A significantly higher prevalence of elbow/hand complaints and diagnoses were found following a workstation design change that required much greater use of a computer mouse in a prospective Swedish study involving 148 air traffic controllers. Work-related elbow/hand complaints jumped from 16 percent to 40 percent.
The workstation design change had little impact on the prevalence of neck/shoulder/upper back complaints and diagnoses – but, 50 percent of the subjects complained of symptoms in this region.
At baseline, there was little difference between full time and part time volunteers in the prevalence of upper quadrant disorders. Following the workstation change, full time workers had significantly more elbow/hand complaints (35 percent versus 12 percent) and neck/shoulders/upper back complaints (54 percent versus 27percent) than part time workers. However, physical examination did not support a diagnostic difference between the two groups.
A psychosocial evaluation revealed that the workstation change brought about higher support but lower decision latitude. There was no relationship between lower decision latitude cases and the prevalence of upper quadrant complaints/diagnoses.
The Bottom Line – How This Applies To Ergonomists
A change in work activities can have a dramatic impact on employee wellbeing. Specifically, increasing the use of a single tool/work method (such as a computer mouse) should prompt a detailed risk factor analysis of the new approach, with recommendations for appropriate engineering and administrative controls.
This study shows the importance of the design and use of a computer mouse. It also demonstrates the value of an ergonomist to a design team.
At baseline, 187 air traffic controllers participated in the study (90 females and 97 males). The median age was 37 years and median length of employment was 11 years. Full time workers (30 – 40 hours/week) composed 68 percent of the study group (n = 128) while 32 percent of the study group (n = 59) worked part time (20 hours/week).
Follow up evaluations were performed nearly five years later with 148 of the original volunteers participating (71 females, 77 males). The follow up group had 78 percent full time workers and 22 percent part timers.
Workstation/Work Method Changes
There were 45 identical workstations at two airport air-traffic control centers. Prior to the workstation change, an air traffic controller viewed a radar screen and used a keyboard and trackball. Aircraft height, speed and direction were documented on paper through manual writing.
The new workstations were composed of a large square video display unit (505 x 505 mm), computer monitor, keyboard and an “ordinary” mouse. Almost all commands were made through operating the mouse based on information that was displayed on the large video display unit. The keyboard was seldom used.
Based on a prior study by the authors, this workstation change led to task physical demand changes of:
• Reduced postural variation of body segments
• Greater muscular activity/less rest in the forearm extensor muscles of the mouse operating arm
• Lower movement velocity
Baseline and Follow-Up Evaluation
The Standardized Nordic Questionnaire was applied at baseline and follow-up examinations. Subjects were asked to describe musculoskeletal complaints that they had experienced over the prior seven days.
Physical examination of the neck, shoulders, upper back, elbows, wrists, and hands was performed by the same practitioner at both baseline and follow-up. Diagnoses were made based on defined criteria.
Controllers had worked in the new system for a median duration of 20 months at the time of the follow up evaluation.
Information was gathered about:
• Family situation
• Sporting activities
• Spare time computer use
• Opinion on the usability of the new workstation design
• Psychosocial work conditions
There was no significant difference between the baseline musculoskeletal health of the study drop-outs and subjects who completed the study.
Study limitations discussed by the authors included:
1) The lack of a reference group.
2) The aging of the study volunteers may explain some of the increase in complaint-disorder prevalence.
3) Observer bias because the authors were aware of increased forearm extensor muscles activity identified in a prior study.
Article Title: Follow-up study of musculoskeletal disorders 20 months after the introduction of a mouse-based computer system
Publication: Scandinavian Journal of Work, Environment & Health, 34(5), 374-380, 2008
Authors: I Arvidsson, A Axmon, and S Skerfving
This article originally appeared in The Ergonomics Report™ on 2008-12-03.