The sacrum has the tough job of mediating between the lower extremities, devoted to stability and support, and the versatile and mobile upper torso, arms and head, which must move to perform their functions. If the heart is the center of the circulatory system, then the sacrum is the heart of the skeleton. Almost every weight-bearing joint in the body is horizontal, which, given gravity, just makes sense. However, our upright posture makes the joints between the sacrum and the pelvis, the sacroiliac joints, nearly vertical. Evolution has not caught up with our cultural mandate of standing. Therefore it is not surprising that the joint frequently goes out of its proper alignment, and given the sizable pressures that develop there, this may incur great pain. Sacroiliac joint derangement is purely a clinical diagnosis. In all but the most egregious cases, imaging studies are worthless, and electrodiagnosis is only valuable to rule out other conditions. Treatment is best done on an empirical basis.
A combination of physical therapy and yoga, gradually introduced, relieves 90% of this condition. In difficult cases Alexander technique, oral medications or even an injection into the joint have proven quite helpful.