The sacroiliac joint injection or SI injection is usually performed to either diagnose or treat low back pain and/or sciatica symptoms associated with sacroiliac joint dysfunction. The sacroiliac joints lie next to the spine and connect the sacrum with the hip on both sides. There are two sacroiliac joints, one joint on the right and one on the left. You can see these joints from the outside as two small dimples on each side of the lower back at the belt line. The sacrum is a triangular-shaped bone formed by the fusion of several vertebrae during development. It sits at the lower end of the spine, just below the lumbar spine. The SI joint is one of the larger joints in the body. Very little motion occurs in the SI joint. The motion that occurs is a combination of tilting, sliding and rotation. The SI joint hardly moves in adults. It appears the primary function of the joint is to be a shock absorber and provide just enough motion and flexibility to lessen the stress on the pelvis and spine. During a sacroiliac joint injection, a mixture of a local anesthetic and steroids are injected into one or both joints. The local temporarily numbs the area and the steroids calm the swelling and inflammation. When the medication is injected into painful, inflamed joints, it can reduce inflammation, and therefore reduce pain. A patient may get several weeks to several months of relief from pain. In cases where the first injection does not relieve symptoms within two weeks, patients may be recommended to have one more injection.
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