Patent Claim Construction: Why ‘Cavity’ Became a Battleground, According to Kathryn V.

In a recent LinkedIn post, Kathryn V. highlights a critical pitfall in patent litigation: the danger of reinterpreting claim definitions after an agreement has been reached. Kathryn V. uses a recent Federal Circuit case, Little Giant v. Tricam, to illustrate how deviating from agreed-upon claim constructions can lead to the exclusion of expert testimony and the failure of infringement claims.

Kathryn V. begins by emphasizing the core principle at stake:

You don’t get to change the meaning of the claims after the game starts.

This succinct statement, according to Kathryn V., encapsulates the stern reminder from the U.S. Court of Appeals for the Federal Circuit.

The ‘Cavity’ Conundrum in Little Giant v. Tricam

The crux of the Little Giant v. Tricam case, as explained by Kathryn V., hinged on the interpretation of a single word: “Cavity.” Both parties in the litigation, along with the court, had previously agreed that “cavity” referred to “a hollowed-out space that does NOT pass all the way through.” However, Kathryn V. points out that Little Giant’s expert witness subsequently applied a definition of “cavity” that extended beyond this established construction.

This broader interpretation, Kathryn V. argues, effectively attempted to include pass-through spaces, which the initial claim construction had explicitly excluded. This divergence from the agreed-upon meaning had significant consequences.

Expert Testimony Excluded and Infringement Claims Barred

Kathryn V. details the fallout from the expert’s divergent interpretation:

• Expert testimony was excluded.
• Literal infringement was not found, as the expert’s definition of “more than a majority” (referring to ~20% inside) did not meet the claim construction’s limitations.
• The doctrine of equivalents was barred due to prosecution history estoppel.
• The court ultimately affirmed a summary judgment against Little Giant.

Kathryn V. underscores the Federal Circuit’s sharp observation on this matter:

An expert opinion based on a materially different claim construction doesn’t get a seat at the table.

This statement, Kathryn V. suggests, serves as a clear warning against attempting to redefine terms mid-litigation.

Prosecution History as a Binding Commitment

Drawing a broader lesson from the case, Kathryn V. stresses the importance of the words used during patent prosecution. “The words you choose during prosecution matter. The concessions you make matter. And you don’t get to ‘reinterpret’ them later because it’s convenient,” Kathryn V. writes.

In Kathryn V.’s view, this case reinforces the idea that patent claims and their definitions represent firm technical commitments. These definitions are not subject to later reinterpretation based on convenience or evolving litigation strategy. As Kathryn V. concludes:

From the examiner’s desk to the courtroom: Claims are technical commitments. Definitions are not open to reinterpretation. And prosecution history never forgets.

Kathryn V. advises patent holders and litigators to “protect accordingly,” emphasizing the lasting impact of every word and agreement made during the patent process.