Epidemiology

The annual survey of occupational injuries and illnesses conducted by the BLS is the most frequently referenced source of information on WMSDs in the United States. The US Department of Labor defines an MSD as an injury or disorder of the muscles, nerves, tendons, joints, cartilage, or spinal discs. MSDs do not include disorders caused by slips, trips, falls, motor vehicle accidents, or similar accidents.

In the United States, between the years 2003 and 2017, the nonfatal occupational injury and illness incidence rates in private industry have gradually and consistently decreased from 5.0 cases per 100 full-time equivalent workers to 2.8 per 100. However, in 2018 there were 2.8 million nonfatal workplace injuries and illnesses reported by private industry employers, unchanged from 2017. One-third of these cases caused a worker to miss at least 1 day of work. The incidence rate of occupational illness was greatest in the agriculture, forestry, fishing, and hunting sector (one category), followed by health care and social assistance and manufacturing (29.8, 27.6, and 24.2 cases per 10,000 full-time equivalent workers, respectively).

The 2004 to 2013 National Health Interview Survey showed that approximately 30% of adults reported experiencing MSDs during the preceding 30 days. UE shoulder pain was the second leading cause, with 9%, after knee pain (18%). Furthermore, the survey showed that the prevalence of current activity limitations due to any arthritis or joint symptoms was 7.32%. ^, In Europe, approximately 35% of workers reported muscular pain, and 20% of workers complained of upper limb pain. For example, in France, reported shoulder pain reached 29.5% during the years 2000 to 2004.

Despite a general decline in the reported annual incidence of work-related MSDs, they remain the most common occupational disease in the European Union and affect workers in all sections and occupations. Specifically, according to BLS data, the incidence rate of WUEMSDs has gradually increased from 23.2 per 10,000 workers in 2007 to 32.6 per 10,000 in 2015 in private industries. Fortunately, this climbing trend has been interrupted in 2018, according to the latest BLS report of the nonfatal occupational injuries and illnesses involving days away from work by nature of injury or illness in the private industry. Based on this report, in 2018 the incidence rate of WUEMSDs and shoulder disorders was 28.6 per 10,000 and 6.8 per 10,000, respectively. The highest rates of shoulder injuries and disorders were demonstrated among hoist and winch operators (129.6 per 10,000), athletes and sports competitors (114.4 per 10,000), cargo and freight agents (84 per 10,000), and flight attendants (75.5 per 10,000).

In 2018 the median number of days away from work due to shoulder injuries or disorders was 27. There were 68,070 cases of nonfatal OSDs involving days away from work. Sprains, strains, or tears accounted for 44,220 cases (64.9%), followed by 13,570 cases of soreness or pain (19.9%) and 2950 (4.3%) cases of bruises and contusions. Injuries and illnesses to men accounted for 61% of all cases; this ratio may change in the near future because women affected by MSDs are still underrecognized. Furthermore, in some sectors and occupations women are highly exposed to MSDs risk factors. The highest number of days away from work was found among those aged 45 to 54 years ^, in the United States and among those aged 40 to 59 years in Europe.

The 2015 Safety & Health Assessment & Research for Prevention program of the Washington State Department of Labor and Industries used Washington State Fund–accepted claims data to estimate the burden of Workers’ Compensation claims for RCS and shoulder WMSDs. Men accounted for approximately 61.5% of the claims, and the median age of the claimants was in the mid-40s. Of all WUEMSDs, shoulder disorders incurred the highest median state fund total direct cost per compensable claim, equaled to $28,228. The mean work time lost per claim was 354.7 days for shoulder WMSDs. During 2002–10 there were 12,121 nontraumatic RCS claims, which accounted for 3% of all compensable claims. The mean direct claim cost for RCS was $74,061, and the mean time loss per claim was 428 days. The data for Washington State are likely to be representative of other states because the data for WMSDs of the UE collected by Liberty Mutual across the United States (covering 10% of the private Workers’ Compensation market) were similarly skewed. These costs may seem to underestimate the magnitude of work-related musculoskeletal injuries’ financial burden: in New York State only, the cost of Worker’s Compensation claims in 2007 was estimated to be $2,982,619,640.

