There is a specific gesture patients make that tells me what I am dealing with before the examination starts. Asked where it hurts, they reach behind and press one thumb into a spot just below the belt line, off to one side. That spot is the sacroiliac joint, and pain there is one of the most commonly misattributed problems in musculoskeletal medicine.
What the SI Joint Actually Does
Your sacroiliac joints connect the sacrum — the triangular bone at the base of your spine — to the pelvis on each side. They are built for stability rather than motion, transferring load between your spine and your legs every time you take a step. They move only a few millimetres. But when that small motion is lost on one side, or when the joint becomes hypermobile, the result is pain that can be genuinely severe.
How to Tell SI Joint Pain From Other Low Back Pain
The pattern is fairly distinctive once you know it:
- Location: one-sided, below the belt line, often pinpointed with a single finger or thumb. Lumbar pain tends to be described with a whole hand across the low back.
- Referral: commonly into the buttock and back of the thigh, but usually stopping above the knee. Pain travelling past the knee into the calf or foot points more toward true sciatica.
- Aggravators: standing from a chair, rolling over in bed, climbing stairs, standing on one leg to put on trousers, sitting with the weight on one buttock.
- Relief: often eased by lying down or by shifting weight off the painful side.
Why It Gets Missed So Often
Two reasons. First, imaging is usually unremarkable — SI joint dysfunction is a mechanical problem, not a structural one, so an MRI of the lumbar spine comes back showing some unrelated disc bulge that then gets blamed. Second, if the assumption is that low back pain means lumbar spine, the examination never tests the SI joint properly.
The result is patients treated for months for a lumbar problem they do not have. It is a close cousin to the confusion between piriformis syndrome and sciatica — same region, different structure, different treatment.
Who Tends to Get It
- Pregnant and postpartum women. Relaxin loosens pelvic ligaments and the SI joints lose their stability. This is one of the most common sources of pregnancy-related low back pain.
- People with a leg length difference or altered gait. Asymmetric loading, thousands of steps a day. This is where gait analysis earns its keep.
- After a fall onto one buttock, or a misjudged step off a kerb.
- Runners and people who sit asymmetrically — wallet in one back pocket, legs always crossed the same way.
How It Is Diagnosed and Treated
Diagnosis is clinical, using a cluster of provocation tests rather than any single one. No individual test is reliable alone; agreement across several is what makes the diagnosis solid.
Treatment works when it addresses both parts of the problem. Specific adjustment restores the lost motion in the joint. But that correction will not hold if the muscles that stabilise the pelvis — glute medius in particular — are not doing their job, which is why soft tissue work and targeted stabilisation are part of the plan rather than an optional add-on. SI joint problems that are adjusted but never stabilised come straight back.
What You Can Do Now
Stop sitting on your wallet. Alternate the leg you cross. Avoid standing with all your weight parked on one hip. If you are postpartum, be cautious with wide-stance movements and single-leg loading until stability returns.
Get the Right Joint Examined
If your low back pain is one-sided, pinpointed low, and worse getting out of a chair, ask specifically whether your SI joints have been assessed. Contact Bromberg Chiropractic in Cambridge for an examination that tests the pelvis properly rather than assuming the lumbar spine is the culprit.
