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1.  Study protocol title: a prospective cohort study of low back pain 
Few prospective cohort studies of workplace low back pain (LBP) with quantified job physical exposure have been performed. There are few prospective epidemiological studies for LBP occupational risk factors and reported data generally have few adjustments for many personal and psychosocial factors.
A multi-center prospective cohort study has been incepted to quantify risk factors for LBP and potentially develop improved methods for designing and analyzing jobs. Due to the subjectivity of LBP, six measures of LBP are captured: 1) any LBP, 2) LBP ≥ 5/10 pain rating, 3) LBP with medication use, 4) LBP with healthcare provider visits, 5) LBP necessitating modified work duties and 6) LBP with lost work time. Workers have thus far been enrolled from 30 different employment settings in 4 diverse US states and performed widely varying work. At baseline, workers undergo laptop-administered questionnaires, structured interviews, and two standardized physical examinations to ascertain demographics, medical history, psychosocial factors, hobbies and physical activities, and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of low back pain. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. The lifetime cumulative incidence of low back pain will also include those with a past history of low back pain. Incident cases will exclude prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.
Data analysis of a prospective cohort study of low back pain is underway and has successfully enrolled over 800 workers to date.
PMCID: PMC3599364  PMID: 23497211
Epidemiology; Ergonomics; Cohort; Low back pain; NIOSH lifting equation
2.  Incidence of ulnar nerve entrapment at the elbow in repetitive work 
Despite the high frequency of work-related musculoskeletal disorders (WRMD), the relations between working conditions and ulnar nerve entrapment at the elbow (UNEE) has not been the object of much study. We studied the predictive factors for UNEE in a three-year prospective survey of upper-limb WRMD in repetitive work.
In 1993–1994 and three years later, 598 workers whose jobs involve repetitive work were examined by their occupational health physicians and completed a self-administered questionnaire. Predictive factors associated with the onset of UNEE were studied with bivariate and multivariate analysis.
Annual incidence was estimated at 0.8% per person year, based on 15 new cases during this three-year period. Holding a tool in position was the only predictive biomechanical factor (OR = 4.1, CI 1.4–12.0). Obesity increased the risk of UNEE (OR = 4.3, CI 1.2–16.2), as did presence of medial epicondylitis, carpal tunnel syndrome, radial tunnel syndrome, and cervicobrachial neuralgia. The associations with “holding a tool in position” and obesity were unchanged when the presence of other diagnoses was taken into account.
Despite the limitations of the study, the results suggest that UNEE incidence is associated with one biomechanical risk factor (holding a tool in position, repetitively), with overweight, and with other upper-limb WRMD, especially medial epicondylitis and other nerve entrapment disorders (cervicobrachial neuralgia, carpal and radial tunnel syndromes).
PMCID: PMC2988822  PMID: 15250652
Adult; Comorbidity; Cubital Tunnel Syndrome; epidemiology; etiology; Cumulative Trauma Disorders; complications; epidemiology; Female; France; epidemiology; Humans; Incidence; Logistic Models; Male; Middle Aged; Musculoskeletal Diseases; classification; epidemiology; Obesity; complications; Occupational Diseases; complications; epidemiology; Occupations; classification; Posture; physiology; Prospective Studies; Questionnaires; Risk Factors; Workplace; psychology; elbow; repetitive work; ulnar nerve entrapment; work-related musculoskeletal disorder
3.  Psychological factors at work and musculoskeletal disorders: a one year prospective study 
Rheumatology International  2013;33(12):2975-2983.
The etiology of musculoskeletal disorders is complex, with physical and psychosocial working conditions playing an important role. This study aimed to determine the relationship between psychosocial work conditions, such as psychological job demands, decision latitude, social support and job insecurity and musculoskeletal complains (MSCs) and (repetitive strain injuries (RSIs) in a 1-year prospective study. The job content questionnaire, the Nordic musculoskeletal questionnaire and provocation tests were used to study 725 employees aged 20–70 years. Pain in the lower back (58 % of subjects), neck (57 %), wrists/hands (47 %) and upper back (44 %) was most frequent. The carpal tunnel syndrome (CTS) (33.6 %), rotator cuff tendinitis (15.4 %), Guyon’s canal syndrome (13.4 %), lateral epicondylitis (7.6 %), medial epicondylitis (5.3 %), tendinitis of forearm–wrist extensors (7.8 %) and tendinitis of forearm–wrist flexors (7.3 %) were the most frequent RSIs. Logistic analysis showed that increased psychological job demands statistically significantly increased the probability of lateral and medial epicondylitis, and increased control (decision latitude) statistically significantly decreased the risk of CTS. There was no relationship between job insecurity, social support and the studied RSIs. Psychosocial factors at work predict prevalence of MSCs and RSIs, irrespectively of demographic factors, e.g., age or gender, and organizational and physical factors.
PMCID: PMC3832752  PMID: 23934521
MSDs; Psychosocial factors; Work demands
4.  Why are manual workers at high risk of upper limb disorders? The role of physical work factors in a random sample of workers in France (the Pays de la Loire study) 
To investigate the reasons for the excess risk of upper limb musculoskeletal disorders among manual workers compared with other workers in a random sample of 2656 French men and women (20–59 years old) participating in a study on the prevalence of work related upper limb disorders conducted by France's National Institute of Health Surveillance.
