| ObjectiveThis study is designed to evaluation the occipito-atllanto-axial posterior fixation, using different biomechanical technique so as to provide the guidelines for clinical selection of fixations. we attempt to achieve the following goals.Seek applicability of occipitocervical measurement by using the spinal cord three-dimension measuring system built up upon the principle of digital correlation, on the basis of measurement and analysis of three-dimensional movements of the normal human ,destabilized atlantoaxial model and destabilized occipito-atlanto-axial model. Evaluate stability of biomechnical of atlantoaxial reconstruction with differential posterior of atantoaxial fixationEvaluate biomechanical properties of occipito-atlanto-axial reconstruction with differential posterior of occipito-atlanto-axial fixationAnalyze stress of the screws under physiological load which were implanted by three different posterior modalities, and their respective mechanical properties under normal three-dimensional the atlantoaxial movement Establish an occipito-atlanto-axial unstable three-dimensional limited elements model, with which posterior fixations with the occipito-atlanto-axial on was testified. Materials and methodsSix fresh human occipitocervicle specimens (C0-C3) were prepared, on which motor indexes of C0-2 and C1-2 segments were measured by using the spinal cord three-dimension measuring system, and the data obtained were statistically analyzed.Two occipitocervical unstable models were prepared: the odontoid fractured model and the odontoidectomy model. Motor indexes of C0-2 and C1-2 segments were measured and statistically analyzed.destabilized atlantoaxial models were reconstruction by four posterior internal fixations: brook +Ti-cable fixation, Gallie+Ti-cable fixation, posterior C1 lateral mass combined with C2 pedicle screw rod and Gallie (PLM + Gallie) fixation, and Posterior C1-C2 transarticular screw and Gallie (PTS + Gallie) fixation, whereby motor indexes of C1-C2 segment were measured and statistically analyzed.Occipitocervical unstable models (odontoidectomy) were reconstruction by three posterior internal fixations: Ti-cable + graft fixation, SUMMIT fixation and craniovertebral transarticular screw (CTS) fixation, whereby motor indexes of C0-1 and C1-2 segments were measured and statistically analyzed.Posterior transarticular fixation and posterior C-1 lateral mass combined with C-2 pedicle screw rod were performed in succession on 6 fresh craniovertebral junction specimens (containing C0-C3). Using the strain electronic measure, the extracting stress was measured C1-C2 transarticular screws(C1-C2 TA group), C2 pedicle screws(C2 PS group) and C1 lateral mass screws(C1 LS) that were bearing biological load under the condition of three-dimensional motion in six directions. The results were statistically analyzed.Using auto reconstruction technique of computed tomography (CT), occipito-atlanto-axial unstable three-dimensional limited elements models were established, and assembled by SUMMIT group and CTS group. The loaded models were testified to confirm the stabilizing action of the internal fixations on the unstable occipital atlas.ResultsMotor indexes of normal C0-C1 and C1-C2 segments were measured by using the spinal cord three-dimension measuring system built up on the principle of digital correlation. The results showed that The maximal rotation of C0-C1 occurred at 22.45゜ of posterior extension, and at 7.9゜ of rotation on condition that posterior extension was greater than anterior flexion. The maximal displacement of C1-C2 was at 40.2゜ of rotation.Compare with normal and two destabilized group respectively. Comparison of the normal model and destabilized atlantoaxial model showed no significant difference at C0-C1 (p>0.05). there were significant differences in posterior flexion and rotation (p<0.05), but there was no significant difference in posterior extension and lateral flexion (p>0.05). Comparison of the normal model and destabilized occipi...
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