The Strain Index (SI) and Threshold Limit Value (TLV) for Hand Activity Level (HAL): risk of carpal tunnel syndrome (CTS) in a prospective cohort

Musculoskeletal complaints, physical work demands, and functional capacity in individuals with a brachial plexus injury: An exploratory study

BACKGROUND

Musculoskeletal complaints (MSCs) may be more common in individuals with brachial plexus injury (BPI), whose physical work demands exceed their functional capacity (FC).

OBJECTIVES

(a) To assess the concurrent validity of five methods for measuring upper extremity work demands and the Dictionary of Occupational Titles (DOT). (b) To explore the relations between MSCs, physical work demands, and FC in individuals with BPI.

METHODS

This study had a descriptive correlational design. Physical work demands of 16 individuals with BPI (12 males, 6 one-handed workers) were assessed during work using five assessment methods and the DOT. Spearman correlation coefficients between work demand methods were determined. FC was assessed using the functional capacity evaluation one-handed (FCE-OH). A questionnaire was used to examine MSCs. The relationship between MSCs, physical work demands and FC was analyzed visually, using Spearman correlation coefficients, and by comparing FCE-OH results to FCE reference values.

RESULTS

Spearman correlation coefficients for the DOT and four out of five assessment methods for determining work demands on upper extremities were significant and moderate (four combinations: r = 0.65-0.79) to strong (five combinations: r = 0.81-0.94). Correlations of the fifth method with the other methods were weak to fair. No significant relationships were found between MSCs, physical work demands and FCE-OH results.

CONCLUSION

The relationships between MSCs, physical work demands, and FC are evidently complex and require further investigation. In this small sample the concurrent validity of the DOT and four methods for determining work demands on upper extremities was moderate to good.

Workplace Psychosocial Factors and Their Association With Musculoskeletal Disorders: A Systematic Review of Longitudinal Studies

This systematic review examines literature regarding the relationship between workplace psychosocial factors and musculoskeletal disorders (MSDs). Musculoskeletal disorders are the leading cause of work disability, resulting in billions of dollars of financial losses. Evidence suggests that workplace psychosocial factors can lead to the development and progression of MSDs. A data search was conducted in MEDLINE, EMBASE, PsychINFO, Scopus, and CINAHL (Cumulative Index to Nursing and Allied Health Literature) from August 2009 to May 2020 inclusive. Other eligibility criteria included studies published in English, conducted on adults within a workplace setting, conducted in developed economies, and were stability-control longitudinal observational studies. Studies were independently screened for eligibility, using COVIDENCE (software for managing and streamlining systematic reviews) and assessed for quality by multiple authors, using the JBI Evidence synthesis tool. From 6,812 studies, 47 articles were included in the final analysis. The most common MSDs investigated were lower back pain, neck and shoulder pain, and upper extremity symptoms and disorders. Included articles identified that psychosocial workplace factors of support, collaboration, job control, and job demands were statistically significantly associated with risk and progression of MSDs. Review of the articles included in this article supports the theory that MSDs have a multifactorial, complex etiology that includes psychosocial factors. Interventions to enhance psychosocial work environment provide opportunities to reduce the risk of MSDs.

Cardiovascular Disease Risk Factors Predict the Development and Numbers of Common Musculoskeletal Disorders in a Prospective Cohort

OBJECTIVE

The aim of the study is to assess risk of common musculoskeletal disorders (MSDs) based on cardiovascular disease (CVD) risk scores.

METHODS

Data from a 9-year prospective cohort of 1224 workers in three states were analyzed. Baseline data included questionnaires, structured interviews, physical examinations, anthropometric measurements, nerve conduction studies, and individualized measurement of job physical factors. Monthly follow-ups were conducted. Framingham risk scores were calculated. A priori case definitions were constructed for carpal tunnel syndrome, lateral epicondylopathy, medial epicondylopathy, and rotator cuff tendinopathy.

RESULTS

Adjusted RRs for one or more MSDs increased to 3.90 (95% confidence interval, 2.20-6.90) among those with 10-year cardiovascular disease risk scores greater than 15% and 17.4 (95% confidence interval, 3.85-78.62) among those with more than 4 disorders.

CONCLUSIONS

Cardiovascular disease factors are strongly associated with the subsequent development of common MSDs. Risks among those with multiple MSDs are considerably stronger.

Comparison of the observer, single-frame video and computer vision hand activity levels

Observer, manual single-frame video, and automated computer vision measures of the Hand Activity Level (HAL) were compared. HAL can be measured three ways: (1) observer rating (HALO), (2) calculated from single-frame multimedia video task analysis for measuring frequency (F) and duty cycle (D) (HALF), or (3) from automated computer vision (HALC). This study analysed videos collected from three prospective cohort studies to ascertain HALO, HALF, and HALC for 419 industrial videos. Although the differences for the three methods were relatively small on average (<1), they were statistically significant (p < .001). A difference between the HALC and HALF ratings within ±1 point on the HAL scale was the most consistent, where more than two thirds (68%) of all the cases were within that range and had a linear regression through the mean coefficient of 1.03 (R2 = 0.89). The results suggest that the computer vision methodology yields comparable results as single-frame video analysis.Practitioner summary: The ACGIH Hand Activity Level (HAL) was obtained for 419 industrial tasks using three methods: observation, calculated using single-frame video analysis and computer vision. The computer vision methodology produced results that were comparable to single-frame video analysis.

Job satisfaction and job security as moderators in the relationships among job demands, musculoskeletal symptoms, and work performance

PURPOSE

This study examined whether job satisfaction and job security moderate the path from physical demands and job strain to impaired work performance via musculoskeletal symptoms in the upper extremities (MSUE). Moderation effects on five paths were examined: (1) from job strain to MSUE; (2) from job strain to work performance; (3) from physical demands to MSUE; (4) from physical demands to work performance; (5) from MSUE to work performance.