Prevalence ratios (PR) of physician‐diagnosed musculoskeletal disorders of the shoulder, elbow, wrist, and hand (any of six leading disorders, rotator cuff syndrome, carpal tunnel syndrome) in manual versus non‐manual workers were calculated using Cox regression models with a constant time of follow up and robust variance.
11.3% of men and 15.1% of women were diagnosed with an upper limb disorder. The risk was especially high in manual workers (PRs: 1.40 to 2.10). Physical work factors accounted for over 50% of occupational disparities overall, 62% (men) to 67% (women) for rotator cuff syndrome, and 96% (women) for carpal tunnel syndrome. The authors calculated that under lower levels of physical work exposures, up to 31% of cases among manual workers could have been prevented.
In working men and women, upper limb musculoskeletal disorders are frequent. Physical work exposures, such as repetitive and forceful movements, are an important source of risk and in particular account for a large proportion of excess morbidity among manual workers.
PMCID: PMC2077990  PMID: 16787978
biomechanical exposures; manual worker; musculoskeletal diseases; occupational exposures; upper extremity
5.  Why are manual workers at high risk of upper limb disorders? The role of physical work factors in a random sample of workers in France (the Pays de la Loire study) 
We investigated occupational disparities in the risk of upper limb musculoskeletal disorders in a random sample of 2 656 French workers (age 20–59) participating in a study on the prevalence of work-related upper limb disorders, launched by the National Institute of Health Surveillance. Prevalence ratios (PR) of physician-diagnosed musculoskeletal disorders of the shoulder, elbow, wrist and hand (any of six leading disorders, rotator cuff syndrome, carpal tunnel syndrome) in manual vs. non-manual workers were calculated using Cox regression models with a constant time of follow-up and robust variance. 11% of men and 15% of women were diagnosed with an upper limb disorder. The risk was especially high in manual workers (PRs: 1.44 to 2.10). Physical work factors accounted for over 50% of occupational disparities overall, 62 (men) to 67% (women) for rotator cuff syndrome, and 96% (women) for carpal tunnel syndrome. We calculated that under lower levels of physical work exposures, up to 31% of cases among manual workers could have prevented. In working men and women, upper limb musculoskeletal disorders are frequent. Physical work exposures, such as repetitive and forceful movements, are an important source of risk, particularly among manual workers.
PMCID: PMC2077990  PMID: 16787978
Adult; Cross-Sectional Studies; Female; France; epidemiology; Humans; Male; Middle Aged; Musculoskeletal Diseases; epidemiology; etiology; Occupational Diseases; epidemiology; etiology; Prevalence; Regression Analysis; Risk Factors; Upper Extremity
6.  Work-organisational and personal factors associated with upper body musculoskeletal disorders among sewing machine operators 
To assess the contribution of work-organisational and personal factors to the prevalence of work-related musculoskeletal disorders (WMSDs) among garment workers in Los Angeles.
This is a cross-sectional study of self-reported musculoskeletal symptoms among 520 sewing machine operators from 13 garment industry sewing shops. Detailed information on work-organisational factors, personal factors, and musculoskeletal symptoms were obtained in face-to-face interviews. The outcome of interest, upper body WMSD, was defined as a worker experiencing moderate or severe musculoskeletal pain. Unconditional logistic regression models were adopted to assess the association between both work-organisational factors and personal factors and the prevalence of musculoskeletal pain.
The prevalence of moderate or severe musculoskeletal pain in the neck/shoulder region was 24% and for distal upper extremity it was 16%. Elevated prevalence of upper body pain was associated with age less than 30 years, female gender, Hispanic ethnicity, being single, having a diagnosis of a MSD or a systemic illness, working more than 10 years as a sewing machine operator, using a single sewing machine, work in large shops, higher work–rest ratios, high physical exertion, high physical isometric loads, high job demand, and low job satisfaction.
Work-organisational and personal factors were associated with increased prevalence of moderate or severe upper body musculoskeletal pain among garment workers. Owners of sewing companies may be able to reduce or prevent WMSDs among employees by adopting rotations between different types of workstations thus increasing task variety; by either shortening work periods or increasing rest periods to reduce the work–rest ratio; and by improving the work-organisation to control psychosocial stressors. The findings may guide prevention efforts in the garment sector and have important public health implications for this workforce of largely immigrant labourers.
PMCID: PMC2095384  PMID: 17522131
work organisation; musculoskeletal disorder; ergonomic; psychosocial; sewing machine
7.  Natural history and predictors of long-term pain and function among workers with hand symptoms 
To evaluate predictors of hand symptoms and functional impairment after three years of follow-up among workers with different types of hand symptoms including carpal tunnel syndrome (CTS). Functional status and job limitations were also analyzed as key secondary objectives.
Cohort design of 3-years duration
Working population-based study
1107 newly employed workers without a pre-existing diagnosis of CTS. Subjects were categorized into four groups at baseline examination: no hand symptoms, any hand symptoms but not CTS (recurring symptoms in hands, wrist or fingers without neuropathic symptoms), any hand symptoms of CTS (neuropathic symptoms in the fingers and normal nerve conduction study), or confirmed CTS (CTS symptoms and abnormal nerve conduction study). Among workers with hand pain at baseline, subject and job characteristics were assessed as prognostic factors for outcomes, using bivariate and multivariate regression models.
