The effect on wear of lift-off in total knee arthroplasty.

Femoral lift-off has been reported in total knee arthroplasty using dynamic fluoroscopic analysis. However, the effect of femoral lift-off on ultra-high-molecular-weight polyethylene (UHMWPE) is not clear. The objective of this study was to evaluate the effect of lift-off movement on the wear of UHMWPE using a pin-on-disc testing machine. Using oxidised UHMWPE, delamination was observed in 70% of the discs with lift-off movement, as against none in without lift-off movement (p=0.0603). In non-oxidised UHMWPE the depth of the wear track was increased in the impact area after lift-off, but there was no delamination and no increase in wear as measured by weight loss. UHMWPE can sustain the impact of after lift-off with neither delamination nor wear by other mechanisms. In contrast, degraded (i.e., oxidised) UHMWPE undergoes delamination after lift-off. Since it is probable that lift-off cannot be prevented, oxidised UHMWPE should never be used in TKA.