Sacroiliac Joint X-ray (3 or more views)

What it is

The sacroiliac joints are the two narrow seams where the sacrum, at the base of the spine, meets the wing of the pelvis on each side. They barely move — their job is to transfer weight between the spine and the legs — and they sit at an oblique angle inside the body. That angle is the reason for a dedicated series: on a straight-on picture the two surfaces of the joint overlap and the space between them cannot be judged. Taking at least three views, including ones angled up and turned to each side, lines the beam up with the joint so the edges of the bone on either side of it can actually be seen. What the radiologist looks at is whether those edges are crisp, eroded, hardened, or fusing together.

Why it is done

• To look for inflammation and erosion at these joints, which is a characteristic finding in some forms of inflammatory arthritis of the spine
• To investigate persistent one-sided low back and buttock pain that is worse after sitting and eases when lying down
• To look at both joints side by side, since a difference between them is often more telling than either one alone
• To follow known changes at these joints over time

What to expect

No preparation, a gown, and no metal at the waist. Most of the series is taken lying on the back, with the technologist tilting the tube for the angled view and asking the patient to roll partway onto one hip and then the other. Holding still for a second per exposure is all that is required, and nothing is felt. Someone whose pain is worst in one position may need a moment between views. Expect around ten minutes. X-rays show established bone change; earlier inflammation, before the bone has altered, is generally a question for MRI, so a normal series does not necessarily close the matter.

Questions worth asking

• Are both joints covered by this one study, or is each side billed separately?
• If MRI is the test that would actually answer my doctor's question, is this x-ray a required first step for my insurer, or an extra cost?
• Is a rheumatologist ordering this, and will they want the images themselves rather than only the report? Ask for a disc or a portal link so it is not repeated.
• Does the quoted price include the radiologist's interpretation, or only the imaging?