Not applicable
Main outcome measure
The primary outcome assessed by questionnaire at 3 years was “severe hand pain” in the past 30 days.
At baseline, 155 workers (17.5% of 888 followed workers) reported hand symptoms, 21 had confirmed CTS. Presence of hand pain at baseline was a strong predictor of future hand pain and job impairment. Subjects with confirmed CTS at baseline were more likely to report severe hand pain, (adjusted prevalence ratios 1.98 [1.11 – 3.52]) and functional status impairment (adjusted prevalence ratios 3.37 [1.01 – 11.29]) than workers with other hand pain. Among subjects meeting our case definition for CTS at baseline, only 4 (19.1%) reported seeing a physician in the 3 year period.
Hand symptoms persisted among many workers after 3 year follow-up, especially among those with CTS, yet few symptomatic workers had seen a physician.
PMCID: PMC3695071  PMID: 23416766
hand; pain; Carpal Tunnel Syndrome; functional status; work
8.  Risk factors for carpal tunnel syndrome in a general population. 
OBJECTIVE: To determine the individual, physical, and psychosocial risk factors for carpal tunnel syndrome in a general population. METHODS: Population based case-control study in Marshfield epidemiological study area in Wisconsin, USA. Cases were men and women aged 18-69 with newly diagnosed carpal tunnel syndrome (n = 206 (83.1%) of 248 eligible). Controls were a random sample of residents of the study area who had no history of diagnosed carpal tunnel syndrome (n = 211 (81.5%) of 259 eligible). Cases and controls were matched by age. Telephone interviews and reviews of medical records obtained height and weight, medical history, average daily hours of exposure to selected physical and organisational work factors, and self ratings on psychosocial work scales. RESULTS: In the final logistic regression model, five work and three non-work variables were associated with risk of carpal tunnel syndrome, after adjusting for age. For each one unit of increase in body mass index (kg/m2), risk increased 8% (odds ratio (OR) 1.08; 95% confidence interval (95% CI) 1.03 to 1.14). Having a previous musculoskeletal condition was positively associated with carpal tunnel syndrome (OR 2.54; 95% CI 1.03 to 6.23). People reporting the least influence at work had 2.86 times the risk (95% CI, 1.10 to 7.14) than those with the most influence at work. CONCLUSIONS: Carpal tunnel syndrome is a work related disease, although some important measures of occupational exposure, including keyboard use, were not risk factors in this general population study. The mechanism whereby a weight gain of about six pounds increases the risk of disease 8% requires explanation.
PMCID: PMC1128928  PMID: 9404321
9.  Prediction of chronic disability in work-related musculoskeletal disorders: a prospective, population-based study 
Disability associated with work-related musculoskeletal disorders is an increasingly serious societal problem. Although most injured workers return quickly to work, a substantial number do not. The costs of chronic disability to the injured worker, his or her family, employers, and society are enormous. A means of accurate early identification of injured workers at risk for chronic disability could enable these individuals to be targeted for early intervention to promote return to work and normal functioning. The purpose of this study is to develop statistical models that accurately predict chronic work disability from data obtained from administrative databases and worker interviews soon after a work injury. Based on these models, we will develop a brief instrument that could be administered in medical or workers' compensation settings to screen injured workers for chronic disability risk.
This is a population-based, prospective study. The study population consists of workers who file claims for work-related back injuries or carpal tunnel syndrome (CTS) in Washington State. The Washington State Department of Labor and Industries claims database is reviewed weekly to identify workers with new claims for work-related back injuries and CTS, and these workers are telephoned and invited to participate. Workers who enroll complete a computer-assisted telephone interview at baseline and one year later. The baseline interview assesses sociodemographic, employment-related, biomedical/health care, legal, and psychosocial risk factors. The follow-up interview assesses pain, disability, and work status. The primary outcome is duration of work disability over the year after claim submission, as assessed by administrative data. Secondary outcomes include work disability status at one year, as assessed by both self-report and work disability compensation status (administrative records). A sample size of 1,800 workers with back injuries and 1,200 with CTS will provide adequate statistical power (0.96 for low back and 0.85 for CTS) to predict disability with an alpha of .05 (two-sided) and a hazard ratio of 1.2. Proportional hazards regression models will be constructed to determine the best combination of predictors of work disability duration at one year. Regression models will also be developed for the secondary outcomes.
PMCID: PMC428578  PMID: 15157280
10.  Ergonomic stressors and upper extremity musculoskeletal disorders in automobile manufacturing: a one year follow up study 
Aims: To estimate the one year cumulative incidence and persistence of upper extremity (UE) soft tissue disorders, in a fixed cohort of automotive manufacturing workers, and to quantify their associations with ergonomic exposures.
Methods: At baseline and at follow up, cases of UE musculoskeletal disorders were determined by interviewer administered questionnaire and standardised physical examination of the upper extremities. The interview obtained new data on psychosocial strain and updated the medical and work histories. An index of exposure to ergonomic stressors, obtained at baseline interview, was the primary independent variable. Cumulative incidence and persistence of UE disorders (defined both by symptoms and by physical examination plus symptoms) were analysed in relation to baseline ergonomic exposures, adjusting for other covariates. The incidence of new disorders was modelled using multivariate proportional hazards regression among workers who were not cases in the first year and the prevalence on both occasions was modelled by repeated measures analysis.
