SI Joint Injury: Mechanisms, Causes, Risk Factors, and Prevention

How do you injure your SI joint?

Injuries to the sacroiliac (SI) joint typically arise from excessive or repetitive stress, often due to a combination of traumatic events, biomechanical imbalances, degenerative changes, or inflammatory conditions, leading to either excessive motion (hypermobility) or restricted motion (hypomobility).

Understanding the Sacroiliac Joint (SIJ)

The sacroiliac joints are two robust, weight-bearing joints connecting the sacrum (a triangular bone at the base of the spine) to the ilium (the largest bone of the pelvis) on both sides. Unlike many other joints, the SIJs have limited movement, primarily functioning to transmit forces between the upper body and the lower limbs, absorb shock, and maintain pelvic stability during activities like walking, running, and standing. Their stability is largely provided by strong ligaments and surrounding musculature.

Mechanisms of SI Joint Injury

Injuries to the SI joint are rarely due to a single, isolated factor but rather a combination of acute trauma and chronic predisposing conditions.

• Acute Traumatic Events:

  • Falls: Landing directly on the buttocks or experiencing a fall where one leg is extended can impart significant shearing forces on the SI joint.
  • Motor Vehicle Accidents: High-impact collisions, especially side impacts, can cause sudden, forceful displacement or compression of the pelvis, leading to SI joint sprains or subluxations.
  • Direct Impact: A direct blow to the sacrum or ilium.
  • Sudden, Awkward Movements: A misstep, a forceful twist, or a sudden lift that overloads the joint.

• Repetitive Stress and Microtrauma:

  • Unilateral Loading: Activities that repeatedly load one side of the body more than the other, such as running on an uneven surface, golf, tennis, or certain dance movements, can lead to asymmetrical stress on the SI joints.
  • Asymmetrical Postures: Prolonged sitting with legs crossed, habitually standing with weight shifted to one side, or sleeping in positions that twist the pelvis can contribute to imbalances over time.
  • Occupational Demands: Jobs involving repetitive bending, twisting, lifting, prolonged sitting, or standing on hard surfaces can cumulatively strain the SIJs.

• Biomechanical Imbalances:

  • Leg Length Discrepancy: Even a small difference in leg length can lead to compensatory movements in the pelvis and spine, creating uneven loading and stress on one SI joint.
  • Muscle Imbalances:
    • Weak Core Muscles: Insufficient strength in the deep abdominal and pelvic floor muscles reduces stability around the lumbar spine and pelvis, forcing the SIJs to compensate.
    • Weak Gluteal Muscles: Weakness in the gluteus medius and maximus can lead to altered gait mechanics and increased stress on the SI joint.
    • Tight Hip Flexors, Adductors, or Hamstrings: Muscular tightness can pull the pelvis into unfavorable positions, altering SI joint alignment and mechanics.
  • Gait Abnormalities: Any deviation in walking pattern, whether due to pain elsewhere (e.g., knee or foot) or neurological conditions, can alter force distribution through the SIJs.
  • Spinal Conditions: Scoliosis, lumbar spine degeneration, or previous lumbar fusion surgery can alter the biomechanics of the entire lumbopelvic region, increasing stress on the SI joints.

• Pregnancy and Postpartum:

  • Hormonal Changes: During pregnancy, the hormone relaxin increases ligamentous laxity throughout the body, including the SI joints, to prepare for childbirth. This increased laxity can make the joints less stable and more susceptible to injury.
  • Altered Biomechanics: The shifting center of gravity, increased weight, and changes in posture during pregnancy and postpartum can significantly alter pelvic mechanics and stress the SIJs.
  • Childbirth: The stresses of labor and delivery can directly injure the SI joints or surrounding ligaments.

• Degenerative Changes:

  • Osteoarthritis (OA): Like other joints, the SI joints can develop osteoarthritis over time due to wear and tear, leading to cartilage breakdown, bone spurs, and inflammation within the joint. This can result in hypomobility and pain.

