Possible explanation for the white band artifact seen in clinically retrieved polyethylene tibial components

Studies have focused attention on the appearance of a subsurface white band in clinically retrieved polyethylene components and the possible contribut ion of this phenomenon to early polyethylene delamination. Unconsolidated p olyethylene particles and oxidation have been suggested as possible reasons for the appearance of the white band. Calcium stearate and other additives used in processing ultra-high molecular weight polyethylene may also contr ibute to formation of the white band. A quantitative investigation was cond ucted on 11 retrieved tibial components that exhibited a subsurface white b and to determine whether the amount of calcium stearate particles and addit ives were greater in the white band region when compared with the mid-porti on of the same section of polyethylene. Calcium stearate particles and othe r additives were quantified using backscattered electron imaging with corre lated elemental analysis. The particles were identified based on morphology and elemental patterns similar to reference calcium stearate particles and known additives. Significantly more (p < 0.0001) calcium stearate particle s and additives were present in the while band region (4578 +/- 418 particl es/ mm(2); mean +/- standard error) than the mid-portion region (1250 +/- 1 47 particles/mm(2)) of the sectioned tibial inserts. The percent area occup ied by calcium stearate particles and additives was five times higher (p < 0.0001) within the white band region (0.81 +/- 0.10%) than the mid-portion region (0.16 +/- 0.03%). The increased presence of calcium stearate and oth er additives in the white band region suggests that they may play a role in the formation of the white band. In future investigations it may be import ant to consider how calcium stearate and other additives in polyethylene re sins affect white band formation and the possible contribution to crazing, early delamination, and osteolysis in total joint replacement. (C) 2000 Joh n Wiley & Sons, Inc.