The sacroiliac joint is one the biggest joints in the body. It is located in the low back, between the upper part of the tailbone and the pelvic bone. When it becomes inflamed from degenerative disease and arthritis, it is a frequent cause of chronic low back pain. Injecting this joint with a combination of local anesthetic (Novocaine type medicine) and a steroid (potent anti-inflammatory) will help reduce the pain, hopefully for a prolonged period of time. There is a sacroiliac joint on the right and left sides of the tailbone.