PURPOSE

To determine the reliability of sagittal radiographic variables across multiple positions and radiographic views and to correlate measures obtained on anteroposterior (AP) radiographs to lateral pelvis imaging.

METHODS

Subjects undergoing hip surgery with complete AP and lateral pelvic imaging were included. Images were evaluated by 4 independent reviewers. Sagittal radiographic variables included the sacral slope, spinopelvic tilt (SPT), anterior pelvic plane (APP), pelvic inclination, and pelvic incidence. AP pelvic measures of sagittal pelvic position included the sacrococcygeal to pubis distance (SC distance) and the trans-teardrop to pubis ratio. Interobserver reliability for each measure was evaluated through the intraclass correlation coefficient (ICC). Bivariate linear correlations between AP and lateral standing, supine, and sitting images were obtained.

RESULTS

In total, 60 subjects who underwent hip surgery with complete AP and lateral pelvic imaging were included. The sacral slope and SC distance showed excellent reliability (ICC >0.90) across all positions. Additional parameters showed good reliability (ICC >0.85) in standing and supine positions, with moderate-to-good reliability (ICC 0.76-0.79) for the APP, SPT, and pelvic inclination in the sitting position. Measures of pelvic tilt on AP radiographs had variable correlations to sagittal parameters, with the strongest correlation occurring between the SC distance and sacral slope in the supine and standing positions (r = 0.72 and 0.70, respectively; < .001 for both positions).

CONCLUSIONS

Spinopelvic radiographic parameters are reliable in the supine and standing positions. The APP, SPT, and pelvic inclination had lower reliability when compared with the sacral slope in the sitting position. There were significant correlations between multiple spinopelvic parameters on the AP and lateral radiographs, the strongest of which were between the SC distance and sacral slope. These findings support the routine evaluation of positional spinopelvic parameters before both hip-preservation and reconstruction surgery.

CLINICAL RELEVANCE

Evaluation of spinopelvic parameters across multiple functional positions will increase the understanding of dynamic hip motion as it relates to the lumbar spine and pelvis.