The difference in our clinic is that we assess the SIJ not as an isolated joint, but as the mechanical crossroads of the entire lumbopelvic-hip complex — and we treat it accordingly.
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What Is Sacroiliac Joint Syndrome?
The sacroiliac joint (SIJ) is the articulation between the sacrum — the triangular bone at the base of the spine — and the ilium, the large wing-shaped bone of the pelvis. There are two SIJs, one on each side, and they form the posterior boundary of the pelvic ring.
Despite being among the largest joints in the body, the SIJ has a remarkably small range of motion — typically just 2–4 degrees of rotation and 1–2 mm of translation — and its primary role is not movement, but load transfer.
The SIJ transfers load between the spine and the lower limbs in every upright activity — standing, walking, running, climbing stairs. It does this through a combination of bony form closure (the irregular, interlocking joint surfaces that resist shear) and force closure (the compressive force generated by the muscles and ligaments surrounding the joint, including the thoracolumbar fascia and its associated myofascial slings).
SIJ syndrome describes a clinical state in which the SIJ is a primary or contributing source of pain and dysfunction. This can arise from:
- Excessive mobility (instability) — common in pregnancy and hypermobile individuals
- Reduced mobility (fixation) — common after trauma, degenerative change, or following prolonged asymmetrical loading
- Altered force closure mechanisms — where the surrounding fascial and muscular system is no longer adequately stabilising the joint
Key Facts
| Location of pain | Posterior pelvic pain typically within 3 cm of the PSIS; may refer into the buttock, groin, posterior thigh and occasionally below the knee |
| Prevalence | Estimated 15–30% of chronic low back pain cases have SIJ involvement as a primary source (Sembrano & Polly, 2009) |
| Aggravating activities | Climbing stairs, rolling over in bed, rising from sitting, prolonged standing on one leg, asymmetrical loading (e.g. carrying a bag on one side) |
| Easing factors | Lying symmetrically, gentle walking, temporary relief with a sacroiliac belt in unstable presentations |
| Common misdiagnosis | L4/5 or L5/S1 disc pathology, lumbar facet syndrome, piriformis syndrome, greater trochanteric pain |
Who Typically Experiences SIJ Syndrome?
SIJ syndrome does not discriminate — but in practice, several distinct populations present with it more commonly than others:
Pregnant and Post-Partum Women
Pregnancy is the most common predisposing factor for SIJ instability. Relaxin — a hormone produced from the first trimester — increases ligamentous laxity throughout the body, including at the SIJ and pubic symphysis. Combined with the progressive anterior weight shift of a growing uterus and the biomechanical changes of an altered gait, the SIJ is placed under sustained and asymmetric stress.
In our clinical experience, post-partum SIJ dysfunction frequently persists well beyond the cessation of relaxin production, because the force closure mechanisms — particularly gluteal and deep abdominal function — have been significantly inhibited during pregnancy and have not been systematically restored.
Runners and Endurance Athletes
The SIJ is loaded asymmetrically during every stride of running — the stance-side SIJ experiences compressive and shear forces while the swing-side rotates forward. In athletes with adequate force closure, this is managed effortlessly. In those with inhibited gluteal function, reduced thoracolumbar fascial stiffness, or a history of hamstring or groin injury (which can alter the function of the posterior oblique and deep longitudinal slings), the SIJ is repeatedly stressed beyond the capacity of its passive stabilisers.
Insidious, progressive posterior pelvic pain in a runner — particularly if it is worse at the end of a run than the beginning — should always raise suspicion of SIJ involvement.
Desk Workers with Sustained Asymmetrical Sitting
Prolonged sitting in a habitually rotated or side-loaded position — common in office workers who reach repeatedly to one side, or who habitually cross one leg over the other — creates asymmetric loading of the SIJ. Over time, this can produce a relative positional asymmetry at the joint, with one ilium gradually rotating anteriorly relative to the other. The thoracolumbar fascia adapts to this asymmetric position, fascial densification occurs along one posterior oblique sling more than the other, and a chronic low-grade SIJ irritation develops that the patient typically describes as 'my back is out' — without being able to say exactly where.
Post-Surgical and Post-Trauma
Following lumbar spinal fusion surgery — particularly at L4/5 or L5/S1 — the SIJ is at significantly elevated risk of developing symptomatic dysfunction. This is a well-documented phenomenon in the spinal surgery literature: when a lumbar motion segment is fused, the adjacent SIJ assumes a greater share of the movement and load that was previously distributed across the spinal segment. The result is an accelerated mechanical stress on the SIJ that frequently produces pain within 2–5 years of surgery.
Similarly, falls onto the buttocks, motor vehicle accidents, and direct pelvic trauma can acutely disrupt SIJ mechanics and create both ligamentous and fascial sequelae that persist if not addressed.
