Analysis of Parameters That Can Predict the Cervical Sagittal Vertical Axis in Cervical Fusion Surgery

OBJECTIVE: The absolute value of the cervical sagittal parameters cannot be guaranteed with certainty on all follow-up cervical radiographs. With the assumption that neck posture changes can occur at any time at each follow-up radiographic session, we examined whether the sagittal parameters change meaningfully and identified the factors most closely related to the C2-C7 sagittal vertical axis (SVA). METHODS: We enrolled 200 patients who had undergone either anterior cervical fusion (n = 100) or posterior cervical fusion (n = 100). The craniovertebral angle (CVA), mandible angle (MA), occipital slope (Os), C2 slope (C2s), C7 slope (C7s), and C2-C7 SVA were measured on 2 different follow-up radiographs after surgery. The C2-C7 angle (C2-C7A) and changes (Delta) in the sagittal parameters between the 2 radiographs were then calculated. RESULTS: The Delta C2s and Delta CVA showed a very strong correlation with the Delta C2-C7 SVA (r = 10.70-0.931). An independent t test showed a statistically significant difference for multiple sagittal parameters (i.e., Delta MA, .Delta Os, Delta C2s, Delta C7s, and Delta CVA) between the large and small Delta C2-C7 SVA groups. In contrast, the change in the C2- C7A was without statistical significance. A stepwise multivariate regression analysis revealed a high adjusted R2 value (0.841) between the Delta C2-C7 SVA and 2 parame- ters (standardized coefficient: Delta CVA, - 0.563; Delta C2s, - 0.398). CONCLUSIONS: During cervical fusion surgery, the CVA was the most predictable parameter reflecting the C2-C7 SVA in various analyses. The upper cervical parameters (Os and C2s) provided more explanatory power regarding the C2-C7 SVA changes than did the lower cervical parameter (C7s) or the presence of cervical lordosis (C2-C7A).

Automated summary

Through follow-up X-ray examinations of 200 cervical surgery patients, it was found that CVA is the most predictable parameter for C2-C7 SVA, and upper cervical parameters are more explanatory for C2-C7 SVA changes than lower cervical parameters.