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Introduction

Work-related musculoskeletal disorders (WRMDs) have intrigued and challenged clinicians and researchers since the beginning of the eighteenth century. These disorders are generally characterized as injuries or dysfunctions that primarily involve the major supporting structures of the body, including the nerves, muscles, bones, joints, and cartilage (National Institute of Occupational Safety and Health [NIOSH], 1997). These disorders have been attributed to the cumulative impact of repetitive movements and/or prolonged awkward postures that often occur in the work environment and ultimately result in overuse, sprains, strains, tears, hernias, and/or other connective tissue injuries (NIOSH, 2001). It is important to distinguish WRMDs from general pain disorders that are attributed to off-duty injuries (e.g., falls, motor-vehicle accidents, etc.), autoimmune disease, and/or other etiological factors unrelated to occupational duties.

Clinicians and researchers refer to these painful and oftentimes disabling afflictions using a variety of terms including repetitive motion injuries, repetitive strain injuries, cumulative trauma disorders, overuse syndrome, regional musculoskeletal disorders, soft tissue disorders, ergonomic disorders, etc. (Gatchel, Peng, Peters, Fuchs, & Turk, 2007; Huang, Feuerstein, & Sauter, 2002). Examples of more commonly recognized WRMDs include low back pain, neck pain, tennis elbow, and carpel tunnel syndrome. The inconsistent nomenclature can be attributed to the fact that these disorders largely defy traditional disease classification systems (NIOSH, 2001). Furthermore, there is significant disagreement regarding the causal mechanisms underlying the development and/or maintenance of musculoskeletal disorders in the workplace. The current literature largely emphasizes the impact of occupational duties on the development and maintenance of musculoskeletal disorders. For instance, the impact of computerized work environments, subsequent repetitive upper limb movement, and a prolonged sedentary posture on musculoskeletal disorders of the upper limbs has garnered significant empirical support (Griffiths, Mackey, & Adamson, 2007). In fact, the NIOSH (1997) stated that multiple studies have demonstrated evidence of a causal relationship between physical activity at work and WRMDs, based on a review of the most rigorous epidemiological research available. Still, the relationship between musculoskeletal disorders and work-related factors remains the subject of substantial debate due to the multiple factors (e.g., physical, occupational, organizational, psychosocial, individual, and sociocultural) that contribute to the development and maintenance of such disorders (World Health Organization, 1985). The current chapter provides an overview of the most commonly studied WRMDs, including those injuries and diseases that are the result of events and exposures in the work environment that cause or contribute to the condition.

Epidemiology

The incidence and prevalence rates of WRMDs vary greatly across epidemiological studies due to differences in study populations and diagnostic criteria. The US Department of Labor’s Bureau of Labor Statistics (BLS) provides what may be the most representative and comprehensive data ­currently available on the prevalence of WRMDs in the USA. Estimates are calculated from the BLS Annual Survey of Occupational Injuries and Illnesses, which surveys over 230,000 private industry establishments across 44 US states and territories. The epidemiological evidence suggests that musculoskeletal disorders represent the single largest category of illnesses recorded as occupational diseases in the USA (Bureau of Labor Statistics [BLS], 2010; National Research Council [NRC], 1999). A recordable case includes work-related injuries, disorders, or illnesses that result in medical treatment, restricted activity or job transfer, loss of consciousness, days away from work, and a diagnosis by a physician or other licensed health professional. More specifically, WRMDs accounted for 28 % of the 3.3 million reported cases of nonfatal occupational injuries and illnesses reported in 2009 (BLS, 2010). Of the 3.3 million nonfatal occupational injury and illnesses reported, over 1.2 million workers required time away from work to recover (BLS; see Fig. 4.1).

Fig. 4.1
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Incidence and median days of work missed across private industry, local government, and state government, 2009. Source: Bureau of Labor Statistics, 2010

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Of these occupations, the specific occupations that reported the highest incidence of WRMDs were among psychiatric aides (256.0 per 10,000 full-time workers), emergency medical technicians and paramedics (233.5 per 10,000 full-time workers), and nursing aides and orderlies (232.5 per 10,000 full-time workers). As indicated in Fig. 4.2, the vast majority of WRMD cases occur to the back, ­followed by injuries to the upper extremities.

Fig. 4.2
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Percent and incidence rate (per 10,000) of part of body affected, 2008. Source: Bureau of Labor Statistics, 2010

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Sprains, strains, and tears of various connective tissues account for three quarters of the 236,260 musculoskeletal disorders cases reported in the private industry, with similar patterns exhibited among government employees (Fig. 4.3).

Fig. 4.3
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Distribution of musculoskeletal disorders in the private industry by nature of injury or illness, 2008. Source: Bureau of Labor Statistics, 2010

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Economic Burden of Work-Related Musculoskeletal Disorders

WRMDs account for more disability and costs to the US health care system and commercial industries than any other condition (NIOSH, 2001). Within the Department of Defense, WRMDs result in more missed duty day, medical profiles, and medical discharges from active duty than any other medical condition (Amoroso & Canham, 1999; Feuerstein, Berkowitz, & Peck, 1997; Jones, Amoroso, Canham, Schmitt, & Weyandt, 1999). Given the aging population, the economic burden of WRMDs is likely to increase. WRMDs affect the economy by contributing to increased absenteeism, health care costs, and worker compensation expenditures. For example, nearly one million people each year report taking time away from work for treatment to recover from WRMDs, with most individuals returning to work within 31 days (BLS, 2010). In 2008, WRMDs required a median of 10 days away from work, with significant variability across disorders. For instance, carpal tunnel syndrome (CTS) accounted for a substantial percentage of absenteeism where an average of 28 days of leave were taken per incident, whereas more commonly reported disorders, such as low back pain, accounted for 7 days of leave per incident (BLS, 2010). Health care and compensation expenditures related to WRMDs continue to increase and place a significant burden on private and public industries. WRMDs account for nearly 70 million physician office visits in the USA annually, and an estimated 130 million total health care encounters including outpatient, hospital, and emergency room visits. In 2007, the National Academy of Social Insurance reported that cash benefits to injured workers and medical payments for their health care exceeded $55 billion, with total costs to employers reaching approximately $85 million (Sengupta, Reno, & Burton, 2009). These figures are conservative and represent only reported cases, as many disorders that can be attributed to work go unreported and therefore are not counted in any of the existing databases. Regardless of the estimates used, the problem is large both in terms of health and economic impact.

