Impact of Cervical Sagittal Alignment Parameters on Neck Disability.

STUDY DESIGN Retrospective cross-sectional study. OBJECTIVE Determine if pre-operative cervical alignment serves as an independent predictor of pre-operative disability as measured by the neck disability index (NDI). SUMMARY OF BACKGROUND DATA There is growing interest in the relationship between cervical sagittal alignment and clinical outcomes. While prior studies have shown that C2-C7 sagittal vertical axis (SVA) correlates with worse NDI scores in post-operative patients, no studies to date have examined the impact of cervical sagittal parameters on pre-operative disability in patients indicated for surgery. METHODS Patients with pre-operative standing cervical radiographs, no prior cervical spine procedures and a pre-operative NDI score were identified. Measurements were made by two observers at two different time points. Parameters measured were: Occiput-C2 angle, C1-C2 angle, C2-C7 angle (CL), T1 slope (TS), TS minus CL (TS-CL), C2-C7 SVA, and C1-C7 SVA. Intra- and inter-observer reliability was calculated. Subgroup analyses of myelopathy vs. radiculopathy and deformity vs. no deformity was performed. A multivariate linear regression was performed. RESULTS Ninety patients were included. Indications included cervical myelopathy (n = 63), cervical radiculopathy (n = 25), cervical stenosis (n = 9), and others (n = 5). CL averaged -13.7 ± 14.9 degrees. TS averaged 30.7 ± 10.4 degrees and C2-C7 SVA averaged 28.8 ± 13.2  mm. Intra- and inter-observer reliability was good to excellent (ICC > 0.8). Increasing CL (r = 0.277, P = 0.009), increasing TS (r = -0.273, P = 0.011) and increasing TS-CL (r = -0.301, P = 0.005) were correlated with decreasing NDI. CL, TS and TS-CL were also strongly correlated with each other (r > 0.65, P < 0.001 for all bivariate correlations). A multivariate regression adjusting for age and indication showed TS-CL (P = 0.040) and C2-C7 SVA (P = 0.015) were independent predictors of NDI. CONCLUSION Increasing CL, increasing TS and increasing TS-CL are correlated with decreasing pre-operative NDI. Low TS-CL and high C2-C7 SVA are independent predictors of high pre-operative NDI. LEVEL OF EVIDENCE 4.