The sacroiliac (SI) joint connects the iliac bones of the pelvis to the sacrum, the triangular bone at the base of the spine. This pairing of joints transfers the weight and forces of the upper body to the legs, providing a small but necessary amount of shock absorption. Sacroiliac joint dysfunction (SIJD) occurs when the normal movement pattern of the joint is altered, leading to pain. Accurately identifying SIJD can be challenging because its symptoms frequently overlap with other common causes of lower back and buttock pain. A definitive diagnosis requires a systematic approach that moves from patient history and physical examination to advanced confirmation techniques.
Recognizing the Symptoms
The diagnostic process begins with a detailed patient history to characterize the nature and onset of the pain. A common presentation of SIJD is a deep, dull ache localized primarily in the lower back and buttock region, often on one side. This discomfort may radiate down the leg into the thigh or groin, sometimes mimicking the pattern of sciatica. The physician will inquire about specific activities that aggravate the pain to help differentiate SIJD from other conditions.
Pain caused by SIJD is worsened by activities that load or twist the joint. Patients frequently report increased discomfort when standing up from a seated position, climbing stairs, or standing for prolonged periods. The history often reveals that the pain began following a specific trauma, such as a fall, pregnancy, or a spinal fusion surgery.
Manual Diagnostic Tests
Following the patient interview, the next stage of diagnosis involves a physical examination using specific hands-on maneuvers called provocation tests. These tests are designed to mechanically stress the SI joint and determine if this action reproduces the patient’s familiar pain. Individual tests alone are not conclusive, but a cluster of positive results significantly increases diagnostic accuracy.
Common Provocation Tests
Clinicians use several tests to stress the joint:
- The Thigh Thrust test involves applying a backward force through the femur to shear the SI joint while the patient lies on their back.
- The Compression test requires the patient to lie on their side while the clinician applies downward pressure to the pelvis, compressing the joint surfaces.
- The Distraction test applies an outward force to the anterior pelvis, attempting to gap the joint.
- The FABER test (Flexion, Abduction, and External Rotation) stresses the joint by placing the leg in a figure-four position and applying gentle downward pressure on the knee.
To reliably attribute the pain to the SI joint, clinicians often look for a positive result in a cluster of three or more of these provocation tests. This multi-test approach establishes a high clinical suspicion for SIJD.
When Imaging is Necessary
Imaging studies, such as X-rays, Computed Tomography (CT) scans, and Magnetic Resonance Imaging (MRI), are generally not used to confirm SIJD but rather to exclude other serious pathologies. The diagnosis of SIJD is primarily functional, meaning it is based on the reproduction of pain during physical maneuvers, not on structural findings. Therefore, a normal image does not rule out the condition.
X-rays are commonly used to visualize the bony structure of the pelvis and lumbar spine, helping to identify conditions like severe degenerative hip arthritis or fractures. CT scans offer more detailed images of bone, allowing the clinician to check for joint erosion, bony sclerosis, or fusion, which can be signs of long-standing inflammatory disease.
The MRI is useful for assessing soft tissues and inflammation, such as fluid within the joint or bone marrow edema, indicative of active inflammation in the surrounding bone. The primary benefit of these imaging modalities is to definitively rule out other sources of pain, such as a herniated disc, spinal stenosis, or tumors, which can present with identical symptoms.
The Diagnostic Injection
The most definitive method for confirming sacroiliac joint dysfunction remains the diagnostic injection, which is considered the “gold standard.” This procedure involves injecting a local anesthetic directly into the SI joint space. Because of the joint’s complex and deep location within the pelvis, the injection must be performed under continuous image guidance, typically fluoroscopy (a moving X-ray) or sometimes ultrasound.
Before the anesthetic is delivered, a small amount of contrast dye is injected to confirm accurate needle placement within the joint capsule. Once correct placement is verified, the numbing agent is injected. The test is considered positive if the patient experiences a significant, immediate reduction in pain, usually defined as 50% to 75% relief, lasting for the expected duration of the anesthetic.
Patients are monitored immediately following the injection and are often asked to keep a detailed pain diary to track the exact percentage and duration of relief. Some protocols require a second, controlled diagnostic injection using a different anesthetic to further validate the initial findings. A definitive diagnosis of SIJD is made only after this specific, image-guided injection confirms the SI joint as the pain generator.