Using an eight-station hip wear simulator, radiation-crosslinked polyethylenes were tested for their resistance to wear-related weight loss and the results compared to results for studies conducted on the same machine using polyethylene that was being implanted at the time. The testing results showed that the wear rate of crosslinked (60 kGy) Slab Compression Molded (SCM) polymer was about 63% lower than standard (30 kGy) SCM cups and 69% less than Ram Extruded 4150 (30 kGy) cups. The Near-net Final Shape molded (NFS) crosslinked (60 kGy) specimens had an 89% reduction in wear rate over the standard (30 kGy) NFS cups, regardless of whether GUR 1020 or GUR 1050 crosslinked cups were tested. All wear rates for nitrogen packaged materials were significantly superior to those for cups sterilized in air and for earlier generation GUR 4150 products sterilized and stored in contact with oxygen.
The results confirm that both the SCM and NFS molding processes produce acetabular cups with excellent wear properties as compared to previous processes. The additional crosslinking process, described herein, provided a major improvement in the wear resistance with either molding process with greater improvement occurring in the NFS specimens.