Biomechanical Witnesses by Sam Elder Two defense biomechanical witnesses based in Seattle, Dr. Allan Tencer and Bradley Probst, are often excluded under Gilmore v. Jefferson Cnty. Pub. Transp., 190 Wn. 2d 483 (2018), in Washington cases, so they now routinely testifying in Oregon trials. These defense witnesses look at pictures of the vehicles involved in a collision and a repair bill, then either run calculations or use a computer program to support testimony regarding the forces involved in the collision. It’s an approach Washington Supreme Court Justice Mary Yu referred to as “dubious.”1 This article addresses some ideas for cross-examination because Oregon courts often allow these witnesses to testify. I hope to provide some insight into dealing with defense biomechanical witnesses generally, and Dr. Tencer and Probst specifically. What Biomechanical Witnesses Are and What They Aren’t Both Dr. Tencer and Probst provide a “biomechanical analysis” of a collision. They do this by analyzing the circumstances of the crash. Dr. Tencer runs calculations as described in his published paper “Whiplash Mechanics in Low Speed Rear-end Automobile Collisions”. Probst uses a computer program called EDCRASH to calculate the forces. Both will describe the magnitude of the forces and compare the forces to everyday activities or relatively benign and impliedly non-injury inducing events. Biomechanics itself is an accepted science with various applications, but applying biomechanics to determine injury risk, injury thresholds or injury to any particular individual is more controversial. For example, a 2021 review of studies found the activities of daily living (ADL) approach employed by Dr. Tencer, Probst and other biomechanical witnesses is not reliable.2 Both defense biomechanical witnesses speak with apparent authority on biomechanical science and are experienced enough to come across as credible within their field. However, it’s important to remember that — as with most biomechanical witnesses — Dr. Tencer and Probst are not health care providers and they are not qualified in any way to opine on causation of injury. Their analysis generally does not include any consideration of the specific susceptibility to injury of the vehicle’s occupants. Their opinions generally stress the magnitude of the forces – not the specific application of the forces to the particular occupant. Their analogies and comparisons are generally designed to minimize the severity of the collision. These shortcomings provide for openings against both witnesses on cross-examination, especially if the Plaintiff has special circumstances or a particular susceptibility to injury. The jury should already know a lot about your Plaintiff by the time they hear from a defense biomechanical witness and there may be relevant factors the witness ignored. Here are some questions you can use to point out the limits of a biomechanical witness’s expert opinion: • You are not a medical doctor • You have not been brought in to provide medical opinions • You did not examine or interview the Plaintiff • You did not personally witness the collision • You did not inspect the vehicles yourself • You did not measure the forces involved in the collision • You did not obtain data event recorder information from the vehicles involved in the collision • You did not consider the plaintiff’s particular susceptibility to injury Learning about the defense biomechanical witness helps as well, as some witnesses may appear more credible than others. Dr. Tencer holds a Ph.D. in Mechanical Engineering and has been active in the Washington biomechanical community for decades. He routinely provides opinions on what he refers to as the worst-case scenario in terms of the forces involved SAM ELDER practices in personal injury, insurance coverage, insurance bad faith and heath care provider law, with special expertise in courtroom technology. He is the owner of the Law Office of Sam Elder located at 5170 NW Sammamish Rd., Issaquah, WA 98027. He can be reached at [email protected] and 425-999-8170. 36 Trial Lawyer | Winter 2025
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