Comparison of pelvic incidence measurement using lateral x-ray, standard ct versus ct with 3d reconstruction

Pelvic incidence (PI) is a position independent parameter used to quantify spinopelvic sagittal balance. PI is generally measured on lateral radiographs, but more recent studies have suggested better accuracy with standard CT scans versus three-dimensional (3D) CT scans. This study compares PI obtained from lateral XR, standard CT scan and CT scan with 3D reconstruction.

A total of 77 subjects with lateral XRs of the pelvis or lumbosacral spine and CT scans of the pelvis were randomly selected. Pelvic incidence on lateral XRs, standard CT scans and CT scans utilizing multiplanar reconstruction were measured and compared using intraclass correlation coefficients (ICC). PI was also measured on serial images in 28 individuals using the same imaging modality within 3 years and evaluated using ICC.

Mean ± SD of PI measurements on XR, standard CT and CT with 3D reconstruction were 56° ± 13°, 53° ± 12° and 53° ± 12°, respectively, demonstrating a small but significant elevation of PI measurement on XR (P < 0.001). ICC values demonstrated a higher correlation between standard CT and 3D CT (ICC 0.986), compared to XR and standard CT (ICC 0.934) and XR and 3D CT (ICC 0.937). PI measurements on repeated imaging of the same individual also demonstrated that both CT methods produced more consistent measurements (ICC 0.986 for standard CT, 0.981 for 3D CT, 0.935 for XR).

Although standard XR does provide a high level of reliability, it appears to slightly overestimate PI. CT scans do provide increased reliability, with no additional benefit of 3D reconstructions over standard CT.