The reliability of sagittal pelvic parameters: the effect of lumbosacral instrumentation and measurement experience.

Abstract

Sagittal pelvic parameters (SPPs) of a representative patient sample drawn from a consecutive adult spinal deformity database were measured using Surgimap Spine. Estimated coefficient of reliability intraclass coefficient (95% confidence interval), standard error of measurement, and mean absolute deviation were used for the analysis. The primary objective of this study was to assess the reliability of SPP measurements using Surgimap Spine. The secondary objective was to evaluate the impact of pelvic instrumentation as well as the impact of user expertise. The radiographical measurement of SPP is increasingly recognized as playing a critical role in establishing the surgical goals and surgical strategy of many spinal disorders. Although instrumented flatback is a common cause of sagittal malalignment, to our knowledge, SPP measurement reliability has never been assessed in instrumented spines. Sixty-three adult full-spine standing lateral radiographs (31 with lumbosacral instrumentation) were measured twice by 13 observers using Surgimap Spine. Observers were stratified into 3 levels of experience: high (research coordinators, 4), mid (senior surgeons, 5), and low (junior surgeons, 4). Research coordinators trained all surgeons for less than 30 minutes. Parameters measured were pelvic incidence, pelvic tilt, and sacral slope. Thirteen observers and 63 radiographs generated 817 observations (2 misses). Overall inter- and intraobserver reliability of SPP measurement was excellent (intraclass coefficient > 0.85). Lumbosacral instrumentation did not modify intraobserver reliability but reduced significantly interobserver reliability of pelvic tilt (P = 0.006) and sacral slope (P = 0.007). Experience did not affect intraobserver reliability but interobserver reliability of highly experienced observers was significantly lower (P < 0.05) than among less experienced observers. Measurement of SPP using Surgimap Spine equals or improves previously reported reliability data. Lumbosacral instrumentation reduces interobserver reliability taking it from excellent to moderate in the sacral slope measurement. Inexperienced observers can measure SPP reliably after a short tutorial. 4.