The Impact of Upper Cervical Spine Alignment on Patient-reported Outcome Measures in Anterior Cervical Decompression and Fusion

Study Design: This was a retrospective cohort study. Objective: To determine the extent to which the upper cervical spine compensates for malalignment in the subaxial cervical spine, and how changes in upper cervical spine sagittal alignment affect patient-reported outcomes. Summary of Background Data: Previous research has investigated the relationship between clinical outcomes and radiographic parameters in the subaxial cervical spine following anterior cervical discectomy and fusion (ACDF). However, limited research exists regarding the upper cervical spine (occiput to C2), which accounts for up to 40% of neck movement and has been hypothesized to compensate for subaxial dysfunction. Materials and Methods: Patients undergoing ACDF for cervical radiculopathy and/or myelopathy at a single center with minimum 1-year follow-up were included. Radiographic parameters including cervical sagittal vertical axis, C0 angle, C1 inclination angle, C2 slope, Occiput-C1 angle (Oc-C1 degrees), Oc-C2 degrees, Oc-C7 degrees, C1-C2 degrees, C1-C7 degrees, and C2-C7 degrees cervical lordosis (CL) were recorded preoperatively and postoperatively. Delta (Δ) values were calculated by subtracting preoperative values from postoperative values. Correlation analysis as well as multiple linear regression analysis was used to determine relationships between radiographic and clinical outcomes. Alpha was set at 0.05. Results: A total of 264 patients were included (mean follow-up 20 mo). C2 slope significantly decreased for patients after surgery (Δ=-0.8, P=0.02), as did parameters of regional cervical lordosis (Oc-C7 degrees, C1-C7 degrees, and C2-C7 degrees; P<0.001, <0.001, and 0.01, respectively). Weak to moderate associations were observed between postoperative CL and C1 inclination (r=-0.24, P<0.001), Oc-C1 degrees (r=0.59, P<0.001), and C1-C2 degrees (r=-0.23, P<0.001). Increased preoperative C1-C2 degrees and Oc-C2 degrees inversely correlated with preoperative SF-12 Mental Composite Score (MCS-12) scores (r=-0.16, P=0.01 and r=-0.13, P=0.04). Cervical sagittal vertical axis was found to have weak but significant associations with Short Form-12 (SF-12) Physical Composite Score (PCS-12) (r=-0.13, P=0.03) and MCS-12 (r=0.12, P=0.05). Conclusion: No clinically significant relationship between upper cervical and subaxial cervical alignment was detected for patients undergoing ACDF for neurological symptoms. Upper cervical spine alignment was not found to be a significant predictor of patient-reported outcomes after ACDF. Level of Evidence: Level III.