Biomechanical Effects of Bone Quality and Implant Design on Femoral Damage Mechanism in Total Hip Arthroplasty

Abstract

Total hip arthroplasty (THA) has become a common solution to solve end-stage hip diseases of middle and old age patients. However, the complications following THA such as bone fracture might depend on the bone quality and implant design. A better outcome after THA could be achieved through the risk assessment from the early stage. Therefore, the aim of this study was to investigate the effects of bone quality and THA stem design on the mechanisms of micro-damage formation in femoral bones using CT-image based finite element method (CT-FEM). Two inhomogeneous bone models were developed from the CT images of 61 and 87-year-old patients and three types of stem were introduced to represent the corresponding THA models. Finite element analyses with a nonlinear damage analysis were then performed under the lateral bending and tortional conditions. It was observed that the implant geometries such as shoulder size, stem length, and cross-section shape influenced the damage behaviour of the models. The results suggested that the elderly patient had higher risk of implant loosening even at lower loading magnitude, compared to the younger patient. Several fracture locations were also predicted on both femoral models upon the complete failure. It was found that the fracture types can be clearly classified according to the Vancouver classification and the AO Foundation/Orthopaedic Trauma Association.