JBJS | Repetitive Stress Injury: Diagnosis or Self-Fulfilling Prophecy?*

The Journal of Bone & Joint Surgery, Volume 82, Issue 9

Current Concepts Review | September 01, 2000

Repetitive Stress Injury: Diagnosis or Self-Fulfilling Prophecy?*

Robert M. Szabo, M.D., M.P.H.†; Kenneth J. King, J.D.‡

*One or more of the authors has received or will receive benefits for personal or professionaluse from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Department of Orthopaedics, University of California, Davis, School of Medicine, 4860 Y Street, Sacramento, California 95817. E-mail address: rmszabo@ucdavis.edu.
‡Brobeck, Phleger & Harrison, 1633 Broadway, 47th Floor, New York, N.Y. 10019. E-mail address: kking@brobeck.com.

The Journal of Bone & Joint Surgery. 2000; 82:1314-1314

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Introduction

The vague definitions of so-called repetitive stress injuries are indicative of the fact that scientific studies have failed to show that repetitive motion causes injury.

Given the uncertainty about causation, work-related musculoskeletal disorders (WRMSDs) is a more readily accepted term to describe these phenomena.

There is little doubt that most ergonomic interventions increase comfort in the work environment, which is of great benefit to the worker.

Many proponents of ergonomics assert that the elimination of certain risk factors related to force, repetition, and posture can prevent or even cure work-related musculoskeletal disorders of the upper extremity. However, there is little scientific support for this position.

Undue reliance on ergonomics to treat musculoskeletal disorders, to the exclusion of proper diagnosis and attention to medical and health risk factors, can have adverse consequences for the patient.

Science rather than politics and public policy should determine what causes injury and disease.

The failure of numerous plaintiffs in litigation regarding repetitive stress injury due to use of computer keyboards is important because, when judges and lay jurors were presented with both sides of the issue, they rejected these claims in a forum (the judicial system) that traditionally compensates individuals bringing so-called mass-tort cases.

Understanding the Relevant Definitions

Repetitive motion disorders include a spectrum of musculoskeletal symptoms that are attributed to occupations believed to be hazardous. Terms such as repetitive stress (strain) injury (RSI), cumulative trauma disorder, and repetitive trauma injury are used interchangeably to describe a constellation of symptoms related to the soft tissues of the musculoskeletal system. These so-called disorders, which are believed to be due to repeated exertions and movements of the body, supposedly develop over periods of weeks, months, or years². These terms are being used to describe any painful condition of the upper extremity in workers engaged in repetitive activities.

The vague definitions of these disorders are indicative of the fact that scientific studies have failed to show that repetitive motion causes injury. One of the consequences of this uncertainty has been the politicization of the issue and the involvement of the legal system. At the same time, there has been an increased advocacy of ergonomics as a solution to the prevalence of repetitive motion injury in the workplace. This has resulted in a proliferation of ergonomic literature in which conclusions are based on associations and suggestions^38,47. Many proponents of ergonomics assert that the elimination of certain risk factors related to force, repetition, posture, and duration can prevent or even cure disorders that are due to repetitive motion; however, there is scant scientific support for this position^44,50. More importantly, reliance on ergonomics to the exclusion of medical and health risk factors can have adverse consequences for the patient. Investigators of repetitive stress injuries have largely failed to control for confounders other than age and gender, and therefore the literature has been greatly criticized. When confounders have been controlled for, a causal relationship has not been established^45,50. Prospective studies will be of the greatest value; however, none are available at the present time, to our knowledge.

The case for repetitive stress injuries being work-related has been made by authors who consider that repetitive movements and static postures assumed by individuals at work can cause a well defined injury that is analogous, for instance, to a stress fracture of the foot due to repetitive loading in an athlete or a dancer. Tissue damage depends on the duration, frequency, and amount of exposure to physical stressors. The contention is that the pace of work, insufficient recovery time, and level of muscular effort will likely cause tissue damage more quickly in people who have jobs involving high force and high repetition²⁵. This contention has been supported somewhat at the tissue level; for instance, studies of tendons have shown stress-strain curve changes as a function of the frequency and duration of loading¹⁷. The degree of association between work factors and musculoskeletal disorders varies greatly in the epidemiological literature, as confirmed by a comprehensive but controversial review by the National Institute for Occupational Safety and Health⁷. Variation in individual physical capability is not accounted for in the literature, thus compounding the issue.