• Inflammatory Conditions:

  • Spondyloarthropathies: Systemic inflammatory diseases like ankylosing spondylitis, psoriatic arthritis, or reactive arthritis can cause inflammation of the SI joints (sacroiliitis) as a primary manifestation, leading to pain and stiffness.

• Prior Surgery:

  • Lumbar Fusion: Fusion of segments in the lower back can alter spinal mechanics and increase the load transmitted through the SI joints, potentially leading to degenerative changes or pain in these adjacent segments over time.

Types of SI Joint Dysfunction/Injury

SI joint injuries typically manifest as two primary types of dysfunction:

• Hypermobility (Too Much Movement): This occurs when the ligaments supporting the SI joint become lax or stretched, allowing for excessive motion. This can lead to instability, inflammation, and pain as the joint moves beyond its normal physiological limits. It's often associated with repetitive microtrauma, pregnancy, or generalized ligamentous laxity.
• Hypomobility (Too Little Movement): This occurs when the SI joint becomes stiff or "locked," restricting its normal, limited motion. This can be due to muscle guarding, degenerative changes, inflammation, or prolonged immobility. Restricted movement can also lead to pain as forces are not properly dissipated through the joint.
• Inflammation (Sacroiliitis): This is inflammation within the joint itself, which can accompany both hypermobility and hypomobility, or be a primary issue in conditions like spondyloarthropathies. Inflammation leads to pain, tenderness, and sometimes swelling.

Risk Factors for SI Joint Injury

Several factors can increase an individual's susceptibility to SI joint injury:

• Age: While SI joint dysfunction can occur at any age, degenerative changes become more common with advancing age.
• Gender: Women are more prone to SI joint issues, particularly due to the anatomical differences in the female pelvis (wider, less stable) and the hormonal and mechanical changes associated with pregnancy and childbirth.
• Occupation: Jobs requiring prolonged sitting, standing, heavy lifting, or repetitive twisting movements.
• History of Spinal Surgery: Especially lumbar fusion.
• Athletic Activities: Sports involving repetitive unilateral movements, high impact, or significant rotation (e.g., running, golf, soccer, gymnastics).
• Obesity: Increased body weight places additional stress on the weight-bearing joints, including the SIJs.
• Prior Injury: A history of previous trauma to the pelvis or lower back can predispose to future SI joint issues.

Recognizing Potential SI Joint Injury

Symptoms of an SI joint injury typically include:

• Localized pain in the lower back, often on one side, directly over the SI joint (just below the belt line, lateral to the spine).
• Pain that may radiate into the buttock, groin, or down the back of the thigh, rarely extending below the knee.
• Pain that worsens with prolonged sitting or standing, standing on one leg, climbing stairs, or transitional movements (e.g., getting out of a car, turning in bed).
• Stiffness or a feeling of the joint "giving way."
• Tenderness to touch over the SI joint.

If you suspect an SI joint injury, particularly if pain is persistent, severe, or accompanied by neurological symptoms, it is crucial to consult a healthcare professional for an accurate diagnosis and appropriate management plan.

Prevention Strategies

While not all SI joint injuries can be prevented, several strategies can significantly reduce your risk:

• Maintain Core and Gluteal Strength: A strong core and robust gluteal muscles are essential for stabilizing the pelvis and supporting the SI joints.
• Address Muscle Imbalances: Regular stretching of tight muscles (e.g., hip flexors, hamstrings, piriformis) and strengthening of weak muscles can optimize pelvic alignment.
• Practice Proper Lifting Mechanics: Always lift with your legs, keeping the weight close to your body, and avoid twisting while lifting.
• Vary Postures: Avoid prolonged static postures. If you sit for long periods, take regular breaks to stand and move. If standing, shift your weight periodically.
• Ergonomics: Ensure your workstation, car seat, and sleeping arrangements support neutral spinal and pelvic alignment.
• Manage Leg Length Discrepancy: If a significant difference is identified, a shoe lift or orthotic may be recommended by a healthcare professional.
• Listen to Your Body: Avoid pushing through pain, especially during exercise. Gradually increase the intensity and duration of new activities.