Implantation techniques and experience with percutaneous intramuscular electrodes in the lower extremities

Innervated paralyzed muscles have been implanted with temporary percutaneous intramuscular electrodes in order to allow selective stimulation of as many muscles as necessary to achieve a cosmetically acceptable and energy-efficient gait in paraplegic subjects. Fine wire electrodes were implanted under sterile conditions at the motor points (MP) of hip extensors, flexors, abductors and adductors; knee extensors; and ankle plantar- and dorsi-flexors. Electrodes were routed to the MP's from one of four skin sites on the legs where the wires emerged. Employed were both a direct approach from the skin site to the MP and an indirect approach which involved one or more subcutaneous passages of the electrode wire from the MP to the skin site. Muscles were stimulated approximately 12 hours per week in daily electrical exercise and gait training. Electrodes were removed when they exhibited one of two types of failure: breakage, as determined by high impedance, or loss of adequate function as a result of electrode movement. Of 1025 electrodes implanted in 6 subjects over a period of 38 months, 35 percent failed within the first 4 months; more than 75 percent of those early failures resulted from electrode movement. Complete withdrawal of those electrodes was usually possible. The probability of electrode failure decreased exponentially during the first 4 months and reached less than 4 percent per month for electrodes implanted for longer than 6 months. These procedures have allowed multiple revisions toward a more functional neuro-orthotic system.