A major criticism of the term repetitive stress is that it implies that the etiology is repetition. The word injury implies damage to tissues. Repetitive and stress imply that repetitive mechanical forces applied to tissues cause the injury; however, there is no information regarding the frequency, magnitude, duration, or rate that renders these forces harmful. We know that forces exceeding the mechanical limits of tissue lead to irreversible damage, yet physiological forces allow for normal maintenance and enhanced wound-healing¹. The relationship between physical loads and musculoskeletal disease still has not been quantified, and contradictory evidence persists because of poor measurement of exposures and a lack of specific diagnoses. Arguably, it is important to recognize the aches and pains that precede disease or injury, as many patients present with such symptoms. Progression to disease, however, is the exception rather than the rule, or one would expect a greater prevalence of such preceding symptoms in reports of disease states. The relative contributions of occupational and nonoccupational physical loads to symptoms have not been addressed sufficiently in epidemiological studies. Nevertheless, ergonomists promote the concept that, from the perspective of prevention and treatment, all work-related factors that can be modified should be modified⁵¹.

In order to determine the association between risk factors (exposures) and disease (outcome variable), both the risk factors and the disease should be well defined. When a fall on an outstretched hand results in a fracture of the wrist, the relationship between the trauma and the injury is clear. This is often not the case for work-related musculoskeletal disorders. Some conditions, such as carpal tunnel syndrome, have a pathogenesis that can be defined and measured objectively with electrodiagnostic studies. However, the majority of work-related musculoskeletal disorders of the upper extremity fall into a more amorphous category, such as hand pain, with no objective way to define the condition or to measure its severity and no clear anatomical basis for the symptoms. Reports from workers and survey data tend to overestimate the prevalence of disorders because social, cultural, and medicolegal factors have a major influence. In 1988, according to the National Health Interview Survey, 1.4 percent (1.87 million) of working adults in the United States reported that they had a condition affecting the wrist and hand called carpal tunnel syndrome; however, only 675,000 of these individuals indicated that a health-care provider had made this diagnosis⁴⁶.

Much of the confusion surrounding work-related musculoskeletal disorders arises from a misunderstanding of the definitions of the relevant terms. An occupational disease is one in which there is a direct cause-and-effect relationship between a hazard and the disease. Silicosis is a clear example of an occupational disease; silica, the hazard, is essential to producing the disease. Medically, a disease is considered work-related when the work environment and the performance of work contribute significantly, but as two of a number of factors, to the causation of disease. Legally, aggravation of a condition may be enough for a disease to be labeled as work-related. Epidemiologists refer to risk factors as associated with, rather than as causes of, a particular disease because often it is not possible to establish a link between cause and effect. Causal inference is the logical development of a theory, based on observation and a series of arguments, that attributes the development of a disease to one or more risk factors. Inference depends on prior knowledge, intuition, insight, and uncertainty (probability)^24,40.

Given the uncertainty about causation, work-related musculoskeletal disorders (WRMSDs) is a more readily accepted term to describe these phenomena. Under this broad definition, the prevalence of these disorders is high, accounting for 48 percent of all reported workplace illnesses in 1990, up from 18 percent in 1980⁴². According to Bureau of Labor and Statistics data from 1994, work-related musculoskeletal disorders thought to be associated with repeated trauma accounted for more than 60 percent of all newly reported occupational disorders (332,000 cases per year)³⁰. The Bureau of Labor and Statistics identified 92,576 cases of alleged repetitive motion injury of the upper extremity that resulted in days lost from work. A diagnosis of carpal tunnel syndrome was made in 37,804 (41 percent) of these cases²⁵.

A high prevalence of work-related musculoskeletal disorders has been reported in jobs requiring high-force wrist motions, such as assembly-line work, meat-packing, and materials handling. Much of the recent focus has been on keyboard operators, whose activities, while extremely repetitive, do not require high force. The publicity surrounding a veritable epidemic of allegations that typing on computer keyboards caused repetitive stress injuries led to prominent, well financed plaintiffs' lawyers filing litigation against computer manufacturers under the products liability theories of defective design and failure to warn¹¹. Their efforts were completely unsuccessful before juries and judges, and such litigation has since been abandoned¹⁹. Few, if any, so-called mass-tort actions have met with similar failure. The failure of the plaintiffs in this litigation is important because, when judges and lay jurors were presented with both sides of the issue, they rejected these claims in a forum (the judicial system) that has traditionally favored the individual over industry.