Conceptual Model for the Development of Work-Related Musculoskeletal Disorders

Several conceptual models have been created to delineate the potential relationships between external and internal factors that impact the development of WRMDs. The majority of models for the development of WRMDs take into account individual, social, organizational, and occupational factors. One of the most oft-cited models was provided by the National Institute for Occupational Safety and Health (NIOSH, 2001). The NIOSH synthesized numerous reviews of the literature on WRMDs, and proposed that the physical activities that place an individual at increased risk for the development of musculoskeletal disorders are impacted by individual, social, and organizational factors (Buckle & Devereux, 1999; Frank, Pulcins, Kerr, Shannon, & Stansfeld, 1995; Frank et al., 1996; Katz et al., 1998; Krause, Dasinger, & Neuhauser, 1998; Moore, 1992; Szabo, 1998; see Fig. 4.4).

Fig. 4.4
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Conceptual model for work-related musculoskeletal disorders development. Source: National Institute of Occupational Safety and Health, 2001

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In this model, the initial load (e.g., static or dynamic muscle load) to which an individual is exposed to is dependent upon work requirements, duration of exposure, and the environment in which the individual is interacting. This initial load is applied to the musculoskeletal system either by external or by internal forces, which lead to internal tissue responses in the muscles, ligaments, and at the joint surfaces. Depending upon the magnitude of the load and other individual, organizational, or social factors, one or more outcomes may result. These may include adaptation effects (such as increases in strength, fitness, or conditioning) or potentially harmful outcomes (such as pain or other symptoms, and structural damage to tendons, nerves, muscles, joints, or supporting tissues) that may result in symptoms, impairment, or disability. Whether the exposure leads to a WRMD depends upon the physical demands of the job, the adaptation response of the worker, and other individual physical and psychological factors. These factors, in turn, may regulate the effects of the external load.

Recent findings largely support the assertions made by this model, in which physical occupational requirements, organizational influences, individual characteristics, and psychosocial factors contribute to increased risk of WRMDs (Bigos et al., 1992; Hoogendoorn, van Poppel, Bongers, Koes, & Bouter, 2000). For instance, several studies have demonstrated the negative impact that excessive physical load has on the musculoskeletal system using three-dimensional modeling of physical load on various joints and measures of tissue disintegration and inflammatory processes (Marras, Cutlip, Burt, & Waters, 2009). More recently, research has also demonstrated the association of individual (e.g., personality traits), organizational (e.g., job satisfaction and safety climate), and psychosocial factors (e.g., social support and work stress) with both lower extremity and upper extremity musculoskeletal disorders (Andersen et al., 2003; Bigos et al., 1992; Hoogendoorn et al., 2000, Marras, Davis, Ferguson, Lucas, & Gupta, 2001; NRC, 1999). Psychosocial factors include nonphysical influences that concern the mental stress response of the worker in the workplace. Reviews of epidemiological studies indicate that between 11 and 80 % of low-back injuries and 11–95 % of extremity injuries are attributable to workplace physical factors, whereas between 14 and 63 % of injuries to the low back and between 28 and 84 % of injuries of the upper extremity are attributable to psychosocial factors (NRC, 1999). It is understood that the contribution of each factor to the risk of a WRMD varies with the nature of the disorder and the anatomical area involved.

Types of Work-Related Musculoskeletal Disorders

Much confusion surrounds the accurate classification and diagnosis of these conditions. As a result, a variety of classification schemes have been proposed, but none has been universally adopted (Buckle & Devereux, 2002). This significantly hinders clinicians’ and researchers’ ability to communicate in a consistent, accurate, and meaningful manner about these disorders, thereby preventing progression towards the identification of the most effective strategies for their prevention and treatment. For the purposes of this chapter, the most commonly reported WRMDs will be described and organized by affected anatomical area, as this is the manner in which they are classified in the literature. It is understood that individual, biomechanical, and psychosocial risk factors vary with the nature of the disorder and the anatomical area involved. It is important to note that the current state of the science is such that the temporal relationship between risk factor and disorder cannot be clearly established. As such, the risk factors associated with each category of musculoskeletal disorders will be addressed separately within each category.

Work-Related Musculoskeletal Disorders of the Upper Body

Neck and/or Shoulder

Musculoskeletal complaints in the neck and/or shoulder (part of the cervicobrachial area) are common among adults in developed nations and are showing increasing trends. Common symptoms associated with WRMDs of the neck and/or shoulder include pain, tenderness, and stiffness at the base of neck and upper back; signs of hardened muscle bands or nodularity; headaches due to tension in neck muscles; intermittent muscle spasms in neck muscles; and/or dull pain referred to the upper limbs. These contribute to the demand for medical services and the economic burden of absence from work due to sickness. Population-based studies suggest a lifetime prevalence of over 70 %, and point-prevalence rates ranging from 12 to 34 % (NIOSH, 1997; van Rijn, Huisstede, Koes, & Burdorf, 2010). More than 40 epidemiological studies have been published that focus on the relationship between neck and shoulder pain and occupation. The studies are heterogeneous in design, classification of disorder (e.g., neck pain, tension neck syndrome, rotator cuff syndrome, cervical strain, tension myalgia, etc.), population (e.g., dental professionals, automobile assembly workers, computer workers, factory workers, secretaries, poultry workers, scissor makers, sewing machine operators, healthcare employees, grocery checkers, etc.), symptom assessment (e.g., self-report, physician examination, etc.), outcome measurement (neck pain, neck, and/or shoulder pain, physical examination), and analysis.

Biomechanical Risk Factors

The majority of these studies investigated the impact of repetitive work movements and/or improper static postures on neck and/or shoulder disorders. Repetitive work activities are defined as continuous head, neck, arm, and/or hand movements that affect the muscles of the neck and shoulder areas. Multiple studies have shown that employees who are exposed to prolonged and improper postures involving the neck and/or shoulder muscles and to forceful and/or repetitive tasks, are at significantly greater risk for neck and/or shoulder WRMDs. For example, Morse et al. (2007) noted that dental hygienists frequently work with their neck flexed over 30 °, while leaning sideways or rotating their shoulders. These prolonged static postures create high static loads and fatigue within the trapezius muscles (Finsen, Christensen, & Bakke, 1998). These repeated exposures have been tied to self-reported pain symptoms and to abnormal physician exam findings, suggesting that these demands place employees at greater risk of developing neck and/or shoulder WRMDs. Similar findings have been demonstrated among individuals across a variety of occupations, including computer workers, factory employees, and other employees who are exposed to similar biomechanical risk factors in their respective work setting.

