The Sacroiliac Joint Injection (SI) involves injecting local anesthetic and steroids into the joint. A sacroiliac joint injection is used to reduce inflammation and/or swelling of nerves. SI injections may reduce pain in the low back, groin, buttock, and leg from nerve inflammation/irritation or swelling in your sacroiliac joint. Six hours after the injection, the local anesthetic or numbing medication will wear off. If you are experiencing pain in your sacroiliac joint, your healthcare provider may prescribe you a sacroiliac joint injection. Your spine (sacrum) is connected to your pelvis (ilium) through this joint. Each side of your body has a sacroiliac joint. The sacrum is connected to each side of the pelvis by these bones. Joints such as these act as shock absorbers. Their purpose is to transfer weight and forces from the upper body to the legs.