A very helpful to-be-published opinion from the California Court of Appeal caught our eye this week because it comes out the correct way on an issue that has always bothered us:  Does a defendant (not the plaintiff) in a product defect case have to offer evidence on medical causation to a reasonable degree of medical probability?  The answer should obviously be “no.”  Of course the plaintiff has to offer such evidence.  The plaintiff bears the burden of proof, and anything less than expert opinion to a reasonable degree of medical probability is not sufficient to make the prima facie case.  The defendant bears no comparable burden.

Some courts nevertheless have held defendants to that standard and have excluded causation evidence—whether from retained experts or otherwise—where the defense witness could not say his or her opinion was more than 50 percent.  One trial court ruled that way in a hip replacement case in California, and the Court of Appeal reversed in the opinion that prompted today’s post.  In so ruling, the appellate court expressly held that the trial court erred in excluding the defendant’s medical causation opinion evidence merely because it was expressed to less than a reasonable medical probability.

The case is Kline v. Zimmer, Inc., No. B302544, 2022 WL 1679539 (Cal. Ct. App. May 26, 2022).  The plaintiff had hip replacement surgery in 2007, and after allegedly experiencing persistent pain, he sued the hip device manufacturer in California state court.  Id. at *1.  One trial ended in a plaintiff’s verdict, but the trial court granted a new trial because of excessive damages and misconduct of plaintiff’s counsel.  Id.  The second trial also proceeded to a plaintiff’s verdict, with the plaintiff’s expert testifying that the plaintiff’s alleged injuries were the result of a defect in the hip replacement device.  Id. *2.

The defendant had a causation expert too, plus testimony from treating physicians on potential alternate causes.  The jury, however, heard none of it, because the trial court excluded the evidence on the basis that the defendant offered it to less than a reasonable degree of medical probability.  Id.

That was the rub.  The trial court, like many others, confused the admissibility of the evidence with the sufficiency of evidence and held the defendant to a standard that did not apply.  It was undisputed that a plaintiff’s expert who cannot opine to a reasonable degree of medical probability is properly excluded “because the opinion could not sustain a finding in the plaintiff’s favor.”  Id. at *3.  However,

[t]he same does not apply to a defendant’s efforts to challenge or undermine the plaintiff’s prima facie case.  Even after the plaintiff has made its prima facie case, the general rule is that the burden to prove causation remains with the plaintiff. . . .  [Defendant] was entitled to put on a case that [the plaintiff] failed to satisfy that burden.

Id. at *4.  That is the critical point.  The defendant does not have to prove what caused the plaintiff’s alleged injury, much less prove that the alleged injury was caused by something other than the defendant’s product.  The defendant’s job is to discredit, poke holes, cast doubt, and otherwise persuade the jury that the plaintiff and the plaintiff’s experts did not prove their case.  In other words,

[Defendant] did not need to show that a different cause was more likely than not the cause of [the plaintiff’s] injuries.  All that [Defendant] need to show was that [the plaintiff’s] evidence was insufficient to prove [his] injuries were more likely than not caused by [Defendant].

Id.  Thus, because the defendant’s burden is fundamentally different (or absent) compared to the plaintiff’s, the defendant does not have to abide by the reasonable-degree-of-medical-probability standard.  This grants the defendant fair and substantial leeway.  As the court held,

[Defendant] should have been permitted to . . . offer[ ] expert opinions offered to less than a reasonable degree of medical probability that [the plaintiff’s] injuries may have been attributable to other causes.  Such defense expert opinions could cast doubt on the accuracy and reliability of a plaintiff’s expert.  The jury is entitled to consider such evidence in deciding whether the plaintiff’s expert is exaggerating his or her opinion.

Id.  This is a reasoned and correct result, and having been on the wrong end of cases like this, we feel some vindication in seeing our home courts state this reasoned and correct result so clearly.

Of course, rules of evidence still apply, and defendants do not get to put into evidence whatever they want.  Speculation is still out of order, and a defense expert’s opinions may not be based on conjecture or assumptions without evidentiary support.  Id. *5.  Take for example evidence that a Vitamin D deficiency could cause pain similar to the plaintiff’s pain.  Without evidence that the plaintiff was actually deficient in Vitamin D, that opinion was not admissible.  Id. at n.7.  By comparison, the evidence did show that the plaintiff experienced lower back pain, suffered from arthritis, and was overweight.  The defense expert should have been allowed to testify that these factors could have caused plaintiff’s pain.  Id.

One final tidbit is that the Court of Appeal considered the trial court’s error to be “structural”—an error that “affects the framework within which the trial proceeds, rather than simply an error in the trial process itself, thus affecting the entire conduct of the trial from beginning to end.”  Id. at *6 (citations omitted).  Structural errors require per se reversal, without the need to engage in “harmless error” analysis.  It’s an automatic do over.

The case now heads back for a third trial.  Will the third time be the charm for this defendant?  We have no idea, but at least the evidentiary slates will be more balanced this time around.