Establishment And Evaluation Of Biomechanical Model Similar To Lumbar Vertebrae Osteoporosis In Sheep

Since in 1959 the long pedicle screw was introduced by Boucher to screw from lamina,pedicle into Vertebrae for fixed lumbosacral joint and achieveing good clinical results, Pedicle screw fixation has been a rapid development, and was widely used in common clinical illness of spinal surgery. At present, the pedicle screw fixation has become the most frequently used methods of spinal posterior fixation in the area of spinal surgery. The study found: the stability of pedicle screw depends on the friction force in interface between bone and screw.However,with the application of pedicle screw fixation widely in clinic Loosening and failure of the screws are the most common complication reported,especially for osteoporosis. Therefore, at present the methods to solve those problems used clinically mainly was confined to two aspects: one was improvements of the pedicle screw design; another was using technology of Strengthen the path of pedicle screw. However, pre-clinical studies for the two aspects was mostly confined to the normal bone of the animal or the health of people on the vertebral body and rarely used in osteoporosis or severe osteoporosis vertebral body of animals or human vertebral body.Therefore, osteoporosis animal models is a prerequisite for the orthopedic experimental study.Recently,used for osteoporosis cases, bio-mechanics study of animal models, the most common use of animals were adult sheep (goats), the method of eatablishing the models are Ovariectomy, Glucocorticoid-induce and Low calcium diet, their shortcomings included: firstly, modeling, long modeling cycle and the high cost of rearing at least 6 months leading to extend the experimental study period; secondly, the modeling process was complicated; thirdly, poor reliability of the model: BMD, biochemical, and bone morphology and other indicators were affected by these uncertain factors ,such as reprodution, nutritional status, health status, receiveing light conditions. If you wan to get initial biomechanical assessment for new surgical instruments and Surgical technique aming to improve the fixtion about pedical screw in osteoprosis patient, it is not a reasonable choice to do biomechanical test under vivo animal model of osteoporosis,which is a time-consuming,and can not in time send experimental results back to researchers,so it will extend research period.Therefore, it is neccessay to establish in a short time a biomechanical model which need to be a simple and controllable degree of osteoporosis and to meet the needs of spine biomechanics research.Objective:1).To place sheep lumbar vertebrae into a beher-glass filled with hydrochloric acid and infuse hydrochloric acid by infusion pump into it as an in-vitro method to establish a biomechanical model similar to osteoporosis in sheep lumbar vertebrae.2). For the first time to comprehensively evaluate osteoporotic and biomechanical model from multiple levels ,which are two-dimensional and three-dimensional, macro and micro, qualitative and quantitative.and to analyze the related factors about the mechanical properties of this model.and analysis of the mechanical properties of the model of reasons for the decline.Material and Methods: 1) Designing a cylindrical perfusion connector with side hole as a bridge connecting the vertebrae and the infusion pump. 2): Forty-eight fresh lumbar vertebrae from 3±0.5years sheep, were randomly assigned to four groups by completely randomized design: Group A (no decalcification, the control group), Group B (decalcified with Hcl for 2 hours ), Group C (decalcified with Hcl for 4 hours), Group D (decalcified with Hcl for 6 hours). 12 verterbraes of each group. 3): For the first time to comprehensively evaluate osteoporotic and biomechanical model from multiple levels ,which are two-dimensional and three-dimensional, macro and micro, qualitative and quantitative,and are in detail X ray, spiral CT, MicroCT, pathology; BMD; biomechanical testing ( the axial pullout strength, maximum compressive strength)and bone histomorphometry analysisResult: 1): model assessment:①After decalcification, vertebrae's BMD in A, B, C, D groups respectively decreased by 0,18%, 28% 39%;②we can observed fromX-ray, CT that with the extend of decalcification vertebrae's density image gradually became darker and vertebrae's Cortical bone became thinner and Cancellous bone became wider.③the results of three-dimensional reconstruction by MicroCT show that with the prolong of decalcification time trabecular bone harvested from pedicle and central vertebrae in group B,C,D respectively became wider than that in group A,and its connection density gradually broke off,and the thickness of cortical bone havested from pedicle and anterior vertebrae in group B,C,D is respectively obvious thinner than that in group. Accompanied by a decline in bone mineral density Tb.th,Tb.N,BV/TV and Cor.th of pedicle and central vertebrae in group B,C,D were significantly lower than those in group A,while Tb.sp was higher ( P< 0.05) compared with group A. BS/BV of pedicle in each group has no significant difference,but BS/BV of vertebrae in each group gradually increased with the extendence of decalcification time.④Histopathological examination revealed that the trabecular bones from pedicle became thinner, their number decreased and the space between them widened, and the antrum of bone marrow enlarged in group B,C and D compared with group A.⑤Biomechanical tests show means of Fmax ,εult and its energy absorption of group B, C and D were significantly lower than those of group A( P < 0. 05) . while these values in each group are continuously falling With the extendence of decalcification time.2)Correlation analysis:After decalcification, the mechanical properties of vertebral body(Fmax andσult) have closely related to BMD and decalcification time, and also have significant relationship with space parameters of bone structure (tb.th, tb.N, tb.sp, BV / TV, BS / BV, Cor . th) , which is similar to mechanical changes in human vertebral osteoporosis.Conclusion:The method of acid decalcification may be useful for producing a quick, effective, and controllable biomechanical model similar to osteoporosis, it can provide reference data for biomechanical study in vivo model of osteoporosis.