Biomechanical Evaluation Of Unilateral Fractured Vertebral Pedicle Screw Fixation In Treatment Of Thoracolumbar Fracture

ObjectiveTo evaluate the biomechanical properties of unilateral fractured vertebral pedicle screw fixation by comparing adjacent upper and lower vertebrae of fractured vertebra pedicle fixation with three-level 6 pedicle fixation in treatment of thoracolumbar fracture by vitro test so as to provide theoretical basis and experimental guidance in treatment of thoracolumbar burst fracture with unilateral vertebral pedicle screw fixation.MethodsEighteen fresh calf thoracolumbar spine specimens involved five vertebrae segement(T11-L3) were obtained. To take the posteroanterior and lateral radiograph, removing muscles tissue carefully with the ligment and disc reserved. According to Panjabi's high speed trauma apparatus,the specimens were made into the burstfracture specimen,which measured and observed. Posteroanterior, lateral radiograph and CT scans were taken to confirm that all the burstfracture specimen should comform to the following srandard: one of pedicle and one of the endplate of all the models were normal. The specimens were divided into three groups: A. adjacent upper and lower vertebrae of fractured vertebra pedicle fixation (fixed with 4 pedicle screws); B. unilateral fractured vertebral pedicle screw fixation (fixed with 5 pedicle screws); C. three-level 6 pedicle fixation. Each group divides into three status:1) normal 2)fractured 3)reconstructed. All the internal fixation device were General Spine System(GSS). During the experiment, the flexion, extension, bilateral bending and axial rotation loading were appied to the specimens and the range of motion (ROM)were determined.Stiffness under flexion-compression were measured on the MTS testing system. The last part is the test of comparison of axial extraction force. The specimen were split into three parts,and all the vertebrae were divided into two groups: A. normal vertebrae; B. fractured vertebrae. All the screws were placed in the pedicle and vertebral body, and the extraction force test was performed on MTS testing system. In the group of normal vertebrae, the long and short pedicle screws were implanted separately, then compared the extraction force on MTS testing system. SPSS10.0 was used to process the statistical figure.ResultsThe three kind ways for transpedicular fixation (fixed with 4, 5 or 6 pedical screws) can enhence the stability of injured thoracolumbar vertebrae in flexion, extension, bilateral bending ,axial rotation loading.Both of unilateral vertebral pedicle screw fixation (fixed with 5 pedicle screws) and three-level 6 pedicle fixation had statistical difference of spine stability capacity compare with upper and lower vertebrae of fractured vertebra pedicle fixation (fixed with 4 pedicle screws)(P<0.05).No statistical difference of spine stability capacity was found between 5-screws fixation and three-level 6 pedical fixation(P>0.05).In the test of extraction force, the mean extraction force of normal vertebrae group was stronger than that of fractured vertebrae group (P<0.05).The extraction srength of long pedicle screw was bigger than that of short pedicle screw(P<0.05).Conclusion1.The stability of unilateral fractured vertebral pedicle screw fixation is better than adjacent upper and lower vertebra of fractured vertebra pedicle fixation. There is no statistical difference of spine stability capacity between unilateral fractured vertebral pedicle screw fixation and bilateral fractured vertebral pedicle screw fixation.2. The extraction force of pedicle screw declined after burst fractured.The longer internal fixation, the more stable fixed.