Peripheral Nerve Stimulation With the SPRINT® System in Chronic PSIJC Pain

Chronic low back pain (CLBP) is a leading cause of disability in the United States, with a recent review finding a prevalence between 21-68% of all people aged 60 or older. Posterior sacroiliac joint complex (PSIJC) pain affects a large percentage of these patients, with a prevalence of 15-30% of all CLBP cases. The etiology of sacroiliac dysfunction is complex and often includes multiple factors. Patients may experience pain from inflammation of the SI joint itself, or dysfunction of the supporting tendons and ligaments may produce pain by affecting the ability of the joint to effectively transfer loads. The verbiage used for this clinical syndrome has been altered to PSIJC to include the posterior connective tissues as a consideration in the diagnosis and treatment. The cause of pain may be from the joint itself, associated tendons, muscles, or a combination of sources. The innervation of the sacroiliac complex is extensive, but a large component of the posterior complex innervation is from the lateral branches of the sacral dorsal rami. The gold standard for diagnosis has been analgesic response to SIJ injection with local anesthetic. Therapeutic injections of the joint are utilized, but reimbursement from payors has been restricted due to the small sample sizes and limited difference in pain medication use and functional improvement. Since the restrictions on therapeutic injections, radiofrequency ablation has become a mainstay interventional modality.

Sacral lateral branch radiofrequency ablation (SLBRFA) has been used to treat PSIJC pain for many years, with multiple studies finding a majority of subjects receiving ≥50% relief at 1, 3, 6, and 12 months. One study examining the effectiveness of endoscopic radiofrequency ablation of PSIJC for CLBP found a 61% reduction in Visual Analog Scale (VAS) score and 50% reduction in Oswestry Disability Index (ODI) at 24 months following the procedure. Despite the evidence for utilizing SLBRFA to treat PSIJC pain, on March 19, 2023, the Centers for Medicare \& Medicaid Services (CMS) joined private payors in deeming SLBRFA as "not reasonable and necessary," all but eliminating access to this treatment for most Americans. The rationale for no longer covering SLBRFA includes a lack of high-quality evidence for SLBRFA over placebo for PSIJC pain, as studies conducted have been hindered by small sample sizes and variability in patient selection and procedure technique. They also noted remaining concerns over the safety profile of this procedure and the lack of clear diagnostic criteria for determining patients that will benefit from SLBRFA. Unfortunately, the denial of access to SLBRFA has left a gap regarding interventional solutions in the treatment of PSIJC pain. Symptoms are often refractory to medical and physiotherapies and the evidence for these modalities is limited by small sample sizes and a limited number of studies. Recent evidence for spinal cord stimulation for non-surgical low back pain made headlines, however PSIJC pain has never specifically been examined. There is great concern among physicians treating this disease that the lack of less invasive treatment options will result in more unnecessary or ineffective SIJ fusions.14 SIJ fusion technology has been limited by conflicting data on efficacy, a complication rate of up to 16%, and the changing loads on the joint and surrounding structures after fusion. The lack of options also limits the ability to treat PSIJC pain in patients deemed to not be surgical candidates for SIJ fusion.

Unfortunately, interventional providers have little to offer those suffering from PSIJC pain in this new paradigm. An alternative is desperately needed for patients and providers prior to considering SIJ fusion. Previous studies have shown that peripheral nerve stimulation (PNS) can successfully treat multiple types of chronic pain. There is a nascent body of evidence for treating PSIJC pain with PNS, and this evidence has been promising. Notably, one trial of 16 patients by Guentchev et al. implanted a permanent neurostimulator targeting the S1-S3 lateral branches (Prime Advanced™ Medtronic, Dublin, Ireland) following a successful trial (>50% pain relief for up to 1 week). Results of this trial have demonstrated PNS to be effective as both a short term and long-term treatment of PSIJC pain, finding average ODI decreased to 23% from 58% at 1 year and average VAS decreased to 1.6 and 2.0 (from 8.8 pre-implantation) at 1 and 3 years post-implantation, respectively. Similar effectiveness in treating intractable PSIJC pain with permanent neurostimulators has been shown in case reports. One case report involved a 41-year-old woman with PSIJC pain that was successfully treated (VAS decreased to 3 from 9) with permanent sacral nerve stimulation to the left first sacral foramen after she did not sustain lasting pain relief from intramuscular piriformis injection, SIJ intra-articular injection, and radiofrequency denervation. Another case report demonstrated permanent peripheral nerve field stimulation for SIJ pain was able to cut pain medication requirements by half while also providing >50% improvement in functional status in 2 patients who failed to receive >3 months of relief from injections or RFA. An interesting case report of a 74-year-old female with SIJ pain demonstrated the effectiveness of permanent neurostimulation via leads placed both epidurally and in the subcutaneous tissue overlying the bilateral SI joints. A three-day trial of epidural spinal cord stimulation yielded no improvement before a trial of subcutaneous field stimulation was performed with relief. She has received a 90% improvement in symptoms with a drop in her VAS from 10 to 1 and increased independence with her activities of daily living ongoing at 2 years. Lastly, there is also one randomized trial actively recruiting patients to SLB PNS versus best medical treatment in Germany.

While there is evidence permanent PNS can be effective and durable, temporary PNS for PSIJC pain has not been examined. Investigators have reason for optimism that the temporary SPRINT system may provide durable relief. The platform has demonstrated its utility and cost effectiveness in similar chronic pain syndromes. A trial performed by Gilmore et al. examined the long-term effectiveness after a 30-day implantation period of the percutaneous SPRINT PNS System (SPR Therapeutics) targeting the medial branches of the dorsal rami for the treatment of facetogenic CLBP. This trial demonstrated durable long-term relief at 12-months post-explanation, with 50% of participants having a clinically significant reduction (≥ 50%) in pain intensity and in disability as measured by the ODI. Given the recent changes in access to SLBRFA, combined with promising results of temporary PNS in treating chronic pain syndromes, further investigation into the effectiveness of temporary PNS for PSIJC pain is warranted. Investigators aim to examine the effectiveness of temporary sacral lateral branch PNS with the SPRINT® system as a minimally invasive long-term solution for the treatment PSIJC pain. To do this, investigators initially propose performing a ten patient prospective case series to prove the viability of the application and examine its effectiveness.