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Cross Examination of the Defense Biomechanical Engineer

July 11, 1998 2:25 PM
Leesfield & Partners
2350 South Dixie Highway
Miami, Florida 33133
(305) 854-4900


Cases today often require the use of complex science to prove difficult issues at trial. Expert witnesses can often help juries understand these difficult issues. But as every trial attorney knows, expert witnesses can do much more than help juries understand. An expert's opinion can be highly persuasive to a jury, or even completely dispositive to the outcome of a case.

Perhaps expert opinions are so persuasive because it is human nature to defer to so-called "expert" opinions. Whatever the reason, trial attorneys have consistently scrambled to find definitive experts to whom the jury will defer. If one side is calling an expert, the other side must do so as well. The classic "battle of the experts" ensues. This infusion of experts into the court system has created great controversy. Moreover, courts have had to create ways to sort through all of the experts being proffered at trials as some "expert" testimony may be inappropriate in any given case. To this end, courts have looked to Rule 702 of the Federal Rules of Evidence and to the Supreme Court's application of Rule 702 in Daubert v. Merrell Dow Pharmaceuticals(1) for guidance.

This paper addresses how courts have dealt with just one kind of scientific expert witness: the biomechanical engineer. As biomechanical engineers testify more frequently in trials, and especially in tort cases, it is becoming increasingly important for the plaintiff's attorney to know how to deal with these experts. In light of the courts' treatment of biomechanical engineers, this paper addresses how plaintiffs can: (i) potentially keep biomechanical engineers from testifying at trial altogether, and (ii) effectively cross examine biomechanical engineers when that becomes necessary.

II. Understanding Biomechanical Engineering

Biomechanical engineering, according to the simple statement of at least one expert, is the "study of how a device should be designed and constructed."(2) Biomechanics, according to that same expert, is more generally "the study of the effect of external and internal forces on the movement of the body and internal stresses and deformations of biological tissue, which includes muscles, bones, and nerves." What do these definitions mean for lawyers? Simply put, a biomechanical engineer can explain the dynamics of an accident. For example, in an automobile crash, a biomechanical engineer can scientifically explain what forces acted on an injured plaintiff. Why would a plaintiff's attorney need to use a biomechanical engineer? Suppose that your plaintiff has been injured in a three car accident involving him/herself, the defendant, and a phantom tortfeasor. Also suppose that it is not entirely clear whether the defendant or the phantom caused your plaintiff's damages. A biomechanical engineer will be able to explain that the forces which came from the defendant's car, as opposed to the phantom's car, were the harmful forces in the accident. A defendant might use a biomechanical engineer in the same hypothetical example to show that the forces which came from the phantom's car were the harmful ones. Thus, biomechanical engineers can basically help both attorneys and juries understand causation and damage issues better in personal injury cases.

Biomechanical engineers have testified in personal injury cases involving: (a) automobile roll overs(3), (b) seat belt problems(4), (c) defective football helmets(5) (d) infant car seats(6), (e) temporomandibular ("TMJ") disorders(7), and (f) bone screws(8). In each of these cases, the biomechanical engineers were called to explain the dynamics of the injury in question.

The case of Arnold v. Riddell, Inc., more specifically illustrates how plaintiffs have used biomechanical engineering experts at trial.(9) In Arnold, a high school football quarterback, J.R. Arnold, was trying to recover a fumble when he collided head first with a player from the opposing team. Upon impact, Arnold's spine fractured at the C4-C5 level causing permanent quadriplegia. Arnold's parents sued Riddell, Inc., the manufacturers of the football helmet that J.R. Arnold was required to wear as part of his uniform. The plaintiffs alleged that Riddell's football helmet was defective in that it was not designed to minimize forces to the neck despite Riddell's knowledge that quadriplegic injuries were occurring. With the help of two professors of biomechanical engineering, the plaintiffs were able to convince the jury that the Riddell helmet's "energy attenuation system" was in fact defective. The plaintiff's experts testified about how they performed scientific tests on various football helmets in the market to see which helmets minimized forces on the neck the best. Riddell's helmet did not perform as well as other helmets, and the jury handsomely compensated the plaintiffs.

