DESIGN AND CLINICAL-APPLICATION OF A DOUBLE HELIX ELECTRODE FOR FUNCTIONAL ELECTRICAL-STIMULATION

An electrode, designed to be implanted without a surgical incision, wa s developed for skeletal muscle stimulation. Stainless steel, Teflon(R )-insulated wire was wound into a helical lead around a polypropylene core and then rewound into a double helix configuration for stress rel ief during muscle contractions. The electrode tip was augmented with s tainless steel barbs to increase anchoring strength. Electrodes were i mplanted with the help of specially modified hypodermic needles, sheat hs, and passing tubes. 775 electrodes were implanted in a five year pe riod in 22 subjects; accumulated implant time was 1,080 electrode year s. 453 electrodes (65%) continue to produce strong, stable, muscle con tractions. Electrode longevity varied with the location of implant. El ectrodes were removed because of (1) inability to locate and properly place the electrode in a suitable site for stimulation during surgery (28, 4%), (2) unwanted changes in muscle response to stimulation (91, 12%; one-third occurring during the first six weeks post implant), (3) increase in electrode impedance (74, 10%; assumed breakage, mostly oc curring during the first year after implant), (4) intolerable pain dur ing stimulation (8, 1%), and (5) infection (4, 0.5%). 67 (8%) electrod es were removed by accident or when the subjects left the program. Thi s double helix electrode design has proven practical for achieving chr onic stimulation of selected muscles in hemiplegic, paraplegic, stroke and brain-injured subjects with minimally invasive surgery.