The sacroiliac joints are located at the bottom of the spine, below the lumbar spine and above the tailbone. There are two of them, located on each side of the lower spine. Using x-rays to assist in guiding the injection, the physician will then insert a needle into the sacroiliac joint. The needle delivers a local anesthetic directly into the source of the pain. The injection may also include an anti-inflammatory medication, such as a corticosteriod.