METHODS

This was a cross-sectional study of 669 full-time workers from 9 manufacturing and 3 healthcare facilities. Data were collected via health interviews, on-site physical exposure assessments, and computation of the Strain Index by ergonomists, and self-administered questionnaires on psychosocial factors. Structural equation modeling and zero-inflated negative binomial regression analysis were performed to examine the moderation effect on each path.

RESULTS

Job satisfaction moderated the relationship between MSUE and impaired work performance (B = - 0.09, 95% CI: - 0.15, - 0.04) and job security moderated the relationship between physical demands and MSUE (B = - 0.64, 95% CI: - 1.17, - 0.11). Interaction between job satisfaction and MSUE was significant on both the occurrence (OR: 0.92, 95% CI: 0.87, 0.97) and the degrees of impaired work performance (mean ratio: 0.99, 95% CI: 0.97, 0.99), while the interaction between job security and physical demands was significant only on the degrees of MSUE (mean ratio: 0.94, 95% CI: 0.89, 0.99).

CONCLUSION

Job satisfaction and job security can, respectively, mitigate the adverse impacts of working with MSUE and physical demands on work performance. Workplace interventions to improve workers' job satisfaction and job security can contribute to their musculoskeletal health and work performance.

Reliability and Validity of Six Selected Observational Methods for Risk Assessment of Hand Intensive and Repetitive Work

Risk assessments of hand-intensive and repetitive work are commonly done using observational methods, and it is important that the methods are reliable and valid. However, comparisons of the reliability and validity of methods are hampered by differences in studies, e.g., regarding the background and competence of the observers, the complexity of the observed work tasks and the statistical methodology. The purpose of the present study was to evaluate six risk assessment methods, concerning inter- and intra-observer reliability and concurrent validity, using the same methodological design and statistical parameters in the analyses. Twelve experienced ergonomists were recruited to perform risk assessments of ten video-recorded work tasks twice, and consensus assessments for the concurrent validity were carried out by three experts. All methods' total-risk linearly weighted kappa values for inter-observer reliability (when all tasks were set to the same duration) were lower than 0.5 (0.15-0.45). Moreover, the concurrent validity values were in the same range with regards to total-risk linearly weighted kappa (0.31-0.54). Although these levels are often considered as being fair to substantial, they denote agreements lower than 50% when the expected agreement by chance has been compensated for. Hence, the risk of misclassification is substantial. The intra-observer reliability was only somewhat higher (0.16-0.58). Regarding the methods ART (Assessment of repetitive tasks of the upper limbs) and HARM (Hand Arm Risk Assessment Method), it is worth noting that the work task duration has a high impact in the risk level calculation, which needs to be taken into account in studies of reliability. This study indicates that when experienced ergonomists use systematic methods, the reliability is low. As seen in other studies, especially assessments of hand/wrist postures were difficult to rate. In light of these results, complementing observational risk assessments with technical methods should be considered, especially when evaluating the effects of ergonomic interventions.

Biomechanical Assessments of the Upper Limb for Determining Fatigue, Strain and Effort from the Laboratory to the Industrial Working Place: A Systematic Review

Recent human-centered developments in the industrial field (Industry 5.0) lead companies and stakeholders to ensure the wellbeing of their workers with assessments of upper limb performance in the workplace, with the aim of reducing work-related diseases and improving awareness of the physical status of workers, by assessing motor performance, fatigue, strain and effort. Such approaches are usually developed in laboratories and only at times they are translated to on-field applications; few studies summarized common practices for the assessments. Therefore, our aim is to review the current state-of-the-art approaches used for the assessment of fatigue, strain and effort in working scenarios and to analyze in detail the differences between studies that take place in the laboratory and in the workplace, in order to give insights on future trends and directions. A systematic review of the studies aimed at evaluating the motor performance, fatigue, strain and effort of the upper limb targeting working scenarios is presented. A total of 1375 articles were found in scientific databases and 288 were analyzed. About half of the scientific articles are focused on laboratory pilot studies investigating effort and fatigue in laboratories, while the other half are set in working places. Our results showed that assessing upper limb biomechanics is quite common in the field, but it is mostly performed with instrumental assessments in laboratory studies, while questionnaires and scales are preferred in working places. Future directions may be oriented towards multi-domain approaches able to exploit the potential of combined analyses, exploitation of instrumental approaches in workplace, targeting a wider range of people and implementing more structured trials to translate pilot studies to real practice.

Interaction between physical demands and job strain on musculoskeletal symptoms and work performance

This study investigated the interaction between physical demands and job strain on musculoskeletal symptoms in upper extremities (MSUE) and work performance. Two years of prospective data were analysed from 713 full-time workers from twelve manufacturing and healthcare facilities in Washington in the United States. Physical exposure was measured by the Strain Index and Threshold Limit Value for hand activity, giving rise to safe, action, and hazardous physical demand groups. Job strain was calculated as the ratio of psychological job demands to job control. Multilevel modelling analysis showed that job strain affected MSUE and limited work performance less in the high physical demand group than the safe group because the protective effect of job control was smaller in these groups. Findings may suggest that high physical demand jobs are structured such that workers have low job control or high physical demand groups experience job strain not adequately captured by psychosocial variables.Practitioner Summary: The effects of job strain and job control on musculoskeletal symptoms in upper extremities and work performance were smaller among workers with higher physical demands. This could imply that high physical demand jobs limit job control or psychosocial variables may not adequately capture job strain among high physical demand groups.

Ratings of Hand Activity and Force Levels among Women and Men Who Perform Identical Hand-Intensive Work Tasks

We compared hand activity and force ratings in women and men doing identical hand-intensive work tasks. Musculoskeletal disorders are more common in women and hand-intensive work leads to an increased risk of these disorders. Knowledge of the gender influence in the rating of work exposure is lacking. The aim of this study was to investigate whether women and men performing identical hand-intensive work tasks were equally rated using hand activity and normalized peak force levels with the Hand Activity Threshold Limit Value^®. Fifty-six workers participated, comprising 28 women-men pairs. Four observers-two woman-man pairs-were also involved. Self-ratings and observers' ratings of hand activity and force level were collected. The results of these ratings showed no significant gender differences in self-rated hand activity and force, as well as observer-rated hand activity. However, there was a significant gender difference in the observer-rated force, where the women were rated higher (mean (SD): women 3.9 (2.7), men 3.1 (1.8) (p = 0.01)). This difference remained significant in the adjusted model (p = 0.04) with grip strength and forearm-finger anthropometrics. The results provide new insights that observers' estimates of force can be higher in women compared with men in the same work tasks. Force should be further investigated and preferably compared to objective measurements.

