The Strain Index (SI) and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for hand activity level (TLV for HAL) have been shown to be associated with prevalence of distal upper-limb musculoskeletal disorders such as carpal tunnel syndrome (CTS). The SI and TLV for HAL disagree on more than half of task exposure classifications. Similarly, time-weighted average (TWA), peak, and typical exposure techniques used to quantity physical exposure from multi-task jobs have shown between-technique agreement ranging from 61% to 93%, depending upon whether the SI or TLV for HAL model was used. This study compared exposure-response relationships between each model-technique combination and prevalence of CTS. Physical exposure data from 1,834 workers (710 with multi-task jobs) were analyzed using the SI and TLV for HAL and the TWA, typical, and peak multi-task job exposure techniques. Additionally, exposure classifications from the SI and TLV for HAL were combined into a single measure and evaluated. Prevalent CTS cases were identified using symptoms and nerve-conduction studies. Mixed effects logistic regression was used to quantify exposure-response relationships between categorized (i.e., low, medium, and high) physical exposure and CTS prevalence for all model-technique combinations, and for multi-task workers, mono-task workers, and all workers combined. Except for TWA TLV for HAL, all model-technique combinations showed monotonic increases in risk of CTS with increased physical exposure. The combined-models approach showed stronger association than the SI or TLV for HAL for multi-task workers. Despite differences in exposure classifications, nearly all model-technique combinations showed exposure-response relationships with prevalence of CTS for the combined sample of mono-task and multi-task workers. Both the TLV for HAL and the SI, with the TWA or typical techniques, appear useful for epidemiological studies and surveillance. However, the utility of TWA, typical, and peak techniques for job design and intervention is dubious.

BackgroundThere is growing use of a job exposure matrix (JEM) to provide exposure estimates in studies of work-related musculoskeletal disorders; few studies have examined the validity of such estimates, nor did compare associations obtained with a JEM with those obtained using other exposures.ObjectiveThis study estimated upper extremity exposures using a JEM derived from a publicly available data set (Occupational Network, O*NET), and compared exposure-disease associations for incident carpal tunnel syndrome (CTS) with those obtained using observed physical exposure measures in a large prospective study.Methods2393 workers from several industries were followed for up to 2.8 years (5.5 person-years). Standard Occupational Classification (SOC) codes were assigned to the job at enrolment. SOC codes linked to physical exposures for forceful hand exertion and repetitive activities were extracted from O*NET. We used multivariable Cox proportional hazards regression models to describe exposure-disease associations for incident CTS for individually observed physical exposures and JEM exposures from O*NET.ResultsBoth exposure methods found associations between incident CTS and exposures of force and repetition, with evidence of dose–response. Observed associations were similar across the two methods, with somewhat wider CIs for HRs calculated using the JEM method.ConclusionExposures estimated using a JEM provided similar exposure-disease associations for CTS when compared with associations obtained using the ‘gold standard’ method of individual observation. While JEMs have a number of limitations, in some studies they can provide useful exposure estimates in the absence of individual-level observed exposures.

Background: The Strain Index (SI) and the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value for Hand Activity Level (TLV for HAL) use different constituent variables to quantify task physical exposures. Similarly, time-weighted-average (TWA), Peak, and Typical exposure techniques to quantify physical exposure from multi-task jobs make different assumptions about each task's contribution to the whole job exposure. Thus, task and job physical exposure classifications differ depending upon which model and technique are used for quantification. This study examines exposure classification agreement, disagreement, correlation, and magnitude of classification differences between these models and techniques. Methods: Data from 710 multi-task job workers performing 3,647 tasks were analyzed using the SI and TLV for HAL models, as well as with the TWA, Typical and Peak job exposure techniques. Physical exposures were classified as low, medium, and high using each model's recommended, or a priori limits. Exposure classification agreement and disagreement between models (SI, TLV for HAL) and between job exposure techniques (TWA, Typical, Peak) were described and analyzed. Results: Regardless of technique, the SI classified more tasks as high exposure than the TLV for HAL, and the TLV for HAL classified more tasks as low exposure. The models agreed on 48.5% of task classifications (kappa = 0.28) with 15.5% of disagreement between low and high exposure categories. Between-technique (i.e., TWA, Typical, Peak) agreement ranged from 61-93% (kappa: 0.16-0.92) depending on whether the SI or TLV for HAL was used. Conclusions: There was disagreement between the SI and TLV for HAL and between the TWA, Typical and Peak techniques. Disagreement creates uncertainty for job design, job analysis, risk assessments, and developing interventions. Task exposure classifications from the SI and TLV for HAL might complement each other. However, TWA, Typical, and Peak job exposure techniques all have limitations. Part II of this article examines whether the observed differences between these models and techniques produce different exposure-response relationships for predicting prevalence of carpal tunnel syndrome.

