Sacroiliac joint hypermobility refers to increased and/or abnormal movement of the sacroiliac joint, which lies next to the spine and connects the sacrum with the pelvis. The condition is the result of the joint becoming too loose and the ligaments designed to hold it in place have become overly loose.

Pain from a hypermobile sacroiliac joint can be sharp and intense. It is typically felt on one side of the low back or buttocks, and can radiate down the leg.