Prevención de síntomas visuales y músculo-esqueléticos asociados al uso de ordenador en el trabajo / Workplace interventions to prevent musculoskeletal and visual symptoms and disorders among computer users: A systematic review

Antecedentes: La literatura científica sobre el efecto de las intervenciones en el puesto de trabajo, en la compensación de un defecto refractivo y en la conducta sobre los síntomas músculo-esqueléticos y visuales en los usuarios de ordenador, es amplia y heterogénea. Método: Se realizó una revisión sistemática de la literatura como la mejor síntesis de la evidencia para abordar la siguiente cuestión general: ¿Tienen las intervenciones en trabajadores de oficina que son usuarios de ordenador un efecto sobre la salud músculo-esquelética o visual? También se realizó una evaluación de intervenciones específicas. Resultados: La búsqueda inicial identificó 7.313 artículos que se redujeron a 31 estudios tras analizar contenido y calidad. En general, se observó un nivel mixto de evidencia para la pregunta general. Se observó una evidencia moderada de que: (1) la adaptación de los puestos de trabajo no tenía ningún efecto, (2) tampoco la realización de descansos y ejercicio y (3) utilizar dispositivos alternativos a los ratones convencionales sí tenía un efecto positivo. Para el resto de intervenciones se observó una evidencia del efecto mixta o insuficiente. Conclusión: Se encontraron pocos estudios de alta calidad que examinaran los efectos de las intervenciones en oficinas sobre los problemas musculo-esqueléticos y de la salud visual

No disponible

Dairy farm worker exposure to awkward knee posture during milking and feeding tasks.

Musculoskeletal disorders are common among agricultural workers, particularly among dairy farm workers. Specifically, dairy farm workers have been identified as being at risk for knee osteoarthritis. Physical risk factors that may contribute to knee osteoarthritis include awkward postures of the knee, such as kneeling or squatting. The purpose of this study was to quantify exposure to awkward knee posture among dairy farm workers during milking and feeding tasks in two common types of milking facilities (stanchion and parlor). Twenty-three dairy farm workers performed milking and feeding tasks; 11 worked in a stanchion milking facility, and 12 worked in a parlor milking facility. An electrogoniometer was used to measure knee flexion during 30 min of the milking and feeding tasks. Milking in a stanchion facility results in a greater duration of exposure to awkward posture of the knee compared with milking in a parlor facility. Specifically, the percentage of time in >or=110 degrees knee flexion was significantly greater in the stanchion facility (X = 17.7; SE 4.2) than in the parlor facility (X = 0.05; SE 0.04; p

Effect of concrete block weight and wall height on electromyographic activity and heart rate of masons.

Work-related musculoskeletal disorders (MSDs) are common among construction workers, such as masons. Few interventions are available to reduce masons' exposure to heavy lifting, a risk factor for MSDs. The purpose of this study was to determine whether one such intervention, the use of light-weight concrete blocks (LWBs), reduces physiological loads compared to standard-weight blocks (SWBs). Using a repeated measures design, 21 masons each constructed two 32-block walls, seven courses (rows) high, entirely of either SWBs or LWBs. Surface electromyography (EMG), from arm and back muscles, and heart rate was sampled. For certain muscles, EMG amplitudes were slightly lower when masons were laying LWBs compared to SWBs. Upper back and forearm extensor EMG amplitudes were greater for the higher wall courses for both block weights. There were no significant differences in heart rate between the two blocks. Interventions that address block weight and course height may be effective for masons.

A randomised controlled trial of postural interventions for prevention of musculoskeletal symptoms among computer users.

AIMS: To examine the effect of two workstation and postural interventions on the incidence of musculoskeletal symptoms among computer users. METHODS: Randomised controlled trial of two distinct workstation and postural interventions (an alternate intervention and a conventional intervention) among 376 persons using computer keyboards for more than 15 hours per week. The incidence of neck/shoulder symptoms and hand/arm symptoms during six months of follow up among individuals in the intervention groups was compared to the incidence in computer users who did not receive an intervention (comparison group). For individuals in the intervention groups, study staff adjusted workstations, where possible, and trained individuals to assume the intervention postures. Individuals reported musculoskeletal symptoms in a weekly diary. Participants who reported discomfort intensity of 6 or greater on a 0-10 visual analogue scale or who reported musculoskeletal symptoms requiring use of analgesic medication were considered symptomatic. RESULTS: There were no significant differences in the incidence of musculoskeletal symptoms among the three intervention groups. Twenty two (18.5%) participants in the alternate intervention group, 25 (20.2%) in the conventional intervention group, and 25 (21.7%) in the comparison group developed incident arm or hand symptoms. Thirty eight (33.3%) participants in the alternate intervention group, 36 (31.0%) in the conventional intervention group, and 33 (30.3%) in the comparison group developed incident neck or shoulder symptoms. Compliance with all components of the intervention was attained for only 25-38% of individuals, due mainly to the inflexibility of workstation configurations. CONCLUSIONS: This study provides evidence that two specific workplace postural interventions are unlikely to reduce the risk of upper extremity musculoskeletal symptoms among computer users.

