Biomechanical characteristics of posterior transpedicular screw fixation combined with calcium sulfate vertebroplasty in treatment of thoracolumbar compression fracture / 中国组织工程研究

ABSTRACT

BACKGROUND: The biomechanical studies about calcium sulfate cement vertebroplasty are only limited to the single fracture vertebra, not performed in spinal compression fracture unit with posterior transpedicular screw fixation. Furthermore, performing experimental study in the whole function spine unit (FSU) conforms to actual clinical situation. OBJECTIVE: To assess the biomechanical properties of calcium sulfate vertebroplasty combined with posterior transpedicular screw fixation in treatment of thoracolumbar compression fractures. DESIGN, TIME AND SETTING: A controlled experiment was performed at the Biomechanical Laboratory of Shanghai University in March 2009. MATERIALS: Fifteen fresh thoracolumbar spines were harvested from male calves and made into T_(11)-L_1 FSU, then divided into 3 groups randomly: normal control group, posterior transpedicular screw fixation group and transpedicular screw fixation plus vertebroplasty group. METHODS: T_(12) flexion-compression fracture models were made in all specimens of posterior transpedicular screw fixation group and transpedicular screw fixation plus vertebroplasty group, undergoing reduction and posterior transpedicular screw fixation, and calcium sulfate vertebroplasty combined with posterior transpedicular screw fixation respectively. MAIN OUTCOME MEASURES: All specimens were placed on the WE-10A universal testing machine for mechanical test. Load-straining, load-displacing, rigidity, strength and torsion of the FSU were performed in axial compression, flexion, extension and lateral bending states. The experimental outcomes were collected and compared by statistic analysis. RESULTS: The load-strain and loed-displacement showed a linear relationship. Straining values in vertebral body and intervertebral disc of calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 14% and 12% less than that of posterior transpedicular screw fixation group, 21% and 13% less than that of normal control group. The thoracolumbar displacement in calcium sulfate vertebroplasty Plus posterior transpedicular screw fixation group decreased 25% and 37% as compared with other 2 groups respectively. Compared with normal control and posterior transpedicular screw fixation group, the thoracolumbar stiffness in calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group increased 53% and 44% respectively. The strength in vertebral body and intervertebral disc of calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 14% and 24% higher than that of posterior transpedicular screw fixation group, 13% and 20% higher than that of normal control group. The maximal twisting strength of FSU in calcium sulfate vertebroplasty plus posterior transpedicular screw fixation group were 18% and 30% higher than that of other 2 groups, the twisting stiffness were 30% and 40% higher than that of other 2 groups. The data above were significant differences statistically (P < 0.05). CONCLUSION: Posterior transpedicular screw fixation combined with calcium sulfate vertebroplasty show superior biomechanical properties for treatment of thoracolumbar compression fractures, which exhibits not only strong strength and stiffness, but also stable FSU, thus could decrease the stress loading of the internal fixation, the incidences of screw breakage and avoid the altitude loss of vertebral body.