United States Court of Appeals
`For the Eighth Circuit
`No. 19-2899
`In re: Bair Hugger Forced Air Warming Devices Products Liability Litigation
`George Amador
` Plaintiff - Appellant
`3M Company; Arizant Healthcare, Inc.
` Defendants - Appellees
`Appeal from United States District Court
`for the District of Minnesota
`Submitted: March 16, 2021
` Filed: August 16, 2021
`Before GRUENDER, KELLY, and GRASZ, Circuit Judges.
`GRUENDER, Circuit Judge.
`In December 2015, the Judicial Panel on Multidistrict Litigation created and
`centralized the In re Bair Hugger Forced Air Warming Devices Products Liability
`Litigation (“MDL”) in the District of Minnesota (“MDL court”) for coordinated


`pretrial proceedings. Plaintiffs1 in the MDL have brought claims against 3M
`Company and its now-defunct, wholly owned subsidiary Arizant Healthcare, Inc.
`(collectively, “3M”). Plaintiffs assert that they contracted periprosthetic joint
`infections (“PJIs”) due to the use of 3M’s Bair Hugger, a convective (or “forced-
`air”) patient-warming device, during their orthopedic-implant surgeries. In July
`2019, on 3M’s motion, the MDL court excluded Plaintiffs’ general-causation
`medical experts as well as one of their engineering experts, and it then granted 3M
`summary judgment as to all of Plaintiffs’ claims. Subsequently, the MDL court
`entered an MDL-wide final judgment.
`Plaintiffs appeal. First, they argue that the MDL court abused its discretion
`in excluding their general-causation medical experts and engineering expert.
`Second, they argue that the MDL court erred in granting 3M summary judgment
`whether or not those experts were properly excluded. Third, they argue that the
`MDL court abused its discretion in denying Plaintiffs’ request for certain discovery.
`And fourth, they argue that the MDL court abused its discretion in ordering certain
`filings on its docket to remain sealed. Additionally, on appeal, Plaintiffs ask us to
`unseal those parts of the appellate record that duplicate the filings whose sealing on
`the MDL court’s docket they challenge.
`We reverse in full the exclusion of Plaintiffs’ general-causation medical
`experts and reverse in part the exclusion of their engineering expert. We reverse the
`grant of summary judgment in favor of 3M. We affirm the discovery order that
`Plaintiffs challenge. We affirm the MDL court’s decision to seal the filings Plaintiffs
`seek to have unsealed. And we deny Plaintiffs’ motion to unseal those same filings
`on our own docket.
`1Although George Amador is the captioned Plaintiff-Appellant, this appeal is
`brought by all Plaintiffs in the MDL to challenge several MDL-wide rulings.


`In the mid-1980s, Dr. Scott Augustine invented the Bair Hugger, a forced-air
`device used to keep patients warm during surgery so as to stave off hypothermia-
`related complications that can arise during or after surgery. The device consists of
`a central heating unit, a hose, and a disposable perforated blanket that is placed over
`the patient. The central unit, which is often situated on or near the floor when in use,
`draws in air through a filter, warms that air (usually to a temperature significantly
`above the operating-room temperature), and blows it through the hose into the
`perforated blanket. The air exits the blanket through the perforations and keeps the
`patient warm. Typically, both the patient and the blanket are covered with surgical
`draping during operations, and the blanket is placed on a part of the body away from
`the surgical site, so the air does not blow directly onto the surgical site.
`Dr. Augustine marketed and sold the Bair Hugger through Augustine Medical,
`Inc., the company he founded and led as CEO until 2004. Around that time, Dr.
`Augustine was forced to leave Augustine Medical while under investigation for
`Medicare fraud. Augustine Medical then reorganized, and the division of the
`company that retained the Bair Hugger product line changed its name to Arizant
`Healthcare. In 2010, 3M acquired Arizant Healthcare and the Bair Hugger product
`line. Arizant Healthcare was dissolved in December 2014.
`After leaving Augustine Medical, Dr. Augustine developed the HotDog, a
`patient-warming device that transfers heat conductively to the patient by direct
`contact with the patient’s skin rather than by forced hot air. He then began a
`campaign to discredit his old invention and promote his new one. These efforts bore
`fruit. In March 2013, a plaintiff sued 3M and Arizant Healthcare in Texas state
`court, claiming that he contracted a PJI due to the Bair Hugger’s use in his hip-
`replacement surgery. Dr. Augustine worked with the law firm representing that
`plaintiff to prepare a “litigation guide” and solicitation letter for the purpose of
`fomenting more litigation against 3M. By December 2015, more than sixty
`materially similar cases against 3M had been filed in or removed to federal district


