Epidemiology of WMSDs

The number of cases of work-related musculoskeletal disorders (WMSDs) in the United States has been gradually declining since the mid-1990s ( Fig. 138-1 ). However, the number of WMSD cases was 335,900 in 2007 and accounted for approximately one in three occupational injuries and illnesses associated with lost workdays. According to the U.S. Bureau of Labor Statistics database, illnesses in the workplace resulting from overexertion (including lifting) and repetitive motion have followed a trend similar to that of WMSDs but have continued to account for approximately 35% to 40% and 3% to 4%, respectively, of all lost-workday injuries and illnesses in U.S. private industry since 2003 ( http://www.bls.gov ). Approximately 40% of lost-workday injuries and illnesses are sprains and strains ( Fig. 138-2 ). Though representing only a small proportion, carpal tunnel syndrome (CTS) and tendinitis have also remained relatively constant since 1995 (see Fig. 138-2 ). The proportion of lost-workday injuries and illnesses affecting the shoulder, wrist, and hand has also remained constant at approximately 4% each, as has the proportion affecting the fingers, at approximately 8%. In 2007, the longest work absences were attributed to CTS (median of 28 days); repetitive motion, such as grasping tools, scanning groceries, and typing (median of 20 days); and injuries to the shoulder (median of 18 days) and wrist (median of 14 days).

Histograms showing the number (A) and proportion (B) of cases of work-related musculoskeletal disorders (WMSDs) associated with lost workdays in U.S. private industry from 1995 to 2006.

(Data provided by the U.S. Bureau of Labor Statistics: http://www.stats.bls.gov/ .)

Histograms showing the proportion of sprains and strains (A) , carpal tunnel syndrome (CTS) (B) , and tendinitis (C) associated with lost workdays in U.S. private industry from 1995 to 2006.

(Data provided by the U.S. Bureau of Labor Statistics: http://www.bls.gov/ .)

While the Bureau of Labor Statistics database remains a rich source of information regarding the scope of WMSDs, a recent report by investigators involved in a state-based surveillance program suggests that upper extremity WMSDs are severely under-reported, possibly by an order of magnitude, and estimates that, over the 7-year time span from 1995 to 2001, the number of cases of WMSDs was increasing rather than declining. An investigation using active surveillance of work-related upper limb disorders in the Pays de la Loire region in France from 2002 to 2003 showed that as many as 50% of the 2685 subjects experienced nonspecific musculoskeletal symptoms over the preceding 12 months, and approximately 30% in the preceding week. Rotator cuff syndrome, CTS, and lateral epicondylitis were among the most prevalent diagnoses, and more than half of workers were exposed to at least two risk factors for WMSD. Furthermore, the prevalence of WMSDs increased with age.

Risk Factors for WMSDs

Epidemiologic studies continue to find positive relationships between workplace risk factors and the development and severity of upper extremity WMSDs. These risk factors include, for example, awkward postures, task repetition, task force, duration of exposure, job stress/dissatisfaction, work style and other psychosocial factors, and risk factor combinations ( Box 138-1 ). There has been increasing interest in the role of psychosocial and work organization factors in the development of WMSDs. A recent review of epidemiologic studies that focused on WMSDs of the neck and upper extremities concluded that high work demands and low decision control in the workplace contribute to or exacerbate neck and upper extremity WMSD symptoms. In a case-control study of 3798 working adults, Warren et al. showed that the risk factors with strong associations to upper extremity WMSDs were both biomechanical (i.e., static postures; repeated pushing, pulling, and lifting; and repeated neck bending) and psychosocial/organizational (i.e., high demands and low organizational support). In a 2-year prospective study of 1081 newly employed workers, Harkness et al. showed that the onset of widespread body pain was associated with mechanical and postural exposures (i.e., repeated lifting, prolonged squatting, prolonged working with hands at or above shoulder level) as well as with psychosocial exposures (i.e., low job satisfaction, low social support, and monotonous work).

