Is a Medical Doctor Enough? The Role of a Biomechanical Expert

Mar 4, 2000 by

By Dr. Kerry Knapp

A biomechanical analysis provides the critical link to understanding the relationship between personal injury and injury-producing events. Whether the events and injuries are minor or fatal, a rigorous biomechanical analysis is critical to demystifying the relationship between the events and the damage to human tissue, especially when there are no witnesses, when witness testimony conflicts, or when the economic stakes are high.

What are Biomechanics and Injury Biomechanics?

The discipline of biomechanics integrates the laws of physics, human structural anatomy, and engineering to describe the motion of the body and body segments. Injury biomechanics then couples the knowledge of force and motion with a thorough understanding of functional human anatomy and human tissue mechanics to explore the possible relationships between external events and mechanically induced human tissue injury. Because biomechanics is an integrated science, the body of literature applicable to the biomechanics profession is diverse, encompassing both medical and engineering literature. Research on occupant response and loading in motor vehicle and aircraft accidents appears predominantly in automotive engineering publications and Armed Services publications. Tissue damage and tolerance data are presented in biomechanics and select medical publications. Issues related to radiology, bone fracture, and structural changes in human tissue with time are presented in the medical literature. Texts and papers from these various disciplines form the scientific basis for safety regulations, surgical techniques, organ transplants, medical treatment plans, and teaching curriculum. These materials also define the underlying scientific data necessary to understanding and explaining human injury, and form the basis of injury biomechanics.

Who are Biomechanists? What is their Role?

As discussed, biomechanics is an integrated science requiring parallel courses of study. A biomechanist might be an engineer or medical doctor; biomechanics, however, is not within the sole domain of either of these easily recognized professions. Review of an individual’s education, training, and work experience is necessary to determine whether a biomechanist is qualified to offer expert opinions regarding injury. The minimum training-education for the biomechanist must include Newtonian mechanics, structural and functional human anatomy, human physiology, and injury biomechanics including a knowledge of human soft and hard tissue tolerances. Medical practitioners are generally skilled in identifying and healing tissue damage, but they are not extensively trained in the mechanisms of tissue damage, occupant kinematics, or the response of human tissues to loading. Engineers, on the other hand, understand the physics of movement and the principles necessary to analyze the mechanics of materials, but traditionally lack the detailed knowledge of human anatomy and physiology.

The biomechanist integrates aspects of both disciplines and fills the gap between the engineer’s explanation of external loading and the medical practitioner’s diagnosis and treatment of damage to human tissues. The biomechanist plays a valuable role in both criminal and civil litigation when human tissue injury is an issue. Where external forces have caused tissue damage, the result may vary from mild muscle strain to death. The results of the event are generally documented by a medical practitioner (injury) or medical examiner (death). The external event that produced the forces may or may not be known. Often, the event has been described by an engineering analysis or accident reconstruction.

The role of the biomechanist is to function as the “interdisciplinary integrator”, discovering and describing how the interaction of the human body with the external environment occurred and determining the injury producing probability. The use of biomechanical experts in personal injury, wrongful death, and criminal cases has increased dramatically over the past decade because of the biomechanical expert’s ability to “assist the trier of fact to understand the evidence or to determine a fact at issue” as described by Federal Rule of Evidence 702. Well-qualified and well-prepared experts in the field of injury biomechanics have become increasingly influential and persuasive witnesses regarding injury causation and other aspects of injury-producing events. The proliferation of “experts” in the field of injury biomechanics is likely to continue, as the expertise becomes better known; this will, of course, also increase the likelihood of opportunists. The increase in “experts” offering biomechanical opinions has led at times to motions to exclude biomechanical testimony. Attempts have been made to exclude the biomechanical expert on the basis of Frye and Daubert rulings by challenging several specific points from those opinions:

1. Biomechanics and/or injury biomechanics are not legitimate areas of science.

2. The biomechanical expert is not qualified to offer opinions on injury causation when those opinions refer to a specific individual, injury, or event. Attorneys often argue that injury causation is a medical opinion and therefore only a medical practitioner is qualified to offer such an opinion.

3. Literature based on the use of human-subject and animal study data cannot be applied to specific individuals. Especially in low-speed motor vehicle cases, the validity and utility of the low-speed impact human-subject literature has been attacked on a publication-bypublication basis. The attacks attempt to discredit the methods, subject numbers, and findings expressed in the publications with the hope of excluding the expert testimony of the biomechanist based on misuse of the literature.