Results: A total of 820 workers (69% of eligible cohort members) was examined. Follow up varied slightly by department group but not by baseline exposure level or other characteristics. Among the non-cases at baseline, the cumulative incidence of UE disorders was 14% by symptoms and 12% by symptoms plus examination findings. These rates increased with index of physical exposures primarily among subjects who had the same jobs at follow up as at baseline. Increased exposure during follow up increased risk of incidence. The persistence of UE disorders from baseline to follow up examination was nearly 60% and somewhat associated with baseline exposure score.
Conclusions: These longitudinal results confirm the previous cross sectional associations of UE musculoskeletal disorders with exposure to combined ergonomic stressors. The exposure-response relation was similar for incident cases defined by symptoms alone and those confirmed by physical examination.
PMCID: PMC1740826  PMID: 15258272
11.  Prevalence of work related musculoskeletal disorders in active union carpenters 
OBJECTIVES: To determine the prevalence and risk factors for work related musculoskeletal disorders among union carpenters. METHODS: A detailed questionnaire on musculoskeletal symptoms and work history was administered to 522 carpenters. The symptom questions assessed if carpenters experienced pain, numbness, or tingling in a particular body region. A subset of this group then received a physical examination of the upper extremities and knees. RESULTS: The study group was primarily white (94.9%) and male (97.8%) with a mean age of 42.3 years. The highest prevalence of work related musculoskeletal disorders cases by carpentry specialty ranged from 20%-24% for those doing drywall or ceiling, finishing or framing, and the building of concrete forms. Generally, as duration of employment increased, the prevalence of symptoms increased. An adjusted logistic regression analysis showed that the group with the longest (> or = 20 years) duration of employment in carpentry was significantly associated with work related musculoskeletal disorders of the shoulders (odds ratio (OR) 3.2, 95% confidence interval (95% CI) 1.1 to 8.9), hands or wrists (OR 3.1, 95% CI 1.1 to 8.4), and knees (OR 3.5, 95% CI 1.3 to 9.2). Also, analyses showed that carpenters who reported that they had little or no influence over their work schedule had significant increases of work related musculoskeletal disorders of the shoulders, hips, and knees with ORs of 1.9 (95% CI 1.1 to 3.2), 2.9 (95% CI 1.1 to 7.2), and 2.3 (95% CI 1.2 to 4.1), respectively. Feeling exhausted at the end of day was also a significant risk factor for work related musculoskeletal disorders of the knee (OR 1.8, 95% CI 1.1 to 3.1). Upper extremity disorders were the most prevalent work related musculoskeletal disorders reported among all carpenters. Drywall or ceiling activities involve a considerable amount of repetitive motion and awkward postures often with arms raised holding heavy dry walls in place, whereas form work is notable for extensive lumbar flexion and had the two highest rates of work related musculoskeletal disorders. The psychosocial element of job control was associated with both upper and lower extremity disorders. These union carpenters, who were relatively young, already were experiencing considerable work related physical problems. CONCLUSION: This study supports the need for vigilant ergonomic intervention at job sites and early ergonomic education as an integral part of apprenticeship school training to ensure that carpenters remain fit and healthy throughout their working lifetime.
PMCID: PMC1757596  PMID: 9764103
12.  A prospective study of prognostic factors for duration of sick leave after endoscopic carpal tunnel release 
Endoscopic carpal tunnel release with a single portal technique has been shown to reduce sick leave compared to open carpal tunnel release, claiming to be a less invasive procedure and reducing scar tenderness leading to a more rapid return to work, and the purpose of this study was to identify prognostic factors for prolonged sick leave after endoscopic carpal tunnel release in a group of employed Danish patients.
The design was a prospective study including 75 employed patients with carpal tunnel syndrome operated with ECTR at two hospitals. The mean age was 46 years (SD 10.1), the male/female ratio was 0.42, and the mean preoperative duration of symptoms 10 months (range 6-12). Only 21 (28%) were unable to work preoperatively and mean sick leave was 4 weeks (range 1-4). At base-line and at the 3-month follow-up, a self-administered questionnaire was collected concerning physical, psychological, and social circumstances in relation to the hand problem. Data from a nerve conduction examination were collected at baseline and at the 3-month follow-up. Significant prognostic factors were identified through multiple logistic regression analysis.
After the operation, the mean functional score was reduced from 2.3 to 1.4 (SD 0.8) and the mean symptom score from 2.9 to 1.5 (SD 0.7). The mean sick leave from work after the operation was 19.8 days (SD 14.3). Eighteen patients (24%) had more than 21 days of sick leave. Two patients (3%) were still unable to work after 3 months. Significant prognostic factors in the multivariate analysis for more than 21 days of postoperative sick leave were preoperative sick leave, blaming oneself for the hand problem and a preoperative distal motor latency.
Preoperative sick leave, blaming oneself for the hand problem, and a preoperative distal nerve conduction motor latency were prognostic factors for postoperative work absence of more than 21 days. Other factors may be important (clinical, demographic, economic, and workplace) in explaining the great variance in the results of sick leave after carpal tunnel release between studies from different countries.
