Model of reduced pediatric supracondylar humeral fracture with residual displacements: a finite element analysis of mechanical responses

doi:10.3969/j.issn.2095-4344.2015.13.029

Abstract

Abstract:

BACKGROUND: Displacement of the distal fracture fragment is one of the most important facts that lead to cubitus varus following pediatric supracondylar humeral fracture. Mainstream technique emphasized the restoration of posterior-ulnar deviation of the distal fragment. However, there is an absence of supportive evidences from biomechanical studies.
OBJECTIVE: To establish models of extension-ulnar type of supracondylar humeral fracture and investigate the mechanical stability of reduced fracture with residual displacements within functional restoration standard, so as to provide mechanic evidences supporting the empirical rule of manipulative reduction-“better anterior than posterior, better radial than ulnar”.
METHODS: The fresh cadaveric bone of right upper extremity from a 7-year-old child was scanned using CT. Models of supracondylar humeral fracture differing in contact area of the fracture site and displacement direction of the distal fragment were established and underwent loading tests. Stress in both anterior and posterior margin of the fracture site and Baumann angle were recorded, and data were analyzed and compared.
RESULTS AND CONCLUSION: In comparison of stress in the posterior margin, the value was significantly greater in the posteromedial-displacement group than the others. Stress value in fracture with 75% contact area was significantly greater than the other three groups. In comparison of stress in the anterior margin, a significantly greater value was obtained in the posteromedial-displaced group. Stress value in fracture with 85% contact area was significantly greater. When comparing stress in posterior margin and anterior margin, the absolute increment of stress value was greater in posterior displacement group than in anterior displacement group. Baumann angle increased significantly when fragment displaced medially. Above findings indicated that displacement direction altered the location of stress concentration. Stress augmentation was greater in posterior displacement group. Stress in related area significantly increased constantly when contact area of the fracture site reduced. Baumann changed obviously when fragment displaced medially. The results preliminarily verify the hypothesis that displacement of the distal fragment was the main contributor to cubitus varus following supracondylar humeral fracture. These findings provided certain evidences supporting the empirical rule “better anterior than posterior, better radial and ulnar”.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

全文链接：

Key words: Finite Element Analysis, Humerus, Fractures, Bone

CLC Number:

R318

Chen Lin-wei, Zhao Jing-tao, Zheng Ting-qu, He Chang-qiang, Sun Han-qiao, Huang Feng, Zheng Xiao-hui, Gan Yan-qun. Model of reduced pediatric supracondylar humeral fracture with residual displacements: a finite element analysis of mechanical responses[J]. Chinese Journal of Tissue Engineering Research, 2015, 19(13): 2125-2132.

Figures/Tables 2

2.1 模型建立图5为建模过程，实际建成肱骨远端有限元模型共含有四面体单元89 252个单元，48 752个节点。 2.2 模型验证在体外尸体骨实验中，Dunham等[29]对肱骨远端骨组织的力学性能进行了测试，按照其描述的分层和取值方法，本次实验所建有限元模型相应分层应力加载结果与Dunham等提供数据对比见图6，Dunham等研究的对象为成人骨，载荷-位移曲线反映骨材料具有一定的弹塑性，且弹性阶段线斜率高于本实验模型，本次实验模型所用CT图像来自于儿童，材料赋值时设定为不均质弹性，所得曲线斜率较一直，弹性模量略低于Dunham实验，总体而言本次实验所建立的模型在材料属性上与真实情况贴近，能够反映肱骨远端骨组织加载后的响应特征，可以用于下一步的生物力学分析。 2.3 后侧缘应力方差齐性检验示差异无显著性意义(P=0.09)，可进行下一步方差分析，主效应检验结果示移位方向、接触面积的主效应及它们之间交互作用对骨折端后侧缘应力值影响显著(P < 0.01)，事后检验示骨折端后侧缘的平均应力由大到小排列依次为：后内侧移位、后侧移位、前内侧移位、无移位及内侧移位，其中后内侧移位下应力值显著高于其余4组(P < 0.01)，其余4组组间对比差异均无显著性，当接触面积为75%时，骨折端后侧缘的应力值显著增高(P < 0.01)，表1示多重组间比较结果与事后检验相符，同移位方向内比较，接触面积小者应力值大，同接触面积下比较，后内侧移位组应力值大，应力高值出现在75%接触后内侧移位组，75%接触后侧移位组次之，此两组应力值与其他各组相比差异存在显著性意义，其余组间对比差异基本无显著性意义。 2.4 前侧缘应力方差齐性检验示无显著性(P=0.36)，主体效应检验中移位方向、接触面积的主效应及它们之间交互作用对骨折端前侧缘应力值影响显著(P < 0.01)，事后检验示前内侧移位、内侧移位、后内侧移位、后侧移位及完全复位下骨折端前侧缘应力值逐渐降低，方向刚好与后侧缘应力值结果相反，对比下前内侧移位与后内侧移位、完全复位应力值差异有显著性意义，接触面积比较结果呈现"

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