Health effects of long-term mercury exposure among chloralkali plant workers.

BACKGROUND: Inorganic mercury is toxic to the nervous system, kidneys, and reproductive system. We studied the health effects of mercury exposure among former employees of a chloralkali plant that operated from 1955 to 1994 in Georgia. METHODS: Former plant workers and unexposed workers from nearby employers were studied. Exposure was assessed with a job-exposure matrix based on historical measurements and personnel records. Health outcomes were assessed with interviews, physical examinations, neurological and neurobehavioral testing, renal function testing, and urinary porphyrin measurements. Exposure-disease associations were assessed with multivariate modeling. RESULTS: Exposed workers reported more symptoms, and tended toward more physical examination abnormalities, than unexposed workers. Exposed workers performed worse than unexposed subjects on some quantitative tests of vibration sense, motor speed and coordination, and tremor, and on one test of cognitive function. Few findings remained significant when exposure was modeled as a continuous variable. Neither renal function nor porphyrin excretion was associated with mercury exposure. CONCLUSIONS: Mercury-exposed chloralkali plant workers reported more symptoms than unexposed controls, but no strong associations were demonstrated with neurological or renal function or with porphyrin excretion.

Reliability of some tremor measurement outcome variables in field testing situations.

OBJECTIVE: Many summary measures of data obtained from tremor measurement procedures are commonly reported. The reliability of many of these summary measures of tremor measurements made in field testing situations is unknown. The purpose of the present investigation was to assess the reliability of a number of summary measures produced by the software of a widely used, commercially available tremor measurement instrument using data collected in three field epidemiologic studies. METHODS: Tremor data were obtained from 689 participants in 3 previously conducted studies of groups exposed to elemental mercury or arsenic. A widely used, commercially available tremor measurement instrument was used. Two-axis accelerometer measurements were obtained on 2 or more trials from each hand for each participant. Estimates of trial-to-trial and internal consistency reliability were calculated for 5 summary measures calculated by instrument manufacturer's software and 5 additional summary measures calculated from data output by the software. RESULTS: An RMS acceleration measure had the highest reliability in all 3 studies. The average over 4 trials of RMS acceleration and its logarithm had high reliability (>0.9). Recalculation of a tremor summary index and a harmonicity index as suggested by Edwards and Beuter (1999) resulted in measures with higher reliability and better distributional shape than the corresponding measures provided by the instrument manufacturer's software. The results in all three studies were similar. CONCLUSIONS: For the tremor measurement instrument and testing procedure that we employed, we recommend using the common logarithm of the RMS accelerations and recalculated tremor index as summary measures. We also recommend employing multiple trials of each type (e.g., with each hand) and averaging summary measures from those trials to derive outcome measures of tremor for use in epidemiologic studies. We recommend at least 2 trials for RMS acceleration measures and more for less reliable measures, particularly for designs employing repeated measurements of individuals. Summary measures averaged over at least 4 trials for mean frequency, dispersion of frequency, and power in the 3-6.5 and 6.6-10 Hz frequency ranges have sufficiently high reliability for use in epidemiologic studies.

Relationships between quantitative measures and neurologist's clinical rating of tremor and standing steadiness in two epidemiological studies.