Background The pathophysiology of lateral epicondylitis (LE) is unclear. Recent evidence suggests some common musculoskeletal disorders may have a basis in cardiovascular disease (CVD) risk factors. Thus, we examined CVD risks as potential LE risks. Methods Workers ( n = 1824) were enrolled in two large prospective studies and underwent structured interviews and physical examinations at baseline. Analysis of pooled baseline data assessed the relationships separately between a modified Framingham Heart Study CVD risk score and three prevalence outcomes of: 1) lateral elbow pain, 2) positive resisted wrist or middle finger extension, and 3) a combination of both symptoms and at least one resisted maneuver. Quantified job exposures, personal and psychosocial confounders were statistically controlled. Odds ratios (ORs) and 95% Confidence Intervals (CIs) were calculated. Results There was a strong relationship between CVD risk score and lateral elbow symptoms, resisted wrist or middle finger extension and LE after adjustment for confounders. The adjusted ORs for symptoms were as high as 3.81 (95% CI 2.11, 6.85), for positive examination with adjusted odds ratios as high as 2.85 (95% CI 1.59, 5.12) and for combined symptoms and physical examination 6.20 (95% CI 2.04, 18.82). Relationships trended higher with higher CVD risk scores. Conclusions These data suggest a potentially modifiable disease mechanism for LE.

BACKGROUND:Between 2001 and 2010, six research groups conducted coordinated prospective studies of carpal tunnel syndrome (CTS) incidence among US workers from various industries to estimate exposure-response relationships. OBJECTIVE:This analysis examined the presence and magnitude of confounding between biomechanical and workplace psychosocial factors and incidence of dominant-hand CTS. METHODS:1605 participants, without CTS at enrolment, were followed for up to 3.5 years (2471 person-years). Demographic information, medical history and workplace psychosocial stress measures were collected at baseline. Individual workplace biomechanical exposures were collected for each task and combined across the workweek using time-weighted averaging (TWA). CTS case criteria were based on symptoms and results of electrophysiological testing. HRs were estimated with Cox proportional hazard models. Confounding was assessed using causal diagrams and an empirical criterion of 10% or greater change in effect estimate magnitude. RESULTS:There were 109 incident CTS cases (IR=4.41/100 person-years; 6.7% cumulative incidence). The relationships between CTS and forceful repetition rate, % time forceful hand exertion and the Threshold Limit Value for Hand Activity Level (TLV-HAL) were slightly confounded by decision latitude with effect estimates being attenuated towards the null (10-14% change) after adjustment. The risk of CTS among participants reporting high job strain was attenuated towards the null by 14% after adjusting for the HAL Scale or the % time forceful hand exertions. CONCLUSIONS:Although attenuation of the relationships between CTS and some biomechanical and work psychosocial exposures was observed after adjusting for confounding, the magnitudes were small and confirmed biomechanical and work psychosocial exposures as independent risk factors for incident CTS.

Objective: The goal is to assess the relationships between psychosocial factors and both medial and lateral epicondylitis after adjustment for personal and job physical exposures. Methods: One thousand eight hundred twenty-four participants were included in pooled analyses. Ten psychosocial factors were assessed. Results: One hundred twenty-one (6.6%) and 34 (1.9%) participants have lateral and medial epicondylitis, respectively. Nine psychosocial factors assessed had significant trends or associations with lateral epicondylitis, the largest of which was between physical exhaustion after work and lateral epicondylitis with and odds ratio of 7.04 (95% confidence interval = 2.02 to 24.51). Eight psychosocial factors had significant trends or relationships with medial epicondylitis, with the largest being between mental exhaustion after work with an odds ratio of 6.51 (95% confidence interval = 1.57 to 27.04). Conclusions: The breadth and strength of these associations after adjustment for confounding factors demonstrate meaningful relationships that need to be further investigated in prospective analyses.

