Sacroiliac or SI joint dysfunction is a term that is used to describe a painful low back condition. For many injured workers in Wisconsin McCormick Law Office attorneys determine if SI joint dysfunction is a work-related condition - if the condition is caused by a work accident or job duties over time.
At the lower end of the spine, just below the lumbar spine lies the triangular shaped sacrum, a bone that is actually formed by the fusion of several vertebrae during development. The sacroiliac (SI) joint sits between the sacrum and the iliac bone (thus the name "sacroiliac" joint). You can see these joints from the outside as two small dimples on each side of the lower back at the belt line.
The SI joint is one of the larger joints in the body. The surface of the joint is wavy and fits together similar to the way Legos® fit together. Very little motion occurs in the SI joint. The motion that does occur is a combination of sliding, tilting and rotation. The most the joint moves in sliding is probably only a couple of millimeters, and may tilt and rotate two or three degrees.
The SI joint is held together by several large, very strong ligaments. The strongest ligaments are in the back of the joint outside of the pelvis. Because the pelvis is a ring, these ligaments work somewhat like the hoops that hold a barrel together. If these ligaments are torn, the pelvis can become unstable. Generally, these ligaments are so strong that they are not completely torn with the usual injury to the SI joint.
The SI joint hardly moves in adults. Other than the role the joint plays in pregnancy, it does not appear that motion is important to the function of the joint. The older one gets, the more likely that the joint is completely ankylosed, a term that means the joint has become completely stiffened with no movement at all. It appears that the primary function of the joint is to be a shock absorber and to provide just enough motion and flexibility to lessen the stress on the pelvis and spine.