The decision by a worker to report a symptom or injury is influenced by personal, psychosocial, and economic factors. The progression from symptom or injury to disability is strongly influenced by these same factors. Monotonous work, a perceived high workload, time pressure, lack of control on the job, and lack of social support all are related to musculoskeletal symptoms¹⁰. When a worker reports an upper-extremity musculoskeletal symptom while at work, the workplace paradigm automatically labels the symptom as a work-related disorder and the search begins for the workplace physical factor that caused the symptom. Many risk factors, including force, repetition, posture, and vibration, have been implicated in repetitive stress disorders.

In the general population, the prevalence of carpal tunnel syndrome is the same whether or not people perform repetitive activities³. In order to provide rational preventive measures for workers with carpal tunnel syndrome, valid and scientifically sound information about the true association between repetitive exposures and median neuropathy must be established⁴⁵. Primary prevention is aimed at reducing or controlling workplace risk factors. Although some investigators have reported that keyboarding actually appears to have a protective effect against the development of symptoms of median nerve compression compared with many other occupations²⁸, a tremendous amount of money is being spent on the creation, promotion, and use of new keyboard designs. Many of these ergonomic designs, which are credited with reducing symptoms, are based on changing the forearm rotation to less pronation. One study suggested that 45 degrees of pronation is the ideal position to reduce carpal tunnel pressures³⁷. The usual shoulder position of 20 to 30 degrees of abduction when a person is seated in front of a computer terminal rotates the forearm to that optimal position with the common keyboard design. Some physical conditions tend to precipitate symptoms of the forearm, wrist, or hand when a computer is used. Anatomical abnormalities, such as limitation of pronation of the forearm, may cause a person to bring the shoulder and elbow into major abduction in order to place the hand in a neutral position. For these few people, alternative keyboard designs may prove useful. Wrist splints have long been used in the treatment of carpal tunnel syndrome but now are marketed as protection for people in so-called high-risk occupations. It seems reasonable to use a splint that maintains the wrist in a neutral position, since wrist flexion and extension increase pressure in the carpal tunnel, which in turn can inhibit median nerve function. One study, however, demonstrated that carpal tunnel pressures were higher with splint use than without splint use at baseline and during repetitive hand activity (typing), perhaps suggesting that the splint created some external compression³⁶.

Barsky and Borus considered repetitive stress injury to be a functional somatic syndrome characterized by a variety of symptoms, suffering, and disability rather than by any demonstrable tissue abnormality⁶. As such, this entity (as opposed to specifically diagnosed conditions, such as carpal tunnel syndrome) is a product of somatization. Somatic symptoms that have no pathophysiological explanation are amplified by medicalization wherein uncomfortable bodily states and isolated symptoms are reclassified as diseases for which medical treatment is sought⁵. Other functional somatic syndromes include multiple-chemical sensitivity, sick-building syndrome, chronic-fatigue syndrome, Gulf War syndrome, and fibromyalgia. Patients with these syndromes experience an exacerbation of suffering as a result of a "self-perpetuating, self-validating cycle in which common, endemic, somatic symptoms are incorrectly attributed to serious abnormality, reinforcing the patient's belief that one has a serious disease."⁶ Because the condition is portrayed as catastrophic and disabling, it is likely to worsen, with the person assuming the "sick role."⁶

Sociological Basis for the Epidemic

Both the scientific community and nonmedical journalists are reporting an epidemic of disability due to work-related musculoskeletal injuries. In order to understand why work-related disability is becoming more prevalent, one must examine overall societal trends in disability. Since the middle of the twentieth century, consecutive generations in the United States have become more disabled, as assessed from self-reports; it is unclear whether this is due to improved survival of the chronically ill, to lowered cultural thresholds for defining disability, or to real increases in the prevalence of disability¹⁶.

The United States is not the first country to experience an epidemic of so-called work-related musculoskeletal problems. Between 1960 and 1980, Japan experienced an epidemic of cervicobrachial disorders²⁷. The problem became so pervasive that, in 1964 (even before the widespread introduction of personal computers), the Japanese Ministry of Labor set ergonomic standards for keyboard operators. These standards ultimately failed, however, to decrease the number of new reported cases²⁷.