4. Finally, is a thorough questioning of the biomechanist’s education, training, and experience. What qualifies the biomechanist as an expert in the field?

A qualified biomechanist, however, is the best professional based on education, training, and experience to function as the integrator of interdisciplinary and multi-disciplinary information for the court.

To fulfill this integrator function objectively, the biomechanist must systematically organize, rigorously analyze, and impartially evaluate each case; available evidence must be used to illuminate important relationships, and the lack of important evidence (along with its significance) must also be documented. The strengths and weaknesses of the case must be clearly understood and presented. Each case must be approached analytically; although the specific focus of the case may vary with the issues, injuries, and events, a consistent analytical approach must be maintained. The biomechanist must then communicate the analysis and its results effectively via performance/presentation so that the court clearly sees the relationship between the event(s) and the probable relationship to the actual documented tissue damage (i.e., injury or death).

Biomechanics and Human Biomechanics as Professional Disciplines

Biomechanics is a scientific discipline concerned with understanding and improving the biological function and response of various species, while human biomechanics limits the focus to the mechanics of human systems. Human biomechanics also incorporates some aspects of physiological and biochemical functions; for example, when effects of aging and tissue remodeling after injury are essential elements for analysis. Human biomechanical research has addressed a broad range of topics related to human function and performance, including:

· The mechanical function and performance changes of muscles, connective tissue, cartilage, skin, nerves, bones, joints, and internal organs.

· Human movement and performance where the interactions of internal and external forces (and moments and torques that produce movement) are examined. For example, movement during high performance swimming or jet pilot ejection.

· Internal and external loading and overloading that may lead to injury or remodeling of biological tissues and organs.

· Projects such as the mechanical heart, joint resurfacing and replacement; as well as new work on tissue engineering and the development of biomaterials for the replacement or healing of human tissue.

Biomechanics has developed from a relatively obscure area of study to a recognized professional discipline. Today the study of human biomechanics is a widely recognized area of scientific study and professional practice. Biomechanics is offered as an area of study in university graduate programs in over 85 universities in the United States and Canada. Many more universities offer biomechanics courses at the undergraduate and graduate levels as a part of other degree-focus areas (e.g., exercise science and engineering). Professionally, there are thousands of biomechanistsscientists working in universities, institutes, and a variety of industries worldwide.

Biomechanical Causation vs. Medical Causation


A. Biomechanics – The science concerned with the action of forces, internal and external, on the living body. (From Stedman’s Medical Dictionary for the Health Professions, 3rd Edition, 1997)

B. Medicine – the art of preventing, diagnosing and treating disease. (From Stedman’s Medical Dictionary for the Health Professions, 3rd Edition, 1997)

The above definitions illustrate the basis for clearly distinguishing between a biomechanicalcausation opinion and a medical diagnosis of injury. Medicine focuses on diagnosing the reasons for symptoms expressed by a patient; when symptoms are related to tissue injury, the casual event and its relationship to the injury is absent from the medical diagnosis except as reported by the patient and recorded in the medical history. Consider the example of an individual who presents to a physician with complaints of upper extremity loss of strength and “tingling” in the hands. The physician immediately recognizes that the expressed symptoms may be due to psychological, organic neurological (i.e., brain or spinal cord related), or neuromuscular (i.e., motor neuron and/or skeletal muscle patho-physiological) causes.

By history, the patient may attribute the symptoms to a horseback-riding fall. Based on the patient history, the physician may quickly determine that the problem is organic neurological, and then test to determine if the problem is brain-centered or cord-centered. If the physician ascertains that the problem is cord-centered, he/she must determine whether the problems are due to a cord lesion or to cord compression. Finally, if the symptoms are secondary to cord compression, the physician must determine if the compression is due to a vertebral fracture, intervertebral disc failure, spinal instability (e.g., retrolisthesis or spondylolisthesis), or cord swelling. The end product of the medical thought process is the diagnosis of the physiological cause of the cord compression, which constitutes a medical-causation opinion (i.e., diagnosis) and leads the medical provider toward a specific treatment regime.