Objective: The aim of this study was to identify relationships between work organizational variables (job rotation, overtime work, having a second job, and work pacing) (These work organizational variables and their relationships with biomechanical and psychosocial exposures were studied previously and published in a separate paper.) and health outcome measures [carpal tunnel syndrome (CTS), lateral and medial epicondylitis (LEPI/MEPI)]. Methods: Using a pooled baseline cohort of 1834 subjects, the relationships were studied using logistic regression models. Results: Varied degrees of associations between the work organizational and outcomes variables were found. Job rotation was significantly associated with being a CTS case [odds ratio (OR) = 1.23, 95% confidence interval (95% CI): 1.00 to 1.50]. Overtime work was significantly associated with lower LEPI prevalence (OR = 0.48, 95% CI: 0.28 to 0.84). No statistically significant associations were found between having a second job and different work pacing and any of the three health outcome measures. Conclusions: Work organizational variables were only partially associated with the studied health outcomes.

BACKGROUND Little is known about the work-related injury and illnesses experienced by certified athletic trainers (AT). METHODS The incidence and characteristics of injury/illness claims filed in two workers' compensation systems were described from 2001 to 2011. Yearly populations at risk were estimated from National Athletic Trainers' Association membership statistics. Incidence rate ratios (IRR) were reported by job setting. RESULTS Claims were predominantly for traumatic injuries and disorders (82.7%: 45.7% sprains/strains, 12.0% open wounds, 6.5% bruises) and at these body sites (back 17.2%, fingers 12.3%, and knee 9.6%) and over half were caused by body motion and overexertion (51.5%). Compared with school settings, clinic/hospital settings had modestly higher claim rates (IRR = 1.29, 95% CI: 1.06-1.52) while other settings (e.g., professional or youth sport, nursing home) had lower claim rates (IRR = 0.63, 95% CI: 0.44-0.70). CONCLUSIONS These first known estimates of work-related injuries/illnesses among a growing healthcare profession help identify occupational tasks and settings imposing injury risk for ATs. Am. J. Ind. Med. 59:1156-1168, 2016. © 2016 Wiley Periodicals, Inc.

BACKGROUND:Few large epidemiologic studies have used rigorous case criteria, individual-level exposure measurements, and appropriate control for confounders to examine associations between workplace psychosocial and biomechanical factors and carpal tunnel syndrome (CTS).METHODS:Pooling data from five independent research studies, we assessed associations between prevalent CTS and personal, work psychosocial, and biomechanical factors while adjusting for confounders using multivariable logistic regression.RESULTS:Prevalent CTS was associated with personal factors of older age, obesity, female sex, medical conditions, previous distal upper extremity disorders, workplace measures of peak forceful hand activity, a composite measure of force and repetition (ACGIH Threshold Limit Value for Hand Activity Level), and hand vibration.CONCLUSIONS:In this cross-sectional analysis of production and service workers, CTS prevalence was associated with workplace and biomechanical factors. The findings were similar to those from a prospective analysis of the same cohort with differences that may be due to recall bias and other factors.

BACKGROUND:Six research groups independently conducted prospective studies of carpal tunnel syndrome (CTS) incidence in 54 US workplaces in 10 US States. Physical exposure variables were collected by all research groups at the individual worker level. Data from these research groups were pooled to increase the exposure spectrum and statistical power.OBJECTIVE:This paper provides a detailed description of the characteristics of the pooled physical exposure variables and the source data information from the individual research studies.METHODS:Physical exposure data were inspected and prepared by each of the individual research studies according to detailed instructions provided by an exposure subcommittee of the research consortium. Descriptive analyses were performed on the pooled physical exposure data set. Correlation analyses were performed among exposure variables estimating similar exposure aspects.RESULTS:At baseline, there were a total of 3010 participants in the pooled physical exposure data set. Overall, the pooled data meaningfully increased the spectra of most exposure variables. The increased spectra were due to the wider range in exposure data of different jobs provided by the research studies. The correlations between variables estimating similar exposure aspects showed different patterns among data provided by the research studies.CONCLUSIONS:The increased spectra of the physical exposure variables among the data pooled likely improved the possibility of detecting potential associations between these physical exposure variables and CTS incidence. It is also recognised that methods need to be developed for general use by all researchers for standardisation of physical exposure variable definition, data collection, processing and reduction.

