Buttock Pain After Spine Surgery: Is the SI Joint Really to Blame?
A multicenter study of 346 patients finds that true sacroiliac joint pain following adult spinal deformity surgery is far rarer than screening questionnaires suggest — but the source of pain in a quarter of patients remains an open question.
OPENING SUMMARY
When patients report significant buttock or groin pain after adult spinal deformity surgery, the sacroiliac joint is a natural suspect — particularly when the fusion extends to the pelvis. But suspicion and confirmation are not the same thing. This study systematically screened patients for new-onset sacroiliac joint pain following pelvic fixation surgery, then followed up positive questionnaire responses with a structured clinical examination. What it found challenges a commonly held assumption: true, examination-confirmed sacroiliac joint pain was rare — occurring in just 1% of patients at both one and two years. At the same time, nearly one in four patients reported significant regional pain that didn't trace back to the SI joint, leaving an important clinical question unanswered.
STUDY SNAPSHOT
Study type – Multicenter study with prospective screening and clinical examination
Number of patients – 346
Mean age – 65 years
Female – 71%
Inclusion criteria – ASD surgery with pelvic fixation; no baseline SIJP; minimum 1-year follow-up
Screening method – Self-reported buttock/groin or PSIS pain score ≥4, followed by structured clinical examination (5 provocative maneuvers)
Follow up – 1 and 2 years postoperatively
Pelvic fixation types compared – Traditional iliac fixation (n=162) vs. S2-alar-iliac screws (n=184); 4-point fixation (n=85) vs. fewer than 4 points (n=261)
Published in – Journal of Neurosurgery: Spine
PMID – 41569924
DOI – 10.3171/2025.7.SPINE25454
WHY THIS MATTERS
Pelvic fixation — anchoring a spinal fusion into the ilium or sacrum — is a common and often necessary component of adult spinal deformity surgery. Because the sacroiliac joint sits in close anatomical proximity to the fixation hardware, postoperative buttock and groin pain is frequently attributed to SI joint involvement. In some cases, this leads to additional diagnostic workup, injections, or even further surgery.
But if the true rate of examination-confirmed SI joint pain is much lower than the rate of regional pain complaints, then a significant number of patients may be receiving workup — or treatment — for a diagnosis that isn't actually driving their symptoms. At the same time, if a quarter of patients are experiencing significant unexplained regional pain after surgery, that is a clinically important finding in its own right, regardless of whether the SI joint is involved.
This study is among the first to rigorously separate questionnaire-based screening from examination-confirmed diagnosis in this population — a distinction that turns out to matter enormously.
KEY FINDINGS
1. Confirmed SI joint pain was rare: 1% at both one and two years. Despite the anatomical proximity of pelvic fixation hardware to the sacroiliac joint, examination-confirmed new-onset SIJP occurred in only 3 of 346 patients at one year and 2 of 138 patients assessed at two years — a rate of approximately 1% at both timepoints. This held true across all fixation types and configurations examined.
2. Questionnaire screening vastly overstated the rate of SI joint involvement. At one year, 24% of patients screened positive for possible SIJP based on self-reported pain scores. At two years, 22% screened positive. But when those patients underwent a structured clinical examination — five provocative maneuvers specifically designed to implicate the SI joint — the vast majority did not have confirmed SIJP. The gap between questionnaire-positive and examination-positive patients was substantial at both timepoints.
3. Fixation type made no significant difference. Patients who received traditional iliac fixation and those who received S2-alar-iliac (S2AI) screws showed no statistically significant difference in confirmed SIJP rates at one or two years. Similarly, patients with four points of pelvic fixation versus fewer than four points showed no significant difference in SIJP incidence. The type and extent of pelvic fixation did not appear to drive SI joint complications in this cohort.
4. Iliac crest harvesting was not associated with SIJP. Of the 79 patients who underwent iliac crest bone graft harvesting — a procedure sometimes associated with donor site pain in the posterior pelvis — none developed confirmed SIJP at one or two years. This finding may help address a specific patient concern that arises when iliac crest harvesting is part of the surgical plan.
5. A significant proportion of patients have unexplained regional pain — and the source remains unclear. The study's authors explicitly flag the large discrepancy between questionnaire-positive screening rates (roughly 22–24%) and examination-confirmed SIJP (1%) as a finding that warrants further investigation. Nearly one in four patients is experiencing at least moderate buttock or groin pain after surgery that is not explained by SI joint pathology. Identifying the true source of that pain is identified as an important direction for future research.
PRACTICAL IMPLICATIONS
Accurate diagnosis should precede treatment decisions. The gap between self-reported regional pain and examination-confirmed SIJP reinforces the importance of structured clinical examination — not questionnaire screening alone — before attributing postoperative pain to the sacroiliac joint. Patients and clinicians alike may benefit from a more deliberate diagnostic pathway before pursuing SI joint-specific interventions.
Pelvic fixation hardware choice and configuration appear safe from an SI joint perspective. Neither the type of fixation (iliac vs. S2AI) nor the number of fixation points was associated with increased SI joint pain in this cohort. Surgeons can consider these hardware decisions on the basis of biomechanical and patient-specific factors without additional concern about differential SI joint complication risk.
The unexplained pain signal deserves clinical attention. The fact that roughly one in four patients reports significant regional pain without a confirmed SI joint source is not a reassuring finding to simply set aside — it is an important unresolved question. Until the source of that pain is better understood, patients experiencing this symptom after ASD surgery deserve thorough evaluation rather than a default assumption about its origin.
CONCLUSION
This study offers meaningful reassurance on one front and an important challenge on another. The reassurance: pelvic fixation in adult spinal deformity surgery carries a very low risk of causing true, examination-confirmed sacroiliac joint pain — regardless of fixation type or extent. The challenge: a substantial proportion of patients experience significant unexplained regional pain after surgery, and the field does not yet have a clear answer for what is driving it. Both findings have direct implications for how surgeons counsel patients before surgery, evaluate symptoms after surgery, and prioritize future research questions.
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