As discussed in Avoiding Patent Infringement, patent claims define the boundaries of patent protection. Patent infringement can occur either literally—where the accused product directly practices the claimed invention without variation—or under the Doctrine of Equivalents. This doctrine covers cases where the accused product includes minor modifications to the claimed invention. However, the Doctrine of Equivalents has limits, especially if the patentee made narrowing statements during prosecution.
Case Study: Depuy Spine, Inc. v. Medtronic Sofamor Danek, Inc.
In Depuy Spine, Inc. v. Medtronic Sofamor Danek, Inc., 2008-1240 (Fed. Cir. 2009), a jury found that Medtronic did not literally infringe Depuy’s patent but did infringe under the Doctrine of Equivalents. Medtronic argued that the Doctrine of Equivalents should not apply because it would “ensnare” the prior art—in other words, broaden the scope of Depuy’s claims to cover prior art devices, which is prohibited.
Ensnarement Defense Explained
The ensnarement defense prevents a patentee from expanding the doctrine’s reach to cover prior art, which would unfairly limit competition. To assess ensnarement, courts use a hypothetical claim analysis:
- A hypothetical claim is drafted to encompass the accused device.
- The court then determines if this hypothetical claim would be patentable over prior art.
If the hypothetical claim is not patentable over prior art, then the Doctrine of Equivalents cannot be used to cover the accused product.
Application of Ensnarement in Depuy Spine
In Depuy Spine, the patented technology involved spinal screws. The accused device used a screw in a receiver with a compression member that allowed the screw to be “rigidly” secured. Medtronic, the accused infringer, brought two prior art references, Puno and Anderson, asserting that the hypothetical claim would not be patentable over these references.
- Puno Reference: Both parties agreed that Puno disclosed all limitations of the hypothetical claim except for the compression member.
- Anderson Reference: Anderson taught the use of a compression member.
Depuy argued that the combination of Puno and Anderson would be non-obvious, as Puno teaches away from incorporating a compression member due to its emphasis on shock absorption. The Federal Circuit agreed, noting that adding a compression member to Puno’s device would eliminate its shock-absorbing capability, a valuable feature for spinal screws. As a result, the court found the proposed combination non-obvious, thus rejecting Medtronic’s ensnarement defense.
Key Takeaway
The ensnarement defense is a critical tool for alleged infringers, allowing them to limit the scope of the Doctrine of Equivalents by preventing claims from covering prior art. This case highlights the importance of thoroughly analyzing prior art to either support or challenge hypothetical claims.
For guidance on patent infringement defenses or for help navigating complex patent cases, feel free to reach out at (949) 433-0900. As an experienced patent attorney serving Orange County, Irvine, Los Angeles, San Diego, and surrounding areas, I’m here to help protect your intellectual property rights.