Three-dimensional finite element analysis of different quantity and configuration of cannulated lag screws for femoral neck fractures

Abstract

Objective To analyze biomechanical differences among quantity configurations of four common cannulated screws using three-dimensional finite element analysis. Methods The Dicom CT images of the right proximal femoral neck of a 65-year-old Chinese healthy volunteer were used to establish models of three kinds of different Pauwels types of femoral neck and four kinds of different quantity and configuration models (triangle, inverted triangle, rectangle, diamond) through three-dimensional virtual softwares. Models were imported into the finite element analysis software Ansys. After axial load application, the stress and displacement on the screws and femoral head were compared. The peak stresses on the screws, peak stresses on the femoral head break side and displacement peaks were observed. Results Four kinds of quantity and configuration models (triangle, inverted triangle, rectangle, rhombus) had different peak stress on the screws and femoral head break side and different displacement peak. Among Pauwels typeⅠfractures, the peak stresses on the screws were 46.382, 32.159, 43.985, and 24.342 MPa; the peak stresses on the femoral head break side were 5.840, 7.440, 3.731, and 6.311 MPa; the displacement peaks were 0.610, 0.608, 0.598, and 0.595 mm. Among Pauwels type Ⅱ fractures, the peak stresses on the screws were 46.763, 39.979, 49.619, and 25.692 MPa; the peak stresses on the femoral head break side were 4.971, 7.332, 3.161, and 5.734 MPa; the displacement peaks were 0.634, 0.635, 0.622, and 0.631 mm. Among Pauwels type Ⅲ fractures, the peak stresses on the screws were 51.432, 39.477, 51.515, and 26.949 MPa, and the peak stresses on the femoral head break side were 6.163, 10.070, 5.257, and 9.552 Mpa; the displacement peaks were 0.662, 0.654, 0.644, and 0.644 mm. Conclusion The fixation of femoral neck fractures with four screws in a diamond position can guide clinical application, for the procedure has better stress dispersion effects, ensure fracture stablility, provide effective sliding compression and anti-torsion and have biomechanical advantages. Key words: Femoral neck fractures; Finite element analysis; Fracture fixation, internal