Dynamic simulation of the edge load caused by the separation of the ceramic cup and femoral head

doi:10.3969/j.issn.2095-4344.0106

Abstract

Abstract:

BACKGROUND: The edge load contact caused by joint separation causes great stress concentration and then produces a large amount of wear. The edge contact caused by hip joint separation is a dynamic process of femoral head touching the rim of the acetabulum and sliding into the acetabulum quickly, so a dynamic contact mechanical model is needed.

OBJECTIVE: To obtain the dynamic mechanical simulation model of ceramic acetabulum under the edge load contact, so as to provide the contact mechanics foundation for the wear analysis of hip joint under the condition of edge load, and provide theoretical basis for prosthesis design and surgeon operation.

METHODS: By using 3D modeling software SolidWorks and dynamic simulation software ADAMS, edge load contact dynamics simulation model of ceramic femoral head and acetabular cup was established to verify the edge load contact deformation by numerical method. The effects of acetabular abduction angle and initial separation distance on edge load contact were analyzed.

RESULTS AND CONCLUSION: (1) The contact stiffness coefficient used in the model is reasonable and effective. This model can be used to study the parameters that influence the edge load contact of hip joints. (2) The excessive cup inclination angle and initial separation distance will increase the severity of the edge load. (3) Acetabular cup inclination angle and initial separation distance are two important factors that affect the edge load contact.

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

Key words: Hip Joint, Femur Head, Acetabulum, Tissue Engineering

CLC Number:

R318

Feng Li, Wang Jun-yuan, Liu Feng, Cheng Bo. Dynamic simulation of the edge load caused by the separation of the ceramic cup and femoral head [J]. Chinese Journal of Tissue Engineering Research, 2018, 22(7): 985-990.

Figures/Tables 3

2.1 步态条件下股骨头-臼杯动态分离及边缘接触力在图6中，初始分离距离代表手术安装位置误差(如图1A)。图6所示为动态仿真下股骨头与臼杯分离距离和接触力在一个稳定周期内的变化结果。当分离距离为0 mm时(髋关节负重阶段)，股骨头在臼杯内部接触，接触力大小以及变化趋势与外载荷一致，接触力的两次峰值为3 000 N，与外载相同。当动态分离距离大于0 mm时(摆动阶段)，外载荷迅速减小，股骨头与臼杯开始分离，产生边缘接触，当初始分离距离为4 mm时，产生的最大动态分离距离为3.4 mm。结果还显示，当人体脚后跟着地时，股骨头将从臼杯的边缘快速滑进臼窝中(在循环周期的3%-5%)，该过程中接触力值快速增大，说明当股骨头从边缘滑进臼窝时，臼杯边缘容易产生应力集中。同时说明了条纹磨损的形成以及高磨损量的产生与股骨头与臼杯的边缘接触密切相关，且其主要发生在股骨头从臼杯边缘快速回到臼窝的过程中。减少股骨头与臼杯之间的边缘接触现象，可以减少接触力在臼杯边缘的集中，对假体起到一定的保护作用。 2.2 臼杯边缘接触变形验证选取步态周期的60%(0.6 s)和80%处(0.8 s)(图6a，b分别选取了股骨头与臼杯发生边缘接触的两个瞬时位置的变形)来计算变形，图7为对比结果。如图7所示，在步态周期60%处，随着臼杯外展角的增加，赫兹接触与ADAMS接触模型所计算的臼杯边缘变形都在增大，而在步态周期80%处，随着臼杯外展角的增加，臼杯边缘变形都在减小，在不同外展角和不同接触瞬时，仿真模型与理论模型的计算值呈现出一致的变化趋势。该验证结果表明，仿真模型中的接触刚度系数设置较好地反映了理论模型的结果。"

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