两种内固定方式固定青壮年不稳定型股骨颈骨折生物力学特性的有限元分析

A finite element analysis of two internal fixation methods for unstable femoral neck fractures in young adults

目的应用有限元方法比较3枚空心螺钉与3枚空心螺钉加前内侧支撑钢板固定垂直不稳定型(PauwelsⅢ型)股骨颈骨折的力学稳定性。方法选取1名男性志愿者,34岁,身高为173 cm,体重为75 kg。应用螺旋CT对髋关节至胫骨中段行薄层连续扫描,在股骨CT数据基础上,通过数字医学软件建立股骨三维模型。对股骨颈进行必要的切割,模拟PauwelsⅢ型股骨颈骨折,分别行3枚空心螺钉倒"品"字形固定(单独空心钉组),3枚空心螺钉倒"品"字形+前内侧钢板固定(空心钉联合钢板组)。对两组模型施加同样的约束和3种载荷(缓步行走、扭转、单腿站立),比较两组模型在同种载荷作用下的应力及形变分布。结果两组模型在各种载荷作用下的最大形变量都发生在股骨头,缓步行走时空心钉联合钢板组模型位移为1.97 mm,低于单独空心钉组模型的2.26 mm;扭转和单腿站立时两组模型形变近似。各种载荷作用下,模型的最大应力都发生在最下面一枚空心螺钉的中段、骨折线处。单独空心钉组模型缓步行走、扭转、单腿站立时的应力峰值分别为318.09、92.11、147.21 MPa,高于空心钉联合钢板组模型(229.86、86.94、124.48 MPa)。结论空心螺钉加前内侧支撑钢板固定可有效分担空心螺钉上的应力,对骨折端的力学稳定性优于单独3枚空心螺钉固定,能有效预防股骨颈缩短,是青壮年不稳定型股骨颈骨折值得推荐的内固定方式。

Objective To compare internal fixation with 3 cannulated screws versus with an anteromedial support plate plus 3 cannulated screws using finite element analysis for unstable femoral neck fractures(Pauwels typeⅢ).Methods Recruited for this study was a 34-year-old male volunteer with a height of 173 cm and a weight of 75 kg.Continuous thin-layer helical CT was conducted to scan the segment from his hip joint to the middle shaft of his tibia.Digital medical software was used to establish three-dimensional models of the femur based on his femoral CT data.The digital femoral necks were dissected as necessary to simulate femoral neck fractures of Pauwels typeⅢ.The fractures were fixated with 3 ordinary cannulated screws in a mode of inverted triangle(screw group)and with 3 ordinary cannulated screws in a mode of inverted triangle plus an anteromedial steel plate(screw-plate group).After the 2 groups of models were subjected to identical constraints and 3 kinds of load(slow walking,twisting and standing on one leg),they were compared in terms of distribution of Von Mises stress and deformation.Results Under various loads in both groups,the maximum deformation occurred in the femoral head.In the condition of slow walking,the deformation in the screw-plate group was 1.97 mm,which was smaller than that in the screw group(2.26 mm).In the conditions of twisting and standing on one leg,similar deformations were observed in both groups.Under all kinds of load,the maximum stress occurred in the middle part of the bottom screw and the fracture line in all the models.In the screw group,the peak stresses were 318.09 MPa,92.11 MPa and 147.21 MPa for conditions of slow walking,twisting and standing on one leg,greater than those in the screw-plate group(229.86 MPa,86.94 MPa and 124.48 MPa).Conclusions The cannulated screws plus an anteromedial support plate are a recommendable fixation method for young adults with unstable femoral neck fracture,because they can effectively share the stress on the cannulated screws,lead to better mechanical stability of the fracture ends than the fixation with merely 3 cannulated screws and effectively prevent shortening of the femoral neck.