Work-relatedness of carpal tunnel syndrome: Systematic review including meta-analysis and GRADE

Background and Aims

Carpal tunnel syndrome (CTS) is the most common peripheral nerve entrapment syndrome with a high prevalence among workers. Insights on the physical work-related risk factors is necessary to develop appropriate preventative methods. The objective of this systematic review, including meta-analyses, is to assess which physical work-related risk factors are associated with carpal tunnel syndrome.

Methods

Systematic literature searches were carried out using PubMed and Embase until September 6, 2021. Studies were included if: (1) CTS was clinically assessed, (2) the studies were prospective cohort studies, and (3) the exposure was reported using terms of exposed/less or nonexposed. Risk of bias was assessed using the Quality in Prognosis Studies (QUIPS) tool. Quality of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE).

Results

In total, 9270 patients with CTS from a population of 1,051,707 workers were included from 17 studies. Meta-analyses revealed high-quality evidence for associations between CTS and high exposures to repetition (hazard ratio [HR] 1.87, 95% CI 1.42-2.46), force intensity (HR 1.84, 95%CI 1.22-2.79), exposures above hand activity level of ACGIH (HR 1.75, 95%CI 1.40-2.17), and the Strain Index >10 (HR 1.58, 95% CI 1.09-2.30). No significant associations were found for pinch gripping, hand-arm vibration or force duration. High computer-use exposure was significantly associated with a decreased rate of work-related CTS (HR 0.28, 95% CI 0.12-0.64).

Conclusion

This systematic review of prospective cohort studies found high certainty for an increased rate of CTS due to a high Strain Index, exposures exceeding the Activity Level of ACGIH, and high force intensity and high repetition. Workers performing tasks requiring both high force and high repetition even have a higher rate of developing CTS.

A comparison of laparoscopic and robotic ergonomic risk

INTRODUCTION

Work related injuries in minimally invasive surgery (MIS) are common because of the strains placed on the surgeon's or assistant's body. The objective of this study was to compare specific ergonomic risks among surgeons and surgical trainees performing robotic and laparoscopic procedures.

MATERIALS AND METHODS

Ergonomic data and discomfort questionnaires were recorded from surgeons and trainees (fellows/residents) for both robotic and laparoscopic procedures. Perceived discomfort questionnaires were recorded pre/postoperatively. Intraoperatively, biomechanical loads were captured using motion tracking sensors and electromyography (EMG) sensors. Perceived discomfort, body position and muscle activity were compared between robotic and laparoscopic procedures using a linear regression model.

RESULTS

Twenty surgeons and surgical trainees performed 29 robotic and 48 laparoscopic procedures. Postoperatively, increases in right finger numbness and right shoulder stiffness and surgeon irritability were noted after laparoscopy and increased back stiffness after robotic surgery. Further, the laparoscopic group saw increases in right hand/shoulder pain (OR 0.8; p = 0.032) and left hand/shoulder pain (0.22; p < 0.001) compared to robotic. Right deltoid and trapezius excessive muscle activity were significantly higher in laparoscopic operations compared to robotic. Demanding and static positioning was similar between the two groups except there was significantly more static neck position required for robotic operations.

CONCLUSION

Robotic assisted surgeries led to lower postoperative discomfort and muscle strain in both upper extremities, particularly dominant side of the surgeon, but increased static neck positioning with subjective back stiffness compared with laparoscopy. These recognized ergonomic differences between the two platforms can be used to raise surgeon awareness of their intraoperative posture and to develop targeted physical and occupational therapy interventions to decrease surgeon WMSDs and increase surgeon longevity.

Association of psychological factors with limb disability in patients with cervical radiculopathy: comparison with carpal tunnel syndrome

Background

Regarding musculoskeletal conditions, patient’s psychological distress, are shown to be associated with higher disability. Cervical radiculopathy (CR) and carpal tunnel syndrome (CTS), are two conditions caused by entrapment of cervical nerve roots and carpal median nerve, respectively. This study aims to investigate the association of psychological factors including depression, anxiety, and pain catastrophizing, with measures of upper limb patient-reported and performance-based disability, in patients with CR, and compare the obtained results with our similar study on CTS.

Methods

In a cross-sectional study, we recruited 92 patients with CR, and investigated their disability level using patient-reported questionnaires (Quick Disabilities of the Arm, Shoulder and Hand (DASH) and pain Likert Scale) and by measuring grip and pinch strength. We also assessed their psychological status with Hospital Anxiety and Depression Scale questionnaire for depression (HADS-D) and anxiety (HADS-A) and also Pain Catastrophizing Scale (PCS) tools. We performed correlational coefficient analysis between disability and psychological scores and regression analysis of dependent variables (Pain, DASH, grip and pinch scores) and independent (psychological) variables. Finally, Z observed value was calculated to compare correlational coefficients between two diseases of CTS and CR.

Results

The results of the correlational coefficient analysis indicate that all three HADS-A, HADS-D and PCS scores correlated with DASH score (r = 0.49, 0.37, 0.38 for HADS-A, HADS-D and PCS, respectively; p < 0.001 for all three). HADS-A also significantly correlated with VAS pain score (r = 0.41, P < 0.001) and grip strength (r = − 0.25, P = 0.016). Linear regression analysis revealed that anxiety has a notable value for DASH and VAS pain scores as well as grip strength. Fisher’s r correlation coefficient to z transformation, revealed that there was no difference between two diseases of CTS and CR in terms of the resulted r coefficients from correlational coefficient analysis between disability and psychological distress.

