Guilherme Barros and Lynn McGrath are Resident Physicians and Mikhail Gelfenbeyn is an Attending Physician, all in the Department of Neurological Surgery, University of Washington in Seattle. Mikhail Gelfenbeyn is the Chief of Neurosurgery at VA Puget Sound Health Care System in Seattle. Correspondence: Guilherme Barros (gbarros@uw.edu)
Author disclosures The authors report no actual or potential conflicts of interest with regard to this article.
Disclaimer The opinions expressed herein are those of the authors and do not necessarily reflect those of Federal Practitioner, Frontline Medical Communications Inc., the US Government, or any of its agencies. This article may discuss unlabeled or investigational use of certain drugs. Please review the complete prescribing information for specific drugs or drug combinations—including indications, contraindications, warnings, and adverse effects—before administering pharmacologic therapy to patients.
Pain from the SIJ is localized to an area of approximately 3 cm × 10 cm that is inferior to the ipsilateral posterior superior iliac spine.4 Referred pain maps from SIJ dysfunction extend in the L5-S1 nerve distributions, commonly seen in the buttocks, groin, posterior thigh, and lower leg with radicular symptoms. However, this pain distribution demonstrates extensive variability among patients and bears strong similarities to discogenic or facet joint sources of LBP.5-7 Direct communication has been shown between the SIJ and adjacent neural structures, namely the L5 nerve, sacral foramina, and the lumbosacral plexus. These direct pathways could explain an inflammatory mechanism for lower extremity symptoms seen in SIJ dysfunction.8
The prevalence of SIJ dysfunction among patients with LBP is estimated to be 15% to 30%, an extraordinary number given the total number of patients presenting with LBP every year.9 These patients might represent a significant segment of patients with an unrevealing standard spine evaluation. Despite the large number of patients who experience SIJ dysfunction, there is disagreement about optimal methods for diagnosis and treatment.
Diagnosis
The International Association for the Study of Pain has proposed criteria for evaluating patients who have suspected SIJ dysfunction: Pain must be in the SIJ area, should be reproducible by performing specific provocative maneuvers, and must be relieved by injection of local anesthetic into the SIJ.10 These criteria provide a sound foundation, but in clinical practice, patients often defy categorization.
The presence of pain in the area inferior to the posterior superior iliac spine and lateral to the gluteal fold with pain referral patterns in the L5-S1 nerve distributions is highly sensitive for identifying patients with SIJ dysfunction. Furthermore, pain arising from the SIJ will not be above the level of the L5 nerve sensory distribution. However, this diagnostic finding alone is not specific and might represent other etiologies known to produce similar pain, such as intervertebral discs and facet joints. Patients with SIJ dysfunction often describe their pain as sciatica-like, recurrent, and triggered with bending or twisting motions. It is worsened with any activity loading the SIJ, such as walking, climbing stairs, standing, or sitting upright. SIJ pain might be accompanied by dyspareunia and changes in bladder function because of the nerves involved.11
The use of provocative maneuvers for testing SIJ dysfunction is controversial because of the high rate of false positives and the inability to distinguish whether the SIJ or an adjacent structure is affected. However, the diagnostic utility of specific stress tests has been studied, and clusters of tests are recommended if a health care provider (HCP) suspects SIJ dysfunction. A diagnostic algorithm should first focus on using the distraction test and the thigh thrust test. Distraction is done by applying vertically oriented pressure to the anterior superior iliac spine while aiming posteriorly, therefore distracting the SIJ. During the thigh thrust test the examiner fixates the patient’s sacrum against the table with the left hand and applies a vertical force through the line of the femur aiming posteriorly, producing a posterior shearing force at the SIJ. Studies show that the thigh thrust test is the most sensitive, and the distraction test is the most specific. If both tests are positive, there is reasonable evidence to suggest SIJ dysfunction as the source of LBP.
If there are not 2 positive results, the addition of the compression test, followed by the sacral thrust test also can point to the diagnosis. The compression test is performed with vertical downward force applied to the iliac crest with the patient lying on each side, compressing the SIJ by transverse pressure across the pelvis. The sacral thrust test is performed with vertical force applied to the midline posterior sacrum at its apex directed anteriorly with the patient lying prone, producing a shearing force at the SIJs. The Gaenslen test uses a torsion force by applying a superior and posterior force to the right knee and posteriorly directed force to the left knee. Omitting the Gaenslen test has not been shown to compromise diagnostic efficacy of the other tests and can be safely excluded.12
A HCP can rule out SIJ dysfunction if these provocation tests are negative. However, the diagnostic predictive value of these tests is subject to variability among HCPs, and their reliability is increased when used in clusters.9,13
Imaging for the SIJ should begin with anterior/posterior, oblique, and lateral view plain X-rays of the pelvis (Figures 1 and 2), which will rule out other pathologies by identifying other sources of LBP, such as spondylolisthesis or hip osteoarthritis. HCPs should obtain lumbar and pelvis CT images to identify inflammatory or degenerative changes within the SIJ. CT images provide the high resolution that is needed to identify pathologies, such as fractures and tumors within the pelvic ring that could cause similar pain. MRI does not reliably depict a dysfunctional ligamentous apparatus within the SIJ; however, it can help identify inflammatory sacroiliitis, such as is seen in the spondyloarthropathies.11,14 Recent studies show combined single photon emission tomography and CT (SPECT-CT) might be the most promising imaging modality to reveal mechanical failure of load transfer with increased scintigraphic uptake in the posterior and superior SIJ ligamentous attachments. The joint loses its characteristic “dumbbell” shape in affected patients with about 50% higher uptake than unaffected joints. These findings were evident in patients who experienced pelvic trauma or during the peripartum period.15,16
Fluoroscopy-guided intra-articular injection of a local anesthetic (lidocaine) and/or a corticosteroid (triamcinolone) has the dual functionality of diagnosis and treatment (Figure 3). It often is considered the most reliable method to diagnose SIJ dysfunction and has the benefit of pain relief for up to 1 year. However, intra-articular injections lack diagnostic validity because the solution often extravasates to extracapsular structures. This confounds the source of the pain and makes it difficult to interpret these diagnostic injections. In addition, the injection might not reach the entire SIJ capsule and could result in a false-negative diagnosis.17,18 Periarticular injections have been shown to result in better pain relief in patients diagnosed with SIJ dysfunction than intra-articular injections. Periarticular injections also are easier to perform and could be a first-step option for these patients.19