The diagnostic value of MRI with regard to sacroiliitis depends on the disease duration. In patients with symptoms for more than a year there may be changes detectable by conventional radiography at the first examination. If the symptoms have been present for less than one year, the value of MRI depends on their duration and how characteristic the symptoms are for inflammation.
General recommendations are:
INFLAMMATORY BACK PAIN
Symptoms for less than 3 months: Await the course.
3 to 12 months with classic symptoms: Primary MRI.
3 to 12 months with less typical symptoms: Radiography with regard to other diseases. Additional MRI or CT when radiography is inconclusive.
Symptoms for more than 12 months: Primary radiography; if negative MRI or CT.
Always consider the possibility of spondyloarthropathy in young patients with hip arthritis or inflammatory changes at tendon attachments. This is an indication for MRI of the sacroiliac joints.
The images illustrate a young man with active synovial inflammation in both hip joints and at the left heel (arrows). Supplementary MRI of the sacroiliac joints (bottom right) demonstrates bilateral sacroiliitis as a sign of ankylosing spondylitis.