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.