Hypermobile Individuals (including Pilates and Yoga Practitioners)
Individuals with generalised joint hypermobility — whether constitutional or acquired through years of flexibility training — often present with SIJ instability as a primary complaint. The passive stabilisers of the SIJ (the interosseous, posterior and sacrotuberous ligaments) are under chronic low-level stress in hypermobile individuals, and the active stabilisers (gluteal complex, deep abdominals, TLF) are frequently not adequately developed to compensate.
This population often has significant pain with high-range movements — deep hip flexion, single leg loading, or the transition from floor to standing — and requires a markedly different management approach from the hypomobile or post-traumatic SIJ.
The Fascial Lens: Why We See SIJ Syndrome Differently
The SIJ is a joint held together almost entirely by soft tissue — the ligaments, muscles and fascia surrounding it provide the compressive force that keeps the joint surfaces congruent under load. This is why a joint-focused treatment approach to SIJ syndrome, without addressing the force closure mechanism, may not fully resolve the underlying problem — it is the equivalent of fixing a gate hinge while leaving the posts loose in the ground.
At the centre of the force closure story is the thoracolumbar fascia — specifically, the way it transmits tension from the posterior oblique sling and deep longitudinal sling across the posterior pelvis to compress and stabilise the SIJ.
Force Closure and the Posterior Oblique Sling
Vleeming et al.'s foundational work on the self-bracing mechanism of the SIJ demonstrated elegantly that when the gluteus maximus on one side co-contracts with the contralateral latissimus dorsi — connected via the posterior layer of the thoracolumbar fascia — the resulting diagonal tension across the posterior pelvis creates a compressive force on the SIJ that significantly increases joint stiffness and load tolerance.
This is the posterior oblique sling in action, and it is the primary active stabiliser of the SIJ during gait and single-leg loading tasks.
When this sling is dysfunctional — whether because of a weak or inhibited gluteus maximus, a restricted or poorly-gliding TLF, or reduced latissimus dorsi activity — the SIJ loses a significant proportion of its force closure. The passive ligamentous structures must compensate, are progressively loaded beyond their optimal range, and the nociceptors within the posterior SIJ ligaments and joint capsule begin to signal.
→ See our article: Understanding the Posterior Oblique Sling
The Deep Longitudinal Sling and Sacrotuberous Ligament Tension
The deep longitudinal sling — connecting the erector spinae via the TLF to the sacrotuberous ligament, biceps femoris and peroneal chain — also plays a critical role in SIJ stability. The sacrotuberous ligament is one of the primary passive restraints against sacral nutation (forward rotation of the sacral base), and the deep longitudinal sling applies tensile load to this ligament during gait, helping to stiffen the posterior pelvic ring and transfer load efficiently between the spine and lower limb.
When the deep longitudinal sling is restricted — as commonly occurs with chronic hamstring tightness, restricted ankle dorsiflexion, or thoracolumbar fascial densification — the sacrotuberous ligament is not adequately tensioned during gait, and the SIJ is relatively under-supported during the load-transfer phase of the stride.
This is a particularly important pattern in runners with recurrent SIJ pain: addressing hamstring and TLF mobility in the context of the deep longitudinal sling is an approach that may support more sustained improvement than mobility work alone.
→ See our article: Understanding the Deep Longitudinal Sling
The Anterior Oblique Sling and Pelvic Asymmetry
The anterior oblique sling — the internal oblique on one side working with the contralateral external oblique and adductors — coordinates rotational forces across the pelvis during all crossing-midline and rotational activities.
In the context of the SIJ, the anterior oblique sling matters because imbalance within it — one side hypertonic relative to the other — is one of the primary drivers of pelvic asymmetry and relative ilial rotation. A right-sided anterior oblique sling that is chronically shortened will tend to rotate the right ilium anteriorly relative to the left, creating an asymmetric positional stress at the right SIJ.
This is a pattern we commonly identify through palpation and movement assessment, and it responds well to a combination of fascial work at the lateral raphe and anterior abdominal wall, combined with sling-loading rehabilitation.
→ See our article: Understanding the Anterior Oblique Sling
The Thoracolumbar Fascia, Lateral Raphe and SIJ
As we discussed in our lumbar facet syndrome page, the lateral raphe — the dense fascial thickening at the lateral border of the TLF where the posterior and middle layers converge — is a critical tensional node for force distribution across the posterior trunk and pelvis.
In the context of the SIJ, densification at the lateral raphe (particularly at the L5-S1 level and gluteal aponeurosis attachment) directly reduces the capacity of the posterior oblique sling to generate appropriate compressive force across the SIJ. A restricted lateral raphe is not just a source of local pain — it is a mechanical bottleneck that limits the function of every sling that passes through it.
