Multi-waveform Spinal Cord Stimulation with High Frequency Electromagnetic Coupled (HF-EMC) Powered Implanted Electrode Array and Receiver for the Treatment of Chronic Back and Leg Pain (SURF Study).

BACKGROUND: Novel externally powered spinal cord stimulation technology can be fully implanted when trialing the effectiveness of the therapy, since no percutaneous leads are needed, and the trial period lasted 30 days. Multiple tests of different stimulation modalities and parameters are possible, thus improving the chances that the therapy will lead to effective pain reduction.

OBJECTIVES: The objective of this study was to analyze the effectiveness of the Freedom Spinal Cord Stimulator System (Stimwave LLC, Pompano Beach, FL) for the treatment of failed back surgery syndrome due to postlaminectomy syndrome utilizing multiple waveforms.

STUDY DESIGN: This was a prospective, single cohort study. Patients were enrolled and implanted with up to 2 permanent, 8-contact electrode arrays with receiver, controlled regularly during 6 months of follow-up after a one month trial period. Pain and overall improvement were evaluated at 3 months and 6 months following an initial one-month implanted trial period.

SETTINGS: A variety of frequency stimulation waveforms (tonic as well as subthreshold) at frequencies of 10 Hz to 1500 Hz* and 50 to 800 µs pulse width, were provided. (*Note: While 1500 Hz was utilized in the study, Stimwave Technologies is currently only permitted to provide spinal cord stimulation therapy at frequencies below 1500 Hz, therefore pulse rates used in this study are not commercially available on Stimwave Technologies' products).

METHODS: Endpoints evaluated included the Visual Analog Scale (VAS) for pain intensity, Oswestry Disability Index (ODI) for functionality, Patient Global Impression of Change (PGIC) for overall health improvement, and quality of life as measured by the European Quality of Life 5 Dimension questionnaire (EQ-5D-5L).

RESULTS: Thirty-nine patients completed the study. At 6 months, the responder rate (? 50% reduction VAS for back pain) was 33/39 = 85%. Mean VAS for back pain decreased 62%. The mean ODI decreased 46% from 54 to 29.2, indicating a reduction from severe to moderate disability. The median satisfaction as measured with the PGIC was 6 out of 7. The mean EQ-5D-5L utility score increased from 0.54 to 0.75. At the 6-months endpoint, 44% (17/39) of patients preferred tonic stimulation with a back pain per protocol responder rate of 82%; 41% (16/39) preferred surge with a responder rate of 56%; and 15% (6/39) preferred high density, with a responder rate of 83%. Fifteen patients reported 28 adverse events. Migration of the electrode array (n = 10) was the adverse event most reported. Two serious adverse events related to infection were reported.

LIMITATIONS: This study had several limitations. Trial failures were excluded from the analysis, there was a small sample size, and there was a lack of blinding due to the suprathreshold nature of tonic stimulation.

CONCLUSION: The study demonstrates that spinal cord stimulation with multiple stimulation patterns demonstrates clinical and functional efficacy when using an externally powered stimulation system.