Sacroiliitis: Inflammatory Pain at the SI Joints

An Early Symptom of Ankylosing Spondylitis

Physical therapist explaining something to patient
Isaac Lane Koval/Corbis/VCG/Getty Images

Sacroiliitis, which is inflammation located at the sacroiliac joints, is a key symptom of several forms of inflammatory arthritis and is often the first to make itself known in these diseases.

Osteoarthritis (think wear and tear, rather than inflammation, at joints,) trauma, postural misalignment, and other mechanical issues are some of the conditions that can result in sacroiliac joint pain. Sacroiliitis causes pain in the same area, but in a much different way.

The pain associated with sacroiliitis, along with joint changes that can be viewed on an MRI is related to chronic inflammatory arthritis in the spine. You might think of the difference between sacroiliitis and mechanical causes in this way: Sacroiliitis comes about by an internal process that some people experience and others don't; mechanical causes of SI joint pain are due to external and/or biomechanical forces that may affect the area.

Chronic inflammatory spinal arthritis is also called spondylitis. As a clinical sign, sacroiliitis plays a major role in diagnosing spondylitis.


Sacroiliitis is often felt as deep pain in the low back or buttocks that gets better with activity. It might also affect the entire expanse of your lower extremity from the groin area(s), all the way down to your feet.

Pain from sacroiliitis tends to be worse at night or in the early morning, and exacerbated with standing, as well. Standing related pain can be made worse when you have more weight on one leg than on the other. Climbing stairs, walking with large strides, and running are other weight bearing activities that make the pain worse.

Symptoms of sacroiliitis tend to occur early on in the course of ankylosing spondylitis (AS,) as does evidence of it on MRI. If you have pain in and around your SI joint and/or your MRI shows certain kinds of joint changes, this may explain why your sacroiliac joints are tender (if, indeed you have AS.)

Note that AS is the most common type of spondylitis, but chronic inflammatory arthritis takes a number of other forms, as well. Sometimes sacroiliitis is among the symptoms in the other forms and sometimes it is not.


To diagnose sacroiliitis, your doctor may order an x-ray, MRI or CT scan. She may also order lab tests to find out if infection is the cause.


An x-ray shows what's going on in your bones, making it a good tool for following the changes in your pelvic and spinal bones as the disease progresses.

For decades, the x-ray was the only imaging test used to diagnose sacroiliitis (and spondylitis). The problem with using x-rays, though, is that it takes a long time (years) for evidence of the condition to become visual.


More recently, MRI techniques have been developed to the point where they can be useful in the diagnostic process. These techniques allow doctors to see the active inflammation that is responsible for bone changes (subsequently picked up by x-rays.) For this reason, the use of MRI has, in some cases, greatly sped up the time it takes for patients to get an accurate diagnosis of their SI joint pain.

If early on your doctor suspects spondylitis, she may order an MRI done with a specialized technique called short tau inversion recovery (STIR). Another common MRI technique for sacroiliitis is the gadolinium T1 MRI. If you have the gadolinium test, you'll need to undergo a dye injection.

CT Scans

A CT scan may also be valuable in diagnosing spondylitis. But, the specialized MRIs often prove the most useful of all the diagnostic imaging options.


The overarching goal for treatment of sacroiliitis, and axial sponylitis (of which sacroiliitis is one sign,) is to help you develop long term quality of life by controlling both the inflammation and the resulting symptoms. It may require a multidisciplinary approach, with your rheumatologist as main coordinator. 

In the process of achieving this, you'll likely find your ability to carry out your daily activities, as well as to participate socially, improves. Another important outcome of treatment is preventing structural damage from progressing. 

To those ends, your doctor may prescribe pain-relieving medication, muscle relaxers, corticosteroid injections, DMARDs or TNF-alpha blockers, along with physical therapy. In physical therapy, you'll likely get an exercise program tailored right to you that includes stretching, strengthening and posture exercises. Your doctor may also suggest procedures such as radiofrequency denervation or electrical stimulation to control pain. Surgery is rarely suggested. 

Was this page helpful?
Article Sources
  • Bollow M, Braun J, Hamm B., Sacroiliitis: the key symptom of spondyloarthropathies. 1. The clinical aspects. Rofo. 1997 Feb;166(2):95-100.
  • Elyan, M. MD, Asim Khan, M., MD. Spondyloarthropathies: Update on Diagnosis and Therapy. UBM Medica. Musculoskeletal Network.
  • Sacroiliitis. CHORUS Collaborative Hypertext of Radiology. Last updated: 1 September 2006.
  • van der Heijde, D., 2016 update of the ASAS-EULAR management recommendations for axial spondyloarthritis. Annals of the Rheumatic Diseases. Jan. 2017.