Most of what is known about the risk factors for MSDs comes from epidemiologic studies. However, the published prevalence and incidence data should be viewed critically. As discussed earlier, there is a lack of agreement on case definitions, which has resulted in epidemiologic studies reporting widely different estimates for the burden associated with these disorders. In the literature reporting on neck and shoulder WMSDs, results from contrasting definitions have produced differences in prevalence (55% vs. 20% to take the most extreme), overall disability (14.6% vs. 23.2%), difficulty at work (8% vs. 15.5%), and the proportion of patients reporting that pain interfered with work (27.3% vs. 16.2%). Studies using different case definitions therefore lack comparability. Furthermore, this literature demonstrates that MSDs are not unique to any specific occupational group, with reported occupations ranging from meat processors to apparel workers, line assemblers in the manufacturing industries to office-based data entry operators or flight attendants to medical health system workers. Therefore etiologically MSDs may be activity related rather than work related, and further discussion will focus on the roles of type, intensity, and duration of activity as they relate to OSDs.

Risk factors

The common trait of the occupational groups for which high OSD rates are reported is intense exposure to specific activities or work attributes. The attributes associated with an increased probability of MSDs are considered to be risk factors. Attempts have been made to improve understanding of the relationships between activity and OSD, and thus several studies, systematic reviews, and meta-analyses have examined which work-related risk factors are associated with specific soft tissue shoulder disorders.

Bodin et al. examined 3710 French workers and demonstrated that workers with RCS were significantly older (44.9 ± 8.3 years) than those suffering from nonspecific shoulder pain (37.6 ± 10.2 years).

In 2017, van der Molen et al. published a systematic review and meta-analysis that identified the occupational risk factors for shoulder disorders based on the level of evidence and calculated by odds ratio (OR). This article reviewed approximately 2.4 million workers in the Netherlands, 16,000 of whom suffered from shoulder disorders. Based on this meta-analysis, only two risk factors were stratified based on moderate-quality evidence and the rest were based on low-quality evidence.

Arm elevation, based on moderate quality evidence, was demonstrated to increase the incidence of SAPS, with an OR of 1.91. Shoulder load was shown to increase the incidence of SAPS, with an OR of 2.00, based on moderate-quality evidence. Based on low-quality evidence, hand-arm force exertion increased the incidence of SAPS, with an OR of 1.53. Arm-hand repetition was weakly correlated with an increased risk of SAPS (OR 1.42), according to low-quality evidence.

Hand-arm vibration increased the risk of SAPS with an OR of only 1.34, based on low-quality evidence.

Psychosocial factors have been evaluated as a risk factor for shoulder disorder as well. Psychosocial demands may increase the incidence of SAPS, with an OR of 1.12 based on low-quality evidence. Low social support did not seem to correlate significantly to SAPS, with an OR of 1.03 based on low-quality evidence. Decision latitude did not seem to significantly increase the incidence of SAPS, with an OR of 1.08. Low-quality evidence failed to demonstrate increased incidence of SAPS due to job control or job security, with ORs of 1.22 and 1.12, respectively. Working beside a temporary worker for female workers might increase the incidence of SAPS (OR 2.2) based on very low-quality evidence.

Breslin et al. performed a systematic review and found moderate evidence that new workers were at an elevated risk of injury.

In 1997 the National Institute of Occupational Safety and Health (NIOSH) studied the epidemiologic evidence for the work relatedness of neck, shoulder, and UE disorders. The focus of the review was to assess the evidence for relationships between MSDs and workplace exposure to the following factors: (1) repetitive exertion, (2) awkward posture, (3) forceful exertion, and (4) hand-arm vibration. Evidence for the risk factors of UE MSDs is summarized in Table 67.1 .

The review found evidence of a positive association between highly repetitive work and OSDs (OR 1.6 to 5.0), based on limited quality evidence.

Evidence of a relationship between OSDs and repeated or sustained shoulder postures with greater than 60 degrees of flexion or abduction was presented, with an OR between 2.3 and 10.6. There was evidence for both shoulder tendinitis and nonspecific shoulder pain. The evidence for risk involved in maintaining specific shoulder postures was strongest in those with combined exposure to several physical risk factors, such as holding a tool while working overhead. This result was consistent with evidence in the biomechanical, physiologic, and psychosocial literature.

Similar to the aforementioned study conducted by van der Molen et al., the NIOSH report found insufficient evidence for a positive association between shoulder MSDs and either force or exposure to segmental vibration .

