The sacroiliac (SI) joint connects the spine to the pelvis, linking the sacrum—the triangular bone at the base of the spine—with the iliac bones. This strong, weight-bearing joint acts as a shock absorber and transfers forces between the upper body and the legs. When the joint becomes inflamed or moves improperly, a condition known as SI joint dysfunction, it can cause chronic low back pain. Because its symptoms often mimic other common back problems, diagnosing SI joint dysfunction requires specific physical maneuvers and advanced procedures to isolate the cause of pain.
Understanding Sacroiliac Joint Pain
Pain originating from the SI joint is frequently felt in the lower back and buttock region, but it can also radiate into the groin or the back of the thigh. This radiating discomfort is often mistaken for sciatica or a lumbar disc problem because the pain pattern can extend down the leg, sometimes even past the knee. SI joint pain is usually unilateral, affecting only one side, and is often aggravated by specific movements such as standing up, climbing stairs, or lying on the affected side.
The dysfunction arises when the joint moves either too much (hypermobility) or too little (hypomobility), leading to inflammation. Common causes include trauma, degenerative arthritis, or changes related to pregnancy and childbirth due to hormonal ligament laxity. Biomechanical issues, such as a leg length discrepancy or an altered gait, can also place uneven stress on the joint. Because symptoms mimic other conditions, a physical examination must actively try to provoke the pain to confirm the SI joint’s involvement.
Three Primary Provocative Tests
Clinicians utilize specific physical maneuvers, known as provocative tests, to stress the SI joint and attempt to reproduce the patient’s typical pain. A single positive test is insufficient for diagnosis. However, when three or more tests provoke the familiar pain, it strongly suggests the SI joint is the pain generator. These tests apply either compressive or distraction forces across the joint to confirm that mechanical stress is the source of discomfort.
The Distraction Test, also called the Supine Gapping Test, is performed with the patient lying face up. The examiner applies a steady force downward and outward on the front of the pelvis, specifically on the anterior superior iliac spines (ASIS). This maneuver attempts to separate the front of the SI joint, which can reproduce pain if the anterior ligaments are strained or unstable.
The Compression Test is performed with the patient lying on their side. The clinician applies downward pressure to the upper hip bone (ilium), which compresses the SI joint. This force pushes the two sides of the pelvis together, stressing the posterior ligaments. If this compression reproduces the patient’s low back or buttock pain, the test is positive.
The Thigh Thrust Test (Posterior Shear Test) is considered one of the most diagnostically accurate physical tests. The patient lies on their back while the clinician flexes the hip and knee to 90 degrees. The examiner then applies a strong, posterior-directed force through the femur, driving the thigh bone back toward the SI joint. This action creates a strong shear force directly on the SI joint, and pain reproduction is a highly specific indicator of dysfunction.
Definitive Diagnostic Procedures
While positive provocative tests suggest SI joint dysfunction, they are generally followed by more definitive diagnostic procedures. Imaging studies (X-rays, CT scans, or MRIs) are often used initially, but their purpose is primarily to rule out other causes like fractures, tumors, or severe spinal issues. These scans cannot definitively prove the SI joint is the source of pain, as they may appear normal even when dysfunctional.
The Diagnostic Injection is considered the gold standard for confirming SI joint pain. This procedure involves injecting a local anesthetic directly into the SI joint space under image guidance, typically fluoroscopy. Using real-time X-ray, the clinician ensures the needle is accurately placed within the joint capsule before injection.
A positive diagnosis is confirmed if the patient experiences a significant, temporary reduction in pain, often defined as 50% to 75% relief, within minutes of the injection. This rapid relief following the targeted anesthetic block confirms that the SI joint is the primary source of discomfort. Patients are often asked to perform movements that normally cause pain to assess the immediate relief.
Next Steps After Confirmation
Once the diagnostic injection confirms the SI joint is the source of pain, treatment focuses on a conservative and multimodal plan. Initial treatment includes physical therapy, which aims to restore proper muscle balance and stabilize the pelvic girdle. Therapists focus on exercises that strengthen the core and surrounding muscles to reduce stress on the joint.
Anti-inflammatory medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), are commonly used to reduce joint inflammation. If pain is severe or persistent, a therapeutic injection of a corticosteroid, often combined with a local anesthetic, may be performed. This injection delivers a powerful anti-inflammatory agent into the joint space to provide longer-lasting relief and facilitate physical therapy.