Abstract
Background
To prevent excessive tension on the posterior cruciate ligament (PCL) in cruciate-retaining total knee arthroplasty (CR-TKA), some knee prosthesis-systems offer the option of creating a posterior slope for the tibial polyethylene insert. Vanguard® Complete Knee System offers two different types of tibial bearing for CR
-TKA. CR Lipped Bearing (LB) has a slightly raised posterior lip, whereas CR Standard Bearing (SB) is recessed downward at the posterior margin and has 3° posterior slope. The objective of this study was to investigate the effect of the tibial bearing slope on PCL load using the original devise in vivo conditions.
Material and Methods
Twenty osteoarthritic varus knees were included in this study. After implantation of the trial components, PCL stiffness was measured using the original tension analyzer intra-operatively. Elastic modulus of PCL was calculated at 90 and 120 degrees knee flexion on two types of bearing surface.
Results
Elastic modulus of PCL was 7.2±0.9 N/mm (mean±SE) at 90 degrees knee flexion, and 9.5±1.1 N/mm (mean±SE) at 120 degrees knee flexion with the Lipped Bearing (no slope). With the Standard Bearing (3 degrees posterior slope), elastic modulus decreased to 6.0±0.5 N/mm (mean±SE) at 120 degrees knee flexion.
Discussion and Conclusion
Higher PCL stiffness was observed at 120 degrees knee flexion than 90 degrees knee flexion with Lipped Bearing surface (no slope), but using the Standard Bearing (3 degrees posterior slope), PCL stiffness decreased significantly at 120 degrees knee flexion. Therefore a posterior tibial slope of bearing insert prevents an excessive load on PCL at high knee flexion angles.
