BACKGROUND:C2 transpedicle screw fixation for Hangman fractures has been paid more attention due to reliability and no loss of physiological function.However,there are lacks of biomechanical evidences for indication treatment because the fixation is single segmental.OBJECTIVE:To investigate the biomechanical stability of C2 transpedicle screw fixation for Hangman fractures.DESIGN,TIME and SEITING:This was a contrast study which was performed at the General Key Laboratory of Biomechanics,First Military Medical University of Chinese PLA from May to August 2004.MATERIALS:AO-universal titanium alloy transpedicle screw of 18 25 mm in length and 3.5 mm in diameter was adopted in this study.Six fresh C1-C4 cervical vetebrae samples were ordiually made into type Ⅰ,ⅡA,and Ⅱ Hangman fracture models.METHODS:After transpedicle screw fixation.Hangman fracture models were measured by non-destroyed style with spinal anterior flexion/posterior extension,left/right lateral curvature,and left/right axial direction.Loading/unlonding circulation was performed three times during each testing.Kinematics indicators were measured on the 3rd circulation.MAIN OUTCOME MEASURES:Spinal motor images at zero load and maximal load were obtained with laser photoscanning(0.1% in precision),and the corresponding systematic software was adopted to calculate 3D range of movement.RESULTS:The relative stability of type Ⅰ Hangman fracture models after C2 transpedicle screw fixation was 100.62%(inflexion),96.91%(posterior extension),99.19%(lateral curvature),and 97.12%(rotation)as compared to control group (P＞0.05).The relative stability of type Ⅱ Hangman fracture models after C2 transpedicle screw fixation was 47.84%(inflexion),21.29%(posterior extension),65.98%(lateral curvature),and 41.69%(rotation)as compared to control group (P＜0.05).CONCLUSION:Biochemical evaluation suggests that type Ⅰ and Ⅱ A Hangman fractures do fit for C2 transpedicle screw fixation,and the fixation may generate well physiological fixation or stability.However,stability of type Ⅱ Hangman fracture is poor,so it is not suitably adopted single transpedicle screw fixation.