The spine consists of a column of bones (vertebrae), each of which has a cylindrical body with bony projections at the back. The cylindrical bodies are separated by shock absorbing cushions (disks). The bony projections connect each vertebra to the one above and below at small joints called facet joints. Just below the column of vertebrae, there's a triangular bone called the sacrum, which connects to the pelvic bones. This three- to four-inch long connection is called the sacroiliac joint.