Abstract
Aim
The aim of this FE study was to analyse the comparative behaviour of cement and metal based augments in TKR and quantify the stresses within these different augments and underlying cancellous bone.
Materials and methods
A three-dimensional FE model was constructed from a CT scan of the proximal tibia using SIMPLEWARE v3.2 image processing software. The tibial component of a TKR was implanted with either a block or wedge-shaped augment made of either metal or cement. The model was axially loaded with a force of 3600N and testing was conducted with both evenly and eccentrically distributed loads.
Results
Upon loading the FE model, the von-Mises stresses in the cancellous bone underneath the augments was higher with cement based augments in comparison their metal counterparts. When evenly loaded the maximum recorded compressive stresses within the metal augments were 5 times less than the endurance limit of the material, whilst the stresses within cement augments were only half the endurance limit of the material. Upon eccentric loading compressive stresses within the cement based augments in excess of the endurance limit were recorded.
Discussion
The FE model has demonstrated that cement based augments undergo greater deformation when loaded and transfer greater loads to the underlying cancellous bone thus reducing the possibility of stress shielding. However, the compressive stresses within cement based augments are too close to the endurance limit of the material and with uneven loading even exceed it. This would imply that cement based augments are more prone to fatigue failure than their metal counterparts.
Conclusion
This study supports the use of metal over cement based augments in augmented and revision TKR surgery.
