Is it possible to have fully or partially ruptured my ilio-lumbar ligament? if so, how is this diagnosed & what are potential surgical treatments?

It's possible: But the iliolumbar ligament endures little stress compared to the quadratus lumborum and iliopsoas muscles that are in that are. An MRI would show inflammation, but it is of very little value to image that area, as an MRI is a presurgical test. I think a course of physical therapy is beneficial first before spending an exorbitant amount of money to locate inflammation that doesn't change treatment.

Yes: Acute and/or chronic injury causes.  is non-inflammatory & nuclear scans cannot diagnose.  provocation maneuvers (occupational disabilities guides) & fluoroscopic guided diagnostic block can diagnose.  yoga, prolotherapy, & sacroiliac joint belts (boa.Com) might help.  severe cases helped by fusion, overnight hospitalization, and 2 inch buttock scar ("chronic pain" at quora.Com).