Conclusion

It is concluded that psychological disorders are associated with disability in CR patients, with anxiety also correlating with objective disability parameter of grip strength. Finally, both CTS and CR patients’ disabilities associate with anxiety, depression, and catastrophysing thinking in a similar manner.

Level of evidence

Level IV (cross-sectional study).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05593-2.

Validation of the Revised Strain Index for Predicting Risk of Incident Carpal Tunnel Syndrome in a Prospective Cohort

The Revised Strain Index (RSI), a model that quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs, was used to quantify exposure for 1372 incident-eligible manufacturing, service and healthcare workers. Workers were followed for an average of 2.5 years (maximum 6 years) and had an average carpal tunnel syndrome (CTS) incidence rate of 4.6 per 100 person-years. Exceeding the a-priori RSI limit of 10.0 showed increased risk of CTS (Hazard Ratio (HR) = 1.45, 95% CI: 1.11-1.91, p = 0.01). There also was a dose-response relationship using proposed low (RSI ≤ 8.5, HR = 1.00), medium (HR = 1.42 (95% CI: 0.96-2.09, p = 0.08)), and high limits (RSI > 15, HR = 1.79 (95% CI: 1.19-2.69, p = 0.01), respectively. RSI as a continuous variable showed CTS risk increased steadily by between 1.9% and 3.3% per unit increase in RSI (p ≤ 0.03). These results suggest that the RSI is a useful tool for surveillance as well as for job intervention/design and continuous improvement processes.Practitioner Summary The Revised Strain Index (RSI) quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs. Increased cumulative RSI scores (i.e. daily exposure score) are associated with increased risk of carpal tunnel syndrome (CTS). The RSI is potentially useful as a risk surveillance and intervention design tool.

Anthropometrics and electromyography as predictors for maximal voluntary isometric wrist torque: Considerations for ergonomists

The purpose of this study was to evaluate anthropometry and forearm muscle activity as predictors of maximal isometric wrist torque. Thirteen anthropometric measures, forearm electromyography from flexor carpi radialis (FCR) and extensor carpi radialis (ECR), and maximal isometric wrist flexion/extension torque were obtained from 25 male participants. Pearson correlation coefficients assessed relationships between peak isometric torque and: (1) anthropometrics, (2) FCR and ECR activation, (3) FCR/ECR antagonist/agonist coactivation ratios. Based on significant correlations, linear regression equations were developed (SPSS v.25; p < 0.05). Hand thickness, forearm circumference and ECR activation or hand thickness, elbow circumference, FCR activation and body weight were most highly correlated with extension or flexion torque, respectively. Hand thickness, forearm circumference, and ECR activation (R² = 54.5%; p = 0.001) and hand thickness, elbow circumference, FCR activation (R² = 68.3%; p < 0.001) explained similar variance in torque regressions as did the addition of body weight to extension (R² = 58.0%; p = 0.001) and flexion (R² = 69.9%; p < 0.001) torque regression equations, respectively. Circumference measurements, a pseudo for muscle size, and activation amplitude influenced wrist force output more than limb length or coactivation.

The Coexistence of Carpal Tunnel Syndrome in Workers With Trigger Digit

Background: The objective of this study was to investigate the prevalence of carpal tunnel syndrome (CTS) in workers with trigger digit. There are few cross-sectional studies that assess this relationship. Methods: A baseline examination of 1216 workers from 17 diverse manufacturing facilities was conducted. Worker demographics, medical history, and symptoms of trigger digit were assessed. Age, sex, and body mass index were obtained. Biomechanical factors were individually measured using the Strain Index (SI). Prevalence was assessed with univariate and multivariate logistic regression. Results: Unadjusted prevalence of trigger digit was 12.0%, and among those workers, there was an unadjusted CTS prevalence of 26.7%. The adjusted multivariate model found an odds ratio (OR) of CTS of 1.56 (95% confidence interval [CI], 1.03-2.36) among the workers with trigger digit. The ORs of CTS for SI (OR = 1.53 [95% CI, 1.04-2.23]), age (OR = 1.03 [95% CI, 1.01-1.04]), and current smoking (OR = 1.76 [95% CI, 1.12-2.75]) were also significant. Sex and diabetes were not statistically significant covariates. Conclusion: The prevalence of CTS is higher among workers with trigger digit.

Physical Ergonomic Improvement and Safe Design of an Assembly Workstation through Collaborative Robotics

One of the key interesting features of collaborative robotic applications is the potential to lighten the worker workload and potentiate better working conditions. Moreover, developing robotics applications that meets ergonomic criteria is not always a straightforward endeavor. We propose a framework to guide the safe design and conceptualization of ergonomic-driven collaborative robotics workstations. A multi-disciplinary approach involving robotics and ergonomics and human factors shaped this methodology that leads future engineers through the digital transformation of a manual assembly (with repetitive and hazardous operations) to a hybrid workstation, focusing on the physical ergonomic improvement. The framework follows four main steps, (i) the characterization of the initial condition, (ii) the risk assessment, (iii) the definition of requirements for a safe design, and (iv) the conceptualization of the hybrid workstation with all the normative implications it entails. We applied this methodology to a case study in an assembly workstation of a furniture manufacturing company. Results show that the methodology adopted sets an adequate foundation to accelerate the design and development of new human-centered collaborative robotic workstations.