→ See also: Lumbar Facet Syndrome — The Lateral Raphe Explained
The Fascial Picture — SIJ Syndrome
The SIJ is not stabilised by the joint itself — it is stabilised by the tensional network around it. The posterior oblique sling, the deep longitudinal sling, the sacrotuberous ligament complex, and the thoracolumbar fascia all contribute to force closure. When any of these are restricted, inhibited or asymmetrically loaded, the SIJ cannot adequately distribute force — and it tells you about it.
Our assessment systematically identifies which part of the force closure system has failed, and our treatment targets that system — not just the joint.
What the Research Says
Prevalence and Diagnosis
Sembrano and Polly (2009) conducted a systematic review of SIJ pain prevalence in low back pain populations, concluding that the SIJ is a primary pain generator in approximately 15–30% of cases — a figure consistent across multiple diagnostic injection studies.
The diagnostic challenge is significant: the SIJ shares referral patterns with L4/5 and L5/S1 disc pathology and lumbar facet syndrome, and no single clinical test has sufficient sensitivity and specificity to confirm the diagnosis in isolation. A cluster of provocation tests — including the FABER, FADIR, posterior pelvic pain provocation (P4), and distraction tests — improves diagnostic accuracy substantially when interpreted alongside the clinical history and movement findings.
Force Closure and the TLF
Vleeming et al. (1995, 1996) contributed the foundational biomechanical studies demonstrating the role of the posterior oblique sling in SIJ force closure. Their cadaveric studies showed that simulated contraction of the gluteus maximus combined with contralateral latissimus dorsi produced a measurable increase in SIJ compression and stiffness — a finding with significant clinical implications for how we rehabilitate SIJ instability.
Subsequent in-vivo studies using electromyography have confirmed that this diagonal co-activation pattern is indeed present during normal gait and is reduced in patients with posterior pelvic pain.
The Sacrotuberous Ligament and Deep Longitudinal Sling
Vleeming et al. (1989) demonstrated that the sacrotuberous ligament is directly loaded by tension applied to the biceps femoris — confirming the anatomical basis of the deep longitudinal sling's contribution to SIJ stability. Posterior thigh tightness and restricted hamstring extensibility are therefore not merely a feature of lumbar disc problems — they directly reduce the tensile pre-load on the sacrotuberous ligament and reduce passive SIJ stability.
This is why hamstring management is an important component of SIJ rehabilitation that is often not adequately addressed in conventional protocols.
Post-Partum SIJ Dysfunction
Wu et al. (2004) published a systematic review of pelvic girdle pain in pregnancy and the post-partum period, establishing that posterior pelvic pain with an SIJ component affects approximately 20% of pregnant women and persists beyond delivery in a significant subset. The review highlighted the importance of active stabilisation strategies — specifically targeting gluteal and deep abdominal function — in the management of this population, as passive approaches (belts, rest, medication) did not produce lasting improvement in function or pain.
Fascial Densification and Manual Therapy
Stecco et al. (2011, 2013) demonstrated histologically that fascial densification — an alteration in the viscosity of the hyaluronan-rich loose connective tissue that allows fascial layers to glide — is a reversible process that responds to sustained manual pressure applied at specific thicknesses and durations.
This provides a mechanistic basis for the application of Fascial Manipulation by Stecco in SIJ syndrome: the technique is directed at specific anatomical locations — centres of coordination within the TLF and lateral raphe — where densification may be disrupting the force closure mechanism, with the aim of restoring fascial gliding to support sling function.
Our Approach to SIJ Syndrome
Because SIJ syndrome can arise from instability, hypomobility, or impaired force closure — and frequently from a combination of all three — our assessment must first determine which of these mechanisms is dominant before we can select an appropriate treatment strategy.
Assessment
- SIJ provocation testing — a cluster of validated orthopaedic tests to confirm SIJ involvement and differentiate from lumbar and hip sources
- Form closure assessment — palpation of the SIJ and posterior pelvic ligaments to assess joint position and passive stability
- Force closure assessment — evaluation of gluteal function, deep abdominal activation, TLF stiffness generation, and sling loading capacity through specific movement tasks
- Fascial palpation — systematic assessment of the TLF, lateral raphe, gluteal aponeurosis, sacrotuberous ligament region and anterior abdominal wall using Stecco FM palpation protocols
- Gait and movement analysis — observing how load is transferred through the lumbopelvic region during walking, single-leg standing, and functional tasks
- Lower limb assessment — hip mobility, hamstring extensibility, and ankle dorsiflexion as contributors to deep longitudinal sling function
Treatment
- Fascial Manipulation by Stecco (FM) — targeted manual therapy at identified centres of coordination within the TLF, lateral raphe, gluteal fascia and anterior abdominal wall to restore fascial gliding and improve sling force transmission. In unstable presentations, FM is sequenced carefully to avoid overstimulating an already sensitised joint.