PMCID: PMC2784750  PMID: 19930598
13.  Risk Factors for Neck and Upper Extremity Disorders among Computers Users and the Effect of Interventions: An Overview of Systematic Reviews 
PLoS ONE  2011;6(5):e19691.
To summarize systematic reviews that 1) assessed the evidence for causal relationships between computer work and the occurrence of carpal tunnel syndrome (CTS) or upper extremity musculoskeletal disorders (UEMSDs), or 2) reported on intervention studies among computer users/or office workers.
Methodology/Principal Findings
PubMed, Embase, CINAHL and Web of Science were searched for reviews published between 1999 and 2010. Additional publications were provided by content area experts. The primary author extracted all data using a purpose-built form, while two of the authors evaluated the quality of the reviews using recommended standard criteria from AMSTAR; disagreements were resolved by discussion. The quality of evidence syntheses in the included reviews was assessed qualitatively for each outcome and for the interventions.
Altogether, 1,349 review titles were identified, 47 reviews were retrieved for full text relevance assessment, and 17 reviews were finally included as being relevant and of sufficient quality. The degrees of focus and rigorousness of these 17 reviews were highly variable. Three reviews on risk factors for carpal tunnel syndrome were rated moderate to high quality, 8 reviews on risk factors for UEMSDs ranged from low to moderate/high quality, and 6 reviews on intervention studies were of moderate to high quality. The quality of the evidence for computer use as a risk factor for CTS was insufficient, while the evidence for computer use and UEMSDs was moderate regarding pain complaints and limited for specific musculoskeletal disorders. From the reviews on intervention studies no strong evidence based recommendations could be given.
Computer use is associated with pain complaints, but it is still not very clear if this association is causal. The evidence for specific disorders or diseases is limited. No effective interventions have yet been documented.
PMCID: PMC3093401  PMID: 21589875
14.  Risk Factors of Work-related Upper Extremity Musculoskeletal Disorders in Male Shipyard Workers: Structural Equation Model Analysis 
Safety and Health at Work  2010;1(2):124-133.
This study was conducted to develop a model describing the interaction between lifestyle, job, and postural factors and parts of the upper extremities in shipyard workers.
A questionnaire survey was given to 2,140 workers at a shipyard in Ulsan City. The questionnaire consisted of questions regarding the subjects' general characteristics, lifestyle, tenure, physical burden, job control, posture and musculoskeletal symptoms. The overall relationship between variables was analyzed by a structural equation model (SEM).
The positive rate of upper extremity musculoskeletal symptoms increased in employees who worked longer hours, had severe physical burden, and did not have any control over their job. Work with a more frequent unstable posture and for longer hours was also associated with an increased positive rate of musculoskeletal symptoms. Multiple logistic regression analysis showed that unstable posture and physical burden were closely related to the positive rate of musculoskeletal symptoms after controlling for age, smoking, drinking, exercise, tenure, and job control. In SEM analysis, work-related musculoskeletal disease was influenced directly and indirectly by physical and job stress factors, lifestyle, age, and tenure (p < 0.05). The strongest correlations were found between physical factors and work-related musculoskeletal disease.
The model in this study provides a better approximation of the complexity of the actual relationship between risk factors and work-related musculoskeletal disorders. Among the variables evaluated in this study, physical factors (work posture) had the strongest association with musculoskeletal disorders.
PMCID: PMC3430892  PMID: 22953172
Work-related musculoskeletal disorders; Risk factors; Shipyard; Structural equation model
15.  Epidemiological study to investigate potential interaction between physical and psychosocial factors at work that may increase the risk of symptoms of musculoskeletal disorder of the neck and upper limb 
Objectives: To investigate potential interactions between physical and psychosocial risk factors in the workplace that may be associated with symptoms of musculoskeletal disorder of the neck and upper limb.
Methods: 891 of 1514 manual handlers, delivery drivers, technicians, customer services computer operators, and general office staff reported on physical and psychosocial working conditions and symptoms of neck and upper limb disorders using a self administered questionnaire (59% return rate). Of the 869 valid questionnaire respondents, 564 workers were classified in to one of four exposure groups: high physical and high psychosocial, high physical and low psychosocial, low physical and high psychosocial, and low physical and low psychosocial. Low physical and low psychosocial was used as an internal reference group. The exposure criteria were derived from the existing epidemiological literature and models for physical and psychosocial work factors. The frequency and amplitude of lifting and the duration spent sitting while experiencing vibration were used as physical exposure criteria. Ordinal values of mental demands, job control, and social support with managers and coworkers were used as psychosocial exposure criteria.
Results: In the multivariate analyses, the highest and significant increase in risk was found in the high physical and high psychosocial exposure group for symptoms of hand or wrist and upper limb disorders after adjusting for years at the job, age, and sex. A potential interaction effect was found for the symptoms of the hand or wrist and upper limb disorders but not for the neck symptoms.
Conclusion: This study showed that workers highly exposed to both physical and psychosocial workplace risk factors were more likely to report symptoms of musculoskeletal disorders than workers highly exposed to one or the other. The results suggest an interaction between physical and psychosocial risk factors in the workplace that increased the risk of reporting symptoms in the upper limbs. Psychosocial risk factors at work were more important when exposure to physical risk factors at work were high than when physical exposure was low. Ergonomic intervention strategies that aim to minimise the risks of work related musculoskeletal disorders of the upper limb should not only focus on physical work factors but also psychosocial work factors.