In the example above, the biomechanist would not dispute the medical diagnosis. The biomechanist would not argue that the symptoms expressed by the patient were due to brain trauma versus spinal cord compression, nor would the biomechanist argue that the spinal cord compression was the result of vertebral body fracture/failure rather than retrolisthesis. The biomechanist, unless he/she is a medical doctor, is not qualified to express such opinions. The biomechanist accepts the medical diagnosis and instead focuses on the process that produced the diagnosed injury; in this case, the internal or external forces on the structures of the human vertebral column and the spinal cord. How did the physician-diagnosed pathology (i.e., medical-causation opinion) occur? Systematic analysis leads the biomechanist to an understanding and expression of an injury-causation opinion (i.e., a biomechanical opinion).

As another example, Mr. Jones (a 56 year-old man) was an unrestrained driver who experienced an injury-producing event leaving him unable to move his arms and legs and with a feeling of numbness throughout his body. Medical examination and testing led to the identification of retrolisthesis of C3 on C4 with compression of the spinal cord at that level in the cervical spine –i.e., the medical diagnosis or medical causation opinion for Mr. Jones’ expressed symptoms. Based on the medical diagnosis, the biomechanist is faced with determining how and why the retrolisthesis of C3 on C4 occurred – the process of identifying and documenting how the injury occurred is the biomechanical-causation opinion. The medical diagnosis answers the question: What injury produced the observed symptoms? The biomechanical opinion answers the question: How did (or how could) the observed injury occur given the specific circumstances of the injury-producing event?

In most instances, it is the biomechanical expert rather than the medical practitioner who is most qualified on the basis of education, training, and experience to express opinions on issues of injury causation.

How To Work with a Biomechanist (A Low-Impact Collision Example)

The low-speed impact automobile accident case can be especially difficult to resolve; with low speeds and minimal damage, it is often difficult for insurance companies to justify the payment of thousands of dollars for treatments that seem excessive and unnecessary in light of the documented information on human tolerance to impact. Generally, treating physicians do not know the vehicle dynamics or the occupant kinematics when treating a patient (except by patient self report), and a biomechanical analysis is not within the field of expertise of most physicians. The biomechanist, however, is able to offer important insight.

For the biomechanist to render an opinion on injuries sustained in a low-impact motor vehicle accident, it is necessary to first obtain the vehicle dynamics of the event from a qualified expert. Usually, the biomechanist will limit his/her field of expertise to the biomechanical aspects of the accident. Performing both the vehicle dynamics and the injury biomechanics analyses can lead to prejudiced assumptions that bias or invalidate an otherwise completely objective report. An accident reconstructionist will, therefore, need to provide vehicle dynamics information to the biomechanist, including the change in linear velocity, the principal direction of force, the acceleration impulse applied to the vehicle (or at least the assumed time to maximum engagement), and any angular displacement/velocity (i.e., rotation) applied to the vehicle (rotation is important to occupant loading and occupant motion).

The biomechanist is then able to take the loading history during the motor vehicle accident and formulate an analysis of the occupant kinematics (i.e., occupant movements). Determining an accurate estimate of the forces, moments, and torques acting on an occupant’s body results in an accurate description of the occupant displacements, velocities, and accelerations (i.e., occupant kinematics). The biomechanical analysis also involves an examination and summary of the available medical reports, including radiographs, CT-scans, or other diagnostic reports. Finally, the biomechanist must perform an analysis of fit between the medical records (i.e., injury claim) and the occupant kinematic-kinetic response. Generally at this phase of the analytical process, the published human tissue literature is incorporated in the analysis. If there is a good match, then the plaintiff’s medical claims are probably justified. If there is a mismatch, however, then the plaintiff’s injuries may have been exaggerated/nonexistent, or the result of some other event (e.g., a chronic medical condition).

In biomechanics, as with medicine and engineering, human individuality and variability due to age, disease, and injury means that not all individuals have the same tissue tolerances. Within a probability framework, however, the biomechanist can state with some descriptive degree of certainty that the loading applied to the occupant either could or could not have been reasonably linked to the medical pathology of the plaintiff.

