利用有限元分析股骨颈骨折内固定术后前倾角变化对股骨近端力学的影响

Influence of anteversion angles on stress distributions of the proximal femur after femoral neck fracture fixation:A finite element analysis

目的探讨股骨颈骨折闭合复位空心螺钉内固定术后不同股骨颈前倾角对股骨近端力学分布的影响,为临床中内固定术解剖复位的重要性提供生物力学依据。方法采用16层螺旋CT扫描正常成人髋关节数据,基于三维重建软件和CAD软件,分别建立Pauwells角为70°的股骨颈骨折空心螺钉内固定术后前倾角为0°、5°、10°、15°、20°的股骨近端三维有限元分析模型,对所有模型施加人体缓慢行走时的载荷和约束,观察不同模型间股骨近端结构应力分布的变化。结果当前倾角未改变时(10°模型),股骨所受应力、产生的位移及发生的等效应变最小,股骨近端最大应力值为1.7 MPa,产生的位移为1.1 mm。随着前倾角的增大或减小,股骨近端所承受的有效应力及产生位移呈逐渐增大趋势。当前倾角为20°时,股骨近端及螺钉所受应力最大;当前倾角为0°时,股骨近端产生的位移及发生的等效应变值最大。股骨近端应力集中的部位由股骨距区域转移至头颈交界处的外上方。3枚空心螺钉承受的应力较周围骨组织高,最下方螺钉承受的应力较上方两枚螺钉明显增高。结论股骨颈骨折闭合复位空心螺钉内固定术中恢复前倾角达到解剖复位至关重要;股骨颈骨折术后生物力学因素的改变可能在术后股骨头坏死中起一定作用。

Objective To investigate the effects of different anteversion angles on stress distributions of the proxi- mal femur after femoral neck fracture fixation by cannulated screw, and to provide biomechanical evidences for the importance of anatomical reduction in internal fixation in clinic. Methods Femoral neck fracture with Pauwells angle 70~was treated with cannulated screw internal fixation, and its three-dimensional finite element models with five different anteversion angles set at 0°,5°,10°,15°and 20°, respectively, were constructed based on normal human anatomical data from multi-slice spiral CT as well as reverse engineering and CAD software. Loads were applied on each model to simulate normal walking status. Changes in stress distributions of the proximal femur in each model were observed. Results When the anteversion angle was 10°, the stress, displacement and equiv-alent strain of the femur was were the minimum, as the maximum stress of the proximal femur was 1. 7 MPa, and the displacement was 1. 1 mm. With the anteversion angle increasing or decreasing, the effective stress and dis- placement of the proximal femur was gradually increasing. When the anteversion angle was 20°, the stress of on the proximal femur and on the cannulated screw was became the maximum. When the anteversion angle was 0°, the displacement and equivalent strain of the femur also became the maximum. The stress concentration site of the femoral neck was gradually transferred from the inside rear to the outer top of the head and neck junction. The three cannulated screws there stood the higher stress than the surrounding bone tissues, and with the bottom screw stood the higher stress than the other top two screws. Conclusions Anatomic reduction is essential for femoral neck fracture fixation treated by cannulated screw. Changes in biomechanical factors after femoral neck fracture may play an important role in postoperative femoral head necrosis.