Biomechanical Research Of Thoracocalumbar (L2) Burst Fractures After Posterior Fixation Or Both Anterior Of Posterior Short-segment Fixation By Means Paste Stress Of Method

Objective:To elvate and compare the strain of normal L1 and L3 vertebra, the strain of normal L1 and L3 vertebra with L2 bust fracture after anterior or anterior-posterior fixation. To analysize the causes of secondary kyphosis after operation of thoraclumbar, the fixed vertebral body stress and strain distribution, patient appear chronic pain, adjacent disc degeneration , provide the basis of biomechanics for clinical to selection anterior or posterior fixation operation .Methods: Six cadaveric thoracolumbar spine specimens, each of the T12-L4 spinal units included were studied. Each specimen was intervened successively in three levels: all the spinal units was intact, made vertebral body burst fracture in L2 and fixed the fracture posteriorly using pedicle screw-rod system,made vertebral body burst fracture in L2 and then perform the anterior-posterior fixation. We set the intact level as the blank group. In each level the specimens were loaded by different forces from the following directions, in axial compression, flexion, extension, right side bending,left side bending , and obtain data.The maximum load was 500N, in line with the human thoracolumbar spine physiological status, so that specimens can be reused.All the data were analysed by SSPS13.0.Results: Three groups of models,by the loading- strain, loading - bais, torsional strength,were analysed. results showed that:1. By loading- strain in axial compression, flexion, extension, left side bending, the strain of L1 and L3 were the greatest in the blank group,following the posterior fixation group, the strain is smallest in the anterior-posterior fixation. the difference was statistically significantly (p=0.000<0.01). Biomechanical stability after all internal fixation operation is less than that of normal thoraculmbar spine. the stability of the combine anterior-posterior internal fixation is better than that of posterior internal fixation in vertical compression, flexion, extension, left side bending. When in right side bending, there is a stress increase regional in the right side L1 vertebral body, the stress is distributed the injured spinal again by fixation system。2. Under 500N loading, the bais of blank group is the smallest than the posterior internal fixation group and the anterior-posterior fixation. The difference was statistically significantly (p=0.000<0.01). The stability of normal thoracolumbar is better than any internal fixation operation . the stability of the anterior-posterior fixation is better than posterior fixation . 3. In 4 degree,the torque of control group is much than any internal fixation operation. The troque of combine anterior-posterior fixation is much than posterior fixation. the difference was statistically significantly (p=0.000<0.01).So the stability of normal thoracolumbar is the best, the stability of combine anterior-posterior fixation is better than posterior fixation .Conclusions: 1. the spinal fixation system has obscured the role of stress transfer,which response to the role in the portential stability of spinal fracture.2. Fixation system lead to the stress of injured spinal secondary distribution, which lead to the stress in some regional centralized or significantly decreased, it is probably main reason leading to neighboring joints for the degeneration. 3. the stability of anterior- posterior fixation is better than posterior fixation ,especially for treatment the thoracolumbar burst fracture with the neurological injury.