ROLE OF POLYETHYLENE OXIDATION AND CONSOLIDATION DEFECTS IN CUP PERFORMANCE

Quality factors such as particle consolidation and oxidation have been claimed to impair the performance of ultrahigh molecular weight polye thylene implants, but no definite data estimate their real effect. To assess the influence of these quality determinants in wear, wear rate, and time in service at a single, well proven design, the percentage a rea of polyethylene sections occupied by nonconsolidated polyethylene particles, the presence of a white band, and the amount of polyethylen e oxidation (through density curves) were evaluated in 92 retrieved Ch arnley acetabular components with available clinical data. The average percentage area of nonconsolidated polyethylene particles in cup sect ions was 3.1%. There were 11 cups showing a subsurface white band. The authors observed an average density in the deep polyethylene of 0.942 0 g/cc after an average in vivo use of 9.8 years (range, 0.08-20.3 yea rs). Banded cups showed significantly higher subsurface densities. Whe n studying the relationship among clinical and material factors with p erformance variables, wear measurements (obtained through radiographic methods and direct measurements of polyethylene thickness in the coll ected implants) correlated with age at implantation, activity, and tim e in service. Weight was a determinant of the wear rate, None of the s tudied polyethylene quality factors showed a definite association with wear performance or time to failure in this series. Implant survivors hip was not significantly impaired in the 22.225-mm Charnley low frict ion replacement by a subsurface white band or by a higher area occupie d by nonconsolidated particles. Fewer nonconsolidated particles were n ot associated with longer survivorship. This design proved tolerance t o polyethylene quality variations, in the signaled ranges, without a s ignificant effect in the system performance.