|Alternative Title||Study of the mechanical properties of femoral head and the selection method of head nails|
|Place of Conferral||北京|
本文旨在建立一种股骨头力学性能模拟方法用于头钉内固定效果的预测。主要内容包括：提出了一种股骨头分区域弹塑性模拟方法(Subregional Method with Elastoplasticity，SMEP)，并通过大尺度球头压痕实验对该方法的有效性进行了验证，进而利用该方法对两种类型头钉在不同股骨头内的力学效果进行模拟。具体内容如下：
1、提出了一种股骨头力学模拟方法。该方法利用患者的QCT(Quantitative Computed Tomography)，将股骨头不同骨密度部位分成多个具有不同弹塑性力学属性的区域，从股骨头模型的网格处理、股骨头内松质骨材料赋值、加载条件和结果提取几个方面进行了建模。
3、选择最常用的两种头钉（拉力螺钉和螺旋刀），运用SMEP方法对7个股骨头样本的头钉选择问题进行模拟。计算结果以应变超过特定屈服应变的单元体积作为判断哪种头钉力学效果更佳的指标。以股骨头内打钉位置处柱体的平均CT(Computed Tomography)值作为不同股骨头之间对比的参数。模拟结果显示，在现有7个样本中，头钉打入位置处柱体的平均CT值≤162.99 Hu时，两种头钉对股骨头的力学效果基本相同；当平均CT值为208.96 Hu～228.21 Hu时，拉力螺钉承载大载荷的能力好于螺旋刀片，但在小载荷情况下二者基本相同；当平均CT值≥260.48 Hu时，不论载荷大小，拉力螺钉的效果都比螺旋刀片的效果好。
Older people are more likely to have the proximal femoral fractures due to osteoporosis. A common clinical treatment is to insert the head nail into the femoral head to fix the fracture. External load is mainly sustained by the head nail and the femoral head before the fracture heals. Therefore, if the type of the head nail used for internal fixation is not suitable, which means the mechanical properties mismatching of the femoral head and the head nail, the head nail will retract or shift, even penetrate the femoral head. All these phenomena mean the failure of the clinical operation. At present, it is urgent to predict the mechanical effect of the femoral head and head nail before clinical operation. The core problem involved is the simulation of the mechanical properties of the femoral head.
This article aims to establish a mechanical simulation method of femoral head in order to forecast the internal fixation effect of head nail. The main contents include: a Subregional Method with Elastoplasticity (SMEP) for femoral head is developed. The effectiveness of the method is verified by large-scale ball head indentation experiments. Then the mechanical effects of two types of head nails in different femoral heads are simulated. The details are as follows:
1. A mechanical simulation method of femoral head is developed. The method makes use of the patients’ QCT (Quantitative Computed Tomography). The whole bone with inhomogeneous density is divided into multiple subregions with different elasto-plastic properties. The following works are performed: model mesh processing of the femoral head, material assignment of cancellous bone in the femoral head, loading conditions, and extraction of results.
2. The large-scale spherical indentation experiment of the femoral head is used to verify the effectiveness of SMEP. The actual femoral head is selected as the research object. A large-scale indentation experiment with a spherical indenter is performed on the specific position of the femoral head. The force-depth curve obtained from the SMEP is compared with that obtained from experiment. The two results are basically consistent, which verified the effectiveness of SMEP.
3. Two kinds of the common head nails (leg screw and spiral blade) are selected as the research object, SMEP method is used on seven femoral head’s femoral head sample samples. The element volume, whose strain exceeds the specific yield strain, is selected as the parameter for judging the mechanical effect of head nails. The average CT (Computed Tomography) value at the position of the nail in the femoral head is taken as the parameter for the comparison of different femoral head. The results show three different situations in the existing seven samples. When the average CT value is not more than 162.99 Hu, the mechanical effects of the two head nails are almost identical. When the average CT value is between 208.96 Hu and 228.21 Hu, the femoral head model with the lag screw shows better carrying ability for heavy load than that of the screw blade, but similar ability for small load. When the average CT value is greater than 260.48 Hu, the effect of the lag screw is better than that of the spiral blade, no matter how large the load is.
The SMEP method of the femoral head developed in this article can basically simulate the mechanical behavior of the femoral head, and predict the mechanical effects of different types of head nails. This provides a scientific basis for clinical precision diagnosis and treatment.
|加海友. 股骨头力学性能与头钉选择方法研究[D]. 北京. 中国科学院大学,2018.|
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