The Sagittal Balance of the Cervical Spine: Radiographic Analysis of Interdependence between the Occipitocervical and Spinopelvic Alignment

Abstract

Study Design: This was a prospective clinical study.Purpose: Previous studies have indicated that cervical lordosis is a parameter influenced by segmental and global spinal sagittal balance parameters. However, this correlation still remains unclear. Therefore, a better understanding of the normal values and interdependencies between inter-segmental alignment parameters is needed. This is a preliminary analysis that helps to understand these factors.Overview of Literature: Change in global sagittal alignment is associated with poor health-related quality of life. Questions regarding which parameters play the primary roles in the progression of spinal sagittal imbalance and which might be compensatory factors remain unanswered.Methods: Prospectively, 420 adults (105 asymptomatic, 105 cervical symptomatic, 105 lumbar symptomatic, and 105 post-surgical) were selected. Whole-spine standing lateral radiographs were taken, and spinopelvic, thoracic, and cervical parameters were measured. Then, the data were analyzed using correlation coefficient test and multiple regression analysis.Results: All the parameters showed a normal distribution. The mean values of the cervical parameters are as follows: C₁C₂ Cobb angle, −27.07°±4.3°; C₂C₇ Cobb angle, −16.4°±5.6°; O_CC₂ Cobb angle, −14.5°±3.8°; O_CC₇ Cobb angle, −29.8°±5.6°; C₂C₇ Harrison angle, 20.4°±4.3°; and C₇ slope, −25.4°±5.6°. The analysis of these parameters revealed no statistically significant difference between asymptomatic, symptomatic, and post-surgical patients. C₇ sagittal vertical axis (SVA) correlated with the C₂C₇ Cobb angle (<i>r</i> =0.7) in all groups. No significant correlation was noted between cervical and spinopelvic parameters in asymptomatic patients. However, C₁C₂ Cobb angle correlated significantly with pelvic incidence (PI, <i>r</i> =−0.2), lumbar lordosis (LL, <i>r</i> =0.2), and pelvic tilt (PT, <i>r</i> =−0.2) in cervical symptomatic patients. Irrespective of the patient symptom sub-group (n=420), C₁C₂ Cobb angle correlated with LL (<i>r</i> =0.1) and C₂C₇ Harrison angle correlated with PI and PT (<i>r</i> =0.1).Conclusions: Our results indicate significant interdependence between the spinopelvic and cervical alignment, especially in cervical symptomatic patients. In addition, strong correlation was found between the C₇ SVA and C₂C₇ Cobb angle. Overall, the results of this study could help to better understand the cervical sagittal alignment and serve as preliminary data for planning surgical reconstruction procedures.