When assessing combinations of the presented risk factors, the NIOSH review found the strongest associations with WMSDs of the lower part of the back. For the UEs, NIOSH needed to combine risk factors (e.g., force exertion and exposure to hand-arm vibration while operating powered hand tools) to estimate some risk indicators for pathology. Few independent studies at that time had attempted to investigate combined effects on OSDs. The combined effect of forceful movement and vibrating machinery was later empirically demonstrated by Armstrong and colleagues, but a true appreciation of the effect of multiple factors remains poorly investigated.

An additional confounding variable on the risk of a given job-related activity may be the environment in which the activity is performed. Hildebrandt and colleagues reviewed 27 studies that related climatic (i.e., damp, wind, or cold) or seasonal (i.e., summer, winter) factors to MSDs, although none of these studies specifically addressed the subject. In addition, they distributed a questionnaire to 2030 workers in 24 different occupations and found that one-third of the work-related symptoms at the lower back and neck-shoulder region could be attributed to climatic conditions, perceiving that these conditions either caused or aggravated their symptoms. Sick leave as a result of neck-shoulder symptoms was associated with climatic factors, particularly drafts and wind. The authors concluded that researchers, workers, and patients consider such a relationship plausible. A recent study by Farbu et al. examined the effect of working in a cold environment on musculoskeletal pain in workers in Finland. They found that the prevalence of shoulder pain among workers who worked in a cold environment for less than 25% of the time was 13%. The prevalence of shoulder pain among patients who worked in a cold environment for more than 25% of the time was 9% for those who never felt being cold at work, 18% for those who sometimes felt being cold at work, and 35% for those who often felt being cold. When adjusted for age and sex only, the OR was 1.96, and when adjusted for age, sex, education, body mass index, insomnia, physical activity at work, leisure time physical activity, and smoking, the OR decreased to 1.39.

The relationship between arm posture to shoulder disorders was studied by Bodin et al. Moderated arm abduction of 60 to 90 degrees for 2 hours or more per day was associated with shoulder pain (OR 1.6) and abduction of greater than 90 degrees was a stronger risk factor for RCS (OR 2.4). Beach et al. found that lifting more than 10 kg above shoulder height for 15 minutes or longer per day was strongly associated with shoulder pain (OR, 2.3; P < .01). As expected, longer exertion of more than 2 hours was even a stronger risk factor for shoulder pain (OR, 2.62; P < .001).

OSDs are multifactorial in origin and may be associated with both occupational and nonoccupational factors. The relative contributions of these covariates may be specific to particular disorders. For example, the confounders for nonspecific shoulder pain may differ from those for shoulder tendinitis. Two of the most important confounders or effect modifiers for shoulder tendinitis appear to be age and sport activities. Subjects who have been extremely active in sports seem to have an increased risk for shoulder tendinitis and acromioclavicular osteoarthrosis, with those who have been extremely active in sports and also report high exposure to load lifting during work at even greater risk. In other words, sports activities add to the workload on the shoulder and increase the risk for OSDs. Most of the shoulder studies considered the effects of age in their analysis. However, the NIOSH review concluded that it is unlikely that the majority of the positive associations between physical exposure and OSDs are due to the effects of non–work-related confounders, of which age is the most significant.

Pathophysiology

The pathophysiology of OSDs, in particular trapezius myalgia, is uncertain. Two theories have been proposed: the organic or physiologic theory and the psychosocial theory.

The organic or physiologic theory is based on the premise that shoulder pain is secondary to statically sustained contraction of the trapezius. Sustained contractions result in increased intramuscular pressure and decreased blood flow. Ischemic conditions occur when intramuscular pressure exceeds the capillary closing pressure at approximately 30 mm Hg. The increased metabolic demands of the working muscle and the relative ischemia caused by increased intramuscular pressure may contribute to intracellular pH/lactic acid, calcium, and potassium imbalance.

Green et al. reported no significant differences in high-energy phosphate levels between patients with trapezius myalgia and control, whereas Lindman et al. found a significantly lower adenosine triphosphate level in trapezius myalgia patients. In a study of 20 assembly line workers with neck and shoulder pain, Bjelle and colleagues found significantly high levels of muscle enzymes, including creatinine phosphokinase and aldolase, in eight workers without any underlying pathology. ^, The elevated muscle enzyme levels were found to diminish after 2 to 8 weeks of sick leave. In addition, elevated serum creatinine kinase levels have been observed in welders, cash register operators, and assembly line workers but not in control groups consisting of controllers and forklift drivers. The sustained load necessary for light, static work has been theorized to cause severe adenosine triphosphate depletion, increased permeability, and the resultant release of muscle enzymes.

