The Finite Element Method And The Clinical Results Analysis Of Indirect Reduction And Fixation Without Fusion For Thoracolumbar Burst Fracture

Part One: The Finite Element Method Analysis of Thoracolumbar Burst FractureTreated with indirect reduction and fixation without fusion[Objective](1) To establish the three-dimensional finite element model of L1burst fracture.(2)To investigate the stress and the displacement of posterior internal fixation with pediclescrew post-operatively, supply some information for clinical care.[Methods]A L1burst fracture finite element model of a31-year-old man was established from CTimages. Simulate the process of reduction of the fracture treated with indirect reductionand fixation without fusion，put into ANASYS10.0finite element program. the movementand stress distribution of the vertebral body and intervertebral disc were observed underthe load of axial displacement1-10mm.[Results]Under load axial displacement1-10mm，we found that when the displacement loadwas6mm, the height and VBA of the vertebral body almost recovered to nomal. When thephysiological reset load of the displacement was6mm, the maximum stress distributionappeared in the T12-L1intervertebral disc,the value was51.8Mpa,the displacement ofthe posterior longitudinal ligament was less than T12vertebral body,the value was only4.6mm.When we increased the displacement load to8mm, the stress distribution of T12-L1intervertebral disc obviously increased to69.1Mpa.Under the distraction reduction load,wefound the the maximum displacement appeared in the posterior longitudinal ligamentbehind L1.The value was11.3mm when the displacement load was6mm,and increased to15.0mm when the load was8mm. under the distraction reduction load,the maximum stressdistribution did not appear in the intervertebral disc.[Conclusion]A L1burst fractue finite model was built up and simulate the process of reduction of the fracture treated with indirect reduction and fixation without fusion on the model. Weobserved the movement and stress distribution of the vertebral body and intervertebral discunder different displacement load. Under the physiological reset load,intervertebral disccould well correct the height and VBA of the injured vertebral body,and provide somespace in the injured vertebral body. Under the distraction reduction load, the posteriorlongitudinal ligament could effectively pushed the fragment into the space of the injuredvertebral body. Part Two: The Clinical Results of Thoracolumbar Burst Fracture Treated withindirect reduction and fixation without fusion[Objective]To evaluate the results of thoracolumbar burst fracture treated with indirect reductionand fixation without fusion and to analyze the treatment outcomes as well as its correlationfactors.[Methods]Thoracolumbar burst fractures and treated with indirect reduction and fixation withoutfusion between1998and2010were followed up.112cases that had integrity data wereanalyzed. The radiographic, neurological, and functional outcomes were assessed. All ofthe cases were checked with radiography pre-and post-operation and at final follow up.Some of them were checked with CT pre-and post-operation.Anterior and posteriorvertebral height of the fractured vertebral body, vertebral body angle, Cobb angle andsagittal index were measured at the lateral X-ray plains. The narrowing of midsagittaldiameter of injured segment were measured on the CT scan.Neurological status wasassessed pre-operation and final follow up using the Frankel Scales. Patient’s pain andback status were assessed using the Denis Pain Scale and Oswestry Disability Index (ODI).[Results]All the112cases, AVH were restored from59.2%±17.2%to96.4%±8.1%, PVH from91.2%±7.1%to98.0%±5.9%, VBA from19.0°±7.7°to4.0°±4.5°, Cobb angel from17.6°±9.5°to2.8°±8.7°°, SI from16.3°±8.6°to1.9°±4.3°. After pedicle screwinstrumentation to final follow up（39.6months in average）, the losses were that, AVH：4.5%±6.3%, PVH：2.2%±5.1%, VBA：2.7°±3.9°, Cobb angle6.1°±5.9°, SI：3.8°±4.6°. There was significant deference in targets（AVH、PVH、VBA、Cobb、SI） betweenpre-operation and post-operation（P<0.01）, post-operation and at final follow up（P<0.05）.At the final follow-up, all of the patients’ neurological status was Frankel A in1cases,C in1cases, D in4cases and E in106cases. There were still2patients suffering sphinctermuscle functional impairment. Neurological status improved at least1Frankel grade inpatients who had preoperative incomplete paraplegia, while no improvement was obtainedin those who had preoperative complete paraplegia. According to Denis Pain Scale,61cases were P1,40cases were P2,10cases were P3,and1case was P4. Of the106patientswhose neurological status were E, the average ODI score was11±16，83cases wereexcellent,20cases were good,3cases were poor. Complications were rare, there were4cases occurred pedicle screw breakage in112cases. The rate of reduction was connectedwith AVH(P<0.01) and VBA(P<0.05).[Conclusion]Posterior pedicle screw systems combined with indirect reduction and without fusionis successfully used in management of thoracolumbar burst fracture. It can restorevertebrae height, correct local kyphosis and reduct canal compromise. Posterior pediclescrew fixation has the advantage of less invasion, shorter operative time, simple technicalrequirements and fewer complications. Neurological status improved at least1Frankelgrade in the patients who had preoperative incomplete paraplegia. There were some loss inAVH, PVH, Cobb angle and SI, but most patients’ pain and back function were satisfactory.In brief,indirect reduction and fixation without fusion for thoracolumbar burst fracture issafe and effective.