How does cervical and cervicothoracic alignment impact horizontal gaze?

Background: Cervical sagittal alignment maintains horizontal gaze, supports the axial load of the skull, and has a reciprocal relationship to the cervicothoracic sagittal alignment. Studies are being conducted on different ethnicities, but little literature exists about cervical sagittal alignment and correlation chains in the Indian population. Therefore, we decided to study the impact of cervical and cervicothoracic alignment on horizontal gaze.

Methods: This is a retrospective cross-sectional study where an asymptomatic adult population from India was enrolled between 18 and 50 years old. The following parameters were measured on lateral cervical x-ray: McGregor slope (McGS), C0-C2 angle, C1-C2 angle, C2 slope, Cervical Lordosis (CL) C2-C7, C7 slope, sagittal vertical axis C2-C7, thoracic inlet angle, neck tilt and T1 slope (T1S). The results were stratified in upper and lower cervical alignment, cervicothoracic alignment, and horizontal gaze parameters (McGS) using Pearson's correlation coefficient.

Results: One hundred and four individuals were included. C7 Slope strongly correlated with T1S (r = 0.675, P = 0.000) and a chain of correlation was found between T1S with CL: C2-C7 (r = --0.602), then C0-C2 angle (r = --0.483) and C1-C2 angle (r = --0.592), finally, the McGS (Horizontal Gaze) (r = -0.709), all with P ≤≤ 0.000. The highest correlation was between the C2 Slope and T1S - CL mismatch (r = -0.946, P = 0.000).

Conclusion: In the Indian population, a statistically significant correlation chain was found between the upper and lower cervical alignment parameters, cervicothoracic alignment parameters, and horizontal gaze parameters. T1S and C7 Slope are the foundation for starting this correlation chain between the cervical sagittal alignment and the horizontal gaze. In addition, a very important role of the C2 Slope in the cervical sagittal alignment was observed.