by Dennis Crouch
The Federal Circuit has a new expert witness case — this time siding with the patentee and finding that two experts were improperly excluded mid-trial. But, the case includes a sharp dissent over where to draw the line between a court’s Daubert gatekeeping function and the jury’s role as factfinder. Barry v. DePuy Synthes Companies, No. 2023-2226 (Fed. Cir. Jan. 20, 2026).
In the case, the experts had presented testimony that strayed somewhat from the court’s claim construction and also included survey results using questionable methodology. Writing for the majority, Judge Stark concluded that this testimony was (1) permissible applications of the court’s claim construction and (2) that methodological criticisms went to evidentiary weight rather than admissibility. Judge Prost dissented, warning that the majority’s approach “contravenes the principles embraced in EcoFactor and the 2023 amendments” to Federal Rule of Evidence 702 and “will undermine district courts’ abilities to exercise their important gatekeeping function.”
The dispute in this case highlights a conceptual tension in how we think about expert testimony standards. All testimony must clear a basic relevance threshold to be admissible. At the other end of the spectrum, we have a higher standard for actually carrying the burden of proof and sustaining a verdict. Expert testimony occupies middle ground. Rule 702 and Daubert impose reliability requirements that exceed ordinary admissibility standards, recognizing that experts wield particular influence over juries. But, where exactly expert testimony sits on this spectrum (and who decides) is the central tension between the majority and dissent.
The patents at issue cover surgical techniques for treating spinal deformities using linked “derotation tools” that allow surgeons to manipulate multiple misaligned vertebrae simultaneously. Dr. Mark Barry sued DePuy for induced infringement, relying on two experts: Dr. Walid Yassir, an orthopedic surgery professor who opined that DePuy’s tools infringed the asserted claims when assembled in certain configurations, and Dr. David Neal, a survey expert who assessed how often surgeons actually used the accused tools in allegedly infringing ways. The key claim limitation was “handle means,” which the district court construed as “a part that is designed especially to be grasped by the hand.” Before trial, the district court denied DePuy’s Daubert motions against both experts, reasoning that the challenges “go to the weight, not the admissibility” of the testimony. Then, mid-trial and after both experts had testified on direct and cross-examination, the court reversed course. It excluded Dr. Yassir’s testimony for “impermissibly contradict[ing]” the claim construction and Dr. Neal’s survey for methodological unreliability, then granted judgment as a matter of law for DePuy.
The Federal Circuit’s reversal turns on a fundamental question about the boundary between legal error and factual dispute. The majority frames the issue this way: “contradiction does not mean mere tension, arguable inconsistency, or lack of persuasiveness.” When an expert recites the court’s claim construction and purports to apply it, disagreements about whether the expert’s application is correct or persuasive belong to the jury. The dissent sees it differently, arguing that the majority “conflat[es] admissibility with whether evidence is sufficient to sustain a verdict” by asking “whether a reasonable jury could have ‘accepted’ Dr. Yassir’s testimony as persuasive” rather than whether the district court reasonably found a contradiction.
Claim construction is a question of law for the court under Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996). Once construed, experts must apply the court's construction when offering infringement opinions. An expert who contradicts the construction offers testimony that is "unhelpful" under Rule 702 because it asks the jury to decide infringement under the wrong legal standard. The dispute in Barry is whether the expert contradicted the construction or merely applied it in a way the judge found unpersuasive.
The testimony at the center of the dispute came primarily on cross-examination. Dr. Yassir testified that “everything is a handle means” in a linked system “because everything is linked together.” He agreed that he equated the court’s construction of “handle means” (a part designed especially to be grasped by the hand) with “parts that cannot be assembled without grasping them by hand.” The district court found this testimony contradictory: just because a part must be grasped during assembly does not mean it was designed especially to be grasped. The majority disagreed, emphasizing that Yassir repeatedly qualified his answers by reference to the “linked system” and “once it’s connected,” which tracked the court’s own recognition that the claim term “encompasses both a single handle and the linked handle array.” Judge Stark wrote that the district court “erred by seizing on the testimony that ‘everything’ is a handle means without crediting Dr. Yassir’s qualifying refrain that such is the case only ‘in a linked system.'”
Judge Prost’s dissent views the same testimony quite differently. She identifies what she considers a clear contradiction: Yassir equated “designed especially to be grasped” with anything that “cannot be assembled without grasping,” which are “plainly different things.” The dissent also points to Yassir’s testimony that certain parts “are not the places that you generally would want to grab” yet still constitute handle means. “It is not clear to me,” Judge Prost writes, “how parts that one ‘generally would [not] want to grab’ could be parts designed especially to be grabbed.”
