2022, Vol. 26 ›› Issue (18): 2807-2811

Finite element analysis of Pauwels type III femoral neck fracture fixed with three configurations of cannulated screws

Yan Kun, Mou Limin, Yang Xiaohui, Wang Jian, Ran Jian   

Abstract: BACKGROUND: Cannulated screw is widely used in the clinical treatment of femoral neck fracture, while the traditional inverted triangle configuration has a high failure rate in the treatment of Pauwels III femoral neck fracture. Some scholars have proposed to use “F” configuration and off-axis configuration to obtain better therapeutic effects. However, there are few reports on the comparative analysis of the above-mentioned three configurations from the perspective of biomechanics.   
OBJECTIVE: To compare the biomechanical properties of Pauwels type III femoral neck fracture with three cannulated screw placement methods of inverted triangle configuration, “F" configuration, and off-axis configuration by three-dimensional finite element method.
METHODS: A healthy male volunteer aged 35 years old with a body mass of 70 kg was recruited in this study. Image data (.dicom format) of his right proximal femur were obtained by computed tomography scanning. The three-dimensional images of the proximal femur was reconstructed using mimics 15.0 software. Solidworks 2017 software was used to construct the models of Pauwels type III femoral neck fracture fixed with inverted triangle configuration, “F” configuration, and off-axis configuration. The maximum displacement of the broken end of the fracture in the X, Y, and Z axes, the maximum stress in internal fixation, the total displacement of the proximal femur and the maximum stress distribution of the proximal femur in the three groups were compared under loading stress.   
RESULTS AND CONCLUSION: The maximum stresses of inverted triangle configuration, “F” configuration, and off-axis configuration on the screw were 71.896, 66.792, and 59.071 MPa, respectively. The maximum stresses of inverted triangle configuration, “F” configuration, and off-axis configuration in the proximal femur were 12.791, 11.886, and 11.949 MPa, respectively. The maximum displacements of inverted triangle configuration, “F” configuration, and off-axis configuration at the fracture end were 0.844, 0.587, 0.538 mm on the X axis, 0.491, 0.295, 0.340 mm on the Y axis, and were 0.832, 0.752, 0.741 mm on the Z axis, respectively. The overall maximum displacements of inverted triangle configuration, “F” configuration, and off-axis configuration in the proximal femur were 1.707, 1.396, and 1.325 mm, respectively. To conclude, the stress of off-axis configuration and “F” configuration are more dispersed, and the displacement of fracture end is smaller, which is a better choice for the treatment of Pauwels type III femoral neck fracture. The off-axis configuration is slightly better than the “F” configuration in anti-inversion stress and longitudinal shear stress.
Key words: internal fixation configuration, femoral neck fracture, finite element, cannulated screw, biomechanics, F configuration, inverted triangle configuration, off-axis configuration