We’ve written many blogposts kvetching about rulings in the Bair Hugger Multidistrict Litigation (MDL) out in Minneapolis. See here, for example. The rulings on expert admissibility in the Bair Hugger MDL were particularly weak. But surely the rulings would be much better in our home district of the Eastern District of Pennsylvania, right? And what if the case was in hard-scrabble Allentown, subject of the Billy Joel song? We cannot believe that junk science would find any purchase in the Lehigh Valley.
Well, now we believe it. (Add these lyrics to Joel’s elegy: “When we litigate in Allentown/expert rulings make defendants frown”).
Boncher v. 3M Co., 2025 U.S. Dist. LEXIS 26753, 2025 WL 511116 (E.D. Pa. Feb. 14. 2025), was an unlovely Valentine’s Day gift to drug and device defense hacks throughout E.D. Pa., from the Lehigh Valley to Dutch Wonderland to Valley Forge to the Liberty Bell. It is like a Whitman Sampler that sat on the CVS shelf too long, and the one or two decent candies somehow disappeared. Mind you, Boncher contains an interesting and potentially useful ruling concerning law of the case in the MDL context — but then it delivers a decision on the merits not likely to gladden the hearts of anyone on the right side of the v.
The plaintiff in Boncher alleged that the Bair Hugger warming device used during her knee surgery caused her to develop a periprosthetic joint infection. She brought claims for negligence, failure to warn, design defect, breach of implied warranty of merchantability, fraud, and unjust enrichment. The defendant moved to exclude the testimony of the plaintiff’s general and specific medical causation experts under Federal Rule of Evidence 702. The defendant also moved for summary judgment. The court denied those motions. We’d like to say that the journey is more important than the destination (you know – the friends we met along the way). We’d like to. But we cannot.
Boncher was sent to E.D. Pa. by the Minnesota MDL court to serve as a bellwether trial. A preliminary issue was whether the defendant’s Rule 702 challenges to the plaintiff’s general causation experts were barred by the Eighth Circuit’s ruling in the MDL concluding that the opinions of the general causation experts were reliable. The Boncher court gave the defendant hope by holding that the law of the case does not require a court on remand from an MDL in a different circuit (with different federal law) automatically to apply MDL expert rulings. Being in an MDL with another case does not erase the separateness of the cases. They are different cases with different parties. The bottom line is that a district court has no obligation to follow a decision from another circuit.
That is a correct, well-reasoned ruling. It is an important ruling that might look facially neutral. Ex ante, we could see that ruling cutting in favor of either plaintiffs or defendants. But, as we have pointed out, defendants tend to do better in remand courts than in the aggregated MDL proceedings. Remand courts usually look to resolve individual cases on their merits (or lack thereof), while MDL courts often explicitly prioritize the settlement process and act as if rulings against plaintiffs would stymie settlement efforts. (If anything, separating the wheat from the chaff makes it easier to set a fair price for the wheat.).
We applaud the Boncher court’s limitation on the law of the case doctrine. So far, so good.
And then it becomes so bad. After determining that it is not bound by the Bair Hugger MDL’s feckless approach to Rule 702, the Boncher decision proceeds to embrace all of the horrible rulings that the Eighth Circuit Bair Hugger decision made, importing them into the Third Circuit, or at least one corner of the Circuit. The Boncher decision deploys much of the now problematic pre-2023 Rule 702 amendments language, covered occasionally by a judicial fig leaf. Thus, we still find “liberal admissibility,” but supposedly only as long as the rule’s “ requirements are met.” The 2023 amendments to Rule 702 are mentioned only insofar as not making any “substantive” changes. That observation is partly true, but it misses the important point that the amendments to Rule 702 were needed because too many courts had misinterpreted the rule to favor admissibility of expert opinions. We think that the Bair Hugger MDL was one of those courts that misinterpreted Rule 702.
Sadly, the Boncher decision disagrees with us. Since the author of the Boncher decision is an Article III judge, while the authors of this blog are most definitely not, what the Boncher decision says matters a lot more than our scribblings do. The Boncher court reasoned that the Bair MDL decision, while it predated the Rule 702 amendments, basically applied them. For example, the Bair Hugger MDL decision said that it applied the preponderance of the evidence standard. True enough. That is what it said. But the Eighth Circuit’s application rendered the preponderance standard a mere rhetorical gesture. The Eighth Circuit Bair Hugger opinion was one of many examples where courts talked like gatekeepers but acted like Walmart greeters.