`courts around the country. At that time, the Judicial Panel on Multidistrict Litigation
`ordered these cases centralized in the District of Minnesota for consolidated pretrial
`proceedings. See 28 U.S.C. § 1407(a). Nearly 6,000 lawsuits have since been filed
`as part of the MDL.
`In these cases, Plaintiffs allege that they suffered PJIs from the use of the Bair
`Hugger during their orthopedic-implant surgeries. PJIs are frequently caused by the
`introduction of microbes into the surgical site during surgery. Bacterial
`contamination is a particularly significant threat in orthopedic-implant surgeries
`because a PJI can be caused by very few microbes, possibly even a single bacterium.
`For this reason, it is standard for such surgeries to take place in “ultra-clean
`ventilation” operating rooms, where air is blown into the operating room through
`high-efficiency particulate air (“HEPA”) filtration at a uniform velocity. This
`HEPA-filtered “laminar” airflow blows over the patient, reducing the likelihood that
`operating-room airflow will carry ambient bacteria from nonsterile areas of the
`operating room into the surgical site.
`Plaintiffs advance two theories for how the Bair Hugger caused their PJIs
`during their orthopedic-implant surgeries. According to the “airflow disruption”
`theory, waste heat from the Bair Hugger creates convection currents that carry
`ambient bacteria from nonsterile areas of the operating room to the surgical site
`despite the laminar airflow, resulting in PJIs. According to the “dirty machine”
`theory, the Bair Hugger is internally contaminated with bacteria, which are blown
`through the blanket into the operating room, where they become ambient and
`eventually reach the surgical site, resulting in PJIs.
`In the master long-form complaint filed in the MDL, Plaintiffs asserted
`fourteen state-law claims against 3M, including negligence and strict liability (for
`failure to warn, defective design, and defective manufacture), among others.
`During discovery, Plaintiffs subpoenaed a third party, VitaHEAT Medical,
`LLC, to produce discovery regarding its “UB3,” a conductive patient-warming


`device. Plaintiffs alleged that the UB3 was an alternative design to the Bair Hugger,
`making this discovery ostensibly relevant to their design-defect claims. See
`generally 63A Am. Jur. 2d Products Liability § 894 (May 2021 update) (“The
`existence of an alternative design may be used to establish that a product was
`unreasonably dangerous due to a design defect, and in some jurisdictions may be
`required.”). VitaHEAT objected on relevancy grounds, arguing that the UB3 was
`too different from the Bair Hugger to count as an “alternative design” for product-
`liability purposes. Plaintiffs then filed what they captioned a “motion to overrule”
`this relevancy objection. The MDL court denied this motion, agreeing that
`conductive patient-warming devices like the UB3 are too dissimilar from the Bair
`Hugger to qualify as “alternative designs,” meaning that this discovery was not
`relevant. Cf. United States v. One Assortment of 93 NFA Regulated Weapons, 897
`F.3d 961, 966 (8th Cir. 2018) (“The Federal Rules of Civil Procedure limit discovery
`to that which ‘is relevant to any party’s claim or defense . . . .’” (quoting Fed. R. Civ.
`P. 26(b)(1))).
`The parties jointly agreed to a protective order to limit the disclosure of
`confidential information that might be contained in filings entered on the MDL
`docket. Pursuant to this protective order, the parties submitted numerous filings
`under seal over the course of the litigation. As relevant to this appeal, 3M sought to
`keep seven such filings under seal over Plaintiffs’ objection, asserting that it would
`suffer competitive harm if any was unsealed. The MDL court agreed and ordered
`these files kept under seal.
`As the litigation progressed, 3M moved to exclude Plaintiffs’ general-
`causation medical experts (Dr. Jonathan M. Samet, an epidemiologist; Dr. William
`Jarvis, an infectious-disease specialist; and Dr. Michael J. Stonnington, an
`orthopedic surgeon) as well as Plaintiffs’ engineering experts (including Dr. Said
`Elghobashi and Michael Buck). 3M also filed a motion for summary judgment
`contingent on the exclusion of Plaintiffs’ general-causation medical experts. The
`MDL court denied in pertinent part the motion to exclude those experts and denied
`the motion for summary judgment.


