Like any other bone and joint in the body, the large bones of the pelvis and the SI joint can become damaged either through injury or normal wear and tear. The joint can become disrupted or its support ligaments can become loose. Potential causes of SI joint pain include degenerative disease, history of trauma, and other unknown reasons. Symptoms may be immediately obvious (acute) or over time (chronic). When this happens, people can feel problems in their upper leg(s), buttocks and sometimes even higher on the spine. This is especially true with sitting, lifting, running, walking, or even sleeping on the involved side. In all of these cases, the symptoms can be felt anywhere from the lower leg to the lower spine.
The SI joint is a real yet underappreciated pain generator in an estimated 15% to 25% of patients with axial low back pain.1