Knee, shoulder and hip replacements work quite well. The artificial surfaces are Teflon. Like everything, they wear out because the body has no way of healing the artificial surfaces. The replacement parts aren’t the problem; the recovery from surgery is long and not fun. I’ve heard they’re working on 3D printed hip, knee and shoulder replacement parts. That’ll revolutionize the surgery because it’s allegedly minimally invasive. The current surgeries are quite traumatic. I’ve sat in on a few. Picture sawzalls, drills and brass hammers. Seriously. They have to wear face shields and nurses have to wipe them off from all the “sawdust” aka bone fragments flying around.