The sacroiliac joint supports the spine, the sacrum is the base bone of the spine that is attached to the ilium, which is the junction with the pelvis, the hip bone. This sacroiliac joint gives stability and allows cushioning movements when running, when inflamed they can cause pain in the lower back and buttocks.
Sacrum injuries can occur from blows or direct trauma to the joint, wear and tear over the years, degenerative diseases, tumors, etc. Even hormonal changes during pregnancy.
Symptoms may be intensified by prolonged standing, climbing stairs, taking long steps, or bearing more weight on one leg than the other.