- Joint mobilisation or manipulation — for hypomobile presentations, gentle specific mobilisation of the SIJ to restore normal articular motion; for unstable presentations, high-velocity techniques are avoided
- Graduated force closure rehabilitation — progressive loading of the posterior oblique sling (gluteus maximus, latissimus dorsi via TLF), deep longitudinal sling (posterior chain and hamstring complex), and deep abdominal system. Sequencing is critical: form must be established before load is added.
- Pelvic symmetry re-education — identifying and correcting habitual asymmetric loading patterns in sitting, standing and movement
- Pregnancy and post-partum specific protocols — where appropriate, management is tailored to the specific biomechanical and hormonal context of the perinatal period
AHPRA Note
The above describes our general clinical approach. Individual presentations vary, and the specific assessment and management of your condition will be determined in consultation with your practitioner at your first visit. Nothing on this page constitutes clinical advice for your specific situation.
Self-Help Starting Point — What You Can Do Right Now
The following strategies are commonly recommended as a starting point for people with SIJ-related posterior pelvic pain. They are not a substitute for assessment but they represent meaningful, evidence-informed first steps.
1. Load Symmetrically — Reduce Asymmetric Stress on the Joint
The single most impactful lifestyle change for most SIJ sufferers is to become aware of habitual asymmetric loading. Avoid habitually crossing the same leg, carrying weight on one shoulder, or sitting rotated to one side. When standing for long periods, use a small footstool to alternate which foot bears more weight.
These seem like minor adjustments, but for a joint that moves only a few degrees, a small postural change repeated thousands of times per day has a profound cumulative effect.
2. Activate the Posterior Oblique Sling — Side-Lying Clam and Single-Leg Bridge
The side-lying clam — lying on your side with hips and knees bent, rotating the top knee upward while keeping the pelvis still — is a low-load starting point for gluteus medius activation. Progress from this to the single-leg glute bridge, which begins to load the posterior oblique sling through the glute-to-contralateral-TLF diagonal.
The key coaching cue for the bridge is to feel the working glute fully contract before the spine extends — this ensures the gluteal muscle is the prime mover, not the lumbar extensors. Perform slowly, 3 sets of 8 per side.
3. Protect the Joint During High-Risk Activities
Until force closure is restored, certain activities are particularly provocative for an unstable or irritated SIJ:
- Rolling over in bed — log-roll by moving the shoulders and hips together
- Rising from sitting — squeeze the glutes before you stand
- Carrying loads asymmetrically — prefer a backpack to a handbag during flare-ups
A simple sacroiliac belt, worn during high-demand activities, can temporarily improve force closure and allow you to remain active while rehabilitation progresses — but it is a support tool, not a long-term solution.
Want to know where to start?
Download our free 2-week SIJ & Pelvic Girdle Intro Rehab Program — a practitioner-designed starting point we commonly recommend in the early stages of managing SIJ syndrome. You will receive a PDF with graded exercises, load guidance and progressions, along with clear instructions on when to seek further assessment.
Enter your email below to receive it instantly.
Ready to Take the Next Step?
If the above resonates with your experience — particularly if you have been told you have a 'disc problem' or 'arthritis' but the diagnosis has never quite fitted — we would love to help you get a clearer picture.
SIJ syndrome is frequently under-diagnosed and under-treated. A thorough assessment is the starting point.
Ready to get on top of this?
📞 Call Now — speak with our team
🗓 Book Online — available 24/7
📄 Free 2-Week Rehab Program — request your copy
Our clinic is based in Melbourne, Victoria. Telehealth assessments are available for patients unable to attend in person.
References
- Sembrano JN & Polly DW (2009). How often is low back pain not coming from the back? Spine, 34(1), E27-32.
- Vleeming A et al. (1995). The posterior layer of the thoracolumbar fascia. Its function in load transfer from spine to legs. Spine, 20(7), 753-758.
- Vleeming A et al. (1996). The role of the sacroiliac joints in coupling between spine, pelvis, legs and arms. Movement, Stability and Low Back Pain. Churchill Livingstone.
- Vleeming A et al. (1989). Relation between form and function in the sacroiliac joint. Spine, 14(2), 163-167.
- Wu WH et al. (2004). Pregnancy-related pelvic girdle pain (PPP). European Spine Journal, 13(7), 575-589.
- Stecco A et al. (2013). Fascial components of the myofascial pain syndrome. Current Pain and Headache Reports, 17(8), 352.