How might a defendant use a biomechanical engineer at trial? A defendant would use a biomechanical engineer the same way a plaintiff would: to explain the dynamics of an accident. In Baerwald v. Flores, the plaintiff claimed that she suffered temporomandibular ("TMJ") as a result of a car accident.(10) The defendant in Baerwald was able to call a biomechanical engineer to the stand to explain that the plaintiff was very unlikely to get "TMJ" as a result of a car accident.

III. How to Exclude the Biomechanical Engineer's Testimony

If a defendant is going to unilaterally call a biomechanical engineering expert at trial, it may be to the plaintiff's advantage to try to exclude the expert altogether. Indeed, if the defendant's biomechanical engineer is allowed to testify and is a professional, it may be difficult to counteract a harmful direct examination. The damage done to the plaintiff's case may be severe. Thus, the first step in dealing with a defendant's biomechanical engineering expert may be to try to have the testimony completely excluded. Potential exclusion of the defendant's expert witness begins with an understanding of Federal Rule of Evidence 702.

A. Rule 702 and the Replacement of the Frye Standard

Federal Rule of Evidence 702 expressly governs expert testimony at trial and reads: "[i]f scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise."

The Supreme Court has interpreted Rule 702 in a variety of ways over the years. Most recently in Daubert v. Merrell Dow Pharmaceuticals, the Supreme Court displaced the Frye standard which focused the admissibility of expert testimony exclusively on whether the proffered expert's opinion had gained "general acceptance" in the relevant scientific community.(11) The Supreme Court in Daubert held that although Frye's "general acceptance" remains a relevant factor under Rule 702, it is just one of many relevant factors.(12)

B. The "Gatekeeping" Responsibility

In Daubert, the Supreme Court emphasized that federal judges maintain a "gatekeeping responsibility" to ensure that admitted scientific testimony is both relevant and reliable.(13) When performing the "gatekeeping" task, district courts must apply a two-pronged test. First, courts must determine whether the proffered expert testimony consists of scientific knowledge (the "reliability" inquiry). While a variety of factors speak to the reliability of a particular opinion, the Supreme Court has noted four factors of particular importance: testability, peer review, rate of error and acceptance.(14)

1. Testability- The concern with testability is whether the theory or technique used by the expert can be, and has been tested. In Cavallo v. Star Enterprise, the court found that "testability is central to the scientific method."(15)

2. Peer Review- Have the expert's opinions been published and are they available for review, criticism or support by peers? In any trade or practice which spawns new theories and innovations, peer review is seen as a very important part of the acceptability process.

3. Rate of Error- The rate of error of a particular method or study that is being relied upon is obviously relevant.

4. Acceptance- Courts will be concerned over the general degree to which the method or theory has been embraced by the scientific community.

If the "reliability" inquiry is satisfied, courts must next ascertain whether the proposed scientific testimony is relevant.(16) This relevance inquiry requires courts to look for a "fit" between the tested theories relied upon by the experts and the ultimate conclusions reached. The Cavallo court gives a good example of what the relevance "fit" means: "A study regarding the mating habits of gypsy moths may be scientifically valid for certain purposes, and an expert's conclusion that a particular chemical caused a certain illness may be relevant in a certain case. But if the expert purports to base her causation conclusion on the gypsy moth study, then the opinion can hardly be said to have met the requirements of Rule 702."(17)

C. Applying Daubert to Biomechanical Engineers

Given the Supreme Court's interpretation of Rule 702 in Daubert, how are biomechanical engineers treated by the courts? Until recently, biomechanical engineering experts have had little trouble expressing their expert opinions in courts across the country. In a recent case out of the Sixth Circuit, however, Smelser v. Norfolk Southern Railway Company,(18) the court held that a biomechanical engineering expert's opinion should have been excluded from trial due to Daubert considerations. Thus, a detailed understanding of the Smelser case may help plaintiff's attorneys exclude potentially harmful biomechanical engineering testimony in the future.

