What causes sacroiliac joint pain?

Sacroiilititis!: Sacroiilitis is the most common cause. This is inflammatory. See a rheumatologist.

See below: I see it in the following scenarios. After car accidents, especially when someone is pressing really hard on the brake with one foot. I see it after falls on the buttock. I see it in women whose pelvic ligaments relax during pregnancy and cause instability in the joint. I see it in people who have had fusion surgery that crosses the lowest lumbar segments and then get excess movement in the si.

Ligament Injury: Abnormal joint function, usually due to damaged joint ligaments or from joint hypermobility syndrome.  symptoms can include popping sounds, shifting feeling, radiation of pain into groin region (confused with hernia pain), chronic low back pain, sciatica to knee, pelvic pain, painful intercourse, frequent urination &, to my experience, ibs. See my complete discussion on my board on quora.Com.