Objective To evaluate biomechanical properties of internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate in reconstructing stability of the upper cervical vertebra, and compare them with conventionally used anterior internal fixation after C2-3 intervertebral fusion and posterior internal fixation by C2 transpedicle screws. MethodsSix fresh human upper cervical vertebra specimens (including C2-4) were divided into five groups: the intact specimen group(control group), the incision of the C2-3 group (Hangman group), the posterior internal fixation by C2 transpedicle screw group (posterior fixation group), the anterior internal fixation after C2-3 intervertebral fusion with Zephir plate group (anterior fixation group), and the internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate group (C2-4 incision +internal fixation group). Range of motion (ROM) of the C2-3 and C3-4 segments was tested respectively under 0.5, 1.5 and 2.5 N?m moment by measurement system for three-dimensional spinal movement, and the statistical analysis was also conducted. Results(1) C2-3 segment: ROM of anterior fixation group and C2-4 incision +internal fixation group was significantly smaller than that of Hangman group and posterior fixation group in all six directions under various loading conditions (P<0.05); there was no significant difference between anterior fixation group and C2-4 incision +internal fixation group. ROM of posterior fixation group was larger than that of intact group in all six directions under various loading conditions (P<0.05); There was no significant difference in flexion and extension direction under all loading conditions between posterior fixation group and Hangman group, but significant difference was found in left/right and right/left axial rotation and under 2.5 N?m moment between posterior fixation group and Hangman group (P<0.05). (2) C3-4 segment: there was no significant difference in ROM in six directions under various loading conditions among all groups except for C2-4 incision +internal fixation group. ROM of C2-4 incision +internal fixation group was significantly smaller than that of other groups in all six direction (P<0.05). Although ROM of anterior fixation group was slightly larger than that of Hangman group and posterior fixation group, the difference was not statistically significant. Conclusions From the view of biomechanics, internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate is a better surgical option for stabilizing the fracture than that of posterior internal fixation by C2 transpedicle screws to treat type II Hangman fracture with C2-3 intervertebral disc injury.