Probability of mechanical loosening of the femoral component in high flexion total knee arthroplasty can be reduced by rather simple surgical techniques

Some follow-up studies of high flexion total knee arthoplasties report disturbingly high incidences of femoral component loosening. Femoral implant fixation is dependant on two interfaces: the cement–implant and the cement–bone interface. The present finite-element model (FEM) is the first to analyse both the cement–implant interface and cement–bone interface. The cement–bone interface is divided into cement–cancellous and cement–cortical bone interfaces, each having their own strength values. The research questions were: (1) which of the two interfaces is more prone to failure? and (2) what is the effect of different surgical preparation techniques for cortical bone on the risk of early failure.?

FEM was used in which the posterior-stabilized PFC Sigma RP-F (DePuy) TKA components were incorporated. A full weight-bearing squatting cycle was simulated (ROM = 50°–155°). An interface failure index (FI) was calculated for both interfaces.

The cement-bone interface is more prone to failure than the cement implant interface. When drilling holes through the cortex behind the anterior flange instead of unprepared cortical bone, the area prone to early interface failure can be reduced from 31.3% to 2.6%.

The results clearly demonstrate high risk of early failure at the cement–bone interface. This risk can be reduced by some simple preparation techniques of the cortex behind the anterior flange.

High-flexion TKA is currently being introduced. Some reports show high failure rates. FEM can be helpful in understanding failure of implants.