Treatment of chronic axial back pain with 60-day percutaneous medial branch PNS: Primary end point results from a prospective, multicenter study

Abstract

Background: The objective of this prospective, multicenter study is to characterize responses to percutaneous medial branch peripheral nerve stimulation (PNS) to determine if results from earlier, smaller single-center studies and reports were generalizable when performed at a larger number and wider variety of centers in patients recalcitrant to nonsurgical treatments.

Materials & methods: Participants with chronic axial low back pain (LBP) were implanted with percutaneous PNS leads targeting the lumbar medial branch nerves for up to 60 days, after which the leads were removed. Participants were followed long-term for 12 months after the 2-month PNS treatment. Data collection is complete for visits through end of treatment with PNS (primary end point) and 6 months after lead removal (8 months after start of treatment), with some participant follow-up visits thereafter in progress.

Results: Clinically and statistically significant reductions in pain intensity, disability, and pain interference were reported by a majority of participants. Seventy-three percent of participants were successes for the primary end point, reporting clinically significant (≥30%) reductions in back pain intensity after the 2-month percutaneous PNS treatment (n = 54/74). Whereas prospective follow-up is ongoing, among those who had already completed the long-term follow-up visits (n = 51), reductions in pain intensity, disability, and pain interference were sustained in a majority of participants through 14 months after the start of treatment.

Conclusion: Given the minimally invasive, nondestructive nature of percutaneous PNS and the significant benefits experienced by participants who were recalcitrant to nonsurgical treatments, percutaneous PNS may provide a promising first-line neurostimulation treatment option for patients with chronic axial back pain.

Keywords: axial low back pain; chronic back pain; medial branch stimulation; multifidus activation; neuromodulation; non-opioid; percutaneous peripheral nerve stimulation (PNS); peripheral nerve stimulation (PNS).

FIGURE 1

Implantation of percutaneous PNS targeting the medial branch nerves via ultrasound and/or fluoroscopic guidance for chronic axial back pain. Participants received percutaneous PNS (SPRINT PNS System, SPR Therapeutics, Inc) (a) targeting the medial branches of the dorsal rami at the spinal level in the center of the region of axial back pain. All leads were placed using ultrasound and/or fluoroscopic image guidance. (b) Shows stimulation test probe insertion targeting the medial branches of the dorsal rami, medial, and inferior to the facet joint, with an anteroposterior (AP) fluoroscopic view. (c) Shows an ultrasound image of the lumbar paraspinal anatomy (as viewed with a transverse probe orientation), illustrating example out‐of‐plane PNS lead implantation to target the medial branch of the dorsal ramus over lamina. Ultrasound guidance enabled visualization of multifidus muscle responses, confirming selective activation of the medial branch nerves with PNS in all participants. PNS, peripheral nerve stimulation

FIGURE 2

Subject participation flow diagram. Participants with chronic axial low back pain were consented, evaluated for eligibility, enrolled, and underwent implantation of percutaneous PNS. Ten participants were enrolled under this study’s IRB approval as part of a prospectively designed substudy with revised eligibility criteria, designed to be reported independently from the primary end point analysis of participants without a history of prior lumbar surgery, and are not analyzed here. Eight participants were not included in the primary end point analysis after monitoring identified they did not meet the prospectively defined eligibility criteria at baseline (e.g., radicular leg pain, new medications at baseline, and scoliosis). * Of the 81 eligible participants receiving PNS leads, 74 completed the PNS treatment and primary end point (2 months after start of treatment) and 7 participants were lost to follow‐up. Prospective follow‐up is ongoing and will continue until all participants reach 14 months (12 months after end of treatment with PNS). *A post hoc sensitivity analysis confirmed that not including participants who did not meet the predefined eligibility criteria at baseline did not have a meaningful impact on interpretation of the primary end point results (see results: Primary End Point and Reductions in Pain Intensity section). IRB, institutional review board; LTFU, lost to follow‐up; MV, missed visit; PNS, peripheral nerve stimulation

FIGURE 3

Reductions in average back pain intensity. (a) Shows the proportion of participants responding with clinically meaningful reductions in average pain intensity (Brief Pain Inventory, question 5 [BPI‐5]) over time. Data collection is complete for follow up visits through 8 months (including the primary end point at 2 months), with data reported thereafter (months 11–14) as observed, while prospective follow‐up is ongoing. (b) Shows the average pain intensity scores (mean ± SD) among responders. PNS, peripheral nerve stimulation

FIGURE 4

Reductions in back pain‐related disability. (a) Shows the proportion of participants responding with clinically meaningful reductions in back pain‐related disability (Oswestry Disability Index [ODI]) over time. Data collection is complete for visits through 8 months, with data reported thereafter (months 11–14) as observed, while prospective follow‐up is ongoing. (b) Shows the disability scores (mean ± SD) among responders. PNS, peripheral nerve stimulation

FIGURE 5

Reductions in pain interference. (a) Shows the proportion of participants responding with clinically meaningful reductions in pain interference (Brief Pain Inventory [BPI]‐9) over time. Data collection is complete for visits through 8 months, with data reported thereafter (months 11–14) as observed, while prospective follow up is ongoing. (b) Shows the pain interference scores (mean ± SD) among responders. PNS, peripheral nerve stimulation