Effects of mirror placement on sagittal alignment of the spine during acquisition of full-spine standing X-Rays

Abstract

The line of sight when whole-spine radiographs are taken has not been defined. In our 2012 health screening study (TOEI study), whole-spine radiographs were taken with the volunteers in the most relaxed position and with a horizontal gaze. However, in the TOEI 2014 study, a mirror was placed in front of their faces to unify their line of sight. To our knowledge, there are no reports on how the sagittal alignment changes when radiographs are taken using a mirror. The purpose of this study was to investigate how mirror placement impacted sagittal spinal alignment in whole-spine radiographs taken while standing. Volunteers who participated in both the TOEI 2012 and 2014 studies were recruited. Pelvic tilt (PT), lumbar lordosis (LL), thoracic kyphosis (TK), cervical lordosis (CL), slope of McGregor's line (McGS), and C7 sagittal vertical axis (C7 SVA) were examined using software. Three hundred fifty-four volunteers (142 males, 212 females, average age in 2012: 72years) whose radiographs were evaluated in both previous studies were enrolled. The average parameters of 2012 and 2014 were: PT: 18° and 21° (P<0.01), LL: 40° and 40°, TK: 34° and 34°, CL: 13° and 23° (P<0.01), McGS: 2°±11° and -9°±8° (P<0.01), and C7 SVA: 46 and 23mm (P<0.01), respectively. In the Levene test, the McGS variation in 2014 [95% confidence interval (CI) 0.9-3.4] was significantly smaller than that in 2012 (95% CI -9.7 to -8.0, P<0.01). The smaller McGS variation in the TOEI 2014 study suggested that mirror placement could standardize the head's position. These results showed that the mirror placement retroflexed cervical alignment and caused the head to lean backward. It is important that a mirror is placed to unify the line of sight.