Background
Treehouse Avatar LLC owns U.S. Patent No. 6,724,403, which covers a method for collecting data from an information network in response to user choices made while navigating “character-enabled network sites.” Treehouse sued Valve Corporation, the developer behind the Steam gaming platform and popular titles like Team Fortress 2 and Dota 2, alleging that certain in-game features infringed its patent.
The central disputed question was what the claim phrase “character-enabled network sites” means. The district court adopted a specific construction of that term. Treehouse’s infringement expert, however, prepared his analysis using a materially different and broader construction than the court had adopted. Valve moved to strike the expert’s testimony as unreliable and inconsistent with the court’s claim construction, and also moved for summary judgment of noninfringement. The district court agreed on both motions, struck the expert report, and then granted summary judgment because without the expert’s testimony Treehouse had no admissible evidence showing that Valve’s games met the “character-enabled network sites” limitation. Treehouse appealed.
The Court’s Holding
The Federal Circuit affirmed both rulings. First, it upheld the exclusion of Treehouse’s expert testimony. An expert witness in a patent infringement case must apply the district court’s claim construction when forming opinions about infringement. When an expert builds an infringement analysis on a different construction — even if the expert believes it is the correct one — the resulting opinion is unreliable and inadmissible because it does not map the accused product to the claims as the court has interpreted them. The court found that Treehouse’s expert had done exactly that: his analysis applied a construction that differed in a material way from what the court had adopted.
Second, having affirmed the exclusion, the Federal Circuit upheld summary judgment of noninfringement. Without admissible expert testimony to establish that Valve’s games satisfied the “character-enabled network sites” limitation under the court’s construction, Treehouse could not survive summary judgment. A patentee asserting infringement of a technical claim generally needs expert testimony to explain to the jury how the accused product satisfies the claim limitations, and the absence of admissible expert evidence left an unbridgeable gap in Treehouse’s case.
Key Takeaways
- Expert infringement opinions must be grounded in the district court’s adopted claim construction — opinions built on a materially different construction are properly excluded as unreliable under Daubert.
- Patentees who disagree with a court’s claim construction must challenge that construction on appeal, not work around it by using a different construction in expert testimony.
- The loss of an expert witness due to claim construction misalignment can be fatal to an infringement case, particularly for technical inventions where lay jurors need expert guidance to understand whether the accused product meets claim limitations.
- Patent litigants should ensure their infringement experts are briefed on the court’s claim construction order and are clearly building their analysis on those constructions — not on counsel’s preferred alternative constructions.
Why It Matters
Treehouse Avatar v. Valve is a cautionary tale about the pivotal role of claim construction in patent litigation. Once a district court construes a claim, that construction becomes the law of the case for all subsequent proceedings in the trial court. Experts who ignore or work around the court’s construction are not just building on shaky ground — their entire opinions can be struck, potentially ending the infringement case before trial.
For patent owners who feel a court’s claim construction is wrong, the correct path is to challenge the construction through the litigation process — seeking reconsideration, certification for interlocutory appeal, or raising the issue on appeal from final judgment. Attempting to preserve a broader infringement theory by having an expert apply a different, preferred construction is a litigation strategy that the Federal Circuit has now clearly rejected. Patent counsel should carefully align expert reports to the actual claim constructions entered by the court, even when those constructions are adverse to their client’s position.