Individual and personal factors also contribute to the development of WMSDs. In a prospective cohort study lasting 5.4 years, it was shown that the predictors of upper extremity tendinitis were age over 40, body mass index (BMI) greater than 30, a complaint of shoulder or neck discomfort at baseline, a history of CTS, and a job with more awkward or extreme shoulder postures. The annual incidence of upper extremity tendinitis in this cohort of 501 active workers was 4.5%. In this same cohort, predictors of upper extremity discomfort, most likely precursors to diagnosable upper extremity conditions, included age over 40, a BMI greater than 28, a complaint of baseline discomfort, and a job that required highly repetitive and forceful hand activity.

These studies illustrate several key points regarding the etiology of WMSDs of the upper limb: they are multifactorial in origin, they are exacerbated with continued exposure to risk factors, the risk factors include both physical and psychosocial aspects of the workplace and of the individual, and they are difficult to identify and diagnose early in their development. Recent work in animal models and in humans confirms that there is worsening tissue injury with increasing physical exposure, that tissue damage and the subsequent inflammatory response is widespread and even systemic, and that the affective domain is influenced by the underlying tissue pathophysiology (e.g., see Chapter 137, “Pathophysiology of Work-Related Musculoskeletal Disorders,” and references , , and ). These complex interrelationships between the worker and the workplace make the management of such disorders challenging, to say the least.

WMSDs continue to represent a small but significant proportion of workers’ compensation claims. These work-related injuries may incur high direct medical costs as well as lost workdays, lost worker productivity, and diminished quality of life. These injuries have the potential to develop into chronic health problems if they are not detected and managed early. Unfortunately, the criteria by which individual patients enter the U.S. workers’ compensation health-care system favor a clear diagnosis suggestive of a definitive plan of care. In the case of work-related health problems, health-care delivery within the workers’ compensation system is further complicated by the need to assign injury causation to the workplace and to quantify employee disability to determine reimbursement for care and lost wages. WMSDs may be of insidious onset with vague early symptoms, are of multifactorial etiology, and frequently are exacerbated by non-workplace factors. As a result, clinicians frequently do not intervene until the advanced stages of the development of these disorders, which diminishes treatment prognosis and contributes to long-term disability.

OSHA Regulation of WMSDs

The Occupational Safety and Health Administration (OSHA) has been unable to spearhead an Ergonomics Program Rule through the U.S. Congress and has therefore developed a voluntary approach to the management of workplace ergonomics. This four-pronged approach includes the development of industry-specific guidelines (currently available for poultry processing, retail grocery stores, nursing homes, and shipyard employment); enforcement (enabled under the General Duty Clause to conduct inspections and issue citations for ergonomic hazards); outreach and assistance (to promote proactive approaches to prevention and management with a particular goal to reach small businesses), and the establishment of a National Advisory Committee (whose charter ended in 2004) authorized to identify gaps in research relevant to the application of ergonomics and ergonomic principles in the workplace ( http://www.osha.gov ). In this chapter, recent clinical research evidence concerning the effectiveness of such ergonomic programs is presented, the various components of effective workplace ergonomics programs are summarized, and the role of health-care providers in the clinical management of these disorders is emphasized ( Box 138-2 ).

