儿童肱骨髁上骨折模型克氏针固定构型的三维有限元分析

Three-dimensional finite element analysis of Kirschner wire fixation configuration for supracondylar fracture of humerus fracture in children

目的:建立带骺软骨儿童肱骨远端新力学模型,模拟肱骨髁上骨折并进行三维有限元分析,研究克氏针的数量、针道、出口高度及穿针构型对固定稳定性的影响。方法:于图片存档及通信系统(picture archiving and communications system,PACS)中挑选1名6岁男孩的正常肱骨远端三维CT,将图像数据导入Simpleware及SolidWorks 2016软件,构建1个含有肱骨小头骨化中心及远端骺软骨的儿童肱骨远端模型。制作常见伸直型儿童肱骨髁上骨折模型,并模拟交叉克氏针及单纯外侧克氏针的多种固定构型,在屈伸、内外翻方向施加30 N,内外旋方向施加5 N的力,通过远折端的位移情况分析其稳定性。结果:2枚克氏针固定构型中,出口在骨干-干骺端交界区(metaphyseal-diaphyseal junction,MDJ)上缘的2枚交叉针最稳定,可对抗超过2585 Nmm/°的旋转应力;而在对抗屈伸及内外翻应力测试中,低位针经过肱骨小头骨化中心的2枚外侧针最稳定,分别可对抗接近45 N/mm及190 N/mm的应力。在最稳定的外侧2枚克氏针构型中加入第3根针,所有方向上的稳定性显著增加,其中3枚交叉针最稳定,屈伸、内外翻及内外旋时分别可对抗198 N/mm、395 N/mm及6251 Nmm/°的应力。结论:2枚外侧分散针可为儿童肱骨髁上骨折提供足够的稳定性。在2枚交叉针构型中,出口高度在MDJ区域上缘的交叉针最稳定。3枚交叉针构型在所有研究构型中最稳定。

Objective:To establish a new mechanical model of distal humerus in children with epiphysial cartilage,stimulate supracondylar humerus fracture and perform three dimensional finite elements,and study effect of pins numbers,pin tract,outlet height and pin configurations on stability of fixation.Methods:Three dimensional computed tomography(CT)data of 6-year-old boy with distal humerus was downloaded from picture archiving and communications systems software(PACS),the data of picture was imported into Simpleware and SolidWorks 2016 software to establish distal humerus fracture in children contained ossific nucleus of the capitellum(ONC)and distal cartilage.Normal extense supracondylar humerus fracture model was established to stimulate configurations of crossed and lateral pinning fixation,30 N was added on the direction of flexion-extension and varus-valgus,while 50 N was added on the direction of internal and external turning.Stability was analyzed by displacement degree of distal fracture.Results:Among 2-pin configurations,2-crossed pins were more stable against rotation forces which could resist rotation stress over 2585 Nmm/°,while low position through ONC of 2-divergent lateral pins were more stable,which could resist stress of 45 N/mm and 190 N/mm during the test of resistant strains and varus-valgus stress.The third pins was added into the more stable lateral 2-pins,the stability in all directions were increased obviously,and 3-crossed pins is the most stable,stress of flexion-extension,varus-valgus and internal-external turning were 198 N/mm,395 N/mm and 6251 Nmm/°.Conclusion:Two-divergent lateral pins could provide enough stability for supracondylar humerus fracture in children.In two-crossed pins,the upper border of MDJ could provide the best stability.Three-crossed pins could offer the best stability against both translation and rotation forces.