Reasonable Medical Probability

Kline v. Zimmer, Inc., No. B302544 (D2d8 May 26, 2022)

This is an ancient medical device case where a plaintiff jury verdict was already reversed on an excessive damages issue. It still not over.

Plaintiff in a medical negligence or products liability case needs to prove that his injuries were caused by the allegedly defective act or instrumentality—here a defective hip transplant. To do that he needs to prove that the transplant caused his injury by “reasonable medical certainty.” For that, he needs an expert. And for that expert’s opinion to be admissible it must be expressed to a “reasonable medical probability.” That is really a way of saying that the plaintiff’s doc must be capable of saying that transplant more likely than not was the cause. Otherwise the testimony is inadequate to satisfy the burden of proof.

Plaintiff here did that. Defendant tried put up its own doc, who identified numerous other causes as “possible.” But he couldn’t testify that any particular one of them was the medically probable cause. The trial court held that wasn’t good enough and excluded the expert. Plaintiff won a big verdict.

That was error. The reason why has to do with the burden of proof. Plaintiff needs to prove, by 51/49, that the transplant was a proximate cause. So his expert needs to testify that the medical evidence could meet that test. But Defendant doesn’t bear any burden at all to prove something else was instead. Defendant just needs to stop Plaintiff from reaching 51%. And to do that, it does not require a defense expert to opine that any particular thing was the cause by a reasonable medical certainty. It is enough that Defendant’s expert offers sufficiently reliable testimony that throws doubt on the fact that Defendant’s conduct or product is the cause.

The Court draws an example from a 30 year old First Circuit case that makes it clear. Say the overwhelming scientific consensus is that a particular injury could be caused by A, B, C, or D, each with equal probability. Plaintiff finds an outlier expert who is willing to go all in on A. Testimony about the consensus would certainly be relevant to shoot down Plaintiff’s expert’s claim that A is a sufficient cause, even if nobody in that consensus could testify that something else was the cause by a reasonable medical certainty.

A trickier issue is that to get a reversal based on the exclusion of evidence, the appellant needs to show prejudice—a likelihood of a different result had the evidence been admitted. In this kind of context, that’s a real hard call to make as an epistemic matter. The Court of Appeal here declines to make that call. It instead finds that the error is “structural.” That is, that it fundamentally affected the process of the trial in such a substantial way that, yet, is not susceptible to measurement. The quintessential structural error is the denial of the right to jury trial. 

Exclusion of evidence usually doesn’t cut it for structural errer. But in a medical injury case, to deprive a defendant of any expert testimony at all on the crucial element of causation—an element that can only be proven with an expert—makes it across the line. Quoting a 2009 case, the Court explains that “when a trial court erroneously denies all evidence relating to a claim, or essential expert testimony without which a claim cannot be proven, the error is reversible per se because it deprives the party offering the evidence of a fair hearing and of the opportunity to show actual prejudice.”

Reversed and remanded for a new trial on causation and damages.