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Occupational ergonomics and injury prevention.

Ergonomics is the study of people at work. The current focus is on the prevention of work-induced musculoskeletal injuries through the application of sound ergonomic principles. This chapter has briefly outlined ergonomics and its history, has described low back pain and upper extremity cumulative trauma disorders from an ergonomic perspective, and has discussed control and prevention approaches for a few scenarios. Ergonomic principles are based on a combination of science and engineering and a thorough understanding of human capabilities and limitations. When these principles are applied to the design of a job, task, process, or procedure, the incidence and severity of musculoskeletal injuries decrease. In many cases productivity and morale also improve. Workers are spared suffering, and employers are spared costs. It is hoped that this discussion will encourage more health, safety, and business professionals to learn about and apply ergonomics in their workplaces for the improvement of the worker, product, and business. Finally, many additional epidemiologic studies on the individual and joint effects of the CTD risk factors are needed. The knowledge gained from these studies will promote the more effective application of ergonomic principles to reduce worker suffering, improve products, and reduce costs.

Back Pain↗

Work-related symptoms and checkstand configuration: an experimental study.

Supermarket checkers are known to be at risk of upper-extremity cumulative trauma disorders. Forty-two experienced checkers checked a standard "market basket" of items on an experimental checkstand. The counter height could be adjusted (high = 35.5, low = 31.5 inches), and the pre-scan queuing area length (between conveyor belt and laser scanner) could be set to "near" or "far" lengths. Each subject scanned under the high-near, high-far, low-near, and low-far conditions in random order. Seven ordinal symptom scales were used to describe comfort. Analysis showed that both counter height and queuing length had significant effects on symptoms. Furthermore, the height of the subject affected the degree and direction of the impact of the checkstand configuration differences. The study suggests that optimization of design may be experimentally evaluated, that modification of postural as well as frequency loading may be beneficial, and that adjustability for the individual may be advisable.

Adult↗

[Risks for construction workers: analysis of the upper limb posture].

Our work focuses on the analysis of risks associated with onset of cumulative trauma disorders (CTD) among construction workers, and the goal is to evaluate the different degree of involvement of articular segments of the upper limbs. A number of workers with different qualification were analyzed using the OCRA Index and check-list protocols, applied to highly or moderate repetitive activities. In order to evaluate the involvement of the various upper limbs segments, we have extracted the information contained in the "posture section" of the protocols, before they are grouped together in the final posture risk value, and analyzed them considering the observed working activities. We obtained an "involvement index" related to any of the upper limb segments, highlighting the information about local involvement during the various phases of work. This "involvement index" may help in analyzing and evaluating the ergonomic risk referring to each articular segment during activity, and can be useful in the analysis and prevention of work related CTDs.

Arm↗

Influence of VDT monitor positions on discomfort and performance of users with or without bifocal lenses.

The difficulty of video display terminal users with bifocal lenses through a traditional workstation increases the complaints and risks for upper extremity cumulative trauma disorders. Furthermore, the regular and no lens users also have problems with traditionally designed workstations over prolonged periods of video display terminal use. A study was conducted on 14 subjects to investigate the effect of computer monitor location for video display terminal users with or without bifocals on subjective assessment and performance. The two monitor locations were 15 degrees and 40 degrees below horizontal eye level. The experimental task consisted of reading words from computer screens and typing them from the reverse side to the next column. Each experimental session lasted one hour. Males with bifocal lenses had less discomfort in the neck, shoulders, forearms, and wrists, less tiredness and eyestrain and higher performance with a 40 degrees angle monitor than with a 15 degrees angle monitor. A similar conclusion has been reached for females. Users with bifocal lenses had significantly higher neck discomfort and lower performance than nonbifocal users. The 40 degrees angle monitor caused less neck discomfort than the 15 degrees angle monitor did. Overall, females had less physical discomfort, less tiredness, and higher performance than males.

Adult↗

Wrist motions in industry.