National Occupational Research Agenda

Two major reviews of the scientific literature concerning WMSDs help define a framework for the workplace management of these disorders. The first was conducted under the auspices of the National Institute of Occupational Safety and Health (NIOSH) and was concerned with epidemiologic investigations of workplace risk factors that contribute to the development of WMSDs. Among the 600 epidemiologic studies that were reviewed, evidence for relationships between specific workplace risk factors and WMSDs was stratified. Strong evidence (a causal relationship was shown to be very likely between exposure to risk factor[s] and WMSD) for work relatedness was found for neck and neck and shoulder WMSDs resulting from posture; for hand-arm vibration syndrome as a result of vibration; and for elbow WMSDs, for CTS, and for hand and wrist tendinitis resulting from risk factor combinations. Some convincing epidemiologic evidence showed a relationship between exposure to risk factor(s) and WMSDs for neck and neck and shoulder WMSDs caused by force or repetition; for shoulder WMSDs resulting from posture or repetition; for elbow WMSDs caused by force; for CTS resulting from force, repetition, or vibration; and for hand and wrist tendinitis caused by force, repetition, or posture. The available studies were of insufficient number, quality, consistency, or statistical power to permit a conclusion regarding the presence or absence of a causal association for work relatedness for neck and neck and shoulder WMSDs resulting from vibration; for shoulder WMSDs resulting from force or vibration; for elbow WMSDs caused by repetition or posture; and for CTS caused by posture. None of the 600 studies reviewed provided evidence of no effect of workplace risk factors. In the executive summary of this review, the editor noted that the amount of detailed and quantitative information concerning the relationship between risk factor exposure and WMSDs was limited and depended on a variety of factors, both physical and nonphysical, and both work-related and non-work-related.

Following the NIOSH review, the National Institutes of Health asked the National Research Council (NRC) to assemble a steering committee of experts to conduct an independent review of the literature relevant to WMSDs of the lower back, neck, and upper extremities. The conclusions of this review were similar to the NIOSH review in terms of the causal relationship between physical risk factors and WMSDs. The NRC review further examined the literature concerning clinical interventions. Many studies did demonstrate that various types of interventions, including exercise, employee education, and engineering controls, do help prevent the development of WMSDs. The NRC steering committee also pointed out that many studies demonstrated effectiveness of multicomponent interventions in the prevention and management of WMSDs. Like the NIOSH review, the NRC review indicated the need for additional research into the mechanisms of disorder development; the exposure-response relationships between workplace risk factors and WMSDs; and development of targeted interventions for workplace prevention, detection, and management of these potentially disabling conditions.

The data compiled in these reviews assisted NIOSH in setting the WMSD portion of the National Occupational Research Agenda, in which federal funding priorities were determined for research concerning the physical and psychosocial risk factors contributing to the development of WMSDs from 1996 to 2006. Currently, the second iteration of the National Occupational Research Agenda is under development, and WMSDs continue to remain a focus of occupational health concerns requiring further investigation and application of both prevention and intervention in the workplace ( http://www.cdc.gov/niosh/nora/ ).

Evidence for Effective WMSD Management

Clinical research studies are beginning to report more long-term treatment effects regarding the various components of intervention programs. Several systematic reviews have examined recent evidence for the effectiveness of interventions for upper extremity WMSDs. In addition to highlighting promising aspects of effective interventions, these reviews have helped to identify gaps in the literature and in practice that must be addressed in future studies.

Verhagen et al. performed a systematic review targeting conservative management (i.e., ergonomic or physical therapy interventions) programs published through March of 2005. They included randomized and nonrandomized controlled trials studying conservative interventions in adults with work-related complaints of the arm, neck, or shoulder. Twenty-one different trials including 25 different interventions were evaluated. The types of interventions could be grouped into five major categories: exercise, manual therapy, massage, ergonomics, and energized orthotic positioning (i.e., a custom-fit wrist orthosis that incorporated high-voltage pulsed current stimulation for 30 minutes per day while worn at work). The authors report that the overall quality of the studies was poor, and the evidence for the effectiveness of these interventions was limited or inconsistent. Among the most important limitations were the heterogeneity of the subjects, and lack of clear diagnostic definitions of work relatedness. In addition, methodologic flaws and low power contributed to the poor quality of the literature on this subject. On the other hand, no adverse effects of any of these treatments were reported. It is also important to note that these disorders are diverse, not amenable to clear diagnosis (particularly early in their development), and that the types of treatments targeted in this review ignored the psychosocial-organizational factors whose importance has been recently emphasized.

