Finding the right tests…
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Finding the right tests…
X-Ray
Your sacroiliac joints sit where the base of your spine meets the two wing-shaped hip bones, one on each side, and this front-on X-ray pictures both joints together in a single image. It is a different test from a general lower back X-ray, ordered mainly when a doctor suspects an inflammatory cause of back or buttock pain, such as ankylosing spondylitis, rather than a mechanical or disc-related one. Because the joints sit deep in the pelvis and overlap heavily from the side, doctors use this one front-facing view rather than a side angle, and read it against a standard 5-point grading scale, from normal to fully fused.
This image shows both sacroiliac joints together, letting a radiologist compare one side against the other for blurred margins, small erosions, bone hardening around the joint, or narrowing of the joint space. Findings are graded on a standard scale from normal to complete fusion, which your doctor interprets alongside your symptoms and blood tests.
Sacroiliitis, inflammation of the sacroiliac joints, is one of the patterns doctors look for when back or buttock pain is worse at night, improves with movement, and does not fit the usual mechanical low back pain picture. This X-ray, along with blood tests such as HLA-B27, is one of the standard checks used when ankylosing spondylitis or a related inflammatory condition is suspected.
Radiologists grade each joint from 0, normal, to 4, complete fusion, based on how blurred the joint margins are and whether erosion, bone hardening, or joint narrowing is present. Diagnostic criteria for ankylosing spondylitis generally call for a moderate-to-advanced grade in both joints, or a more advanced grade in just one.
Bone changes from sacroiliitis can take time to develop, so an early-stage inflammatory condition may not yet show up on X-ray even if a person has real symptoms. When early disease is suspected despite a normal film, an MRI is more likely to pick up the change, since it can show inflammation before bone changes appear.
A lumbar spine X-ray looks at the vertebrae and disc spaces of the lower back, while this test looks specifically at the two joints connecting the spine to the pelvis. Doctors order it when an inflammatory cause of pain, rather than a mechanical one, is suspected.
The sacroiliac joints sit deep in the pelvis and overlap heavily when viewed from the side, so a single front-facing view is the standard way to assess them and compare left against right.
Not fully. Bone changes from this condition can take time to appear, so early disease sometimes looks normal on X-ray. Your doctor may add an MRI or blood tests like HLA-B27 if suspicion remains.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Radiologists grade each joint from 0, meaning normal, to 4, meaning complete fusion, based on joint margin blurring, erosion, and narrowing. Your doctor will explain what your specific grade means for you.
No. It's ordered based on your symptoms and exam findings, though a family history of ankylosing spondylitis or related conditions can be part of what prompts your doctor to consider it.
This is not a fasting-dependent test. Confirm with your doctor or the centre if there is anything specific they want you to do beforehand.
The image includes part of the surrounding pelvis and hip bones, but it is centred on the sacroiliac joints specifically. Tell your doctor if hip pain, rather than lower back or buttock pain, is your main concern.