Changing crystallinity of polyethylene in the acetabular cups of Weller hip prostheses.

We performed thermal analysis of polyethylene samples obtained from 73 new cups of the Weller hip prosthesis. There were marked individual differences in the degree of their crystallinity, ranging from 37.8% to 67.2% with a mean of 53%. Analysis of polyethylene from removed cups also showed differences in crystallinity in individual cups, with the mean value being higher in the removed implants than in the new ones. This difference in crystallinity between the groups was statistically significant. Marked individual differences in the degree of cup wear may result from these changes.