Psychosocial Risk Factors

Greater emphasis has been placed on psychosocial risk factors that may contribute to the development of WRMDs. Research suggests that several psychosocial factors place workers at risk for neck pain, including poor workplace support from supervisors/colleagues, high occupational demands, and poor control over working patterns (Cagnie, Danneels, Van Tiggelen, De Loose, & Cambier, 2007; Griffiths et al., 2007). For instance, Cagnie et al. (2007) found that individuals who perceived a shortage of personnel and an inability to meet company demands were at increased risk of reporting neck pain. This may be an indirect reflection of work overload which, in turn contributed to increased opportunity for the development of WRMDs. Furthermore, a review conducted by Griffiths et al. (2007) suggests that multiple risk factors place workers at increased risk for pain, including excessive workload, time/deadline pressures, and reduced opportunities for social interactions. These issues are particularly salient among nonprofessional office workers due to low levels of job control, social support, and task clarity (Griffiths et al.). These factors are assumed to interact with other individual and biomechanical factors to increase a person’s individual risk factors. For example, the cumulative stress placed on the neck and shoulder area, as a result of longer hours at a computer terminal due to personnel shortage or increase work demands, is one example of combinations of factors that contribute to the development of WRMDs. Taken together, therefore, the evidence suggests that neck pain and neck disorders are associated with mechanical and psychosocial workplace factors.

Individual Risk Factors

Cross-sectional and prospective studies have provided inconsistent evidence for associations between individual factors among workers (e.g., gender, age, physical activity, and personality factors) and neck and/or shoulder pain symptoms (Viikari-Juntura et al., 2001). Individual factors are largely conceptualized as confounding factors that influence the relation between environmental demands of the job and the occurrence of neck pain in the employee. Studies suggest that women are at greater risk of reported neck and/or shoulder pain compared to men; however, the mechanisms underlying this relationship are not fully understood (Cagnie et al., 2007; Korhonen et al., 2003; Leclerc et al., 1999). More specifically, prevalence rates suggest that neck pain is twice as common among female full-time employees compared to their male counterparts (Cagnie et al., 2007; Korhonen et al., 2003; Leclerc et al., 1999; Marcus et al., 2002). However, these higher rates are not exclusive to neck and shoulder pain, as this pattern is found across most forms of body pain. Research suggests that smaller stature and lower muscular strength in the neck and shoulder areas explain the gender differences (Korhonen et al., 2003). Several other physical, cultural, and sociological factors have been proposed as explanations, although none have been supported in the empirical literature (Guez, Hildingsson, Nilsson, & Toolanen, 2002). In addition, an inverse U-shaped relationship has been demonstrated between age and prevalence of neck pain, where the risk of neck pain increases until approximately 50 years of age, and decreases slightly thereafter (Bot et al., 2005; Leclerc et al., 1999; Viikari-Juntura et al., 2001). Research suggests that increased pain is associated with increased degeneration of the cervical spine. However, the decrease in neck and/or shoulder complaints may be attributed to other, more debilitating disorders taking precedence later in life (Bot et al., 2005).

A relationship between physical activity and neck and/or shoulder pain has been identified in observational studies. For example, Korhonen et al. (2003) found in their cohort study that employees who exercised less frequently demonstrated a higher risk of neck pain. However, it is unclear if individuals do not engage in physical activity as a result of the pain or are at greater risk for the development of WRMDs due to poor muscle strength and sedentary lifestyle. This may have some clinical implications, as an increase in physical activity may be one way to of reduce musculoskeletal morbidity in sedentary workers (Hildebrandt, Bongers, Dul, van Dijk, & Kemper, 2000). Finally, the study of personality traits and neck and/or shoulder pain among workers has yielded inconsistent results. Some studies found an association between neck and shoulder pain symptoms and Type A behavior (Malchaire, Cock, & Vergracht, 2001), while others did not (Andersen et al., 2003). Also, introversion (Malchaire et al., 2001) and neurotic perfectionist traits (van Eijsden-Besseling, Peeters, Reijnen, & de Bie, 2004) were reported to be associated with WRMDs of the neck and upper limbs. It is hypothesized that these individual factors interact with biomechanical and psychosocial mechanisms in the development and maintenance of WRMDs. However, additional research is warranted given the sparse and inconsistent literature investigating the impact of personality factors on WRMDs.

Assessment and Diagnosis

WRMDs of the neck and/or shoulder are assessed using a variety of methods across research and clinical settings, suggesting a lack of agreement regarding the appropriate way to assess for the presence of these particular disorders. Epidemiological studies utilize data gathered from interviews or questionnaires to assess the intensity, frequency, and duration of pain, tingling, and/or numbing in the neck and shoulder region. The criterion used to diagnose the presence of a neck and/or shoulder WRMD varies across studies, accounting for the wide-ranging prevalence rates. General recommendations regarding the clinical assessment of musculoskeletal disorders include inspection of the affected area; testing for range of motion, pain, and muscle strength; palpitation of muscle tendons; and specific tests including computerized tomography (CT). CT scans are usually reserved for individuals who experienced a blunt trauma or are at high risk for more serious pathology. Despite the availability of assessment techniques, the majority of clinicians utilize a clinical physical examination in determining the presence of a disorder in the neck and/or shoulder region (Nordin et al., 2009).