In Australia, at a telecommunications company (Telecom Australia), which had 90,000 workers, the rate of repetitive stress injuries began to rise in late 1983; it peaked in late 1984 (when it was thirty times higher than the 1982 rate) and declined in 1985, reaching 1983 levels in 1987. Most of the patients were keyboard operators who complained of pain; the pain was not consistent among patients, and it did not conform to any known neurological pathway, anatomical structure, or physiological pattern. There were no objective clinical findings other than random tenderness; clinical investigations revealed negative findings, and symptoms failed to respond to any form of physical treatment²¹. Patients such as these, who respond to no form of treatment, usually have symptoms that are psychogenic in origin.

In Australia, there was little evidence of a dose-response relationship between repetitive stress injury and keystroke rate, age, or job duration¹⁸. Neither ergonomics, new technology, nor psychosocial theory explained the Australian epidemic. Miller and Topliss studied 229 consecutive patients who had been referred with symptoms that had been labeled repetitive stress injury²⁶. Twenty-nine patients fulfilled the usual criteria for a specific disorder, such as de Quervain tenosynovitis or rheumatoid arthritis. Of the remaining 200 workers, 100 percent had anxiety, irritability, and/or lowering of mood; 91 percent had sleep disturbances; 84 percent had chronic fatigue; 61 percent had frequent tension headaches; and 78 percent had decreased sensation involving both hands in a nondermatomal distribution. Ergonomic measures that the investigators instituted for all office workers in the study, including cessation of keyboard use, writing, or other activities that aggravated the arm pain, failed to relieve symptoms in 78 percent. Medications were used by all patients, and 94 percent had physiotherapy. All patients reported that the treatment had little effect on their long-term progress²⁶.

Ultimately, the prevalence of repetitive strain injury in Australia fell just as precipitously as it had increased. What caused the Australian epidemic? In a time of relative prosperity, with technological changes and computerization of clerical tasks that threatened those less adaptable to change, and in a country with as many physicians and pharmacists per capita as any industrialized nation, the inability to work because of a physical ailment became more socially acceptable^20,21. Kiesler and Finholt concluded that the repetitive stress-injury epidemic in Australia was more indicative of social problems than of workplace factors and that dissatisfaction was a major contributor, as was social legitimization of complaints related to repetitive stress injury²³. Political and social factors can act in both directions. The single factor that had the greatest influence on the decline of repetitive stress injury in Australia was a judicial decision in the 1987 case Cooper v. the Commonwealth, in which the Australian Supreme Court found that the employer was not guilty of negligence and the plaintiff had not suffered an injury²¹. All costs were awarded against the plaintiff, and the repetitive-stress injury epidemic disappeared soon thereafter.

Ergonomics Unchained

Ergonomics is defined as the study of how human beings use machines²; however, it often refers to the craft of designing workplace equipment, including computers, to minimize health problems or injuries³⁹. Despite the widespread use of ergonomic measures in industry, there is controversy over their effect. Some have asserted that there is little substantive evidence that these measures are either valid or reliable⁴⁴. Others have found that ergonomic measures have resulted in substantial improvements in the workplace^29,48. There is little doubt that most ergonomic interventions increase comfort in the work environment, which is of great benefit to workers; however, work-related musculoskeletal disorders have led ergonomists to recommend legislation requiring expensive redesign of the workplace on the basis of the unproven claim that work-related musculoskeletal disorders are disabling physical conditions. While ergonomists may create a more comfortable environment, they have not lowered the prevalence of these disorders. In fact, an Australian study showed an increase in the prevalence of repetitive stress injury even after ergonomic redesign of the workstation and institution of rest periods from keyboarding every hour¹⁸.

Despite the absence of proof that ergonomics has effects beyond comfort, the National Institute for Occupational Safety and Health (NIOSH) promotes the ideas that there is a higher prevalence of pain and disability in occupations with high levels of exposure to physical factors; that there is a strong biological plausibility for a relationship between prevalence and causative exposure factors in high-exposure settings; that research clearly demonstrates that special interventions can reduce the rate of musculoskeletal disorders for workers performing so-called high-risk tasks, although none of these measures are universally effective; and that high levels of exposure, especially in combination with exposure to more than one physical factor, provide strong evidence of a causal relationship between physical factors and work-related musculoskeletal disorders⁷.

