SI Joint Pain: Your Joint Isn't Slipping Out of Place

You can usually put one finger on it. It sits low and off to one side, right about where that little dimple is in your back, and it flares when you roll over in bed or push up a flight of stairs. Somewhere along the way, someone probably told you that your SI joint "goes out," and that you need it put back in. I want to offer you a different explanation, because the one you were given is doing you a disservice.

So can your SI joint really go out of place?

Not in the way the phrase suggests. Your sacroiliac joints are where the sacrum, the triangular bone at the base of your spine, meets the two halves of your pelvis. They are built for stability rather than motion, wrapped in some of the thickest ligaments in the body, and the movement available to them is measured in millimeters. A joint like that does not slip out and sit crooked until someone shoves it back.

What can happen is that the joint gets irritated and starts reporting pain, usually after a specific event: a fall, a car accident, a pregnancy, or months of repetitive one-sided loading [1]. That last one matters, because it means the pain often has less to do with the joint itself and more to do with how well the muscles around it are managing load. The clicks and pops you feel when you stretch are not the joint relocating. They are just a joint doing what joints do.

Why does it hurt right there, and sometimes down my leg?

Most people with SI joint pain point to a spot just below and inside the bony bump at the top of the pelvis, and that pointing test is one of the more useful things we have [1]. From there it tends to travel. Deep buttock pain is common, pain down the back of the thigh is common, and one review found eighteen different referral patterns, with about half of people feeling it in the posterior or lateral thigh and a smaller group feeling it below the knee or even into the foot [1].

That is exactly why this gets mislabeled as sciatica so often. The leg pain looks the same from the outside.

None of this is a substitute for an exam, but if your pain lives in the groin, the hip deserves a look, and I have written more about that in groin pain in women.

How common is this, really?

Common enough that it surprises people. Up to a quarter of low back pain appears to involve the SI joint [1], and one study that specifically screened the sacrum instead of only the lumbar spine found joint involvement in more than half of the low back pain cases it looked at [2]. The authors' explanation is the part I think about most: clinicians often do not screen outside the immediate area of the complaint, so a sacrum that is contributing to the problem never gets examined [2].

If your pain started during pregnancy or in the year after a baby, this joint deserves an even closer look. It is one of the first places the pelvis complains when tissue is more mobile and demands are higher.

Where the pelvic floor comes in

Here is the piece that usually gets skipped. Your pelvic floor is part of the muscular system that compresses the two halves of the pelvis toward each other, which is what gives the SI joints their working stability. In cadaver research that simulated pelvic floor tension, that tension increased stiffness of the sacroiliac joints by about 8.5% in female specimens and rotated the sacrum backward [4]. It is a small number on paper, and it tells you the pelvic floor is on the team.

The clinical picture is more striking. In a study of women who came to outpatient orthopedic clinics with lumbopelvic pain, 95.3% had some form of pelvic floor dysfunction, with 71% showing pelvic floor muscle tenderness and 66% showing weakness [3]. Nearly all of them. These were women who came in for their backs and hips, not for pelvic symptoms.

In my practice, when someone has had SI joint pain for months and has already done a round of glute strengthening without much to show for it, an internal assessment is often what finally explains the plateau. A tender, guarded pelvic floor on one side does not usually announce itself as pelvic pain. It shows up as a back that keeps giving out on the same side, and that is a very fixable problem once you know it is there.

How I actually check for it

Imaging is honestly not the deciding factor here. Scans do a good job of ruling out inflammatory disease and other structural problems, but they do not reliably confirm or exclude a painful SI joint on their own [1]. So the exam carries the weight.

I use a group of provocation tests that load the joint in different directions. When three or more out of six of them reproduce your familiar pain, the cluster identifies the SI joint with about 94% sensitivity and 78% specificity, and just as usefully, when none of them reproduce your pain, we can reasonably take the joint off the list [5]. That second half saves people a lot of time chasing the wrong structure.

From there I look at how you load: single-leg stance, step-up, the way your ribs and pelvis stack when you stand. And if the picture points that way, I will talk with you about an internal pelvic floor assessment. That is always your call, and we can learn a good deal from external work if you would rather start there.