Treatment Approaches

Researchers, clinicians, and occupational health professionals have prescribed numerous interventions in an attempt to limit the disabling and costly effects of neck and shoulder pain on employees (Gatchel et al., 2007; Schultz, Stowell, Feuerstein, & Gatchel, 2007). The vast majority of WRMDs interventions focus on modifying the ergonomics, or design, of the workplace or equipment in an attempt to minimize the load placed on the neck and/or shoulder muscles (Hurwitz et al., 2008; Leyshon et al., 2010). Ergonomic interventions aim to decrease the strain on the neck and/or shoulder muscles by altering the workstation and the environment. For instance, employers have utilized improved lighting, lumbar support, alternative keyboards, and pointing devices among computer users. Unfortunately, evidence supporting the effectiveness of these conservative approaches is largely inconsistent. While some reviews lend support to the use of ergonomic interventions (Boocock et al., 2007), other reviews failed to find associations (Kennedy et al., 2010). Other conservative approaches include the use of chiropractic manipulation, massage, frequent rest breaks, exercise, and biofeedback. However, these interventions lack long-term effects, as indicated by the high rate of recurring neck and/or shoulder pain symptoms after treatment (Hurwitz et al., 2008). More recent research has investigated the potential benefit of incorporating a cognitive-behavioral approach to the management of WRMDs (Leon et al., 2009). Preliminary research suggests that a cognitive-behavioral intervention, which included psychoeducation, cognitive restructuring, and breathing retraining in conjunction with standard rheumatic care, can significantly decrease pain ratings and prevent relapse (Leon et al.). More recently, Transcutaneous Electrical Nerve Stimulation (TENS) units have also been used to treat neck and/or shoulder WRMDs. A TENS unit is a device that provides light electrical current via electrodes attached to the skin surrounding the painful area. It is hypothesized that the electrical stimulation interrupts and modulates the pain signals sent from the affected area to the brain; however, there is no consensus regarding the pain relief mechanism(s). One study suggests that relief from neck pain symptoms can be reached with a single TENS session (Maayah & Al-Jarrah, 2010). As with the other interventions mentioned above, the long-term efficacy of the TENS unit is undetermined. Furthermore, neck and/or shoulder WRMD intervention studies are plagued by small sample sizes, non-random assignment, lack of comparison groups, and inconsistent classification and diagnosis of disorders. These limitations—combined with the prevalence and physical, emotional, and economic costs of neck and/or shoulder WRMDs—highlight the need for further high-quality intervention research.

Elbow

Epicondylitis is one of the most common disorders of the elbow, and it is associated with significant pain, functional impairment, and a reduction in productivity (da Costa & Vieira, 2010; NIOSH, 2001). Epicondylitis can be further classified as medial or lateral epicondylitis, conditions commonly referred to as “golfer’s or tennis elbow,” respectively. Epicondylitis is attributed to the overuse of the extensor and flexor muscles in the elbow, which often leads to inflammation of the tendon (Park, Lee, & Lee, 2008). However, specifics regarding the pathogenesis of medial and lateral epicondylitis are not well understood. Epicondylitis is also one of the most costly WRMDs and contributes to lost workdays, decreased productivity, and worker’s compensation claims (Kurppa, Viikari-Juntura, & Kuosma, 1991; Verhaar, 1994). For example, work-related epicondylitis had an annual workers’ compensation incidence rate of 4.7 per 10,000 full-time employees in the state of Washington alone. This translated to an average of 136 lost workdays per claim, and more than $12 million in direct costs (Foley, Silverstein, & Polissar, 2007; Foley, Silverstein, Polissar, & Neradilek, 2009; Silverstein & Adams, 2007). Employees in certain industries are said to be at greater risk for developing medial and/or lateral epicondylitis including, but not limited to, assembly line workers, cashiers, cooks, and packaging workers. Research suggests that biomechanical, psychosocial, and individual factors interact with the physical and environmental demands of these occupations and contribute to the development of WRMDs of the elbow.

Biomechanical Risk Factors

Research largely emphasizes the role of biomechanical risk factors in the work place in relation to WRMDs of the elbow. Numerous biomechanical risk factors have been identified, including forceful and repetitive physical work, extreme nonneutral position of the hands and arms, high grip forces, and vibrating hand tools (da Costa & Vieira, 2010; Shiri, Viikari-Juntura, Varonen, & Heliövaara, 2006). Many manufacturing and service industries require that employees engage in activities that require prolonged engagement in these types of movements. For example, assembly workers are often required to the use force, tight grips, and vibrating hand tools for several hours a day when assembling products. Research suggests that the risk of developing medial or lateral epicondylitis increases as the frequency and duration of such physical exertion increases (Shiri et al., 2006; van Rijn et al., 2010). While multiple systematic reviews support these findings, researchers are cautious in establishing a causal link between these biomechanical factors and medial and lateral epicondylitis, as the vast majority of these studies are cross-sectional (da Costa & Vieira, 2010; Shiri et al., 2006).

Psychosocial Risk Factors

Less is known about the potential role that psychosocial risk factors play in the development of ­epicondylitis. There are some cross-sectional data to suggest that factors such as poor job control, negative affectivity, dissatisfaction with work, and high psychosocial demands place employees at greater risk for developing WRMDs of the elbow (Macfarlane et al., 2009; NIOSH, 1997; Shiri et al., 2006). These factors are not unique to epicondylitis and are apparent risk factors for the development of several other WRMDs. Interestingly, there are preliminary data to suggest that psychosocial factors may influence lateral and medial epicondylitis differently. For instance, a review by van Rijn et al. (2010) found that psychosocial factors, such as low job control and low social support, were related to lateral but not medial epicondylitis. This suggests that, while the majority of studies focus on lateral or both lateral and medial disorders together, future research may benefit from investigating potential unique risk factors.

Individual Risk Factors

Studies have identified several individual factors that may place an individual at greater risk for the development of lateral and/or medial epicondylitis. For instance, research suggests that risk factors include older age, female gender, smoking, obesity, and diabetes (Shiri et al., 2006; da Costa & Vieira, 2010). However, the manner in which these factors place a worker at greater risk is unclear. The association between age and WRMDs of the elbow is believed to be due to the fact that this is a more common disorder among individuals who are of working age, as opposed to younger individuals (e.g., 30–64). Female gender has also been found to be associated with WRMDs of the elbow, but potential mediators have not been identified (Macfarlane et al., 2009; NIOSH, 1997 Shiri et al., 2006). In addition, interestingly, research suggests that smoking serves as a risk factor for epicondylitis. Smoking may interference with the circulation of tendons, which not only places the tissue at risk for injury but also slows or prevents their healing during recovery period. This pattern is also found in previous tobacco users, suggesting that tobacco may have a persistent effect on the vascular system (Shiri et al.). Other factors, such as obesity and diabetes, have been associated with the development of epicondylitis among workers; however, it is unclear as to the manner in which these variables are related. Researchers propose that obesity contributes to insulin resistance, a component of a metabolic syndrome, which may lead to Type II diabetes and increase the risk of developing WRMDs in general (Shiri et al., 2006; van Rijn et al., 2010). Further research is needed to clarify the potential relationship between smoking, obesity, and epicondylitis.

