Anatomical variations with joint space measurements on CT.

This study has been performed to demonstrate the type and frequency of the anatomical variations of the sacroiliac joint according to age, gender, Body Mass Index and childbirth, and the influence of the anatomical variants to the uniformity and width of the joint space. It was conducted on 400 consecutive patients without sacroiliac complaint who underwent pelvic CT scanning for various reasons. Patients' ages were 15 or above. Anatomical variants that we observed were accessory sacroiliac joint (70 patients, 17.5%), iliosacral complex (38 patients, 9.5%), bipartite iliac bony plate (22 patients, 5.5%), semicircular defects on iliac/ sacral side (19 patients, 4.8%), crescent like iliac bony plate (14 patients, 3.5%) and ossification centers (4 patients, 1.0%). The mean joint space width of the 400 patients was 1.72+/-0.57 mm (from 0.77 mm to 4.39 mm). In adults below 40 years of age, the measured width was 2.49+/-0.66 mm. In older patients, 1.47+/-0.21 mm. Joints which presented anatomical variants (206 articulations) had a non-uniform joint space in 164 (79.6%), whereas uniform joint space were seen in 42 (20.4%) articulations. The joint width were less than 2 mm in 193 (93.7%) articulations and in 13 (6.3%) articulations were greater or equal to 2 mm. This study has demonstrated that anatomical variations and joint space are independently related to age, gender, Body Mass Index and childbirth in patients. We believe that all this information is helpful to interpret and examine the sacroiliac computed tomography images.