If you have a positive for the "supposed stuckSIJ" . Try this
Landmark PSIS to sacrum. Have the patient do hip abduction directly lateral in the coronal plane. For every positive "fixation" of the SIJ, this test will show a superior and lateral movement of the PSIS to the sacrum with little variance.
My reseach was published as an article in a Canadian journal and is being pursued in the USA by a Lincoln Nebraska Clinic. The paper should be published in 2008 or early 2009.
APAS, asymmetric pelvic angle syndrome is the true cause of most of the supposed SIJ problems - form closure, force closure et al included.
Hope you find this helpful.
Best regards,
Neuromuscular.