Assessment and Diagnosis

Assessment of lateral and medial epicondylitis disorders requires a thorough patient history, physical examination, and radiographic and imaging studies. However, radiographic and imaging studies are primarily utilized to rule out more serious pathology. Diagnostic criteria differ slightly across clinical settings and research studies, but generally require the presence of local pain at the elbow, tenderness at the epicondyle on palpitation, and pain at the epicondyle on resisted isometric extension or flexion of the wrist. More specifically, a lateral epicondylitis diagnosis requires the presence of pain in the lateral epicondyle that is exacerbated by resisted forearm pronation and wrist and digital flexion. Medial epicondylitis is characterized by pain along the medial elbow, which is also worsened by resistance to forearm pronation and wrist and digital flexion (Shiri et al., 2006). The duration in which symptoms must be present range from 1 week to 6 months, depending on the clinical or research guideline being used.

Treatment Approaches

While a wide range of treatments for lateral and medial epicondylitis are available, there is no ­consensus among clinicians and researchers regarding the most efficacious treatments. This is largely due to the fact that large-scale randomized clinical trials have not been conducted. As such, clinicians are unable to confidently prescribe one treatment over another, as there are no data to support the relative effectiveness of a particular treatment. First-line treatments for lateral and medial epicondylitis are largely conservative in nature and are used in combination with one another. The most important components of these conservative approaches include rest from the aggravating activity, activity modification, watchful waiting, and the use of nonsteroidal inflammatory medications (NSAIDs). Various orthotic devises, such as elastic bands placed on the forearm, have also been utilized, but numerous reviews have been unable to find support for their effectiveness. While some researchers suggest that bracing alleviates pain and improves grip strength, there is no evidence to suggest that it is better than sham bracing and other conservative therapies, and it may in fact be inferior to topical NSAIDs and corticosteroid injections (Bisset, Paungmali, Vicenzino, & Beller, 2005; Struijs et al., 2001). Individuals with chronic, reoccurring elbow pain that is unresponsive to more conservative approaches also have the option to use more aggressive procedures, including physical therapy, corticosteroid injections, extracorporeal shock therapy, and acupuncture. Corticosteroid injections have been shown to alleviate painful symptoms and improve grip strength for approximately 2–6 weeks. While corticosteroids are effective in the short term, their long-term effectiveness and advantages over more conservative approaches are uncertain. Technological advances have led clinicians to experiment with extracorporeal shock therapy, which delivers low- or high-frequency electrical current to the affected area. It is believed that these electrical currents trigger a healing response in the damaged tendon. However, research to date does not support the efficacy of this form of treatment for epicondylitis (Bisset et al., 2005; Trudel et al., 2004). Exercise is commonly prescribed as a way to manage and treat elbow pain. Physical therapy regimens used to treat WRMDs of the elbow typically involve strength training and stretching. While these exercises have been effective in reducing pain, there is less evidence to suggest that it results in improved grip strength (Bisset et al.; Trudel et al.). Acupuncture has garnered some attention as a potential treatment for epicondylitis. Interestingly, the National Institutes of Health (NIH, 1998) released a consensus statement supporting the use of acupuncture in the treatment of epicondylitis despite conflicting evidence of its efficacy.

Given the often self-limiting nature of the disorder, and the effectiveness of some conservative approaches, most individuals do not need to undergo surgery. However, epicondylitis can be a chronic and debilitating disorder for a small minority of sufferers. Surgery is usually reserved for those cases where conservative approaches have not provided any relief over the previous 6 months to a year. While various surgical procedures are utilized in the treatment of epicondylitis, the main objective is to remove abnormal tissue within the tendon or release the tendon altogether. While there is some evidence that such invasive procedures provide relief, more stringent research testing the relative effectiveness of surgery to more conservative approaches is lacking. Interestingly, one of the few randomized controlled trials conducted in this area suggest that more conservative approaches, such as watchful waiting and rest combined with NSAIDs, were more effective, relative to aggressive approaches such as corticosteroid injections (Smidt et al., 2002). While many interventions for lateral and medial epicondylitis exist and are commonly put into practice, little is known about best practices for managing this disorder. This is unfortunate given the high prevalence and economic impact of epicondylitis. For chronic elbow pain, a comprehensive interdisciplinary treatment approach will provide the best chance of decreasing pain, increasing function, and returning to work (Gatchel & Okifuji, 2006; Gatchel et al., 2007; Schultz et al., 2007).

Hand and Wrist

There are few occupations that do not require use of the hands as a major part of daily work requirements. As a result, WRMDs of the hand and wrist have a greater impact on work attendance, productivity, and wages than WRMDs affecting any other region of the body (BLS, 2010). One of the most costly and prevalent WRMDs of the hand and wrist is CTS. CTS is caused by a combination of biomechanical and biobehavioral work-related factors involving excessive and repetitive forceful use of the hand, such as higher levels of computer keyforce during typing (Feuerstein, Armstrong, Hickey, & Lincoln, 1997; Harrington & Feuerstein, 2010; Nicholas, Feuerstein, & Suchday, 2005; Palmer, 2011). This excessive force results in compression of the median nerve in the wrist that supplies feelings and movement to the hand, which in turn leads to sensorimotor dysfunction in parts of the hand (Patijn et al., 2011). Individuals with CTS endorse symptoms such as numbness, tingling, weakness, or pain in the hand and fingers. Prevalence estimates indicate that about 14 % of the general US population reports symptoms of recurring pain, numbness, and/or tingling in the median nerve distribution in the hands (Atroshi et al., 1999). Upon clinical and electrophysiological examination, about 4 % of the population meets diagnostic criteria for CTS. While CTS can be caused by a variety of chronic ­illnesses, such as rheumatoid arthritis, gout, and diabetes, this disorder has been primarily linked to workplace factors. In fact, it is estimated that half of all medically diagnosed cases of CTS are work-related (Lawrence et al., 2008). Estimates suggest that employers expend approximately $45,000–$89,000 per CTS claimant when losses of earning, productivity, and workers compensation claims are taken into account (Foley et al., 2007). Employee health stakeholders are highly motivated to identify and potentially modify those variables that contribute to the development of WRMDs of the hand and wrist such as CTS.

