By Mr Ahmed-Ramadan Sadek, Neurosurgeon · Last reviewed October 2026 · 6 min read

What are the sacroiliac joints?

At the bottom of your spine sits the sacrum, a broad, triangular bone. On either side it meets one of the large wing-shaped bones of the pelvis, called the ilium. The place where these bones meet is the sacroiliac joint, so most people have two: one on the left and one on the right, roughly beneath the dimples at the top of the buttocks.

These joints move only a little, but their job is important. They act as a cushion between the spine and the pelvis, softening the jolts of walking and standing and carrying the load of your trunk down to your hips and legs.

Why do they become painful?

Like any other joint, a sacroiliac joint can run into trouble. The main reasons are:

• Wear and tear: the smooth cartilage lining the joint can thin with age, leading to arthritis and inflammation.
• Altered movement: the joint may become either too stiff or too loose, which doctors sometimes call sacroiliac dysfunction.
• Injury: a fall, a sudden twist or other strain on the pelvis can damage the joint.

What does it feel like?

Most people describe aching and stiffness low down at one side of the back, directly over the joint. The discomfort may spread behind the hip, into the groin, or down the back of the thigh.

Because the pain can travel in this way, it often looks very much like a hip problem or pain coming from the lumbar spine (the lower back). Leg pain from a trapped nerve, such as sciatica, can also overlap. Telling these apart is one of the main reasons a specialist assessment is helpful.

How is it diagnosed?

Your clinician will ask where the pain is, what brings it on and what eases it, and will examine your back, hips and pelvis. Pressing over the joint or putting it under gentle stress during the examination may reproduce your usual pain.

Scans such as X-rays or an MRI can help rule out other causes. However, a scan cannot always prove the joint is the source. For that reason, the response to an injection of local anaesthetic into the joint is sometimes used to confirm the diagnosis: if the pain eases noticeably, even for a short time, the joint is very likely to be involved.

Treatment options

Exercise and rehabilitation

Strong muscles around the pelvis, hips and trunk act like a natural support belt for the joint. A regular programme of stretching and strengthening is the most important long-term treatment, whether or not you also have an injection. A physiotherapist can tailor this for you. Typical exercises include:

• gentle stretches for the hamstrings (back of the thigh), quadriceps (front of the thigh) and inner thigh muscles, each held for a short count;
• squeezing a cushion between your knees while seated, to work the inner thigh muscles;
• tightening the buttock muscles while lying face down;
• lying on your back and slowly rolling both bent knees from side to side;
• drawing one or both knees towards your chest to stretch the buttocks and lower back.

Keeping active and, where needed, losing some weight can also reduce the load on the joint.

Sacroiliac joint injection

If pain has lasted a long time and is getting in the way of everyday life, your specialist may suggest injecting medicine directly into the joint. This is usually a corticosteroid (a strong anti-inflammatory) with or without local anaesthetic (numbing medicine).

The injection is not a stand-alone cure. It is best seen as a window of relief that lets you get on with your exercises. Most specialists advise starting the rehabilitation programme around a week after the injection.

What happens during the injection?

1. You will either have a local anaesthetic to numb the skin or sedation given through a vein so that you are drowsy or asleep.
2. You lie face down on a couch, and the skin of your lower back is cleaned with antiseptic.
3. Using live X-ray images to guide the way, the doctor places a fine needle into the joint and injects a small amount of medicine.
4. The injection itself typically takes only a few minutes.

Afterwards you rest in a recovery area while a nurse checks your pulse and blood pressure. Most people go home within a few hours.

After the injection

• If you had sedation, the British Association of Spine Surgeons (BASS) advises that driving is off-limits for 48 hours, and an adult should stay with you overnight. Arrange for someone to take you home.
• You may want to take the following day off work, longer if pain persists.
• The steroid can take several weeks to reach its full effect, so keep taking your usual pain relief in the meantime.
• Do not suddenly stop medicines such as morphine, gabapentin, pregabalin or amitriptyline; these need to be reduced gradually, and your GP can help with this.

How well does it work?

When the sacroiliac joint has been confirmed as the source of pain beforehand, the BASS patient booklet reports that more than 85 to 90% of patients gain significant benefit from the injection. How long that relief lasts is unpredictable: for some it is a few weeks, for others months or even years.

If the first injection helped, it can usually be repeated, though BASS notes that most specialists wait at least six months between injections. Some people who have had one episode of sacroiliac pain are more prone to further episodes, which is another reason to keep up with exercises.

If the injection does not help

If there is little improvement by around six weeks, or relief is only brief, the next step may be a referral to a pain clinic. One option there is radiofrequency denervation, in which heat is used to disable the small nerves that carry pain signals from the joint. If injections, physiotherapy and denervation all fail, surgery to fuse (permanently join) and stabilise the joint may occasionally be considered.

Risks and complications of injection

The BASS patient booklet describes sacroiliac joint injections as carrying very few risks and does not give numerical rates for them. The uncommon problems it lists are summarised below.

Risk	What it means
Bleeding	Very uncommon. Tell your team if you take blood thinners such as warfarin, rivaroxaban or clopidogrel, as these may need to be paused.
Infection	Rare. The risk is higher if the skin on your back is affected by eczema, psoriasis or similar conditions.
Steroid side effects	Temporary facial flushing; in women, changes to periods or post-menopausal bleeding.
Raised blood sugar	People with diabetes may see higher readings for a few days.
Less effective injection	Bony overgrowth around the joint can make accurate needle placement difficult, reducing the benefit.

Outlook

Most people improve with the right exercises, sensible activity and, where needed, a well-placed injection. Strong supporting muscles give you the best chance of staying well.

• BASS patient booklet: Sacro-iliac Joint Pain
• Spinemathema: Acute back pain
• Spinemathema: Facet joint injections

This guide is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist.