Analysis of stress distribution around total hip stems custom-designed for the standardized Asian femur configuration

In total hip replacement (THR), bone resorption related to the foreign body reaction around the implant causes bonding failure at the bone-prosthesis interface and adversely affects the function and longevity of femoral implants. Stress shielding is thought to be one of the possible biomechanical factors that causes bone resorption, and is related to prosthesis design. We therefore investigated stress distribution at the bone-implant interface of implant models custom-fitted to Asian individuals, using a finite-element method. Based on the standard geometry of Asian femurs, we designed four different custom-fitted implant stems and applied boundary conditions, including a stationary loading of 1750 N. Even though stress shielding was observed for all four different prostheses, the custom-designed implant with a stepped groove in the proximal-medial region had the largest maximum principal stress distribution along paths on the bone-implant interface. This implant type also showed the highest maximum principal stress distribution at the proximal (0.308 MPa), mid (0.872 MPa) and distal (12.981 MPa) regions of the cortical surface of the femur. In conclusion, the implant design with a stepped groove in the proximal-medial region showed an overall increase in stress distribution due to minimization of stress shielding afforded by the reduced effective area in the bone-implant interface. Therefore, this hip implant type could be a possible geometry to remain functional over the long term in THR patients.