Biomechanical Risk Factors

As is the case of other WRMDs, the majority of the literature surrounding WRMDs of the hand and wrist focuses on mechanical forces that act on the body as a result of occupational duties (Palmer, 2011; Patijn et al., 2011; Viikari-Juntura & Silverstein, 1999). For example, a significant amount of force is placed upon, and exerted from, the tendons of the hand and wrist by factory workers, who oftentimes are required to manually assemble products using repetitive forceful movements of the hand and wrist. The research has identified several biomechanical risk factors across various occupations that increase the likelihood of the development of hand and wrist WRMDs, including awkward static and dynamic forearm, wrist, and finger postures; repetitive work; hand and/or wrist vibration; and prolonged computer work (NIOSH, 1997). Researchers hypothesize that hand and wrist WRMDs occur in the tendons as a result of movements that stimulate an acute inflammatory response. This response may resolve with tissue repair or tissue degeneration depending on the use of appropriate interventions. Barr, Barbe, and Clark (2004) suggest that CTS is due to central nervous system reorganization, which occurs after the performance of repetitive hand and wrist movements. This repeated activation or overstimulation of nociceptive afferents causes a greater release of excitatory neuropeptides and amino acids. These nociceptors become hypersensitive and increase the excitability of secondary neurons in the spinal cord, thereby contributing to the hyperalgesia associated with chronic pain and inflammation (Dubner & Ruda, 1992; McCarson, 1999). The underlying mechanisms that account for the associations between biomechanical force and WRMDS of the hand and wrist continue to be debated. As such, there is no consensus regarding the independent influence of biomechanical factors on the hand and wrist.

Psychosocial Risk Factors

Studies indicate that psychosocial factors in the workplace, such as intense deadlines, a poor social work environment, and low levels of job satisfaction, are major contributors to CTS pain. Research suggests that psychosocial conditions are more likely to be important factors in contributing to CTS in office workers, although they also complicate the condition in employees whose work is primarily physical (Nordstrom, Vierkant, DeStefano, & Layde, 1997). For example, people reporting the least influence at work had 2.86 times the risk (95 % CI, 1.10–7.14) as those with the most influence at work (Nordstrom et al., 1997). Therefore, the risk of developing CTS appears to be more prevalent in occupations where employees lack control or influence over their work environment and responsibilities. Such psychosocial issues have been repeatedly noted in many other chapters of this Handbook.

Individual Risk Factors

The most significant individual risk factor for CTS is the use of excessive force in the performance of work-related duties involving the hands (Feuerstein et al., 1997; Harrington & Feuerstein, 2010; Nicholas et al., 2005). For example, the generation of excessive force while working on a computer keyboard has been shown to directly contribute to the severity of CTS symptoms (Feuerstein et al., 1997). Similar findings have been reported in professional sign language interpreters with CTS (Feuerstein & Fitzgerald, 1992). By comparison with the control group, those working with CTS pain exhibited fewer rest breaks, more frequent hand/wrist deviations from a neutral position, more frequent lateral excursions from an optimal work envelope, and more rapid finger/hand movements while interpreting. Many of the additional individual risk factors for CTS have also been identified for other WRMDs. For instance, individual risk factors, such as older age, female gender, smoking, overweight, and diabetes, have been shown to place a worker at increased risk for CTS. As with other pain disorders, studies indicate that women have a significantly higher risk for CTS than men. While an explanation for this greater risk has not been determined, it is hypothesized to be related to smaller wrist size. However, there are some individual risk factors that are unique to WRMDS of the hand and wrist, including pregnancy (Burt et al., 2011). Hormonal changes also appear to play a major role in the development of CTS in women who are pregnant. CTS that begins during pregnancy is not usually severe and persistent enough to require treatment, as most cases go away on their own after delivery. Being overweight has been highlighted frequently as a risk factor for CTS and may play a direct causal role on CTS. Greater body mass appears to reduce nerve flow speed into the hand. Obesity is also related to poor physical fitness, which may also increase risk. A 2005 analysis indicated that weight is strongly linked to the onset of CTS in patients under the age of 63, but it may be a less important factor as patients increase in age (Bland, 2005).

Assessment and Diagnosis

Assessment of WRMDs of the hand and wrist can take various forms. For example, CTS is diagnosed using a combination of techniques, including self-report, physical examination, and imaging studies. A physical examination typically entails inspection of the wrist for tenderness, swelling, warmth, and discoloration. Specific tests, such as the Tinel and Phalen tests, are also used to reproduce the symptoms of CTS (Dale, Descatha, Coomes, Franzblau, & Evanoff, 2010). The Tinel test requires that the health professional tap or place moderate pressure on the median nerve in the patient’s wrist. The test is positive for CTS when symptoms such as pain and/or tingling occurs in the hand and fingers. The Phalen, or wrist-flexion, test involves having the patient hold his or her forearms upright by pointing the fingers down and pressing the backs of the hands together. The presence of CTS is suggested if one or more symptoms, such as tingling or increasing numbness, are felt in the fingers within 1 min. Often, it is necessary to confirm the diagnosis by use of electrodiagnostic tests that include nerve conduction tests, ultrasounds, and magnetic resonance imaging (MRI). In a nerve conduction study, electrodes are placed on the hand and wrist. Small electric shocks are applied and the speed with which nerves transmit impulses is measured and used to determine the presence of CTS. Ultrasound imaging can show impaired movement of the median nerve, while MRI can show the anatomy of the wrist and help identify any abnormalities.

Some disease-specific self-report questionnaires have been developed for use in research and ­clinical settings. Levine et al. (1993) introduced the first disease-specific questionnaire—called the Boston Carpal Tunnel Questionnaire—to assess the outcome after carpal tunnel release. Since then, various other upper-limb outcome measures have been used in the assessment of carpal tunnel patients. Some of the commonly used outcomes measures include the Disability of Arm, Shoulder and Hand (Greenslade, Mehta, Belward, & Warwick, 2004); Patient Evaluation Measure (Dias, Bhowal, Wildin, & Thompson, 2001); Michigan Hand Outcome Questionnaire (Chung, Pillsbury, Walters, & Hayward, 1998); and Upper Extremity Functional Scale (Pransky, Feuerstein, Himmelstein, Katz, & Vickers-Lahti, 1997). These self-administered questionnaires assess severity of symptoms and functional ­status. Despite the numerous assessment strategies, there is no consensus regarding a formal assessment of CTS.

