Contrasted Biomechanical Research On Posterior Lower Cervical Fixation

Objective:To compare the screw pull-out strength of three techniques including lateral mass screw, transpedicular screw and transarticular screw in the lower cervical spine, and the relation between the maximum pull-out load and the BMD, screw-path length was analysised, in order to provide the biomechanical basis for the clinical selection of fixation method.Methods:To selecteing cervical spine fresh specimens (C3～C7)from 6 adult cadavers,Then,to resolving cervical spine specimens become 30 functional spinal units, According to the principle of paired grouping ,these specimens were divided into three groups:LMS,TPS and TAS. Implanted with screws using lateral mass screw, transpedicular screw and transarticular screw respectively. The maxiumu pull-out strength,pull-out engery and screw-path were tested.Results:The results of cervical spine pull-out testing: The maxiumu pull-out strength was (426±0.38)N for lateral mass screw, (502±42)N for transpedicular screw, (482±40)N for transarticular screw; The maxiumu pull-out engery was( 5.26±0.39)J for lateral mass screw, (7.18±0.67)J for transpedicular screw, (6.68±0.47)J for transarticular screw; The stiffness was (80.83±23.51N/mm) for lateral mass screw, (117.75±34.62N/mm) for transpedicular screw, (100.38±27.89N/mm) for transarticular screw. The maxiumu pull-out strength,pull-out engery and stiffness of lateral mass screw were less than transpedicular screw and transarticular screw(P﹤0.05), The pull-out strength,pull-out engery and stiffness of the transpedicle screw and the transarticular screw were equal. Therefore, this fact can prove that the group transpedicular screw 's pull-out srength was greatest, group transarticular screw was less, group lateral mass screw was least. Correlation was found between the maximum pull-out load and the BMD, screw-path length.Conclusions:The study biomechanically shows that the pull-out strength of transpedicular screw staff fixation was the largest, the transpedicular srew have good gripe effection, The transarticular screw fixed 4 cortieal. the pull-out srength was larger, Bacause the lateral mass screw fixed 2 cortical only, the lateral mass was relatively weak, and the screw was short, which make the effect of griping unsatisfactory. As for the selection of clinical surgery, and has a great advantage. Besides, the study shows that the high BMD's specimens which screw-bone interface firmly. Correlation was found between the maximum pull-out load and the screw-path length, in the clinical should increase the screw-path length as far as possible to raise the pull-out load.