Politics and public policy, rather than science, are deciding what causes disease. This may be due to the default of organized medicine to present intelligent and workable information in the political and public-policy spheres. The media also are falsely filling a void that medical education has failed to address adequately. On February 19, 1999, the Occupational Safety and Health Administration (OSHA) announced a plan to require employers to take steps to ensure that workers are less likely to suffer from musculoskeletal disorders that occur in the workplace³¹. It has long been known that musculoskeletal disorders are associated with assembly-line jobs; however, from a political perspective, the need for ergonomic standards became more important when computers became prevalent in the workplace and white-collar workers began to report problems. The media industries, which traditionally are drawn to controversy, at times mislead the public. Statements such as "The Clinton Administration promised relief today to millions of workers with aching backs, crippled fingers, sore wrists and other physical problems caused or aggravated by their jobs"³¹ lead the public to believe that repetitive activity is dangerous and causes incapacitating disease.

Congressmen John Porter, Robert Livingston, and Henry Bonilla of the Subcommittee on Labor, Health and Human Services, and Education Appropriations, called for a National Academy of Science (NAS) study on musculoskeletal disorders and any link to the workplace³³. Congress decided to support this study for three reasons: to provide a thorough, independent review of the medical and scientific literature on musculoskeletal disorders; to establish standard criteria for the evaluation of each piece of literature; and to answer seven questions specifically and weigh the evidence of causation. The seven questions are:

Question 1: What are the conditions affecting humans that are considered to be work-related musculoskeletal disorders?

Question 2: What is the status of medical science with respect to the diagnosis and classification of such disorders?

Question 3: What is the state of scientific knowledge, characterized by the degree of certainty or lack thereof, with regard to occupational and nonoccupational activities causing such conditions?

Question 4: What is the relative contribution of any causal factors identified in the literature to the development of such conditions in (a) the general population; (b) specific industries; and (c) specific occupational groups?

Question 5: What is the incidence of such conditions in (a) the general population; (b) specific industries; and (c) specific occupational groups?

Question 6: Does the literature reveal any specific guidance to prevent the development of such conditions in (a) the general population; (b) specific industries; and (c) specific occupational groups?

Question 7: What scientific questions remain unanswered, and may require further research, to determine which occupational activities in which specific industries cause or contribute to work-related musculoskeletal disorders?³³

In a preliminary report that is to be followed by a more detailed review, the Steering Committee for the NAS Workshop on Work-Related Musculoskeletal Disorders attempted to characterize the state of the evidence that physical factors can cause musculoskeletal disorders³². After a review of the biomechanical loads and biomechanical stressors, the committee made several very stark observations:

•Strong associations between measured biomechanical stressors at work and musculoskeletal disorders were observed in most studies; however, temporal contiguity between the stressors and onset of effects, as well as evidence of amelioration after reduction of stressors, could not always be established. . . . This shortcoming, though inherent to practical requirements of such research, makes it difficult to make strong causal inferences on the basis of the evidence from any individual study.

•Methods used for the assessment of exposures and health outcomes vary, rendering the task of merging and combining evidence more challenging than in some other areas of occupational risk assessment. But this variability does provide the benefit of multiple perspectives on a common set of problems.

•It is not feasible to assess the relative contribution of task and other factors to musculoskeletal disorders in the general population. In addition, high rates of workplace participation complicate characterization of the nonworking population (e.g., the prevalence of health-related reasons for not working). Therefore, evidence about the prevalence and incidence of even the most common musculoskeletal disorders in nonworking populations, which could be readily compared to results of epidemiological studies of workers, is largely lacking.

•Some published studies that show associations between biomechanical stressors and musculoskeletal disorders are difficult to interpret because of the possibility that plausible but unmeasured factors could explain some or all of the observed differences in rates of musculoskeletal disorders. In other words, whether biomechanical stressors or something else have caused higher rates of musculoskeletal disorders could not be definitively answered. This problem is common to epidemiological research in general³².

The Demise of Products Liability Litigation Involving Keyboard-Related Repetitive Stress Injury: Judges and Juries Weigh in

The seven questions posed by the congressional subcommittee have been debated often in the courtroom, although they were addressed primarily to the scientific community. Many computer companies have been confronted with large-scale litigation under products liability law. This area of law is particularly dangerous for companies because, once a product has been proven defective and proven to cause injury, the potential plaintiffs' pool (all users of the product) can be enormous. One need only consider the recent bankruptcy of Dow Corning in the breast-implant litigation, even in the absence of proof that breast implants cause systemic disease, to recognize the magnitude of these kinds of lawsuits^9,12,49.

