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

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 degrees +/- 4.3 degrees; C2C7 Cobb angle, -16.4 degrees +/- 5.6 degrees; OCC2 Cobb angle, -14.5 degrees +/- 3.8 degrees; OCC7 Cobb angle, -29.8 degrees +/- 5.6 degrees; C2C7 Harrison angle, 20.4 degrees +/- 4.3 degrees; and C-7 slope, -25.4 degrees +/- 5.6 degrees. The analysis of these parameters revealed no statistically significant difference between asymptomatic, symptomatic, and post-surgical patients. C-7 sagittal vertical axis (SVA) correlated with the C2C7 Cobb angle (r =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, r =-0.2), lumbar lordosis (LL, r = 0.2), and pelvic tilt (PT, r =-0.2) in cervical symptomatic patients. Irrespective of the patient symptom sub-group (n=420), C1C2 Cobb angle correlated with LL (r =0.1) and C2C7 Harrison angle correlated with PI and PT (r =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 C-7 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.