Risk Of Cumulative Trauma Disorders Research Articles

Fuzzy linear regression models for assessing risks of cumulative trauma disorders

Cumulative trauma disorders (CTDs) are a major problem in industry and today's office environments, especially for keyboard users. Since comprehensive knowledge about individual or a combination of risk factors contributing to CTDs of the hand and forearm is still lacking, developing methodologies to quantify relationships of risk factors is greatly needed. The purpose of this research was to build fuzzy linear regression models to reveal the relationship of CTD risk factors, to predict the injuries, and to evaluate risk levels of individuals. Twenty-seven keyboard users (twenty-two for model building and five for model validation) and three CTD experts participated in the model building. Four fuzzy models were built corresponding to four risk categories, and a final fuzzy linear model was established using AHP pairwise comparisons. Multicolinearity effects were addressed and a partial standard deviation scaling method was used to eliminate the effects. From a methodological point of view, fuzzy linear regression models provide useful insight into risk factors-CTD relationship.

An ergonomic comparison of industrial spray paint guns

Two spray guns were used by 10 subjects in a laboratory. One gun was a `traditional' spray gun. The other was the OMX gun which had `ergonomic' features including reduced gun and hose weight and two triggers (one for horizontal surfaces and one for vertical). The 10 subjects (5 experienced industrial spray painters and 5 inexperienced students) used each gun for 4 h. The criteria used to evaluate the two guns were: (1) Wrist deviation in all three axes, (2) EMG frequency shift of 3 shoulder muscles over the test period, (3) integrated EMG activity of the forearm flexors, and (4) body discomfort ratings. It was found that the OMX gun resulted in significantly less radial/ulnar deviation in the wrist, and moderately increased flexion/extension and pronation/supination deviations from neutral. During the painting period, up to 50% less fatigue in the shoulder muscles was found for the OMX gun. Additionally, the triggering activation levels for sustained grip contractions were found to be acceptable for the OMX gun when using the short trigger. Finally, the amount of discomfort reported by the subjects was statistically lower in the shoulder, upper back, arm, elbow, forearm, wrist, and hand with the OMX gun design. Collectively, these results indicate that the OMX gun would be expected to reduce exposure to occupational risk factors for workers. This study demonstrated how the incorporation of ergonomic design principles can be used to minimize occupationally-related risk. Relevance to industry Cumulative trauma disorders (CTDs) are soft tissue disorders resulting from repeated exertions and excessive movements of the body. Industrial spray painting fits the profile of a highly repetitive task. Improving spray paint gun design could potentially reduce the risk of CTDs in industrial spray painting tasks.

Musculoskeletal Symptoms Among Cytotechnologists

We measured the prevalence of musculoskeletal symptoms among cytotechnologists in the metropolitan Washington, DC, area. We surveyed cytotechnologists to assess the prevalence of neck, shoulder, upper-back, elbow/forearm, hand/wrist, and lower-back symptoms in the prior year. Eighty-two (69%) of 125 cytotechnologists returned questionnaires, of which 95% were working as cytotechnologists. The prevalences of neck (61.5%), hand/wrist (56.4%), and lower-back (42.3%) symptoms were highest. Laboratory workers routinely involved in microscope-related work may be at risk for cumulative trauma disorders. We concluded that an ergonomic approach to this problem can help prevent musculoskeletal symptoms.

Goniometer measurement and computer analysis of wrist angles and movements applied to occupational repetitive work

In epidemiological studies of occupational musculoskeletal disorders there is a need for quantitative exposure measurements of the physical work load. In studies of neck and upper limb disorders the so-called cumulative trauma disorders (CTDs), in particular the carpal tunnel syndrome, the positions and movements of the wrist are of special interest. A biaxial flexible electrogoniometer was used to measure continuously, with a sampling rate of 20 Hz, wrist flexion/extension and abduction/adduction angles up to 27 min. Evaluation of the influence of rotation on the goniometer showed some inherent crosstalk, which, however, did not invalidate the results. For occupational repetitive work, 99.5% of the signal power was contained in the 0–5 Hz band. Two-dimensional angle distributions and power spectra gave comprehensive information about wrist postures and movements. Measures reflecting both static and dynamic properties were derived from time and frequency domains. These measures give quantitative information on different potential risk factors and are therefore useful in epidemiological studies. Mean power frequency (MPF) is suggested as a generalized measure of repetitiveness. The method was applied in field studies of fish processing industry workers with highly repetitive work and risk of CTD.

