Injury causation experts prevent cases from crashing.

Attorneys handling crashworthiness cases must prove exactly how and why their clients' injuries occurred.

An amateur analysis of injury causation may be sufficient for some personal injury cases--even at trial--but when handling a vehicle crashworthiness case, expert testimony detailing exactly how and why a plaintiff suffered injuries is essential.

For example, a plaintiff attorney probably doesn't need to present a biomechanical engineer to the jury to explain precisely how a client's ankle broke when he or she slipped in a puddle of water at the local grocery store. But the same attorney will likely need expert testimony to prove how a backseat car passenger received a devastating brain injury in a low-impact crash. An injury causation expert is essential in this regard.

Most plaintiff attorneys know experts who have education and technical backgrounds that make them especially well suited to consulting work. But an expert's background is only one of the considerations that plays into the way he or she presents to a jury and explains what happened in a case.

For example, an expert in occupant kinematics and an expert in biomechanics will focus on different aspects of a collision. While these terms are sometimes used interchangeably in crashworthiness cases, there are important differences in their areas of study.

Occupant kinematics concerns the movement of people during a collision sequence. For example, if a passenger stayed inside a vehicle during a crash, an expert who does an occupant kinematics analysis will study marks showing contact with the vehicle's interior and restraints in an attempt to account for the passenger's body position throughout the entire collision sequence.

Biomechanics experts study the forces necessary to cause particular responses within the body. These experts apply the principles and techniques of mechanics to the structures and functions of living organisms. The educational background of a biomechanical expert in a crashworthiness case typically includes the study of engineering as well as human anatomy. Many of the more popular experts testifying today have biomechanical backgrounds. However, some popular experts testifying on both sides of motor vehicle crashworthiness cases do not.

For example, medical training, without the engineering background, can be a sufficient basis for expert opinion on injury causation. A physician who has treated motor vehicle accident victims may knowledgeably discuss typical injury patterns, or a medical examiner who sees many accident-related fatalities is competent to testify about the body's response to crash forces.

When choosing an expert, it is important, therefore, that plaintiff lawyers find the person with the experience and credentials that are most appropriate for a case. This may be a biomechanical engineer or another type of expert, depending on the facts of the case.

Attorneys looking to employ experts to prove injury causation must make multi-layered decisions that consider not only an expert's background, but also the facts of the case, the characteristics of the injury, and the forum--including the trial court's likely take on the expert's reliability. In the end, the most important consideration is whether the expert can help persuade the jury to reach a verdict that provides just compensation for the injured client.

In some cases, injury causation may not be a hotly disputed issue, but plaintiff lawyers may be wise to retain such an expert anyway. For instance, my office was involved in a passive-restraint collision case in which the driver, restrained only by the car's automatic shoulder harness, was found outside her vehicle, which had rolled several times. A crush injury to her skull resulted in severe brain damage. A close inspection of the car revealed hair and scalp tissue on a piece of the vehicle's suspension, demonstrating that the driver was clearly outside the vehicle when it struck and injured her.

Although the cause of the injury was obvious and uncontested, a causation expert was still needed to carry the burden of showing the enhanced nature of the injuries over those the plaintiff likely would have sustained had she not been ejected from the car.

Proving injury causation

The plaintiff must show how he or she sustained an injury and, just as important, the level of injury one would expect in the same collision with nondefective equipment or with safety equipment the plaintiff alleges should have been in the vehicle.

For example, in a roof crush case, the expert will show how the roof intruded into the occupant compartment and caused the injury. An occupant kinematics analysis will show that adequate space between the roof and the occupant's head would have prevented the injury.

A surrogate occupant--someone with similar physical characteristics of the injured person--may be placed inside the accident vehicle or in an exemplar vehicle to help the expert explain the plaintiff's injuries to jurors. Consequently, in the early stages of a potential case, it is wise to collect by medical records or otherwise--some information about the injured party's height and weight at the time that the collision occurred.

The extent of the expert's work with the surrogate will depend on the case. For example, in a rear-seat lap belt case, it may be sufficient to place a child surrogate in the child's seat position with a retrofit shoulder belt to demonstrate the adequate fit of that belt and how it would have prevented injury to the actual child in the same seating position.

