The U.S. Food and Drug Administration (FDA) has proposed requiring metal on metal hip implant manufacturers to apply for premarket approval. This is the strictest level of review for the FDA. This would be a change from evaluation at a level that allowed manufacturers to piggyback on devices already on the market they claimed were substantially similar in design without conducting any clinical trials. The problem is that no procedure was in place if the predicate devices are found to be defective, thus making the piggybacked devices defective.
The defect with metal on metal hip implants is that when the metal parts grind against one another from walking or running, metal particles can be released and cause damage to the surrounding tissue and bone. Also, metal ions can enter the bloodstream and travel to different parts of the body causing problems and a condition called metallosis. Symptoms to watch for including pain, noise (popping, squeaking, grinding or clicking), swelling, numbness and a change in the ability to walk. Anyone with such an implant experiencing the symptoms should take action. The remedy can include a revision surgery.
There are ongoing lawsuits against multiple manufacturers of metal on metal hip implants. The area of law dealing with dangerous and defective devices is called products liability.