Motion and its Effects on the Cement Mantle – A Biomechanical Analysis of Femoral Stem Displacement during Implant Cementation

Abstract

Background: It is a common notion that motion of a femoral component during cementation should be avoided as it may weaken the cement mantle. We created an in vitro model of cemented femoral components and subjected them to varying rotational motion during the cement curing process, to measure the effect on the pullout strength of the stem. Methods: 21 sawbones femurs were separated into four groups. The first group served as control and was cemented in a standard fashion. The remainder of the stems were divided into groups and subjected to angular rotational displacement within the cement mantle during curing . Anteroposterior and lateral radiographs were obtained of each model to evaluate for cement defects. Pullout strength testing was performed. Results: Despite rotational displacement, no cement defects were noted on imaging. The control stems showed an average pullout strength of 3735.79N. The experimental groups showed a trend for lower failure loads but it was not statistically significant (P=0.063). Of the 21 stems tested, three encountered cement mantle failure and associated stem pullout and the remainder failed by peripros-thetic fracture. Conclusion: Despite conventional thinking that rotational displacement during the cementing process leading to disruption of the cement mantle integrity, this was not borne out in our study. This should give surgeons confidence that in the set-ting of unintended rotational displacement of a femoral stem, returning the stem to its original position does not significantly compromise the integrity of the cement mantle or the pullout strength of the femoral implant. Small displacement of the femoral stem with prompt correction during cement curing does not cause evident cement mantle defects or a loss of femoral stem pullout strength.