Convened under the auspicious of esteemed endorsers - ISTA

Corne van Loon - rijnstate hospital - arnhem, The NetherlandsMaarten De Waal Malefijt - Radboud University Nijmegen Medical Centre - Nijmegen, TheNetherlandsAlbert van Kampen - UMC St Radboud - Nijmegen, The NetherlandsNico Verdonschot - Radboud University Nijmegen Medical Centre - Nijmegen, NetherlandsIntroduction*Email: hjmeijerink@hotmail.comWithin the reconstruction of unicondylar femoral bone defects with morselized bone grafts inrevision total knee arthroplasty (TKA), a stem extension appears to be critical to obtainadequate mechanical stability. Whether the stability is still secured by this reconstructiontechnique in bicondylar defects has not been assessed. Long, rigid stem extensions havebeen advocated to maximize the stability in revision TKAs. The disadvantage of relatively stiffstem extensions is that bone resorption is promoted due to stress shielding. Therefore, wedeveloped a relatively thin intramedullary stem which allowed for axial sliding movements ofthe articulating part relative to the intramedullary stem. The hypothesis behind the design is thatcompressive contact forces are directly transmitted to the distal femoral bone, whereas adequatestability is provided by the sliding intramedullary stem. A prototype was made of this new kneerevision design and applied to the reconstruction of uncontained bicondylar femoral bonedefects.Materials and MethodsFive synthetic distal femora with a bicondylar defect were reconstructed with impacted bonegrafting (IBG) and this new knee revision design. A custom-made screw connection betweenthe stem and the intercondylar box was designed to lock or initiate the sliding mechanism,another screw (dis)connected the stem. A cyclically axial load of 500 N was applied to theprosthetic condyles to assess the stability of the reconstruction. Radiostereometry was used todetermine the migrations of the femoral component with a rigidly connected stem, a slidingstem and no stem extension.ResultsWe found a stable reconstruction of the bicondylar femoral defects with IBG in case of arigidly connected stem. After disconnecting the stem, the femoral component showedsubstantially more migrations. With a sliding stem rotational migrations were similar to those ofa rigidly connected stem. However, the sliding stem allowed proximal migration of the condylarcomponent, thereby compressing the IBG.DiscussionA stable reconstruction of uncontained bicondylar femoral defects could be created with IBGand a TKA with a thin stem extension. It appeared that the presence of a functional stemextension was important for the stability of the bicondylar reconstruction. In an effort to reducestress shielding, we developed a sliding stem mechanism. This sliding stem provided adequatestability, while compressive contact forces are still transmitted to the distal femoral bone.Clinical studies have to confirm that our sliding stem mechanism leads to long term bonemaintenance after revision TKAs.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]