The dissent frames the analytical error as one of standard of review: the majority asks what a jury might have thought about admitted evidence, when the question should be whether the district court was “arbitrary, fanciful, or clearly unreasonable” in finding a contradiction.
This disagreement also reflects a deeper tension about the scope of judicial gatekeeping. The majority opinion emphasizes restraint. Effective cross-examination “will almost always reveal the type of tensions and ambiguities the Dissent characterizes, wrongly in our view, as contradictions.” The majority warns that the dissent’s approach would “invite district courts to dismantle parties’ cases at trial based on ordinary evidentiary imperfections.” The proper remedy for “shaky but admissible evidence” is “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof,” quoting Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). The majority notes that DePuy did exactly this: its own experts criticized Yassir’s application of the claim construction and explained why the jury should not credit it.
Judge Prost invokes the Federal Circuit’s recent en banc decision in EcoFactor, Inc. v. Google LLC, 137 F.4th 1333 (Fed. Cir. 2025), which reasserted that the judge must ensure reliability of expert testimony before permitting it to be considered by a jury.
The 2023 amendments to Federal Rule of Evidence 702 added the phrase "the proponent has demonstrated to the court" before the reliability requirements. The Advisory Committee explained this clarified that reliability is determined by the court by a preponderance of the evidence, rejecting approaches that treated reliability concerns as merely going to weight. The amendment responded to cases that "have been read to suggest that" expert reliability disputes should go to the jury.
The survey expert exclusion presents a related but distinct question. Dr. Neal administered a survey to determine how often surgeons used DePuy’s tools in allegedly infringing configurations. The district court found multiple methodological flaws: the survey used non-probability sampling, had a 4.1% response rate without adequate analysis of nonresponse bias, and contained what the court viewed as incompatible anchoring questions. But, the majority reversed, holding that “the many criticisms the district court had of Neal and his survey may well have persuaded a reasonable jury not to place any substantial weight on his testimony,” but “they do not justify excluding it.” The majority faulted the district court for not citing “any actual evidence, either particularized or introduced at trial,” to support its conclusion that the flaws rendered the testimony inadmissible.
The dissent responds that the majority’s approach “treats all of the district court’s admissibility concerns as only involving jury issues.” She emphasizes that Dr. Neal candidly admitted the only support for the representativeness of his sample was his own assertion: “The only support that we have for your statement that this is a representative sample is the fact that you said it, correct?” “That’s correct.” The dissent argues that the majority’s blanket characterization of these flaws as weight issues “harkens back to the very approach that prompted recent amendments to Rule 702.”
The procedural posture of this case may matter as much as the substantive doctrine. Both expert opinions survived pre-trial Daubert challenges. The district court expressly found that DePuy’s criticisms went to weight, not admissibility. The experts then testified at trial, subject to cross-examination. Only after they had testified did the court grant renewed Daubert motions and exclude both witnesses.
The majority explicitly warns against what it views as an invitation to “dismantle parties’ cases at trial based on ordinary evidentiary imperfections.” The court emphasizes that “the evidentiary requirement of reliability is lower than the merits standard of correctness,” This framing treats admissibility and sufficiency as related but distinct inquiries. Evidence can be admissible even if it would not, standing alone, support a verdict. The jury’s task is to weigh competing evidence and assess credibility. The court’s task is to ensure the evidence meets minimum thresholds of reliability, not to predict how the jury will ultimately resolve factual disputes.
The case also reveals tension in how courts should treat expert testimony elicited on cross-examination. The majority characterizes the problematic statements as “responses [Yassir] gave to questions asked of him on cross-examination” and notes that the district court’s pre-trial ruling found DePuy’s concerns arose “only [in response to] hypotheticals presented by DePuy’s counsel.” The implication is that a party should not be able to engineer grounds for exclusion through artful cross-examination. The dissent responds that “the most concerning testimony came out on cross-examination” and that characterizing direct testimony as unobjectionable “does little to answer whether, as a whole, his testimony was properly excluded as unreliable.”
The case is remanded for a new trial at which both experts may testify, though the majority instructs that Dr. Yassir “must again testify consistent with, and not in contradiction to, the court’s claim construction” and that “[b]oth parties should be permitted to object to questions or answers that contradict that construction.” This guidance may cabin how the retrial proceeds, though it leaves unresolved the fundamental disagreement about what constitutes contradiction versus application. The parties will presumably relitigate these issues, and the district court will need to navigate the line the Federal Circuit has drawn without much more specificity than before.