In 1990, scores of products liability cases alleging that various upper-extremity injuries, most notably carpal tunnel syndrome, were caused by typing on computer keyboards were filed. By 1995, more than 1000 cases were pending and the plaintiffs' lawyers threatened to file tens of thousands more cases given the size of the computer-user population. Three law firms that had achieved great wealth and success in litigation involving asbestos-related disease devoted their considerable resources in the hope of achieving similar success in litigation involving keyboard-related injury¹¹. From the outset, the goal of the plaintiffs' lawyers was to consolidate a large number of cases into one proceeding, as they believed that consolidated cases weaken defendants' arguments concerning lack of causation. Toward that end, the plaintiffs' lawyers filed approximately 1000 cases in one New York federal court alone, hoping that this would result in consolidated trials.

Under the law of products liability, two main claims were made: it was asserted that keyboards were defective in their design and that they were improperly used because they did not have a warning placed on them. The design-defect claim was based on a theory that excessive force was required to press a key and that this supposed defect should have been eliminated. In addition, the design-defect claim alleged that the standard keyboard layout was itself defective and should have been replaced by one of the so-called alternative designs. The failure-to-warn claim alleged that warnings, which would have prevented these injuries, should have been placed on the keyboards.

Both of these claims are based on the theory that typing on a computer keyboard causes an array of upper-extremity injuries, most notably repetitive stress injury and carpal tunnel syndrome. In order to show medical causation, the plaintiffs' attorneys called on individuals who claimed expertise in ergonomics and biomechanics. In many of the cases, these experts were permitted to testify that there was clearly a direct cause-and-effect relationship, despite the great scientific controversy surrounding the issue. In other cases, the computer companies' attorneys convinced the judges to preclude this type of testimony. The core of the plaintiffs' case was that the practice of proper ergonomic measures while typing would prevent injury, despite the fact that this theory is unproven in the scientific literature. In order to make their case, the attorneys for the plaintiffs cited the internal ergonomics programs of the individual computer manufacturers as evidence that these companies warned their own employees but not end users^34,43.

The lawyers for the plaintiffs also attempted to take advantage of the Workers' Compensation system by using documents, signed by physicians, that described the injuries as work-related. However, many of these documents were authored solely for the purpose of facilitating the treatment of the patients. The plaintiffs' lawyers focused on the Australian experience with the repetitive-strain-injury phenomenon and argued that the computer companies had failed to warn the public about repetitive stress injury despite their awareness of the outbreak in Australia. Finally, aware that the medical literature did not support a causal connection between typing and carpal tunnel syndrome, the lawyers for the plaintiffs alleged that thoracic outlet syndrome, another extremely controversial diagnosis, also was related to keyboarding.

Central to the strategy employed by the computer industry in defending these cases was its resolve to try cases to verdict and, if necessary, to appeal. From the outset of the litigation, it was made clear to the plaintiffs' lawyers that whatever success they hoped to achieve would have to be gained in the courtroom before jurors and not through settlement.

Much of the defendants' case relied on the most recent scientific literature, which states that typing does not cause carpal tunnel syndrome or other upper-extremity conditions⁴⁵. The defendants also argued that the existence of in-house ergonomics programs was not evidence of any duty to place warnings on the keyboard because these programs relate to the duty of the company, as an employer, to create a comfortable work environment.

With respect to alternative keyboard designs, the defendants contended that the benefits of these keyboards are at best unproven. None have been shown to prevent injury, and their acceptance by the public has been minimal. One of the defendants' most compelling arguments was that placing a warning on a keyboard is analogous to putting a warning on any tool used repeatedly in the workplace, such as pens used by writers, trowels used by bricklayers, or hammers used by carpenters. The computer companies countered the arguments by the plaintiffs' lawyers about repetitive strain injury in Australia by citing evidence that the prevalence of repetitive stress disorders rose and fell in Australia without warnings being placed on keyboards or any change in keyboard design.

One of the most powerful arguments made by the defendants in the keyboard cases involved the issue of alternative cause. Without exception, each of the plaintiffs whose cases were tried had evidence of various personal and health factors that have been proven to be linked with carpal tunnel syndrome and the other upper-extremity conditions claimed in the lawsuits. In numerous instances, these alternative causes had been ignored when these injuries were diagnosed as being work-related. In fact, throughout this litigation, there were numerous cases in which health-care professionals focused solely on the workplace and the keyboard as the cause of the condition, to the exclusion of all other possible causes, thereby depriving the patient of appropriate medical treatment^4,8,41.

