Comparisons of wrist postures in VDT operators using wrist rests and forearm supports.
OBJECTIVE
The purpose of this study was to examine wrist motions in video display terminal (VDT) workers using the Greenleaf Medical WristSystem. This study was developed because of the limited research about the effectiveness of ergonomic equipment for VDT operators, as well as the recent increase in cumulative trauma disorders (CTDs) among these workers.


METHODS
Twenty adult VDT operators with no history of CTD were recruited from Boston University and surrounding businesses. WristSensorTM gloves containing dual-axis sensors for detection of dynamic wrist movements were worn by participants. Calibrations were then performed through the Movement Analysis System (MAS) software, after which participants were requested to type using a wrist rest (condition A), using forearm supports (condition B), using the wrist rest and forearm supports together (condition C), and finally using no form of wrist or forearm support (condition D). It was assumed by the investigators that wrist extension and ulnar deviation would decrease when using the wrist rest or forearm support, with the greatest change occurring when using both types of support. Questionnaires requesting demographic information were completed by each participant. Contrast scores were also calculated and converted into t -tests and their corresponding P -values.


RESULTS
The average degrees of motion for both right and left hands were: flexion 4.5°, extension 18.9°, ulnar deviation 15.3°, and radial deviation 2.0°. P-values for all four conditions in the left hand were found to be significant and are as follows: extension t(19) = 2.35, P < 0.025, flexion t(19) = 2.17, P < 0.025, ulnar deviation t(19) = 3.41, P < 0.0025, and radial deviation t(19) = 2.5, P < 0.025. The only significant P-value in the right hand was during ulnar deviation: t(19) = 2.7, P < 0.01.


CONCLUSIONS
Research suggests that wrist extension greater than 15° and ulnar deviation greater than 20° can be predisposing factors to the development of CTDs. In this study, all four wrist motions remained under 20° during the three conditions using the wrist rest and forearm supports. A trend of continued decreases in ulnar deviation and wrist extension from using no supports to that requiring both types of supports was also observed. Specifically, the smallest degree of wrist extension appeared when participants used only the wrist rest; ulnar deviation was smallest when both supports were used. Right hand degree values were found to be generally larger than those for the left hand. It is hoped that these results can serve as a foundation for future investigation into the effectiveness of wrist and forearm supports in reducing CTDs.
1640 Worcester Road, D 209, Framingham, MA 01701, USA.
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Hagglund
Department of Occupational Therapy, Boston University, 635 Commonwealth Avenue, Boston, MA 02215, USA.
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Jacobs
Constrained postures; Ergonomic support; Keyboard operators