Background: The correlation between spinal radiographic parameters and severity of cervical spondylotic myelopathy (CSM) is controversial. This study aimed to investigate the associations between spinal radiographic parameters and CSM severity, as well as between cervical and other spinopelvic radiographic parameters. Methods: Patients diagnosed with CSM (N = 118; 77 men) at our hospital from March 2013 to February 2017 were included. The patients’ demographic data and the following radiographic parameters were investigated: cervical lordosis (CL), C2–C7 sagittal vertical axis (C2–C7 SVA), T1 slope, thoracic kyphosis, lumbar lordosis, pelvic incidence, sacral slope, pelvic tilt, and sagittal vertical axis (SVA). Cervical cord compression ratio (CCCR) was evaluated on sagittal magnetic resonance imaging. The Japanese Orthopaedic Association (JOA) scoring system was used for clinical evaluation. Correlation analyses were performed among the clinical and radiographic parameters. Results: The JOA score had the strongest correlation with SVA (r = −0.46, p < 0.01), followed by CCCR (r = −0.33, p < 0.01), CL (r = −0.29, p < 0.01), T1 slope (r = −0.29, p = 0.01), and C2–C7 SVA (r = −0.20, p = 0.03). Multivariate linear regression analysis revealed a model predicting the JOA score; JOA = 13.6 − 0.24 × SVA − 4.2 × CCCR (r = 0.51, p < 0.01). Although there was no significant correlation between the cervical and lumbopelvic radiographic parameters, the sequential correlation among the investigated spinopelvic parameters was identified. Conclusions: CSM severity worsened with spinal malalignment, such as a larger SVA. Though lumbopelvic radiographic parameters did not significantly impact cervical alignment and CSM severity, the sequential correlations among cervical-thoracic-lumbopelvic radiographic parameters were observed. Therefore, SVA is the most relevant radiographic parameter for CSM, but we cannot preclude the possibility that lumbopelvic alignment also affects cervical alignment and CSM severity.
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