| 1. ObjectivesFor the past few years patients with Hangman's Fracture increased gradually because of the deceleration injury and the fall injury,and more surgeon claimed early surgery for these patients.Nevertheless, choice for different surgeries has still more dispute,and their Biomechanical Evaluation all are technically demanding and requiring considerable experience. This study aimed to set up the model of different type Hangman's Fracture,and then perform different surgeries,evaluated their biomechanics stability and the biomechanical fixation intensity of C2 pedicle screw through the experiment on screw pull-out strength(AU these experiment is based on our clinic use of posterior cervical oligo-segmental fixation for Hangman's Fracture )Including:l.To establish different type Hangman's fracture model made on the diagnostic standard established by Levine-Edwards and evaluate their biomechanical stability.2.To evaluate the indication of uni-segment transpedicle fixation for treament of Hangman's fracture.3.To evaluate the biomechanical stability of three different inter-segment internal fixation for treament of unstable Hangman's fracture.4. To evaluate the biomechanical fixation intensity of C2 pedicle and C2 lateral mass screw through the experiment on screw pull-out strength to provide the biomechanical performance for choice of different internal fixation method.2. Materials and Methods1. Eight fresh adult human cervical specimen was simulated to establish different type Hangman's fracture model made on the diagnosticstandard established by Levine-Edwards, and then perform different internal fixation method. ROM of each state was tested to compare their three-dimensional motion stability.Their were divided to ten groops: (1) control(intact); (2) Type I Hangman's fracture; (3) Transpedicle screw fixtion in Type I fracture;(4)Type IIA Hangman's fracture; (5)Transpedicle screw fixtion in Type IIA Hangman's fracture; (6)Type II Hangman's fracture(7)Transpedicle screw fixtion in Type II Hangman's fracture(Becase type IE Hangman's fracture can't be simulated in this experiment,so we didn't test its ROM);(8)C2-3 pedicular-lateral mass plate fixtion in TypeIII Hangman's fracture;(9)Anterior titanium locking screw plate fixtion in Type III Hangman's fracture;(10) Anterior trans-vertebrane screw fixtion in Type III Hangman's fracture.The atlantoaxial motion segment was tested by a non-destructive flexibility method using a nonconstrained testing apparatus (MTS-858,USA).The pure moment was applied to 2.0Nm.The ROM of C2-3 motion segament was measured.With the flexion-extension,lateral bending and axial rotation ROMs of these ten groups compared each other,the stability of C2-3 using various internal fixations was analyzed.2. Eight fresh adult human C2 -C3 specimen and the fractured C2 specimen of three dimensional ROM test was designed to compare screw pull-out strength (tested by sensor) of C2 and C3.They were divided into Eight groups:(1)C2 vetebraa screw;(2)C2 uni-cortical pedicle screws;(3)C2 bi-cortical pedicle screws;(4)Hangman's fracture C2 uni-cortical pedicle screws;(5) Hangman's fracture C2 bi-cortical pedicle screws;(6)C3 vetebraa screw;(7)C3 uni-cortical lateral mass screws;(8)C3 bi-cortical lateral mass screws.Test speed was lmm/min with maximum pull strengh being 3000N and maximum displacement being 10mm. Screw head was caught by special clamp.After load had been applied ,test would be terminated once the screw was mostly pulled out.The practically inserting depth(screw path length) was measured by electrical caliper whose precision was 0.01mm.Pull-out strength and screw failure failure length could be worked out by the software directly.Subsequently,pull-out strength,path length of each screws wereanalyzed.3.In the three-dimension ROM test we used standard implement and method in each internal fixtion.The length of C2 pedicle screws was 18-25mm,and their diameter was 3.5mm,The entrance of C2 pedicle screws was located at 3mm under the superior margin of axis vertebral plate a...
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