Sacroiliac joints: anatomical variants on CT.

The purpose of this work was to examine the type and prevalence of anatomical variants of the sacroiliac joints (SJs) in patients without SJ disease on CT examinations. The study comprised 534 consecutive patients undergoing pelvic CT with various indications not related to diseases that could involve the SJ. Images printed on bone window settings were evaluated with reference to any deviation from the usual appearance of the SJ. Physical data and history of low back pain were recorded in each patient. Six types of anatomical variants were observed: accessory joints in 102 patients (19.1%), "iliosacral complex" in 31 (5.8%), bipartite iliac bony plate in 22 (4.1%), crescent-like iliac bony plate in 20 (3.7%), semicircular defects at the sacral or iliac side in 16 (3%), and ossification centers in 3 patients (0.6%). Accessory joints were more common in obese than in normal-weight individuals (p < 0.05) and in older than younger (<60 years) patients (p < 0.001) and presented degenerative alterations especially in patients with episodes of low back pain. Three of these variants (iliosacral complex, bipartite iliac bony plate, and crescent-like iliac bony plate) had higher incidence in women than in men (p < 0.05) and were not associated with degenerative changes. Knowledge of the normal variations in the SJ appearance broadens the understanding of SJ anatomy, facilitating image interpretation.