In a head-on collision case, the surrogate may need to move forward against the belts in the accident vehicle until his or her knees contact the dashboard, matching indentations made by the plaintiff's knees. Surrogate work is usually documented with photographs that the expert uses to demonstrate his or her opinions to the jury.

How did the injury occur?

The expert must be able to explain the occupant kinematics that led to the injury. Take, for example, the passive belt restraint systems that do not incorporate a lap restraint. Vehicle drivers using these restraints are susceptible to abdominal injuries, including liver lacerations in frontal collisions--especially collisions where the principal direction of force is to the front and the right of the vehicle.

The injury causation expert must offer more than a description of the fatal liver injury so the jury will have a framework for evaluating the plaintiff's allegations of defect. The expert must describe in detail the occupant's movements during the crash and the mechanics of the injury. Marks inside the vehicle, such as scuffs or cracks on the lower part of the instrument panel, can be matched up with fractures, bruises, or abrasions of the occupant's knees or lower limbs in order to show exactly how his or her body moved in the collision.

The expert might show the jury how the forward excursion of an occupant's lower body moved the belt into his or her abdomen, allowing the belt to interact with a weak part of the body not suited for such forces. In a fatal crash, autopsy photographs of body bruises will likely aid in this description.

This analysis must take place in every case in which an injury causation expert is used. If the plaintiff was ejected during a rollover, the expert must show where that occurred. If the plaintiff was injured by a deploying air bag, the expert must demonstrate the occupant's position when that happened. It is essential to the plaintiff's burden of proof that the expert explain to the jury the plaintiff's movements throughout the collision sequence, accounting for marks on the plaintiff's body as well as on the vehicle, in the context of an accident reconstruction.

There are several fundamental considerations, such as belt use or seat and passenger position, that need to be addressed in every crashworthiness case. The importance of any one factor depends on the nature of the defect, the facts of the case, and the positions taken by the defendant. To some extent, the injury causation expert will need to account for the variables that follow to explain the plaintiff's theory and debunk the defendant's positions.

Seat belt use. Seat belt use will almost always be a key factor in any crashworthiness case. The injury causation expert must offer opinions about whether and how seat belts were used by the plaintiff. This should happen even if another plaintiff's witness, such as the restraint design expert, has forensic evidence of belt use such as stretched, or loaded, belt webbing. If the belt wasn't used, there will be no evidence of this.

Some occupants can be observed placing the shoulder belt under their arms--a foreseeable misuse of the belt system but a misuse nonetheless. Wearing a shoulder belt in this way will leave telltale marks on the occupant's body in frontal collisions, offering a good basis for the expert's opinion about belt use.

Marks on the body can also demonstrate correct belt use. Abrasions on the pelvis of a lap-belted occupant will show that the belt was worn correctly--low and snug. An improperly positioned or loose belt would likely allow some occupant submarining with resultant belt loading at the abdomen. An intact windshield following a high-impact frontal collision also suggests proper belt use.

Seat and occupant position. A significant aspect of the injury causation expert's opinion may address how the injured occupant was seated. Auto manufacturers often rely on the "out of position" defense, arguing that the occupant was positioned so that the effectiveness of the restraint system was compromised or the likelihood of injury was increased.

In restraint systems that use knee bolsters, or the lower portion of the instrument panel, rather than lap belts for lower body restraint, occupants would be considered out of position if their legs were crossed, turned to the side, or in any position other than straight ahead. Other out-of-position scenarios include child occupants riding on their knees or with the belt too close to their necks and adult passengers lying in a reclined seat. The injury causation expert must be prepared to address the occupant's position to explain the injury and to counter the defense arguments about the occupant's position.

The position of the seat on its track and the extent to which the seat back is reclined will also affect the performance of a restraint system, including air bags. An understanding of the seat position variables should be part of the expert's analysis.

For example, if a seat back collapses and injures a rear-seat passenger, the location of the front seat on its track must be identified in order to establish the are of the fallen seat back. Similarly, the performance of restraints involved in frontal collisions are profoundly affected by the extent of seat recline and, to a lesser extent, by the distance between the occupant's knees and the dashboard.

