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We confess:  we spend much too much time on a prominent social media platform.  We post way too many pictures of the Drug and Device Little Rescue Dogs.  We follow the progress of our impending addition, a Standard Poodle show puppy, currently in utero.  We engage in pointless, angry, political debate.  And we look at recipes we will never prepare.  One of our favorite recurring memes is the “you had only one job” meme.  A package of hot dog rolls is labeled “Hamburger Buns.”  A “One Way” street sign points into oncoming traffic.  Each of the boxes in a towering pile is emblazoned with “Do Not Stack.”  You get the idea.

Correct application of Fed. R. Evid. 702 is the “one job” of a judge considering a motion to exclude experts.   And there’s the rub in today’s case, in a cop-out recurring throughout the opinion.  Don’t get us wrong – there is a lot of good in Cantrell v. Coloplast Corp., 2022 WL 2806390 (D. Minn. July 18, 2022), including the ultimate result.  But it is pockmarked.  Let’s work our way through and you’ll see what we mean.

Cantrell is a pelvic mesh case.  The plaintiff’s pelvic organ prolapse (‘POP”) was repaired with the defendant’s polypropylene mesh implant, a product designed to be implanted trans-abdominally, not trans-vaginally (this becomes important).  The plaintiff alleged that she “continued to experience pain and pelvic floor dysfunction” after the mesh implant and that she needed several revision surgeries.  Cantrell, 2022 WL 2806390 at *1.   She disclosed six expert witnesses, and the defendant moved to exclude all of them.  We will take them in turn.

Urogynecologist/“design defect” expert:

The plaintiff disclosed a urogynecologist, who opined that the defendant’s “POP products [were] defectively designed, that the implantation of the . . . products [did] not result in superior functional outcomes, and that [the defendant] knew about problems with its transvaginal POP products.”  Id. at *2.  But here was the problem:  as we mentioned, the plaintiff was not implanted with a transvaginal product – hers was transabdominal.  The defendant argued that, as a result, the expert’s report did not encompass the product at issue.   The plaintiff contended that the report “pertain[ed] to the properties of mesh, not the method by which the mesh was implanted.”  Id.   Not so, as the court observed:  the report made clear that the defendant used the same mesh for all of its similar products but that the opinions pertained “specifically to the risks inherent in transvaginal implantation of pelvic-mesh implants.”  Id. (emphasis in original).  The court concluded, “. . . [B]ecause the opinions in [the expert’s] report pertain only to transvaginal implantation, [the] testimony would be unhelpful to a jury. . . . Accordingly the court grants [the] motion to exclude [the expert’s] testimony.”  Id.   So far, so good.

Polymer scientist:

The plaintiff’s polymer science expert sought to testify that the surface layer of polypropylene mesh degrades in the human body.   The defendant argued that the opinion was unreliable because peer-reviewed literature contradicted it.  The court held that that a conflict between competing scientific theories was “fodder for cross-examination;” that “Daubert neither requires not empowers trial courts to determine” which of such theories “has the best provenance.”  Id. (citation omitted).  But the court also said this – the first of many similar comments:  “. . . [D]isputes about the factual basis of an expert’s testimony ordinarily implicate the credibility—not the admissibility—of the testimony.”  Id. (citation omitted).   We submit that this assertion flies in the face of Rule 702.  To wit, the “factual basis” of an expert’s testimony is a key factor in determining the reliability of the expert’s methodology.  And the lack of a reliable methodology has always demanded exclusion of an expert’s opinion, under an honest application of the Rule.  This is the “cop-out” to which we referred and which, in our humble opinion, has been invoked to permit plaintiffs’ experts’ sloppy opinions to survive countless Daubert/Rule 702 motions.   The Rules committee knew this, and it is amending Rule 702 accordingly.  But stay tuned – there’s much more of this later in Cantrell.

Before we get to that, a little more about the polymer scientist:  the court granted the defendant’s motion to exclude the expert’s opinion that the human body attacks mesh implants with oxidants as long as the implants remain in the body, because the expert’s conclusion “overreach[ed] the limits set by the authors of the article on which he relie[d].”  Id. at *4.  It held that the expert could testify about the general process of mesh degradation, but not about the specific properties of the defendant’s mesh, as he sought to rely on analysis of a different company’s mesh implants.  And it held that he was not qualified to testify that antioxidants used to prevent degradation of the mesh were toxic, because he was not a toxicologist or a pathologist.  

Regulatory expert:

The plaintiff’s regulatory expert sought to offer the opinions that the defendant did not conduct adequate clinical testing on its mesh implants, did not include adequate warnings in the instructions for use (IFU) that accompanied the implants, and did not conduct adequate post-market surveillance on the products. 

The defendant argued that the expert was not qualified to testify about the adequacy of the defendant’s testing because she lacked relevant education and experience.   The court stated (cop-out #2), “[The expert’s] lack of experience with pelvic-mesh devices goes to the weight of her testimony, not its admissibility.” Id. at *6.   Again, as the Rules Committee emphasized in the course of the recent amendment proceedings, it has always been the case that every element of Rule 702—including qualifications—is a threshold admissibility question.   The new language of the Rule underscores this, but it was always the case.   If this expert lacked the qualifications to testify about pelvic mesh, she should have been excluded.  Plain and simple.

