Back pain is something that many patients struggle with on a regular basis and determining the source of the pain can often be difficult. There are many overlapping clinical signs that patients present with and many potential causes for their pain.
The sacroiliac (SI) joints are diarthrodial synovial joints that are located between the iliac bones and the sacrum, connecting the spine to the hips. The anterior third of the joint is a true synovial joint and the posterior capsule consists of extensive ligamentous structures. The surface of the joint is rough and rigid. Altogether, the overall joint minimizes movement and enhances stability. Patients often present with back pain sometimes accompanied by radiating pain that extends into the lower extremities as well as the hips. Radiating pain caused specifically by the SI joint is due to there being an insufficient capsular envelope and leakage of local pain mediators into the surrounding neural structures. Diagnosing whether the source stems from a disc herniation, the hips, the surrounding musculature, spinal stenosis, the sacroiliac joint or other etiologies can be challenging.
When working patients up for sacroiliitis, it is important to rule out SI joint related pathologies including trauma, infections and inflammatory diseases such as ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis and Reiter syndrome. Secondary conditions can include scoliosis, leg length discrepancies and spinal fusions. Patients will complain of a combination of localized buttock pain, back pain and/or leg pain as well as pain that is exacerbated when going from a sit-stand position. A physical exam should consist of gait evaluation, a straight leg raise test, determining leg length inequality, a neurological and lumbar exam and assessing hip ROM/performing a Trendelenburg test to rule out potential hip pathologies. The SI joint is approximately 2 centimeters inferomedial to the PSIS and patients can often localize this area with one finger, often called the Fortin Finger Test. Certain diagnostic tests can be performed during a physical exam including a FABER test, Gaenslen test, thigh thrust test, sacral thrust test, compression test and distraction test. These are not reliable but if 3 or more are positive, it can support the diagnosis of sacroiliitis.
No imaging studies exist that are significantly accurate or indicated in diagnosing sacroiliac joint dysfunction. Obtaining lumbar and hip/pelvis radiographs can be helpful in ruling out other causes of back pain. Sacroiliac joint enhanced injections under fluoroscopic guidance is the best diagnostic and therapeutic option. Injections are indicated in patients that have failed at least 6 weeks of NSAIDS, physical therapy and activity modifications. If the patient does not get any relief after the first injection, a subsequent injection is often indicated. If either injection leads to 75% pain relief, it is likely that the SI joint is the pain generator.
Overall, it is important to remember that patients with sacroiliac joint dysfunction may present with a variety of symptoms including radiculopathy, groin pain and/or low back pain. Ruling out other causes for their pain is important in narrowing down the diagnosis.
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