This post is from the non-Butler Snow side of the blog.

In Hill v. Medical Device Business Services, Inc., No. 24-5797, 2025 U.S. App. LEXIS 17835, 2025 WL 1950300 (6th Cir. July 16, 2025), the Sixth Circuit affirmed an expert exclusion/Rule 702/Don’t Say Daubert decision in a case that we last wrote about when it was before the Middle District of Tennessee.  Although the Sixth Circuit’s opinion is “unpublished” it still may be cited pursuant to FRAP 32.1 and Sixth Cir. L.R. 32.1.

As we summed up the dispute last time:

The plaintiff in Hill had two hip replacement surgeries.  A 2014 surgery was for the initial implant of his total hip replacement system, and a 2015 surgery was to replace certain components, although one component, the femoral stem, was left unchanged.  Five years later, the femoral stem component fractured, and the entire hip implant construct was explanted and replaced. 

The parties agreed that the femoral stem component broke due to a small flaw in its metal, but disagreed as to whether that flaw was introduced during the implant surgery or was a manufacturing defect that existed at the time the implant left the manufacturer’s control.

Plaintiff’s manufacturing defect theory depended on two experts, including a materials scientist/metallurgist expert, but the district court judge found that the opinions fell short under Rule 702’s requirements because they lacked adequate foundation. 

You’ve seen this type of thing before: 

• An expert opinion that something was performed the wrong way, followed by the expert admitting to not knowing what the proper way was;

• An expert opinion ruling out one potential cause, followed by the expert admitting to not knowing the evidence showed that potential cause actually had occurred;

• An opinion blaming the manufacturing process for introducing a flaw, even though the expert admitted to not knowing what the manufacturing process required, including the steps intended to prevent or minimize such flaws. 

On appeal, the Sixth Circuit came out the right way and affirmed the Middle District’s expert exclusion order.

The Sixth Circuit agreed that although the materials science expert was qualified in metallurgy, she lacked experience with hip implants, the relevant manufacturing processes, and the surgical context.  Her methodology relied on a process of elimination to attribute the flaw to manufacturing, but she was unfamiliar with the surgical procedures and could not reliably rule out surgical causes. Notably, her report claimed reliance on the orthopedic surgeon’s opinion, but her deposition contradicted this, admitting she did not meaningfully rely on that analysis.  The court found this contradiction and her lack of direct knowledge of the manufacturer’s processes fatal to her opinion’s reliability.

The Sixth Circuit also affirmed the exclusion of a biomedical engineer who parroted the metallurgist’s conclusions without independent analysis or microscopic evaluation of the device, and it emphasized that experts may not simply regurgitate another expert’s opinion—particularly when the regurgitated opinion was itself excluded.

Having affirmed the exclusion of plaintiffs’ expert testimony, the Sixth Circuit affirmed the grant of summary judgment for the defendant, finding no direct or circumstantial evidence tracing the injury to a specific manufacturing error, as required under Tennessee law.

In doing so, the appellate court affirmed the need for expert testimony on the issue of defect, and rejected plaintiffs’ attempt to invoke the “malfunction theory” (a res ipsa loquitur-like inference of defect from product failure).  It noted that both plaintiffs’ experts conceded that all metals contain microscopic flaws and that medical devices can fail for unknown reasons.  Thus, the mere occurrence of a device failure, particularly where such failures are a known risk, is insufficient to infer a manufacturing defect.

All that is good and fine and makes us happy.

What is a disappointing is this: 

In excluding the experts, the Middle District of Tennessee discussed at some length the 2023 amendments to Rule 702, and how old-Rule 702 opinions too often punted on expert issues—under the “misguided” notion that expert problems go to weight or credibility rather than admissibility.  It also discussed how these problems led to the update of Rule 702, and it noted there was a question about whether Sixth Circuit authorities interpreting the old Rule 702 were controlling under the new rule.   See Hill v. Med. Device Bus. Servs., Inc., No. 3:21-cv-0440, 2024 U.S. Dist. LEXIS 140272, 2024 WL 3696481 (M.D. Tenn. Aug. 7, 2024).

Thus, on appeal the Sixth Circuit could have availed itself of the opportunity to answer the questions that the District Court raised in Hill.  It could have swept away those misguided old-Rule 702 authorities while bringing the Circuit’s current Rule 702 test into the modern era, by recognizing that rules changes, like statutory changes, overturn prior judicial precedent, and by clearly recognizing the new, more aggressive gatekeeping role required by Rule 702.

But, alas, the Sixth Circuit did not.

Maybe we are being too picky here, but we find it odd that the Sixth Circuit references to Rule 702 in Hill, and in another opinion, In re Onglyza (Saxagliptin) and Kombiglyze (Saxagliptin and Metformin) Prods. Liab. Litig., 93 F.4th 339, 345 (6th Cir. 2024), never mention that Rule 702 was changed.  For example, in Hill, the Sixth Circuit mentions the four admissibility factors of Rule 702, but does not acknowledge that now, it clearly is “the proponent” of the expert witness who must “demonstrate [ ]” reliability on a “more likely than not” standard, and it certainly does not discuss the Rule 702 changes like the District Court did. 

Indeed, some of the Sixth Circuit’s language in Hill veers too close to the hands-off, let it in,  “goes to weight not admissibility approach” that Rule 702 was amended to stop.  Like this passage:

Still, the district court enjoys considerable “discretion in determining whether or not a proposed expert’s testimony is admissible, based on whether it is both relevant and reliable.” Johnson v. Manitowoc Boom Trucks, Inc., 484 F.3d 426, 429 (6th Cir. 2007) (citing Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 147, 119 S. Ct. 1167, 143 L. Ed. 2d 238 (1999)). The district court need not admit expert testimony “that is connected to existing data only by the ipse dixit of the expert,” or where there is “too great an analytical gap between the data and the opinion proffered.” [Nelson v. Tenn. Gas Pipeline Co., 243 F.3d 244, 254 (6th Cir. 2001)] (quoting Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146, 118 S. Ct. 512, 139 L. Ed. 2d 508 (1997)). Because this inquiry is often fact-driven, the district court’s gatekeeping role is “very flexible,” and commands a high degree of deference by the reviewing court. Johnson, 484 F.3d at 430.…”

Hill, 2025 U.S. App. LEXIS 17835, at *13 (emphasis added).

Sorry, no.  Because Rule 702 now requires the proponent of expert testimony to demonstrate an opinion’s reliability before it can be admitted, district courts do not have “considerable discretion” to admit expert opinions that fall short; they must not admit (mandatory) not “need not admit” (discretionary) unreliable expert testimony; and the gatekeeping role is not any longer “very flexible”.

At the end of the day, we have a good Sixth Circuit outcome after a reasonably rigorous assessment of expert admissibility in this instance, but nothing broader to use going forward. No ringing endorsement of the new Rule 702 standard and no sense that the Sixth Circuit is really attuned to the changes.  Maybe it is not so bad the court left Hill unpublished after all.