Computed tomography-based assessment of sacroiliac joint variations: associations with sacral types, sex, and side

To evaluate sacroiliac joint (SIJ) variations and to examine their associations with sacral morphology types across sex and side using computed tomography.

This retrospective study included computed tomography images of 400 adults (200 females, 200 males). Sacral morphology was classified on sagittal images based on the presence and morphology of the S1-S2 intervertebral disc. SIJ variations were identified on corresponding axial images. The distribution of SIJ variations according to sex and side and their associations with sacral types were analyzed.

SIJ variations were observed in 43% of individuals with type 1 sacrum, 41% of those with type 2 sacrum, and 25% of those with type 3 sacrum. Overall, variations were detected 60.5% of females and 25.5% of males, indicating a significantly higher prevalence in females. Most variations demonstrated bilateral involvement. The accessory SIJ was the most frequent variation, followed by the iliosacral complex and semicircular defect. Sacral morphology was predominantly type 1, followed by type 2, with a significant sex-related difference in distribution. Although SIJ variations were observed across different sacral types, no clear linear association with sacral morphology was identified.

SIJ variations are common, predominantly bilateral, and more frequently observed in females, supporting a mechanical rather than inflammatory origin. The high prevalence of accessory SIJ highlights its importance as a potential source of diagnostic confusion in SIJ imaging. Combined evaluation of sacral morphology and SIJ variations provides an integrated anatomical framework that improve radiological interpretation and reduce diagnostic uncertainty in clinical practice.