UC Berkeley

Introduction

Wrist tendinosis is a common distal upper extremity disorder that can be work-related. Workplace cross-sectional (Franzblau, 2005) and prospective studies (Leclerc 2001, Thomsen 2007) have linked distal upper extremity pain and disorders to forceful or repetitive hand exertions, but the associations are not consistent across studies. A study rigorously assessing both workplace physical exposures and wrist tendinosis would be useful in clarifying the dose-response relationships which could provide guidance for prevention. This dissertation presents the results from a prospective study of right wrist tendinosis among blue-collar workers, and includes a comparison of exposure measurement methods, a cross-sectional analysis of the cohort at baseline, and a prospective analysis of the association between exposure to physical risk factors and the subsequent development of right wrist tendinosis during a 28 month follow up period.

Methods

Workers (N=450) at four manufacturing industries participated in this study and were followed up for up to 28 months (n=413) with questionnaires and physical examinations every 4 months to identify incident cases of right wrist tendinosis. Workers were eligible to participate if they performed primarily hand intensive manual (not office) work and were not assigned to more than four tasks. Exposure assessment was based on job evaluations by experienced ergonomists and video analyses of tasks. A variety of self-report, observer-rated, direct measure, and video analysis methods were used to quantify workers exposure to force and repetition at baseline. Detailed video analysis determined percent time the right hand applied a high force pinch (> 1 kg-force) or power grip (>4kg-force) for each task. No load and low force pinch (<= 1 kg-force) and grasp (<=4kg-force) were also determined. Repetition was quantified by observer-rated hand activity level (HAL) scale and video analysis of repetition rate (reps/min) in heavy or light grip or pinch postures. A comparison of each worker's longest duration task was performed using the Pearson correlation. All exposure variables were measured on the individual task level and time weighted averages for overall exposure were calculated for each worker. Logistic regression was used to model the log odds of tendonitis at baseline, as a function of exposure variables and relevant confounders. Survival analysis using the Cox Proportional Hazards Model was used to assess the relationship between individual and workplace factors and wrist tendinosis for all prospective data. Force, repetition, and composite measures with p<0.2 in the univariate analyses were evaluated in multivariate models. Potential covariates with p<0.2 in the univariate analysis or a correlation (r>0.3) with the exposure variable of interest were included in the multivariate model and consecutively removed and replaced to assess for confounding.

Results

There were 37 cases of right wrist tendinosis at baseline and 26 incident cases during the 28-month follow up. Analysis of exposure measures revealed correlations (r=0.63) between the visual analog scale (VAS) for hand fatigue and the rate of perceived exertion (RPE). The HAL repetition scale and the Speed of Work observer-rated scales were moderately correlated (r=0.65). The scales' stronger correlation with the percent time spent in grip (r= 0.41) versus pinch (r=-0.25) could be based on the difficulty discerning distinct repetitions while in pinch.

For the prospective analysis, job satisfaction, smoking status, annual income, BMI, education level, job strain, and general health were not significant predictors in the univariate analysis and were therefore not included in multivariate models. Age, gender (HR= 4.8; 95%CI: 2.01-11.45), ethnicity, medical condition, and shift were all assessed for confounding, though only age and gender remained in the final models. The two most predictive models included the percent time spent in high force pinch adjusting for repetition (HR = 2.27; 95% CI: 0.72-7.19 and HR=3.42; 95%CI: 0.9-13.01 for medium and high groups), and the ACGIH TLV Hand Activity Level (HR = 3.95; 95% CI: 1.52-10.26 and HR=2.8; 95%CI: 0.8-9.87 for medium and high groups).

Discussion

In this prospective study, the workplace factors predicting wrist tendinosis were time weighted average values of the percent time spent performing a high force pinch, the normalized peak force, and the ACGIH TLV Hand Activity Level. The percent time spent in power grip was not a significant workplace predictor, nor were any of the measures of repetition. Individual factors including job satisfaction, general health, and BMI were not significant predictors, but gender was. The most predictive measure of force was the video of the work task quantified for the percent time spent in high force pinch; the relationship followed a dose-response pattern. Based on this study, in order to prevent wrist tendinosis, it is recommended that the tasks of workers performing repetitive, hand intensive tasks be designed so that less than 10% of the task time requires pinch force greater than 1 kg.