Experimental and numerical analyses of the pull-out response of a steel post/bovine bone cementless fixation

Effect of initial interference fit on pull-out strength in cementless fixation between bovine tibia and smooth stainless steel post was investigated in this study. Compressive behavior of bovine spongious bone was studied using mechanical testing in order to evaluate the elastic-plastic properties in different regions of the proximal tibia. Friction tests were carried out in the aim to evaluate the friction behavior of the contact between bovine spongious bone and stainless steel. A cylindrical stainless steel post inserted in a pre-drilled bovine tibia with an initial interference fit was taken as an in vitro model to assess the contribution of post fixation to the initial stability of the Total Knee Arthroplasty (TKA) tibial component. Pull-out experiments were carried out for different initial interference fits. Finite Element Models (FEM) using local elastic-plastic properties of the bovine bone were developed for the analysis of the experimental ultimate pull-out force results. At the post/bone interface, Coulomb friction was considered in the FEM calculations with pressure-dependent friction coefficient. It was found that the FEM results of the ultimate force are in good agreement with the experimental results. The analysis of the FEM interfacial stresses indicates that the micro-slip initiation depends on the local bone properties.