A finite element analysis of two internal fixation methods for unstable femoral neck fractures in young adults / 中华创伤骨科杂志

ABSTRACT

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 type Ⅲ).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 type Ⅲ. 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.