PMCID: PMC1740269  PMID: 11934955
16.  Epidemiology of musculoskeletal upper extremity ambulatory surgery in the United States 
Musculoskeletal disorders of the upper extremity are common reasons for patients to seek care and undergo ambulatory surgery. The objective of our study was to assess the overall and age-adjusted utilization rates of rotator cuff repair, shoulder arthroscopy performed for indications other than rotator cuff repair, carpal tunnel release, and wrist arthroscopy performed for indications other than carpal tunnel release in the United States. We also compared demographics, indications, and operating room time for these procedures.
We used the 2006 National Survey of Ambulatory Surgery to estimate the number of procedures of interest performed in the United States in 2006. We combined these data with population size estimates from the 2006 U.S. Census Bureau to calculate rates per 10,000 persons.
An estimated 272,148 (95% confidence intervals (CI) = 218,994, 325,302) rotator cuff repairs, 257,541 (95% CI = 185,268, 329,814) shoulder arthroscopies excluding those for cuff repairs, 576,924 (95% CI = 459,239, 694,609) carpal tunnel releases, and 25,250 (95% CI = 17,304, 33,196) wrist arthroscopies excluding those for carpal tunnel release were performed. Overall, carpal tunnel release had the highest utilization rate (37.3 per 10,000 persons in persons of age 45–64 years; 38.7 per 10,000 persons in 65–74 year olds, and; 44.2 per 10,000 persons in the age-group 75 years and older). Among those undergoing rotator cuff repairs, those in the age-group 65–74 had the highest utilization (28.3 per 10,000 persons). The most common indications for non-cuff repair related shoulder arthroscopy were impingement syndrome, periarthritis, bursitis, and instability/SLAP tears. Non-carpal tunnel release related wrist arthroscopy was most commonly performed for ligament sprains and diagnostic arthroscopies for pain and articular cartilage disorders.
Our data shows substantial age and demographic differences in the utilization of these commonly performed upper extremity ambulatory procedures. While over one million upper extremity procedures of interest were performed, evidence-based clinical indications for these procedures remain poorly defined.
PMCID: PMC3893587  PMID: 24397703
Rotator cuff repair; Arthroscopy; Utilization; Epidemiology
17.  Effects of computer keyboarding on ultrasonographic measures of the median nerve 
Keyboarding is a highly repetitive daily task and has been linked to musculoskeletal disorders of the upper extremity. However, the effect of keyboarding on median nerve injuries is not well understood. The purpose of this study was to use ultrasonographic measurements to determine whether continuous keyboarding can cause acute changes in the median nerve.
Ultrasound images of the median nerve from twenty-one volunteers were captured at the levels of the pisiform and distal radius prior to and following a prolonged keyboarding task (i.e., one hour of continuous keyboarding). Images were analyzed by a blinded investigator to quantify the median nerve characteristics. Changes in the median nerve ultrasonographic measures as a result of continuous keyboarding task were evaluated.
Cross-sectional areas at the pisiform level were significantly larger in both dominant (p=0.004) and non-dominant (p=0.001) hands following the keyboarding task. Swelling ratio was significantly greater in the dominant hand (p=0.020) after 60 minutes of keyboarding when compared to the baseline measures. Flattening ratios were not significantly different in either hand as a result of keyboarding.
We were able to detect an acute increase in the area of the median nerve following one hour of keyboarding with a computer keyboard. This suggests that keyboarding has an impact on the median nerve. Further studies are required to understand this relationship, which would provide insight into the pathophysiology of median neuropathies such as carpal tunnel syndrome.
PMCID: PMC4297618  PMID: 21739468
carpal tunnel syndrome; computer keyboarding; median nerve; ultrasonography; ultrasound
18.  Gender-related Factors Associated with Upper Extremity Function in Workers 
Safety and Health at Work  2010;1(2):158-166.
This study aimed to find gender distinctions in terms of the sociology of the population; to determine work-related factors; to analyze gender differences in daily living, work, sports, and art performances; and to identify gender-related factors that limited performance of daily living and work activities.
A questionnaire was designed that included disabilities of the arm, shoulder, and hand (DASH), accident history, disease history, work duration at current workplace, marital status, job satisfaction, job autonomy, and physical demands of the job. Out of 1,853 workers surveyed, 1,173 questionnaires (63.3%; 987 males, 186 females) included responses to DASH disability and DASH optional work and were judged acceptable for analysis.
Upper extremity functional limitation during work and daily living was higher for females than males. The limitations for males increased according to their household work time, accident history, work duration, job satisfaction, physical demand, and job autonomy. Meanwhile, female workers' upper extremity discomfort was influenced by their disease history, job satisfaction, and physical demands. In addition, the size of the company affected male workers' upper extremity function, while marriage and hobbies influenced that of female workers.
This study addressed sociodemographic factors and work-related factors that affect each gender's upper extremity function during daily living and working activities. Each factor had a different influence. Further studies are needed to identify the effect that role changes, not being influenced by risks at work, have on musculoskeletal disorders.
