See Biomechanical Witnessess p. 38 in the collision for the vehicle speeds and accelerations, and the linear acceleration and rotational acceleration for the occupant’s head. He usually compares the forces involved in the collision to backing into a pole at a low speed. Dr. Tencer is credentialed and experienced within his field, and jurors who violate court rules by googling him will find a seemingly impressive background. Probst has a master’s degrees in mechanical and biomedical engineering, but he does not hold a Ph.D. and is less prevalent within the scientific community. Compared to Dr. Tencer, the majority of his background is as an expert witness and he works almost exclusively for the defense. Because he uses a computer program to derive the forces involved in the collision, his work is less transparent and, for this reason, his responses on cross-exam can be harder to predict. Using the Kinematics of Whiplash in Cross-Examination Cross-examining a defense biomechanical witness provides you an opportunity to use the field of biomechanics to your advantage by educating the jury about your client’s injury. Dr. Tencer’s article “Understanding and Managing the Impact of Vehicle Crashes: Reconstructing the ‘Accident’”3, can be a great source for cross-examination. It provides a good description of the four phases of whiplash: retraction, extension, rebound and flexion. Here are some questions you could ask the defense biomechanical witness on cross-examination, based on Dr. Tencer’s article: • Can you please explain the four phases of whiplash? • Isn’t it true that during the retraction phase the occupant’s body is thrust forward relative to the head? • Isn’t it true that during the extension phase there are sheer and extension loads that are applied to the neck resulting in unnatural distortion of the lower part of the cervical spine? • Isn’t it true that most head restraints are very elastic and during contact they bend backwards then propel the head forward like bouncing off a trampoline? • Isn’t it true that an instant later, the forward motion of the torso is stopped by the shoulder belt, but the head continues forward, again inducing a horizontal or sheering force in the neck? • Isn’t it true that as the head continues forward, it bends the neck into forward flexion and these horizontal translations between adjacent vertebrae is an important mechanism by which soft tissues in the neck can be injured in a whiplash event? Most biomechanical witnesses do not testify regarding the kinematics on direct examination because discussion of the four phases of whiplash makes it sound like people probably get hurt in motor vehicle collisions. By asking these types of questions, you can help the jury understand whiplash analysis goes beyond simply discussing the magnitude of the forces involved, the science of whiplash injuries and why your client’s injury was caused by the collision. 37 Trial Lawyer | Winter 2025
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