`Subsequently, Gareis v. 3M Co. became the first bellwether trial in the MDL.
`See generally 156 Am. Jur. Trials § 219 (May 2021 update) (explaining the
`bellwether-trial process in mass-tort litigation). Ruling on pretrial motions in
`Gareis, the MDL court excluded evidence of Plaintiffs’ dirty-machine theory. The
`case then proceeded to trial on the airflow-disruption theory, and Plaintiffs’ experts
`Dr. Jarvis, Dr. Stonnington, and Dr. Elghobashi (among others) testified. After an
`approximately two-week trial, the jury returned a verdict for 3M.
`After the Gareis trial, 3M moved for reconsideration of the MDL court’s
`orders refusing to exclude Plaintiffs’ general-causation medical experts as well as
`Dr. Elghobashi and denying 3M summary judgment. The MDL court granted 3M’s
`motion, excluding Plaintiffs’ general-causation medical experts as well as Dr.
`Elghobashi and granting 3M summary judgment on all claims. The MDL court then
`entered an MDL-wide final judgment. See In re Temporomandibular Joint (TMJ)
`Implants Prods. Liab. Litig., 97 F.3d 1050, 1055 (8th Cir. 1996) (“A transferee court
`has the authority to enter dispositive orders terminating cases consolidated under 28
`U.S.C. § 1407.”).
`Plaintiffs appeal, challenging the MDL court’s exclusion of their general-
`causation medical experts and Dr. Elghobashi, the MDL-wide grant of summary
`judgment in favor of 3M, the discovery ruling regarding conductive patient-warming
`devices, and the sealing of seven MDL docket entries. Plaintiffs also ask us on
`appeal to unseal on our own docket the records that they argue should have been
`unsealed on the MDL court’s docket.
`We begin by considering Plaintiffs’ challenge to the MDL court’s exclusion
`of their general-causation medical experts (Dr. Samet, Dr. Jarvis, and Dr.
`Stonnington) and engineering expert (Dr. Elghobashi). Dr. Samet, Dr. Jarvis, and
`Dr. Stonnington each offered general-causation opinions—that is, opinions that the
`Bair Hugger “is capable of causing the [PJIs] from which” Plaintiffs allegedly