OBJECTIVE: The purpose of the present investigation was to 1) compare a neurologist's physical examination (NPx) rating of severity of postural tremor to several summary measures derived from quantitative measurements of tremor and 2) compare a NPx rating of standing steadiness and related clinical findings to quantitative sway speed measurements. METHODS: Comparisons were performed on data obtained from two epidemiological field studies: 1) retired heavy industrial workers (n= 198, approximately half previously exposed to elemental mercury), and 2) small town residents (n=234, approximately 40% with environmental exposure to arsenic). A commercially available tremor measurement instrument was used in both studies. To obtain standing steadiness measures, a head position monitoring device was used in the mercury study, and a force platform was used in the arsenic study. The NPx included assessment of postural tremor, as well as evaluation of vibration perception and proprioception of the great toe, Achilles tendon reflex activity, Romberg test status, and tandem gait. One neurologist performed all the NPx in both studies and results were graded as normal, equivocal, or abnormal. The square root of the proportion of variance accounted for by a linear trend term in ANOVA models was used as an estimate of association between quantitative tests and clinical examination grade. An estimate of agreement, kappa, was also calculated after both NPx and quantitative test results were dichotomized. RESULTS: Most tremor summary measures varied monotonically with NPx tremor severity grade. Moderately good associations were observed between the tremor acceleration measure and NPx postural tremor grade (correlations up to approximately 0.5). Sway speed with eyes open and with eyes closed increased monotonically with NPx grade for most of the clinical signs. The NPx signs showing the strongest relationships with sway speed were Romberg test performance, tandem gait, and proprioception and vibration sensation of the great toe (correlations up to approximately 0.5). CONCLUSIONS: Quantitative tremor measurements were related to a neurologist's grading of postural tremor. Sway speed was associated with several NPx findings related to standing stability. Quantitative measurements of tremor and standing stability may provide more precise and objective measures of neurological function than NPx by a neurologist and are likely to be more consistent across times and examiners.

Epidemiological case definitions of peripheral neuropathy: experience from two neurotoxicity studies.

OBJECTIVE: The purpose of this investigation was to develop and apply case definitions of peripheral neuropathy (PN) derived from a set of individual measures of peripheral nerve function obtained in two epidemiological studies. METHODS: In the first study, retired workers of an industrial plant who were either previously exposed to mercury or not underwent a set of peripheral neurological tests. In the second study, persons living in an arsenic contaminated community in rural Georgia, USA, and unexposed comparison subjects were tested. In both studies all participants received a neurological physical examination, functional quantitative tests of vibrotactile thresholds and standing stability, and nerve conduction measurements. Two types of analyses were performed. First, the effect of exposure group status was examined for each individual test. For tests with continuous outcomes, the effect of exposure group was estimated while controlling for covariates. For tests with categorical outcomes (all of the neurological examination outcomes), exposure group effects were estimated by comparison of the proportion of abnormal test results among the exposed and unexposed groups. Second, case definitions of PN were constructed using combinations of results of the tests performed. Each of the continuous measures was categorized as normal, equivocal, or abnormal on the basis of adjusted standardized scores. Separate "abnormality scores" were constructed for 1) the nerve conduction tests and 2) the functional quantitative tests and physical examination findings. Five case definitions for PN were constructed based on combinations of these two abnormality scores. RESULTS: Generally, small differences were observed between exposed (n=79 arsenic exposed and 85 mercury exposed) and unexposed (n=84 arsenic unexposed and 118 mercury unexposed) groups when results of each clinical, functional or electrophysiological test were examined separately. Clearer group differences were observed in the proportions of each group who met case definitions for PN, however. For example, for both studies, the largest difference in nerve conduction measures between exposed and unexposed groups was approximately 0.33 SD, while the composite case definition showed an odds ratio of more than 3.1 for the mercury study and 5.1 for the arsenic study. CONCLUSIONS: These results suggest improved efficiency (and avoidance of the multiple-comparisons problem) for detecting peripheral nerve effects when case definitions of PN are constructed rather when results of individual tests of PN function are compared.

Work-related upper extremity musculoskeletal disorders.

Upper extremity musculoskeletal disorders such as DeQuervain's tendonitis, carpal tunnel syndrome, and rotator cuff tendonitis have become increasingly common among working people in the United States. Extensive epidemiological investigation indicates that the adverse ergonomic exposures of force, repetition, vibration and certain postures are risk factors for development of many of these disorders. Assessment of patients with possible work-related upper limb disorders requires eliciting information about the illness, performing an examination about the illness, and obtaining information about adverse ergonomic exposures on and off from work. Treatment can only be successful when exposure to adverse ergonomic risk factors is reduced or eliminated.

Work-related low back pain.

Low back pain is a common problem among working adults in the United States. Occupational risk factors for low back pain include forceful lifting, bending and twisting of the trunk, whole body vibration and heavy manual labor. The initial assessment of the patient with low back pain requires obtaining an occupational history to identify risk factors in the workplace in addition to the usual inquiries and physical assessment. For those with uncomplicated low back pain, minimal use of medical tests and rapid return to limited activity are indicated. Long-term prevention of low back pain requires modification of occupational or other risk factors.

Residual neurologic deficits 30 years after occupational exposure to elemental mercury.

