Determining the Reference Values of the Measurements of Cervical Sagittal Alignment Using the Extrapolated Norms...

To investigate the feasibility of the extrapolated norms (e-norms) method for establishing a reference range for the measurements of cervical sagittal alignment and to explore the differences in these ranges according to sex and age.

We applied the e-norms method to calculate reference values for the angle between occipital and C2 vertebrae, C2-7 Cobb angle, C2-7 sagittal vertical axis, and C7 slope in 1720 subjects. The e-norms values of these measurements were measured in different age subgroups of male or female subjects.

According to the data points within the plateau obtained via e-norms method, normal angle between occipital and C2 vertebrae was 18.5± 2.6°, C2-7 Cobb angle was 8.8± 4.5°, C2-7 sagittal vertical axis was 1.5± 0.4 cm, and C7 slope was 20.1± 3.5°. These data points involved a total of 1617 (1617/1720, 94.0%) subjects, with only 191 (11.1%, 191/1720) subjects having all the cervical sagittal measurements included in the plateau. Both C2-7 Cobb angle and C7 slope e-norms values increase with age in females, whereas only C7 slope e-norms values increase with age in males. The males showed greater e-norms values in at least one of cervical sagittal measurements compared with females in different age subgroups (P < 0.05).

This study demonstrated that e-norms may be a simple, reliable and cost-saving approach for establishing reference values for cervical sagittal measurements. This new method allows us to establish reference values for sex or age subgroups to study the sex differences and trends with age of cervical sagittal alignment.