Understanding the SI Joint
An under-recognized cause of lower back pain
The sacroiliac joint sits in the pelvis, linking the iliac bones (pelvis) to the sacrum — the lowest part of the spine above the tailbone. It's an essential component for transferring energy between your legs and your torso, and like any other joint in the body, it can be injured or undergo degeneration.
When that happens, people typically feel pain in the buttock, and sometimes in the lower back, hips, and legs — especially while lifting, running, walking, or even lying on the involved side. Clinical publications cited by SI-BONE have identified the SI joint as a pain generator in 15–30% of patients with chronic lower back pain1–4 — and in up to 43% of patients with continued or new-onset low-back pain after a lumbar fusion.5
It's common for SI joint pain to feel like disc or lower back pain, or sometimes hip or groin pain. That's exactly why SI joint disorders should be considered in any lower back, hip, or pelvic pain workup — and why careful diagnosis comes before any talk of treatment.
Do these symptoms sound familiar?
SI joint problems can show up in more ways than "back pain." Common patterns include:
- Lower back pain
- Pain, numbness, tingling, or weakness in the leg
- Pelvis or buttock pain
- Hip or groin pain
- A feeling of leg instability — buckling or giving way
- Sleep disturbed by pain
- Trouble sitting for long periods, or sitting shifted to one side
- Pain going from sitting to standing
Having one or more of these symptoms doesn't confirm an SI joint problem — other conditions can cause the same picture, and can co-exist with it. An evaluation is the way to find out.
How We Get There
Diagnosis before treatment
Confirm the source
A focused exam plus a diagnostic injection helps confirm the SI joint is the pain generator.
Minimally invasive fusion
When appropriate, the joint is stabilized through a small, muscle-sparing approach.
Guided recovery
Physical therapy supports your return to daily activity.
Making the Diagnosis
How we confirm the SI joint is the problem
Because SI joint pain mimics so many other conditions, we don't guess — we test.
Focused physical exam
Specific exam maneuvers that stress the SI joint can help reveal it as the cause of your symptoms.
Imaging to rule out other sources
X-rays, CT, or MRI help exclude other common pain generators such as the lumbar spine or hip joint. Conditions like a disc problem can also co-exist with an SI joint disorder.
Diagnostic SI joint injection
The most relied-upon test. Local anesthetic is injected into the SI joint under image guidance. If your pain decreases by at least 50%, the SI joint is likely the source — or a major contributor. If it does not change, the SI joint is less likely the cause.
Treatment Options
Conservative care first — fusion when it's earned
Non-surgical care comes first
Once the SI joint is confirmed as the source, many patients respond well to physical therapy, oral medications, or injection therapy — and options like radiofrequency ablation may also play a role. We're honest about the trade-off: these treatments are often repeated, and the relief they provide is frequently temporary. Surgery is only considered when non-surgical options have been genuinely tried and haven't provided lasting relief.
SI joint fusion with the iFuse Implant System®
Our practice uses the iFuse Implant System from SI-BONE for minimally invasive SI joint fusion. The procedure stabilizes and fuses the joint using titanium screws placed across the sacroiliac joint — a minimally invasive SI joint fusion approach that has been clinically evaluated with more than 100 peer-reviewed publications per SI-BONE.
- Titanium screws placed across the SI joint
- Performed through a small incision of about one inch
- Takes about an hour
- Designed to stabilize and fuse the joint — to reduce pain and improve function
An honest word about risks. As with any surgical procedure, there are potential risks associated with the iFuse Implant System. It may not be appropriate for all patients, and not all patients benefit. We'll review the risks, benefits, and alternatives for your specific situation — SI-BONE also publishes risk information at si-bone.com/risks.
The iFuse Implant System® is intended for sacroiliac fusion for conditions including sacroiliac joint dysfunction that is a direct result of sacroiliac joint disruption and degenerative sacroiliitis, including conditions whose symptoms began during pregnancy or in the peripartum period and have persisted postpartum for more than 6 months. It is also intended for sacroiliac fusion to augment immobilization and stabilization of the SI joint in skeletally mature patients undergoing sacropelvic fixation as part of a lumbar or thoracolumbar fusion, or for acute, non-acute, and non-traumatic fractures involving the SI joint.
See It In Action
Watch: the iFuse procedure
A step-by-step animation of the minimally invasive SI joint fusion technique.
Video is an educational animation from the device manufacturer, not a promise of results. Whether SI fusion fits your situation is determined by careful evaluation and shared decision-making.
Research & Evidence
Grounded in careful patient selection
Diagnosis-driven
Evidence emphasizes confirming the SI joint as the pain source — typically with a diagnostic block — before considering fusion.
Minimally invasive
Modern SI fusion uses small, muscle-sparing techniques studied for SI-joint dysfunction in appropriately selected patients.
Part of a plan
Fusion is considered only after conservative care; it's one option within a broader treatment pathway.
Educational summaries simplified from the orthopedic literature; not a promise of results. Candidacy is individualized. Evidence supports minimally invasive SI-joint fusion in carefully selected patients whose pain is confirmed to originate from the SI joint (typically with a diagnostic block) after conservative care.
Evidence & Research
What the evidence says about SI joint pain & fusion
The sacroiliac joint is an under-recognized pain generator, and SI joint fusion has been studied more rigorously than many people realize. Here is a plain-language summary of clinical publications cited in SI-BONE patient literature — with the honest limits.
