Two-part total knee arthroplasty: evolution and present status.

The inception of a 2-part total knee arthroplasty consisting of a Vitallium femoral component and a polyethylene tibial component occurred in 1970. It was termed "geometric," because it was not anatomic in design. This geometric design was altered during the ensuing years to allow better fixation of the tibial unit, because loosening of this unit became apparent in an appreciable percentage of patients. As biomechanical research and clinical evidence progressed, less need for the constraint built into the geometric prosthesis became evident. So a less constrained, more anatomic total knee, called the "anametric" total knee arthroplasty, was developed. There was duplication of the normal anatomic configuration of the femoral component for both left and right sides, a femoral flange so that the patella could be surfaced with polyethylene, and a flatter surface for the tibial unit. The tibial unit was first anchored with the geomatric triflanged system, but eventually comprised a medullary stem and a metal T-tray to contain the polyethylene. At this time, we believe that sufficient constraint necessary in the usual total knee arthroplasty is realized with the anametric design. The anametric design has proved itself and is now our prosthesis of choice.