If you’ve ever felt a sharp or deep ache right around that “dimple” at the top of your buttock, you’ve likely encountered the SI joint. The sacroiliac (SI) joint sits right where your spine meets your pelvis. It’s a powerhouse of a joint, responsible for transferring the weight of your upper body down to your legs.

When it gets grumpy, it can be incredibly stubborn. But there is a lot of misinformation out there about why it hurts—so let’s clear the air on what the science actually says.

It’s Probably Not “Out of Place”

There’s a common myth that SI joint pain happens because the joint has “slipped out” or is “misaligned.” However, the anatomy tells a different story.

I co-authored a study looking specifically at the deep structures of this joint. We found that as we age (particularly past 55), the joint surfaces actually develop ridges and the ligaments begin to harden (ossify).

The takeaway? Your SI joint is built for massive stability, not mobility. For most people, pain isn’t about a bone being out of place; it’s about the surrounding tissues becoming irritated or losing their “tolerance” for the loads you’re putting on them.

Identifying the Culprit

The tricky thing about the SI joint is that it’s a bit of a chameleon—it can easily be mistaken for a lower back issue or a hip problem. Usually, SI pain shows up as:

  • Pain strictly on one side of the tailbone or upper glute.
  • A “twinge” when rolling over in bed or getting out of the car.
  • Discomfort that flares up during long walks or when climbing stairs.

How We Solve It

We don’t just poke around to see if things “feel” straight. Because the joint is so stable, we can’t reliably feel it move with our hands. Instead, we use a “cluster” of provocation tests—specific movements designed to see if we can reproduce your familiar pain.

Once we confirm it’s the SI joint, the goal is to calm it down and then build it back up. Here’s how:

  • Smart Activity Modification: We don’t advocate for total bed rest (that usually makes things stiffer). Instead, we find ways to tweak your movement so you aren’t constantly “picking the scab” of the injury.
  • Building Tolerance: The “gold standard” for recovery is targeted exercise. We focus on strengthening the hips and trunk to support the pelvis, gradually teaching the joint to handle more weight and movement again.
  • Strategic Manual Therapy: Hands-on treatment can be a great “window of opportunity.” It helps desensitize the area and improve movement in the short term, making it much easier for you to get through your rehab exercises.

When Should You See Someone?

If you’ve been “waiting it out” for two or three weeks and the pain isn’t budging—or if it’s starting to dictate whether or not you can go for a walk or get a good night’s sleep—it’s time for an assessment.

At Body in Balance Physiotherapy, we’re not interested in quick fixes that don’t last. We’ll help you figure out exactly where the pain is coming from (Back? Hip? SI?) and give you a concrete roadmap to get back to moving confidently.

References

  • Rosatelli AL, Agur AM, Chhaya S. Anatomy of the Interosseous Region of the Sacroiliac Joint (2006).
  • Laslett M. Evidence-based diagnosis and treatment of the painful sacroiliac joint (2008).
  • Vleeming A, et al. European guidelines for the diagnosis and treatment of pelvic girdle pain (2008).