Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, K01-OH-007826, 2008 Jun; :1-22
Although the incidence of computer-related musculoskeletal disorders of the upper extremity (MSD-UE) is relatively small when compared to repetitive industrial jobs, the number of workers using a computer at work is large and growing making computer use a significant risk factor for worksite injury. Therefore, the ability to prevent computer related injuries should be a priority for occupational health personnel. To be able to prevent injuries, there must be an easy, reliable, and clinically relevant method to describe and measure postures and behaviors during computer use that are considered to be risk factors for the development of MSD-UE. Although there are several generic observational methods to evaluate upper extremity work there is no a reliable and valid observational instrument that can be used in the workplace to document and assess the parameters of keyboarding that may be risk factors for MSD-UE. This project's overall aim was to develop and refine an observational instrument, the Keyboard - Personal Computer Style instrument (K-PeCS), which had the ability to document postures and behaviors identified as risk factors for MSD-UE. For this project we developed the K-PeCS in two phases. The specific aim of Phase I was to develop the K-PeCS and refine the psychometrics of the instrument including content and concurrent criterion validity, and inter-rater and intra-rater reliability. The specific aim of Phase II was to develop a model using K-PeCS items that could discriminate between those with and without MSD-UE. To accomplish our aim in Phase I we first developed the content validity of the K-PeCS instrument. Risk factors for musculoskeletal disorders of the upper extremity (MSD-UE) that could be related to keyboard use were identified from the literature and from expert opinion. Items for the K-PeCS were developed and sent to seven experts who rated the items for validity and operationalization. Based on these ratings, items were included or excluded from the K-PeCS. Once K-PeCS items were identified and operationalized we digitally video recorded 45 keyboard users, and simultaneously obtained the kinematics of their hands using a 3 dimensional motion capture system. To ascertain the inter-rater reliability of the K-PeCS, 3 trained raters independently rated video clips of these 45 computer users. To ascertain intra-rater reliability the same raters re-rated a sub-sample of 15 video clips one week later. The ratings were assessed using intraclass correlation coefficients (ICC). The overall K-PeCS had excellent reliability (inter-rater: ICC = .90; intra-rater: ICC = .91). Most individual items had from good to excellent reliability, although three items fell below ICC = .70. To assess concurrent criterion validity we compared the ratings obtained on the K- PeCS to the 3 dimensional motion capture results. Those K-PeCS items that were assessed for concurrent validity compared favorably to the motion capture data for all but 2 items. Thus, at the end of Phase I we had ascertained that the K-PeCS was a reliable and valid measure of keyboarding postures and behaviors. To accomplish Phase II, we obtained digital video recordings of 42 subjects as they worked at their own computer workstation: 21 subjects had a diagnosed MSD-UE (cases) and 21 matched subjects were without MSD-UE (controls). The K-PeCS items were rated from a video clip by an expert rater blinded to subject status. The ratings from the 42 worksite subjects were used to generate models to discriminate between cases and controls using Classification and Regression Tree (CART) methods. From these analyses a CART model was generated which could accurately discriminate between cases and controls when the cases had any diagnosis of MSD-UE (69% accuracy). The model had the single item, "neck flexion angle greater than 20 degrees"; subjects who did not have a neck flexion angle of greater than 20 degrees were accurately identified as controls. The results of this study indicate that the K-PeCS is a reliable and valid instrument that can be used in the workplace to document the postures and behaviors of computer users. The K-PeCS can be used in two ways in the workplace. Due to its observational nature, and the selection and criterion of the items, clinicians who assess computer workstations to prevent injury or provide reasonable accommodation for an existing injury can use the K-PeCS to assess computer workstations and develop interventions. In addition, since the KPeCS is a highly portable and reliable tool, it can be used as an outcome measure for research studies examining the effect of interventions in the workplace.