Introduction: There is a growing body of research connecting musculoskeletal diseases to both job physical exposures and psychosocial exposures. Associations between job physical exposures and psychosocial factors have not been well studied or measured. These exploratory analyses evaluate relationships between quantified exposures and psychosocial outcomes. Methods: Personalized measures of duration, repetition, force and composite scores of the Strain Index (SI) and the Threshold Limit Value for Hand Activity Level (TLV for HAL) were compared to 10 psychosocial measures. Associations and predicted probabilities were evaluated using ordered logistic regression. Results and Discussion: Among 1834 study participants there were numerous significant relationships. Overall, as job physical exposures increased, psychosocial measures worsened. However, both general health and mental exhaustion improved with higher job exposures. Depression was most strongly related with higher repetition, while physical exhaustion was most strongly related with higher force. SI and TLV for HAL were significantly related to numerous psychosocial factors. Relationships remained after adjustment for confounders of age, BMI and gender. Conclusion: This study measured multiple associations between job physical exposures and both occupational and non-occupational psychosocial factors. Further research is needed to quantify the impacts on occupational health outcomes.

Carpal tunnel syndrome (CTS), though widely investigated, remains a troubling and costly disease for both employers and workers. Recent studies have consistently shown that combinations of force and repetition are occupational risk factors for CTS. However, it remains unclear which of these two factors is primarily responsible for the increase in risk. This study uses pooled prospective data to compare exposure-response relationships for peak force and several measures of repetition, including the integrated measure of peak force and hand activity level, the ACGIH TLV for HAL. Results suggest that peak force acts as an independent risk factor for CTS, while repetition is only a risk factor if the exertions are “forceful”. Thus, it appears that applied hand/wrist force is the dominant occupational physical exposure risk factor for CTS.

BACKGROUND Numerous aspects of construction place workers at risk of musculoskeletal disorders and injuries (MSDIs). Work organization and the nature of MSDIs create surveillance challenges. METHODS By linking union records with workers' compensation claims, we examined 20-year patterns of MSDIs involving the upper extremity (UE) and the knee among a large carpenter cohort. RESULTS MSDIs were common and accounted for a disproportionate share of paid lost work time (PLT) claims; UE MSDIs were three times more common than those of the knee. Rates declined markedly over time and were most pronounced for MSDIs of the knee with PLT. Patterns of risk varied by extremity, as well as by age, gender, union tenure, and predominant work. Carpenters in drywall installation accounted for the greatest public health burden. CONCLUSIONS A combination of factors likely account for the patterns observed over time and across worker characteristics. Drywall installers are an intervention priority.

Insufficient sample size causes lower statistical power that may hinder findings of relationships between occupational physical exposures and musculoskeletal disorders. To solve this problem, researchers often want to pool data with similar study designs together to increase the statistical power. However, a recent consortium study on the relationships between physical exposures and Carpal Tunnel Syndrome (CTS) found that due to slight differences in variable definitions, data collection procedures, data processing approaches, and data analysis methods, pooling data from multiple studies can be challenging. Using data independently collected by six research groups in 54 US workplaces in 10 US States, this paper presents some of the challenges in data pooling, and final selections of comparable variables. Distributions of the selected exposure data of 3010 subjects and variable definitions are presented. This abstract is based on a recent publication in Occupational and Environmental Medicine.

Objective: Evaluate associations between personal and workplace factors and median nerve conduction latency at the wrist. Methods: Baseline data on workplace psychosocial and physical exposures were pooled from four prospective studies of production and service workers (N = 2396). During the follow-up period, electrophysiologic measures of median nerve function were collected at regular intervals. Results: Significant adjusted associations were observed between age, body mass index, sex, peak hand force, duration of forceful hand exertions, Threshold Limit Value for Hand Activity Limit, forceful repetition rate, wrist extension, and decision latitude on median nerve latencies. Conclusions: Occupational and nonoccupational factors have adverse effects on median nerve function. Measuring median nerve function eliminates possible reporting bias that may affect symptom-based carpal tunnel syndrome case definitions. These results suggest that previously observed associations between carpal tunnel syndrome and occupational factors are not the result of such reporting bias.