Treatment Approaches

Treatment of hand and wrist WRMDs can be broadly divided in nonsurgical and surgical approaches. Initial treatment generally involves resting the affected hand and wrist for at least 2 weeks, avoiding activities that may worsen symptoms, and immobilizing the wrist with a splint in order to avoid further damage from twisting or bending. Nonsteroidal anti-inflammatory drugs, such as aspirin, ibuprofen, and other nonprescription pain relievers may ease symptoms that have been present for a short time or have been caused by strenuous activity. Corticosteroids, such as prednisone, can be injected directly into the wrist or taken by mouth to relieve pressure on the median nerve and provide immediate, temporary relief to persons with mild or intermittent symptoms. In addition, stretching and strengthening exercises can be helpful in people whose symptoms have abated. Behavioral interventions can also be used for individuals using excessive force in the performance of their work-related duties involving the hands (Feuerstein et al., 2004; Nicholas et al., 2005; Sullivan, Feuerstein, Gatchel, Linton, & Pransky, 2005). For example, feedback and training to use appropriate amounts of force and to promote self-management of rest breaks has been found to decrease CTS symptoms. In addition, the use of frequent micro-breaks during computer use can allow for sufficient muscle recovery while typing, and to allow for sustained performance without muscle fatigue and over-use symptoms (Henning et al., 1996; Henning, Jacques, Kissel, Sullivan, & Alteras-Webb, 1997). As with other treatments for WRMDS, little is known regarding the long-term effectiveness of these interventions. For chronic CTS, the best chance of decreasing pain, increasing function, and returning to work is likely to come from a multicomponent, interdisciplinary treatment approach (Gatchel & Okifuji, 2006; Gatchel et al., 2007; Schultz et al., 2007).

Surgical options for WRMDs of the hand and wrist vary widely and are one of the most commonly conducted surgical procedures in the USA (Huisstede et al., 2010). Generally, surgery is recommended if symptoms persist for 6 months after all conservative treatments have failed. Surgery involves severing the band of tissue around the wrist to reduce pressure on the median nerve. Although symptoms may be relieved immediately after surgery, full recovery from carpal tunnel surgery can take months as the wrist may lose strength because the carpal ligament was cut. Patients oftentimes undergo physical therapy after surgery to restore wrist strength. Recurrence of CTS following treatment is rare, as the majority of patients recover completely. This suggests that surgery may be a viable option for individuals suffering from chronic CTS symptoms.

Work-Related Musculoskeletal Disorders of the Lower Body

Lower Back

WRMDs of the lower back, as is the case with all other WRMDS, originate in the context of work and/or are exacerbated by occupational duties. Lifetime prevalence rates of low back pain are as high as 84 % in the general adult population (Cassidy, Carroll, & Côté, 1998). It is estimated that up to 95 % of low back pain cases in the working population are the result of muscle, tendon, and ligament strain or sprain (Agency for Health Care Policy and Research, 1994). Health-care costs associated with low back pain were estimated at $85.9 billion in the USA in 2005 (Martin et al., 2008). However, the majority of cases are classified as “nonspecific” low back pain, as our current knowledge does not allow health care providers to determine, by clinical, laboratory, and/or imaging tests, the exact cause of pain in most cases. Multiple risk factors have been identified and are presented below.

Biomechanical Risk Factors

Most of the published literature examining biomechanical risk factors for work-related low back pain is based on cross-sectional data, thereby limiting our understanding of the potential causal relationships between work-related physical activity and low back pain. While some studies suggest an association between workplace biomechanical exposures such as heavy lifting, motor vehicle driving, and whole-body vibration, nonneutral postures and low back pain, methodological flaws prevent any inferences regarding causality (Marras et al., 2001; Punnett, Fine, Keyserling, Herrin, & Chaffin, 1991). A ­case–control study by Punnett et al. (1991) used detailed assessments of the postures of individual automobile assembly line workers and demonstrated a fivefold increase in low back pain risk from prolonged bending and twisting on the job. Similar work by Marras et al. (2001) also has demonstrated an increased risk among people working in jobs with higher biomechanical demands (a combination of lifting frequency, load moment, and trunk motion). In general, these studies have found that biomechanical factors produced large risk estimates, underscoring the risk associated with the physical demands of work in the context of low back pain.

Psychosocial Risk Factors

There is limited but growing empirical evidence linking psychosocial risk factors to the occurrence of low back pain (Hoogendoorn et al., 2000). However, the complex relationship between work-related psychosocial factors (such as job dissatisfaction) and the physical demands of work (such as spinal loading) make it difficult to reach definitive conclusions about their relative risk of developing low back disorders. Still, research suggests that high perceived workload and time pressure are related to low back pain. One of the most often cited studies conducted by Bigos et al. (1992) found that worker dissatisfaction was the only work-related risk factor associated with subsequent reporting of low back pain, while none of the variables assessing the physical demands of work significantly predicted back pain. Still, it may be premature to conclude that psychosocial factors are a more important predictor of low back pain than the physical demands of work given the paucity of corroborative research.

Individual Risk Factors

Observational studies have identified potential individual risk factors for low back pain, including younger age, female gender, smoking, and obesity (Garg & Moore, 1992; NIOSH, 1997). However, these risk factors are not unique to low back pain, as they also place workers at risk for other WRMDs. Additionally, the underlying mechanisms that account for the associations between low back pain and age, gender, smoking, and obesity are unknown. Further research is needed to clarify the relationship between individual risk factors and the various WRMDs described above before any conclusions regarding causality can be made.

Assessment and Diagnosis

The Clinical Efficacy Assessment Subcommittee of the American College of Physicians and the American Pain Society has established a clinical practice guideline for the assessment and diagnosis of low back pain through their Low Back Pain Guidelines Panel (Chou et al., 2007). These guidelines recommend that clinicians conduct a focused history and physical examination to help place patients with low back pain into one of three broad categories: (1) nonspecific low back pain, (2) back pain potentially associated with radiculopathy or spinal stenosis, or (3) back pain potentially associated with another specific spinal cause. The clinical assessment should include a review of psychosocial risk factors, which have been found to predict risk for chronic disabling back pain (Gatchel, Polatin, & Mayer, 1995). It is also recommended that clinicians not routinely obtain imaging or other diagnostic tests in patients with nonspecific low back pain. Imaging and other testing for patients with low back pain should only be conducted when severe or progressive neurologic deficits are present, or in cases when serious underlying conditions are suspected on the basis of history and physical examination.

Treatment Approaches

The Low Back Pain Guidelines Panel (Chou et al., 2007) also provides specific treatment recommendations for low back pain. The Panel recommends that clinicians consider the use of medications with proven benefits, in conjunction with back care information and self-care. The first-line medication options for most patients are acetaminophen or nonsteroidal anti-inflammatory drugs. The Panel also recommends that clinicians assess the severity of baseline pain and functional deficits, as well as the potential risks and benefits before initiating therapy. For patients who do not improve with self-care, the Panel recommends that clinicians consider the addition of non-pharmacologic therapy, such as intensive interdisciplinary rehabilitation, exercise therapy, cognitive-behavioral therapy, or progressive relaxation (Gatchel & Okifuji, 2006; Gatchel et al., 2003).

