Patent infringement occurs when an infringer’s product falls within the scope of the patent claims, either literally (the product meets every claim element precisely) or under the “doctrine of equivalents” (which broadens a patent claim to cover products that are “equivalent” to the claim). A longstanding maxim under the “doctrine of equivalents” is that a patent owner cannot assert a scope of equivalency that would encompass, or “ensnare,” the prior art. (“Prior art” includes products, patents, or publications that pre-date the invention covered by the asserted patent).
A recent case decided by the Federal Circuit, Depuy Spine v. Medtronic, 567 F.3d 1314 (Fed. Cir. 2009), held that “ensnarement” is a matter for the judge to decide, rather than a jury. As a practical matter, his will typically benefit an accused infringer, as judges are usually more discerning when deciding equivalency, as well as whether its scope ensnares the prior art. Thus, the ruling provides accused infringers a better avenue to defend against doctrine of equivalents infringement.
