[Fracture of tibial stem in revision total knee arthroplasty].

An unusual case of implant failure after revision total knee arthroplasty (TKA) is presented and the case report is completed with the results of an ensuing biomechanical study made to explain possible causes leading to a fracture of the tibial stem. For this we used electron microscopic and biomechanical analyses. There was no material defect found at the site of fracture. By computerized modelling of the clinical situation, however, we found out that asymmetrical progressive osteolysis of the proximal tibia could have caused significant changes in mechanical straining associated with qualitative alterations in the process of degradation and erosion of the implant, eventually leading to a fracture of the tibial stem. In this way mechanical straining at the site of fracture could have exceeded the failure threshold of titanium alloy. Stem fracture of a current tibial component design has not yet been described in the literature. The only failure so far reported concerns the stem of a femoral component, and this has also been explained by biomechanical reasons. It follows from this study that patients with progressive osteolysis around the TKA should be followed up more frequently. The conclusions of this biomechanical analysis emphasize the importance of a thorough reconstruction of bone defects in order to improve long-term survival of the implant. Key words: revision, total knee arthroplasty, osteolysis, failure, fracture, tibial stem.