Sacroiliac Joint Arthritis and Dysfunction

What is the Sacroiliac Joint?

The Sacroiliac Joints (SI Joints) are located in the lowermost part of the spine, the sacrum. There are 2 joints that connect the sacrum to the pelvic bone (the ilium) on either side of the body. The function of the SI joint is to transfer weight and force between the upper body and legs and absorb pressure when we walk. In doing so the SI joints provide stability for the pelvis while bearing the load of the upper body.

The joint is a ‘synovial joint’ which means it contains cartilage which allows for smooth gliding motion between the bones. The joint only has a small amount of movement because it is covered by ligaments and muscles which act to stabilize and support the joint.                                      

Image Credit: staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762.

Image Credit: staff. “Blausen gallery 2014“. Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762.

Osteoarthritis of the Sacroiliac Joint

Osteoarthritis refers to the process of degeneration of a joint which usually occurs as we age. Osteoarthritis can affect the SI Joint. Over time the cartilage that cushions the joint starts to break down. Without cartilage the bones rub together with movement and cause pain. See Hip and Knee Joint Arthritis for more information on osteoarthritis.

What is Sacroiliac Joint Dysfunction?

Sacroiliac Joint Dysfunction is a term that is used to describe pain in the region of the sacroiliac joint. It is generally caused by abnormal motion of the SI joint, either too little or too much motion. It results in inflammation of the joint.

There are many causes of SI Joint Dysfunction, including:

  • Injury – injuries such as a fall onto the buttocks or a car accident can strain or damage the ligaments and muscles around the SI joint. The ligaments hold the joint together and when the ligaments are torn or damaged there can be abnormal motion of the joint. Injuries can also cause damage to the cartilage in the joint, which can lead to arthritis of the joint.
  • Abnormal development of the Sacrum bone – the Sacrum is a special part of our spine. When our bodies are just developing in the womb usually several vertebrae fuse or join together to form the sacrum. In some cases some of the bones that normally should join together do not join and remain separated which creates an ‘extra joint’ that would normally not be present. In certain cases this condition can cause problems with the SI joint as well as low back pain.
  • Pregnancy – women are at risk of developing SI joint dysfunction due to childbirth. During pregnancy the body produces hormones which allow connective tissue like ligaments to ‘relax’ or loosen so that during delivery the pelvis can stretch enough to allow for birth. This stretching makes the SI joint more movable and prone to dysfunction. Over a period of time these changes can lead to breakdown of the cartilage in the SI joint and arthritis. The SI joints can cause discomfort from the stress of carrying a growing baby in the pelvis as well.