Joint Knowledge: The SI Joint

The SI joint is the sacroiliac joint, a little-known but important joint in the body. It’s located where the sacrum (the triangular bone at the base of the spine) and the ilium (the uppermost bone of the pelvis) meet.

Have you ever wondered whether your back discomfort is originating from somewhere other than your back?

Such is the case for an estimated 15% to 30% of people with chronic low back pain, for whom their primary source of dysfunction is actually the sacroiliac (SI) joint. Often overlooked, this joint can lead to significant impairments if it becomes injured or damaged because we rely on this joint for so much of our day-to-day function.

Anatomy & Function of the SI Joint

You have an SI joint on both the right and left sides of your pelvis. This joint connects the sacrum (the wedge-shaped bone at the very bottom of your spine) to a part of your pelvis called the Ilium (the wing-like bones you can feel when you put your hands on your hips).



Unlike many other joints in the body, the SI joint doesn’t move a lot—as little as 2 to 4 millimeters in any direction. This is important for its function, but if something causes your SI joint to move too much or too little, discomfort can develop within the joint itself or even elsewhere in the musculoskeletal “chain” to which the joint connects and is connected.

There are a few reasons why the SI joint is so stable:

  • The articular sides of the SI joint—that is, the places where the sacrum and ilium attach—have large surface areas. This inherently increases its stability.
  • Bony surfaces inside the SI joint are rough rather than smooth, which helps maintain alignment.
  • The SI joint is also surrounded by strong ligaments, capsules, and muscles which further preserve the balance between mobility and stability.

The SI joint is considered a diarthrodial joint, meaning it contains protective cartilage and synovial fluid (which acts as a joint lubricant). Other examples of diarthrodial joints include the shoulder, elbow, and knee.

The SI joint transfers loads and reduces pressure on the body during weight-bearing tasks like walking and supports the upper body by providing a stable base for the spine.


Common Types of SI Dysfunction

Research on SI joint dysfunction suggests it’s common among young athletes and seniors, but it can affect people of all ages and backgrounds.

You may be more likely to experience SI joint problems if you have certain risk factors, such as:

  • Uneven leg lengths
  • Gait, postural, and biomechanical abnormalities (such as scoliosis)
  • Overuse or exposure to persistent repetitive stress (such as frequent jogging)
  • Pregnancy
  • Spine surgery

Indications of a compromised SI Joint range wildly in terms of type, frequency, duration, and severity.

They may include discomfort (often sharp, stabbing, or numb) in the low back, buttocks, hips, pelvis, and groin; discomfort which worsens when transitioning from sitting to standing or while standing on one leg; stiffness, burning, and/or numbness in the pelvic area; and the feeling that your legs may “give out.”

Such signs could be caused by a number of different things, some of which we’ll mention below. 


Direct Trauma

We often see SI dysfunction following falls, car accidents, and other events which trigger tissue damage and stimulate nearby pain receptors.



Arthritis is an over-the-top immune response within a joint, which can lead to swelling, discomfort, and other symptoms. Several different types of arthritis can affect it, including:

  • Osteoarthritis (OA): the classic “wear and tear” condition common with age, OA leads to degradation of the cartilage inside the joint and can cause painful bone on bone rubbing, reactive bony overgrowth, and joint stiffness.
  • Gout: Joint damage caused by too much uric acid inside the body. Uric acid is a by-product of certain metabolic processes; if there’s too much of it your body becomes more acidic, and uric crystals can build up in joints (the big toe is often affected first).
  • Ankylosing spondylitis: This is a specific type of immune overreaction affecting the spine, and can lead to intermittent episodes of pain, stiffness, and bony overgrowth. It usually appears first in early adulthood.



Women who are pregnant or who recently gave birth often experience SI dysfunction due to weight gain, increased lordosis (curve) in the lower spine, the biomechanical strain of a growing fetus, birth trauma, or even hormone-mediated relaxation of ligaments around the SI joint (which is necessary so that a baby can fit through the pelvic inlet during delivery).

Diagnosing SI joint dysfunction can be tricky. It usually requires a combination of so-called “provocation tests” which aim to reproduce the SI discomfort; injection of analgesic or numbing agents into the SI joint (if discomfort improves or goes away, the SI joint is likely involved); and X-rays and other imaging studies.


Natural Ways to Revitalize & Maintain SI Joint Health

Maintain an active lifestyle.

Exercise helps prevent obesity which increases the amount of load transmitted through the SI joints. Regular physical activity also helps build strong muscles in the core and hips which helps to support the SI joints and optimize postural balance.

Consume a balanced diet.

Avoiding foods and beverages which are known to promote tissue damage (such as sugar and alcohol) as well as eating meals and supplements which are rich in nutrients and minerals is essential for stimulating bone and joint health throughout life. Be sure to drink enough water, too!

Consult with a professional.

Physical therapists, orthopedic surgeons, massage therapists, and other clinicians provide multiple techniques that can manage and alleviate discomfort in your SI joint and address other factors contributing to the dysfunction.


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