Quantitative Biomechanical Analysis of Wrist Motion in Bone-Trimming Jobs in the Red-Meat Packing Industry

This study was motivated by the serious impact that cumulative trauma disorders (CTDs) of the upper extremities have on industrial workers and on industry itself. To date, no quantitative data has been gathered on the kinematics of hand and wrist motion required in bone-trimming jobs in the red-meat packing industry. No information is known about what type and how much wrist motion is currently being used in bone-trimming jobs in the red-meat packing industry, or how much these motions increase the risk of occupational CTDs. The research conducted addressed this current research void and established a preliminary database of wrist and hand kinematics for a bone-trimming job in the red-meat packing industry. This kinematic database could augment the red-meat industry's efforts to reduce the severity and cost of CTDs. Ergonomics practitioners in the red-meat industry could use the kinematic methods employed in this research to assess the CTD risk of current and redesigned jobs that require repetitious, hand-intensive work. The study examined the wrist motions used by nine red-meat packing workers who performed bone-trimming jobs. These jobs are highly repetitive and hand-intensive. Quantitative measures of the kinematic parameters of wrist motions performed on the bone-trimming line were measured using goniometry. The wrist motion measures consisted of the following statistics in the radial/ulnar, flexion/extension, and pronation/supination planes: 1). mean, minimum, and maximum of wrist angle position, 2). mean, minimum, and maximum of angular velocity, and 3). mean, minimum, and maximum of angular acceleration. The kinematic data were compared to manufacturing industry's preliminary wrist motion benchmarks. These benchmarks were the means and variances of nine dependent variables of position, velocity, and acceleration from industrial workers who performed hand-intensive, repetitive work in jobs that were of low and high risk of hand/wrist CTDS (Marras and Schoenmarklin, 1993). Results of this comparison show that numerous wrist motion variables in both the left and right hands of bone-trimming workers are in the high-risk category. This quantitative analysis provides biomechanical support for the high incidence of CTDs in the bone-trimming line of the plant that was investigated.

Quantification of Wrist Motions during Scanning

A laboratory study was performed to help assess the risk of cumulative trauma disorders (CTDs) associated with the use of scanners in the grocery store environment. In this study experienced and inexperienced cashiers scanned a set of 12 standard grocery items using 19 different combinations of scanners, scanner orientations, and check stands. The motion characteristics of both wrists in three-dimensional space were documented and used as dependent measures of performance. These motions were compared with wrist motion benchmarks of high-and low-risk wrist accelerations. It was found that, in general, scanning motions are of sufficient magnitude to contribute to CTDs of the wrist. It was also found that wrist motion characteristics were greatly influenced by the different combinations of scanners, scanner orientations, and check stand designs. It was concluded that the "front-style" check stand minimizes potentially injurious wrist motions because it permits the checker to split the scanning task between the two hands. The type of scanner and scanner orientation that minimized potentially injurious wrist motions was much more unique to the individual workstation condition. Additionally, it appears that scanners perceived by the checkers as needing fewer wrist deviations, such as those with slanted windows, also minimize wrist motions. The implications of these findings for the ergonomic design of the workplace are discussed.

Exposure assessment of biomechanical stress in repetitive manual work using frequency-weighted filters.

A quantitative exposure assessment strategy for physical stress associated with repetitive manual tasks is proposed using continuous biomechanical data measured directly from electrogoniometers or force sensors. This paper describes an efficient method for reducing large quantities of biomechanical data into a quantifiable metric that accounts for recognized musculoskeletal exposure factors, including repetitiveness, postural or forceful exertion stress, and duration. A frequency domain approach is used for averaging elemental data recorded for repetitive cycles. Parameters for frequency-weighted filters are developed using psychophysical data for equivalent discomfort levels resulting from repetitive movements of different amplitudes and frequencies. These filters enable continuous biomechanical data to be filtered and integrated, resulting in a single quantity corresponding to psychophysical response characteristics for repetitive motion stress. It is anticipated that a similar approach may be used for epidemiological response characteristics. Applications of this theory may make it possible for assessing exposure to physical stress in a manner analogous to the way in which sound level meters are used for measuring exposure to acoustic noise. Repetitive wrist flexion and localized discomfort was used for demonstrating the feasibility of this approach. Suitable data reduction techniques are necessary for evaluating work methods, job designs, and for conducting large scale detailed epidemiological investigations of cumulative trauma disorder risk factors. Frequency-weighted filters based on human response to physical stress at different frequencies can greatly simplify exposure analysis and ultimately may make it possible for quantitative exposure limits to be established.

