Movement Notes — Pilates on George — by Olya Kudryavtseva
QUICK ANSWER (TL;DR)
The sacroiliac joint moves only 1–4 mm and about 2 degrees in healthy adults – it’s built for stability, not mobility. The popular notion that the SI joint goes “out of place” isn’t supported by biomechanical research. SI pain is real, but it’s typically a force closure problem (muscular coordination), not a structural misalignment. Glute strength and pelvic floor coordination form the foundation of effective rehab.
Few topics generate more confusion in our field than the sacroiliac joint.
Clients arrive convinced theirs is “out”, “unstable”, “twisted”, or “locked”. Practitioners speak with confidence about putting it “back into place”. Whole certifications exist around correcting things that, based on the biomechanical evidence, don’t really happen the way we say they do.
Time for a more accurate model.
What Is the Sacroiliac Joint?
The sacroiliac joint (SIJ) connects the sacrum (the triangular bone at the base of the spine) to the ilium (the large pelvic bone) on each side. It’s a synovial joint anteriorly and a syndesmosis (a fibrous joint with strong ligaments) posteriorly.
It’s surrounded by some of the strongest ligaments in the body: the interosseous, dorsal sacroiliac, and sacrotuberous ligaments. The SI joint is built to transmit massive load between the spine and the lower limbs without giving way.
Can the SI Joint Go Out of Place?
Not really, in the way it’s commonly described. The most-cited biomechanical work on SIJ motion (Sturesson et al., Vleeming and colleagues) consistently shows minimal physiological range:
• Roughly 1–4 mm of translation
• Around 2 degrees of rotation
That motion decreases with age and is even smaller in men than women. The takeaway: the SIJ is built for stability, not mobility. The idea that it routinely shifts “out of place” and needs to be put back in is not supported by data.
Studies on SIJ palpation also show poor reliability. Practitioners can’t reliably agree on “position” of the SIJ, which makes “my SI is out” a hard claim to sustain.
Form Closure and Force Closure: The Useful Framework
Vleeming’s model of pelvic stability is one of the most useful frameworks we have:
Form closure – the passive stability that comes from joint shape, ligament tension, and articular surfaces. The SIJ has good form closure due to its ridged surfaces and dense ligaments.
Force closure – the active stability provided by muscles compressing the joint surfaces. The posterior oblique sling (latissimus dorsi crossing to opposite gluteus maximus via thoracolumbar fascia) and anterior oblique sling (external oblique to opposite adductor) are the main contributors.
Most SIJ-related pain isn’t a structural issue. It’s a force closure inefficiency – the muscular system isn’t compressing the joint adequately during load transfer.
Is SI Joint Pain Real?
Yes, very. Schwarzer et al. (1995) and Laslett (2008) demonstrated this with diagnostic injections. SIJ-mediated pain is estimated to account for 10–25% of chronic low back pain.
But “SIJ pain” doesn’t equal “SIJ instability” or “SIJ dysfunction.” It means the joint is the pain generator. Those are different things, and conflating them leads to the wrong intervention.
What Exercises Help SI Joint Pain?
Effective SIJ rehab focuses on building the muscular slings that compress the joint:
• Force closure work: bridging with band, contralateral arm-leg lifts, woodchop patterns, single-leg work that demands trunk control
• Glute max strength: the single biggest contributor to posterior force closure. Real glute work, not just clamshells, but loaded extension and bridging
• Pelvic floor coordination: the deep system contributes to pelvic compression. Breath integration, not gripping
• Reframing the language: if you believe your pelvis is fragile and out of alignment, that belief affects pain
Frequently Asked Questions
Can the SI joint really get stuck or locked?
The SI joint can be a source of pain, and movement around it can feel restricted or stiff. But the popular concept of it being “locked” or “out of place” in the way a finger joint dislocates isn’t supported by biomechanical evidence. The joint normally moves only millimetres.
What does SI joint pain feel like?
Typically a unilateral pain just below the lower back, around the dimple of the buttock, sometimes radiating into the groin or back of the thigh. It’s often aggravated by transitional movements (sit-to-stand, rolling in bed) and asymmetric loading (single-leg standing, stairs).
Are SI joint adjustments effective?
Adjustments may provide short-term relief through neuromuscular effects, but research doesn’t support the idea that they’re “realigning” the joint. Long-term resolution typically comes from strengthening the surrounding muscular system to provide better force closure.
Is Pilates good for SI joint pain?
Pilates is particularly well-suited because it builds the glute, deep abdominal, and pelvic floor coordination that creates force closure around the SI joint. Our Sydney CBD studio works with many clients managing SI joint pain through targeted strengthening.
Can pregnancy cause SI joint pain?
Yes, relaxin and other hormonal changes during pregnancy increase ligament laxity, which can reduce form closure at the SI joint. The body increases reliance on force closure, which is why pelvic girdle pain is common in pregnancy and why glute/core work helps.
The Bottom Line
Clients don’t need their SI joint adjusted, twisted, popped, or put back. They need force closure. They need glutes that fire when asked. They need a brain that trusts the joint to handle load.
That’s the work. And it looks a lot like Pilates.
References