Cumulative trauma disorders (CTDs) are disorders of the body's tendons and nerves due to repeated exertions and excessive movements. Workers in industrial tasks who have to move their hands and wrists repeatedly and/or forcefully are susceptible to CTDs. One of the major research voids in the study of occupational wrist CTDs is the lack of quantification of the relationship between the known kinematic risk factors, such as wrist angle and repetition, and CTD risk. A quantitative surveillance study was performed in industry in which workers' three-dimensional wrist motions were monitored on the factory floor. A total of 40 subjects from eight industrial plants participated in this study (20 workers in each of two risk groups, low and high). The wrist motion parameters that were monitored for each subject were position, angular velocity, and angular acceleration measures in each plane of movement (radial/ulnar, flexion/extension, and pronation/supination). Descriptive analyses of these measures indicated that generally the mean of the high-risk subjects was larger in magnitude than that of their low-risk counterparts. However, only the velocity and acceleration parameters resulted in significant differences between low- and high-risk groups. These results demonstrate the importance of dynamic components in assessing CTD risk.

Adult↗

Quantitative biomechanical analysis of wrist motion in bone-trimming jobs in the meat packing industry.

This study was motivated by the serious impact that cumulative trauma disorders (CTDs) of the upper extremities have on the meat packing industry. To date, no quantitative data have been gathered on the kinematics of hand and wrist motion required in bone-trimming jobs in the red-meat packing industry and how these motions are related to the risk of CTDs. The wrist motion of bone-trimming workers from a medium-sized plant was measured, and the kinematic data were compared to manufacturing industry's preliminary wrist motion benchmarks from industrial workers who performed hand-intensive, repetitive work in jobs that were of low and high risk of hand/wrist CTDs. Results of this comparison show that numerous wrist motion variables in both the left and right hands of bone-trimming workers are in the high-risk category. This quantitative analysis provides biomechanical support for the high incidence of CTDs in the meat packing industry. The research reported in this paper established a preliminary database of wrist and hand kinematics required in bone-trimming jobs in the red-meat packing industry. This kinematic database could augment the industry's efforts to reduce the severity and cost of CTDs. Ergonomics practitioners in the industry could use the kinematic methods employed in this research to assess the CTD risk of jobs that require repetitious, hand-intensive work.

Biomechanical Phenomena↗

Supermarket checker motions and cumulative trauma risk.

The relationship between specific motions and symptoms consistent with upper extremity cumulative trauma disorders (UECTDs) was investigated in 50 supermarket checkers. Each completed a questionnaire concerning UECTD symptoms; four composite symptom indices were derived: any arm symptoms, hand-wrist-lower arm (S-DIST), upper arm, and symptoms specifically associated with carpal tunnel syndrome (S-SPC). Each participant was videotaped on at least two occasions while performing checking work. Analysis of these tapes assigned each subject a composite motion index for each of the following motions: wrist flexion, wrist extension, body (lumbar) flexion, pronation, grip type, and tendency to lift objects. "Positive" symptom status was defined by a score in the upper quartile for the symptom index. Relationships between an individual's motion indices and symptom indices were analyzed by determining the percent of subjects "positive" for symptoms in each quartile of motion index, by rank correlation, and by regression of symptom scores on principal components of motions. Trends toward relationship of wrist flexion and extension, lumbar flexion, and pronation with S-DIST and S-SPC were noted. Principal components regression confirmed that extension and flexion were related to these two symptom outcomes. This study suggests that postural loading can be determined on an individual basis in a meaningful fashion and that interventions that decrease such loading may be beneficial. It supports the role of certain repetitive motions as causes of UECTD symptoms.

Adult↗

Data entry workers perceptions and satisfaction response to the "stop and stretch" software program.

