[Normative values of cervical sagittal alignment according to the whole spine balance: Based on 126 asymptomatic Chinese young adults].

OBJECTIVE: To explore the normal distribution of cervical sagittal alignment and the relationship between cervical alignment and global spine balance in asymptomatic young adults.
METHODS: A cohort of 272 asymptomatic Chinese adults (including 161 males and 111 females, with an average age of (23.2±4.4) years, ranging from 18 to 45 years) were prospectively recruited from November 2011 to December 2014. The C0-C2 angle, disk angles from C2-C3 to C6-C7, vertebral angles from C3 to C7, T1 slope, thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), C2-C7 sagittal vertical axis (C2-C7SVA), center of gravity of head to C7SVA (CGH-C7SVA), C7-S1SVA were measured and statistically analyzed. All the subjects were categorized with the Roussouly classification and the cervical morphologies were evaluated as lordotic, straight, sigmoid or kyphotic. Spinal sagittal alignment parameters were compared between different sexes and Roussouly classifications with independent student t test, analysis of variance (ANOVA) or Chi-square test. Correlations between cervical sagittal alignment and global spine sagittal alignment were calculated using the Pearson and Spearman correlation coefficient. Linear regression analysis was performed.
RESULTS: Sixty-seven males and 59 females aged from 18 to 30 years old were included in the study. The mean value of C0-C7 was 26.0°±12.8°, composed of 15.2°±6.7° for C0-C2, 9.1°±12.1° for sum of disk angles from C2-C3 to C6-C7, and 1.4°±10.2° for sum of vertebral angles from C3 to C7. C2-C7SVA [(18.6±7.9) mm] and CGH-C7SVA [(22.9±12.3) mm]were offset ideally by C7-S1SVA [(-21.6±31.0) mm]. Males had a larger T1 slope (P < 0.05) and accordingly, a larger cervical lordosis C2-C7 (P < 0.01) and C0-C7 angle (P < 0.01) than females. Males had a smaller C7-S1SVA (P < 0.01) and accordingly, a smaller CGH-C7SVA (P=0.165) than females. Significant difference was found between cervical alignment of different Roussouly types (P < 0.01). In general, a larger LL was consistent with a set of larger TK, C2-C7angle, C0-C7 angle, and vice versa. There was no significant correlation between cervical morphology and the Roussouly classification (Chi-square=10.548, P=0.308). There was significant correlation between cervical alignment and T1 slope (P < 0.01), TK (P < 0.01). There was significant correlation between adjacent segmental angles from T1 slope up to C0-C2 angle (P < 0.05).
CONCLUSION: Normative values of each vertebral angle and disk angle were established. The cervical lordosis occurred mainly at C0-C2 and disk levels, which was influenced by parameters of other parts of the spine, such as T1 slope, TK and the Roussouly classification. There was significant correlation between adjacent disk angles.