Cross Medical v. Medtronic (Fed. Cir. 2007).
Medtronic brought its lawyers and engineers together to redesign their bone screws -- the point was to avoid infringing the Cross patents while still having a product that was essentially the same. Once-upon-a-time, the doctrine of equivalents would have complicated the issue, but applying Festo, Medtronic modified its design by changing the thread-depth -- a limitation that had been subject to a narrowing amendment by Cross during prosecution of its patent.
In particular, the claim had been amended to include a screw depth "below the [rod] diameter" and Medtronic's design-around used a screw depth that was above the rod diameter.
Under Festo, equivalence usually cannot be asserted for an element that had been subject to a narrowing amendment during prosecution. If, however, the amendment was only "tangentially related" to the accused equivalent then Festo estoppel does not apply.
The district court found that, in fact, the amendment made during prosecution was only tangentially related to the accused equivalent -- thus finding that Medtronic infringed under the Doctrine of Equivalents (DOE).
Tangential exception is narrow: In its decision, the CAFC first noted that the tangential relation exception is "very narrow." Here, the tangential exception cannot apply. As in Rhodia, the equivalent is within the range surrendered by the amendment. According to CAFC law, such a surrender is not tangential.
Reversed and Remanded.
Tangential Concurrence: In a concurrence designed for a casebook, Judge Rader explains why there should be only a narrow possibility of rebutting Festo estoppel based on the tangential relationship between the amendment and the accused equivalent. In almost explicit terms, the concurrence indicates that the tangentiality excuse should probably not even exist (Except for the Supreme Court precedent).