Decreased oxygenated hemoglobin (compared with baseline levels) in response to a UE physical task, was found in cases of symptomatic myalgia patients, but not in healthy controls. Decreased trapezius oxygenated hemoglobin was also observed in patients with trapezius myalgia performing isometric contractures during a computer task.

The level of activity at which a static, isometric contraction of shoulder muscles causes injury is unknown. Several researchers have attempted to identify an endurance limit, defined as the highest force that can be maintained for an “unlimited” period. Jonsson and colleagues suggested that the static load level should always be less than 5% of the maximal voluntary contraction (MVC). In support of this suggestion, Sjogaard and colleagues have shown that muscle fatigue occurs at 5% of MVC after 1 hour of sustained contraction. This endurance was subsequently confirmed by Frey Law and Avin specifically for the shoulder muscles; these authors also provided data to suggest that shoulder muscles were more fatigable than the trunk muscles, which could endure this exertion level for approximately 5 hours. Furthermore, multiple electromyography (EMG) studies have suggested that myalgia patients have abnormally elevated muscle tension. Findings among these patients include (1) higher muscle tension in symptomatic patients, ^, (2) higher muscle tension during sleep, (3) higher muscle tension at the painful site, (4) pain even when static muscle contraction is as low as 2% to 5% of MVC, (5) faster fatigue on the painful side, and (6) shorter muscle endurance. EMG findings that showed decrements in the generation of muscle force during repetitive use have provided evidence of either transient motor unit fatigue or permanent skeletal fiber damage.

One theory for decreased fatigue resistance and force generation in myalgia patients is the “Cinderella hypothesis.” This hypothesis suggests that muscle damage may be mediated by mechanisms related to muscle recruitment. According to this theory, relatively small, low-threshold, type I motor units are persistently activated and loaded. These are the first motor units recruited for low-force, repetitive endurance work. They remain in action throughout low-level contractions. Because they carry a disproportionate burden, they are referred to as Cinderella fibers. Sustained contraction and activation of these motor units cause pain and fatigue and may eventually lead to permanent injury. Muscle fiber damage may ultimately result in interstitial myofibrositis with a persistent reduction in blood flow. Larsson and colleagues performed bilateral open biopsies of the trapezius muscle in 17 patients with chronic myalgia related to static loads during repetitive assembly work and concluded that there was an association between clinical myalgia and the presence of pathologic muscle fibers on histology. Additional muscle biopsy studies have demonstrated degenerated mitochondria and increased glycogen deposits. Fiber structural damage is also accompanied by products of cell inflammation and necrosis, edema, and leakage of intrafiber proteins and enzymes. With dropout of some of the muscle fibers, the overall resistance of the motor unit to fatigue is reduced. Despite all the aforementioned cellular alternations, according to a systematic review performed by De Meulemeester et al., examining the differences between work-related trapezius myalgia patients and healthy controls, no clear differences in muscle morphology and physiology was found.

Clinically, localized fatigue, muscle strain, and pain can occur with very low-level contractions, such as those needed to hold the arms in an elevated posture. The trapezius muscle has been found to be affected by jobs that require static muscle overload. ^{, , ,} For example, a high prevalence of OSDs has been reported among dental care workers; some were 5.4 times more likely to experience symptoms than a control group of pharmacists. This increased risk is considered to be secondary to maintaining an unsupported awkward working posture with cervical flexion of 45 to 90 degrees and shoulder flexion and abduction of more than 30 degrees for extended periods ( Fig. 67.1 ). Excessive scapular elevation as a result of mental stress or workstation design may also contribute to the increased trapezius load. ^,

(A and B) The exceptionally high rate of occupational cervicobrachial disorder among dentists is thought to result from maintaining an awkward posture for extended periods.

