Abstract
Objective
Developing and validating a novel parameter, the modified C2–C7 Cobb angle, as a feasible substitute for the traditional method in assessing cervical sagittal alignment, and exploring its reference range through a large-scale retrospective study.
Methods
The visibility of the C6, C7 upper, and C7 lower endplates was graded and compared. Baseline data such as height, weight, body mass index (BMI), age, and gender were analyzed for their impact on the visibility of the C7 lower endplate. Values of C2-6 Cobb angle, C2-7 Cobb angle, and modified C2–C7 Cobb angle were measured. The intra- and interobserver reliability, differences, and efficacy of evaluation on cervical lordosis of the parameters were compared, and the correlations among the parameters were analyzed. Furthermore, reference ranges for the modified C2–C7 Cobb angle were established based on lateral cervical spine X-rays of 825 asymptomatic Chinese adults across different age groups and genders.
Results
The visibility of the C7 lower endplates was significantly reduced compared to the C6 lower and C7 upper endplates. Age, weight, BMI, and male gender were identified as factors negatively influencing the visibility of the C7 lower endplate. Both intra-observer and inter-observer reliability demonstrated excellence for all tested parameters. The linear regression model unveiled a stronger association of the modified C2–C7 Cobb angle with the C2-7 Cobb angle compared to the C2-6 Cobb angle. Furthermore, the modified C2-7 Cobb angle exhibited excellent efficacy in evaluating cervical lordosis. Age displayed a positive correlation with the modified C2–C7 Cobb angle, and across every age bracket from 20 to 69 years, males exhibited a higher mean modified C2-7 Cobb angle compared to females.
Conclusion
The visibility of the C7 lower endplate diminishes with increasing age, weight, BMI, and male gender. In cases where the C7 lower endplate is unclear, the modified C2–C7 Cobb angle emerges as a reliable method for estimating cervical sagittal morphology. Reference ranges for the modified C2–C7 Cobb angle were established across various age groups and genders among asymptomatic Chinese adults, offering a valuable resource to guide therapeutic interventions for cervical spine disorders and deformities.