Cumulative Trauma Disorder (CTD) is a collection of chronic musculoskeletal disorders caused by frequent, sustained, and repetitive movements, most notably by computer usage at the workplace. A computer based break reminder program (Stop and Stretch) has been developed and installed to prevent CTDs caused by prolonged computer usage at the workplace. We investigated users' opinions to the Stop and Stretch program at their work place. 19 computer users were recruited as the subjects of the study. We conducted a survey after all the subjects used the Stop and Stretch program for one month. Among the nineteen subjects, 52.5% or 10 noticed a difference of symptoms after using the program; 63.3% or 12 thought the program had positive effect on their productivity; 100% or all 19 thought the program was easy to follow; 100% or all 19 thought it was helpful; 94.7% or18 were satisfied with the program; and the same value would recommend the program to others. When grouped into those who had prior experience with using stretch and exercise as part of their work routine15 subjects had no prior experience; and 14 participants within that group were satisfied or very satisfied with the program; 93.3% or 14 would recommend it to co-workers; and over half of those 15 thought the program is easy to use. The study provided insight to the response to using "stretch break software" and provided indicators of satisfaction with the Stop and Stretch program and that the program had sufficient usability and acceptance within a workplace setting which might be applied in other work settings similar to these.

Consumer Behavior↗

Musculoskeletal symptoms among electricians.

This study ascertained the presence of musculoskeletal symptoms among electricians, in order to evaluate the prevalence of cumulative trauma disorders (CTD) in this population. We adapted the CTD surveillance questionnaire used by National Institute for Occupational Safety and Health (NIOSH) to assess the prevalence of neck, shoulder, elbow, hand/wrist, back, and knee symptoms in the year prior to the survey. Questionnaires were completed by 308 apprentices and journeymen enrolled in training classes at the local union hall. The participants were relatively young individuals, and 86% of the participants were currently working as electricians. Participants reported a high prevalence of symptoms which occurred more than three times during the past year or which lasted more than 1 week. Back symptoms and hand/wrist symptoms were experienced most frequently, by about half the population, while elbow symptoms were reported by only 15% of participants. Symptom prevalence was lower, but still notable, when defined as symptoms which had occurred at least once a month or lasted more than a week in the past year. Eighty-two percent of participants reported at least one musculoskeletal symptom using the most inclusive definition, while 57% reported two or more symptoms. This survey highlights that: 1) low back discomfort is common in young construction workers, and resulted in medical care, missed work, or light duty for almost 35% of the participants; 2) neck discomfort is also very common and required doctor visits or work modification for almost one quarter of the participants; 3) these construction workers continued to work with symptoms that are classifiable as a CTD; and 4) history of injury is correlated with the subsequent prevalence of musculoskeletal symptoms.

Accidents, Occupational↗

Muscular dysfunction elicited by creep of lumbar viscoelastic tissue.

The biomechanics, histology and electromyography of the lumbar viscoelastic tissues and multifidus muscles of the in vivo feline were investigated during 20 min of static as well as cyclic flexion under load control and during 7 h of rest following the flexion. It was shown that the creep developed in the viscoelastic tissues during the 20 min of static or cyclic flexion did not fully recover over the 7 h of following rest. It was further seen that a neuromuscular disorder with five distinct components developed during and after the static and cyclic flexion. The neuromuscular disorder consisted of a decreasing magnitude of reflexive EMG from the multifidus upon flexion as well as of superimposed spasms. The recovery period was characterized by an initial muscle hyperexcitability, a slowly increasing reflexive EMG and a delayed hyperexcitability. Histological data from the supraspinous ligament demonstrate significant increase (x 10) in neutrophil density in the ligament 2 h into the recovery and even larger increase (x 100) 6 h into the recovery from the 20 min flexion, indicating an acute soft tissue inflammation. It was concluded that sustained static or cyclic loading of lumbar viscoelastic tissues may cause micro-damage in the collagen structure, which in turn reflexively elicit spasms in the multifidus as well as hyperexcitability early in the recovery when the majority of the creep recovers. The micro-damage, however, results in the time dependent development of inflammation. In all cases, the spasms, initial and delayed hyperexcitabilities represent increased muscular forces applied across the intervertebral joints in an attempt to limit the range of motion and unload the viscoelastic tissues in order to prevent further damage and to promote healing. It is suggested that a significant insight is gained as to the development and implications of a common idiopathic low back disorder as well as to the development of cumulative trauma disorders.