The causal relationship between musculoskeletal pain and exposure to cold environment may be explained by several mechanisms. First, cooling was found to induce acute physiologic alternations in the musculoskeletal and neural systems. Second, muscle contraction velocity is decreased with decreasing temperature. Third, reduced motor control is induced by increased activation of antagonist muscles. Fourth, performing repetitive work in cold environment induces enhanced muscle fatigue. These detrimental effects are reduced with acclimatization, and with long-term cold environment exposure, shivering, vasoconstriction, and cold sensation are reduced.

In contrast to the organic or physiologic theory, the psychosocial theory maintains that emotional stress is an etiologic factor in the development of OSDs. The proponents of this theory contend that OSDs occur in jobs that do not involve excessive muscle strain and consequently are not related to overuse but are more a result of psychosocial factors. In a study of 607 metal industry workers, depression and distress symptoms were found to be predictors of low back pain, neck-shoulder pain, and other musculoskeletal complaints. Workers may fear that if they ignore their symptoms, the symptoms will progress and become permanently disabling. The Workers’ Compensation system can contribute to this problem by awarding benefits based on the recognition that cumulative trauma can cause significant disability. In a study of 201 patients with chronic pain, Tait and colleagues found that patients with litigation claims reported pain of significantly longer duration and had significantly greater disability than nonlitigating patients. Bongers and colleagues found that monotonous work , a high-perceived workload , and time pressures were causally related to musculoskeletal symptoms. A newly investigated factor is cognitive demand . Wixted et al. found that increased cognitive demand was related to higher stress in employees and culminated with a higher incidence of shoulder (and lower back) pain. This finding emphasizes the aforementioned distress as a mediator of shoulder pain. In an attempt to address the complex, multifactorial nature of OSDs, Armstrong and colleagues proposed a model that incorporates both the organic and the psychosocial theories. In this model, exposure refers to external factors, such as work requirements. The external exposure produces an internal dose , which in turn disturbs the internal state of the individual. Such disturbances may be mechanical, physiologic, or psychologic and in turn evoke a certain response , mechanical and/or metabolic changes, that occurs at the tissue level. Finally, capacity , which can be either physical or psychologic, refers to the ability of the individual to resist destabilization after various doses of exposure. This model provides a framework to explain the relationship between work exposure factors and the different responses that occur, both psychologic and physiologic. A similar model was adopted by the panel of the National Research Council.

Several classifications of OSDs have been proposed. A five-grade classification system was developed by the OCD committee of the Japanese Association of Industrial Health ( Box 67.1 ). This system includes tendinitis as well as several neurologic and vascular symptoms that often accompany occupational shoulder pain. A simplified three-stage system was developed by the Occupational Repetition Strain Advisory Committee in Australia. This system is based on the persistence of the symptoms and interference with work ( Box 67.2 ).

Luck and Andersson proposed a pathophysiologic grading system that is a modification of the Australian classification ( Box 67.3 ). This focuses on myogenic pain. The pathophysiologic basis for pain in grade I is metabolic changes that occur in response to a sustained static load. Progression to grade II involves pain that does not resolve overnight and is secondary to muscle inflammation and early interstitial fibrosis. Grade III is characterized by progression to severe myopathy with interstitial fibrosis.

Management

Evaluation of a patient with a suspected OSD involves a thorough history and physical examination. The hallmark of OSDs is musculoskeletal pain or discomfort that occurs on the job. Symptoms will vary based on the patient’s specific diagnosis. Usually, the underlying diagnosis will fall into one of the following categories: myalgia, tendon disorder, or bursitis. In a prospective study of 204 workers with occupationally related upper limb or neck pain, Sikorski and colleagues found that a discrete MSD existed in 58% of cases.

A large proportion of patients diagnosed with an OSD will have signs and symptoms consistent with trapezius myalgia. Symptoms of trapezius myalgia typically include muscle fatigue and stiffness accompanied by subjective pain or headaches. On examination, patients may demonstrate muscle tightness, increased tone, and multiple trigger points. Occasionally, subtle decreases in range of motion will be seen. Risk factors for myalgia are unvarying stationary positioning of the shoulder and neck, along with prolonged static loading.

Neurologic and vascular conditions such as cervical radiculopathy, TOS, and Raynaud phenomenon could also be associated with OSDs. Congenital or developmental deformities of the shoulder or cervical spine can predispose a worker to OSDs and may need to be addressed. Musculoskeletal neoplasms, both benign (such as osteochondroma) and malignant, can be found about the shoulder girdle and should be considered. Referred sources of pain from other organ systems, including the cardiac, pulmonary, and gastrointestinal systems, should be ruled out, and in relevant patients, further investigation is warranted.

