LAUSR

Study Design: A cross-sectional study. Objective: To identify the best indicator for reproducible representation of craniocervical sagittal balance (CCSB). Summary of Background Data: Spinal sagittal balance is considered one of the most critical factors affecting the health-related quality of life. Although standard indicators of spinopelvic balance have been established, these do not include the craniocervical balance and there is no standard parameter for evaluating the CCSB. Materials and Methods: Six kinds of sagittal vertical axis (SVA) were drawn by a total of 9 spine or orthopedic surgeons, from the anterior margin of the external auditory canal: cranial center of gravity (CCG), C1 (center of the anterior arch), C2 (C2vb: center of the vertebral body, C2e: center of the lower endplate), and C7 (C7vb: center of the vertebral body, C7p: posterosuperior corner). Eight SVA distances were measured by using 30 radiographs; CCG–C7vb, C1–C7vb, C2e–C7vb, C2vb–C7vb, CCG–C7p, C1–C7p, C2e–C7p, and C2bv–C7p.The interobserver and intraobserver reliabilities, and the correlations between CCG and C1, C2e, or C2bv were calculated among the main groups or subgroups. Results: In the overall analysis, although the intraclass correlation coefficients (ICC) (1, 1) of all parameters were >0.900, the ICC (2, 1) of CCG–C7p and CCG–C7vb were <0.900. The same trends were noted in the subgroups based on observer’s experience. Comparing C7p-related and C7vb-related parameters, ICC (2, 1) showed 0.901 in C7p-related and 0.849 in C7bv-related parameters. In the analysis of the correlation between cranial SVAs, C1–C7p and C2vb–C7p SVAs correlated highly with CCG–C7p SVA (0.905, 0.805, respectively). Conclusions: Although the CCG SVA represents the center of the head, the current results revealed its low reproducibility. The low values were notable in those unfamiliar with craniocervical anatomy. The correlation analysis indicated that C1–C7p and C2vb–C7p SVA parameters are suitable for CCG–C7p SVA. Therefore, these 2 are considered as possible standard parameters in evaluating CCSB. Level of Evidence: Level III.