Three-year durability of restorative neurostimulation effectiveness in patients with chronic low back pain and functional instability of the lumbar spine

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Objective: Patients with refractory chronic low back pain (CLBP) associated with multifidus muscle dysfunction, functional instability of the lumbar spine and no indications for spine surgery, have a poor prognosis and few treatment options with durable effectiveness. An implantable restorative neurostimulator (ReActiv8^® by Mainstay Medical) stimulates the medial branches of the L2 dorsal rami to override underlying inhibition of the multifidus muscles and facilitate motor control restoration. An international, sham-controlled, pivotal trial provided evidence of safety and effectiveness (clinicaltrials.gov/show/NCT02577354).¹ Here we present the 3-year longitudinal analysis.

Material/Methods: Eligible patients had CLBP (VAS≥6 cm; Oswestry Disability Index ODI≥21 points) despite treatment including at least pain medications and physical therapy, evidence of multifidus dysfunction (positive prone instability test) and no surgical indication. Participants activated stimulation for up to 30 minutes twice daily and outcomes were assessed through 3-years after activation. To provide implicit imputations of randomly missing data, the mixed-effects model repeated measures (MMRM) approach was used for continuous outcomes and Multiple Imputation (MI) for proportions.

Results: At baseline (N=204), participants were 47±9 years of age, had history of 14±11 years of back pain, an average low back pain VAS of 7.3±0.7 cm, ODI of 39±10, EQ-5D of 0.585±0.174 points with pain on 97±8% of days in the year prior to enrollment. After 3 years (N=133), mean average VAS improved by 4.9±0.2 cm, ODI by 22.7± 1.3 points and EQ-5D by 0.220±0.017 (all P<0.0001) approaching the age-matched population norm; 77% of participants had ≥50% VAS improvement; 67% reported LBP-Resolution (VAS≤2.5 cm); 63% had ≥20-point ODI improvement and 83% reported improvement of ≥50% in VAS and/or ≥20points in ODI. Of participants using opioids at baseline, 71% had voluntarily discontinued or decreased consumption. Attenuation of effectiveness in the imputed (N=204) analyses was relatively small and did not affect statistical significance and clinical relevance of these results. Overall safety compares favorably to available neurostimulation systems, and no lead migrations were observed.

Conclusions: Three-year follow-up data of this pivotal trial demonstrates that restorative neurostimulation is effective, durable, and safe. It provides surgeons with a reversible and targeted treatment option for patients with refractory CLBP associated with functional instability of the lumbar spine and no indications for surgery. Robust study design, extended follow-up duration and conservative statistical analysis instill confidence in the presented results and conclusions.

¹Gilligan C, Volschenk W, Russo M, et al. An implantable restorative-neurostimulator for refractory mechanical chronic low back pain: a randomized sham-controlled clinical trial. Pain. 2021;162(00):2486-2498.