Abstract
Introduction
In revision TKA, the management of bone loss depends on location, type, and extent of bony deficiency. Treatment strategies involve cement filling, bone grafting and augments. On the market several solutions are currently available, differing for their shape, thickness and material. While the choice of the shape and the thickness is mainly dictated by the bone defect, no explicit guideline is currently available to describe the best choice of material to be selected for a specific clinical situation. However, the use of different materials could induce different response in term of bone stress and thus changes in implant stability that could worsen long-term implant performance.
For these reasons, an investigation about the changes in bone stress in the femur and in the tibia when augments, with different materials and thicknesses was performed.
Methods
Different configurations have been separately considered including proximal tibial, distal or/and posterior femoral augments with a thickness of 5, 10 and 15 mm.
Apart the control, in which no augments were used, but only the TKA is considered, the augment in all the other configurations were considered made by three different materials: bone cement, to simulate cement filling, tantalum trabecular metal and conventional metal (titanium for the tibia and CoCr for the femoral augments).
Each configuration was inserted on a lower leg model including a cruciate-retaining total knee arthroplasty and analyzed by means of finite element analysis applying the max force achieved during walking.
The bone stress was investigated in the medial and lateral region of interest close to the augment (with a bone thickness of 10 mm) and in an additional bone region of interest of 50 mm thickness.
The bone stress have been compared among the different models and also with respect to the control model.
Results
In general, the use of an augment induces a change in bone stress, especially in the region close to the bone cuts. The stiffness of the augment must be as close as possible to the one of the bone.
Cement has the best results in terms of bone stress, however, it is only suitable for extremely small defects. Tantalum trabecular metal has results very close to cement and it could be consider a good alternative to cement for any size of defect.
Metal (both titanium and CoCr) has the least satisfying results inducing the highest change in bone stress with respect the control.
Conclusions
Tibial and femoral bone augments are adopted in case of bone defects that could be present during a revision knee replacement. Several solutions are available on the market in different shapes and materials. However, very few studies are reported to provide possible guidelines.
The results of this study demonstrate that material stiffness of the augment must be as close as possible to the one of the bone to achieve the best results.
