A DIFFERENTIAL SCANNING CALORIMETRY STUDY OF RETRIEVED ORTHOPEDIC IMPLANTS MADE OF ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE

Differential scanning calorimetry (DSC) was used to examine thermal an d thermooxidative properties of ultrahigh molecular weight polyethylen e (UHMW-PE) of five acetabular components of failed orthopedic implant s retrieved at revision of total hip arthoplasty, The results were com pared with controls (unimplanted acetabular cups, a 20-year-old slab o f UHMW-PE, and raw material), Profiles of exothermic peaks indicated i ncreased levels of oxidation in all retrieved cups, In three retrieved cups, DSC revealed an additional peak of endotherm that was not seen in control samples, The additional endotherm peaks were not artifacts due to oxidation during scanning, heat buildup during cutting of the s amples, or the sterilization method after retrieval, The additional pe ak was associated with the bulk of the polymer that was extracted with hexane, It varied in relative area, depending on its original locatio n of the sample in a cup, implicating local variability in the extent of changes in material property, The distribution of the changes sugge sts that, during implantation, tissue exposure and friction affected t he level of oxidation and degree of crystallinity in the UHMW-PE to a greater degree than did loading alone. Overall results showed that DSC may be a useful tool in evaluating changes in the properties of UHMW- PE orthopedic components in vivo. (C) 1996 John Wiley & Sons, Inc.