Three-dimensional Finite Element Analysis And Clinical Efficacy Of Dimond Fixation With Four Cannulated Screws For Pauwels Type Ⅲ Femoral Neck Fractures

Objective: To investigate the biomechanical properties and clinical efficacy analysis on Pauwels type Ⅲ femoral neck fractures fixed with four diamond-array cannulated screws.Methods: CT data of right femoral neck,cannulated screw and dynamic hip screw(Dynamic Hip Screw,DHS)data provided by Synthes medical device company were used in a healthy male volunteer.Pauwels type Ⅲfemoral neck fracture model and three different internal fixationwere built through Mimics software(Group A,four-screw dimond internal fixation;Group B,three-screw inverted triangle internal fixation;Group C,DHS combined with one anti-rotation screw).Three models were put into the finite element analysis software Ansys to stimulate the motion displacement and stress distribution of internal fixation and fracture site under the condition of human upright position.Retrospective clinical analysis of 20 cases with Pauwels type Ⅲ femoral neck fractures using four dimond-array screws fixation was conducted.Results: For the three groups of internal fixation model A,B and C,the peak stresses on the screws of femoral neck were 26.949 MPa,39.477 MPa and 34.567 MPa.The overall stress peak of group C internal fixation was concentrated at the distal screw of the femoral shaft plate,which was 50.36 Mpa.The peak stresses at fracture site were 9.552 MPa,10.070 MPa and20.101 MPa,the displacement peaks were 0.644 mm,0.654 mm and 0.668 mm.Clinically,20 patients with Pauwels type Ⅲ femoral neck fractures were treated with four dimond-shaped screw configuration.All patients were followed up for an average of 30.9 months(13-57 months).None of the cases was nonunion and the mean union time was 3.7 months(3-6 months).One case(5%)had necrosis of femoral head.The mean Harris score of hip function was 87.1 points(60-92 points),and the excellent-and-good rate was 85%.Conclusions: Compared with the other two internal fixation methods,fixation of Pauwels type Ⅲ femoral neck fractures with 4 diamond-array cannulated screws have better anti-shearing force and dispersion of stress function.In addition,it can provide effective sliding compression effect as well as anti-shortening of femoral neck.It can be used as one of the options for the treatment of Pauwels type III femoral neck fracture.