The Effects of Human Interface Design on Wrist Biomechanics during Scanning

Two window, or “bi-optic” scanners have ergonomic potential to minimize cumulative trauma disorders (CTDs) among grocery checkers. However, not all checkers utilize both windows when scanning. Four, two window scanners were tested to see whether the number of windows used had an effect on wrist acceleration, one of the most predictive indicators of CTD risk. Out of 32 subjects, 14 used only one window while scanning. These subjects were seen to have significantly higher cumulative peak wrist accelerations than those subjects that used both windows. In addition, the productivity of the one window users was significantly lower than two window users. The results indicate that two window scanners can not only increase productivity, but can reduce the risk of CTDs. However, this will only occur if checkers appreciate and choose to use both windows in their scanning activity. The large number of subjects (14 out of 32) that only used one window when scanning indicates a serious human interface problem with these types of scanners. This paper identifies the need for better scanner designs that will indicate to the user the three-dimensional scan zone created by the two windows. The design should influence one to use both windows while scanning so that wrist motions will be reduced. Most importantly, this paper identifies the importance of the relationship between cognitive and biomechanical issues when approaching a human interface problem in a product's design.

Rapid Communication Industrial wrist motions and incidence of hand/wrist cumulative trauma disorders

One of the major research voids in the study of occupational hand/wrist cumulative trauma disorders (CTDs) is the lack of quantification of the relationship between the known kinematic risk factors, such as wrist angle and repetition, and CTD risk. A previously published article in this journal (Marras and Schoenmarklin 1993) reported the descriptive results from a quantitative surveillance study performed in industry in which worker's wrist motions were monitored on the factory floor. The wrist motion components that were monitored on each subject were position, velocity, and acceleration measures in each plane of movement (radial/ulnar, flexion/extension, and pronation/supination). The objective of this article was to form a metric that associates the degree of incidence of hand/wrist CTDs with those types of wrist motions that were significant in the earlier paper. Of all the kinematic parameters measured, multivariate analysis of the motion data revealed that acceleration in the flexion/extension plane discriminated the best between groups of low and high incidence rates of CTDs. The epidemiological association between flexion/extension acceleration and CTD incidence rate is compatible with results from empirical studies and theoretical models in the physiologic and biomechanical literature. The flexion/extension acceleration values from this study can serve as preliminary motion benchmarks that establish relative risk levels of CTDs for hand-intensive, highly repetitive jobs that do not require hand tools. Industrial practitioners can use this methodology, along with other accepted tools, to enhance ergonomic assessments of jobs.

Occupational Cumulative Trauma Disorders of the Upper Extremity

The umbrella term cumulative trauma disorders (CTDs) (also known as repetitive strain injuries, overuse syndromes, and repetitive motion disorders) covers a number of similar conditions arising from overuse of the joints or soft tissues of the upper extremity. Occupational CTDs have become a common problem in the workplace. These disorders are costly to the employer, the worker, and society in terms of time lost from work and resulting disability. Within the past decade, occupational therapists and physical therapists specializing in rehabilitation of work-related musculoskeletal injuries have seen an increase in the incidence of CTDs of the upper extremity in the workplace. Therapists are called upon not just to treat these injured workers, but also to help them regain a functional level for work reentry and to educate them to prevent reinjury. This article reviews the literature on the epidemiology, etiology, pathophysiology, and management of upper-extremity occupational CTDs. Because the ultimate goal of the workplace is to maintain the health and safety of the employee, an educational approach to hand, wrist, elbow, and shoulder use is essential to prevent, decrease, or eliminate the risk of occupational CTDs of the upper extremity.

Work Sampling as a Method for Assessing CTDS

Work sampling is proposed as a method for evaluating aggregate risks for cumulative trauma disorders in jobs. The approach assumes that an assessment of cumulative trauma disorder (CTD) risk factors within individual tasks has been made, and can be used in conjunction with the resulting estimates of proportion of time spent per task or activity to arrive at an overall estimation of CTD risk for the job. Important advantages of work sampling include that it estimates the availability of rest and recovery time within jobs, that the method can be applied to both cyclical and noncyclical jobs, and that small, practical samples may provide reasonable estimates in many cases. A case study utilizing work sampling in a workers compensation carpal tunnel syndrome (CTS) claims investigation using a single day sample interval is presented. Results suggest little or no CTD risk, a finding that was supported by historical evidence from a large population of workers (27,200) performing the same job. Only .0000025% of workers had reported a CTD over a period of 3 years. While support for causation of CTD was not found, the method identified a probability of aggravation of a possible pre-existing condition, which is also compensable. Details regarding the studied job are provided. The use of a work sampling method to assess CTD risks is discussed.

