RESUMEN
Studies have focused attention on the appearance of a subsurface white band in clinically retrieved polyethylene components and the possible contribution of this phenomenon to early polyethylene delamination. Unconsolidated polyethylene 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 contribute to formation of the white band. A quantitative investigation was conducted on 11 retrieved tibial components that exhibited a subsurface white band to determine whether the amount of calcium stearate particles and additives were greater in the white band region when compared with the mid-portion of the same section of polyethylene. Calcium stearate particles and other additives were quantified using backscattered electron imaging with correlated 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 particles and additives were present in the white band region (4578 +/- 418 particles/mm(2); mean +/- standard error) than the mid-portion region (1250 +/- 147 particles/mm(2)) of the sectioned tibial inserts. The percent area occupied 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 other 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 important to consider how calcium stearate and other additives in polyethylene resins affect white band formation and the possible contribution to crazing, early delamination, and osteolysis in total joint replacement.