MIS Fusion of the SI Joint: Does Prior Lumbar Spinal Fusion Affect Patient Outcomes?

BACKGROUND Sacroiliac (SI) joint pain is a challenging condition to manage as it can mimic discogenic or radicular low back pain, and present as low back, hip, groin and/or buttock pain. Patients may present with a combination of lumbar spine and SI joint symptoms, further complicating the diagnosis and treatment algorithm [1-3]. SI joint pain after lumbar spinal fusion has been reported in the literature. Both clinical and biomechanical studies show the SI joint to be susceptible to increased motion and stress at the articular surface with up to 40-75% of patients developing significant SI joint degeneration after 5 years. In a recent case series study of 50 patients who underwent minimally invasive SI joint arthrodesis, 50% had undergone previous lumbar spinal fusion and 18% had symptomatic lumbar spine pathology treated conservatively [4]. The purpose of this study is to determine if history of previous lumbar fusion or lumbar pathology affects patient outcomes after MIS SI joint fusion surgery. METHODS We report on 40 patients with 24 month follow up treated with MIS SI joint fusion using a series of triangular porous plasma coated titanium implants (iFuse, SI-Bone, Inc. San Jose, CA). Outcomes using a numerical rating scale (NRS) for pain were obtained at 3-, 6-, 12- and 24 month follow up intervals. Additionally, patient satisfaction was collected at the latest follow up interval. Patients were separated into 3 cohorts: 1) underwent prior lumbar spine fusion (PF), 2) no history of previous lumbar spine fusion (NF), 3) no history of previous lumbar spine fusion with symptomatic lumbar spine pathology treated conservatively (LP). A repeated measures analysis of variance (rANOVA) was used to determine if the change in NRS pain scores differed across timepoints and subgroups. A decrease in NRS by 2 points was deemed clinically significant [5]. RESULTS Mean age was 54 (±13) years and varied slightly but not statistically between groups. All subgroups experienced a clinically and statistically significant reduction in pain at all time points (mean change >2 points, p<0.001). There was a statistically significant effect of cohort (p=0.045), with the NF cohort (no prior lumbar spinal fusion) having a somewhat greater decrease in pain (by approximately 1 point) compared to the other 2 groups (PF and LP).Patient reported satisfaction by cohort was: 89% (NF), 92% (PF) and 63% (LP).Overall satisfaction rate was 87%. DISCUSSION AND CONCLUSION Patients with SI joint pain, regardless of prior lumbar spine fusion history, show significant improvement in pain after minimally invasive SI joint fusion. The presence of symptomatic lumbar spine pathology potentially confounds the treatment affect, as patients may not be able to discriminate between symptoms arising from the SI joint and the lumbar spine. These patients expressed a lower satisfaction with surgery. Patients without other confounding lumbar spine pathology and who have not undergone previous spine surgery tend to be younger and experience a greater reduction in pain.