Williams et al. evaluated the available evidence on workplace rehabilitation interventions for upper extremity WMSDs. They found only eight studies that met their inclusion criteria, with others being excluded most typically because the intervention did not take place at the workplace, or the sample studied did not have a WMSD. There was, therefore, overall limited evidence for effective workplace interventions due to the small number of studies. However, of these eight studies, there was some indication that exercise (both within and outside the workplace), workplace therapy, worksite analysis, use of case managers, and ergonomic modifications may improve symptoms of upper extremity WMSD and adherence to accommodations for WMSDs. On the other hand, this review highlights the need for a greater number of high-quality research studies demonstrating workplace interventions before conclusive treatment recommendations can be made.

Two years later, Brewer et al. also reviewed the literature regarding workplace interventions, but they focused their attention on the prevention of musculoskeletal and visual symptoms and disorders among computer users. In this occupational group, the authors found moderate evidence for no effect of exercises and rest breaks, no effect of workstation adjustment, but a positive effect of alternative pointing devices. However, there were mixed levels of evidence (i.e., inconsistency between higher quality studies) regarding the effectiveness of interventions. This could have been due in part to the heterogeneity of interventions studied in the 31 articles reviewed, but this still leaves a large gap in our understanding of upper extremity disorders among computer users.

Other recent studies have shed some light on potential management strategies for WMSDs. Marhold et al. examined the effects of a cognitive-behavioral return-to-work program on patients with musculoskeletal pain and sick leave of either short- (2–6 months) or long- (>12 months) term duration. This group format treatment (six subjects per group) focused primarily on teaching the workers coping skills and relaxation techniques, grading and pacing activity, personal goal setting for both leisure and work time, cognitive techniques, social skills training, stress management, and problem solving (weekly 2.5-hour sessions for the first 6 weeks), then guiding workers through the transition from the clinic to the workplace where they applied those coping skills and developed individual long-term maintenance programs (weekly 2.5-hour sessions for the next 6 weeks, then booster sessions at 16 and 48 weeks). Telephone calls lasting 15 minutes were also made between every third session, after 12 weeks, and three times in between the booster sessions. The control group did not receive any cognitive-behavioral interventions but was treated as usual by a physician, a physical therapist, a nurse, an occupational therapist, and/or a psychologist. The cognitive-behavioral group also had free access to usual treatment. The number of days of sick leave was significantly reduced in the short-term leave group, but not in the long-term leave group, as compared to controls. In addition, the short-term leave group experienced greater pain reduction, decreased affective distress, and increased general activity. These findings emphasize the importance of early detection and intervention in workers with musculoskeletal pain, which further supports the need for workplace-based programs in which employers and workers are kept aware of the risks and indicators for WMSDs. This study also points out the importance of frequency and duration of cognitive-behavioral interventions. For example, a study by Feuerstein et al. showed no additional effect of two stress management sessions in an ergonomically based workplace intervention. In their review, Pransky et al. further point out that interventions targeting the physical workplace may also have a stress-reducing effect, thereby reducing the symptoms of WMSDs. In summary, recent work has focused on the psychosocial aspects of these disorders and the importance of a comprehensive approach to their management.

