Tibial Component

Abstract

In the earliest artificial knees, the tibial component designs varied considerably. The Gunston, together with unicompartmental knees, used small separate parts for each condyle. The Freeman-Swanson used a plate of plastic covering the entire proximal tibial surface. The Townley used a single plastic component with a central slot for cruciate ligament preservation. In all cases there were some problems of fixation to the bone, due to excessive stresses on the trabecular bone, to tilting of a component which transmitted all the shear and torque forces, or to deformation of thin all-plastic components. As a result of this experience, designs were made with partial conformity to reduce the shear and torque. Metal-backing was used to stiffen the component. However the most effective change was to use a 40 mm fixation peg in the center of the component. Even if there was inadequate cement penetration on the flat tibial surface, the central peg maintained strong fixation. Another advance in design was modularity, where the plastic insert was fixed into a metal tray. In this way, different thicknesses could easily be tested at surgery to achieve ideal soft tissue balancing. A surprising result has been that in long-term follow-up, all-plastic components have equivalent durability to metal-backed.