Davis J, Hamilton A, Rouzer P, A Radiographic Definition of Sacroiliac Joints: Their Normal Anatomy and Sprain States Transactions of the Consortium for Chiropractic Research Jun 1987.

Much has been written describing the anatomy and physiology of the sacroiliac (SI) articulation. Sacroilitis and the progress of inflammation have been given detailed attention with sophisticated imaging and radioisotope uptake techniques. However, definition of the radiographic appearance of the sacroiliac joint is minimal. The normal appearance, and the injury state, sprain, have not been adequately addressed radiographically. Clinical syndromes of SI dysfunction are widely recognized and treated, yet no radiographic interpretation for this condition exists. Signs of SI joint sprain or separation would be anticipated to be: (1) increased joint space and (2) subchondral sclerosis. Several literature references agree that 2mm is the normal SI joint spacing. Yet extensive studies need to be performed to determine whether signs of pelvis imbalance, such as a PI or AS ilium, or Sacro Occipital Technique (SOT) Category II pelvis can be reliably determined on routine radiographs.