The sacroiliac (SI) joint connects the spine to the pelvis, stabilized by strong ligaments. It transmits weight from the upper body to the lower extremities and absorbs impact during movement. Sacroiliac Joint Dysfunction (SIJD) occurs when this joint moves abnormally, either too much (hypermobility) or too little (hypomobility), leading to inflammation and pain. Diagnosing SIJD presents a challenge because the resulting pain, typically felt in the lower back, buttocks, or posterior thigh, often mimics more common conditions such as sciatica or lumbar disc herniation.
Initial Clinical Evaluation
The diagnostic process begins with a detailed clinical evaluation focused on understanding the patient’s specific pain experience. Gathering a thorough patient history involves identifying the exact onset of the pain, any potential mechanism of injury, and activities or postures that either exacerbate or relieve the discomfort. This history helps narrow the potential sources of pain and differentiate SIJD from other musculoskeletal issues.
A general physical examination follows, which includes assessing the patient’s posture and analyzing their gait for any subtle abnormalities that might suggest pelvic asymmetry or instability. Tenderness is a common finding, and clinicians will often palpate the area directly over the joint, typically just inferomedial to the posterior superior iliac spine. This initial stage is focused on differential diagnosis, working to rule out broad categories of pain before focusing specifically on the SI joint as the primary pain generator.
Physical Provocation Tests
If the initial evaluation suggests SIJD, the next step involves physical manipulation tests designed to stress the joint and reproduce the patient’s familiar pain. These provocation tests are performed in a cluster rather than individually to increase diagnostic accuracy. A positive diagnosis is considered likely when a patient reports pain reproduction with three or more of the five standardized maneuvers, often referred to as a clinical decision rule.
Thigh Thrust, Distraction, and Compression Tests
The Thigh Thrust Test (Posterior Shear Test) involves the examiner applying a strong, posteriorly directed force through the femur to shear the joint while the patient lies supine. The Distraction Test (Gapping Test) involves applying outward pressure to the anterior superior iliac spines, effectively pulling the joint apart. Conversely, the Compression Test is performed with the patient lying on their side, where the examiner pushes downward on the iliac crest to compress the joint surfaces together.
Gaenslen’s and FABER Tests
The Gaenslen’s Test requires the patient to lie near the edge of the table with one leg held to the chest and the other extended over the side, stressing both SI joints simultaneously. The FABER Test (Flexion, Abduction, and External Rotation) involves positioning the leg in a figure-four shape and applying downward pressure to the knee. If this maneuver reproduces pain directly over the SI joint, it suggests the joint is the source of the patient’s discomfort.
The Role of Imaging and Exclusion
Standard medical imaging techniques play a significant role in the diagnostic pathway for SIJD. X-rays, Computed Tomography (CT) scans, and Magnetic Resonance Imaging (MRI) are typically not effective for confirming mechanical SI joint dysfunction, as the issue is often related to abnormal movement rather than a visible structural defect. The primary purpose of using these imaging modalities is to exclude other serious causes of the patient’s low back pain.
Imaging can effectively rule out fractures, tumors, or advanced degenerative arthritis in the lumbar spine or hips. An MRI can be particularly useful for identifying inflammatory sacroiliitis, a condition often associated with specific types of inflammatory arthritis like ankylosing spondylitis. By systematically excluding other possible diagnoses, imaging helps guide the clinician toward focusing on the SI joint as the remaining likely source of pain.
Confirmatory Diagnostic Injection
The definitive method for confirming SI joint dysfunction is a fluoroscopically or ultrasound-guided anesthetic block, considered the “gold standard” of diagnosis. This procedure involves injecting a small amount of local anesthetic directly into the SI joint space under live image guidance to ensure precise needle placement. Image guidance is paramount because the joint is deep and irregularly shaped, making blind injection inaccurate.
Confirmation relies on the patient’s immediate response to the anesthetic, which effectively numbs the joint. If the patient experiences a significant reduction in pain—typically defined as 50% to 75% or greater relief—within minutes of the injection, the SI joint is confirmed as the source of their pain. This positive response provides the evidence needed to distinguish SIJD from other potential pain generators. The diagnostic injection then paves the way for specific, targeted treatments, such as therapeutic injections or physical therapy.