Unicompartmental arthroplasty of the knee. Cadaver study of tibial component placement

In 30 knee preparations the median posterior inclination (tilt) of the medial tibial plateau was 10 degrees (5 degrees-15 degrees). Following medial compartmental arthroplasty in 20 knees, 10 with horizontal, and 10 with 10 degrees tilted tibial components, the point of articulation was determined radiographically. For the combinations of tibial angle and knee flexion that represent the initial 60 per cent of the stance phase, articulation took place more posteriorly on the horizontal components; there was a correlation between the operation-induced change of the tibial inclination and articulation. Articulation took place far posterior on horizontal components inserted in knees with a steep posterior tilt. We concluded that both the component placement and the preoperative inclination of the tibial plateau determine where on the tibial component articulation takes place. An optimal, central articulation with this set-up is obtained when the component is inserted with the same posterior tilt as that of the original articular surface.