic stimulation patterns according to the patients' improvements. The progression in stimulation training to elicit a tetanic contraction - 40 ms pulse duration with a pulse pause of 10 ms and bursts of 2 sec - could last some month in chronic stage after SCI. The stimulation of denervated muscles of the upper extremities gets more attention. It has been investigated that the cross sectional area of denervated muscle fibers could have been increased by early electrical stimulation. Furthermore, the changes in myosin heavy chain isoform, following denervation could be reversed. That indicates that early onset of stimulation could preserve the contractile muscle structure for possible reinnervation or further treatment options. Specially for tetraplegic patients who could benefit from nerve transfers, could win time for their decision.