Wrist Motions in Industry: Variance between Jobs and Subjects

Ergonomists assume that they can design out injurious postures and motions with engineering controls by guiding the worker to use the preferred, less injurious motions. The variance between workers performing tasks in ergonomically-designed jobs is assumed to be dominated by the variance between jobs. However, little research exists that quantified whether this assumption is valid. The present study examined the wrist motions of 40 industrial workers who performed highly repetitive, hand-intensive jobs of low and high risk of cumulative trauma disorders (CTDs). The position and angular velocity and acceleration of these workers' wrists were measured in all three planes (radial/ulnar, flexion/extension, pronation/supination) with goniometry. The results of this study show that for all the kinematic variables, the variance between subjects within jobs accounted for a substantial, and often majority, amount of variance. The results of this study demonstrate that ergonomists should consider the variability in motion patterns between workers when designing existing or new jobs and also should monitor at least two subjects per job in quantitative surveillance studies of wrist motion.

Exposure Assessment of Biomechanical Stress in Repetitive Manual Work Using Spectral Analysis

Theory for a quantitative exposure assessment strategy is presented for measuring physical stress associated with manual tasks containing repetitive motion, postural stress, and forceful exertions. Physical stress is measured directly using electrogoniometers for articular motion, and sensors or electromyography are used for assessing forceful exertions. A method is described for reducing the large quantities of biomechanical data that can be recorded for repetitive manual work into quantifiable metrics based on recognized exposure factors, including repetitiveness, postural stress, forcefulness, and duration. A frequency domain approach is used for averaging elemental data from repetitive cycles. This paper shows how parameters for frequency-weighted filters may be developed from psychophysical data for equivalent discomfort levels. Low force repetitive wrist flexion was used as an example of the feasibility for implementing this approach. Applications of this theory include assessing exposure to physical stress in a manner analogous to the way sound level meters are used for measuring exposure to acoustic noise. A suitable data reduction method is necessary for conducting large scale detailed epidemiological investigations of cumulative trauma disorder risk factors. Development of frequency-weighted filters based on human response to stress at different frequencies may make it possible to establish quantitative exposure limits.

Dynamic capabilities of the wrist joint in industrial workers

The objective of this study was to measure the maximal static and dynamic capability of the wrist joint in industrial workers. Estimates of the wrist's dynamic capability could aid ergonomists in assessing whether an industrial job can be physically executed by a worker and also in evaluating the risk of cumulative trauma disorders (CTDs) from highly repetitive, hand-intensive jobs. Range of motion and peak velocity and acceleration were measured in the radial/ulnar, flexion/extension, and pronation/ Flexion/extension peak velocity and acceleration were approximately twice that of radial /ulnar (approximately 1000 deg/sec and 16,000 deg/sec 2). Pronation/supination peak velocity and acceleration were greater than twice that of flexion/extension (2200 deg/sec and 45,000 deg/sec 2). The differences in dynamic capabilities between planes are probably due to biomechanical components of musculature (size and moment arm) and mximal range of motion. Dynamic capabilities did depend on the direction of movement within a plane. Maximal flexion movements were faster than extension, and supination motions were swifter than pronation. Overall, there were no significant differences in dynamic capabilities between the dominant and nondominant wrists. Generally, anthropometric dimensions of the hand and forearm correlated poorly with static and dynamic measures.

Wrist motions in industry.

Cumulative trauma disorders (CTDs) are disorders of the body's tendons and nerves due to repeated exertions and excessive movements. Workers in industrial tasks who have to move their hands and wrists repeatedly and/or forcefully are susceptible to CTDs. One of the major research voids in the study of occupational wrist CTDs is the lack of quantification of the relationship between the known kinematic risk factors, such as wrist angle and repetition, and CTD risk. A quantitative surveillance study was performed in industry in which workers' three-dimensional wrist motions were monitored on the factory floor. A total of 40 subjects from eight industrial plants participated in this study (20 workers in each of two risk groups, low and high). The wrist motion parameters that were monitored for each subject were position, angular velocity, and angular acceleration measures in each plane of movement (radial/ulnar, flexion/extension, and pronation/supination). Descriptive analyses of these measures indicated that generally the mean of the high-risk subjects was larger in magnitude than that of their low-risk counterparts. However, only the velocity and acceleration parameters resulted in significant differences between low- and high-risk groups. These results demonstrate the importance of dynamic components in assessing CTD risk.

