| Lumbar spondylolysis is a main reason for low back pain occurred very popularly in clinic.Although they still didn' t draw a conclusion on the treatment of spondylolysis,the majority of scholars proposed direct repair of spondylolysis by using intrasegmental fixation construct and bone-grafting of the pars defect.This study aimed to evaluate a new kind of intrasegmental fixator-memory alloy intrasegmental fixator (MAIF) for lumbar spondylolysis.three parts are comprised in this paper.In the first part of this study, the biomechanical tests of memory alloy intrasegmental fixator for lumbar spondylolysis were evaluated in vitro,including tensile strength test and fatigue test. Objective: To evaluate the intrasegmental shape memory alloy fixator for lumbar spondylolysis by self designed with biomechanical method. Methods: Ability of resisting pulling force of 10 fixators was tested with MTS-858 under 0℃ at first,After restoration under normal temperature,the 10 fixators were divided into two grorps :37℃ group and 40℃ group.Ability of resisting pulling force of fixators in 37 ℃ group was tested under 37 ℃,fixators in 40℃ group were tested under 40℃;2 fixators were fatigued with 20N-200N cycling pulling load(lHz) by MTS-858,the deformation of 2 fixators were observed carefully. Results: The ability of resisting pulling force of fixators in 0"C group was far lower than the fixators in 37℃ group and 40℃ group (P<0.01);When fixator was pulled open 2mm under 37℃ and 40℃,the pulling force was over 200N.There was no significant difference between 37℃ group and 40℃ group(P>0.01).when the two fixators were deformed to 6% by pulling load,they had resisted the pulling load 9576 times and 10028 times respectivly. Conclusions: Intrasegmental shape memory alloy fixator is a simple and reliable intrasegmental instrument for direct repair of lumbar spondylolysis.The second part of this study is finite element analysis of memory alloy intrasegmental fixator. Objective: In order to analysis the tensile strength ofmemory alloy intrasegmental fixator and the distribution of tensile stress in it when it's in state of tension with the finite element method(FEM). Methods: The scanning image of parameterized memory alloy intrasegmental fixator and its material property were input into the inherent coordinate of Ansys in which the FEM model was reconstructed. The model was extended with restriction on different place and analysed. The tensile strength on the memory alloy intrasegmental fixator model and the distribution of tensile stress in it was calculated. Results: When the memory alloy intrasegmental fixator was pull out along the two midpoint of hook, the pull is about 281 newton, and the tensile stress distributed more on the middle of memory alloy intrasegmental fixator while less on the two sides. Conclusions: The tensile strength of memory alloy intrasegmental fixator is enough strong; the middle of memory alloy intrasegmental fixator is the concentrated part of tensile stress and is apt to collapse when fatigue alternating stress acts on it.The third part of this study is clinical application of memory alloy itrasegmental fixator for lumbar spondylolysis. Objective: In order to evaluate the efficacy of self-designed memory alloy intrasegmental fixator(MAIF) in treating lumbar spondylolysis. Methods: The MAIF was used to fix the lumbar spine with spondylolysis following bone grafting in situ. The patients were immobilized with corset for 3 months postoperatively. 23 patients with lumbar spondylolysis were treated in the way discribed.All patients were followed-up,ranging from 6 months to 4 years.The henderson's standard was adopted to evaluate the efficacy of memory alloy intrasegmental fixator. Results: The results in the 23 patients who underwent this procedure were 19 patients with a excellent result,3 patients with a good result,1 patient with a fair result.the excellent and good rate was 95.65 % ;The X-ray examination showed that the healing rate of spondylolysis was 97.65 % .No complication was fou...
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