The effects of pistol grip power tools on median nerve pressure and tendon strains

Objectives. Tendonitis and carpal tunnel syndrome are common cumulative trauma disorders that can occur with repetitive usage of pistol grip power tools. The role of reaction torque resulting in a forceful rotary displacement of the tool handle, as well as the role of applied grip force, is not clear in the development of these disorders. This study aimed to quantify the flexor tendon strains and median nerve pressure during a typical power tool operation securing a threaded fastener. Methods. Six fresh-frozen cadaver arms were made to grip a replica pistol grip power tool using static weights to apply muscle forces. A 5-Nm torque was applied to the replica power tool. The median nerve pressure and strains in the flexor digitorum profundus and superficialis tendons were measured using a catheter and strain gauges, at three wrist flexion angles. Results. The peak tendon strains were between 1.5 and 2% and were predominantly due to the grip force more than the transmitted torque. Median nerve pressure significantly increased with the wrist flexed versus extended. Conclusion. The results indicate that the contribution of the grip force to the tendon strain and median nerve pressure was greater than the contribution from the reaction torque.

Quantitative Models for Prediction of Cumulative Trauma Disorders Applied to the Maquiladora Industry

Temperature gradient changes on the surface of the skin or in the middle of the body are signs of a disease. The aim of this study is to develop quantitative models for the prediction of cumulative trauma disorders (CTDs) arising from highly repetitive activities, considering risk factors, such as age, gender, body mass index (BMI), blood pressure (BP), respiratory rate (RR), and heart rate, to prevent injuries in manufacturing factory operators. This research involved 19 individuals from the area of sanding and 14 individuals from the area of tolex in manufacturing factories who had their vital signs and somatometry taken, as well as thermal images of their hands in the dorsal and palmar areas; an evaluation by the OCRA method was also applied. Factors such as BP and heart rate were determined to significantly influence the injuries, but no strong association with BMI was found. Quadratic regression models were developed, the estimates of which were adequately adjusted to the variable (R² and R² adjusted > 0.70). When integrating the factors of the OCRA method to the generated models, a better fit was obtained (R² and adjusted R² > 0.80). In conclusion, the participants who present levels out of the normal range in at least one of the factors have high probabilities of developing injuries in their wrists.

Repetitive Strain in Nonrepetitive Work: A Case Study

In a Québec factory, a woman in a nontraditional job suffered from epicondylitis whereas her male coworkers were unaffected. A study was undertaken in order to enumerate the operations at risk for epicondylitis. Workers were interviewed in order to identify difficult operations and systematic observations were done over 4 work days. Although tasks were extremely varied, certain movements at risk for epicondylitis were repeated many times. Fifty-three valves were turned against resistance as part of this job, and one valve requiring a particularly difficult movement was turned 20 times in one day. There were at least 61 operations at risk for epicondylitis per day over a 4-day period. Strain on the elbow joint was particularly intense for the woman worker because the design of the workplace gave an advantage to taller workers with larger hands. Although this case study does not permit us to conclude that the worker's epicondylitis was due to her job, it enables us to suggest that it would be wise to adapt the dimensions of relevant equipment and worksites to a wider range of potential worker sizes. We also raise some questions about the definition of repetitive strain in epidemiological studies. We suggest that it may be necessary to consider not only the cycle time but also the total of forces exerted on a joint in order to study workplace injuries to the musculoskeletal system.