A biomechanical investigation of different screw head designs for vertebral derotation in scoliosis surgery

The screw head design played an important role in the efficiency and variance of the derotation during the DVD maneuver. The derotational efficiency of the newly designed uniplanar screw was closer to that of the monoaxial screw group than to that of the polyaxial screw group. The polyaxial screw was inferior to DVD owing to a derotational variance between the derotational tube and the apical body that was correlated with the range of motion of the screw head. In the present study, the pedicle strain was similar in all groups. However, the pedicle strain of the uniplanar screw group was lower than that of the monoaxial screw group and was similar to that of the polyaxial screw group when the angle of rotation of the apical body increased.