A battery of tests of peripheral and central nervous system function was administered to 205 former workers of a large heavy industrial plant, 104 of whom were previously exposed to inorganic mercury. The mean age of those examined was 71 years. Exposed subjects had participated in a urine-mercury exposure monitoring program during the time of operation of a process that required the use of mercury and its subsequent clean-up. Mercury exposure had been high (mean peak urine mercury concentration was >600 microg/l) and had ended 30 years or more prior to the investigation. Peripheral nerve function outcomes that were statistically significantly associated with cumulative mercury exposure after controlling for covariates included classification as having peripheral neuropathy, peroneal motor nerve conduction velocity, ulnar motor nerve conduction velocity, and peroneal motor nerve F-wave latency. Quantitative assessment of resting tremor was nearly significantly associated with cumulative mercury exposure (p=0.07). Among tests of central nervous system function, results of the Handeye Coordination test were significantly associated with cumulative mercury exposure after controlling for covariates. Cumulative mercury exposure was not observed to be associated with a quantitative measure of dementia or with a number of cognitive neurobehavioral test outcomes. The statistically significant associations with mercury exposure were observed in spite of greater mortality among the exposed group than the unexposed group. These results suggest that substantial occupational mercury exposure can have long-term adverse effects on the peripheral nervous system detectable decades after cessation of exposure. Such long-term adverse effects were not observed for a measure of dementia or other measures of cognitive function.

Neurological effects of environmental exposure to arsenic in dust and soil among humans.

Persons living in a small town in Georgia, USA, were studied because of known environmental exposure to arsenic-containing dust. To assess the effects of this exposure on the nervous system, a cross-sectional epidemiological study was performed. The health outcome assessments of the study were based on a priori selected clinical examination results and quantitative electrophysiologic and behavioral outcome measures. Because the primary goal was to identify cases of peripheral neuropathy, a clinically relevant case definition, based on results of these outcomes was created. Historical exposure reconstructions were performed on a subset of the exposed subjects for whom such information was available. Of the 238 persons enrolled in the study, 133 were classified as non-exposed (i.e., did not reside in the area of known exposure) and 105 were classified as exposed (i.e., did reside in the area of known exposure). Following exclusions of persons with occupational exposure to neurotoxicants, pre-existing conditions associated with peripheral nerve impairment, or age below 18 years, 118 unexposed subjects and 85 exposed subjects were available for inclusion in the analyses of peripheral nerve outcomes. A total of 4 (3.4%) of the unexposed subjects and 13 (15.3%) of the exposed subjects met the case definitions for peripheral neuropathy (OR=5.1; p=0.004). Comparison of three exposure groups (none, low, high) did not yield statistically significant differences. Statistically significant exposure group differences were observed on quantitative tests of standing steadiness, vibrotactile threshold and tremor intensity but not for nerve conduction measures. These results demonstrate a strong association between community arsenic containing dust exposure and peripheral neuropathy among participants in this investigation.

Computer users' postures and associations with workstation characteristics.

This investigation tested the hypotheses that (1) physical workstation dimensions are important determinants of operator posture, (2) specific workstation characteristics systematically affect worker posture, and (3) computer operators assume "neutral" upper limb postures while keying. Operator head, neck, and upper extremity posture and selected workstation dimensions and characteristics were measured among 379 computer users. Operator postures were measured with manual goniometers, workstation characteristics were evaluated by observation, and workstation dimensions by direct measurement. Considerably greater variability in all postures was observed than was expected from application of basic geometric principles to measured workstation dimensions. Few strong correlations were observed between worker posture and workstation physical dimensions; findings suggest that preference is given to keyboard placement with respect to the eyes (r = 0.60 for association between keyboard height and seated elbow height) compared with monitor placement with respect to the eyes (r = 0.18 for association between monitor height and seated eye height). Wrist extension was weakly correlated with keyboard height (r = -0.24) and virtually not at all with keyboard thickness (r = 0.07). Use of a wrist rest was associated with decreased wrist flexion (21.9 versus 25.1 degrees, p < 0.01). Participants who had easily adjustable chairs had essentially the same neck and upper limb postures as did those with nonadjustable chairs. Sixty-one percent of computer operators were observed in nonneutral shoulder postures and 41% in nonneutral wrist postures. Findings suggest that (1) workstation dimensions are not strong determinants of at least several neck and upper extremity postures among computer operators, (2) only some workstation characteristics affect posture, and (3) contrary to common recommendations, a large proportion of computer users do not work in so-called neutral postures.

Clinical evaluation and management of work-related carpal tunnel syndrome.