In Smelser, the plaintiff-employee was driving his employer's vehicle when he was rear-ended and injured in the course and scope of employment. The plaintiff-employee sued his employer alleging that a defective/damaged seat belt on the driver's side of the employer's vehicle (not the rear-end collision itself) actually caused the plaintiff's injuries. To support his claim, the plaintiff called on a biomechanical engineer to explain how the seat belt in the employer's vehicle (which had been allegedly damaged in a previous accident and was never fixed) caused the plaintiff's injuries. The trial court allowed the plaintiff's expert to testify, and the jury awarded the plaintiff $3.5 million dollars.

On appeal, however, the Sixth Circuit held that the plaintiff's biomechanical engineer should not have been allowed to testify. Specifically, the court held that the expert's opinions were not "reliable" under Daubert because the expert:

(1) failed to perform any tests on the lap belt yet concluded it was in proper working condition; (2) conducted no testing to verify his conclusion that the shoulder belt was damaged in the [earlier] accident; (3) failed to adequately document testing conditions and the rate of error so the test could be repeated and its results verified and critiqued; and (4) failed to discover, use or at least consider the degree the restraint system was actually mounted at in the subject vehicle and explain whether that information would affect his pendulum test for compliance with the federal safety standard.(19)

In short, the Sixth Circuit felt that the expert's methodology in reaching his results was "unreliable." Needles to say, the plaintiff in Smelser will have a difficult time proving his case on remand absent his expert's opinions.

At least one commentator has suggested that Smelser appears to be wrongly decided.(20) Assuming, for the sake of argument, however, that Smelser is correctly decided and can be persuasive precedent, Smelser teaches us that plaintiffs attorneys should scrutinize the defendant expert's methodology to see if weaknesses can be exposed. The expert in Smelser failed to perform any tests on the lap belt, but in the same breath attempted to conclude that it was in proper working condition; such speculative testimony should not slip past the careful attorney's eye. If plaintiffs attorneys can pinpoint serious weaknesses in the defendant's expert's methodology, then that expert may be helpfully excluded from trial altogether.

IV. How to Cross Examine a Biomechanical Engineer

If excluding the defendant's biomechanical engineer under Daubet is unsuccessful and cross examination of the expert becomes necessary, the following steps may be helpful:

A. Background investigation

First, do a background investigation on the defendant's expert. More than likely, the expert has testified in other cases and has a traceable history on his/her position. The following is suggested:

(a) The ATLA Exchange should be contacted for background research on expert.

(b) Other attorneys locally or nationally are a good source of deposition and trial testimony.

(c)Obtain the CV on the expert and do independent research of the organizations he/she has listed. Make sure he/she is actually a member of the organizations he/she has listed and find information about each organization. If possible, get the expert's application to the organization.

(d) Check the expert's license and credentials.

(e) Review and analyze the expert's CV and other claims of expertise.

(f) If the expert is licensed, get a copy of the license and application for state licensing.

(g) Thoroughly document and understand the litigation, educational history and background of the expert (you may want to save some of this information for impeachment and rebuttal at trial as opposed to exposing your strength in deposition).

B. Cross-examination on interest bias--peripheral/ancillary cross examination.

Oftentimes, the biomechanical engineering expert is so poised and polished that regardless of the flaws in his/her opinion, he/she will win over the jury anyway. When you are faced with this type of professional expert, your cross-examination should avoid giving the expert an opportunity to emphatically restate his/her opinions on cross-examination. Rather, the cross-examination should be swift and aggressive on the issues of his/her interest and bias in this particular case or previous work with the same or similar clients. Examples:

(a) How many other matters has this expert worked on for a specific defendant?

(b) How many other matters has this expert worked on within the industry or trade associations?

(c) Has this defendant received research grants or support from the industry you are litigating against?

(d) What are the total levels of compensation over a five or ten year period from a specific manufacturer and/or industry?

(e) Has this expert written articles or advocated the defendant's position before Congress, agencies, associations, governmental or quasi-governmental bodies or at a university?

