Hey there teedlum, sacroiliac joint pathology is something I haven’t thought about for years, including it’s consequences on the function of the pelvis and legs. I had both sides fused (sacroiliac arthrodesis via internal fixation) due to traumatic injury, using the old style procedure where access was through the anteriolateral abdomen, however the ‘new’ method is much simpler, easier, and you end up with much less hardware in your body and difficulty in recovery - the ‘pins’/anchors are simply placed via very small incisions adjacent to and just lateral of the joint (contrary to the scars resultant from the internal fixation procedure that extend from the posterior superior iliac spine to the pubic symphysis, along the entire iliac crest, to provide access vis the abdomen to the anterior surfaces of the SI joint). Having had fixation, I highly recommend it, based on how well it treats the instability and resultant symptoms. And especially if it’s done via the external fixation method! 🙂🌺
The level of instability you describe sounds very mobile; the kind of instability I had (complete rupture of the anterior and posterior sacroiliac ligaments bilaterally) was totally unable to be rectified with exercise and retraining muscle memory - the muscles aren’t designed to ‘take over from’ lax or torn ligaments (that’s kind of like saying that any muscle can do the job of a torn or stretched ligament which is not possible because ligaments provide joint stability while muscles participate in actioning movements, relying on joints to be intact with sufficient ligamentous stability present to facilitate said movement) and ended up ‘pulling’ the alignment of the joint surfaces out of whack due to a compensatory spasm that would inevitably reoccur with each loading of the joint (where ligaments would usually take the load, preventing extreme movement in the joint space). Because primary muscle stability was impossible in my case (as determined by the inability of the muscles to function under the spasm conditions of gripping the instability as tight as possible) I had the fusion procedures, and once I recovered, the muscles returned to normal function. Here’s a link explaining more about how the ligaments and joint ranges of motion function and contribute to movement: https:// http://www.physio-pedia.com/Sacroiliac_Joint (please remove spaces - I am a new member and unable to paste links at this time).
All the best to you 🙂