Two sides of the same coin

In addition to showing how the plaintiff was injured, the expert must also address two other topics: why the injury was sustained in this collision and how it could have been avoided, most typically with safety equipment. Evidence related to these topics is used to prove enhanced injuries, or injuries that would not have occurred with proper vehicle design.

In the earlier cited example, where the passively restrained occupant sustained a fatal liver laceration, the injury resulted from inadequately controlled lower body excursion. By the time the occupant's knees loaded the instrument panel, his or her abdomen was distorted and intruded on by the shoulder belt.

The injury could have been avoided if the passive restraint included a lap belt, or, possibly, if the occupant had been wearing the manually fastened lap belt. With such a restraint, the collision forces would have been spread over a greater portion of the body, and loading would have occurred in the pelvis rather than against the abdomen and liver.

The contours of the expert's opinions will depend on the facts of the case and the involved defect. Our office was recently involved in a case where the captain's chairs of a conversion van failed and bent forward in a frontal collision. The lap-belted occupants struck their heads on the seat backs in front of them, causing them to suffer severe brain injury.

Had the chairs been properly designed and constructed, the rear occupants would have had enough room to bend at the waist from the force of the crash without striking the front seats. Although a proper restraint system would have included three-point belts instead of just a lap belt, the mechanical failure of the chairs caused injuries the occupants otherwise would not have sustained.

Answers to the questions of why a particular injury was sustained and how nondefective equipment would have prevented it are as varied as the list of alleged defects giving rise to suits. An injury may result from a combination of the occupant's position and the deployment of an air bag, or maybe no injury would have occurred if the air bag had not fired at all.

An injury causation expert must be knowledgeable about a plaintiff's defect claims even though another type of expert may testify on that topic. For example, if in a moderate rear-end collision a seat back failed and its occupant was ejected from the seat and sustained a head or spinal cord injury inside the vehicle, a seat design expert may discuss technical literature supporting a claim that seat backs should not collapse in moderate rear collisions. The injury causation expert can and should support this testimony with additional technical literature and case studies showing the historical awareness of the injuries incurred when seat backs collapse.

In passive-restraint cases, articles have been circulated for the past 40 years discussing the dangers of bandoleer-type--torso only--belts, including the risk of liver injuries to passengers who use them. The injury causation expert can compare documented injuries from those articles with the plaintiff's injuries, explaining that the author of an article written 20 years ago attributed the same cause--uncontrolled lower body excursion--to injuries similar to the plaintiff's. That these articles can also be used to show manufacturers knew of the problem and have done little to address it is an added bonus.

Technical materials describing how occupants should be restrained, how air bags should deploy, and how occupant space should be preserved support the injury causation expert's testimony that an injury could have been avoided.

While there may be situations where that expert will only offer opinions as to injury causation, he or she will usually also offer opinions that the vehicle or its components are defective. Technical articles, case studies, and discussions of similarly sustained injuries are important to support the expert's opinions on defects.

The expert team

A crashworthiness case is a large undertaking that usually requires accident reconstruction and equipment design experts in addition to the injury causation expert. It is crucial to an injured plaintiff's case that these experts work together so that they understand the fit between their testimony and the role each expert plays in the trial presentation.

Some of this communication will be facilitated by the attorney speaking separately with the experts, but direct contact among the experts is advisable before they are deposed. This is especially true of the injury causation and design experts. Their opinions are closely related in terms of what vehicle occupant dangers were present, how they manifested themselves in a crash, and how they could have been avoided or minimized. It is imperative that each expert's opinions mesh with and provide support for the opinions of other plaintiff's experts.

Proof of causation in an enhanced injury case will entail a complex review of the collision details and the injury. An injury causation expert is crucial to the plaintiff's case. The jury must understand exactly which injuries are attributable to the vehicle's defects and how those injuries could have been avoided.

For further reading

Larry E. Coben, Seat Safety, TRIAL, Feb. 1998, at 35.

James J. Murphy, Proving Rollover Crashworthiness Claims, TRIAL, Feb. 1998, at 42.

William Petrus practices law in Springfield, Missouri.