Finite element analysis of novel femoral neck system for unstable femoral neck fractures

doi:10.3969/j.issn.2095-4344.3810

Abstract

Abstract: BACKGROUND: Treatment strategies for femoral neck fractures include cannulated screw fixation, dynamic hip screw fixation, intramedullary nail fixation, locking plate fixation, and hip replacement. However, the best treatment for Pauwels type III femoral neck fractures is still controversial.
OBJECTIVE: To analyze the biomechanical characteristics of a novel femoral neck system for unstable femoral neck fractures by using a three-dimensional finite element analysis method.
METHODS: The CT imaging data of the femur of a healthy volunteer were selected and imported into the medical three-dimensional reconstruction software Mimics 21.0 to obtain the original three-dimensional model of the femur. The model was exported to an STL format file and imported into the Geomagic Wrap2017 software for optimization so as to construct femoral cortical bone and cancellous bone structure. The optimized model was imported into Solidworks2017 software, and the 3D model of Pauwels type III femoral neck fracture was reconstructed through Boolean operation. The Pauwels angles are set to 50°, 60° and 70°, respectively. Solidworks2017 software was used to establish three types of internal fixation models (femoral neck system, positive triangular hollow screw, and inverted triangular hollow screw) based on clinical fixation procedures and engineering geometric data modeling. Finally, Abaqus2017 software was used for meshing. After applying load and data calculation, the stress distribution, peak stress and maximum displacement of femur and internal fixation were analyzed in each model.
RESULTS AND CONCLUSION: (1) No matter what the angle of the fracture, the stress of the proximal femur in the three internal fixation models was mainly distributed near the medial femoral talus and spread to the surroundings. Among them, the inverted-triangular hollow screw group had the largest stress. The femoral neck system group had the smallest stress. (2) Regardless of the angle of the fracture, the stress of the internal fixation device in the three internal fixation models was mainly distributed on the middle surface of the screw near the fracture line, and the inverted triangle hollow screw group had the least stress, and the femoral neck system group had the largest stress. (3) No matter what the angle of the fracture, the peak displacement of the femur in the three internal fixation models was mainly concentrated on the top of the femoral head. Among them, the peak displacement was the largest in the inverted triangular hollow screw group, and the smallest in the femoral neck system group. (4) No matter what angle of fracture, the peak displacement of the internal fixation device in the three internal fixation models was mainly at the top of the screw. The peak displacement was the largest in the positive triangle hollow screw group, and the smallest in the femoral neck system group. (5) The results show that the biomechanical stability of the femoral neck system for the treatment of unstable femoral neck fractures is better than that of hollow screws, and the risk of internal fixation failure is lower than that of hollow screws.

Key words: bone, internal fixation, fracture, femoral neck, femoral neck fracture, internal fixation system, finite element analysis, biomechanics

CLC Number:

Fan Zhirong, Su Haitao, Zhou Lin, Huang Huida, Zhou Junde, Jiang Tao, Liu Zitao. Finite element analysis of novel femoral neck system for unstable femoral neck fractures[J]. Chinese Journal of Tissue Engineering Research, 2021, 25(15): 2321-2328.

Figures/Tables 5

2.1.2 Pauwels角60°股骨颈骨折 3种内固定模型股骨近端应力峰值均集中在骨折线内下侧，靠近股骨距附近。股骨颈内固定系统组、正三角形空心螺钉组、倒三角形空心螺钉组的股骨近端应力峰值分别为48.8，58.9，56.2 MPa，正三角形空心螺钉组最大，股骨颈内固定系统组最小，见图4、表2。 2.1.3 Pauwels角70°股骨颈骨折 3种内固定模型股骨近端应力峰值均集中在骨折线内下侧，靠近股骨距附近。股骨颈内固定系统组、正三角形空心螺钉组、倒三角形空心螺钉组的股骨近端应力峰值分别为54.3，62.6，63.6 MPa，倒三角形空心螺钉组最大，股骨颈内固定系统组最小，见图4、表2。 2.2 内固定装置应力分布及峰值 2.2.1 Pauwels角50°股骨颈骨折 3种内固定模型内固定装置的应力峰值主要集中在骨折线附近的螺钉表面。股骨颈内固定系统组、正三角形空心螺钉组、倒三角形空心螺钉组的内固定装置应力峰值分别为586.5，181.2，156.0 MPa，股骨颈内固定系统组最大，倒三角形空心螺钉组最小，见图5、表2。 2.2.2 Pauwels角60°股骨颈骨折 3种内固定模型内固定装置的应力峰值主要集中在骨折线附近的螺钉表面。股骨颈内固定系统组、正三角形空心螺钉组、倒三角形空心螺钉组的内固定装置应力峰值分别为618.4，201.4，179.9 MPa，股骨颈内固定系统组最大，倒三角形空心螺钉组最小，见图5、表2。 2.2.3 Pauwels角70°股骨颈骨折 3种内固定模型内固定装置应力峰值主要集中在骨折线附近的螺钉表面。股骨颈内固定系统组、正三角形空心螺钉组、倒三角形空心螺钉组的内固定装置应力峰值分别为706.1，242.7，222.4 MPa，股骨颈内固定系统组最大，倒三角形空心螺钉组最小，见图5、表2。在内固定装置中，应力主要集中在骨折线附近的螺钉中间表面。由于结构的特殊性，股骨颈内固定系统的主钉与锁定防旋螺钉使用同一个套筒分出，同时存在一个大小为7.5°的角度，所以当轴向载荷加载时最大应力无可避免地集中在两钉连接处。股骨颈内固定系统组内固定装置的应力峰值高于两空心螺钉组。但是在应力分布云图中可以看出，股骨颈内固定系统模型中的应力分布比其他2个模型更均匀、更分散，见图5。这表明股骨颈内固定系统在股骨近端应力及应力分布传导方面优于正三角形空心螺钉和倒三角形空心螺钉，有利于为骨折愈合创造良好的力学环境。 "

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