Animals↗

Soft tissue disorders of the upper extremities.

The incidence of occupationally induced cumulative trauma disorders of the upper extremities appears to be in the rise in the United States. Such disorders account for a significant amount of human suffering, loss of productivity and economic burden. The author defines the problem and its etiology, reviews appropriate screening procedures and the diagnosis, summarizes treatment approaches, and concludes with a discussion of preventative measures that should be considered.

Arm Injuries↗

An Approach to Work-Related Disorders of the Upper Extremity.

Management of work-related musculoskeletal disorders has been frustrating for the orthopaedist. The so-called cumulative-trauma disorders have few objective findings, and patients often do not respond to well-established orthopaedic treatments, both nonsurgical and surgical. In some areas of the country the rate of reimbursement is low; that factor, combined with the excessive paperwork and the legal burden, discourages many orthopaedists from treating patients with these conditions. However, the incidence and cost of work-related disorders continue to increase, and the orthopaedic community is being called on to help understand their etiology and to attempt to control the "epidemic" that has significantly affected the survival of certain industries. The authors review the current orthopaedic and occupational medicine literature and suggest a management approach that has been found effective in reducing both costs and disability due to these disorders.

Journal Article↗

Biomechanics and electromyography of a common idiopathic low back disorder.

STUDY DESIGN: In vivo feline preparation groups loaded into lumbar flexion at different magnitudes and an unloaded control group. OBJECTIVE: To demonstrate that a static, constant load flexion of the lumbar spine results in a complex neuromuscular disorder. SUMMARY OF BACKGROUND DATA: Epidemiology suggests that static lumbar flexion is a cause of low back disorders. There is little direct experimental evidence describing the physiologic and biomechanical processes that elicit the disorder. Recent evidence shows that static flexion of the spine under constant displacement results in muscular spasms and a prolonged recovery period. The response of the spine to flexion under constant load of various magnitudes (as opposed to constant displacement) is not known. It was hypothesized that static lumbar flexion under constant load may elicit creep in spinal ligaments, discs, etc., causing microdamage and development of a neuromuscular disorder. METHODS: The lumbar spine of the feline was subjected to 20 minutes of constant load static flexion at physiologic load intensities from light to heavy while creep of lumbar viscoelastic tissues and EMG from the multifidus muscles of L3-L4 to L5-L6 were recorded. Recordings were continued over a 7-hour rest period after the static flexion was terminated. RESULTS: Spasms and decreasing reflexive EMG were evident during the loading period, and a transient surge of EMG activity occurred at the beginning of the rest period. A second surge of EMG activity was seen 3-4 hours later. The four components of the neuromuscular disorder were present regardless of the load magnitude. A model was developed to quantify the disorder. CONCLUSION: A four-component neuromuscular disorder was elicited by a 20-minute constant load static flexion even when very light loads were applied. The disorder was elicited by creep of the viscoelastic tissues, which resulted in spasms and muscular hyperexcitability lasting for >24 hours. Although the disorder was transient, the physiologic and biomechanical principles associated with its development could also explain cumulative trauma disorders.

Animals↗

Work to rest durations ratios exceeding unity are a risk factor for low back disorder; a feline model.

