The ilio-sacral-joints however are, like the joint of the pubic bone, unstable structures. The starting function of the subluxation within the scope of a pelvic damage does not only depend on a subluxation of the joint of the pubic bone, but also on the subluxation of the Ilio-sacral-joints. A subluxation of the Ilio-sacral-joints automatically causes a tilt of sacrum and pelvis.
Causes for subluxations of the pubic bone and the Ilio-sacral joints are: not only the arising of shearing forces at the pelvis (pictures in the article about the subluxation of the pubic bone are,
The Iliosacral joints are tilting joints. The most important horiziontally running tilting axis of the sacrum is positioned in the upper third of the sacrum, on a level with the rear tip of the iliac crest, the Spina iliaca superior posterior.
The wings of ilium lie on the Ilio sacral joints like roof tiles.
At a subluxation of one Ilio-sacral joint the sacrum tilts over its horizontal transverse axis with the shorter part, positioned above the axis, forward towards the belly, and the longer lower part with the coccyx at the same time moves automatically backwards. The forward movement of the upper, smaller part of the sacrum is less - due to the shorter lever arm - than the backward movement of the (much longer) lower part of the sacrum.
As subluxations of the joint of the pubic bone and the Ilio-sacral joints are taking place at the same time and, how already said, contain a tilting of sacrum and pelvis, a one-sided high standing of the pelvis is the consequence. The one-sided high standing of the pelvis again is the reason for the inclination of the pelvis.
The Ilio-sacral joints never subluxate on both sides at the same time, but there happens always a mutual damage.
On the side of the higher standing part of the pelvis the Ilio-sacral joint also stands higher than the opposite one. Therefore in the lower standing joint a tension arises, which is reduced when it subluxates and consequently than stands higher than the originally higher standing joint of the opposite side, now being the lower standing one. The whole process then takes its course in reverse direction. The Ilio-sacral joints make, so to speak, a sea-saw motion, which again worsens the damage at the pelvis in the course of time.