Razmjou et al. investigated the efficacy of imaging investigation as part of a newly developed Early Shoulder Physician Assessment (ESPA) program. Their program’s algorithm was structured as follows. Every patient who sustained a shoulder injury underwent a plain radiograph and shoulder sonography arranged by the patient’s primary care physician within 16 weeks. If a clear indication for surgical consultation was established (full-thickness rotator cuff tear, osseous impingement, traumatic superior labral tear, or shoulder instability), the patient was referred directly to a surgical specialty program. If an initial nonoperative diagnosis was suspected (tendinitis, bursitis, partial-thickness rotator cuff tear, degenerative labral tear, or contusion), patients were referred to the ESPA program for further timely clinical investigation to identify potential surgical candidates. In this study, 24% of the workers were referred to ESPA for further evaluation of their shoulder problem. These further evaluation studies have changed the diagnosis or management in 32% of patients and 49% required surgery. The diagnosis for the majority of patients who underwent further evaluation by ESPA and were subsequently referred to surgery were based on the cheaper sonography (71%), the more costly magnetic resonance imaging (56%), or both.

Successful management of the patient requires a multidisciplinary approach. Treatment of physical disorders, psychosocial evaluation, and an appropriate understanding of the work demands are all equally important. Feuerstein and Hickey suggested the use of a multidisciplinary approach that focuses on physical, ergonomic, and psychologic factors. They noted that patients treated with a multidisciplinary approach had a significantly higher rate of return to work than did those treated with usual care. Johansson and colleagues reported a significant decrease in sick leave, pain intensity, and analgesic use in patients treated with a cognitive-behavioral pain management program. The treatment team included a clinical psychologist, physical therapist, occupational therapist, physical education teacher, vocational counselor, physician, and nurse.

The medical/surgical management of rotator cuff disease, biceps tendonitis, bursitis, and adhesive capsulitis has been covered elsewhere in this textbook. The management of myalgia consists of modalities such as the application of ice and heat. Range-of-motion exercises together with strengthening exercises should also be instituted. Antiinflammatory agents may be used in moderate cases, supplemented with low doses of tricyclic antidepressants in more refractory cases. A recent evidence-based systematic review provided evidence for the efficacy of conservative treatments in the management of rotator cuff tendonitis, biceps tendonitis, and trapezius myalgia.

Changes in the workplace can also be beneficial. Introducing more frequent rest breaks and altering the posture and exertion of force at work can help to prevent or alleviate OSDs. For example, Hallman and colleagues reported that workers who sat for approximately 9 hours a shift were almost three times more likely to report high neck and shoulder pain intensity than those who sat for more moderate durations (approximately 7 hours). Mekhora and colleagues showed that simple ergonomic interventions, such as adjusting monitor height, seat height, and keyboard height could help to reduce symptoms in patients suffering from trapezius myalgia. This, in turn, resulted in less lost work time and higher productivity.

Finally, the psychosocial element of OSDs should not be underestimated. High job demands, leading to distress and worry, predict future neck/shoulder pain. It has been suggested that high job demands may increase strain and subsequently increase muscle activity and tension or other physiologic reactions that put individuals at a greater risk for developing neck/shoulder pain. ^, Most theoretical models that describe the relationship between occupational factors and musculoskeletal problems, such as the dose-response or biopsychosocial models, assume that psychosocial stressors at work lead to MSD by eliciting physiologic responses (e.g., by increasing the individual’s muscle tension, hyperventilation). Thus the psychologic state resulting from the experienced occupational stressors initiates a bodily response that over time may manifest in the form of health problems. Eijckelhof and colleagues found some support for this view: applying simulated workplace stressors (cognitive/emotional stress, work pace, and precision) resulted in increased neck-shoulder and forearm muscle activity; decreased control was not a significant predictor. These elements at work require work organizational changes. In addition to medical management, more aggressive approaches to improve sense of control over symptoms and functional loss, avoidance of unnecessary surgery, assistance to patients in managing residual pain and stress, and attention to employer-employee conflicts are all important in preventing prolonged work disability secondary to UE disorders.