PMCID: PMC3430891  PMID: 22953176
Gender; DASH; Disability; Upper extremity; Work
19.  Musculoskeletal health and work ability in physically demanding occupations: study protocol for a prospective field study on construction and health care workers 
BMC Public Health  2014;14(1):1075.
Musculoskeletal disorders have a profound impact on individual health, sickness absence and early retirement, particularly in physically demanding occupations. Demographics are changing in the developed countries, towards increasing proportions of senior workers. These senior workers may have particular difficulties coping with physically demanding occupations while maintaining good health.
Previous studies investigating the relationship between physical work demands and musculoskeletal disorders are mainly based on self-reported exposures and lack a prospective design. The aim of this paper is to describe the background and methods and discuss challenges for a field study examining physical demands in construction and health care work and their prospective associations with musculoskeletal disorders, work ability and sickness absence.
Methods and design
This protocol describes a prospective cohort study on 1200 construction and health care workers. Participants will answer a baseline questionnaire concerning musculoskeletal complaints, general health, psychosocial and organizational factors at work, work demands, work ability and physical activity during leisure. A shorter questionnaire will be answered every 6th months for a total of two years, together with continuous sickness absence monitoring during this period. Analysis will prospectively consider associations between self-reported physical demands and musculoskeletal disorders, work ability and sickness absence. To obtain objective data on physical exposures, technical measurements will be collected from two subgroups of N = 300 (Group A) and N = 160 (Group B) during work and leisure. Both group A and B will be given a physical health examination, be tested for physical capacity and physical activity will be measured for four days. Additionally, muscle activity, ground reaction force, body positions and physical activity will be examined during one workday for Group B. Analysis of associations between objectively measured exposure data and the outcomes described above will be done separately for these subpopulations.
The field study will at baseline produce objectively measured data on physical demands in the construction and health care occupations. In combination with clinical measurements and questionnaire data during follow-up, this will provide a solid foundation to prospectively investigate relationships between physical demands at work and development of musculoskeletal disorders, work ability and sickness absence.
PMCID: PMC4203897  PMID: 25318646
Physical exposures; Work ability; Musculoskeletal disorders; Accelerometer; Heart rate monitoring; Electromyography; Ground reaction force
20.  High physical work load and low job satisfaction increase the risk of sickness absence due to low back pain: results of a prospective cohort study 
Objective: To determine whether physical and psychosocial load at work influence sickness absence due to low back pain.
Methods: The research was a part of the study on musculoskeletal disorders, absenteeism, stress, and health (SMASH), a 3 year prospective cohort study on risk factors for musculoskeletal disorders. Workers from 21 companies located throughout The Netherlands participated in the part of this study on sickness absence due to low back pain. The study population consisted of 732 workers with no sickness absences of 3 days or longer due to low back pain in the 3 months before the baseline survey and complete data on the reasons for absences during the follow up period. The mean (range) period of follow up in this group was 37 (7–44) months. Physical load at work was assessed by analyses of video recordings. Baseline information on psychosocial work characteristics was obtained by a questionnaire. Data on sickness absence were collected from company records. The main outcome measure was the rate of sickness absences of 3 days or longer due to low back pain during the follow up period.
Results: After adjustment of the work related physical and psychosocial factors for each other and for other potential determinants, significant rate ratios ranging from 2.0 to 3.2 were found for trunk flexion, trunk rotation, lifting, and low job satisfaction. A dose-response relation was found for trunk flexion, but not for trunk rotation or lifting. Non-significant rate ratios of about 1.4 were found for low supervisor support and low coworker support. Quantitative job demands, conflicting demands, decision authority, and skill discretion showed no relation with sickness absence due to low back pain.
Conclusions: Flexion and rotation of the trunk, lifting, and low job satisfaction are risk factors for sickness absence due to low back pain. Some indications of a relation between low social support, either from supervisors or coworkers, and sickness absence due to low back pain are also present.
PMCID: PMC1740286  PMID: 11983847
21.  Nerve conduction in relation to vibration exposure - a non-positive cohort study 
Peripheral neuropathy is one of the principal clinical disorders in workers with hand-arm vibration syndrome. Electrophysiological studies aimed at defining the nature of the injury have provided conflicting results. One reason for this lack of consistency might be the sparsity of published longitudinal etiological studies with both good assessment of exposure and a well-defined measure of disease. Against this background we measured conduction velocities in the hand after having assessed vibration exposure over 21 years in a cohort of manual workers.
The study group consisted of 155 male office and manual workers at an engineering plant that manufactured pulp and paper machinery. The study has a longitudinal design regarding exposure assessment and a cross-sectional design regarding the outcome of nerve conduction. Hand-arm vibration dose was calculated as the product of self-reported occupational exposure, collected by questionnaire and interviews, and the measured or estimated hand-arm vibration exposure in 1987, 1992, 1997, 2002, and 2008. Distal motor latencies in median and ulnar nerves and sensory nerve conduction over the carpal tunnel and the finger-palm segments in the median nerve were measured in 2008. Before the nerve conduction measurement, the subjects were systemically warmed by a bicycle ergometer test.
There were no differences in distal latencies between subjects exposed to hand-arm vibration and unexposed subjects, neither in the sensory conduction latencies of the median nerve, nor in the motor conduction latencies of the median and ulnar nerves. Seven subjects (9%) in the exposed group and three subjects (12%) in the unexposed group had both pathological sensory nerve conduction at the wrist and symptoms suggestive of carpal tunnel syndrome.