Cumulative trauma disorders of the hand and wrist in the auto industry.

Surveillance for cumulative trauma disorders (CTDs) of the hand and wrist was carried out in five US automotive plants from 1985 to 1986, using Occupational Safety and Health Administration (OSHA) Form 200 injury and illness logs and medical insurance claims. Results using both record sources indicated that hand and wrist disorders may be more common in foundries than in other types of automotive plants. Similarly, in assembly plants, employees in certain departments appeared to be at higher risk for CTDs. Although our results are based on small numbers of cases, they suggest plants and departments that might be targeted for more detailed investigation.

Maf for Males Performing Drilling Tasks

A laboratory experiment was conducted using the psychophysical approach to determine maximum acceptable frequency (MAF) for a simulated sheet metal drilling task under varying angles of wrist flexion. Fifteen male students served as subjects for this study. The subjects were asked to perform a simulated drilling task in five different wrist flexion postures. Results indicated that MAF was significantly reduced (p<0.001) for deviated wrist postures in the transverse plane. It was noted that there was a 33% decrease in MAF values from 0 degree wrist flexion (neutral posture) to 40 degree wrist flexion. These results imply that industrial guidelines for drilling operations involving wrist flexion must consider the MAPs in order to reduce the risk of cumulative trauma disorders.

Application of Survival Analysis to CTD Risk Assessment

This paper demonstrates the application of survival models to CTD (Cumulative Trauma Disorder) studies. Survival analysis techniques are usually applied to the analysis of prospective epidemiological studies examining related risk factors. However, survival models have never been used in CTD etiology, perhaps due to mathematical complexities imposed on survival analysis techniques and its interpretation. The other reason might be the fact that it has not been considered as serious as other diseases usually studied in epidemiology. However, the conditions and assumptions of survival models fit completely into CTD studies (the existence of concomitant variables, a heterogeneous study population, censored observations etc.). Thus it is inappropriate to analyze CTD problems (specifically etiology and prevention) using typical statistical technique (ANOVA or ordinary regression). In this study, 143 subjects participated from an automobile carpet manufacturing plant which was experiencing a high number of CTD cases (107 cases, 1988–1989) and two groups of potential risk factors were examined. They were mainly categorized into personal and job-related information. This information was collected through survey questionnaires and video-taping. As the first step of analysis, survival, hazard and probability density functions were estimated. The estimated survival function shows that CTD incidence rate remained relatively constant, fluctuating 5–15%, through the first 12 years. Also, univariate associations between survival time and individual risk factors were tested using log rank and Wilcoxen rank test. Finally, the CTD data was fitted to ‘Proportional Hazard Model' (the most generalized survival model with distribution-free baseline hazard function). This model explains 75% (R2=0.75) of CTD data with the following covariates; cycle time per part, number of meals a day, dominant hand, general attitude, hand posture, degree of physical fitness, hobby and job title. The feasibility of the Proportional Hazard Modeling was investigated by test and plot. The test was conducted under the global null hypothesis about the significance of the overall model and t vs. log(-log(S(t))) was plotted to check with the assumption of proportionality. Both results ascertain the feasibility of Proportional Hazard Modeling for CTD studies.

Physical ergonomics job design: An accident prevention approach to control upper extremity cumulative trauma disorders in manufacturing industry : J Occupat Accidents, 1990, 13.4, 303–320, 8 refs.

Industrial tasks are a major cause of cumulative trauma disorders (CTDs) of the upper extremity in the workplace. Thus, ergonomie job analysis was used in a manufacturing industry to identify five operations which posed employees to a high risk of CTDs. Moreover, the risk factors associated with these operations were recognized and quantified using physical ergonomics job design principles. Based on the analysis, engineering controls were recommended.

Use of Workersʼ Compensation Claims Data for Surveillance of Cumulative Trauma Disorders

Workers' compensation claims in Ohio were evaluated as a source of surveillance data for identifying workplaces at high risk of cumulative trauma disorders (CTDs) and analyzed for their demographic and industrial characteristics. During a 5-year period (1980 to 1984), 6,849 workers' compensation claims met the case criteria for CTDs. Tenosynovitis due to continuous motion was the most frequently reported condition (58%), and the wrist was the body part most frequently affected (48%). The highest case rate was observed for female workers in the 36 to 45 age group. Incidence rates for individual companies were determined and those with the highest rates for CTDs were identified. The employer-specific rates for CTDs based on workers' compensation claims data can be used as an effective surveillance tool in locating high-risk operations where ergonomic interventions can be implemented to reduce CTD hazards.