The Use Of Screw At The Fracture Level In The Treatment Of Thoracolumbar Burst Fractures A Biomechanical Study

Objective: To determine the effect of adding pedicle screws at the levelof a burst fracture (intermediate screws) and long-segment pedicle system onthe stiffness of pedicle fixation, an in vitro biomechanical study was carriedout.Methods: Eight embalmed specimens were harvested for this study. andtest their normal spinal axial compression, flexion, extension, lateral bendingand axial torsion stability. burst fractures were simulated by completelyresecting the lower aspect of the L1vertebral body and removing the L1–L2intervertebral disc. Then pedicle screws were inserted in vertebral pedicle forfixation with five different methods: A: Long-segment instrumentation (twolevels above and below the fractured vertebra) B: Adding pedicle screws at thelevel of a fractured vertebrae of a short-segment instrumentation(one aboveand below with another one at the fracture level).C: Two levels above and onelevel below pedicle screw fixation with adding pedicle screws at the level ofa fractured vertebrae.D: Two levels above and one level below pedicle screwfixation with anterior fixation and bone grafting. E: short-segmentinstrumentation with anterior fixation and bone grafting. Specimens weretested randomly in order to minimize the error caused by a single process. Theflexibility of the every specimens was tested in axial compression, flexion,extension, lateral bending, and torsion. data was measured and recorded by thecomputer. In this study, our goal was to compare the properties ofload-displacement, axial-stiffness and torsional load-strain. A11of the datawas analyzed by software SPSS13.0,using variance analysis to analyze thedifference, P＜0.05is statisticalsignificance.Results: Under different load, there is statistical significance between thetwo groups (p<0.05)1.The load-displacement of thoracolumbar spine. in flexion,with anterior fixation is more stable than posterior fixation(p<0.05),in lateral bending and extension, long-segment is more stable thanshort-segment,The addition of intermediate screws at the level of a burstfracture significantly increases the stiffness of thoracolumbar spine(p<0.05).2.Axial-stiffness in thoracolumbar spine. The group C is the most stable thanother groups, there is no different between the group A and D(p>0.05).3.Torsional load-strain in thoracolumbar spine. The group C is stillthe most stable than other groups, the group E is the worst group. there isstatistical significance (p<0.05).Conclusion: The addition of intermediate screws at the level of burstfracture can significantly enhance the stability of spine biomechanics; Twolevels above and one level below approach is better than simple addingpedicle screws at the level of a burst fracture (intermediate screws);Long-segment posterior approach pedicle fixation (8nails two rods) andanterior and posterior combined surgery (6nails two rods"two-above-one-below" way anterior and posterior combined cross injuryvertebral) biomechanical stability was not statistically different.