Sacroiliac Joint Pain: Causes, Diagnosis & Treatment

Sacroiliac joint pain is a recognised but frequently overlooked cause of low back and buttock pain. Because its symptoms overlap with disc and hip problems, it can be mistaken for other conditions, and a careful assessment is needed to identify it. The reassuring point is that sacroiliac joint pain is usually managed successfully with non-surgical care, and surgery is reserved for a small minority of carefully selected cases.

What is sacroiliac joint pain?

The sacroiliac joints connect the sacrum — the triangular bone at the base of the spine — to the pelvis, one on each side. These are strong, stable joints that transfer load between the upper body and the legs and allow only small amounts of movement.

Sacroiliac joint pain (sometimes called SI joint dysfunction) describes pain arising from this joint, whether from too much or too little movement, inflammation, injury or arthritis. It is a condition in its own right — not, despite a common misconception, the name of a surgical procedure.

Which parts of the spine are affected?

The sacroiliac joints lie at the very base of the spine, in the sacral region, where the spine meets the pelvis. Pain is typically felt over the buttock and low back, usually on one side, and can spread into the groin, hip or the back of the thigh. Because of where the joint sits, its pain is easily confused with that of the lumbar discs or the hip.

Causes and risk factors

Sacroiliac joint pain can develop from a range of causes:

• Injury, such as a fall onto the buttock or a road accident.
• Pregnancy and childbirth, due to hormonal changes and altered loading.
• Uneven loading, for example from a leg-length difference or altered gait.
• Arthritis, including osteoarthritis and inflammatory conditions.
• Previous lumbar fusion surgery, which can increase stress on the joint.
• Repetitive strain from certain sports or occupations.

Symptoms and warning signs (red flags)

Typical symptoms include pain over the buttock and low back, often on one side, that may radiate into the groin or thigh. It is commonly worse when standing up from sitting, climbing stairs, standing for long periods, or turning over in bed.

Although most sacroiliac joint pain is mechanical, seek prompt assessment if you notice any of these red flags:

• Fever, night sweats or unexplained weight loss.
• Severe pain following a significant injury.
• Weakness or numbness spreading down the leg.
• Problems with bladder or bowel control.
• Pain that is constant, progressive or much worse at night.

These features may indicate infection, fracture, nerve involvement or, rarely, another underlying condition that needs investigation.

How sacroiliac joint pain is diagnosed

Diagnosis is mainly clinical, based on the history and examination. A key part of the assessment is a series of provocation tests, in which the examiner applies controlled stress to the joint in different positions to see whether the manoeuvres reproduce the familiar pain. Several positive tests together make the joint a more likely source.

Imaging such as X-rays or MRI may be used to exclude other causes and to look for arthritis or inflammation. In selected cases, a diagnostic injection of local anaesthetic into the joint can help confirm it as the source of pain if symptoms ease afterwards.

Non-surgical treatment

Non-surgical care is the mainstay and helps most people. Options include:

• Physiotherapy to improve the strength, stability and control of the muscles around the pelvis and lower back.
• Activity modification to reduce aggravating movements while staying generally active.
• Simple pain relief for flare-ups, used for the shortest helpful period.
• A pelvic support belt in some cases, particularly during or after pregnancy.
• Targeted injections into or around the joint, which can relieve pain and support the diagnosis.

Most people find their symptoms settle with a combination of these measures over time.

When surgery is considered

Surgery for sacroiliac joint pain is uncommon and considered only in a small number of carefully selected people whose pain is clearly coming from the joint, has been confirmed with appropriate tests, and has not responded to thorough non-surgical treatment over a sustained period. Sacroiliac joint fusion is one such option. The decision is made cautiously and only after non-surgical measures have been fully explored.

When to see a spine specialist

Consider seeing a spine specialist if low back or buttock pain persists despite several weeks of appropriate care, if the diagnosis is unclear, or if it is significantly affecting daily life. Any red-flag features — fever, unexplained weight loss, leg weakness, or bladder or bowel changes — need prompt review. A specialist can distinguish sacroiliac joint pain from disc and hip problems and guide the most appropriate, usually non-surgical, treatment.