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

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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°; OCC2 Cobb angle, −14.5°±3.8°; OCC7 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 (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 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.

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