Sacroiliac (SI) joint pain: low back and buttock pain on one side
What the sacroiliac joints are, what can irritate them, what tends to help, and which features of back and buttock pain should be checked by a GP.
The sacroiliac (SI) joints sit at the base of the spine, where it joins the pelvis. They are built to be very stable and move very little, so they can pass load between the spine and the legs. An NHS musculoskeletal service leaflet describes them as not a common cause of back pain, but they can be a source of low back and buttock pain, and the label gets used a great deal online.
When to get urgent help
Call 999 or go to A&E straight away if you have back pain together with any of these. They can be signs of a rare but serious condition such as cauda equina syndrome. Do not drive yourself.
- Numbness or tingling around your genitals, buttocks or inner thighs (the saddle area)
- Difficulty passing urine, loss of bladder or bowel control, or being unable to feel when you are passing urine or stool
- Pain, tingling, weakness or numbness in both legs, or sciatica on both sides, or weakness in a leg that is getting worse
- New changes to sexual sensation or function alongside back or leg pain
- Chest pain, or back pain that started after a serious accident such as a car crash
What it can feel like
- Pain low in the back and buttock, often more on one side
- Pain that varies with position and activity
- Discomfort turning over in bed, getting up from a chair or climbing stairs
- Pain that is usually not serious and often improves over time
Common contributors
- The leaflet lists pregnancy (hormone changes and extra load), an injury such as a fall, structural problems such as scoliosis, osteoarthritis and inflammatory conditions
- Rarer causes include infection, gout and tumours, which is one reason persistent or unusual pain should be checked
- Often the pain is mechanical and no single cause is found
General self-care
These are general comfort measures many people find reasonable. They are not a treatment plan, and what suits one person may not suit another.
- Stay active. The leaflet suggests walking, cycling and swimming, and advises against prolonged rest
- Simple movements such as knee-to-chest stretches and gentle pelvic tilts are described in the leaflet
- If it is worse on one side, lying on the unaffected side with a pillow for support may be comfortable
- Change position often and avoid sitting or standing for very long stretches
- If you use over-the-counter pain relief, follow the packet instructions or ask a pharmacist
When to see your GP
See your GP promptly, or call NHS 111, if you have any of the following:
- Feeling hot, cold, shivery or generally unwell, or severe pain that starts suddenly or quickly gets worse
- Unexplained weight loss, or a lump, swelling or change in the shape of your back
- Pain that is worse at night or does not ease with rest, or is worse when you cough, sneeze or open your bowels
- A history of cancer and new, persistent back pain
Consider seeing your GP if:
- Back pain lasting more than three months, particularly if it started before the age of 40, is worse in the morning, does not ease with rest, wakes you at night and eases on getting up, or improves with anti-inflammatory painkillers. The leaflet says to see your GP or a physiotherapist if you have four or more of these features
- Pain that is not improving after a few weeks of home care
- Fever, unexplained weight loss, or feeling generally unwell with the pain
Where an osteopath fits in
There is limited good-quality research showing that hands-on treatment changes the course of sacroiliac joint pain, so I do not claim that osteopathy treats it.
What an osteopath can usefully do is work out whether your pain is coming from the SI joint, the lower back or the hip, which can be hard to tell apart, advise on activity and positions, and guide a graded exercise plan. The leaflet says SI joint pain is usually self-limiting and not serious, and typically improves with physiotherapy, painkillers and time. If the pattern looks inflammatory, I will recommend that you see your GP. If the assessment suggests you need your GP, a physiotherapist or a specialist instead, I will tell you.
If you would like your symptoms assessed, you are welcome to book an appointment. Osteopathic care is not right for everyone, and if something needs medical attention first, I will tell you.
Common questions
Is SI joint pain serious?
The NHS musculoskeletal service leaflet says it is usually self-limiting and not serious. Pain that has lasted over three months with several inflammatory features, such as morning stiffness and waking at night, should be assessed by your GP or a physiotherapist.
Should I rest with SI joint pain?
The leaflet advises staying active with activities such as walking, cycling and swimming and avoiding prolonged rest, plus simple movements such as knee-to-chest stretches and pelvic tilts.
Free 5-minute exercise sheet
A simple, printable sheet of gentle exercises and stretches, about five minutes a day, based on NHS physiotherapy leaflets. It is general information, not a personal treatment plan, and it is not suitable if you have any of the urgent signs listed above.
Sources and further reading
Links open in a new tab. Sources were checked in October 2026.
Related guides
This page is general information to help you understand common aches and pains. It is not medical advice and cannot diagnose your problem. If you are worried about your symptoms, please speak to your GP or call NHS 111.