Workday arm elevation exposure, a comparison between two professions.
Ettinger L; Kincl L; Karduna A
Proceedings of the 35th Annual Meeting of the American Society of Biomechanics, August 10-13, 2011, Long Beach, California. Newark, DE: American Society of Biomechanics, 2011 Aug; :121
INTRODUCTION: Occupations that require repetitive arm motions above 60 degrees and 90 degrees of humeral elevation have been attributed as being potentially injurious professions for the shoulder. 11% - 68% of currently working dental hygienists have shoulder related pain and or dysfunction. Unlike dental hygienists, workers who use computers for the majority of their workday do not share the same risk factors for occupational musculoskeletal injuries of the shoulder. It is hypothesized that because dental hygienists have a greater tendency for shoulder disorders that they will spend a greater percentage of their workday at elevated humeral angles than computer based workers. METHODS: Twenty female dental hygienists with an average age of 42.6 years (24-56 years) and nineteen female computer workers with an average age of 42.6 years (26-62 years) participated in our study. Computer workers were recruited to match the dental hygienist population as closely as possible for age, arm dominance, number of years employed and total number of hours worked per week. All data were collected on an eight hour workday for both dental hygienists and computer workers (8.8 hours, 8.1 hours, respectively). Before the start of the workday subjects were fit with two tri-axial accelerometers (Virtual Corset) bilaterally at the level of the deltoid tuberosity of the humerus. Virtual Corset data were recorded at 7.6 Hz until the device was removed at the end of the workday. Data were converted from linear accelerations to arm elevation angles using a previously validated equation. The total amount of time participants spent with their arm elevated above 30 degrees, 60 degrees and 90 degrees was summed and then averaged as a percentage of total working hours - this measure is treated as the quantitative dependant variable. Independent samples t-tests were used to quantify differences between total arm usage above 30 degrees, 60 degrees and 90 degrees for dental hygienists and computer workers. Percent of workday with arm elevated above 30 degrees, 60 degrees and 90 degrees for dental hygienists and computer workers. Significant differences where p<.05. RESULTS: On average dental hygienists worked with their arms above 30 degrees for 11% of their workday more than computer workers (p<.001) and above 60 degrees for 5% of their workday more than computer workers (p<.001). No significant differences between groups existed above 90 degrees (p=.07). DISCUSSION: Occupational risk factors for shoulder disorders have been attributed to awkward and constrained posture, the intensity and duration of force loads on the shoulder and the repetitious nature of the work being performed. Svendsen et al., composed a cross-sectional analysis comparing arm usage in different overhead professions such as painters, machinists and car machinists. From that study it was identified that the greater duration of working hours with the arm elevated above 60 degrees and 90 degrees yields a stronger correlation with shoulder injuries. The results of our study support our hypothesis that dental hygienists spend a significantly greater percentage of their workday with their arm elevated above 30 degrees and 60 degrees when compared to computer workers. Trends in the literature regarding both dental hygienists and computer workers suggest that dental hygienists have a greater tendency for shoulder disorders than computer workers. Our results may help to explain, at least in part, why dental hygienists may be at greater risk for developing shoulder injuries than other occupations. There could be other occupational factors that could be contributing to the differences in injury rates between these two populations. Dental hygienists did not significantly differ from computer workers above 90 degrees of humeral elevation. Findings from this study suggests that chronic exposure to humeral elevations angles below 60 degrees may be sufficient to increase the risk of occupational shoulder injuries.
Injuries; Musculoskeletal-system; Musculoskeletal-system-disorders; Extremities; Arm-injuries; Dentistry; Exposure-levels; Risk-factors; Computers; Computer-equipment; Humans; Women; Age-groups; Dentists
Proceedings of the 35th Annual Meeting of the American Society of Biomechanics, August 10-13, 2011, Long Beach, California
University of Oregon