Carpal tunnel syndrome (CTS) is a clinical entity characterized by pain, paresthesias, and numbness in the distribution of the median nerve with weakness and atrophy of the thenar muscles in advanced cases. It is universally accepted that CTS is the clinical concomitant of compression of the median nerve as it passes through the carpal canal. It is reported to be the most common of the entrapment neuropathies. Increasing evidence suggests that occupational factors, including forceful use of the hands, repetitive use of the hands, and hand-arm vibration, are etiologic for CTS. When occurring as a result of occupational exposures, the term "work-related carpal tunnel syndrome" is applied. Clinical approaches to the diagnosis and treatment of work-related CTS are described in this paper. Particular attention is paid to the clinical features and pathophysiology of CTS, the epidemiology of work-related CTS, ascertainment of work-relatedness in the clinical setting, treatment including both work and non-work interventions, and control of occupational ergonomic risk factors that may contribute to the illness.

Neurotoxicity in young adults 20 years after childhood exposure to lead: the Bunker Hill experience.

OBJECTIVES: An epidemiological study of young adults was conducted to determine whether environmental exposure to lead during childhood was associated with current adverse neurobehavioural effects. METHODS: The exposed group consisted of 281 young adults who had been exposed environmentally to lead as children and the unexposed referent group consisted of 287 age and sex frequency matched subjects. Information on demographics, past and current health, and past exposures to neurotoxicants, and responses to the Swedish Q16 questionnaire were collected by interview. Standard neurobehavioural and neurophysiological tests were administered by computer or trained technicians. K x ray fluorescence was used to estimate tibial bone lead concentrations among the exposed and unexposed groups. Associations were examined between the exposed group and referents and tibial bone lead concentration and the neurobehavioural and neurophysiological outcomes of interest. RESULTS: Among the measures of peripheral nerve function, after controlling for confounders, sural sensory nerve evoked response amplitude, peroneal motor nerve compound motor action potential amplitude, vibrotactile thresholds of fingers and toes, and standing steadiness were significantly associated with exposure group. Among the neurobehavioural tests, hand-eye coordination, simple reaction time latency, trails B latency, symbol digit latency, serial digit, and learning error score were also significantly associated with exposure group after controlling for confounders. Exposed subjects had significantly more neuropsychiatric symptoms than the referents. Associations between tibial bone lead concentration and scores for vocabulary, vibrotactile thresholds of the fingers, and vibrotactile thresholds of the toes approached significance. CONCLUSIONS: Significant adverse central and peripheral neurological effects were found in a group of young adults 20 years after childhood environmental exposure to lead when compared with non-exposed controls. The absence of a significant association between neurological outcomes and tibial bone lead concentration, and the presence of significant associations between neurological outcomes and exposure group may be due to either the magnitude of measurement uncertainty in K x ray films relative to the actual tibial bone lead concentration in these young non-occupationally exposed subjects, or uncontrolled confounding of the exposure group.

Consensus criteria for the classification of carpal tunnel syndrome in epidemiologic studies.

Criteria for the classification of carpal tunnel syndrome for use in epidemiologic studies were developed by means of a consensus process. Twelve medical researchers with experience in conducting epidemiologic studies of carpal tunnel syndrome participated in the process. The group reached agreement on several conceptual issues. First, there is no perfect gold standard for carpal tunnel syndrome. The combination of electrodiagnostic study findings and symptom characteristics will provide the most accurate information for classification of carpal tunnel syndrome. Second, use of only electrodiagnostic study findings is not recommended. Finally, in the absence of electrodiagnostic studies, specific combinations of symptom characteristics and physical examination findings may be useful in some settings but are likely to result in greater misclassification of disease status.

The sensitivity and specificity of tests for carpal tunnel syndrome vary with the comparison subjects.

The performance of a variety of common office-based clinical tests for detection of carpal tunnel syndrome (CTS) was assessed in 119 subjects with and without electrophysiological evidence of CTS. Symptoms compatible with CTS and electrophysiological tests positive for median mononeuropathy at the wrist were observed in 57 hands, symptoms compatible with CTS and normal electrophysiological test results were observed in 58 hands, and no symptoms compatible with CTS and normal electrophysiological test results were observed in 123 hands. For all the diagnostic tests studied, the proportion of subjects who had a false positive clinical test result was much higher in the electrophysiologically normal subjects who had CTS compatible hand symptoms than in the electrophysiologically normal subjects who were asymptomatic. These results suggest that many studies that have evaluated diagnostic tests for CTS have produced falsely optimistic estimates of the test's performance because of their use of asymptomatic comparison subjects.