`suffered, see Junk v. Terminix Int’l Co., 628 F.3d 439, 450 (8th Cir. 2010)2—based
`on both the airflow-disruption theory and the dirty-machine theory. Dr. Elghobashi
`created a computational-fluid-dynamics (“CFD”) model to support the airflow-
`disruption theory. The MDL court generally treated the medical experts as a
`collective set (their opinions were essentially the same and were founded on much
`of the same evidence), and it excluded their opinions as unreliable because (1) it
`concluded there was “too great an analytical gap between the literature and the
`experts’ general causation opinions”; and (2) “the causal inferences made by the
`experts have not been generally accepted by the scientific community.”3 The MDL
`court also excluded Dr. Elghobashi’s model and opinion because (1) his conclusion
`about the Bair Hugger’s effects in real-world operating rooms relied on an unproven
`and untested premise, (2) there was too great an analytical gap between the results
`of his CFD and his conclusion about the Bair Hugger’s effects in real-world
`operating rooms, and (3) the CFD model was developed for litigation.
`For the following reasons, we reverse in full the exclusion of the medical
`experts’ opinions and reverse in part the exclusion of Dr. Elghobashi’s model and
`opinion. We first recite the principles that govern our analysis. We then analyze the
`reasons given by the MDL court for excluding the experts.
`2The opinions in question did not address specific causation—whether the
`Bair Hugger “in fact caused the harm from which” any particular MDL plaintiff
`suffered. See id.
`3The MDL court articulated a third reason; namely, that “the experts failed to
`consider obvious alternative explanations.” This reason applies specifically to the
`medical experts’ treatment of the epidemiological study on which they relied, see
`infra Section II.B.1, that found an association between forced-air warming and PJIs,
`see Federal Judicial Center, Reference Manual on Scientific Evidence at 597-600 (3d
`ed. 2011) (explaining that “[c]onsideration of alternative explanations” is one of nine
`factors that “guide epidemiologists in making judgments about [general] causation”
`based on a study or studies that find an association). The MDL court discussed this
`same issue in its analysis of the “analytical gaps” between that study and the experts’
`opinions. Accordingly, we consider this point in assessing the MDL court’s
`“analytical gaps” analysis.


`As the proponent of the expert testimony in question, Plaintiffs have the
`burden to prove its admissibility by a preponderance of the evidence. Lauzon v.
`Senco Prods., Inc., 270 F.3d 681, 686 (8th Cir. 2001). Federal Rule of Evidence 702
`governs the admissibility of expert testimony, and under this rule the district court
`is “vested with a gatekeeping function, ensuring that ‘any and all scientific testimony
`or evidence admitted is not only relevant, but reliable.’” Union Pac. R.R. v. Progress
`Rail Servs. Corp., 778 F.3d 704, 709 (8th Cir. 2015) (quoting Daubert v. Merrell
`Dow Pharms., Inc., 509 U.S. 579, 589 (1993)). In exercising this gatekeeping
`function, the district court has “broad discretion,” and “on appeal we will not disturb
`a decision concerning the exclusion of expert testimony absent an abuse of that
`discretion.” Wagner v. Hesston Corp., 450 F.3d 756, 758 (8th Cir. 2006).
`That said, we have recognized that the “liberal thrust” of Rule 702 regarding
`the admissibility of expert testimony creates “an intriguing juxtaposition with our
`oft-repeated abuse-of-discretion standard of review.” Johnson v. Mead Johnson &
`Co., 754 F.3d 557, 562 (8th Cir. 2014). “While we adhere to this discretionary
`standard for review of the district court’s Rule 702 gatekeeping decision, cases are
`legion that, correctly, under Daubert, call for the liberal admission of expert
`testimony.” Id. (collecting authorities).
`Rule 702’s “screening requirement” has been “boiled down to a three-part
`test.” Id. at 561. First, the testimony must be useful to the finder of fact in deciding
`the ultimate issue of fact, meaning it must be relevant. See id. Second, the expert
`must be qualified to assist the finder of fact. Id. Third, the testimony must be
`reliable or trustworthy in an evidentiary sense. Id. At issue here is the third part of
`this test—whether Plaintiffs’ experts’ proposed testimony meets Rule 702’s
`reliability requirement. “The standard for judging the evidentiary reliability of
`expert evidence is ‘lower than the merits standard of correctness.’” Kuhn v. Wyeth,
`Inc., 686 F.3d 618, 625 (8th Cir. 2012) (quoting In re Paoli R.R. Yard PCB Litig.,
`35 F.3d 717, 744 (3d Cir. 1994)).


