Biomechanical Comparative Of The New Sacral Screw Fixation And Conventional Sacral Screw Fixation

Lumbar spondylolisthesis is the common disease of the Orthopedics,while the posterior sacral pedicle fixation technique of the short segment is the effective measure in treatment, because the method can achieve the anterior, middle and posterior three-dimensional space fixation of the vertebra with correcting function and many planes stability. Because of the unique anatomy of sacrum which has rich spongy bone and of which pedicle isn't typical and the position with a great sphere activities,so it result in the inadequate stability of the conventional sacral screw insertion and the insufficient anti-pullout force of sacrum,that are often complicated by pseudarthrosis,screw loosening or dislocation after operation, especially the treatment will be worse for those patients who have osteoporosis. Some authors have studied the problem in order to resolve it, they make use of increasing the length or diameter, selecting the material, altering the placement of the screw and augmentation with the bone cement in the screw orientation, they have not achieve the ideal effect though they make much progress on it, the early complication of internal fixation mainly result from its design and biomechanical property, we base on predecessors' achievement to observe and gauge the anatomy structure by means of the three-dimensional restructure of CT, studying the biomechanical stability of sacrum .we design the new type internal fixation system , which can offer the short arm of force to resist the bendand provide the insertion security of the transpedicle sacral screw , it not only recitifies deformity, but also can produce the instant stability . Meanwhile it could improve the fusion rate of the grafting bone and decrease the postoperative complication, we test the biomechanical in order to testify its property futher .So far, there are few reports on the internal research field.Objective: To compare the biomechanical stability of the new sacral screw and the conventional sacral screw under different physiological activities and loading conditions, to provide the basis of biomechanics for the clinical application of the new type sacral internal fixation in future.Materials and methods :Ten normal adult pelvis specimens which were soaked and fixed in 10% formalin liquid, the diameter and length of the main screw and the assist crossing screw of the new sacral screw is respectively 8m, 45mm; 3mm, 25mm. The specimens were randomly assigned to one side with the new sacral screw and the other side with conventional screw with the same parameters. All specimens were tested with WE-5A universal testing machine (1): normal specimens were measured for biomechanical loading test under four different physiological activities conditions according to biomechanical model.(2): swing test.(3): pullout test. Data were then compared. Result:1. There was not significant difference with 4-5% in the strength of fixationbetween the new sacral screw and the normal specimens(P>O.O5).But there was significant difference with13-14% between conventional sacral screw and the normal specimens(P