Another investigative team conducted a prospective, randomized controlled clinical trial of the effectiveness of an integrated case management (ICM) workplace accommodation program designed to provide a systematic approach for evaluating barriers to recovery and return to work after a diagnosis of upper extremity WMSD. They enrolled 205 federal employees in a 4-month intervention that utilized a self-report measure of physical workplace exposure, an interview assessment of additional nonphysical barriers, and a worksite observer checklist intended to help guide case managers in worker accommodation efforts. These workers had not returned to normal work at the onset of their participation in the study. They were diagnosed with mononeuritis (e.g., CTS), enthesopathies (e.g., lateral epicondylitis), tendon disorders (e.g., tenosynovitis), soft tissue disorders (e.g., myalgia), nerve root and plexus disorders, cervical disorders, osteoarthrosis, disorders of the muscle, ligament, and fascia, and peripheral vascular disorders. Pain, function (self-report), and work status were monitored at 4 months, 10 months, and 16 months after onset of the program. In addition to the worker self-reports, case managers also had regular written updates from treating clinicians, performed chart reviews of monthly progress reports, and performed a worksite walk-through to assess ergonomic exposure. From these sources of information, potential barriers to return to work were identified as the focus for recommending and implementing worksite accommodations. The number of accommodations recommended by the ICM case managers was 1.5 times greater than that of their usual care counterparts, and those accommodations implemented under the auspices of the program were 1.4 times greater than in usual care. In addition, the accommodations were relatively inexpensive, comprehensive, and effective in reducing upper extremity pain and discomfort. Interestingly, half of the accommodations were administrative-organizational in nature as compared with only 20% that were physical-ergonomic in nature, again illustrating the need to consider the psychosocial aspects of WMSD etiology. Finally, the ICM program included a problem-solving training module for affected workers that enabled them to contribute to the identification of barriers to return to work. In this case the case manager could act as a mediator between affected workers and supervisors or managers in conveying the concerns of the workers, facilitating implementation of realistic solutions, and improving communication within the workplace hierarchy. While this approach did not yield perfect adherence to the recommendations (25% were never implemented), it did result in more accommodations than usual care. Finally, those workers who received ICM were significantly more satisfied with their health and work status than those who received usual care.

Very recently, the concept of work style has been introduced as a potential target for workplace WMSD interventions. Conceptually, work style refers to the behavioral, cognitive, and physiologic response that can occur with increases in work demands, and is a construct that helps to explain the link between ergonomic and psychosocial factors that contribute to WMSD symptoms. At the level of the individual worker, work style may be inadequate to cope with increased work demands, whether physical, organizational, or psychosocial, which may in turn lead to a cascade of biobehavioral changes that, over time, contribute to the development and/or exacerbation of WMSDs. Conversely, interventions can theoretically be directed to improve work style so as to prevent or reduce WMSDs. In their randomized, controlled trial to assess the effectiveness of a group-based work-style intervention among computer workers with neck and upper limb WMSD symptoms, Bernaards et al. studied three groups of patients who received either usual care ( n = 158), work-style intervention only ( n = 152), or work-style plus lifestyle physical activity intervention ( n = 156). The two intervention groups attended six group sessions that focused on behavioral change with regard to body posture, workstation ergonomic adjustments, rest breaks, and coping strategies for stress related to high work demands. Questionnaire assessment on the use of these learned strategies occurred at baseline, and after 6 and 12 months. In addition, posture and workstation adjustments were assessed by observation. The work-style intervention was effective in changing body posture, workstation adjustment, and use of sufficient rest breaks, but did not have an effect on work stress outcomes. Bernaards et al. also reported that the work-style intervention alone was effective in reducing all pain measures related to upper extremity WMSD symptoms. In addition, they found that the combined intervention, which included lifestyle physical activity training, was ineffective in increasing physical activity. Therefore, it was not possible to ascertain the effect of increased physical activity on recovery from upper extremity WMSD symptoms.

This recent epidemiologic and clinical research work illustrates some important issues in the current state of knowledge in the area of upper extremity WMSD management. First, many patients suffering from upper extremity WMSDs present with early symptoms involving multiple regions of the upper limb and cervical spine that are not amenable to clear diagnosis. Therefore, it is difficult and unrealistic to select distinct diagnostic groups to study (see Levenstein for a discussion of diagnostic criteria for upper extremity WMSDs). Management programs that address workplace risk factors, both physical and psychosocial, show better treatment outcomes than those that are restricted to usual clinical practices. Finally, patients may not experience complete resolution of symptoms; instead, they often will need to participate in the long-term management of their disorder. This requires effective communication and collaboration between affected employees, their employers, and their health-care providers. It is encouraging that the recent literature reports on such comprehensive intervention programs and that the evidence, though still limited, indicates that they are effective. Ideally, therefore, it would be most advantageous for workplaces to establish WMSD management programs on site. At the very least, there needs to be open communication and follow-up between health-care providers and the workplace so as to optimize treatment outcomes.