BACKGROUND:Carpal tunnel syndrome (CTS) is among the most burdensome of all musculoskeletal disorders as measured by workers' compensation claims costs and lost earnings. But the burden of CTS extends beyond direct claim costs.METHODS:A survey covering health, social, economic and work-related outcomes was administered to 1,255 injured workers whose Washington State Fund workers' compensation claims had closed 6 years previously. Logistic and linear regression methods were used to model the outcomes of CTS claimants across four separate outcome domains.RESULTS:Workers diagnosed with CTS suffer substantial deficits across all four outcome domains as compared to the two comparison groups of claimants. Former CTS claimants were almost twice as likely not to be working as compared to the fractures cohort.CONCLUSIONS:A comprehensive measurement of the burden of CTS shows losses extend beyond direct claims costs to include continuing pain, loss of function, adverse financial impacts and household disruption which extend long after claim closure. Am. J. Ind. Med. 58:1255-1269, 2015. © 2015 Wiley Periodicals, Inc.

Common treatments for lateral epicondylosis (LE) focus on tissue healing. Ergonomic advice is suggested broadly, but recommendations based on biomechanical motion parameters associated with functional activities are rarely made. This review analyzes the role of body functions and activities in LE and integrates the findings to suggest motion parameters applicable to education and interventions relevant to activities and life roles for patients.This study examines LE pathology, tendon and muscle biomechanics, and population exposure outlining potentially hazardous activities and integrates those to provide motion parameters for ergonomic interventions to treat or prevent LE. A disease model is discussed to align treatment approaches to the stage of LE tendinopathy.Integrative reviewWe conducted in-depth searches using PubMed, Medline, and government websites. All levels of evidence were included, and the framework for behavioral research from the National Institutes of Health was used to synthesize ergonomic research.The review broadened the diagnosis of LE from a tendon ailment to one affecting the enthesis of the capitellum. It reinforced the continuum of severity to encompass degeneration as well as regeneration. Systematic reviews confirmed the availability of evidence for tissue-based treatments, but evidence of well-defined harm reducing occupational interventions was scattered amongst evidence levels. Integration of biomechanical studies and population information gave insight into types of potentially hazardous activities and provided a theoretical basis for limiting hazardous exposures to wrist extensor tendons by reducing force, compression, and shearing during functional activities.These findings may broaden the first treatment approach from a passive, watchful waiting into an active exploration and reduction of at-risk activities and motions. Including the findings into education modules may provide patients with the knowledge to lastingly reduce potentially hazardous motions during their daily activities, and researchers to define parameters of ergonomic interventions.

BACKGROUND:Musculoskeletal symptoms and disorders (MSDIs) are common reasons for visits to medical providers in the general population and they are common work-related complaints. Prior reports raise concerns as to whether declines in workers' compensation (WC) rates represent true improvement in occupational health and safety or shifting of care to other payment systems.METHODS:By linking administrative records, we compared patterns of WC claims and private health care utilization for disorders of the upper extremity (UE) and knee among a large cohort of union carpenters over a 20-year period.RESULTS:As WC claim rates declined, private health care utilization increased. The increase was muted somewhat but sustained when adjusting for other patterns of health care utilization.CONCLUSIONS:Findings suggest the decline of WC claim rates do not solely represent improved occupational safety in this population, but also a considerable shifting of care to their private insurance coverage over time.

Objectives To determine if job title based physical exposure measures predicted prevalent carpal tunnel syndrome (CTS) in a large pooled cohort of workers. Method We pooled baseline examination data from six prospective cohort studies, restricting analyses to those employed at least 1 year. CTS was defined as median neuropathy plus typical symptoms. Physical exposure estimates for static strength, dynamic strength, time spent making repetitive motions, and time handling objects were extracted from the Occupational Network (O*NET) database using Standard Occupational Classification codes based on reported job title. Three exposure categories of high force/ high repetition, low force/ low repetition, and mixed high and low exposures were entered into logistic regression models adjusting for age, gender, body mass index (BMI), diabetes, rheumatoid arthritis, employed time and study site. Results Of 3562 in the pooled cohort, 7.6% met a prevalent CTS definition with mean employed time of 7.9 years (SD 8.2). Compared to subjects with low job requirements for dynamic strength and repetitive motion, those with mixed exposures or high exposures showed increased prevalence of CTS (OR 1.46; 95% CI: 1.01–2.11 and OR 2.32; 95% CI: 1.15–4.67, respectively). Similar dose dependent associations of combined exposures were shown for all exposure combinations tested, with high/high combinations having the largest effect sizes (OR range 2.32–3.17) relative to the low force/low repetition exposure combinations. Conclusions Use of job-title based exposures was useful for demonstrating associations with prevalent CTS. Jobs with combined high exposures of force and repetition showed consistently greater risk of CTS compared to jobs with lower exposure levels.