`The reliability inquiry is a “flexible” one, with “[m]any factors” bearing on it.
`Daubert, 509 U.S. at 593-94. In Daubert, the Court articulated “four non-exclusive
`factors” relevant to this inquiry. Johnson, 754 F.3d at 562. These factors are
`(1) whether the expert’s theory or technique can be or has been tested, (2) whether
`the theory or technique has been subjected to peer review or publication, (3) the
`known or potential rate of error of the theory or technique, and (4) whether the
`technique or theory is generally accepted. See id.; Peitzmeier v. Hennessy Indus.,
`Inc., 97 F.3d 293, 297 (8th Cir. 1996). Factors recognized since Daubert include
`“whether the experts are proposing to testify about matters growing naturally and
`directly out of research they have conducted independent of the litigation, or whether
`they have developed their opinions expressly for purposes of testifying.” Daubert
`v. Merrell Dow Pharms., Inc., 43 F.3d 1311, 1317 (9th Cir. 1995).
`Additionally, while Daubert instructed that the focus of the reliability inquiry
`“must be solely on principles and methodology, not on the conclusions that they
`generate,” 509 U.S. at 595, the Supreme Court later clarified that “conclusions and
`methodology are not entirely distinct from one another,” Gen. Elec. Co. v. Joiner,
`522 U.S. 136, 146 (1997). Thus, “a district court’s focus on principles and
`methodology need not completely pretermit judicial consideration of an expert’s
`conclusions,” Kuhn, 686 F.3d at 625 (internal quotation marks omitted), and a
`district court may exclude expert testimony if it finds “that there is simply too great
`an analytical gap between the data and the opinion proffered,” Joiner, 522 U.S. at
`146. Or, to put it in the language we have frequently used both before and after
`Daubert and Joiner, a district court may exclude an expert’s opinion if it is “so
`fundamentally unsupported” by its factual basis “that it can offer no assistance to the
`jury.” E.g., Loudermill v. Dow Chem. Co., 863 F.2d 566, 570 (8th Cir. 1988); United
`States v. Finch, 630 F.3d 1057, 1062 (8th Cir. 2011).
`When a district court excludes an expert’s opinion for being fundamentally
`unsupported, yet another “intriguing juxtaposition” is evident in our case law. See
`Johnson, 754 F.3d at 562. On the one hand, we have recognized that we owe
`“significant deference” to the district court’s “determination that expert testimony is


`excessively speculative,” and we “can reverse only if we are convinced that the
`District Court made a clear error of judgment on the basis of the record before it.”
`Grp. Health Plan, Inc. v. Philip Morris USA, Inc., 344 F.3d 753, 760 (8th Cir. 2003)
`(internal quotation marks omitted). On the other hand, we have stated numerous
`times that, “[a]s a general rule, the factual basis of an expert opinion goes to the
`credibility of the testimony, not the admissibility.” E.g., United States v. Coutentos,
`651 F.3d 809, 820 (8th Cir. 2011); see also Klingenberg v. Vulcan Ladder USA,
`LLC, 936 F.3d 824, 829-30 (8th Cir. 2019) (distinguishing cases where we affirmed
`the exclusion of experts’ opinions as too speculative because, in those cases, the
`experts’ opinions were “wholly speculative,” “connected to the facts by only the
`expert’s ipse dixit,” “patent speculation,” “pure conjecture,” and “vague theorizing
`based upon general principles”).
`Thus, excluding an expert’s opinion for being fundamentally unsupported is
`an exception to the general rule that “[g]aps in an expert witness’s . . . knowledge”
`go to weight, not admissibility. See Robinson v. GEICO Gen. Ins., 447 F.3d 1096,
`1100 (8th Cir. 2006); cf. Finch, 630 F.3d at 1062 (“Doubts regarding whether an
`expert’s testimony will be useful should generally be resolved in favor of
`admissibility.” (brackets omitted)). “Vigorous cross-examination, presentation of
`contrary evidence, and careful instruction on the burden of proof are the traditional
`and appropriate means” of addressing “shaky but admissible evidence.” Daubert,
`509 U.S. at 596.
`With these principles in mind, we analyze the reasons provided by the MDL
`court for excluding Plaintiffs’ general-causation medical experts and Dr. Elghobashi
`(whose CFD model and testimony formed part of the factual basis for the general-
`causation medical experts’ opinions).
`We first consider the MDL court’s determination that “too great an analytical
`gap” existed between “the literature” and Plaintiffs’ medical experts’ general-


