Most people who walk up to me after a callanetics class with their hand pressed to one side of their lower back assume they have sciatica. They've Googled their symptoms. The pain runs from somewhere near their hip into their buttock, sometimes down the back of the leg, and "sciatica" is the word everyone knows.
About half of them don't have sciatica at all. They have SI joint dysfunction. And the distinction matters more than you'd think, because the things that calm an irritated SI joint are not the same things that ease a compressed sciatic nerve. Some movements that help one will actually flare up the other.
So let's sort this out properly.
What's actually going on in each case
Sciatica
Sciatica is not really a diagnosis. It's a description of symptoms caused by something pressing on or irritating the sciatic nerve — the thick nerve that runs from your lower spine, through your buttock, down the back of your thigh, behind the knee, and into your foot.
The "something" is usually one of three things:
- A bulging or herniated disc in the lumbar spine (most common)
- A narrowing of the spinal canal (stenosis), more common as we age
- A tight piriformis muscle squeezing the nerve as it passes through the buttock (piriformis syndrome)
The pain has a very specific signature: it radiates. It travels along the path of the nerve. People describe it as electric, shooting, burning. It often goes past the knee. There's frequently numbness, tingling, or weakness somewhere along the leg or foot.
SI joint dysfunction
The sacroiliac joint is the meeting point between your sacrum (the wedge-shaped bone at the base of your spine) and your ilium (the big flat bone of your pelvis). You have two of them, one on each side. They're held together by some of the strongest ligaments in the body, and they barely move — but when they get irritated, inflamed, or move slightly out of their normal pattern, the pain is very real and very localized.
SI joint pain typically sits right at one of those dimples in your lower back, just below the belt line and off to one side. It can refer down into the buttock and sometimes the back of the thigh, but it almost never goes past the knee. It's usually one-sided. And it has very specific aggravators: standing on one leg, getting in and out of a car, rolling over in bed, climbing stairs.
This is the joint that gets unhappy during pregnancy when the relaxin hormone loosens everything up. It's the joint that flares after a fall onto the buttock, after lifting awkwardly, or after long stretches of asymmetric loading — drivers, people who cross one leg over the other for hours, runners with a leg-length difference.
The quick differential — questions I ask
When someone describes their pain to me, here's what I'm actually listening for.
Where exactly is the pain?
If you can put one finger on a spot just to the side of the base of your spine, right where that little dimple is, and say "here" — that's an SI joint pattern. If you wave your hand in a long line from your lower back, across the buttock, down the back of the thigh, past the knee — that's a sciatica pattern.
Does it go past the knee?
This is the single most useful question. True sciatica very often radiates past the knee, sometimes all the way to the foot. SI joint pain rarely does. If you have shooting pain into your calf or numbness in your foot, the nerve is involved.
Is there numbness, tingling, or weakness?
Nerves give nerve symptoms — pins and needles, a patch of skin that feels different, a foot that catches when you walk, weakness pushing off the toes. SI joint pain is mechanical and dull or sharp, but it doesn't usually come with neurological symptoms.
What makes it worse?
Sciatica from a disc tends to flare with sitting, with bending forward, with sneezing or coughing (anything that increases pressure in the disc). It often eases when you lie down.
SI joint pain flares with single-leg loading — standing on one leg to put on trousers, stepping up a curb, rolling over in bed at night. It often hurts to sit on the affected side. People often describe the SI joint as feeling "stuck" or "out of place."
The Patrick (FABER) test, simplified
Lie on your back. Bring one ankle to rest on the opposite knee, like a figure four. Gently let the bent knee fall out to the side. If this reproduces deep pain in the back of the pelvis on the bent-knee side, the SI joint is suspect. If it shoots down the leg or into the foot, you're looking at something nerve-related.
This isn't a substitute for proper assessment, but it's a useful self-screen.
Why the distinction changes what you do
Here's where it gets practical, and where I see people make things worse with the wrong approach.
If it's sciatica from a disc
The classic advice is to avoid prolonged sitting, avoid heavy lifting and forward bending in the acute phase, and gently work toward extension-based movements (the McKenzie press-up is the textbook example) if those ease the symptoms. A pillow under the knees while sleeping on your back, or between the knees on your side, takes pressure off.
What you don't want to do during a sciatic flare is aggressive forward folding, deep seated stretches, or sitting for hours on end. I see runners try to "stretch out" sciatica with a hard pigeon pose or a deep hamstring stretch, and they make the nerve more irritated.
If it's SI joint dysfunction
The needs are almost opposite. The SI joint typically wants stability, not more stretching. Single-leg work has to be reintroduced carefully. A supportive belt that compresses around the hips — not the abdomen — gives the irritated joint something to push against and calms the muscle guarding around it.
This is exactly the situation our HYKLE Sciatica & Lower Back Support Brace was designed for. Patricia, one of our customers, wrote: "I struggled to work for over a week before I got this belt. I had irritated my SI joint, I couldn't set at my desk for over 15 min at a time and the back pain was so bad I was sick at my stomach. I received the belt on a Friday and it was instant relief. By Saturday evening I was doing all my usual activities."