Lean Manufacturing and Ergonomics Integration: Defining Productivity and Wellbeing Indicators in a Human–Robot Workstation

Lean Manufacturing (LM), Ergonomics and Human Factors (E&HF), and Human–Robot Collaboration (HRC) are vibrant topics for researchers and companies. Among other emergent technologies, collaborative robotics is an innovative solution to reduce ergonomic concerns and improve manufacturing productivity. However, there is a lack of studies providing empirical evidence about the implementation of these technologies, with little or no consideration for E&HF. This study analyzes an industrial implementation of a collaborative robotic workstation for assembly tasks performed by workers with musculoskeletal complaints through a synergistic integration of E&HF and LM principles. We assessed the workstation before and after the implementation of robotic technology and measured different key performance indicators (e.g., production rate) through a time study and direct observation. We considered 40 postures adopted during the assembly tasks and applied three assessment methods: Rapid Upper Limb Assessment, Revised Strain Index, and Key Indicator Method. Furthermore, we conducted a questionnaire to collect more indicators of workers’ wellbeing. This multi-method approach demonstrated that the hybrid workstation achieved: (i) a reduction of production times; (ii) an improvement of ergonomic conditions; and (iii) an enhancement of workers’ wellbeing. This ergonomic lean study based on human-centered principles proved to be a valid and efficient method to implement and assess collaborative workstations, foreseeing the continuous improvement of the involved processes.

Role of Biomechanical Factors in Resolution of Carpal Tunnel Syndrome Among a Population of Workers

OBJECTIVES

Identify if Carpal tunnel syndrome (CTS) symptoms vary by measured biomechanical exposures.

METHODS

A nested prospective cohort within a large, multicenter, 8-year cohort study. The CTS case definition was tingling/numbness in 2+ median nerve-served digits plus a nerve conduction study consistent with CTS. Workers were assigned to: (1) low (strain index [SI] less than or equal to 6.1), and (2) high (SI more than 6.1) job groups.

RESULTS

Among 1201 workers, 106 had CTS. Those in the high SI group became and remained symptom-free for at least 3 months, faster than the low SI group, adjusted hazard ratio (HR) = 2.07 (95% confidence interval [CI] = 1.21 to 3.56, P = 0.008). Only surgical release trended towards resolving CTS. Light duty had no impact, and job change was associated with delayed symptoms resolution.

CONCLUSIONS

High biomechanical exposures paradoxically predicted faster improvement in CTS and light duty did not result in symptom resolution.

Musculoskeletal Complaints in Occupational Therapists Compared to the General Population: A Cross-Sectional Study in Germany

Occupational therapists (OTs) are exposed to physical factors at work, which can lead to an increased risk of musculoskeletal disorders. Most studies examining musculoskeletal complaints in OT report that the neck, shoulders, and lower back are most often afflicted. The aim of the present study was to examine the impact of work as an OT (focusing on specific work tasks) on specific musculoskeletal complaints compared to the general working population. A cross-sectional study involving a self-administered standardized questionnaire was conducted from January until October 2015 in Germany. In OT and the comparison group, the highest 12-month prevalence of musculoskeletal disorders were observed for the lower back, the neck, and the shoulders. In contrast, elevated prevalence ratios (PR) were found for OT in the thumbs (PR = 2.7; 95% CI = 1.9-3.8), the wrists (PR = 1.4; 95% CI = 1.1-1.8), and the elbows (PR = 1.5; 95% CI = 1.0-2.2). OTs were particularly exposed to high exertion hand activity and several stressful postures at work. In conclusion, OTs seem to be at risk of developing work-related musculoskeletal complaints in the thumbs, wrists, and elbows. Preventive measures should help to reduce the exposures caused by highly repetitive and forceful hand activities.

An Upper Extremity Risk Assessment Tool Based on Material Fatigue Failure Theory: The Distal Upper Extremity Tool (DUET)

OBJECTIVE

Musculoskeletal tissues repeatedly loaded in vitro fail in accordance with material fatigue failure theory, and there is evidence to suggest that the same process occurs in vivo. The current paper presents a new upper extremity risk assessment tool, the Distal Upper Extremity Tool (DUET), predicated on material fatigue failure theory.

METHODS

DUET requires an estimate of force exertion level and the number of repetitions performed to derive estimates of damage and probabilities of experiencing a distal upper extremity outcome. Damage accrued over multiple tasks may be summed to estimate the cumulative damage (CD) accrued over a workday. Validation of this tool was performed using five distal upper extremity (DUE) outcomes (involving medical visits and pain) from an existing epidemiological database involving data from six automotive manufacturing plants. Logistic regression was used to assess the association of the log of the DUET CD measure to DUE outcomes.

RESULTS

Results demonstrated that the log of the DUET CD measure was highly associated with all five DUE outcomes in both crude analyses and those adjusted for site, age, gender, and body mass index ( p < .01). A model relating the continuous DUET log CD score to the probability of the DUE outcome Injury + Pain Last Year was developed, which demonstrated a significant dose-response relationship.

CONCLUSIONS

Results suggest that fatigue failure-based risk assessment techniques are highly associated with DUE outcomes and provide support for the notion that an underlying fatigue failure process may be involved in the development of upper extremity musculoskeletal disorders.

Psychosocial Factors Related to Lateral and Medial Epicondylitis: Results From Pooled Study Analyses

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.

Risk assessments using the Strain Index and the TLV for HAL, Part II: Multi-task jobs and prevalence of CTS

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.

Risk assessments using the Strain Index and the TLV for HAL, Part I: Task and multi-task job exposure classifications

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.

Estimating and Interpreting Effects from Nonlinear Exposure-Response Curves in Occupational Cohorts Using Truncated Power Basis Expansions and Penalized Splines

Truncated power basis expansions and penalized spline methods are demonstrated for estimating nonlinear exposure-response relationships in the Cox proportional hazards model. R code is provided for fitting models to get point and interval estimates. The method is illustrated using a simulated data set under a known exposure-response relationship and in a data application examining risk of carpal tunnel syndrome in an occupational cohort.

