ABSTRACT: Injury to peripheral nerves is not uncommon, and spinal injury with fracture dislocation of the vertebrae can damage roots as well as the cord. Both types of trauma leave the corresponding muscles denervated, resulting in a flaccid paralysis and catastrophic loss of muscle mass. When this occurs in the lower limbs, a loss of cushioning over bony prominences, combined with a deterioration in skin condition, greatly increases the risk of developing pressure sores. Furthermore, bones become osteoporotic and the wasted appearance of the affected limbs can be a source of great distress to patients. Although there has been a longstanding interest in the potential therapeutic value of electrical stimulation of denervated muscles in humans it was always regarded as impractical. In the absence of the nerve or intramuscular nerve branches the muscles must be excited directly. The charge delivery needed for this is so high that the approach has been frustrated by regulatory restrictions and a lack of suitable equipment. More recently, however, these problems were addressed, and the value of stimulation was clearly demonstrated, in a remarkable research programme pursued with the support of the EU Commission Shared Cost Project “RISE”. It is hard to explore the benefits and limitations of the technique in patient groups, which are small and inhomogeneous in age, nature and duration of injury, and compliance. Moreover, the intense surface stimulation elicits co-contraction of antagonistic muscle groups, which interferes with the measurement of force or torque. In Project “RISE”, the important clinical work1 was therefore complemented by Laboratory studies. The usual model, total sciatic section in the rat, is unsatisfactory on two counts. First, denervated rat muscles show evidence of extensive degeneration in a few months,2 differing in this respect from the muscles of other species. Denervated human muscles, in particular, do not undergo significant necrosis for at least a year post-injury (U. Carraro, personal communication), and we could confirm that this was also true of the rabbit.3 Second, most published studies of stimulation in the denervated rat start at, or soon after, the moment of lesion, which does not correspond to the clinical situation. The “RISE” experimental studies to be discussed were conducted by the Muscle Research Group, University of Liverpool, UK, in a long-term model of established selective denervation in the rabbit. The Department for Biomedical Engineering and Physics, University of Vienna, designed the implantable stimulator,4 ultrastructural studies were performed at the Interuniversity Institute of Myology, Chieti, and valuable input was provided by clinical colleagues at the Ludwig Boltzmann Institute of Electrostimulation and Physical Rehabilitation, Wilhelminenspital, Vienna, Austria. Through this joint programme we were able to assemble comprehensive physiological, histological, biochemical, and ultrastructural data on muscles subjected to selective denervation alone for up to 1 year, and muscles subjected to denervation and stimulation for up to 3 months.3,5,6 Although this data settled several issues, and may serve to take some of the guesswork out of the design of stimulation protocols for clinical use, it raised some tantalizing questions. These will be worth addressing in future studies.
