The sacroiliac joint is one of those parts of the body that many people hardly think about. That is until they are experiencing pain in this region. These joints connect the base of the spine to the ilium which forms part of the pelvic region. They are essential for balance and movement in the lower body. These joints support the entire weight of the entire upper body. This joint even widens to facilitate both pregnancy and childbirth. It is not difficult to see why pain, weakness and stiffness in this region can reduce your quality of life. It can interfere with day to day activities such as walking, standing and bending. Below, we take a look at SI joint anatomy and the factors that influence movement in this part of the body.

Sacroiliac Joint Anatomy

These joints are located at the base of the spine. They connect the sacrum (the base of the spine) to the inner side of the pelvic region (the ilium). The joints are therefore located on either side of the sacrum. They are stabilized by a strong network of ligaments.

This region provides the transition between the spine and the pelvis. The joints structures are similar to other moveable joints in the body. However, movement in this region is very limited. It is covered by a capsule whose outer part consists of a thick and tough membrane. This covers a more delicate membrane (the synovial membrane) which secretes synovial fluid. This fluid is responsible for lubrication and shock absorption.

The articulation of the sacrum and the ilium to form the joint is quite unique. The joint is formed by two C-shaped bones. The ilium forms the convex or outer part. Thick hyaline cartilage covers this part of the ilium. The inner part is formed by the S1 – S3 sacral bones. Fibrocartilage covers this surface.

Both fibrocartilage and hyaline cartilage are coarse in texture. This is thought to be an adaptation to the stress experienced in this region. The surfaces are in close proximity to each other as the layers of cartilage and the capsule between are thin.

Factors That Influence SI Joint Movement

Although the joints’ structure has resulted in their classification along with other moveable joints, movement is actually quite limited in this part of the body. Movements are limited to:

• Front and back movements i.e. anterior – posterior
• Upward and downward
• Nutation i.e. anterior and inferior movement (forward and downward)
• Counternutation i.e. Posterior and superior movement (backward and upward)

The movements do not occur across a big range of motion. They are limited to between 2 to 5 degrees and 2 to 4 mm. This is because of the strong network of ligaments stabilizing the region as well as the bony structure of the joint.

There are various factors that influence movement in this area. They include age, mechanical loads and sex. For example younger individuals are more flexible. Women are also more flexible in this region during pregnancy and childbirth. People that carry heavy weights or those that are overweight have a greater requirement for stability. Their ligaments are stronger and this limits movement.

Causes of Pain in the Sacroiliac Region

There are mild changes that occur in the texture and angle of the connecting surfaces of the sacroiliac joints as a person ages. Changes may also occur due to strain. These changes occur as the region is continually subjected to pressure and continues to resist the compression. Ridges and depressions form on the surfaces and continue to deepen with age. Structural changes associated with tissues and cartilage in the area can result in pain, stiffness or weakness.

If you are experiencing pain don’t hesitate to contact Dr. Chris Boone for accurate diagnosis. Our clinic provides expert sacroiliac joint surgery Bellevue & Redmond services.