The Doctrine of Equivalents: When Literal Infringement Isn’t Required
Patent law has its own version of “close enough,” called the Doctrine of Equivalents (DOE). It says that even if a product or method doesn’t match the exact words of a patent claim, it can still infringe if it does substantially the same thing, in substantially the same way, to get substantially the same result. For example, your neighbor promised not to build a “fence”. Then he puts up a 10-foot-high “hedge wall” that blocks your view just the same. Because he accomplished the same result, he might still be in trouble.
Prosecution History Estoppel: You Can’t Take Back What You Gave Up
But there’s a counterweight to this rule: Prosecution History Estoppel (PHE). Imagine you narrow your patent claim to get it approved by the Patent office. Maybe you remove certain versions or features. You can’t turn around later and use the DOE to grab back what you gave up. In other words: you made your bed, now you lie in it.
That’s the tug-of-war at the heart of Colibri Heart Valve LLC v. Medtronic Corevalve, LLC.
The Colibri Patent and the Two Deployment Methods
Colibri’s patent covered a heart valve that could be partially deployed, then “recaptured” and repositioned if it wasn’t in quite the right spot — a surgical do-over button. The patent described two ways to deploy the valve:
- Push it out from inside a sheath.
- Retract the sheath to uncover it.
Claim Cancellation During Prosecution Changes the Playing Field
During patent prosecution, Colibri dropped all claims covering the “retract” method after the Patent Office said they weren’t properly supported. That left only the “push” method in the issued patent.
The Accused Device and the Jury’s $106 Million Verdict
Medtronic’s device used a combination of both pushing and retracting to deploy its valve. Colibri argued, “That’s close enough — DOE!” and a jury agreed, awarding $106 million in damages.
The Federal Circuit Applies Prosecution History Estoppel
The Federal Circuit wasn’t buying it. Judge Taranto, writing for the panel, said: Cancelling the “retraction” claim narrowed the scope of the remaining claims. The cancelled and retained claims were so closely related that giving up one told the world you weren’t claiming that territory anymore. PHE barred Colibri from getting that territory back through DOE, even if their remaining claim language wasn’t literally changed.
The Bigger Lesson for Patent Owners and Prosecutors
This case is a reminder that the DOE and PHE are like a patent-law see-saw: the more you give up during prosecution, the less you can later claim as “equivalent.” Once you cancel a claim to get your patent issued, the courts may see it as a binding surrender, even if you think your other claims are worded differently.
For inventors and companies, the takeaway is simple: decisions made during prosecution can come back years later in court — and they can make or break a case worth nine figures.
For a related article on the doctrine of equivalents, see: Doctrine of Equivalents