Cortical and interfacial bone changes around a non-cemented hip implant: Simulations using a combined strain/damage remodelling algorithm

Prostheses alter the loading pattern in bones. For example femoral hip implants cause the cortical bone to remodel and the implant/bone interface to react. To date, simulations of peri-prosthetic bone adaptations have succeeded for the bulk bone remodelling only. In this study we use an approach based on a combined strain/damage algorithm to simultaneously predict both bulk and interfacial peri-prosthetic bone adaptation around a non-cemented hip prosthesis. The influence of stem stiffness is investigated; a flexible iso-elastic stem (20 GPa), an titanium alloy stem (110 GPa), and a stiff cobalt chrome (CoCrMo) stem (210 GPa). The results predict that an iso-elastic stem reduces proximal bone loss because stress shielding is prevented but it increases proximal interface resorption due to damage-stimulated resorption. On the other hand, a stiff cobalt chrome stem increases proximal strain-stimulated resorption but does not induce proximal interfacial damage-stimulated resorption; however damage-stimulated resorption surrounding the distal tip is predicted to increase with stiffer stems. Simulations for the titanium stem were predicted to minimise both strain and damage related remodelling. We propose that this combined strain/damage remodelling algorithm can provide realistic simulations of the response of bone around load-bearing orthopaedic implants.