The Composite Strain Index (COSI) and Cumulative Strain Index (CUSI): methodologies for quantifying biomechanical stressors for complex tasks and job rotation using the Revised Strain Index

The Composite Strain Index (COSI) quantifies biomechanical stressors for complex tasks consisting of exertions at different force levels and/or with different exertion times. The Cumulative Strain Index (CUSI) further integrates biomechanical stressors from different tasks to quantify exposure for the entire work shift. The paper provides methodologies to compute COSI and CUSI along with examples. Complex task simulation produced 169,214 distinct tasks. Use of average, time-weighted average (TWA) and peak force and COSI classified 66.9, 28.2, 100 and 38.9% of tasks as hazardous, respectively. For job rotation the simulation produced 10,920 distinct jobs. TWA COSI, peak task COSI and CUSI classified 36.5, 78.1 and 66.6% jobs as hazardous, respectively. The results suggest that the TWA approach systematically underestimates the biomechanical stressors and peak approach overestimates biomechanical stressors, both at the task and job level. It is believed that the COSI and CUSI partially address these underestimations and overestimations of biomechanical stressors. Practitioner Summary: COSI quantifies exposure when applied hand force and/or duration of that force changes during a task cycle. CUSI integrates physical exposures from job rotation. These should be valuable tools for designing and analysing tasks and job rotation to determine risk of musculoskeletal injuries.

The Revised Strain Index: an improved upper extremity exposure assessment model

The Revised Strain Index (RSI) is a distal upper extremity (DUE) physical exposure assessment model based on: intensity of exertion, frequency of exertion, duration per exertion, hand/wrist posture and duration of task per day. The RSI improves upon the 1995 Strain Index (SI) by using continuous rather than categorical multipliers, and replacing duty cycle with duration per exertion. In a simulation of 13,944 tasks, the RSI and 1995 SI showed good agreement in risk predictions for 1995 SI scores ≤3 (safe) and >13.5 (hazardous). For tasks with 1995 SI scores of >3 and ≤13.5, the two models showed marked disagreement, with the RSI providing much greater discriminations between 'safe' and 'hazardous' tasks for various combinations of force, repetition and duty cycle. We believe the RSI is a substantially improved model that will be useful for DUE task analysis, intervention and design. Practitioner Summary: RSI is a substantial improvement over the 1995 SI. It should be a valuable tool for designing and analysing tasks to determine risk of musculoskeletal injuries. RSI is applicable to a wide variety of tasks including very low force and very high repetition tasks such as keyboard use.

Association between Epicondylitis and Cardiovascular Risk Factors in Pooled Occupational Cohorts

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.

Risk assessment of cheese processing tasks using the Strain Index and OCRA Checklist

The purpose of this study was to conduct and compare two ergonomic risk assessment methods often used in occupational health research and practice: the Strain Index (SI) and Occupational Repetitive Actions (OCRA) Checklist. Seven raters used the SI and OCRA Checklist to assess task-level physical exposures to the upper extremity of workers performing 21 cheese-manufacturing tasks. Of the total task exposures assessed with both methods, nearly half (49.1%) were classified as hazardous using the OCRA Checklist while 60.2% were classified as hazardous using the SI. Although the underlying injury risk characterization constructs of the SI and OCRA Checklist differ, the results indicated that the SI and OCRA Checklist often classified job tasks into similar risk categories. The differences in risk classifications determined by the SI and OCRA Checklist for job tasks were likely related to the definition of variables measured by these assessment methods as well as the complexity of tasks evaluated. By design, the SI is specific to the distal upper extremity while the OCRA Checklist accounts for the entire upper extremity including the shoulder. When conducting risk assessments of industrial work tasks, the choice of analysis tools should be based on the purpose of the assessment and the complexity of task functions. Both the SI and OCRA Checklist yield risk assessment ratings that are similar for cheese processing tasks.

Prevalence, risks and severity of musculoskeletal disorder symptoms among administrative employees of a Brazilian company

BACKGROUND

Musculoskeletal disorders (MSD) are common among office workers.

OBJECTIVE

To evaluate the prevalence, risks and symptoms of MSD among office workers of a Brazilian dairy company.

METHODS

Fifty office workers participated in the study. The following evaluations and questionnaires were completed: Rapid Upper Limb Assessment, Strain Index, Muscle Fatigue Assessment, Nordic General Questionnaire, and Oswestry Disability Index.

RESULTS

Seventy-four percent (n = 37) of the participants had MSD symptoms. The back was most commonly affected body part (81% , n = 30), followed by the upper limbs (70% , n = 26). Fifty-three percent of the workers with low back pain had mild to moderate disability, and the risk for the hands, wrists and fingers was moderate. Changes are required to reduce the risk of MSD among the participating office workers.

CONCLUSION

The prevalence of MSD symptoms was high; the back and upper limbs were most commonly affected. Data from the evaluations and questionnaires supplemented each other. The Rapid Upper Limb Assessment and Strain Index were better indicators of risk of MSD symptoms than the Muscle Fatigue Assessment. The participating office workers were exposed to moderate risk of developing MSD due to biomechanical overload and changes are required.

Impact of Work Organizational Factors on Carpal Tunnel Syndrome and Epicondylitis

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.

Diabetes as a risk factor for carpal tunnel syndrome: a systematic review and meta-analysis

AIMS

To assess whether diabetes increases the risk of carpal tunnel syndrome and to estimate the magnitude of the association with Type 1 and Type 2 diabetes.

METHODS

We conducted a systematic search of PubMed, Embase, Web of Science, Scopus, Google Scholar and ResearchGate for articles published between 1950 and January 2015. A total of 36 studies (eight cross-sectional, 21 case-control and seven cohort studies) qualified for meta-analysis. We used a random-effects meta-analysis and assessed heterogeneity and publication bias.

RESULTS

The pooled odds ratio of 25 studies (including a total of 92 564 individuals) that reported unadjusted estimates for the association between diabetes and carpal tunnel syndrome or carpal tunnel release was 1.97 (95% CI 1.56-2.49). The pooled odds ratio of 18 case-control or cohort studies consisting of >37 million individuals that reported estimates after controlling for potential confounders was 1.69 (95% CI 1.45-1.96). The association did not differ for Type 1 and Type 2 diabetes. Furthermore, there was no publication bias.

CONCLUSION

This meta-analysis suggests that both Type 1 and Type 2 diabetes are risk factors for carpal tunnel syndrome.

