We proposed a new method for the analysis of spinal alignment. Measuring the slope of each vertebral body and plotting it on a diagram enables a clear understanding of the characteristics of the individual whole spinal alignment visually, which includes the magnitude of lordo-kyphosis, apex of curvature, and inflection point. Furthermore, since the measurement is not for a specific section (such as T5-T12 or L1-S1), it is easy to find a portion or degree different from the standard pattern. It also has the potential to classify sagittal alignment by using cluster analysis for the measured spinal slope values of specific sections. This study clarified the difference in spinal alignment between the LORDOSIS and KYPHOSIS groups. This seemed attributable to the difference in T1S associated with the TK difference. No significant between-group difference was observed with respect to LL, TL, or pelvic parameters (PI, PT and SS); however, the lumbar apex level (L3 and L4) was significantly different between groups. These results are also clearly discernible from the shape of the graph. The LORDOSIS group contained older patients with a lower lumbar apex (L4), apparent lordo-kyphosis around the thoracolumbar junction, and a higher TK than the KYPHOSIS group. LL is the sectional angle between the L1 endplate and the S1 endplate, and there was no significant difference between the two groups in this section. However, when the slope of each vertebral body was evaluated, as in this method, the apex level and the inflection point were clearly different. A similar situation was observed with respect to TL alignment. These discrepancies might result from the characteristics of the conventional sectional measurement method. Although there were no significant differences between the TL values of the four groups, the shape of the graph showed clear differences (apparent kypho-lordosis or flat alignment). This is an advantage of this method in that it allows visual evaluation of the entire spine, including each vertebral body element. Roussouly et al. classified lumbar spine alignment of healthy volumteers into four types using apex level, inflection point, number of vertebral bodies in each curvature, total kyphosis and lordosis in degrees, lordosis tilt angle, and the angle of sacral slope . They indicated the difference in apex level and inflection point of each group. Although this study focused on cervical alignment, we observed significant differences in lumbar apex level and lumbar inflection point between the groups, as in their study. This indicates the importance of these parameters in evaluating spinal alignment. The shape of the graph helps clarify individual spinal alignment, including the apex, inflection point, and magnitude of lordosis and kyphosis. Comparing normal spinal alignment patterns and patient patterns makes it easy to understand the alignment of each patient and how much it differs from the normal spine.
Some limitations of our study should be acknowledged. Although this is the first study that analyzed whole spinal alignment with each spinal element, this analysis did not include distance values, such as SVA, or sectional angle values, such as the T1 pelvic angle. Appropriate selection and analysis of spinal elements may allow precise evaluation of spinal alignment and ensure better surgical results. Since the subject of this study was patients who visited our spine clinic and the number of patients in each group may not be sufficient for categorizing or comparing values between the groups in this study, the details of categorization and its characteristics will require a larger study of healthy volunteers in the future. Last, selection bias may have influenced the results because all 88 patients were patients of our hospital, and deformity cases were excluded from this study. The impact of this analysis on the quality of life of patients is unknown.