`causation opinions. This literature falls generally into two categories: (1) an
`epidemiological study reporting an association between forced-air warming and
`PJIs; and (2) studies and reports ostensibly supporting both of Plaintiffs’ mechanistic
`theories of causation. We consider this evidence to assess whether the MDL court
`“made a clear error of judgment on the basis of the record before it” in finding the
`experts’ opinions too speculative to be admitted. See Grp. Health Plan, 344 F.3d at
`760 (internal quotation marks omitted).
`All three medical experts relied on a 2011 observational epidemiological
`study as support for their conclusion that the Bair Hugger is capable of causing PJIs.
`See P.D. McGovern et al., Forced-Air Warming and Ultra-Clean Ventilation Do Not
`Mix, 93-B J. Bone & Joint Surgery 1537 (2011) (“McGovern 2011”). As an
`observational epidemiological study, McGovern 2011 explored whether forced-air
`warming was associated with an increased rate of PJIs by comparing a group of
`individuals warmed convectively to a group of individuals warmed conductively.
`See id. at 1537. See generally Reference Manual, supra, at 552, 555-56.
`Specifically, McGovern 2011 reviewed infection data from 1,437 hip- or
`knee-replacement surgeries performed at a particular hospital for a 2.5-year period.
`Id. at 1537, 1540. From July 2008 to March 2010, the patients were warmed with
`Bair Huggers; from March 2010 to June 2010, the hospital gradually transitioned to
`using conductive patient-warming devices; and from June 2010 to the end of the
`study, the patients were warmed solely with conductive patient-warming devices.
`Id. at 1540, 1543. The investigators found that patients warmed convectively were
`nearly four times more likely to contract a PJI than patients warmed conductively.
`Id. at 1541. The authors of McGovern 2011 acknowledged that the study did “not
`establish a causal basis” for this association. Id. at 1543. And they acknowledged


`that their findings may have been “confounded”4 by “other infection control
`measures instituted by the hospital” during the study period (specifically identifying
`two such potentially confounding measures) and that they were “unable to consider
`all [patient-medical-history] factors” associated with PJIs, including a number of
`“important predictors for deep infection,” due to limited data in the records they
`reviewed. Id.
`The MDL court found that McGovern 2011 itself was sufficiently reliable to
`be admitted. But the MDL court faulted the experts’ reliance on it in ways that
`contributed to the analytical gap it found. For instance, the MDL court deemed it
`unreliable for the experts to draw an inference of causation from this study when the
`study disclaimed having proved causation. The MDL court also faulted how the
`experts handled the study’s limitations.
`As for the first point, we disagree that it is per se unreliable for an expert to
`draw an inference of causation from an epidemiological study that disclaimed
`proving causation. “[E]pidemiology cannot prove causation.” Reference Manual,
`supra, at 598. Instead, epidemiology enables experts to find associations, which by
`themselves do not entail causation. See id. at 552-53, 598. But an observational
`study such as McGovern 2011 “can be brought to bear” on the question of causation,
`id. at 217, and “can be very useful” to answering that question, id. at 221. Ultimately
`“causation is a judgment for epidemiologists and others interpreting the
`epidemiologic data.” Id. at 598; see also id. at 222 (“In the end, deciding whether
`associations are causal typically . . . rests on scientific judgment.”). Thus, it was not
`necessarily unreliable for the experts to rely on McGovern 2011 to draw an inference
`of causation just because the study itself recognized, consistent with these principles,
`that the association did not establish causation. So long as an expert does the work
`4“Confounding occurs when another causal factor (the confounder) confuses
`the relationship between the agent of interest and outcome of interest.” Reference
`Manual, supra, at 591. For instance, if those who drink alcohol are more likely to
`smoke than those who do not, then smoking may be a confounder in a study finding
`an association between drinking alcohol and emphysema. See id. at 592.