The effect of excess body mass on the risk of carpal tunnel syndrome: a meta-analysis of 58 studies

We aimed to estimate the effects of overweight and obesity on carpal tunnel syndrome (CTS), and to assess whether sex modifies the associations. Literature searches were conducted in PubMed, Embase, Web of Science, Scopus, Google Scholar and ResearchGate databases from 1953 to February 2015. Fifty-eight studies consisting of 1,379,372 individuals qualified for a meta-analysis. We used a random-effects meta-analysis, assessed heterogeneity and publication bias, and performed sensitivity analyses. Overweight increased the risk of CTS or carpal tunnel release 1.5-fold (pooled confounder-adjusted odds ratio [OR] = 1.47, 95% CI 1.37-1.57, N = 1,279,546) and obesity twofold (adjusted OR = 2.02, 95% CI 1.92-2.13, N = 1,362,207). Each one-unit increase in body mass index increased the risk of CTS by 7.4% (adjusted OR = 1.074, 95% CI 1.071-1.077, N = 1,258,578). Overweight and obesity had stronger effects on carpal tunnel release than CTS. The associations did not differ between men and women, and they were independent of study design. Moreover, the associations were not due to bias or confounding. Excess body mass markedly increases the risk of CTS. As the prevalence of overweight and obesity is increasing globally, overweight-related CTS is expected to increase. Future studies should investigate whether a square-shaped wrist and exposure to physical workload factors potentiate the adverse effect of obesity on the median nerve.

Occupational mononeuropathies in industry

Peripheral nerve injuries have the potential to cause significant disability and can be commonly associated with recreational and occupational activities. Acute nerve injuries are mainly related to violent trauma, while repeated mechanical trauma due to external forces or repetitive motions can produce chronic nerve compression injury. This chapter will present a narrative review of the existing evidence of the association between peripheral compressive nerve disorders and work-related risk factors. Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy in the general population and in working populations employed in manual repetitive and forceful activities. The work-relatedness of CTS is essentially based on epidemiologic evidence and the results of experimental studies showing the capability of repetitive wrist extreme postures, associated with hand-wrist forceful exertions, to increase the pressure inside the carpal tunnel and to compress the median nerve. Assembly industry, food processing and packaging, hand-arm vibrating tools, and jobs involving high-repetition, high-force tasks put workers at risk for CTS. Less strong evidence exists of the association between ulnar elbow neuropathy and manual tasks or repetitive stretch on squatting and peroneal nerve neuropathy at the fibular head. Very few reports are available about the association between occupation and other compressive peripheral nerve injuries.

The inter-rater reliability of Strain Index and OCRA Checklist task assessments in cheese processing

The purpose of this study was to characterize the inter-rater reliability of two physical exposure assessment methods of the upper extremity, the Strain Index (SI) and Occupational Repetitive Actions (OCRA) Checklist. These methods are commonly used in occupational health studies and by occupational health practitioners. Seven raters used the SI and OCRA Checklist to assess task-level physical exposures to the upper extremity of workers performing 21 cheese manufacturing tasks. Inter-rater reliability was characterized using a single-measure, agreement-based intraclass correlation coefficient (ICC). Inter-rater reliability of SI assessments was moderate to good (ICC = 0.59, 95% CI: 0.45-0.73), a similar finding to prior studies. Inter-rater reliability of OCRA Checklist assessments was excellent (ICC = 0.80, 95% CI: 0.70-0.89). Task complexity had a small, but non-significant, effect on inter-rater reliability SI and OCRA Checklist scores. Both the SI and OCRA Checklist assessments possess adequate inter-rater reliability for the purposes of occupational health research and practice. The OCRA Checklist inter-rater reliability scores were among the highest reported in the literature for semi-quantitative physical exposure assessment tools of the upper extremity. The OCRA Checklist however, required more training time and time to conduct the risk assessments compared to the SI.

Associations between Distal Upper Extremity Job Physical Factors and Psychosocial Measures in a Pooled Study

Introduction. There is an increasing body of literature relating musculoskeletal diseases to both job physical exposures and psychosocial outcomes. Relationships between job physical exposure measures and psychosocial factors have not been well examined or quantified. These exploratory analyses evaluate relationships between quantified exposures and psychosocial outcomes. Methods. Individualized quantification of duration, repetition, and 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. Relationships and predicted probabilities were assessed using ordered logistic regression. Analyses were adjusted for age, BMI, and gender. Results and Discussion. Among 1834 study participants there were multiple statistically significant relationships. In general, as duration, repetition, and force increased, psychosocial factors worsened. However, general health and mental exhaustion improved with increasing job exposures. Depression was most strongly associated with increased repetition, while physical exhaustion was most strongly associated with increased force. SI and TLV for HAL were significantly related to multiple psychosocial factors. These relationships persisted after adjustment for strong confounders. Conclusion. This study quantified multiple associations between job physical exposures and occupational and nonoccupational psychosocial factors. Further research is needed to quantify the impacts on occupational health outcomes.

Association between work-related biomechanical risk factors and the occurrence of carpal tunnel syndrome: an overview of systematic reviews and a meta-analysis of current research

BACKGROUND

Occupational risks for carpal tunnel syndrome (CTS) have been examined in various occupations, and several systematic reviews (SRs) have been published on this topic. There has been no critical appraisal or synthesis of the evidence in the SRs. The aims of this study are (1) to synthesise the observational evidence and evaluate the methodological quality of SRs that assess the effect of biomechanical risk factors on the development of CTS in workers, (2) to provide an update of current primary research on this association, (3) to assess a potential dose-response relationship.

METHODS

We searched MEDLINE, EMBASE, CINAHL, the Cochrane Library and the reference lists of articles. The first step covered SRs (1998-2014), and the second step covered current primary studies (2011-2014). The methodological quality of the SRs was evaluated by using the AMSTAR-R tool; primary studies were assessed using a list of 20 items. A qualitative approach was used for synthesising evidence. In addition, we undertook a meta-analysis of the primary studies to determine risk ratios in the dose-response relationship.

