The influence of stem surface in micromobility and cement bone stresses

Abstract

Cemented hip prostheses have produced excellent clinical results and THR is at that moment one of the most successful surgical techniques, with good success rates. Cemented fixation represents 87% of the total number of replacements according to the Swedish orthopedic register. Therefore, it is important to reduce revisions and understand why revision happens. The purpose of this study was to access the micro mobility and stresses developed in a cemented hip replacement. An in vitro cemented Lubinus SPII stem replacement was performed in synthetic femurs and sectioned. Section 5 was analyzed after fatigue test and was observed to be the most critical in crack incidence. A CAD model of this section was built considering bone and cement boundary geometry. The finite element model was built and the influences of different interface conditions of the cement interfaces (bone and stem) were analyzed. The interface stiffness associated with stresses for interface failure was used to simulate different surface roughness and time after surgery. The surface roughness associated with the interface strength did not present significant influence relatively to cement interface stresses and micro mobility of the stem. The type if interface changes the stress and strain distribution of bone and the most severe factor is friction at the cement/bone interfaces. The cement/bone interface debonding increase the bone strains and suggests pain.