Electrical Stimulation of Chronically Denervated Muscle.

Electrical stimulation of denervated muscle offers similar potential benefits as that for paralysed innervated muscle, such as enhanced tissue viability, cosmesis and retained contractile function. For acute nerve injuries, these benefits may enhance functional reinnervation. Appropriate stimulation parameters are, however, essential in each case to optimise benefits and minimise tissue damage. This pilot study has concentrated on the therapeutic benefits of charge balanced, long pulse, biphasic stimulation treatment of peripheral limb muscle, denervated for more than three years, with quantitative assessment of some clinically important tissue changes. The five study subjects include complete and partial limb denervation arising from T12 level spinal cord, peroneal nerve, and brachial plexus injuries. Treatment consisted of two sessions each day of up to 30 minutes, stimulating a single muscle group with surface electrodes with the contra-lateral limb as control. Non-invasive evaluation measurement of tissue thickness, resting limb segment blood flow, resting skin temperature and muscle excitability occurred before and at regular intervals throughout the 6 month treatment and 6 month follow-up periods. The custom designed portable stimulator unit issued to each subject, was programmed from the clinician’s personal computer, allowing on-line change of treatment parameters and Strength-Duration testing. Pulse widths of 100ms or greater were required initially in all cases, eliciting only twitch contractions. Muscle responsiveness progressively increased, such that tetanic contractions were possible after approximately ten weeks and limited limb movement by the end of the treatment period, but no functional use. Trapezoidal, instead of rectangular, shaped pulses were used initially in cases of partial limb denervation to minimise co-contraction, but nerve accommodation was not possible at tetanic frequencies. No significant changes in resting tissue property measurements occurred and those that did, were confused by high measurement variability including artefacts. However in the case, where treatment was most consistent, some positive changes were detectable in all measurements, suggesting that greater benefit may accrue from a more prolonged treatment period. Subjects remained enthusiastic about the treatment and of its perceived beneficial effects