The defendant also argued that the expert was not qualified to testify about the adequacy of the defendant’s warnings because her career had focused on pharmaceuticals, not medical devices.  Moreover, the defendant argued, the IFU did not need to contain warnings commonly known to surgeons who prescribe the devices, and the expert was not a surgeon and could not opine about what surgeons did or did not already know.   What did the court say?  “Gaps in an expert’s qualifications or knowledge generally go the weight of the witness’s testimony, not its admissibility.”  Cop-out #3.

The defendant also argued that the expert’s proposed opinions about the adequacy of the warnings was inadmissible because the expert did not adequately explain the basis for her opinion and relied on an unreliable methodology.   What did the court say?  You guessed it — #4.  And #5 shows up in the next paragraph, discussing the literature on which the expert relied for her warnings opinions.   The court did exclude the expert’s opinions to the extent that they were based on adverse event reports about another company’s products and her opinion about whether the IFU provided adequate information for surgeons to obtain informed consent.  But it admitted her “post-market surveillance” opinions over the defendant’s arguments about their unreliability because . . . #6.


The plaintiff disclosed a psychiatrist, who sought to testify that the mesh implant had injured the plaintiff’s mental health.  But the expert’s report made only a temporal connection between the mesh implant and the plaintiff’s declining mental health, and the court held that this was not sufficient to constitute a causation opinion. 

General causation expert – Dr. Bruce Rosenzweig:

And now we come to the general causation opinions of Dr. Bruce Rosenzweig, familiar to all who defend pelvic mesh cases.  Dr. Rosenzweig offered his usual opinions:

  • Safer alternative designs:  The defendant argued that Dr. Rosenzweig’s opinions about safer alternatives were unreliable.  The court did not include any detail about the proposed opinions, simply noting that Dr. Rosenzweig “base[d] his opinion on his experience with many of the alternatives he suggests, in addition to his review of medical literature and other materials,” and  concluding that “disputes about the factual basis go to weight, and not admissibility” (#7).  The court did exclude Dr. Rosenzweig’s “alternatives” to the extent that they were surgical procedures, not medical devices.
  • “Small pore, heavyweight” mesh:  The defendant sought to exclude Dr. Rosenzweig’s opinion that the defendant’s mesh was defective because it was “small pore” and “heavyweight,” arguing that the opinions were unreliable. The court held that Dr. Rosenzweig  had cited “multiple medical studies” for his characterization of the mesh, and that disputes about the factual basis go to . . . . You know the rest (#8). 
  • Degradation:  #9 and #10 occur in the context of the court’s decision to admit Dr. Rosenzweig’s opinion that mesh degrades in the body and his opinions about the clinical consequences of the supposed “degradation.”
  • The court did hold that Dr. Rosenzweig was not qualified to offer opinions about the design and testing of medical devices, and it excluded his opinions to the extent that they pertained only to mesh implanted transvaginally.

Specific Causation Expert (Gynecologist):

The plaintiff disclosed a gynecologist to offer, inter alia, specific causation opinions.   The expert opined that the plaintiff’s symptoms “were caused by the defects in the design, testing, and marketing” of the defendant’s product, and that they plaintiff’s symptoms were “the result of her body’s intrinsic foreign body reaction.”  Id. at *14.  But, the court emphasized, the expert “[did] not explain how the materials he reviewed support[ed] his opinion” that the mesh implant caused the plaintiff’s symptoms, and “his failure to include the reasons for his opinions [were] neither substantially justified nor harmless” as the defendant would not be able to prepare its cross-examination without this information.  The court excluded the expert’s specific-causation opinions for these reasons.  We think it was even simpler:  the expert did not identify a reliable methodology, so his opinions were inadmissible.  But the result was correct.  (We should mention that, on the way to this portion of the opinion, the court denied the defendant’s motion to exclude the expert as unqualified.  Guess why.  #11.)

Summary Judgment:

The defendant moved for summary judgment on all of the plaintiff’s claims.  The plaintiff opposed the motion only as to her claims for negligent design, strict liability design defect, and failure to warn.

As to the negligent design claim, the court noted that, “[u]nder California law, a plaintiff advancing product liability claims must prove that a defect in the product caused injury.”  Id. at *17 (citation omitted).  Without the (excluded) testimony of her specific causation expert, the plaintiff could not satisfy this element of her claim.  The strict liability design defect claim failed for this reason as well, but it would have failed in any event because California law does not allow strict liability claims for design defects in medical devices.  And the warnings claim, also doomed by the lack of specific causation testimony, failed for the additional reason that there was no evidence of “warnings causation” – the plaintiff’s implanting surgeon testified that he did not read the IFU and did not depend on what the company told him about the product.   As such, no alleged inadequacy of the defendant’s warnings could have proximately caused the plaintiff’s injuries.   Summary judgment granted on all three claims.

As we said at the beginning, there is a lot of good in Cantrell, including the final outcome.  But whenever the court faced a tough call – or rigorous analysis – of whether an opinion satisfied Rule 702, it threw up its hands and defaulted to “weight not admissibility.”  This is not what Rule 702 demands of a “gatekeeper,” and we only hope that the upcoming amendments drive this point home. In the meantime, as temperatures hover in the upper 90’s in the northeast and COVID proliferates, stay safe out there.