Sacroiliac (SI) Joint Pain: Common Causes and Contributing Factors

What can cause SI pain?

Sacroiliac (SI) joint pain most commonly arises from dysfunction within the joint itself—either excessive movement (hypermobility) or insufficient movement (hypomobility)—or from inflammation, degenerative changes, or trauma affecting the joint and its surrounding structures.

Understanding the Sacroiliac Joint

The sacroiliac (SI) joints are two small, L-shaped joints connecting the sacrum (the triangular bone at the base of your spine) to the ilium (the large bones of your pelvis). While they have limited movement, typically only a few degrees, this small motion is crucial for absorbing shock between your upper body and legs, and for transmitting forces during activities like walking, running, and lifting. Pain occurs when this intricate balance is disrupted.

Primary Causes of SI Joint Pain

SI joint pain is often multifactorial, meaning several factors can contribute to its onset. Understanding these causes is key to proper diagnosis and effective management.

Biomechanical Dysfunction

The most common culprit behind SI pain is a disturbance in the joint's normal biomechanics. This can manifest in two primary ways:

• Hypermobility (Too Much Movement): If the ligaments supporting the SI joint become lax or stretched, the joint can move excessively. This instability can lead to irritation, inflammation, and pain.
  • Causes: Pregnancy (due to hormonal changes like relaxin), trauma, repetitive asymmetrical loading, or underlying connective tissue disorders.
• Hypomobility (Too Little Movement): Conversely, if the SI joint becomes stiff or "locked," it can also cause pain. This immobility forces other structures to compensate, leading to undue stress on the joint itself or surrounding tissues.
  • Causes: Degenerative changes (osteoarthritis), prolonged immobility, or muscular imbalances.

Traumatic Injury

Direct trauma to the pelvis or lower back can directly injure the SI joint, leading to immediate pain and dysfunction.

• Falls: Landing hard on the buttocks or directly on the side of the hip.
• Motor Vehicle Accidents: Especially rear-end collisions or impacts that twist the torso and pelvis.
• Direct Impact: Sports injuries or other incidents involving a direct blow to the SI region.

Inflammatory Conditions (Spondyloarthropathies)

Systemic inflammatory diseases can specifically target the SI joints, leading to chronic pain and stiffness. These are often characterized by inflammation of the entheses (where tendons/ligaments attach to bone).

• Ankylosing Spondylitis (AS): A chronic inflammatory condition primarily affecting the spine and SI joints, leading to stiffness and potential fusion over time.
• Psoriatic Arthritis: An inflammatory arthritis associated with psoriasis, which can affect the SI joints.
• Reactive Arthritis (formerly Reiter's Syndrome): Can develop after certain infections and may involve SI joint inflammation.
• Enteropathic Arthritis: Arthritis associated with inflammatory bowel diseases like Crohn's disease or ulcerative colitis.

Degenerative Changes (Osteoarthritis)

Similar to other joints in the body, the SI joints are susceptible to wear and tear over time, leading to osteoarthritis.

• Age-Related Degeneration: The cartilage cushioning the joint surfaces can erode, leading to bone-on-bone friction, pain, and inflammation.
• Previous Injury: A prior injury to the SI joint can accelerate degenerative changes.

Pregnancy and Postpartum

Pregnancy is a common period for SI joint pain due to several physiological and biomechanical changes.

• Hormonal Changes: The hormone relaxin, released during pregnancy, loosens ligaments throughout the body, including those supporting the SI joints, increasing their mobility.
• Weight Gain: The increased body weight places additional stress on the pelvis and SI joints.
• Postural Shifts: The changing center of gravity and altered posture can lead to increased lumbar lordosis and pelvic tilt, stressing the SI joints.
• Childbirth Trauma: The forces involved in childbirth can sometimes strain or injure the SI joints and surrounding ligaments.

Muscular Imbalances and Dysfunctions

Dysfunction in the muscles surrounding the pelvis and spine can significantly impact SI joint stability and mechanics.

• Core Weakness: Insufficient strength in the deep abdominal and back muscles can compromise pelvic stability.
• Gluteal Weakness/Inhibition: Weakness in the gluteus medius and maximus can lead to altered gait mechanics and increased stress on the SI joint.
• Tight Hip Flexors: Can contribute to an anterior pelvic tilt, altering SI joint loading.
• Tight Adductors: Can pull the pelvis out of alignment.
• Piriformis Syndrome: While distinct from SI joint dysfunction, a tight or spasmed piriformis muscle (which crosses near the SI joint and sciatic nerve) can mimic or contribute to SI pain.

Repetitive Stress and Overuse

Activities that involve asymmetrical loading or repetitive movements can cumulatively stress the SI joints.

• Asymmetrical Activities: Running on uneven surfaces, prolonged standing with weight shifted to one leg, or sports involving rotational movements (e.g., golf, tennis).
• Occupational Hazards: Jobs requiring prolonged standing, heavy lifting, or repetitive twisting motions.

Leg Length Discrepancy

A significant difference in leg length can lead to compensatory pelvic tilting and altered weight bearing, placing uneven stress on the SI joints over time.

Lumbar Spine and Hip Pathology

While distinct, issues in the lumbar spine or hip can refer pain to the SI joint or alter mechanics in a way that secondarily affects it.

• Referred Pain: Pain originating from the lower back (e.g., disc herniation, facet joint arthritis) or hip (e.g., hip osteoarthritis, labral tear) can sometimes be perceived in the SI region.
• Compensatory Mechanics: Dysfunction in the lumbar spine or hip can force the SI joint to compensate, leading to strain and pain.

Conclusion

SI joint pain is a complex condition with a wide array of potential causes, ranging from biomechanical imbalances and trauma to systemic inflammatory diseases. Given its multifactorial nature, an accurate diagnosis by a qualified healthcare professional is crucial. This typically involves a thorough physical examination, imaging studies, and sometimes diagnostic injections, to pinpoint the specific underlying cause and guide the most effective treatment strategy.