Nerve conduction measurements of peripheral hand nerves revealed no exposure-response association between hand-arm vibration exposure and distal neuropathy of the large myelinated fibers in a cohort of male office and manual workers.
PMCID: PMC2923164  PMID: 20642848
22.  Risk factors for incident carpal tunnel syndrome: Results of a prospective cohort study of newly-hired workers 
Work (Reading, Mass.)  2012;41(0 1):4450-4452.
Carpal tunnel syndrome is one of the most costly upper extremity disorders in the working population. Past literature has shown an association between personal and work factors to a case definition of carpal tunnel syndrome but little is known about the combined effects of these factors with the development of this disorder. Few studies have examined these associations in longitudinal studies. The purpose of this paper is to identify risk factors for incident carpal tunnel syndrome in a longitudinal study of workers across a wide range of occupations.
PMCID: PMC3752891  PMID: 22317405
Carpal tunnel syndrome; risk factors; epidemiology
23.  Clinical course, costs and predictive factors for response to treatment in carpal tunnel syndrome: the PALMS study protocol 
Carpal tunnel syndrome (CTS) is the most common neuropathy of the upper limb and a significant contributor to hand functional impairment and disability. Effective treatment options include conservative and surgical interventions, however it is not possible at present to predict the outcome of treatment. The primary aim of this study is to identify which baseline clinical factors predict a good outcome from conservative treatment (by injection) or surgery in patients diagnosed with carpal tunnel syndrome. Secondary aims are to describe the clinical course and progression of CTS, and to describe and predict the UK cost of CTS to the individual, National Health Service (NHS) and society over a two year period.
In this prospective observational cohort study patients presenting with clinical signs and symptoms typical of CTS and in whom the diagnosis is confirmed by nerve conduction studies are invited to participate. Data on putative predictive factors are collected at baseline and follow-up through patient questionnaires and include standardised measures of symptom severity, hand function, psychological and physical health, comorbidity and quality of life. Resource use and cost over the 2 year period such as prescribed medications, NHS and private healthcare contacts are also collected through patient self-report at 6, 12, 18 and 24 months. The primary outcome used to classify treatment success or failures will be a 5-point global assessment of change. Secondary outcomes include changes in clinical symptoms, functioning, psychological health, quality of life and resource use. A multivariable model of factors which predict outcome and cost will be developed.
This prospective cohort study will provide important data on the clinical course and UK costs of CTS over a two-year period and begin to identify predictive factors for treatment success from conservative and surgical interventions.
PMCID: PMC3921988  PMID: 24507749
24.  Prevalence and incidence of carpal tunnel syndrome in US working populations: pooled analysis of six prospective studies 
Most studies of carpal tunnel syndrome (CTS) incidence and prevalence among workers have been limited by small sample sizes or restricted to a small subset of jobs. We established a common CTS case definition and then pooled CTS prevalence and incidence data across six prospective studies of musculoskeletal outcomes to measure CTS frequency and allow better studies of etiology.
Six research groups collected prospective data at >50 workplaces including symptoms characteristic of CTS and electrodiagnostic studies (EDS) of the median and ulnar nerves across the dominant wrist. While study designs and the timing of data collection varied across groups, we were able to create a common CTS case definition incorporating both symptoms and EDS results from data that were collected in all studies.
At the time of enrollment, 7.8% of 4321 subjects met our case definition and were considered prevalent cases of CTS. During 8833 person-years of follow-up, an additional 204 subjects met the CTS case definition for an overall incidence rate of 2.3 CTS cases per 100 person-years.
Both prevalent and incident CTS were common in data pooled across multiple studies and sites. The large number of incident cases in this prospective study provides adequate power for future exposure– response analyses to identify work- and non-work-related risk factors for CTS. The prospective nature allows determination of the temporal relations necessary for causal inference.
PMCID: PMC4042862  PMID: 23423472
CTS; epidemiology; industry; longitudinal study; median nerve; MSD; musculoskeletal disorder; nerve compression; occupational injury; surveillance; work-related injury
25.  A Fluid-Immersed Multi-Body Contact Finite Element Formulation for Median Nerve Stress in the Carpal Tunnel 
Carpal tunnel syndrome (CTS) is among the most important of the family of musculoskeletal disorders caused by chronic peripheral nerve compression. Despite the large body of research in many disciplinary areas aimed at reducing CTS incidence and/or severity, means for objective characterization of the biomechanical insult directly responsible for the disorder have received little attention.
In this research, anatomical image-based human carpal tunnel finite element (FE) models were constructed to enable study of median nerve mechanical insult. The formulation included large-deformation multi-body contact between the nerve, the nine digital flexor tendons, and the carpal tunnel boundary. These contact engagements were addressed simultaneously with nerve and tendon fluid-structural interaction (FSI) with the synovial fluid within the carpal tunnel. The effects of pertinent physical parameters on median nerve stress were explored. The results suggest that median nerve stresses due to direct structural contact are typically far higher than those from fluid pressure.
PMCID: PMC2753487  PMID: 17852181
Carpal tunnel syndrome; Finite element method; Mechanical insult; Median nerve; Flexor tendon; Solid stress; Fluid pressure

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