`“to bridge the gap between association and causation,” a study disclaiming having
`proven causation may nevertheless support such a conclusion. See id. at 218.
`We recognize that there is language from Joiner that, when taken out of
`context, might appear to suggest otherwise. See 522 U.S. at 145 (“Given that [the
`authors of the study in question] were unwilling to say that PCB exposure had caused
`cancer among the workers they examined, their study did not support the experts’
`conclusion that Joiner’s exposure to PCB’s caused his cancer.”). But the context
`indicates that the problem with the experts’ opinions in that case was that they failed
`to bridge the gap left by the study in question. See id. at 145-46 (recounting
`numerous issues with the experts’ factual basis).
`As for the second issue, the MDL court rightly faulted the experts for how
`they handled McGovern 2011’s limitations. “Assessing whether an association is
`causal requires an understanding of the strengths and weaknesses of the study’s
`design and implementation,” and “the key questions” in evaluating epidemiological
`evidence “are the extent to which a study’s limitations compromise its findings and
`permit inferences about causation.” Reference Manual, supra, at 553. The experts
`did not adequately address McGovern 2011’s limitations. Neither Dr. Jarvis nor Dr.
`Stonnington mentioned the identified potential confounders or limitations in
`McGovern 2011 in their reports. Dr. Samet, on the other hand, did address in his
`report the two potential confounders identified by the authors in the study itself, and
`he meaningfully explained why in his view these variables did not confound the
`study’s findings. But Dr. Samet did not meaningfully address the other limitations
`identified by the McGovern 2011 authors except to say that confounding by other
`factors “seems unlikely” for ostensibly logical reasons.5
`5In the context of discussing this point, the MDL court also faulted Dr. Samet
`for departing “from his own description of reliable methodology.” Specifically, it
`noted that, with respect to the criterion of consistency that experts use in making
`judgments about causation, see Reference Manual, supra, at 600, Dr. Samet noted
`that that criterion “is generally applied as a consideration related to interpretation of
`findings of multiple observational studies and hence is not applicable to the single


`However, McGovern 2011 was not the only basis on which the experts relied
`in forming their opinions. In addition to the epidemiological data from McGovern
`2011, the experts also relied on studies and reports ostensibly showing plausible
`mechanisms by which forced-air warming can cause PJIs. See id. at 599-600, 604
`(identifying the “biological plausibility” of a general-causation theory as one factor
`guiding epidemiologists in “making judgments about causation” and noting that
`“[w]hen biological plausibility exists, it lends credence to an inference of
`causality”). Thus, the experts’ failure to handle McGovern 2011’s limitations
`properly is not fatal to the admissibility of their opinions. See id. at 599-600 (listing
`“factors that guide epidemiologists in making judgments about causation”; noting
`that “there is no threshold number that must exist”; and including among these
`factors “[b]iological plausibility” along with “[c]onsideration of alternative
`explanations”). “[A]n inference of causation based on the totality of the evidence”
`may be reliable even if “no one line of evidence support[s] a reliable inference of
`causation” by itself. Milward v. Acuity Specialty Prods. Grp., Inc., 639 F.3d 11, 23
`(1st Cir. 2011); see also United States v. W.R. Grace, 504 F.3d 745, 765 (9th Cir.
`2007) (noting that whether an expert’s opinion testimony satisfies Rule 702
`“requires consideration of the overall sufficiency of the underlying facts and data”).
`Accordingly, we turn to the other evidence these experts considered.
`study by McGovern.” Because there was only one epidemiological study here, Dr.
`Samet instead “point[ed] to the consistency of the findings of studies addressing the
`effect of the Bair Hugger device on particle counts at the surgical site.” In context,
`we do not read this as Dr. Samet misapplying his own methodology but rather
`acknowledging that the consistency factor was not relevant in its conventional sense
`but nevertheless the consistency of the mechanistic studies supported an inference
`of causation from McGovern 2011’s finding of an association. As he explained in
`the next paragraph of his report following the language the MDL court quoted, the
`mechanistic evidence is consistent with McGovern 2011’s findings. The Reference
`Manual directs epidemiologists to consider whether the finding of an association is
`“consistent with other relevant knowledge,” supra, at 606, and we fail to see how
`mechanistic evidence would not count as “other relevant knowledge.”