Knee, Foot, and Ankle

The majority of the WRMD research literature focuses on the upper limbs or lower back. By comparison, there has been limited research on disorders of the knee, ankle, and foot. The most likely explanation for this is the significantly higher prevalence of upper-extremity and lower-back WRMDs. A review of the available occupational literature suggests that certain disorders of the knee (e.g., bursitis, meniscal lesions or tears, and osteoarthritis), ankle (e.g., osteoarthritis), and foot (e.g., plantar fasciitis, heal pain, osteoarthritis) are more common among people in occupations with high physical demands, such as carpet and floor layers, painters, and construction workers (Kivimäki, Riihimäki, & Hanninen, 1994; Reid, 2010). Heel pain is the most common complaint presented to foot and ankle specialists and may be seen in upwards of 11–15 % of adults (Thomas et al., 2010). Heel pain most often has a mechanical pathology, but it can also include arthritic, neurologic, traumatic, or other systemic conditions.

Biomechanical Risk Factors

Biomechanical risk factors identified for the development of WMSD of the lower body include ­prolonged kneeling or squatting, climbing, and lifting heavy loads.

Psychosocial Risk Factors

There is limited research on psychosocial and occupational factors related to musculoskeletal knee, ankle, and foot disorders.

Individual Risk Factors

Individual risk factors, similar to those found among WRMDS of the upper body, have been identified in disorders of the lower body, including smoking and obesity (D’Souza, Franzblau, & Werner, 2005; Merlino, Rosecrance, Anton, & Cook, 2003). However, these associations are based on a very limited cross-sectional research base. As such, conclusions surrounding potential aggravating factors are ­hindered until further research is conducted.

Assessment and Diagnosis

Assessment and diagnosis of disorders of the knee, ankle, and foot are generally accomplished by orthopedic, foot, and ankle specialists according to a variety of clinical practice guidelines. A complete review of assessment and diagnosis approaches for all of the different WRMDs for the knee, ankle, and foot are beyond the scope of this Chapter.

Treatment Approaches

Treatments for such disorders of the knee, ankle, and foot parallel those of the upper limb in that the majority consist of rest, avoidance of aggravating activities, and analgesic use. More aggressive treatments are administered when conservative approaches fail and may include cortisone shots, physical therapy, and surgery. The American Academy of Orthopedic Surgeons (Richmond et al., 2009) has published a clinical practice guideline for the nonsurgical treatment of osteoarthritis of the knee. The guidelines recommend that patients with symptomatic osteoarthritis of the knee participate in self-management educational programs and engage in self-care. Self-care consists primarily of weight loss, engaging in regular physical exercise, and quadriceps strengthening. The guideline also recommends taping of the knee for short-term pain relief, as well as the use of analgesics and intra-articular corticosteroids. The guidelines do not recommend the use of glucosamine or chondroitin.

Heel pain is one of the most common forms of foot pain. The American College of Foot and Ankle Surgeons Heel Pain Committee has published clinical practice guidelines for the diagnosis and treatment of heel pain (Thomas et al., 2010). The Clinical Practice Guideline outlines three tiers of treatment for heel pain. The first tier includes conservative treatments, such as stretching, home-based physical therapy, over-the counter orthotics, and oral anti-inflammatory medication. Second tier treatments include corticosteroid injections, prescriptive physical therapy, and custom orthotics. Surgery for heel pain is included in the third tier, and is only recommended for chronic symptoms and after more conservative treatments have been used for at least 6 months. However, the long-term effectiveness of most of these interventions for pain resulting from WRMDs of the lower limbs has yet to be determined. Clearly, further high-quality research to include prospective studies and intervention trials is needed in this area.

Summary

WRMDs are painful afflictions that result from injury to or dysfunction of nerves, tendons, and muscles largely due to repetitive movements and/or prolonged nonneutral postures required by the work environment. Epidemiological data suggest that WRMDs, such as muscle strains, low back pain, and CTS, account for the vast majority occupational diseases in the USA. In fact, these disorders account for more human suffering, loss of productivity, and economic burden than any other condition. The establishment of a causal relationship between musculoskeletal disorders and occupational duties remains a source of significant controversy. Research suggests that multiple factors (e.g., physical, occupational, organizational, psychosocial, individual, and sociocultural) contribute to the development and maintenance of such disorders. Researchers and clinicians have tested and utilized a wide variety of interventions to include conservative approaches, such as ergonomic modifications, and more invasive procedures, such as surgery. The short- and long-term effectiveness of such interventions varies greatly across conditions. Furthermore research investigating causal mechanisms and potential sources of intervention is necessary in order to limit the disabling and costly effects of these conditions.

Recommendations for Future Research

As people live longer and the average age of the US work force increases, the impact of aging on work-related loading, tolerance, psychosocial stress, and their interactions must be better investigated. Traditionally, high-force, highly repetitive loading of the musculoskeletal system has been the hallmark of work. However, the workplace and the nature of the work are changing rapidly and, as a result, so are the type and frequency of WRMDs. For instance, the number of employees working on a traditional assembly line is decreasing. However, those who remain employed in these environments are increasingly exposed to more frequent but less forceful motions (Punnett et al., 1991). Collectively, these trends indicate that the nature of physical exposure is rapidly evolving to a low force, highly repetitive environment (Westgaard & Winkel, 1997). Improved quantification of physical risk factors, rather than reliance on self-reported measures, would strengthen our knowledge of the relationship between various types of exposure and development of WRMDs (Waters, Dick, Davis-Barkley, & Krieg, 2007). Furthermore, studies evaluating the quantitative link among epidemiological, biomechanical, individual, and psychosocial factors should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies. Moreover, problems such as different diagnostic criteria (due to lack of a gold standard for the clinical diagnosis of most WRMD), different outcome assessments, and different methods for measuring exposure make the establishment of risk factors a very difficult task to accomplish (Punnett & Wegman, 2004). It is recommended that multidisciplinary investigators collaborate in order to standardize the conduct, assessment, and reporting of WMSD research trials. Finally, a continuing need exists for high-quality randomized clinical trials (Frank et al., 1996). In summary, understanding the current body of WRMDs research, and the identification of research gaps, is necessary for the development of more robust and clinically relevant models for assessment and treatment. This will aid in better workplace design, exposure assessments, diagnosis and, ultimately, lower risk, reduced medical costs, and healthier workers.