| With the cross-integration of bioresorbable materials and medicine,materials science,biology and other disciplines,the application field of bioresorbable materials is becoming more and more extensive,and at present,polylactic acid(PLA)composite materials have begun to gradually replace metal materials for surgical fixation due to their good absorbability and mechanical strength.Chevron is a surgical method that combines V-shaped osteotomy of the first metatarsal bone with internal fixation of bone nails,and is a very effective surgical method for the treatment of mild and moderate hallux valgus.The use of bioresorbable materials as internal fixations can effectively avoid the problems of surgical removal of metal bone nails and rejection of human bone and metal,and reduce the pain and risk of secondary surgery.Although bioresorbable materials have various advantages for internal fixation of human bones,the current lack of biomechanical performance analysis data has led to the inability of bioresorbable materials to be widely used in clinical practice,and there is a lack of suitable testing and characterization techniques.Therefore,based on the self-developed six-degree-of-freedom loading platform,this paper proposes an in-situ testing technology for mechanical properties of biomaterials,studies Chevron hallux valgus correction using polylactic acid internal fixation,proposes an optimization scheme suitable for polylactic acid screws,and proposes a Chevron hallux valgus improvement scheme suitable for double polylactic acid screws for severe hallux valgus deformity correction.It provides a technical basis and feasibility analysis for the clinical application of bioresorbable internal fixations.The main research content of this paper is as follows.(1)In view of the lack of biomechanical performance test due to the fact that the strength and stiffness of polylactic acid materials are much lower than those of metal materials,this paper conducts experimental research and performance analysis of the bonding performance of bone nails made of polylactic acid materials instead of metal materials.By ensuring consistent experimental sample preparation(Chevron procedure),the influence of other external factors such as osteotomy position and implant orientation on experimental results is reduced.Using the six-degree-of-freedom loading platform and fatigue testing machine,the quasi-static loading experiment and fatigue loading experiment were carried out,and the three-dimensional digital speckle testing system(DIC)was used to characterize the three-dimensional deformation of the sample during the experiment,and the experimental results showed that Chevron polylactic acid(PLA)screw can replace metal screw for fixation after hallux valgus,and the parameters of the osteotomy scheme have an important influence on the fixation strength of the specimen.(2)In the traditional Chevron procedure,high-strength metal nails are used as internal fixations,so the requirements for osteotomy angle and implantation nail position are low,and this study shows that the surgical parameters have a great influence on the stability of hallux valgus after surgery.The pressure between the first metatarsal bone and the ground at different walking speeds was obtained through the plantar pressure test,and the load was reproduced during the experiment to simulate the real motion state of the human body.Through finite element analysis,the influence of different osteotomy angles and implantation nail positions on the fixation strength was calculated,and then the optimization scheme was preliminarily screened.Quasistatic loading experiments show that the maximum load that the c5 surgical model can withstand is slightly higher than that of the f1 operation,and the bone micro-movement of the c5 operative formula can promote bone tissue growth.The shrinkage curve was obtained by fatigue loading experiment,and it was concluded that both c5 and F1 had a process from compaction of the osteotomy surface to internal failure under fatigue load.(3)Aiming at the traditional Chevron procedure and its optimization that cannot treat patients with severe hallux valgus,a double-screw fixation surgical scheme was proposed to compensate for the instability of the distal bone under the single bone nail structure caused by insufficient material stiffness.Through the well-designed Chevron improvement scheme,the distance of inward movement of the distal bone was determined according to the severity of hallux valgus,and the results of finite element calculation showed that when the distal bone was more than 12 mm away from the proximal bone,it was necessary to use double bone nails to fix the specimen,and the rotation angle was added on the basis of the original observation angle,and the deformation of the distal bone was comprehensively analyzed.Quasi-static loading experiments have shown that the modified Chevron procedure with additional screws can be used to treat patients with severe hallux valgus. |
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