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

Abstract

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 Eb, 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, [Formula: see text], and IF* = 1 mm for which the maximal contact pressure tN = 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, Eb, and IF. For the reference configuration, the optimal pull-out force is obtained for μ = 0.6 (respectively, Eb = 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 Eb, while for µ > 0.2, the optimal value of IF has a nonlinear dependence on µ and decreases as a function of Eb. The results can be used to help surgeons determine the optimal value of IF in a patient specific manner.

Determinants of the primary stability of cementless acetabular cup implants: A 3D finite element study

“…To achieve an optimal primary stability, a compromise should be found between: 1. reducing the relative micro-motions at the bone-implant interface (BII), 2. avoiding large gaps between bone and implant, which may lead to the formation of fibrous tissue in the peri-implant region [5], the formation of low-quality bone tissue or even inhibit bone growth [22,32,41], and 3. avoiding excessive stresses in peri-implant bone tissue, which may lead to bone necrosis or local ischemia [45]. All these phenomena may jeopardize osseointegration processes [22,38,42], and can lead to implant loosening. It remains difficult to predict ACI loosening because of its multi-factorial causes related to the implant properties, the cavity geometry (e.g., its diameter), and to the patient's bone quality [1,18,26].…”

“…For these reasons, several numerical models have been developed to assess the biomechanical behavior of the cementless ACI with simplified bone geometries [17,38,46,54]. While such models offer some initial insight on the biomechanical parameters and the contact behavior of the BII in a controlled environment, their simplified geometry constitutes a strong limitation because it does not properly capture 3D effects that have an important influence on the structural behavior of the pelvis.…”

“…Therefore, geometrically nonlinear FE analyses were performed to simulate the quasi-static insertion and subsequent pull-out of the ACI in a patient's hemipelvis. The influence of a broad range of different implantand patient-specific parameters on the ACI primary stability, such as the friction coefficient at the BII , the bone quality in terms of cortical and trabecular bone Young's moduli c , t , and the diametric interference fit , are analyzed and compared to a previous 2D study [38].…”

Monitoring cementless femoral stem insertion by impact analyses: An in vitro study

“…Moreover, static [27,28] and dynamic [29] finite element models have been developed to understand the mechanical phenomena occurring during and after the AC implant insertion. Eventually, a cadaveric study showed that the instrumented impact hammer could be used in situations closed to the clinics in order to determine the AC implant primary stability [30].…”

Biomechanical behaviours of the bone–implant interface: a review

“…Assessing the friction coefficient is important to understand the behaviour of the BII during and just after surgery and thus to prevent micromotion at the BII, which may cause implant failure. Moreover, the frictional behaviour is an important input parameter to be used in finite-element models [96,97] in order to model implant surgical procedures.…”