Ankylosing spondylitis and the SI joint

These joints connect the base of the spine to the pelvis. Symptoms may alternate between the buttocks, feel worse after rest, and ease with gentle movement. A clinical assessment, supported when appropriate by imaging and blood tests, helps distinguish inflammatory pain from strain or another pelvic problem.

Inflammation at a sacroiliac joint is called sacroiliitis. In ankylosing spondylitis, it belongs to a wider inflammatory process that can also affect the spine, hips, rib joints, eyes, or tendon attachment points. Pain is often felt below the belt line rather than directly over the centre of the lower back.

Early inflammation may not be obvious on a plain X-ray. A clinician interprets the pain pattern, examination findings, and any imaging together; a scan finding alone does not determine how active the condition is or how much it affects daily movement.

Arrange an assessment if buttock or lower-back stiffness keeps returning, interrupts sleep, or improves notably once you move. Record which side hurts, how morning movement changes it, and whether you have eye redness, heel pain, bowel symptoms, or a family history of inflammatory arthritis.

Management may combine prescribed anti-inflammatory medicine with physiotherapy. Regular mobility work, posture practice, and gradually progressed strengthening can preserve comfortable movement. During a flare, adjust the load rather than stopping all activity; a physiotherapist can help choose exercises that do not repeatedly provoke the joint.

Seek urgent assessment for a painful red eye with light sensitivity or blurred vision, because eye inflammation needs prompt treatment. New leg weakness, numbness around the groin, loss of bladder or bowel control, fever with severe back pain, or major trauma also warrants emergency care.

Contact your usual clinician sooner if pain changes sharply, repeatedly wakes you, or continues despite the agreed plan. Those changes call for reassessment rather than simply increasing exercise intensity or medication on your own.

Ask what features support sacroiliac inflammation, whether imaging would change management, how disease activity will be followed, and which movements suit your current symptoms. Also clarify medicine side effects, what to do during a flare, and which eye or nerve symptoms should bypass a routine appointment.