
The million or so artificial hips and knees implanted each year in the United States are normally not guaranteed. Instead, the costs of replacing implants that fail early because of design or mechanical problems — devices that sell for as much as $15,000 each — are largely paid by Medicare, insurance companies and patients. Implants can fail for many reasons, but if only a small percentage of them fail prematurely because they are substandard, the costs to taxpayers, policyholders and
 
				