Primary prevention

For primary prevention, NIOSH has recommended a tiered hierarchy of controls in which engineering changes are viewed as the first preference, administrative changes are a second preference, and personal protective equipment is the last choice.

The increase in reported cases of MSD and the increase in Workers’ Compensation costs in the United States have prompted some regulatory efforts. Until 1991, attempts to standardize or control exposure to MSD risk factors were limited to specific tasks or situations, such as working with video display terminals (VDTs) or exposure to vibration. After high-profile citations, OSHA issued guidelines in 1993 for managing ergonomics programs. These guidelines were limited to the meatpacking industry, an industry targeted because of a high incidence and severity of MSDs of the UEs. OSHA further emphasized that these guidelines were not a standard or regulation. OSHA’s approach focused on ergonomics as a process. The guidelines consisted of the following: a discussion of the importance of management commitment and employee involvement, recommended program elements, and detailed guidance and examples for these elements. NIOSH incorporated most of these program elements in its guidelines for setting up an ergonomic program.

OSHA published its Ergonomics Program Standards in the Federal Register (65: 68282–68870) November 14, 2000, but it was rescinded by Congress and President in February 2001. In 2002 OSHA declared its intention to address ergonomics in the work environment in a multitiered plan that was to include a combination of enforcement measures, workplace outreach, research, compliance assistance activities, and industry-targeted voluntary guidelines. To date, OSHA has issued guidelines for meat and poultry processing, foundries, shipyards, nursing homes, and retail grocery stores (see https://www.osha.gov/SLTC/ergonomics ). The plan is designed to reduce musculoskeletal injuries and focuses on prevention. Rather than deploy specific ergonomic regulations, the enforcement relies still on the General Duty Clause, OSHA Act of 1970, Section 5(a)(1), that states that the employer is to furnish each of his or her employees a place of employment that is free of recognized hazards that are causing or likely to cause death or serious physical harm to employees.

In the absence of federal regulations regarding the prevention of WMSDs, some local initiatives attempted to fill the gap, with varying degrees of success. For example, the Worker’s Compensation Board of Nova Scotia published an eight-step resource manual for prevention of workplace injuries, focusing on creation of a health and safety policy; employer’s recognition of own responsibilities; establishment of a health and safety program; creation of a joint health and safety committee; hazards control (e.g., ergonomic and physical) by recognition, inspection follow-up and monitoring; leadership and training; and establishment of a return to work program.

Educating the employers and employees and providing them with the information on both ergonomic requirements and how to prevent risks associated with workplace requirements were useful tools for the prevention of nontraumatic shoulder disorder.

In many workplaces, ergonomic adjustments have been introduced to prevent or alleviate musculoskeletal pain. However, these adjustments may not suffice, and physical conditioning programs were developed to increase the worker’s physical capacity. These programs used resistance training with weights and resistance elastic bands, which have been considered to reduce pain and disability and improve strength. However, studies investigating these modalities lack convincing evidence of efficacy.

Secondary prevention

To estimate the biomechanical load on the body, it is important to know the locations of the manual controls and where materials, parts, and tools are stored and used, as well as the forces required to handle the work objects. Whether estimated as forces through biomechanical models or as muscle tension by EMG measurements, the workload needs to be compared with the individual’s strength. Anthropometric tables provide some information on the strength of joints and hands by age and occupation. The analyst may either select a value from the literature that corresponds to the population of interest or use data provided by functional evaluation of a specific individual.

In secondary prevention the control strategies focus on individual patients. Ergonomic accommodations for employees with MSDs fall under the category of secondary prevention. Accommodations are interventions intended to reduce exposure to factors that limit the activities of an individual with impairment. More detailed knowledge is required about the residual abilities and limitations of the individual. Design for an individual requires a functional assessment that specifies that person’s strength limits. The clinical evaluator should work closely with the designer during and after design implementation to ascertain that the job can be performed without risk of injury or reinjury.

Three principal means of accommodating impaired or disabled employees may be implemented: client matching, job restructuring, and job modifications.

Client matching , a form of employee selection, is the simplest and most effective way to return a person with a disability to work. It involves ensuring that the job requirements are consistent with the present abilities of the employee. If an employee cannot return to the previous job, an alternative job is found that can be performed without risk of reinjury. This strategy does not attempt to fit the job to the worker, because it requires hardly any modifications to the job.