The SI joint is a significant, often-missed cause of low-back pain. Clinical publications have identified the SI joint as the pain generator in roughly 15–30% of patients with chronic lower back pain.1–4
After lumbar fusion, the SI joint deserves a closer look: it has been identified as a pain generator in up to 43% of patients with continued or new-onset low-back pain following a lumbar fusion.5
The iFuse Implant System is the SI joint fusion device with the most published clinical evaluation, including two randomized controlled trials in which treatment improved pain, patient function, and quality of life compared with non-surgical management in appropriately selected patients.6,7
Evidence supports fusion only after the diagnosis is confirmed — typically with a diagnostic SI joint injection producing at least 50% pain relief — and after conservative care has been tried without lasting benefit.6,7
Prevalence figures and trial results are from clinical publications cited in SI-BONE patient literature. As with any surgical procedure, there are potential risks with the iFuse Implant System; it may not be appropriate for all patients, and not all patients benefit (see si-bone.com/risks). Not everyone is a candidate, and individual results vary. This page is educational and is not a substitute for medical advice.
References
- Bernard TN, et al. Recognizing specific characteristics of nonspecific low back pain. Clin Orthop Relat Res. 1987;217:266–80.
- Schwarzer AC, et al. The Sacroiliac Joint in Chronic Low Back Pain. Spine. 1995;20:31–7.
- Maigne JY, et al. Results of Sacroiliac Joint Double Block and Value of Sacroiliac Pain Provocation Tests in 54 Patients with Low Back Pain. Spine. 1996;21:1889–92.
- Sembrano JN, et al. How Often is Low Back Pain Not Coming From The Back? Spine. 2009;34:E27–32.
- DePalma MJ, et al. Etiology of Chronic Low Back Pain Patients Having Undergone Lumbar Fusion. Pain Med. 2011;12:732–9.
- Polly DW, et al., and the INSITE Study Group. Two-Year Outcomes from a Randomized Controlled Trial of Minimally Invasive Sacroiliac Joint Fusion vs. Non-Surgical Management for Sacroiliac Joint Dysfunction. Int J Spine Surg. 2016;10:Article 28. View source ↗
- Dengler J, et al. Randomized Trial of Sacroiliac Joint Fusion vs. Conservative Management for Chronic Low Back Pain Attributed to the Sacroiliac Joint. J Bone Joint Surg Am. 2019;101(5):400–11. View source ↗
Explore Related Care
Explore related care
2-Minute Check
Am I a candidate for SI joint fusion?
Answer a few quick questions. This is educational and is not a diagnosis — only an evaluation can tell for sure.
Do you have low-back or buttock pain, often on one side?
Does it get worse with sitting, standing, or climbing stairs?
Have physical therapy and injections not given lasting relief?
You may be a strong candidate.
Your answers suggest SI joint fusion could be a good fit. The next step is a simple evaluation, where we'll confirm with an exam and imaging and review every option with you — surgical and non-surgical.
This tool is educational and not a diagnosis. Not everyone is a candidate; only a clinical evaluation can determine what's right for you.
You might be a candidate — let's talk.
Some of your answers point toward SI joint fusion, but the right path depends on the details. A short evaluation will give you a clear, honest answer and a plan.
This tool is educational and not a diagnosis. Not everyone is a candidate; only a clinical evaluation can determine what's right for you.
Let's take a closer look.
Your answers don't point clearly to SI joint fusion yet — but that doesn't mean we can't help. We'll evaluate what's going on and point you to the care that fits, often starting with non-surgical options.
This tool is educational and not a diagnosis. Not everyone is a candidate; only a clinical evaluation can determine what's right for you.
Answer all 3 questions to see your result.
Patient Reviews
What patients say
“I am so grateful and blessed to have come across Dr. Paul Morton. I am home recuperating and started walking on my first day after surgery. A great big shout-out to his staff and nurses. Mahalo nui loa.”
— Ann K.· Yelp review
“Dr. Morton and I have been through both a hip and now a total knee replacement. I am more than satisfied with both operations. I know at least another half dozen people who have had joint replacements, and we all agree — Dr. Morton is the one for us.”
— Verified patient· Google review
Review excerpts reflect individual patient experiences and may be lightly condensed. Results vary.
Questions, Answered
Frequently asked questions
How do you know my pain is from the SI joint?+
We combine a focused exam with a diagnostic injection. If numbing the joint relieves your pain, that helps confirm the SI joint as the source.
Is SI fusion major surgery?+
It's a minimally invasive, muscle-sparing procedure for appropriate patients. We'll explain exactly what to expect for your situation.
Do you try non-surgical care first?+
Yes. Fusion is considered only after physical therapy, activity changes, and injections have been tried and haven't lasted.
Is it covered by insurance?+
Coverage varies by plan and usually requires documentation of a confirmed diagnosis and failed conservative care. Our team helps with authorization.
How common is SI joint pain?+
More common than most people realize. Clinical publications cited by SI-BONE identify the SI joint as the pain generator in roughly 15–30% of patients with chronic lower back pain. Because it can feel like disc, hip, or groin pain, it is often overlooked.
I already had a lumbar fusion — could the SI joint be causing my pain?+
Possibly. In clinical publications cited by SI-BONE, the SI joint was identified as a pain generator in up to 43% of patients with continued or new-onset low-back pain after a lumbar fusion. If your back pain persisted or returned after spine surgery, the SI joint is worth evaluating.
What actually happens during the iFuse procedure?+
Titanium screws are placed across the sacroiliac joint through a small incision of about one inch, to stabilize and fuse the joint. The procedure takes about an hour. We will walk you through exactly what to expect for your situation.
What are the risks of SI joint fusion?+
As with any surgical procedure, there are potential risks with the iFuse Implant System, it may not be appropriate for all patients, and not all patients benefit. We review the risks, benefits, and alternatives with you before any decision. SI-BONE publishes risk information at si-bone.com/risks.
Low-back or buttock pain that won't quit?
Start with an evaluation — we'll pinpoint the source and review every option, surgical and non-surgical.