InterTan compression hip screw versus three parallel cannulated screws for Pauwels III femoral neck fractures: a finite element analysis

Abstract

Objective To explore the biomechanical properties of InterTan compression hip screw versus versus three parallel cannulated screws in the fixation of Pauwels Ⅲ femoral neck fracture and their clinical implications.Methods A healthy male volunteer,28 years of age and 75 kg in weight,was enrolled in the present study.The spiral CT scans of his right proximal femur were used for reconstruction of the 3D model of Pauwels Ⅲ femoral neck fracture together with 3D reconstruction of fixation models of InterTan compression hip screw and of three parallel cannulated screws by means of reverse engineering software.With Ansys software,the 3D finite element models were established of the 2 internal fixations,in which axial stresses of 700 N were loaded.We measured and compared respectively the yon Mises stress and displacement distributions in different fixations and on the femurs fixated by the 2 implants,as well as the stress and displacement peak values.Results The stress on the implant was mainly located on the middle of the screw and near the fracture line.The peak stress was higher in the cannulated screw model (116.4 MPa) than in the InterTan compression hip screw versus model (65.7 MPa).The stress on the femur was mainly located on the inside of the proximal end.The peak stress was also higher in the cannulated screw model (27.6 MPa) than in the InterTan compression hip screw versus model (13.2 MPa).In the lnterTan compression hip screw versus model,the implant displacement was vertically downward,with the peak displacement of 0.84 mm at the fixation and 0.76mm at the bone end.In the cannulated screw model,the implant displacement was along the femoral neck,with the peak displacement of 1.49 mm at the fixation and 1.61 mm at the bone end.Conclusions In the treatment of Pauwels Ⅲ femoral neck fracture,the InterTan compression hip screw versus results in even stress distribution and may be superior to the three parallel cannulated screws in the fixation stability.Since InterTan compression hip screw versus fixation can lead to a vertically downward displacement,coxa vara is a complication that should be prevented.Since the three parallel cannulated screws can lead to a displacement along the lateral femoral neck,shortening of the femoral neck should be taken into consideration as a likely complication. Key words: Femoral neck fracture; Finite element analysis; Computer simulation; Fracture fixation, internal