Then we get the Boncher court’s application of the not-substantively-changed Rule 702, and it consistently steers toward admissibility. For example, the Boncher decision held that a computer simulation that failed to account for critical variables may still be admissible as part of the factual basis of some other expert’s opinion. We get the usual ditty about how the strength of a study goes to its weight, not admissibility. We hear again how the remedy for expert shortcomings is cross-examination, not exclusion. The Boncher decision also ruled that an expert may rely on a study disclaiming causation as a basis for a contrary causation opinion, where other evidence supporting the opinion also exists.
As we said above, the journey in Boncher is just as troubling as the destination. For example, the Boncher decision says that, in order to exclude expert testimony, the gap between the data and opinion proffered must be “extreme.” It is as if the Boncher decision sampled all the worst, pro-admissibility phrases from E.D. Pa. and Third Circuit decisions to fashion a quilt of admissibility. None of this whining on our part suggests that the Boncher decision was in any way lazy or lawless. The opinion goes through the expert challenges in detail. When the Boncher court rolls out all the anti-gatekeeping language quoted above, it (mostly) cites post Rule 702 amendment cases from E.D. Pa. The real problem is the persistence of the presumptions and weight-not-admissibility formulations that the drafters of amended Rule 702 tried to erase. (Take a look at the excellent Behrens/Trask article on amended Rule 702 that we discussed early this year.) As an E.D. Pa. court, it would not have been easy for the Boncher decision to disagree with the bad language in the other post-Rule 702-amendment decisions. Maybe it could have been ignored as dicta. Or maybe what is needed is a clean-up operation by the Third Circuit.
The problematic application of Rule 702 continued with respect to the specific causation experts. To conduct an admissible differential diagnosis, an expert need only rule out “obvious” alternative causes. In developing opinions, an expert may reasonably rely on a “mix” of objective data and subjective analysis from another expert. That a certain system was “likely in place” was enough to rule out an alternative cause without proof that it actually existed. An expert need not rule out an alternative cause where there is minimal evidence to support it. A doctor may opine on any “potential complications” without any further proof of actual expertise. A treater may rely on his own conduct to rule out alternative causes.
As Kurt Vonnegut wrote, “and so it goes.” Or hearkening to an even greater literary source, and our favorite verse of the Bible (Jeremiah 8:20), “The harvest is past, the summer has ended, and we are not saved.” Amended Rule 702 was designed to wring out the loose, pro-admissibility language, but much of that language stubbornly remains.
The Boncher decision went on to deny the defendant’s summary judgment motion. The main issue pertained to the statute of limitations. The defendant invoked the discovery rule. Here is the court’s conclusion, and it tells all you need to know: “It is not undeniably clear to the Court that Plaintiff did not use reasonable diligence in timely ascertaining the cause of her injury. Plaintiff is not expected to know more about her injury than her treating physicians, who never informed her prior to this suit that the Bair hugger might have caused her injuries.” That “undeniably clear” language does not appear in Rule 56, and it seems a bit overwrought.
The Boncher decision also denied summary judgment on causation, failure to warn, fraud, and punitive damages. None of that makes us happy, but, given our undeniably clear bias, you would not expect otherwise. We’ll end with a mild complaint about the failure to warn ruling. The defendant made the point that the most relevant doctor, the anesthesiologist, testified that he continues to use the Bair Hugger. The plaintiff responded that that same doctor admitted he had not been informed by the manufacturer of potential complications. That looks to us like a conflation of absence of warning with warning causation. The Boncher decision concluded that the plaintiff had “demonstrated a dispute of fact over whether a different warning would have made a difference to the treating physicians in her case and prevented them from using the Bair Hugger in her operating room.” We had to read that sentence twice. As far as we can tell, there was no testimony by the anesthesiologist that he would have decided not to use the device if he had been informed of potential complications. As with the expert opinions, there was an important gap. We do not know whether to characterize it as “extreme,” whatever that means. As with the Rule 702 decision, the gap did not make any difference.