SAN FRANCISCO — A state law tort claim of failure to warn about risky medical devices is not pre-empted by the federal medical device law — so long as the state law duty of care runs “parallel” to a duty established by the federal law.

That brain-twisting holding Thursday by an en banc panel of the U.S. Court of Appeals for the Ninth Circuit could expose manufacturers of hundreds of high-risk medical devices to hefty state tort damages.