Novel Angular Measures of Cervical Deformity Account for Upper Cervical Compensation and Sagittal Alignment

Study Design: This is a retrospective review of a prospective multicenter database. Objective: This study introduces 2 new cervical alignment measures accounting for both cervical deformity (CD) and upper cervical compensation. Summary of Background Data: Current descriptions of CD like the C2-C7 sagittal vertical axis (cSVA) do not account for compensatory mechanisms such as C0-C2 lordosis and pelvic tilt, which makes surgical planning difficult. The craniocervical angle (CCA) combines the slope of McGregor's line and the inclination from C7 to the hard palate. The C2-pelvic tilt (CPT) combines C2 tilt and pelvic tilt. Like the T1 pelvic angle, CPT is less affected by lower extremity and pelvic compensation. Methods: Novel and existing CD measures were correlated in 781 patients from a thoracolumbar deformity (TLD) database and 61 patients from a prospective CD database. CD patients were subanalyzed by region of deformity driver: cervical or cervico-thoracic junction. TLD patients were substratified according to whether or not they had CD as well, where CD was defined as cSVA > 4 cm or T1 slope minus cervical lordosis mismatch (TS-CL) > 20. Results: TLD cohort: mean cSVA was 31.7 +/- 17.8 mm. Subanalysis of TLD patients with CD versus no-CD demonstrated significant differences in CCA (56.2 vs. 60.6, P < 0.001) and CPT (32.6 vs. 19.3, P < 0.001). CCA and CPT correlated with cSVA (r = -0.488/r = 0.418, P < 0.001) and C0-C2 lordosis (r = -0.630/r = 0.289, P < 0.001). CD cohort: mean cSVA was 47.3 +/- 32.2 mm. CCA and CPT correlated with cSVA (r = -0.811/r = 0.657, P < 0.001) and C0-C2 lordosis (r = -0.656/r = 0.610, P < 0.001). CD cohort subanalysis indicated that CT patients were significantly more deformed by cSVA (71.3 vs 24.0 mm, P < 0.001), CCA (47.1 vs 59.1 degrees, P < 0.001), and CPT (63.3 vs 43.8 degrees, P = 0.002). Using linear regression analysis, cSVA of 4 cm corresponded to CCA of 53.2 degrees (r(2) = 0.5) and CPT of 48.5 degrees (r(2) = 0.4). Conclusions: CCA and CPT account for both cervical sagittal alignment and upper cervical compensation and can be utilized in assessment of cervical alignment.