Are Flexible Metaphyseal Femoral Cones Stable and Effective? A Biomechanical Study on Hinged Total Knee Arthroplasty

Abstract

BackgroundCones currently available in the market are rigid, and unless they are custom-specific designed, are unable to correctly adapt to the shape of the patient’s bone. Therefore, flexible metaphyseal cones have been recently introduced to reduce potential bone trauma during implantation. Even if a preliminary clinical study on their use has shown promising results, no biomechanical study evaluates and quantifies their mechanical efficacy and safety. MethodsTwo commercial versions of flexible cones were analyzed in this study using finite element analysis, based on a previously validated model. Each cone geometry was modeled both as flexible and as rigid, and implanted following surgical guidelines. Three activities were simulated in this study and compared among configurations: surgical impaction, walking, and chair rise. ResultsDuring impaction, results showed considerably reduced stress in the flexible cones in comparison with rigid ones; the stress resulted was also better distributed and more homogeneous all over the cortical bone, with lower bone peaks. Considering the 2 different activities, the analysis did not show any remarkable differences between flexible and rigid cones both in terms of bone stress and implant micromotion. ConclusionsThe findings demonstrate that metaphyseal flexible cones allow macrodeformation during impaction due to their flexibility, and therefore, are safer in comparison with rigid cones. However, for the daily tasks investigated, results showed no major differences between rigid and flexible cones in terms of bone stress, implant stability, and micromotion. Therefore, their mechanical performances can be considered similar to the rigid cone.