Technology and long-term application of an epineural electrode

An epineural electrode (ENE) was developed to achieve a controllable, progressive muscle contraction and reduce muscle fatigue during functional electrostimulation. In vitro studies of annular (torus-shaped) electrodes have been carried out to select adequate electrode materials and electrode diameters. We investigated the long-term stability of ENEs using different intensities of current (range: 0.8-1.2 mA) in sheep and rat experiments. Depending upon size and material, ENE tolerates anodic and cathodic impulses of up to 1 msec and 8 mA (peak current). ENEs were used during clinical application in four paraplegic patients (16 channel implants) for stimulation of lower extremities, and in nine quadruplegic patients (eight channel implants) for diaphragm pacing, for a total observation time of 37 patient years. The low rate of clinical complications, including no corrosion of the electrodes or significant loss of nerve fibers, seems related to the small dimensions of the electrode (less than 1 mm2).