California Appellate Court Permits Defense Expert Testimony Regarding Causation To Meet Lower Standard When Offered To Challenge Plaintiff's Causation Evidence

• Published date: 15 September 2022
• Subject Matter: Litigation, Mediation & Arbitration, Food, Drugs, Healthcare, Life Sciences, Trials & Appeals & Compensation, Personal Injury, Food and Drugs Law, Biotechnology & Nanotechnology
• Law Firm: Duane Morris LLP
• Author: Mr Michael L. Fox

Causation in personal injury actions, including product liability claims related to drugs and medical devices and toxic tort actions related to exposure to hazardous substances, must be proven within a reasonable degree of medical probability based upon competent expert testimony. That's typically the plaintiff's burden of proof. Do the defendants bear the same burden? In Kline v Zimmer, the California Court of Appeal recently held that, in challenging the plaintiff's causation evidence, defense expert testimony should be held to a standard of "less than a reasonable medical probability."¹

Kline involved the plaintiff's claim that the Durom Cup hip implant, manufactured by defendant Zimmer, Inc. and utilized in his first hip replacement surgery, was defective and caused him to require an additional surgery, which resulted in further injury. Evidence presented by the plaintiff at trial included an expert who testified to a reasonable medical probability that the Durom Cup's defects caused the plaintiff to need the additional surgery, which resulted in changes in his muscles and soft tissues causing him chronic pain.²

Zimmer had offered to present expert testimony that the plaintiff's injuries had possible alternative causes, such as arthritis and excess weight.³ However, the trial court had excluded this evidence, as well as certain parts of the plaintiff's expert testimony that was also not stated to a reasonable medical probability.⁴ The exclusion left Zimmer with no expert testimony, while the plaintiff's experts were permitted to testify.⁵ The trial court relied on existing California personal injury law, which states that causation "must be proven within a reasonable medical probability based upon competent expert testimony."⁶ The jury returned a verdict in the plaintiff's favor, and Zimmer appealed.

The Court of Appeal, reviewing the judgment de novo, found that in offering evidence that undermined the plaintiff's expert's testimony in an effort to demonstrate the plaintiff could not meet his burden of proof on causation, the defense expert was improperly excluded from testifying as to other possible causes of the plaintiff's injury.⁷ The appellate court agreed with Zimmer that the Ortho Pharmaceutical rule cannot apply to a party without the burden of proof.⁸ That is, a defendant, when trying to show that the plaintiff has not met his burden, does not need to prove potential or possible alternative causes of injury to a reasonable medical...