Sacroiliac Joint Pain: Assessment & Ultrasound-Guided Injections

What is the sacroiliac joint?

The sacroiliac, or SI, joints connect the sacrum at the base of the spine to the pelvic bones. There is one on each side. Together with surrounding ligaments, they help transfer forces between the lower limbs and trunk.

The SI region can be a source of lower-back or buttock pain, but pain in this area does not automatically mean the joint is responsible. Problems involving the lumbar spine, hip, muscles or nerves can cause overlapping symptoms.

Are SI joint dysfunction and sacroiliitis the same?

Not necessarily. “SI joint dysfunction” is often used to describe pain associated with the joint or surrounding structures. “Sacroiliitis” means inflammation of the sacroiliac joint.

These labels should not be used interchangeably without assessment. Suspected inflammatory disease may need a different investigation and treatment pathway from mechanically aggravated pain.

What can aggravate pain around the SI joint?

Some people describe discomfort with prolonged sitting or standing, rising from a chair, stairs, running or loading one leg. Injury and repeated loading may be relevant to the history.

These patterns are not specific to the SI joint. They do not prove that your pelvis is “out of place”, that ligaments are torn or that the joint moves too much or too little.

What might the symptoms feel like?

• Aching low in the back or around one buttock.
• Pain extending towards the hip, groin or thigh.
• Stiffness or discomfort when changing position.
• Pain during particular daily activities or exercise.

Leg pain may be referred from several structures. Numbness, tingling or weakness should be assessed rather than assumed to be SI joint pain.

How is the cause assessed?

Your clinician takes a history and examines the back, pelvis and relevant neighbouring areas. This may involve several tests that reproduce symptoms, together with assessment for alternative causes.

No single symptom, physical test or scan is enough to explain every case. Imaging or referral may be appropriate when the history suggests another condition or when findings would change management.

What is a diagnostic SI joint injection?

In selected cases, an image-guided local anaesthetic injection may help assess whether the joint contributes to pain. The clinician reviews the response over an appropriate time period.

Temporary improvement is useful information, but interpretation depends on accurate placement, the technique used and the wider assessment. A routine ultrasound-guided injection should not be described as automatically confirming the diagnosis.

What treatment may help?

Treatment should match the likely cause, symptoms and goals. Options may include tailored physiotherapy, a graded exercise programme, practical changes to aggravating activities and suitable pain-management advice.

For back pain generally, staying active within your tolerance is preferable to prolonged bed rest. Adjust activities that clearly aggravate symptoms rather than assuming you must stop all movement.

If symptoms persist, a clinician may discuss an injection or referral. Inflammatory disease and other specific diagnoses may require specialist care.

See our physiotherapy information for related clinic services, or contact the team about back pain assessment and injection options.

How can ultrasound-guided injections help?

At The Podiatry Clinics, ultrasound guidance may be used for selected SI region injections. It provides real-time views of relevant structures and helps guide needle placement without using X-rays.

A corticosteroid injection may be considered to reduce pain associated with inflammation. It does not guarantee relief, and the response and duration vary. The intended target—within the joint or around it—should be explained before treatment.

Is ultrasound as accurate as X-ray guidance?

A 2022 review of SI joint injection techniques found that CT and fluoroscopy were more accurate than ultrasound for intra-articular needle placement in the studies reviewed. Ultrasound may still be useful, but it should not be presented as equally accurate for every patient or purpose.

Guidance can help with planning and visualisation; it does not eliminate the risk of nerve or vessel injury or other complications.

What should you discuss before an injection?

• The suspected diagnosis and intended injection target.
• The likely benefits, uncertainties and alternatives.
• The medicine proposed and any allergies.
• Other medicines, including blood thinners, and relevant health conditions.
• Possible risks, including infection, bleeding, a temporary pain flare and medicine-specific effects.
• Aftercare, transport arrangements, costs and follow-up.

Do not stop prescribed medicines without advice. Tell the clinician if you have an infection, diabetes or a possibility of pregnancy.

After an injection, follow the individual activity advice. Increasing pain, redness or swelling with fever or feeling unwell needs urgent clinical advice rather than waiting for a scheduled review.

When does back pain need urgent help?

Go to A&E or call 999 for back pain with new bladder or bowel problems, loss of feeling around the genitals or anus, symptoms affecting both legs such as weakness or numbness, chest pain, or after a serious accident.

Seek urgent GP or NHS 111 advice if pain becomes severe suddenly, worsens quickly or is accompanied by fever, shivering or feeling generally unwell.

Arrange a GP assessment for unexplained weight loss, persistent night pain or pain that does not improve after rest. These features should not simply be labelled SI joint dysfunction.