What actually helps

• Progressive stabilization and motor control work. An exercise-oriented stabilization program is the recommended first line for this joint, ahead of injections and procedures [1]. It is less dramatic than an adjustment and it holds better.
• Retraining the pelvic floor as part of the system, not as an add-on. In a recent trial of women with postpartum pelvic girdle pain, adding functional training that targeted dynamic lumbopelvic control to routine pelvic floor physical therapy produced significantly better pain and disability outcomes than the routine therapy alone [6].
• Skip the reflexive kegels. If your pelvic floor is already guarded and tender, more squeezing tends to make the whole area angrier, and sorting out which direction you actually need is a real part of the work.
• Use a support belt as a bridge, not a plan. A belt can settle a painful flare and make walking tolerable while you rebuild capacity [1]. It is a tool with a job and an end date.
• Watch your one-sided habits. Standing with your weight parked on the same hip, carrying a toddler on the same side, sleeping with your top leg dropped forward. Small things, repeated a few thousand times, add up.
• Rebuild load gradually if you are postpartum. Returning to running or lifting on a plan rather than on a feeling protects this joint, and I have written about when it is reasonable to run again after a baby.

A few questions I get

Does SI joint pain need an injection to get better? Usually not as a first step. Conservative care with a stabilization and stretching program is the recommended starting point, and injections sit further down the list for people who do not respond [1].

Is it safe to exercise when it hurts? In most cases yes, with the right exercises. Pain in this joint is generally a load-management problem rather than a sign of damage, so the goal is finding the version of a movement you tolerate and building from there.

Does an SI belt help? It can. A pelvic support belt is a recognized part of conservative care [1], and it works best as short-term help while you build the strength that eventually does the same job.

Why do stairs and rolling over in bed set it off? Both put uneven load through one side of your pelvis. Single-leg positions and transitional movements are the classic provokers, which is also why they show up in the tests I use.

Could it be my tailbone instead? They sit close together and get confused often. If your pain is right at the very bottom, especially with sitting, tailbone pain is a more likely culprit, and if you are not sure where your pain is coming from at all, start with what's actually causing your pelvic pain.

You are not fragile, and it is not stuck

If you have been told your pelvis keeps going out, I hope this reframes it a little. Nothing is slipping around in there. Your pelvis is asking for better support from the muscles that surround it, and that is something we can genuinely change.

If your SI joint pain keeps circling back, let's take a proper look at it, pelvic floor included. You can reach Protea Physical Therapy at (909) 265-3584, and I see patients here in Anaheim Hills, serving Orange County.

References

1. Raj MA, Ampat G, Varacallo MA. Sacroiliac Joint Pain. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470299/
2. Wieczorek A, Campau E, Pionk E, Gabriel-Champine ME, Ríos-Bedoya CF. A Closer Look into the Association between the Sacroiliac Joint and Low Back Pain. Spartan Medical Research Journal. 2021;6(1):21971. https://pmc.ncbi.nlm.nih.gov/articles/PMC8043903/
3. Dufour S, Vandyken B, Forget MJ, Vandyken C. Association between lumbopelvic pain and pelvic floor dysfunction in women: a cross sectional study. Musculoskeletal Science and Practice. 2018;34:47-53. https://doi.org/10.1016/j.msksp.2017.12.001
4. Pool-Goudzwaard A, van Dijke GH, van Gurp M, Mulder P, Snijders C, Stoeckart R. Contribution of pelvic floor muscles to stiffness of the pelvic ring. Clinical Biomechanics. 2004;19(6):564-571. https://pubmed.ncbi.nlm.nih.gov/15234479/
5. Laslett M, Aprill CN, McDonald B, Young SB. Diagnosis of sacroiliac joint pain: validity of individual provocation tests and composites of tests. Manual Therapy. 2005;10(3):207-218. https://pubmed.ncbi.nlm.nih.gov/16038856/
6. Yang et al. Functional training versus conventional physiotherapy for postpartum pelvic girdle pain: a randomized controlled trial. Scientific Reports. 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC13066407/

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This article is for educational purposes and is not medical advice. Please consult a healthcare provider about your own symptoms.