Analysis of retrieved implants: Crystallinity changes in ultrahigh molecular weight polyethylene

Abstract

The extent of in vivo induced structural alterations were evaluated in 13 retrieved implants ranging from two weeks' to seven years' implantation. A statistically significant difference in crystallinity was seen between weight-bearing and non-weight-bearing regions of the implants. Further, in the weight-bearing region, crystallinity was higher in components implanted for two or more years than in those implanted for less than one-half year. These results were consistent with our prior in vitro study on the effects of sterilization and aging. Taken together, the data indicate that UHMW polyethylene is not a static material but is continually dynamic changes in vivo.

Determination of Crystallinity and Crystal Structure of Hylamer™ Polyethylene after in vivo Wear

“…These phenomena were attributed to the oxidation of the material [3], to the decrease in molecular weight, and consequent increase in density and crystallinity [4][5][6].…”

Gamma Inert Sterilization: A Solution to Polyethylene Oxidation?

“…In vivo degradation was first studied by Eyerer, Grood, and colleagues in the 1980s 8,9 . However, until recently, historical polyethylene acetabular liners were not widely recognized to be susceptible not only to shelf aging but also to in vivo oxidation associated with a characteristic regional variation pattern 10,11 .…”

Degradation rate of ultra‐high molecular weight polyethylene

“…The results of other studies provide additional evidence that the average density of gamma-irradiated ultra-high molecular weight polyethylene increases linearly during degradation, although at different rates depending on the severity of the oxidizing environment and the geometry of the specimens (7,12,20). Ultra-high molecular weight polyethylene specimens aged in an air furnace at a temperature near the melting point, as well as specimens aged in distilled water and 0.5% hydrogen peroxide at 37"C, degraded at constant, although different, rates (12).…”

“…2): A&,,, = 0.000186 ( t s h + t, , ) (7) where the change in density is in glcc when the shelf age (tsh) and implantation time (t,m,,) are in months (r2 = 0.54). The correlation with shelf aging and implantation time as independent variables did not significantly (p > 0.05) reduce the residual error when compared with Eq.…”