Fig. 1

Cervical FSU ROM measured by Cobb angle method. Along the upper endplate of the upper vertebral body and the lower endplate of the lower vertebral body of the surgical segment, we draw two reference lines. The angles between these two reference lines were measured in both the extension and flexion positions of the cervical spine on the radiographs. The angles formed on the lateral flexion radiographs are flexion angle. The angles formed on the extension radiographs are extension angles. The calculation formula is as follows: \({\text{Cervical FSU ROM = Cobb angle in extension position}} - {\text{Cobb angle in flexion position}}\).