CLINICAL-EVALUATION OF PARESTHESIA STEERING WITH A NEW SYSTEM FOR SPINAL-CORD STIMULATION

OBJECTIVE: The goal was to evaluate, in a clinical study, the predicte d performance of the transverse tripolar system for spinal cord stimul ation, particularly the steering of paresthesia, paresthesia coverage, and the therapeutic range of stimulation. METHODS: Six transverse tri polar electrodes were implanted in the lower thoracic region in four p atients experiencing chronic neuropathic pain. Electrode positions, re lative to the spinal cord, were estimated from computed tomographic sc ans. A dual-channel stimulator was used for initial percutaneous tests , and an implanted single-channel stimulator was used for follow-up te st sessions. Nine ''balance'' settings and several cathode-anode combi nations were used with the dual-channel and single-channel stimulator, respectively. In each test, the increase of paresthesia coverage from the perception threshold to the discomfort threshold was registered o n a body map and the corresponding; voltages were recorded. RESULTS: P aresthesia steering occurred in all but one patient. The normalized st eering score, enabling quantitative comparisons of paresthesia steerin g among tests and patients, showed that maximum paresthesia steering o ccurred when the electrode was at least 3 mm dorsal to the spinal cord and centered <2 mm from its midline. Paresthesia coverage included 70 to 100% of the body up to the electrode level, unless the electrode m igrated or had broken wires. The therapeutic range, defined as the dis comfort/perception of paresthesia threshold ratio, varied from 1.6 to 4.0. CONCLUSION: The clinical performance of transverse tripolar stimu lation is in accordance with the characteristics predicted by computer modeling. It enables finer control of paresthesia than that achieved by polarity changes in conventional spinal cord stimulation systems.