Dependence of the primary stability of cementless acetabular cup implants on the biomechanical environment

Biomechanical phenomena occurring at the bone-implant interface during the press-fit insertion of acetabular cup implants are still poorly understood. This article presents a nonlinear geometrical two-dimensional axisymmetric finite element model aiming at describing the biomechanical behavior of the acetabular cup implant as a function of the bone Young's modulus E, the diametric interference fit (IF), and the friction coefficient µ. The numerical model was compared with experimental results obtained from an in vitro test, which allows to determine a reference configuration with the parameter set: μ^* = 0.3, $$, and IF^* = 1 mm for which the maximal contact pressure t = 10.7 MPa was found to be localized at the peri-equatorial rim of the acetabular cavity. Parametric studies were carried out, showing that an optimal value of the pull-out force can be defined as a function of μ, E, and IF. For the reference configuration, the optimal pull-out force is obtained for μ = 0.6 (respectively, E = 0.35 GPa and IF = 1.4 mm). For relatively low value of µ (µ < 0.2), the optimal value of IF linearly increases as a function of µ independently of E, while for µ > 0.2, the optimal value of IF has a nonlinear dependence on µ and decreases as a function of E. The results can be used to help surgeons determine the optimal value of IF in a patient specific manner.