RESULTS

We identified ten SRs that covered a total of 143 original studies. Seven primary studies met the criteria for inclusion, of which four provided longitudinal data. We found high quality of evidence for risk factors such as repetition, force and combined exposures. Moderate quality of evidence was observed for vibration, and low quality of evidence was found for wrist postures. An association between computer use and CTS could not be established. Recent primary studies supported the existence of a significant relationship between CTS and repetition, force and combined exposure. The meta-analysis of current research revealed a dose-response relationship between CTS and the American Conference of Governmental Industrial Hygienists' (ACGIH) threshold limit value (TLV) for hand-activity level (HAL). Those between the action limit and TLV and above TLV had RR of 1.5 (95% CI 1.02-2.31) and RR 2.0 (95% CI 1.46-2.82), respectively.

CONCLUSIONS

Occupational biomechanical factors play a substantial role in the causation of CTS. Data from current primary studies on dose-response suggest that the risk of CTS increases with the ACGIH TLV levels.

Relationships between job organisational factors, biomechanical and psychosocial exposures

The relationships between work organisational, biomechanical and psychosocial factors were studied using cross-sectional data from a pooled dataset of 1834 participants. The work organisational factors included: job rotation, overtime work, having second jobs and work pace. Task and job level biomechanical variables were obtained through sub-task data collected in the field or analysed in the laboratory. Psychosocial variables were collected based on responses to 10 questions. The results showed that job rotations had significant effects on all biomechanical and most psychosocial measures. Those with job rotations generally had higher job biomechanical stressors, and lower job satisfaction. Overtime work was associated with higher job biomechanical stressors, and possibly self-reported physical exhaustion. Those having second jobs reported getting along with co-workers well. Work pace had significant influences on all biomechanical stressors, but its impact on job biomechanical stressors and psychosocial effects are complicated.

PRACTITIONER SUMMARY

The findings are based on a large number of subjects collected by three research teams in diverse US workplaces. Job rotation practices used in many workplaces may not be effective in reducing job biomechanical stressors for work-related musculoskeletal disorders. Overtime work is also associated with higher biomechanical stressors.

Predictors Associated With Changes of Weight and Total Cholesterol Among Two Occupational Cohorts Over 10 Years

OBJECTIVE

To ascertain worker health characteristics and psychosocial factors associated with changes in body weight and total cholesterol (TC) among two production operation populations.

METHODS

We performed descriptive and predictive analysis of questionnaire data and biomedical measurements from two prospective cohort studies. Our key outcomes were changes in weight, and TC over 5 to 10 years between baseline and exit assessments.

RESULTS

A total of 146 subjects were analyzed. Increases in weight were associated with belief in being overweight and baseline overweight and obesity. Increases in TC levels were associated with female sex, belief that TC levels were "not good," and feeling depressed.

CONCLUSIONS

Most of the reported associations with increases in weight and TC levels are amenable to interventions and may be a target for workplace intervention programs.

Associations between workplace factors and carpal tunnel syndrome: A multi-site cross sectional study

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.

Computer use and carpal tunnel syndrome: A meta-analysis

BACKGROUND

Studies have reported contradictory results on the role of keyboard or mouse use in carpal tunnel syndrome (CTS). This meta-analysis aimed to assess whether computer use causes CTS.

METHODS

Literature searches were conducted in several databases until May 2014. Twelve studies qualified for a random-effects meta-analysis. Heterogeneity and publication bias were assessed.

RESULTS

In a meta-analysis of six studies (N=4964) that compared computer workers with the general population or other occupational populations, computer/typewriter use (pooled odds ratio (OR)=0.72, 95% confidence interval (CI) 0.58-0.90), computer/typewriter use ≥1 vs. <1h/day (OR=0.63, 95% CI 0.38-1.04) and computer/typewriter use ≥4 vs. <4h/day (OR=0.68, 95% CI 0.54-0.87) were inversely associated with CTS. Conversely, in a meta-analysis of six studies (N=5202) conducted among office workers, CTS was positively associated with computer/typewriter use (pooled OR=1.34, 95% CI 1.08-1.65), mouse use (OR=1.93, 95% CI 1.43-2.61), frequent computer use (OR=1.89, 95% CI 1.15-3.09), frequent mouse use (OR=1.84, 95% CI 1.18-2.87) and with years of computer work (OR=1.92, 95% CI 1.17-3.17 for long vs. short). There was no evidence of publication bias for both types of studies.

CONCLUSIONS

Studies that compared computer workers with the general population or several occupational groups did not control their estimates for occupational risk factors. Thus, office workers with no or little computer use are a more appropriate comparison group than the general population or several occupational groups. This meta-analysis suggests that excessive computer use, particularly mouse usage might be a minor occupational risk factor for CTS. Further prospective studies among office workers with objectively assessed keyboard and mouse use, and CTS symptoms or signs confirmed by a nerve conduction study are needed.

A frequency-duty cycle equation for the ACGIH hand activity level

A new equation for predicting the hand activity level (HAL) used in the American Conference for Government Industrial Hygienists threshold limit value®(TLV®) was based on exertion frequency (F) and percentage duty cycle (D). The TLV® includes a table for estimating HAL from F and D originating from data in Latko et al. (Latko WA, Armstrong TJ, Foulke JA, Herrin GD, Rabourn RA, Ulin SS, Development and evaluation of an observational method for assessing repetition in hand tasks. American Industrial Hygiene Association Journal, 58(4):278-285, 1997) and post hoc adjustments that include extrapolations outside of the data range. Multimedia video task analysis determined D for two additional jobs from Latko's study not in the original data-set, and a new nonlinear regression equation was developed to better fit the data and create a more accurate table. The equation, HAL = 6:56 ln D[F(1:31) /1+3:18 F(1:31), generally matches the TLV® HAL lookup table, and is a substantial improvement over the linear model, particularly for F>1.25 Hz and D>60% jobs. The equation more closely fits the data and applies the TLV® using a continuous function.