Dose effects of cross‐linking polyethylene for total knee arthroplasty on wear performance and mechanical properties

Abstract

Wear performance and mechanical properties of cross-linking polyethylene (XLPE) tibial inserts were investigated using a knee simulator, scanning electron microscopy (SEM), and a small punch test (SPT). Ultrahigh molecular weight PE made from GUR1050 resin was irradiated at doses ranging from 0 to 200 kGy and then machined into tibial inserts followed by annealing. The knee simulator was run for up to four million cycles. As the radiation dose increased from 0 to 100 kGy, the wear rate decreased dramatically, yielding 95% wear reduction at 100 kGy. The microwear features observed by SEM supported the dose-dependent wear reduction. The SPT for XLPE after the simulation test showed that, as the radiation dose increased from 0 to 200 kGy, the ultimate displacement decreased dose-dependently, while the ultimate load increased from 0 to 75 kGy and decreased from 75 to 200 kGy. The resulting toughness of the PE increased to its maximum at a dose of 50 kGy and then decreased with higher doses up to 200 kGy. PE cross-linked with radiation doses from 25 to 75 kGy had greater toughness than virgin, nonirradiated PE. However, PE irradiated with 100 kGy or more had lower toughness than virgin PE. These data suggest that a certain amount of irradiation enhances both wear performance and toughness of PE tibial inserts. Although a certain amount of cross-linking would be effective for clinical application of PE tibial inserts, an optimal radiation dose should be much smaller than that used in current XLPE in total hip arthroplasty.

Design of an Advanced Bearing System for Total Knee Arthroplasty

“…Wear testing of pristine CoCr femoral components against virgin and highly crosslinked UHMWPE tibial inserts reflected documented trends in the literature [14] in that the mean wear rate decreased significantly (p < 0.001) with each increase in the radiation dose examined in this study (Figure 4). The mean wear rates (± standard deviations) of the virgin, 5-XLPE, and 7.5-XLPE tibial inserts were 23.4 ± 2.4 mm 3 /Mc, 10.9 ± 0.9 mm 3 /Mc, and 6.4 ± 0.6 mm 3 /Mc, respectively.…”

“…It is well understood that the degree of crosslinking appropriate for a particular application is a delicate balance between improvements in wear and reduced mechanical properties resulting from increased crosslinking [14]. With that in mind, the crosslinked UHMWPE formulations currently marketed for TKA typically utilize lower crosslink densities than those marketed for THA.…”

The wear of fixed and mobile bearing unicompartmental knee replacements

“…As there are no studies at present directly comparing the wear performance of these two bearing materials, it is difficult to comment upon the relative effect of the material on the wear rates observed within this study. However, several studies have demonstrated a significant reduction with increased cross-linkage for polyethylene tibial inserts [40][41][42]. Both bearings had cobalt-chrome femoral and tibial components, and therefore it may be expected that the contribution of the relative composition of the bearing on the overall wear may be less compared with the effect of bearing design or insert material.…”

Development and Application of the Small Punch Test to UHMWPE

“…Work by Asano et al [6] used the small punch test metrics to investigate the optimum irradiation dose suitable for crosslinking of knee bearings. Work by Asano et al [6] used the small punch test metrics to investigate the optimum irradiation dose suitable for crosslinking of knee bearings.…”