BACKSIDE WEAR FROM POLISHED TIBIAL TRAY PRODUCES HIGHER RATIO OF SUBMICRON PARTICLES

Abstract

TKR backside wear studies have concluded that, compared to rough trays, polished trays decrease total amount of backside wear by 80% to 87%. However, size and volumetric concentration of sub-micron-sized polyethylene particles are critical factors for macrophage-mediated osteolysis. We assessed the size and morphology of polyethylene wear debris from TKR backside wear simulations comparing polyethylene fretting against polished and blasted metal surfaces. A 3-station fretting wear simulator reproduced loads and motions typical of the backside of fixed-bearing inserts of TKRs. 5-million cyclic experiments combined low (50μm) or high (200μm) linear motion with +3o rotational motion. Load profile was double-peak Paul curve (peak 10MPa). Eight 3-station experiments measured polyethylene wear against blasted or polished metal surfaces of Ti6Al4V or CoCr. Polyethylene particles were isolated from serum following gradient separation and filtration on 0.01μm polycarbonate filters. Using SEM analysis, average 200 particles per sample were characterized with Meta-morph™ image analysis software. Concentration of submicron particles in the debris from rough surfaces was 31–32% under 50μm motion, 28–30% under 200μm. Surprisingly, this concentration from polished surfaces was substantially greater: 69–78% (50μm), and 57–63% (200μm). However, total poly wear against rough surfaces was 0.45–1.63mm3/

Mcycles, and 0–0.35mm3/Mcycles against polished. Taking this into account, the volume of submicron particles from polished surfaces is less than 0.1mm3/ Mcycles and from rough surfaces between 0.1 and 0.45mm3/Mcycles.

In conclusion, although polished metal trays produce up to five times less wear than blasted surfaces, they may also lead to an increase in the osteolytic potential of the polyethylene debris.