Low back disorders are prominent among the work force engaged in static anterior flexion during the workday. As a continuing part of a long-term research aimed to identify the biomechanical and physiological processes and corresponding risk factors leading to such cumulative trauma disorder (CTD), we ventured to assess the effect of rest and the work-to-rest duration ratios that may prevent CTD. Three groups of the feline model were subjected to three load/rest paradigms: two 30 min loading periods spaced by 10 min rest in Group I, two 30 min loading period spaced by 30 min rest in Group II and one 60 min loading period for Group III. The cumulative loading duration in the three groups was 60 min. Each of the groups were allowed 7h of rest while monitoring EMG and lumbar viscoelastic tissue creep each hour. The results demonstrate that for two 30 min load periods with a 30 min in between rest, an acute neuromuscular disorder was not present whereas for two 30 min loading with a 10 min rest it was. Similarly, for a 60 min loading with long-term rest, the disorder was present. Post hoc Fisher analysis demonstrated significant differences in the delayed hyperexcitability between the first and second group (P<0.0001) and the third and second (P<0.0001) group. Statistical difference in the displacement data of the three groups was not present. ANOVA showed a significant effect of time post-loading (P<0.0001 and different rest durations (P<0.0001) on the EMG data during the 7h recovery. The new data allow us to conclude that a work-to-rest duration ratio of 1:1 can prevent the development of CTD as long as the work periods are not too long (<60 min). Longer static flexion durations do not respond favorably to rest even if it is of equal or longer duration. It is suggested that appropriate durations of rest may be a viable tool to avert CTD in a certain range whereas long static flexion durations should be avoided at all cost.

Animals↗

Work-related musculoskeletal disorders.

Work-related musculoskeletal disorders continue to be extremely common and to present an important challenge to clinicians. Debate regarding terminology and case definitions has discouraged practitioners from aggressively approaching the diagnosis and management of these conditions. Considerable progress has, however, been made recently. Previously more commonly referred to as repetitive strain injuries or cumulative trauma disorders, the new term work-related musculoskeletal disorders has fewer etiological implications. These disorders, affecting the back, lower limbs, and especially upper limbs and neck, can be extremely costly if not addressed appropriately. Generally resulting from a combination of physical factors (including repetition, force, and awkward postures) as well as other workplace environmental or organizational factors (including excessive work rates or durations, inadequate breaks, and a variety of psychosocial workplace characteristics), work-related musculoskeletal disorders can often be remediated when these factors are appropriately assessed and addressed. Clinicians must play a positive role in ensuring that this approach prevails.

Humans↗

The use of turnover rate as a passive surveillance indicator for potential low back disorders.

Passive surveillance techniques which rely only on injury reporting to locate ergonomic problems within a facility may not be sensitive enough to identify all jobs that place a worker at risk of low back disorder. The current study examines whether turnover rate data provide useful input to a passive surveillance approach. It is hypothesized that the turnover of employees through individual jobs, when not attributable to differential pay scales within a facility, is likely to indicate the presence of ergonomic hazards associated with low back cumulative trauma disorders. This study used the database and multiple logistic regression model developed by Marras et al. (1993) to evaluate this hypothesis. Two data sets were evaluated with the model to determine whether jobs with turnover resemble those with a high historical risk of LB-CTD. The first data set contained trunk motion and workplace data from jobs in which there had been turnover but there were no incidents of LB-CTD. When comparing these data to truly low risk jobs (no LB-CTD incidents or turnover), the model yielded an odds ratio of 5.2. This moderate odds ratio indicates that many of the jobs with turnover have characteristics similar to those found in high LB-CTD risk jobs. The second data set included jobs with turnover and moderate LB-CTD incident rates. The model's resulting odds ratio of 11.0 indicates that jobs with moderate incident rates and turnover are very similar to jobs with a high LB-CTD risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthropometry↗

Unusual occupational rheumatologic and musculoskeletal disorders.

Musculoskeletal disorders are among the most common clinical occupational problems, but occupational rheumatologic diseases are among the rarest. The identification of one or more cases of unusual diseases or epidemiologically unusual presentations must alert the clinician to the possibility of group exposure and risk and emphasizes the need to explore these using the model of "sentinel health event." Cumulative trauma disorders, including thoracic outlet syndrome and reflex sympathetic dystrophy syndrome, and occupational rheumatologic disorders of other etiology (Raynaud's phenomenon, scleroderma, fluorosis, osteomalacia, aseptic necrosis, and Caplan's syndrome) are reviewed.

Humans↗