The FDA began regulating medical devices in 1976, but did not have a classification for certain medical devices like hip replacements at the time. Therefore, they implemented a temporary solution by allowing device makers to release new medical devices on the market if they can prove that a similar device is already on the market.
It quickly became apparent with the first of many trials filed that the manufacturer knew about the serious flaws and chose to leave the medical devices on the market anyway. The exact number of patients affected by the medical implants is unknown because the United States does not keep track of such data. Instead, the U.S. relies on registries from other countries to share results.