Fig. 4From: Free-hand technique of C7 pedicle screw insertion using a simply defined entry point without fluoroscopic guidance for cervical spondylotic myelopathy patients with C3 to C6 instrumented by lateral mass screws: a retrospective cohort studyd1: the horizontal distance between Ep A and Ep B; d2: the vertical distance between Ep A and Ep B. The value was positive if Ep A was above Ep B and negative if Ep A was below Ep BBack to article page