The sacroiliac joint is a small weight-bearing articulation connecting the torso and lower extremities, playing a vital role in load transmission and pelvic stability. Injury or inflammation of this joint leads to sacroiliac joint pain.

Its symptoms closely mimic those of lumbar disc herniation and sciatica, resulting in frequent misdiagnosis. Accurate identification and management rely on analyzing anatomical features, triggering factors and characteristic clinical manifestations.

I. Anatomy and Functions of the Sacroiliac Joint

Anatomical Structure

Located at the posterior pelvis, the sacroiliac joint is formed by the auricular surfaces of the sacrum and ilium, classified as an amphiarthrodial (slightly movable) joint. Its articular surfaces are covered with cartilage, stabilized by tough ligaments including the anterior sacroiliac ligament, posterior sacroiliac ligament and sacrotuberous ligament, which limit excessive joint movement.

Core Functions

1、Load Transmission: Transfers upper body weight from the spine to the pelvis and lower limbs, bearing major mechanical stress during standing, walking and jumping.

2、Pelvic Stabilization: Maintains pelvic stability during dynamic movements such as running and stair climbing, coordinating motion between the torso and legs.

3、Shock Absorption: Cushions impact generated by physical activity via the elasticity of articular cartilage and ligaments, protecting the spine and lower limb joints.

II. Common Causes of Sacroiliac Joint Pain

Mechanical Injury and Overstrain

• Chronic poor posture: Prolonged sitting, standing or crossing legs creates uneven force distribution across the joint, triggering chronic ligament strain.

• Sudden weight bearing or torsion: Improper force exertion while lifting heavy objects or doing intense exercise (squats, running) may cause minor joint subluxation or ligament sprain.

• Asymmetrical movement: Overuse of one limb (e.g., unilateral sports) disrupts pelvic mechanical balance.

Pregnancy and Childbirth

The hormone relaxin secreted during gestation loosens ligaments throughout the body, reducing sacroiliac joint stability.Childbirth subjects the pelvis to extreme pressure as the fetus passes through the birth canal, easily causing joint misalignment or ligament damage. Pain persists without proper postpartum rehabilitation.

Arthritis and Inflammatory Disorders

• Ankylosing Spondylitis: This autoimmune disease primarily attacks the sacroiliac joint, triggering inflammation and cartilage erosion with gradually worsening chronic pain.

• Osteoarthritis: Degeneration of articular cartilage and osteophyte formation in middle-aged and elderly individuals leads to sacroiliac osteoarthritis.

Other Triggers

• Trauma: Pelvic or sacral fractures directly damage the joint, leaving residual pain after healing.

• Infection (rare): Bacterial infection induces septic sacroiliitis accompanied by fever, local redness, swelling and tenderness.

III. Typical Symptoms of Sacroiliac Joint Pain

Pain Location

Pain mainly localizes to the posterior lower back and deep buttocks, occasionally radiating to the posterior thigh, groin or perineum, but rarely extending below the knee — a key distinction from lumbar disc herniation, where pain often travels down to the calves.

Pain Characteristics

• Chronic dull or aching pain: Aggravated by prolonged sitting/standing, relieved by bed rest.

• Activity-induced pain: Sharp discomfort during rolling over, bending, stair climbing or single-leg standing; straining movements such as coughing or sneezing may also trigger pain.

• Unilateral or bilateral pain: Most patients experience unilateral pain; bilateral involvement is typical in ankylosing spondylitis patients.

Associated Manifestations

Some patients exhibit pelvic instability, such as leaning to one side while walking.Those with inflammatory conditions may present systemic symptoms including morning stiffness (alleviated after movement), fatigue and low-grade fever.

IV. Treatment and Rehabilitation for Sacroiliac Joint Pain

Conservative Treatment (First-Line Option)

1、Rest & Posture Correction

Avoid prolonged sitting, standing and unilateral weight bearing. Use a lumbar cushion while seated to preserve spinal physiological curvature; stand with feet shoulder-width apart and wear shock-absorbing footwear for walking.

2、Physical Therapy

Heat therapy, ultrasound, extracorporeal shock wave therapy and electrotherapy boost local blood circulation to ease muscle spasm and inflammation. A pelvic binder restricts sacroiliac joint movement to facilitate ligament repair.

3、Pharmacotherapy

Nonsteroidal anti-inflammatory drugs (NSAIDs) relieve pain and inflammation under medical guidance for severe discomfort. Corticosteroids or local anesthetics can be injected into painful trigger points for nerve block therapy.

4、Rehabilitation Training

The core goal is to strengthen pelvic surrounding muscles to stabilize the joint:

• Core training: Plank, glute bridge, dead bug to fortify abdominal, back and gluteal muscles and reduce joint load.

• Pelvic balance training: Single-leg standing balance, side leg lifts to restore bilateral pelvic mechanical symmetry.

• Stretching: Gentle stretches for the lower back, glutes and hamstrings to release muscle tension pulling on the joint.

Surgical Treatment

Reserved for rare severe cases unresponsive to conservative management, including advanced joint degeneration, deformity or intractable pain. Surgical options include sacroiliac joint fusion and joint arthroplasty.

V. Preventive Measures

1、Maintain proper posture; avoid long-term unilateral weight bearing and extended sitting/standing.

2、Complete full warm-up before exercise to prevent abrupt torsion or heavy lifting; wear supportive gear such as lumbar belts or pelvic binders during workouts.

3、Postpartum women should undergo structured pelvic rehabilitation training and refrain from heavy lifting prematurely.

4、High-risk populations (e.g., ankylosing spondylitis patients) require regular follow-ups for early intervention to slow inflammatory progression.

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