Job restructuring is an administrative control for reducing exposure to a risk factor. Two techniques have been proposed for reducing static load on the shoulder: the introduction of rest breaks and job rotation.

Many studies have attempted to find the optimal rest break frequency, duration, and content to prevent shoulder disorders caused by static, repetitive work. Many of the studies have focused on work at VDTs. NIOSH has recommended a 15-minute rest break after 1 to 2 hours of VDT work. Similarly, the Swedish Work Environment Authority recommended a 5- to 10-minute break/pause for every hour of computer work in ergonomically well-designed places. For less suitably designed workplaces, a more frequent recess is recommended. The optimal frequency and length of breaks will depend mainly on the type of work that is being performed, the length of time that it can be sustained, and the posture or load that is held. Breaks can be active, with static load being relieved by dynamic muscle work. Short exercise and stretch periods are active breaks, and they seem to be more effective than those that involve complete rest.

Static loading of the shoulders can be avoided by rotating from one job to another. This technique requires careful assessment of task demands to ensure that the shoulders will be relieved occasionally. Although this technique is common in manufacturing industries, it is difficult to introduce in office work, which involves fewer tasks with sufficient variability. However, workers may arrange their tasks so that the tasks will periodically take them away from their workstation; for example, they may interrupt typing activities with photocopying, filing, or other duties. This technique can be viewed as a form of active break rather than formal job rotation.

In secondary prevention, job restructuring entails assigning the impaired employee to restricted duties. For example, restructuring the job by assigning heavy lifting tasks to another person would enable a worker with an OSD or low back pain to work while recovering from the injury.

Job modifications and redesign usually involve the use of assistive technology to enable individuals to perform the required tasks. Other employees may also benefit from similar devices. Occasionally, some tasks can be eliminated during the process of introducing new technology.

A future direction for primary or secondary prevention of posture-related shoulder injuries, usually, due to excessive shoulder abduction and flexion and overexertion, is the utilization of an exoskeleton. Schmalz et al. performed an electromyographic evaluation of shoulder muscles while using an exoskeleton and found a significant reduction in the mean EMG amplitude and muscle fatigue index of all assessed muscled when exoskeleton was used. The authors deduced that the drastic reduction in EMG amplitudes with exoskeleton use correlated with a reduction in activated muscle fibers, implying reduced muscle requirement with the use of an exoskeleton. This reduction in deltoid muscle EMG amplitude may lead to a reduced glenohumeral joint compression force and may be considered as having an unloading effect. However, large-scale clinical studies should be performed to determine the true clinical effect the use of exoskeleton may produce.

Case examples

The following are examples of two cases involving the secondary prevention of OSDs. The first outlines the medical management of a clerical worker with an OSD, and the second demonstrates the application of the ergonomic solving process in secondary prevention.

Case 2

A 43-year-old woman complained of pain in her right shoulder, elbow, and index finger. She was living in a suburban area, divorced without children. She had been experiencing the symptoms for approximately 6 months, since a few weeks after starting working on the assembly line of a plant that produced electric engines for adjusting car seats. At first, the symptoms appeared during the second part of her shift work and usually disappeared on the weekend. When a new engine was introduced, production quotas increased. The symptoms became more severe and frequent, and she sought medical care. OSD and lateral epicondylitis were diagnosed. She was on leave for 1 week but, because she was being paid by the piece (i.e., by the number of engines she worked on), she preferred to return to work part-time. She experienced difficulty with shopping, dressing, and washing. OSHA had cited the plant for various violations, including underreporting of WMSDs. A review of the recordable cases revealed that the incidence rate of WMSDs at the plant was 13 times higher than the national rate for the manufacturing sector.

As part of medical management of the case, an ergonomic assessment of the workstations on the assembly line was conducted. The patient was observed at her position while she inserted an element into the assembled fixture with a magnetic clip inserter. The results of the assessment are summarized in Box 67.4 . Detailed analysis revealed that the task required six operations with the right hand, one of which entailed an awkward posture, exertion of force, and repetitive motion. While using the clip inserter, the right shoulder had to be elevated; the arm was abducted more than 45 degrees and stabilized to enable the transmission of force to the hand tool through the forearm and wrist. The hand tool could not be grasped in a power grip and needed to be steered with the index finger. The operation also required leaning forward while flexing the neck to see the insertion.

BOX 67.4

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