i'd like to comment just on the technical aspect of the sacrum not being able to move with respect to the iliums ... i have experienced, with my previous physio, that if he pushed my sacrum down with respect to my iliums, i experienced a very interesting gait pattern (both femurs rotated laterally) and subsequent medial knee pain on both knees. upon pushing my sacrum up (which i had to do to relieve this gait pattern) the knee pain disappeared and my gait was retored to something more "normal". if the sacrum was pushed too high, i felt pain in the lumber spinal region.
however, i do agree that the muscles attaching to the iliums and sacrum can and do affect gait patterns ... which is now why i pay particular attention to muscles like my QL.
i understand that the muscles respond to something ... but i am also sure that my sacrum and iliums can and have been seriously rotated/moved in the past to directly affect my gait ... as, i suspect, a response of muscles to changes in structural orientation of bones.
if you think that your sacrum cannot move up or down or your ilums cannot be rotated, i propose you to try getting somebody to push down (inferiorly) on your sacrum, or anteriorly or posteriorly rotate one of your iliums using a muscle energy technique or brut force and see what happens. of course, first orientating the femur in such a way which facilitates opening of the SI joint.
i would love to see some of the experts have their SI joints manipulated as excessively as mine have been (out of a lack of understanding of the problem) and then try to tell me that restoring correct function and alignment is not that difficult... and that the ilium doesn't rotate THAT much. i understand that alot of the sensation of a rotation etc can be a result of a muscular response to a "slight" change in SI joint orientation, but i propose that hte ilium can move more than expected with respect to the sacrum... if enough force is applied.... which is what happened to me in the beginning by some unsuspecting health professionals
of course this kind of manipulation shouldn't have happened in the first place. but before all that happened, there was one sensation that i experience after the accident which confirms my belief that my sacrum had reorientated itself with respect to my left ilium in particular ... barbara hungerford corrected that "fixation" and now that side has the ability to pop like the other side does if i perform a certain test on myself... previously, this was not possible.
it seems to be that from being out of wack so badly for so long, i actually suspect that i do have some soft tissue changes in the facia or muscle attachments, in particular .. the iliac crest for glut medius, obligues, QL....it's kind of knotty ... which i believe could be forcing my weird gait sensations.