The biomechanist should also address competing etiology when appropriate; the medical pathology may be the result of pre-existing conditions that may or may not have been previously documented. In some cases, there may have been real injury to soft tissues; recreation or chronic work-related activity, however, may have been the true cause of injury, not the event in question. In such cases, a brief analysis of the plaintiff’s physical activity (i.e., work or recreation) often reveals loading which has a much higher probability of being the injury mechanism. Frequently it is possible to make comparisons that clearly illustrate how work or recreational events produced loads that far exceeded the loads that would have been imposed upon the plaintiff during the injury event under consideration. Finally, the biomechanist must be able to do these analyses in a cost effective manner. This is especially true when the total value of the case is minimal.

When Can a Biomechanist Help?

In general, a biomechanist is a useful expert when liability questions involve human motion, human tissue damage, and/or mechanisms of injury. A well-qualified biomechanist is helpful in all types of impact accidents where the match between forces and tissue damage may be in question, especially when there are no witnesses, when witness testimony conflicts, or when the economic stakes are high. Such cases include:

· Slip/trip/fall claims where the mechanics of motion as well as tissue damage may be at issue

· Sports injuries

· Product liability cases where the relationship between the product design/characteristics and the injury biomechanics is at issue;

· Criminal cases where the relationship between human motion or actions and tissue damage and/or the trauma-producing event require analysis

· Situations where the failure to wear protective clothing or equipment (e.g., seatbelts, motorcycle helmets, knee pads, hardhats, gloves, or shoes) causes or increases the eventrelated trauma.

Biomechanical Analysis has been helpful in identifying, understanding, and answering biomechanical questions in the following types of cases:

Motor vehicle accidents,

Bicycle accidents,

Motorcycle accidents,

Industrial injuries,

Dance injuries,

Playground accidents,

Boating accidents,


Athletic injuries,

Construction accidents,


Child abuse,


Gait analysis,

Horse and other farm accidents

Some Non-Automotive Examples

There are a wide variety of cases where the biomechanist can play a central role in understanding the event and its relationship to a plaintiff’s injury claim. Here are a few brief examples to stimulate thought:

1. Trip and Fall — An elderly diabetic amputee fell while walking through a casino lobby. Was the resultant injury to the plaintiff entirely due to the fall, or was the ongoing pre-existing diabetic condition a contributing factor? By carefully examining the video surveillance tape of the incident, it was possible to analyze the gait (i.e., walking mechanics) and to determine the cause of the fall as well as the point of the trip.

2. Amputation of Fingers — An individual suffered a traumatic amputation of all or part of two fingers. Could a person strike his own hand five (5) times or more without eliciting a withdrawal response to the pain stimulus? Biomechanical analysis demonstrated how the amputations could and could not have occurred. Neuromuscular research answered the question regarding the flexor withdrawal response.

3. Ladder Fall and Degloving — A construction worker caught his hand in a large mixing tank producing a traumatic degloving beginning just below the right elbow. A comprehensive biomechanical analysis demonstrated the possible mechanics associated with a slip and fall, displacement of the tank cover, and ultimately the mechanism that produced the exposure resulting in the degloving.

4. The Mystery Fall — An elderly woman fell while being returned home in a small transport van suffering a comminuted supracondylar fracture of the femur. Would an attendant at the exit of the transport van have been of value in preventing the plaintiff’s fall and injury? A thorough biomechanical review of the cause of the fracture, an analysis of the configuration of the transport van, and a study of the preventive value of a trained attendant at the van exit helped demonstrate where and how the fall occurred.

5. Fireman and Epileptic Seizure — Fire department emergency medical personnel responded to the home of an adult male having an epileptic seizure and physically restrained the individual during the seizure. Was the lumbar vertebral fracture suffered by the plaintiff caused by the actions of the trained paramedic/fireman? The biomechanical analysis contrasted the direction of force applied by the emergency medical personnel with the forces necessary to produce the specific vertebral fracture. A comprehensive review of the appropriate literature regarding injury from internal forces of the muscle contractions during grand mal epileptic seizures was also completed.

We would like you to consider the broader use of the analytical skills of our well-qualified biomechanical experts. At times there is no doubt that the injury in question is the result of the incident at hand; the time and place of the injury causing event are known and not in dispute. Complete information about the mechanism of injury is generally lacking, however, and an understanding of the relationship between the plaintiff’s injury claims and the injury-producing event is critical to an appropriate, timely, and equitable resolution of the case. Whether the events and injuries are minor or fatal, a rigorous biomechanical analysis is necessary to fully understanding the relationship between the event and the injuries claimed.

A medical doctor is definitely not enough!

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