In late 1997, the plaintiffs were finally successful in obtaining a mass consolidation of these cases against one manufacturer. Ultimately, nine plaintiffs went to trial on May 4, 1998. One of the nine plaintiffs had previously been awarded $5.3 million in a 1996 trial against the same defendant²². The trial judge set that earlier verdict aside because the plaintiff had concealed evidence that her condition was not work-related. That plaintiff had had three unsuccessful carpal tunnel releases (two on the left and one on the right); she also had a claw hand on the left. Throughout her care and treatment, her principal treating physician (and, at the time of the trial, her medical and ergonomic experts) stated repeatedly that typing was the cause of her condition and that repetitive stress injury in the form of carpal tunnel syndrome was her work-related injury. However, nearly all of these physicians and experts ignored the fact that the cause of her symptoms was related to severe cervical spine degeneration.

The nine-plaintiff trial lasted for seven weeks. During their four-week-long arguments, the plaintiffs called on experts including hand surgeons, an epidemiologist, a design engineer, and several witnesses who claimed expertise in ergonomics. The defendant called on ten experts from various specialties including neurology, hand surgery, epidemiology, occupational medicine, psychiatry, design engineering, and biomechanics. A hand surgeon from Australia, who had extensively studied the repetitive strain problem there, also testified.

The closing arguments presented by the plaintiffs lasted for more than one day, and those presented by the defendant took approximately four hours. On June 16, 1998, the jury deliberated for less than four hours before returning verdicts in favor of the defendant in each of the nine cases¹³. The verdicts were unanimous. To date, of the approximately forty-five plaintiffs whose cases have gone to trial, not one has recovered anything against any computer-keyboard-manufacturer defendant.

At the same time that these cases were being tried, many cases were dismissed. As part of this process, judges rendered opinions rejecting plaintiffs' theories. In Doll v. Digital Equipment Corporation, the judge held: "The plaintiff was essentially asking the jury to make the precipitous leap from keyboard use to CTS and/or tennis elbow. The fact that the plaintiff may have used the defendant's keyboard in a rapid and repetitive fashion is a characteristic not of the keyboard but of the plaintiff's work habits and, possibly, the requirements placed upon her by her employer. The defendant is not an insurer for such activity or responsible for such. . . . Were it so, every carpenter would have a claim arising from every hammered thumb, golfers would spend more time in litigation than on the links and pianists would strive to get to court rather than to Carnegie Hall."¹⁴

The manufacturer-defendants cited several legal doctrines in their dismissal motions. One of the most important of these provides a means to exclude from evidence (and to prevent the jury from hearing) unfounded scientific-opinion testimony. In 1993, the United States Supreme Court stated, in Daubert v. Merrell Dow Pharmaceuticals, Incorporated, that before purported scientific testimony is presented to a jury, the trial judge must act as a "gatekeeper" to evaluate critically this testimony and to ensure that it is both relevant and reliable¹². As part of this exercise, the trial judge examines whether the reasoning and methodology used by the expert is scientifically valid and whether the testimony applies to the facts of the case. In Finley v. NCR Corporation, a New Jersey federal court precluded the testimony of one such witness and dismissed the plaintiff's claim (in which she alleged that use of the defendant's keyboard had caused her carpal tunnel syndrome), stating: "Dr. -'s report suggests that NCR's keyboard is not the most technologically advanced, but it fails to link substantially [plaintiff's] injury to the design of NCR's keyboard. Dr. - is not, and does not claim to be, a treating physician. His report reflects no consideration of personal predisposition, i.e., he did not consider plaintiff's age, gender, or weight. Nor does Dr. - document studies showing how NCR's keyboard design, which presumably is so ill-constructed as compared to other designs, has led to a disproportionately large number of persons developing CTS. Moreover, although Dr. - states what is an appropriate amount of force that a keyboard should require and that NCR's keyboard requires too much force, he fails to show that people who use keyboards requiring less force are less likely to get CTS. Thus, the relevant conclusion drawn from Dr. -'s report is that an undetermined amount of work requiring repetitive manual motion is tangentially related to, but not the substantial cause of, the development of CTS. Moreover, a California Superior Court has previously rejected Dr. -'s testimony for the same reasons. . . . In short, despite Dr. -'s conclusion that NCR's keyboard design contributed to causing [plaintiff's] injury, the report fails to address the question whether her injury was proximately caused by the design of the keyboard as opposed to the manner in which she used it or some physical attribute of [plaintiff]. . . . Thus, Dr. -'s opinion does not pass muster under Daubert."¹⁵

