Physiologic Cervical Alignment Change Between Whole Spine Radiographs and Normal Standing Cervical Radiographs

BACKGROUND: The objective of this study was to evaluate the physiologic change of cervical spine (CS) alignment between 2 radiographs (whole spine [WS] and CS). METHODS: Multilevel cervical segmental angles (horizontal gaze, C2 slope, C7 slope, and T1 slope) were measured, and C0-2 angle, C0-7 angle, and C2-7 angle were also calculated.The relative translation statuses of C2-7 sagittal vertical axis and C0-7 sagittal vertical axis were measured, RESULTS: Generally, statistically significant differences were found for occipitalslope (Delta 7.1 degrees) and C7 slope (Delta 2,1 degrees), and these results induced a significant C0-2 angle (Delta 4.6 degrees) and nonsignificant C2-7 angle (Delta 1.2 degrees) change between the 2 types of radiographs. In the fixed horizontal gaze group analysis, C7 slope and C2-7 angle were significantly different between WS and CS radiographs. In the nonfixed horizontal gaze group analysis, C7 slope exhibited significant upward movement (Delta 3.7), and C7 slope did not showed significant change (Delta 0.1 degrees), which caused the constant value of cervical lordosis (C2-7 angle) between the 2 radiographs (P = 0.084), CONCLUSIONS: Horizontal gaze fixation may induce untruthful results of cervical lordosis (C2-7 angle) and a nonphysiologic distribution ratio of cervical lordosis (C0-2 angle, 92% vs. C2-7 angle, 8%), However, if the horizontal gaze is not controlled, WS radiographs exhibit a constant value of the C7 slope compared with CS radiographs, which may induce the unchanged state of cervical lordosis and physiologic distribution ratio of cervical lordosis (C0-2 angle, 74% vs. C2-7 angle, 26%).