That's a textbook SI presentation — sitting intolerance, one-sided, flared by an awkward movement — and a textbook response to compression around the pelvis.
For sciatica that has a strong muscular component (a tight glute and lower back guarding around an irritated nerve), the same brace can help by reducing the load through the lumbar spine. Susan, another customer, dealt with arthritic SI changes and said the belt became her "lifeline" after sleepless nights.
What you don't want to do during an SI flare is deep, asymmetric stretching like long-held pigeon, lunges into deep hip flexion, or anything that levers one side of the pelvis against the other. Yoga people, I'm sorry — half-pigeon for forty seconds while breathing into the buttock is often the wrong answer here.
The grey area: piriformis syndrome
There's a category that confuses people because it sits between the two. The piriformis is a small muscle deep in the buttock, and the sciatic nerve runs underneath it (and in some people, straight through it). When the piriformis gets tight or spasms, it can compress the nerve and produce sciatica-like symptoms.
This is what gets called "piriformis syndrome," and it's worth knowing about because:
- The pain location is more buttock-centred than back-centred
- It often follows long sitting (drivers, desk workers, cyclists)
- It responds to gentle hip stretching and trigger point release in a way that disc-related sciatica often doesn't
- A tight, irritable SI joint can make the piriformis on the same side go into a protective spasm — meaning you can have both at once
I had a friend last winter, an orienteer, who came back from a multi-day race in the Carpathians convinced he had a disc problem. The pain was deep in his right buttock, occasionally shooting down to mid-thigh. Two days of rest in the car on the drive home, plus a hard fall on his right side during a navigation error, had set off a perfect storm: SI joint guarding plus a piriformis that wouldn't let go. He didn't need disc rehab. He needed the joint calmed down with compression and rest, then careful re-loading. Three weeks later he was running again.
If we'd treated it as a disc, we'd have wasted three weeks.
What about pregnancy?
This deserves its own paragraph because so many of you ask. The SI joint is the prime suspect in pregnancy-related lower back pain, especially in the second and third trimesters. Relaxin loosens the ligaments to prepare the pelvis for birth, and that can mean the SI joints become unstable and painful — often on rolling over in bed, climbing stairs, or getting out of a car.
Sciatic-pattern pain during pregnancy can also happen, sometimes from a baby pressing on the lumbosacral plexus, sometimes from changes in posture as the bump grows.
The treatment principles still hold: pelvic compression and stability for SI pain, careful avoidance of nerve-aggravating positions for sciatic pain, and absolutely no aggressive stretching of the lower back during pregnancy — those ligaments are already loose enough.
I wrote more about pregnancy-related circulatory and musculoskeletal complaints in this article on varicose veins during pregnancy, and many of the same posture and load-management principles apply.
A simple framework for what to do this week
If you're not sure which one you have, here's a conservative approach that won't make either condition worse:
Days 1–3: Reduce the loads that flare the pain. For sciatica, that usually means less sitting; for SI pain, less single-leg loading and asymmetric activity. Walk on flat ground in short bouts. If sleeping is bad, try a pillow between or under the knees.
Days 4–7: Add gentle movement. For both conditions, slow walking is medicine. For SI pain, a supportive belt during work hours and walks can dramatically reduce muscle guarding. Avoid deep stretches.
Week 2: Start gentle strengthening — glute bridges done slowly and symmetrically, dead bugs for core control, light hip-hinge patterns. If a movement flares the pain past the knee, stop. If it makes the SI pain feel "stuck," stop.
Beyond week 2: If you're not noticeably better, see a physiotherapist in person. Some pain warrants imaging, particularly if you have new weakness, foot drop, numbness in the saddle area, or any change in bladder or bowel function — those are red flags and need same-day medical attention.
What I tell my callanetics students
I have a regular student, mid-fifties, who came to class one autumn limping. She was certain she had sciatica because the pain "went down her leg." When I had her point to where it started, her finger landed two inches from the midline, just below the right SI dimple. The pain stopped at the back of her knee. There was no numbness, no tingling.
Three weeks of pelvic compression during her workday, modified callanetics with no asymmetric hip loading, and a few sessions of careful glute medius strengthening — she was back to normal. She didn't need a scan. She needed someone to tell her that her self-diagnosis was wrong.
Most lower back pain isn't catastrophic. Most of it responds to load management, the right kind of stability work, and a bit of patience. The trick is making sure you're treating the actual problem.
If you're stuck in that loop where sitting hurts, standing hurts, and you can't tell what's wrong — start with the questions in this article. Where exactly is the pain? Does it cross the knee? What makes it worse? Those three questions will get you most of the way to the right answer.
And if you decide to try a support brace while you sort it out, the HYKLE Sciatica & Lower Back Support Brace is built specifically to compress around the hips rather than the upper abdomen, which is the design feature that makes it work for SI joint pain without raising blood pressure or restricting breathing. It comes with our 90-day test-and-return guarantee even if used, so there's no risk in finding out whether it helps you.
If you want to talk through your specific situation before ordering, our team is reachable at support@hykle.com or (888) 302-5354 between 9am and 4pm UTC+2. We'll point you in the right direction even if the answer isn't one of our products.