Today’s post is from the Zimmer hip prothesis MDL, which appears to be winding down and which we’ve blogged about here. It’s a Rule 702 decision that excluded a treating surgeon who offered unsupported expert opinions about an alleged product defect. In re: Zimmer M/L Taper Hip Prosthesis Prods. Liab. Litig., 2026 WL 2111824 (S.D.N.Y. July 22, 2026).
Plaintiff claimed that his hip implant fractured six years after implant and caused injury. He offered the surgeon who performed his revision surgery as his expert witness. The surgeon offered opinions that (1) the modular neck component in the hip prothesis was defectively designed and manufactured, (2) the neck component was manufactured in a defective manner which caused it to “cold weld” into the stem, and (3) the component was defectively designed because it was not engineered to withstand “real-world biomechanical loads.” Id. at *2. The defense moved to exclude the surgeon’s testimony under Rule 702.
The district court began its analysis under Rule 702 by citing the full text of the amended rule and included a footnote noting that the “2023 amendments clarified that the preponderance standard governs all admissibility criteria, thus reaffirming the importance of the court’s gatekeeping function.” Id. at * 2, n.1. We like that, but the court also cited to a pre-2023 amendment case for the proposition that the assumptions underlying an expert’s opinion go to weight rather than admissibility. We don’t like that. As we’ve blogged about before, in amending Rule 702 in 2023 the Advisory Committee specifically stated:
[M]any courts have held that the critical questions of the sufficiency of an expert’s basis, and the application of the expert’s methodology, are questions of weight and not admissibility. These rulings are an incorrect application of Rule 702 and 104(a).
F.R.E. 702 advisory committee’s note to 2023 amendment. We will continue to call out pre-amendment citations that are contrary to the expressed intent of the 2023 amendments.
Despite the reference that got us rankled, this expert didn’t stand a chance under any reasonable 702 analysis. The revision surgeon did not review, identify or cite any underlying data, literature or methodology in connection with his opinion that a defect caused the fracture. Nor did he cite or review any documents produced by the defendant related to the device. He also admitted that “he cannot speak to why the device fractured,” testifying in his deposition that “we will never know” why it fractured. Id. at *3. Although the court commended the surgeon for his candor in admitting that he did not know why the fracture occurred, that admission underscored the fact that his opinion was wholly unreliable and did not satisfy the requirements of Rule 702.
Plaintiff argued that the surgeon’s visualization of the device during the revision surgery constituted “direct surgical inspection” which should be considered the “gold standard” for why the fracture occurred. Id. Ha! Neither the expert nor plaintiff offered anything to suggest that the physician had any experience that would allow him to “reliably identify a defect by just looking at the device with his naked eye.” Id. Plaintiff also argued that the expert conducted a differential diagnosis. That went nowhere. The surgeon never referenced a differential diagnosis, and he made no effort to identify or rule out other potential causes of the fracture.
The revisions surgeon’s opinions did not satisfy the requirements of Rule 702, and the court granted the defense motion to exclude his opinions. Since New York law requires expert testimony in “a complicated medical case,” the court also granted summary judgment in the defendant’s favor. Id. at *5.
Separately, the court held that summary judgment would be appropriate even absent the exclusion of plaintiff’s expert. Plaintiff’s only surviving claim was for negligence, and in recognition of the absence of sufficient evidence of a defect, plaintiff relied on a “malfunction theory.” Id. That theory requires that the incident causing the alleged injury be “[1] of a kind that ordinarily occurs as a result of product defects and, [2] that the incident was not . . . solely the result of causes other than the product defect existing at the time of sale or distribution.” Id. That theory didn’t work because the record clearly established that fracture is a known risk for artificial hip devices and that fractures can occur for reasons wholly unrelated to any product defect. The court held that constituted separate, independent grounds to grant summary judgment.
Overall, a very good result, and one we’ll gladly take as we head into the first weekend of August.
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