Introduction
The sacroiliac joint sits at the junction between the sacrum and the ilium, the large bones of the pelvis, and is one of the most controversial pain generators in musculoskeletal medicine. It is estimated to contribute to 15 to 30% of chronic lower back pain cases, yet it is frequently missed in imaging studies and diagnostic algorithms focused on the lumbar discs and facets. Understanding what the SIJ actually is, how it moves (very little), and why it becomes painful is the foundation for effective management. The good news is that most SIJ pain responds very well to a combination of manual therapy, targeted exercise, and load management.
Whether you are dealing with a recent flare-up or something that has nagged you for years, understanding why your body hurts is the most important first step. This guide draws on the latest pain science, physiotherapy research, and practical coaching wisdom meticulously validated and referenced to give you peace of mind.
Understanding the Anatomy
The sacroiliac joint is a large, C-shaped synovial joint between the auricular (ear-shaped) surfaces of the sacrum and the ilium. Despite its synovial character, it has very limited movement, approximately 2 to 4 degrees of rotation and 1 to 2 mm of translation. It is stabilised by the strongest ligaments in the body: the posterior sacroiliac, interosseous sacroiliac, sacrospinous, and sacrotuberous ligaments. The SIJ transfers load between the spine and the lower extremities and is subject to significant shear forces during single-leg activities. Pain is typically felt in the posterior pelvis, buttock, and sometimes the posterior thigh, rarely below the knee. The joint can become irritated by inflammation, ligament laxity (common in pregnancy), trauma, and cumulative shear loading.
Key structures involved: Gluteus maximus (primary SIJ stabiliser via sacrotuberous ligament), Biceps femoris (tension through sacrotuberous ligament), Piriformis, Thoracolumbar fascia (indirect SIJ stabiliser), Latissimus dorsi (force closure mechanism).
Why Does It Hurt? Root Causes
Modern pain science reminds us that pain is your nervous system's threat response, not simply a damage signal. That said, there are real, identifiable drivers.
1. Ligament Laxity in Pregnancy
Relaxin softens the SIJ ligaments, increasing joint mobility and vulnerability to shear stress. SIJ pain is the most common cause of pelvic girdle pain in pregnancy.
2. Cumulative Shear Loading
Activities involving repeated single-leg loading (running, walking uphill, step climbing) place shear forces on the SIJ. Without adequate muscular force closure (gluteal and hamstring strength), these forces can exceed ligamentous tolerance.
3. Inflammatory Arthritis
Sacroiliitis, inflammation of the SIJ, is an early feature of ankylosing spondylitis and other seronegative spondylarthropathies. This presentation has specific features (bilateral, morning stiffness > 1 hour, improves with exercise) and requires medical management.
4. Trauma
A fall directly onto the buttock or a motor vehicle accident involving lateral force on the pelvis can injure the SIJ ligaments and joint capsule.
How Massage Helps
Manual therapy to the sacroiliac region addresses the muscular overload that accompanies SIJ dysfunction, the gluteal muscles and piriformis are typically in protective spasm. Posterior pelvic massage, broad effleurage and petrissage of the gluteals, specific piriformis release, and thoracolumbar fascia techniques, reduces the guarding that maintains SIJ symptoms. SIJ manipulation or mobilisation (high-velocity thrust techniques) is performed by trained physiotherapists and chiropractors and has short-term evidence for SIJ pain reduction. Massage of the biceps femoris and sacrotuberous ligament region is a less commonly employed but valuable technique.
Beyond specific mechanical effects, massage floods the nervous system with safe, rich sensory input, downregulating the threat response and creating conditions in which healing becomes easier.
Stretches to Try
Consistency matters far more than intensity. Gentle, daily stretching with calm breathing reduces perceived tightness and signals safety to the nervous system.
FABER Position Stretch
Lie on your back. Cross one foot over the opposite knee. Gently allow the knee to fall outward. Hold 30 seconds. Benefit: Gently stresses the SIJ in the FABER (Flexion, Abduction, External Rotation) position, both a diagnostic test and a gentle mobilisation.
Posterior Pelvic Tilt and Knee-to-Chest
Lie on your back. Draw both knees to the chest. Gently rock side to side. Hold 30 to 60 seconds. Benefit: Gently mobilises the SIJ into nutation/counternutation, the limited movement available at the joint.
Hip Flexor Stretch (Reduce Anterior Shear)
Kneeling lunge with posterior pelvic tilt. Hold 45 seconds per side. Benefit: Reduces the anterior shear force on the SIJ driven by hip flexor tightness and anterior pelvic tilt.
Strengthening Exercises
Loading tissues progressively tells your nervous system they are capable and resilient.
Posterior Chain Strengthening. Glute Bridge
Supine, feet flat. Push through heels to lift hips. 3 sets of 15. Focus on posterior pelvic tilt at the top. Benefit: Strengthens the gluteus maximus via the sacrotuberous ligament, the primary muscular force closure mechanism for the SIJ.
Single-Leg Stance Strengthening
Stand on one leg for 30 seconds. Progress with eyes closed. Add resistance band around the opposite knee for contralateral hip activation. Benefit: Trains the muscular stabilisation of the SIJ in the single-leg positions where shear loading is greatest.
Bent-Knee Fall-Out (SIJ Stabilisation)
Lie on your back, knees bent together. Slowly lower one knee towards the floor, keeping the pelvis still. Return. 3 sets of 10 per side. Benefit: Trains the deep stabilisers to control rotational forces through the SIJ, a fundamental SIJ rehabilitation exercise.
Practical Self-Care
- A sacroiliac joint belt worn during aggravating activities provides external force closure and is evidence-supported for SIJ pain.
- Avoid asymmetric loading activities during acute phases, single-leg exercises, crossing legs, side-sleeping without a pillow between the knees.
- Sleep with a pillow between the knees in side-lying, reduces overnight adduction that stresses the SIJ.
- Postpartum SIJ pain: pelvic floor and gluteal rehabilitation is the priority, the ligaments return to pre-pregnancy stiffness within months.
- Inflammatory SIJ pain (ankylosing spondylitis spectrum): NSAIDs, exercise, and rheumatology management are required.
When to See a Professional
- Morning stiffness lasting more than 1 hour, bilateral buttock pain, and onset before age 40, ankylosing spondylitis screening.
- SIJ pain following significant trauma, imaging to rule out fracture.
- Neurological symptoms (leg weakness, foot drop), lumbar cause more likely.
- SIJ pain not responding to conservative treatment after 8 to 12 weeks, imaging and specialist assessment.
A qualified physiotherapist, sports therapist, or massage therapist can identify the specific drivers of your pain.
References and Further Reading
- Vleeming A et al. The sacroiliac joint. J Bodyw Mov Ther. 2012.
- Laslett M. Evidence-based diagnosis and treatment of the painful sacroiliac joint. J Man Manip Ther. 2008.
- Forst SL et al. The sacroiliac joint. Curr Sports Med Rep. 2006.
- Ingraham P. Sacroiliac joint pain. painscience.com.
- Mens JM et al. Reliability and validity of the active straight leg raise test. Spine. 2001.
Content is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before beginning any new exercise or treatment programme.