`The studies and reports ostensibly showing the “biological plausibility” of the
`medical experts’ general-causation opinions broadly fall into two categories. One
`set ostensibly supports Plaintiffs’ airflow-disruption theory, and the other ostensibly
`supports Plaintiffs’ dirty-machine theory.
`All three medical experts relied on Plaintiffs’ airflow-disruption theory as a
`plausible causal mechanism to support their general-causation opinions. Again,
`according to this theory, waste heat generated by the Bair Hugger creates convection
`currents that disrupt laminar airflow in operating rooms and transmit nonsterile air
`to the surgical site, causing PJIs. The experts relied on two general categories of
`evidence for this theory: (i) Dr. Elghobashi’s CFD model and (ii) published studies
`examining airflow patterns in operating rooms as well as the correlation between
`particles and bacteria. We consider each category in turn.
`To investigate whether forced-air warming “play[s] a role” in transporting
`squames (skin flakes capable of carrying bacteria that are present in operating
`rooms) to the surgical site, Dr. Elghobashi prepared a CFD model using large eddy
`simulation (a way to model fluid turbulence) to simulate the Bair Hugger’s effect on
`airflow and dispersion of squames in an ultra-clean-ventilation operating room. Dr.
`Samet and Dr. Jarvis relied on Dr. Elghobashi’s model. The parties agree, and the
`MDL court found, that the physics underlying Dr. Elghobashi’s model is reliable.
`Dr. Elghobashi eventually published his model with several coauthors in a peer-
`reviewed journal. See X. He et al., Effect of Heated-Air Blanket on the Dispersion
`of Squames in an Operating Room, 34 Int’l J. Numerical Methods Biomedical
`Eng’g, May 2018, at 1 (“He 2018”).


`Dr. Elghobashi’s model replicated an orthopedic operating room, including
`details such as laminar airflow, an operating table, surgical drapes, a patient
`underneath the drapes prepared for knee surgery, four surgeons (two with hands
`extended over the patient, two with hands down), t

This document is available on Docket Alarm but you must sign up to view it.

Or .

Accessing this document will incur an additional charge of $.

After purchase, you can access this document again without charge.

Accept $ Charge

Still Working On It

This document is taking longer than usual to download. This can happen if we need to contact the court directly to obtain the document and their servers are running slowly.

Give it another minute or two to complete, and then try the refresh button.


A few More Minutes ... Still Working

It can take up to 5 minutes for us to download a document if the court servers are running slowly.

Thank you for your continued patience.

This document could not be displayed.

We could not find this document within its docket. Please go back to the docket page and check the link. If that does not work, go back to the docket and refresh it to pull the newest information.

Your account does not support viewing this document.

You need a Paid Account to view this document. Click here to change your account type.

Your account does not support viewing this document.

Set your membership status to view this document.

With a Docket Alarm membership, you'll get a whole lot more, including:

  • Up-to-date information for this case.
  • Email alerts whenever there is an update.
  • Full text search for other cases.
  • Get email alerts whenever a new case matches your search.

Become a Member

One Moment Please

The filing “” is large (MB) and is being downloaded.

Please refresh this page in a few minutes to see if the filing has been downloaded. The filing will also be emailed to you when the download completes.

Your document is on its way!

If you do not receive the document in five minutes, contact support at

Sealed Document

We are unable to display this document, it may be under a court ordered seal.

If you have proper credentials to access the file, you may proceed directly to the court's system using your government issued username and password.

Access Government Site

We are redirecting you
to a mobile optimized page.

Document Unreadable or Corrupt

Refresh this Document
Go to the Docket

We are unable to display this document.

Refresh this Document
Go to the Docket