Judges have been keenly aware of the consequences of cursorily making the leap to causation on the issue of repetitive stress injury. In a well reasoned decision, which resulted in the dismissal of yet another claim involving keyboard-related injury, a federal judge wrote: "Science coexists uneasily with litigation's adversary system, as the imperatives of partisan advocacy coupled with powerful economic incentives often seem to overwhelm good science. Lawyers, judges, and forensic experts sometimes engage in what literature teachers call willing suspension of disbelief. Scientific propositions that would cause even laymen to gasp in disbelief are routinely argued in courts of law. Such are the dangers of a legal system allowing partisan expert testimony. . . . Imposing carpal tunnel syndrome liability based on alleged defects in keyboard design would result in a nationwide explosion of litigation at societal costs which are almost unimaginable. . . . Presumably Daubert . . . permit[s] a trial court to be sure that this avalanche of litigation is based on something at least resembling good science. The evidence proffered in this case does not cross that threshold."³⁵

Since the verdicts in favor of the defense in the nine-case trial, and after the many judicial opinions rejecting these claims, plaintiffs' lawyers have abandoned the litigation that they once thought so promising. Even in a nine-case consolidation, with each plaintiff claiming an upper-extremity injury caused by typing, the jury relied on the scientific studies presented to it and found for the manufacturer-defendants. One of the points made clear in this litigation is that, while ergonomics is important in creating a comfortable work environment, an overemphasis on its scope can be harmful to employers (by making them more vulnerable to lawsuits) and to workers and patients (by hindering correct diagnosis).

The role of the caring physician is to be knowledgeable and understanding of the social and political issues relevant to patients making Workers' Compensation claims. The importance of determining work-relatedness goes beyond who legally assumes responsibility for paying the medical bills in the Workers' Compensation system. A straightforward discussion early in the medical evaluation of a patient who has carpal tunnel syndrome, for instance, should take place when the patient claims that the computer has caused his or her injury. A frank discussion may often spare the patient the "dehumanizing medical-legal merry-go-round"²⁰ brought into existence by physicians with conflicting opinions, ergonomists, and lawyers. A patient caught up in this morass often becomes bitter, recalcitrant, anxious, and neurotic²⁰. Rehabilitation and the delay until the patient returns to work are prolonged, and proper treatment may never be rendered because no further consideration is given to other potential diagnoses once the patient is labeled as having occupational carpal tunnel syndrome. The majority of patients have no intention of defrauding the Workers' Compensation system. Rather, they become victims of a system that inadvertently promotes incapacity in those whom it was designed to help.

The term repetitive stress injury implies a presumptive etiology. To the orthopaedist treating a patient with a painful upper extremity, this etiological inference may be of only minor relevance. In managing a patient, we face four tasks: three of them medical and one of them bureaucratic. The first task is to make a diagnosis in which the injured tissue is identified and the nature and site-specific location of the injury are determined. There are many unresolved controversies in the area of diagnosis, and the level of accuracy that is desired must be weighed against the increased costs of additional diagnostic studies. Generally accepted medical diagnostic categories or labels have been applied to patients with musculoskeletal disorders of the upper extremity. These terms are specific and imply a well defined anatomical region affected by a well defined pathological process.

The second task is to evaluate the contributing factors once a diagnosis has been made. These include intrinsic factors (anatomical abnormalities and metabolic disorders) as well as extrinsic factors (the nature of the patient's job and avocations). Here, too, data are sparse and interpretation is difficult. Why do some workers suffer from a disorder whereas others in the same job do not? How does the work environment interact with intrinsic risk factors? Does repetitive work simply accelerate a natural aging process, and, if so, should a limit to cumulative exposure be set? Can we quantitate and rank the risk factors?

The third task that we face is to select a treatment program. This may include acute intervention such as drugs, splinting, or surgery. With musculoskeletal injuries, one frequently prescribes a rehabilitative program that includes stretching and muscle-strengthening, alteration of tools, and aerobic conditioning. In this area, too, there are few comprehensive, prospective studies, and reliable data are unavailable to guide the design of a program of treatment and rehabilitation.

The fourth task may require the clinician to make a determination as to whether the condition is caused by the job; this is not a medical mandate but rather a bureaucratic one. Such a determination may be medically impossible. The job may constitute an environment in which the propensity to a condition expresses itself, but this is not causality. Nevertheless, as clinicians we are committed to helping our patients with the medical and social issues that surround this controversial area.

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