C. Cross-examination on the merits.

(a) Does the witness have a complete, accurate and full knowledge of the product topic he/she is testifying about?

(b) Is there key information that the expert has not been provided?

(c) Have all tests and tests results been provided to the witness?

(d) Has the witness taken an inconsistent position in prior litigation before any other court, agency or body?

D. Miscellaneous considerations

As with cross-examination of all experts, a decision as to the length, scope and aggressiveness must be spontaneously made based upon direct examination. If the expert's testimony has not come across as credible, his/her demeanor is "flaky" or if you have not been hurt by any substantive testimony, you may not want to cross-examine this expert at all, or may just want to do so in a very peripheral manner. On the other hand, if the expert has raised a major point or is deprived of key facts and information, you will want to go after the expert's opinion based upon the lack of foundation.

  • Permissible scope of the biomechanical engineer's testimony

A final consideration when dealing with an expert biomechanical engineer at trial is the scope of that expert's opinion. The Sixth Circuit in Smelser noted that biomechanical engineers can improperly testify too specifically about the causes of a plaintiff's injuries. The court in Smelser noted that the expert in that case himself "admitted that biomechanics are qualified to determine what injury causation forces are in general and can tell how a hypothetical person's body will respond to those forces, but are not qualified to render medical opinions regarding the precise cause of a specific injury (emphasis added)."(21) Thus, the court concluded that biomechanical engineers can only testify in general terms "that 'X' forces would generally lead to 'Y' injuries and 'Y' injuries are consistent with those that the plaintiff claims to have suffered."(22) These are important points to remember when the defendant's biomechanical engineer is testifying on direct examination. An alert plaintiff's attorney should make proper objections regarding the scope of the biomechanical engineer's expert testimony.

1. 509 U.S.579, 113 S. Ct. 2786, 125 L.Ed.2d 469 (1993).
2. Dr. Harold Alexander, an expert in the field of orthopedic bioengineering, testified to the above-referenced definition of "biomechanical engineering" in In re Orthopedic Bone Screw Products Liability Litigation, 1997 WL 39583 (E.D. Pa. 1997).
3. Dorsett v. American Isuzu Motors, Inc., 805 F.Supp 1212 (E.D. Pa. 1992).
4. Smelser v. Norfolk Southern Railway Company, 105 F.3d 299 (6th Cir. 1997) cert. denied 118 S.Ct. 67, 139 L.Ed.2d 29 (1997).
5. Arnold v. Riddell, Inc., 882 F.Supp 979 (D. Kansas 1995).
6. Mannino v. International Manufacturing Company, 650 F.2d 846 (6th Cir. 1981).
7. Baerwald v. Flores, 930 P.2d 816 (N.M. Ct. App. 1996).
8. In re Orthopedic Bone Screw Products Liability Litigation, 1997 WL 39583 (E.D. Pa. 1997).
9. See supra, note 5.
10. See supra, note 7.
11. Frye v. United States, 293 F. 1013, 1014 (D.C. Cir. 1923)
12. Daubert, 509 U.S. at 594, 113 S.Ct. at 2797.
13. Daubert, 509 U.S. at 590 & n. 7, 113 S.Ct. at 2795 & n. 7.
14. Daubert 509 U.S. at 592, 595, 113 S.Ct. at 2796-97.
15. 892 F.Supp. 756, 761 (E.D. Va. 1995).
16. Cavallo, 892 F.Supp. at 760.
17. 892 F.Supp. at 760-61.
18. See supra, note 4.
19. Smelser, 105 F.3d at 304.
20. Larry E. Coben, What has Daubert Done to Us? - Or 'Where has All the Evidence Gone?,' 1997 ANDREWS AUTOMOTIVE LITIG. REP. 25399 (1997).
21. Smelser, 105 F.3d at 305.
22. Id.

Reprinted from ATLA's (program title and date), with permission of the Association of Trial Lawyers of America. Copyright Association of Trial Lawyers of America. Further reproduction of any kind is prohibited. For more information, please contact the National College of Advocacy, 1050 31st Street, N.W., Washington, D.C. 20007, 800-622-1791.

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