🦿Hip & Knee Replacement Implants: Polyethylene (plastic) Parts . The success of your joint replacement surgery largely depends on a special plastic called Ultra-High Molecular Weight Polyethylene (UHMWPE). This remarkable material has been the gold standard in joint replacements since the 1960s, and continued innovations are making it even better. Today’s advanced crosslinked polyethylene implants (HXLPE) are engineered to be incredibly wear-resistant while maintaining the strength needed to su