Reliability analysis of spino-pelvic parameters in adult spinal deformity: A comparison of whole spine and pelvic radiographs

Study Design. Retrospective study. Objective. To examine the reliabilities of sagittal spino-pelvic alignment measurements using whole spine-pelvic and local pelvic radiographs and to determine whether spinal deformity affects these reliabilities. Summary of Background Data. Sagittal spino-pelvic alignment is important in adult spinal deformity patients (ASD). Spino-pelvic parameters are closely related to health-related quality of life and indispensable for surgical planning. However, few studies have focused on the reliability of these measurements. Methods. Three spino-pelvic parameters, pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) were measured in 2 patient groups: 33 adult scoliosis (AS) and 33 nondeformity (ND) patients, using whole spine-pelvic lateral radiographs (whole spine radiographs) and local pelvic lateral radiographs (local pelvic radiographs), by 5 experienced spine surgeons. Intra- and interobserver reliabilities for each procedure were evaluated by intraclass correlation coefficients (ICC). The interobserver reliability differences between the 2 procedures were statistically evaluated. The difference between the largest and smallest measurements among the 5 observers was also evaluated in the AS and ND groups. Results. Measurement of the 3 parameters using whole spine or local pelvic radiographs showed good to excellent intraobserver reliability (range of ICC: 0.820-0.935). The interobserver reliabilities of PI and PT from local pelvic radiographs were significantly higher than those from whole spine radiographs (P<0.002). The intraobserver reliabilities of PI and PT from pelvic radiographs tended to be higher than those from whole spine radiographs, but the differences were not statistically significant. The reliability of SS was comparable between the 2 methods. The differences between the highest and lowest PI and PT measurements were smaller with the pelvic compared to whole spine radiographs. These findings were consistent in the AS and ND groups. Conclusion. Local pelvic radiography is more reliable than whole spine radiography for determining spino-pelvic parameters, and we recommend its use for evaluating ASD patients.