Predicting work-related incidence of lateral and medial epicondylitis using the strain index.

BACKGROUND: The Strain Index (SI) has been developed to evaluate the risk for developing a distal upper extremity disorder. The objective of this study is to determine if the SI predicts incidence cases of work-related lateral, medial, or any epicondylities (LEPI, MEPI, and EPI). METHODS: Six hundred seven workers were followed for up to 3.5 years, 70 developed EPI on the dominant side (44 LEPI, 13 MEPI, and 13 both). Survival analyses were conducted adjusting for demographic, psychosocial, and work organizational factors, with the SI as time-dependent variable. RESULTS: High exposure (SI > 5), older age, and self-perceived poor general health were associated with incidence of LEPI and EPI, but not MEPI. There was a significant relationship between higher scores of SI and LEPI, hazard ratio (HR) 2.00 (95% CI 1.04-3.87) for SI 5.1-12, HR 2.12 (95% CI 1.11-4.05) for SI > 12. CONCLUSIONS: The SI can effectively identify jobs with increased risk of developing incidence of LEPI.

The association between combination of hand force and forearm posture and incidence of lateral epicondylitis in a working population.

OBJECTIVE: The objective of this prospective study is to investigate the exposure-response relationships between various workplace physical exposures of force, repetition, and their combination assessed at an individual level with lateral epicondylitis (LE). BACKGROUND: Workplace upper extremity musculoskeletal disorders (UEMSDs) are prevalent, disabling, and expensive. LE is one of the major UEMSDs in active workers. METHOD: We used detailed health history, symptoms, and physical examination for identifying incidence and detailed exposure assessment to capture work tasks of each worker and to measure quantitative mechanical workload. We used counting process style input of proportional hazards regression for modeling cumulative incidence that accounts for changed exposure estimates during the follow-up period when respondents change jobs. RESULTS: The incidence rate of LE on the dominant side was 4.91 per 100 person-years. Adjusted for age and gender, the combined effect of forearm pronation > or = 45 degrees for > or = 40% of time and time spent with forceful exertion, including any power grip (hazard ratio [HR] = 2.8, 95% confidence interval [CI] = [1.35-5.77]), lifting for > or = 3% of time (HR = 2.50, 95% CI = [1.19-5.24]), and duty cycle for forceful exertion for > or = 10% (HR = 2.25, 95% CI = [1.09-4.66]), were significant predictors of dominant side LE, whereas neither the awkward posture nor the forceful exertion alone was significant. Older workers with jobs requiring a high percentage of time working with force in combination with awkward postures of forearm were more likely to predict LE. CONCLUSION: This study shows the evidence of the etiologic role of strenuous manual tasks in the occurrence of LE.

The natural course of carpal tunnel syndrome in a working population.

OBJECTIVE: The aim of this study was to assess prevalence, incidence, and persistence of carpal tunnel syndrome (CTS) and associated symptoms over a one-year period in a working population. METHODS: We conducted a one-year prospective study of 418 active workers in 12 worksites. Detailed health interviews, psychosocial questionnaires, and electrophysiological studies [ie, nerve conduction velocity (NCV) tests] were conducted at baseline and one-year follow-up. Individual-observed exposure assessments of wrist posture, hand activity, and hand forces were conducted. RESULTS: Prevalence of CTS cases at baseline was 10.8% [95% confidence interval (95% CI) 7.8-13.7%] on the dominant side and 6.0% (95% CI 3.7-87.3%) on the non-dominant side; CTS symptoms were 14.1% (95% CI 10.8-17.5%) and 11.0% (95% CI 8.0-14.0%), respectively. Incidence of CTS cases were 7.5% (95% CI 4.8-10.2%) and 5.6% (95% CI 3.3-7.9%), respectively. Higher proportions of subjects with current symptoms or positive electrophysiological test findings at baseline became CTS cases at one year compared to those with neither (28.6% and 13.9%, respectively, versus 0.5%). One-year persistence of CTS case status was 44.4% (95% CI 29.9-59.0%) for the dominant hand and 52.0% (95% CI 32.4-71.6) for non-dominant hand. There were significant differences at baseline between asymptomatic subjects and CTS cases with respect to higher job demands (P=0.027), lower job satisfaction (P=0.036), lower general health (P=0.0009), higher exposure to vibrating hand tool use (P=0.039), and greater time using a forceful power grip (P=0.035) among cases. CONCLUSIONS: CTS symptoms more than positive NCV test results alone appear to predict CTS at one year. Persistence of CTS at one year is high.

Quantitative exposure-response relations between physical workload and prevalence of lateral epicondylitis in a working population.

BACKGROUND: Lateral epicondylitis is a common work-related musculoskeletal disorder. The objective of this study was to identify risk factors associated with lateral epicondylitis among active workers. METHODS: Seven-hundred thirty-three workers in 12 Washington worksites participated in structured interviews, physical examinations, and individual exposure assessments of biomechanical and psychosocial factors. Multivariable logistic modeling was used. RESULTS: Thirty-eight subjects (5.2%) had lateral epicondylitis. Age (36-50 years-old), being female, and low social support at work were significant risk factors. Frequency of forceful exertion (> or =5 vs. < 1 times/min (OR 5.17, 95%CI 1.78-15.02), and > or =1 to <5 vs. <1 (OR 4.47, 95%CI 1.57-13.71)) and forearm supination at > or =45 degrees for > or =5% of the time with high lifting force (OR = 2.98, 95% CI 1.18-7.55) were significant physical load factors. CONCLUSIONS: Frequency of forceful exertion or a combination of forearm supination and forceful lifting were significant physical factors and should be considered for prevention strategies.

Natural course of nontraumatic rotator cuff tendinitis and shoulder symptoms in a working population.

OBJECTIVES: This study assessed the prevalence, incidence, and persistence of nontraumatic rotator cuff tendinitis and shoulder symptoms over a 1-year period in a working population and the predictive value of symptoms and physical findings. METHODS: A 1-year prospective study of 436 active workers was conducted at 12 different worksites. Detailed health interviews, psychosocial questionnaires, and physical examinations were conducted at baseline and again after 1 year, with shorter evaluations at 4 and 8 months. Individual observed exposure assessment of shoulder posture, arm-hand activity, and hand forces was conducted. RESULTS: The prevalence of rotator cuff tendinitis at baseline was 7.6% [95% confidence interval (95% CI 5.1-10.1%)] for the right and 4.8% (95% CI 3.0-7.0%) for the left, compared with shoulder symptoms of 18.6% (95% CI 14.9-22.3%) (right) and 11.2% (95% CI 8.2-14.2%) (left). The incidence of rotator cuff tendinitis was 5.5% (95% CI 2.8-6.8%) and 2.9% (95% CI 1.0-3.8%), respectively. Higher proportions of participants with current symptoms or physical findings at baseline became clinical cases after 1 year than those without symptoms or findings. The 1-year persistence of clinical case status was 31.3% (95% CI 26.9-35.7%) (right) and 31.6% (95% CI 27.2-36.0%) (left). There were significant differences at baseline between the asymptomatic participants and the clinical cases with respect to physical health on the 12-item Short-form Health Survey (P=0.0002), the perception of general health (P=0.0027), and the frequency of high hand force exposure (P=0.0177). CONCLUSIONS: Considerable movement occurs between different stages of shoulder problems. Symptoms and physical findings alone appear to predict clinical case status within 1 year. Frequent follow-up is necessary to capture changes in health and exposure status in prospective studies.