This is the first in a series of articles that will address cross-examining defense biomechanical experts and the field of biomechanics generally.
By way of background, biomechanics is the science of movement of a living body, including how muscles, bones, tendons and ligaments work together to produce movement. Biomechanics is sometimes confused with kinetics. Kinetics is a branch of classical mechanics that is focused on the movements of various bodies and the forces that can act on both bodies in motion and bodies at rest. Biomechanics and kinetics are not the same thing; rather, biomechanics is actually a subcategory of kinetics.
Defendants in personal injury actions will attempt to use the study of biomechanics to dispute the causation of injuries as they relate to the facts alleged in a given occurrence. Biomechanical experts are used predominantly in products liability, premises liability and motor vehicle claims.
Because of cost prohibitions, biomechanical experts are rarely used in workers’ compensation cases. When using a biomechanical expert, the defense in a personal injury action will argue that the relationship between biomechanics and personal injury is obvious because the specific focus of biomechanics is on mechanical movement. This includes the articulation of joints and the participation of tendons and muscles in the coordination of physical activity.
Biomechanics is also crucial to animations, which have become popular in the personal injury setting. The admissibility of an animation is many times contingent upon biomechanical analysis because the human surrogate used in the animation needs to act in a scientifically valid or reproducible fashion.
Backtracking, the first question that needs to be answered in any commentary on biomechanical experts is what qualifies someone to be admitted as an expert in biomechanics. It is important to note that just becomes someone is deemed to be an expert in the field of biomechanics does not mean that the opinions he or she renders in any particular case are admissible. The admissibility of any opinion will be addressed in a later part of this series. For now, I am focusing only on whether someone is even an expert in biomechanics.
An individual who holds him or herself out to be an expert in biomechanics will invariably be required to have some engineering background. The expert will assert that he or she has studied engineering with an emphasis in the field of biomechanics.
Biomechanics is closely related to engineering, because it often uses traditional engineering sciences to analyze biological systems. With that in mind, the experts range in qualifications from a master’s degree in mechanical engineering to a doctorate in mechanical engineering to a combination higher-level engineering and medical degree. The expert will also have to assert a significant degree of training and study in the field of biology.
Obviously, the higher the level of training, the more weight the expert’s testimony may carry. The combination of a medical degree and a doctorate in engineering is certainly the top-level qualification for a biomechanical expert. Medical doctors who have served as forensic examiners (e.g., coroners) will also many times assert an expertise in biomechanics. When picturing why a forensic examiner may have an expertise in biomechanics, I find it helpful to think back to the old television show Quincy M.E. Forensic examiners will many times be able to describe real-life investigative skills that the jury or ultimate fact-finder will find compelling. As a result, if the biomechanical expert does not also have a medical degree and/or actual real-life experience in investigating injuries, it can be an effective tool in any cross-examination.
Assuming the expert is qualified to offer an opinion in the field of biomechanics, the next step in cross-examining a biomechanical expert is gaining an understanding of the basic science behind the opinions rendered. In its simplest form, most experts will agree that the science of biomechanics relies upon Isaac Newton and his three laws of physics.
The first law, sometimes referred to as the law of inertia, is essentially as follows: An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon. The second law establishes that force equals mass times acceleration. It essentially establishes in scientific terms the obvious: that the greater the mass of an object, the more force required to move the object. The third law is essentially that for every action there is an equal and opposite reaction. A classic example of how this law is applied to biomechanics is that if someone runs into a wall, he or she will bounce backwards.
Invariably, the defense biomechanical expert will cherry-pick which of Newton’s laws he or she chooses to apply, ignoring the application of the other laws.
I call this choosing the variables that fit his or her theory of the case. An effective cross-examination should be able to establish that the foundation of the defense expert biomechanical opinion is built upon facts that do not comport with the actual witness testimony. Essentially, the defense witness will discount the witness testimony as impossible based on the physics. The assertion that the events or injuries are impossible is usually nonsense, but, nonetheless, the assertion creates a serious issue that needs to be competently addressed on cross-examination.
In forthcoming articles, I hope to provide some of the tools needed to competently cross-examine the defense biomechanical expert. •
Brandon Swartz is a founding partner of Swartz Culleton. His practice focuses on all types of personal injury cases, including wrongful death, medical malpractice, civil rights violations, motor vehicle, premises liability, products liability, trucking accidents and workers’ compensation.