[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 C-C angle, disk angles from C-C to C-C, vertebral angles from C to C, T slope, thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), C-C sagittal vertical axis (C-CSVA), center of gravity of head to CSVA (CGH-CSVA), C-SSVA 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 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 C-C was 26.0°±12.8°, composed of 15.2°±6.7° for C-C, 9.1°±12.1° for sum of disk angles from C-C to C-C, and 1.4°±10.2° for sum of vertebral angles from C to C. C-CSVA [(18.6±7.9) mm] and CGH-CSVA [(22.9±12.3) mm]were offset ideally by C-SSVA [(-21.6±31.0) mm]. Males had a larger T slope ( < 0.05) and accordingly, a larger cervical lordosis C-C ( < 0.01) and C-C angle ( < 0.01) than females. Males had a smaller C-SSVA ( < 0.01) and accordingly, a smaller CGH-CSVA (P=0.165) than females. Significant difference was found between cervical alignment of different Roussouly types ( < 0.01). In general, a larger LL was consistent with a set of larger TK, C-Cangle, C-C angle, and vice versa. There was no significant correlation between cervical morphology and the Roussouly classification (Chi-square=10.548, =0.308). There was significant correlation between cervical alignment and T slope ( < 0.01), TK ( < 0.01). There was significant correlation between adjacent segmental angles from T slope up to C-C angle ( < 0.05).

CONCLUSION

Normative values of each vertebral angle and disk angle were established. The cervical lordosis occurred mainly at C-C and disk levels, which was influenced by parameters of other parts of the spine, such as T slope, TK and the Roussouly classification. There was significant correlation between adjacent disk angles.