Hip and other Joint Implants If you've ever suffered damage or deterioration of your joints, espe- cially the hip joint. you understand how much disability and suffering such problems can cause. Hip replacements were pioneered using a metal rod(stem) with a metal ball on one end. The stem was forced down the center of the leg bone(femur) and glued in place. The ball then fit into a plastic(usually the common polymer polyethylene) cap that was glued into the hip socket. However, these implants weren't considered a long term solution. Both the metal and plastic would slowly wear, and the resulting wear particles would cause irritation and inflammation. Within about 10 years, either the pain would become too great or the joint would freeze up and stop working; the implant would have to be replaced. Another problem also sometimes required replacement of the implant. The glue between the metal stem and the leg bone would fail, and the rod would come loose.