Three Dimensional Finite Element Analysis And Biomechanical Evaluation Study Of The Crescent-shaped Complex Of Cement

Objective1 To investigate the distribution of stress force in crescent-shaped complex of cement (CCC) in vivo and in vitro by finite element analysis.2 To compare the subsidence of CCC with that of titanium mesh cage on the interface of vertebral bones with different mineral density, examining the interface mechanical properties of them by biomechanical evaluation.Method1. One three-dimensional nonlinear finite element model of the CCC was generated from the real model of CCC, another was based on quantitative computed tomography scans date of a CCC postoperative patient vertebra. Under loading, the distribution of stress force was observed.2. The yield strength of ten same CCCs were investigated by the electronical versatile machine.3. Twenty thoracic and lumbar vertebrae harvested from embalmed male cadavers (n = 2) were used. The vertebrae were divided into two experimental groups according to the different cadavers,then ten vertebrae were divided into two groups randomly to investigate the maximum and minimum load of titanium mesh cage or CCC. Vertebrae were measured from load-deformation data in quasi-static compression loading with a loading rate of 0.5 mm/min by the electronical versatile machine. Bone mineral density(BMD) of the whole vertebral body was measured by X-ray Bone Densitometer.Result1. In vitro, under the action of 2000N axial direction stress force and 10NM torque, the stress force concentrates on the thinnest part of CCC. In vivo, under the action of 500N axial stress, the stress force is biggest at the connecting part of nail and titanium stick; and under the 10NM torque, the biggest stress force appears at the thickest part of CCC.2. The BMD of the low group and the high group is 0.550±0.007g/cm~2 and 0.632±0.008 g/cm~2,separately. The yield strength of CCC is 79.6±0.6MPa. The minimum load of CCC is twice bigger than that of mesh cage both in the high BMD group and the low BMD group (P < 0.05); While the maximum load of CCC is twice bigger than that of mesh cage in the high BMD group (P < 0.05),but with no ststistic difference compared to that mesh cage in the low BMD group(P > 0.05).When it is compared between the different BMD groups, the minimum load in the high BMD group is more than 1.5 times bigger than that in the low BMD group(P < 0.05);While the maximum load in the two BMD groups has no ststistic diference(P > 0.05). Conclusion1 The strength of CCC is fit for use in human body.2 With the same BMD,the stress force to make it subsidence in CCC is much bigger than in mesh cage.3 The circumstance of BMD is an important fator of the chance of subsidence.4 In vitro,the thinnest part of CCC is easy to get fatigued fragmentation. In vivi,under the axial stress the connecting part of nail, and titanium stick is easy to get fatigued fragmentation's while as the thickest part of CCC under the torque.