Performance of the tibial component in total knee replacement.

UNLABELLED: In patients with deficient bone in the proximal end of the tibia, the mechanical support of a conventional total knee replacement may be inadequate. We have developed a custom design for use in situations in which there is extensive deficiency of tibial cancellous bone. To do this, we examined conventional and custom prosthetic tibial components using finite-element analysis. Several loading configurations were tested, and the worst loading conditions were found to be those in which eccentric loads were placed on the margin of the tibial component. The results showed that the stresses on the cancellous bone beneath a conventional-design prosthesis may be lowered if a metal tray and metal peg are employed. A salvage-design concept for revision in the presence of deficient cancellous bone was tested analytically and used successfully. This concept requires that some portion of the applied load be transferred directly to the tibial cortical shell. Stresses in the remaining cancellous bone were lowered by the combination of a thickened metal tray and a metal support buttress. CLINICAL RELEVANCE: This study demonstrates the advantage of metal trays for the tibial plateau and suggests that they should be used whenever the supporting tibial bone is insufficient. In knees in which there are large defects in the bone, direct transfer of the load to the cortical shell through the prosthesis, made possible by a custom design, appears to be necessary.