As previously discussed in “Avoiding Patent Infringement,” the claims define the metes and bounds of patent protection afforded under a patent. The claims can be infringed either literally which means that the alleged infringer practiced the claimed invention without any deviation. If the alleged infringer practiced a variation of the claimed invention, then liability for patent infringement may still be found under the doctrine of equivalents. This doctrine prevents others from making insubstantial changes and easily avoiding the claims. Otherwise, the value of the patent would be greatly diminished. However, this doctrine is still limited to the extent that the patentee made limiting statements during prosecution (i.e., examination) of the patent.
In Depuy Spine, Inc. v. Medtronic Sofamor Danek, Inc. 2008-1240 (Fed. Cir. 2009), the jury found that the alleged infringer did not literally infringe the claims of the patent but did infringe under the Doctrine of Equivalents. The alleged infringer contended that the doctrine of equivalents cannot operate to broaden the claims to cover the accused device because doing so would “ensnare” the prior art.
Ensnarement bars a patentee from asserting a scope of equivalency that would encompass, or “ensnare,” the prior art. As a helpful step in the ensnarement defense analysis, a hypothetical claim that covers the accused device is drafted. Next the court determines whether the patentee has carried its burden of persuading the court that the hypothetical claim is patentable over the prior art.
In Depuy Spine, Inc., the patented technology involved spinal screws. The accused device involved a screw in a receiver with a compression member such that the screw is “rigidly” secured. The alleged infringer brought forth two references, namely, Puno and Anderson asserting that the hypothetical claim is not patentable over these two references. The patentee and the accused infringer agreed that Puno disclosed all of the limitations of the hypothetical claim except for a compression member. Anderson taught the compression member. After consideration of the references, the Federal Circuit held that Puno taught away from incorporating the compression member into the Puno device. The reason is that the Puno device discussed the benefits of a “shock absorption”. If the compression member is incorporated into the Puno reference, then the Puno device would no longer have this “shock absorbing” effect which is useful for spinal screws. Hence, the Federal Circuit held that the proposed combination is non-obvious. Thus, the Court denied the accused infringer’s ensnarement defense.
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