It is important to remember that not all bony degeneration in the low back occurs at the spine. The sacroiliac joint (the joint between the sacrum, the lowest bone of the spine; and the iliac, part of the pelvic bone) has nerve endings that sense pain. Studies have shown that injecting irritating liquids into the sacroiliac joint produces pain in different ways in different people. It may be experienced locally or felt distantly in the buttock, lower back area, leg, and/or groin.
Pain may occur here from arthritic changes to the bones, inflammation of the joint, and/or injury to the ligaments (soft tissue connecting bone to bone) holding it in place. All these lead to either the inflammatory or degenerative processes.