The volume of CT data can be reconstructed in multiple planes permitting multiplanar joint assessment. This is especially advantageous for evaluation of the anatomically complex SIJ, often presenting with shadows from overlaying bowel content by radiography. The sensitivity of CT for detecting SIJ changes is therefore higher than by the two-dimensional radiography.
Semi-coronal reconstructions are often used for the interpretation, corresponding to the scan plane used by MRI because the cartilaginous SIJ facets are C-shaped and placed obliquely thereby demanding oblique reconstruction for full visualization of the cartilaginous joint compartment. Additional axial or semi-axial reconstructions are needed for adequate assessment of the ligamentous joint compartment posteriorly.
Semi-coronal and axial CT reconstructions in relation to the form and orientation of the cartilaginous joint facet. Erosive changes, joint space alteration and sclerosis (arrows) are seen by both slice orientations, but the cartilaginous joint compartment is best visualized on the coronal reconstruction.