| Background:Thoracic and lumbar fracture are the most common injury in the spinal injury. According to Denis theory, two columns or more damage which will be spinal instability, so it would need for surgery treatment. Although the surgery method of thoracolumbar fracture always is a controversy, the most commonly used surgery approach is posterior pedicle screw fixation. The previous way is posterior short-segment fixation(the fixation of a normal vertebral body up and below the fractured body).This segmental fixation retain more motion segments, and provide a strong fixation of three-column. Furthermore, it can reduce operate time and blood-loss, and so on. But different injury types maybe leads to various fixed stability, so this difference probably influents the surgery choices. In recent years, some authors proposed the fixed type which adds the fixation on fractured vertebrae. Because they think that this fixed method could improve fixed stability and reduce postoperative loss of correction and failure-rates. The biomechanical compare of the fixed stability between two-column and three-column injury was not discovered, and the compare of the short and long segmental fixation including fixation on fractured vertebrae or not is not yet clear, so those are the aims of this study.Objectives:1. Biomechanical stability and resist-compressive strength compare of short-segment fixation between2-column and3-column injury. 2. Biomechanical stability and resist-compressive strength compare of various posterior pedicle fixations of3-column injury. Those studied result may provide guidance for selecting the clinical posterior fixation ways.Methods:Obtained16fresh thoracolumbar spinal specimens of homebred pigs(T13-L5),and exclude abnormalities, fracture and other structural lesions by anteroposterior and lateral X-Rays and bone mineral density. Retain the integrality of the inter-vertebral disc, ligaments, articular capsule and other muscle tissue. Dropping test was used to make a L2vertebral body burst fracture model(2-column injury model, AO Classification:A3.1).It must be confirm the pedicle intact and burst fracture of the fracture vertebrae by X-Rays and CT scan. Resection of supra-spinal, inter-spinal ligament, ligamentum flavum and Zygapophysial joint on basis of2-column injury model was3-column injury model(AO Classification:B2.3+A3.1).16specimens were randomly divided into two groups, then start those two experiments:1. Compare this two different injury models. The studied specimen status are:A: intact group; B:2-column injury group; C:short-segment fixation group of2-column injury; D:short-segment fixation group of3-column injury;2. Compare of different posterior fixations of3-column injury. The studied specimen status are:A:intact group; B:short segment fixation Group; C:short segment fixation plus intermediate screws; D:3levels fixation plus intermediate screws; F:long segment fixation.Internal fixation device were The thoracolumbar posterior screw-rod system (Kang-Hui medical device company).To achieve ROM (rang of motion) by3D laser scanning device and Geomagic10.0software when spine species was applied4Nm moment by a three-dimensional spinal movement testing machine to simulate the human body’s flexion, extension,left and right lateral bending, left and right rotation. After ROM testing, the axial compressive stiffness was measured by BOSE3510material testing machine.SPSS13.0software was used for statistical analysis of L1-L3segmental ROM. All data were expressed as Mean±Standard Deviation (x±s). All data were statistically analyzed using1-way repeated-measures ANOVA followed by LSD tests to determine whether measured outcomes were significantly different among the normal condition and various conditions of fixation. For comparing among instrumented conditions, repeated-measures ANOVA and LSD tests were performed.Results:1. The ROMs of3-column injury fixation under extension, lateral bending and rotation directions was significantly higher than2-column injury fixation (P<0.01), but flexion (P=0.086).The rotation ROMs (P=0.017) of3-column fixation was significantly higher than intact group. The all directional ROMs of2-column injury fixation group were significantly less than2-column injury group and intact group (P<0.01).The all directional ROMs of2-column injury group were significantly more than intact group (P<0.05).The compressive stiffness of2-column injury fixation was significantly higher than3-column injury fixation group (P=0.002). The compressive stiffness of3-column injury fixation group was lower than intact group (P=0.023).The compressive stiffness of2-column injury was not significantly different with3-column injury fixation (P=0.716).2. The ROMs of3levels fixation plus intermediate screws under all directions was not significantly different with long segmental fixation (P>0.05). The ROMs of3levels fixation plus intermediate screws under all directions was significantly lower than short-segment fixation plus intermediate screws (P<0.05).The ROMs of short-segment fixation after adding intermediate screws was less(P<0.05).The all compressive stiffness of3levels fixation plus intermediate screws, short-segment fixation plus intermediate screws and long-segment fixation were not significantly different with intact group(P>0.05). The compressive stiffness of short-segment fixation was less than intact group (P=0.023).The compressive stiffness of short-segment fixation after adding intermediate screws increased averagely by38%(P=0.002);3levels fixation plus intermediate screws and long segmental fixation separately improved by averagely82%(P=0.013) and123%(P=0.001) to compare with short-segment fixation. Conclusion:1.The postoperative stabilities of3-column injury fixation under extension, lateral bending and rotation were significantly less than2-column injury fixation, and the resist-compressive strength of3-column injury fixation were significantly less than2-column injury fixation.2. Three levels fixation plus intermediate screws and short-segment fixation plus intermediate screws can obtain good postoperative stabilities and resist-compressive strength;3levels fixation plus intermediate screws not only can achieve the level of long-segmental fixation, but also retain a more motion segment. |
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