Results of the Survey on strategies for minimising discomfort in the wrist and lower arm due to prolongued mouse work

by

David McFarlane
Health and Community Services Industry Team WorkCover Authority
New South Wales, Australia

Brief report on the results.

It all depends on the way you hold your mouse!

Techniques for holding the mouse device

More recent reports of postural problems among workers using computers have shown that mouse use can cause wrist problems. One published paper has described an example of tenosynovitis of the right wrist at the point where the worker rested the wrist on the work surface while operating the mouse in a computer workstation 2 to 3 hours per day for 6 days of the week (Franco, Castelli, Gatti, 1992). The friction and pressure on the wrist joint tendon that caused the injury was due to the faulty positioning of the hand and wrist.

Research by Tichauer (1978) has pointed out that it is desirable to avoid awkward wrists postures during exertion since deviation of the wrist can result in misalignment of the tendons if the wrist is also flexed with the consequence that fatigue and injury may ensure. In order to minimise the deviation (sideward twist) of the wrist as well it is also necessary to ensure that the mouse pad should be placed in line with the elbow and shoulder.

Undesirable postures either overload muscles tendons or load them unevenly or create a static load. Awkward postures are often associated with discomfort and pain especially if they are prolonged and/or forceful.

The National Code of Practice for the Prevention of Occupational Overuse Syndrome states that "frequent or prolonged bending and twisting of the wrist away from the neutral (natural) position increases the risk of injury" (Worksafe, 1994, page 16, clause 7.16 and figure 9).

Clause 7.16 of the code states that "Frequent or prolonged bending and twisting of the wrist from the neutral (natural) position increases the risk of injury." Figure 9 of the code shows the "Neutral (natural) position for the wrist."

Recent research on sloping keypads shows that reducing the flattening (pronation) of the wrist position significantly reduces the activity of the extensor muscles (Extensor Carpi Ulnaris) and is therefore likely to be less uncomfortable and less tiring (Kothiyal and McFarlane, 1997).

The position of the wrist where the hand is horizontal with the palm of the hand facing downwards is an awkward posture. The natural posture of the wrist is regarded as the "position of neutral rotation" where the palm faces medially (Kapandji, 1982). This “natural” position is the best hand position for function (Stevenson, 1985). It can be approximated by on a desk surface by holding the hands with the thumbs uppermost and palms facing each other (somewhat as in clapping) and then resting the hand on the outer edge of the palm so that the small finger touches the surface. The hand that holds the mouse should then only needs to be rotated far enough over to allow the worker to place the fingertips on the buttons. In this position strain to the wrist is minimised.

A photograph of the use of a mouse device with the hand in a natural posture

There appear to be two main problems with preventing mouse-related symptoms. One is the tendency of workers not to seek help until the problems have become severe so that the problem has become incurable. (In some instances the problem has advanced past and the milder overuse syndromes all the way to carpal tunnel syndrome before there are even complaints about the symptoms). The other problem I have found is that a worker who has sought advice often gives up on a new work posture a few hours after first trying it. New work postures often feel odd to the worker even when theory says that they are more natural. One of the main unanswered questions is; how soon should one wait before “ergonomic” modifications to the work system or workplace layout result in improved comfort and a reduction in symptoms?

Recently with assistance from the Human Factors and Ergonomics Society (HFES) Europe Chapter I conducted an on-line survey to determine how valuable his mousing advice is at reducing shoulder and wrist pain. The goal of the survey was to discover how long people need to persist with trying the recommended wrist and shoulder postures before they could expect to notice an improvement. The response to the public survey was not as great as we had hoped for.

However a few trends became evident quite quickly. Most people reported both wrist and shoulder problems in the sample received in the first few weeks. Amongst those people who reported improvements, the reduction in wrist discomfort seemed to happen very quickly, typically less than an hour whereas the reduction of shoulder symptoms took place less quickly - typically within a week. These rapid improvement rates were reported by approximately a third of the respondents. Many of the remainder reported chronic problems that are less likely to respond to ergonomic interventions. As they say in the classics, the early findings of preliminary research look promising but further research is needed.

References

• Franco, G. Castelli, & C. Gatti, C. (1992), Postural tenosynovitis caused by misuse of a computer input device mouse”, Med Lav, 83, 352-355.
• Tichauer, E.R. (1966), Some aspects of stress on Forearm and Hard in Industry, Journal of Occupational Medicine, 8, 63-71.
• Worksafe / National Occupational Health and Safety Commission (1990), National Code of Practice For The Prevention Of Occupational Overuse Syndrome, Canberra: Australian Government Publishing Service.
• Kothiyal, K, & McFarlane, D. (1997), An ergonomic assessment of the design of a segmented computer keyboard, From Experience to Innovation IEA ‘97, Proceedings of the 13th Triennial Congress of the International Ergonomics Association, Tampere, Finland.
• Aaras, A., Horgen, G., Bjorset, H.Ro, O., & Thoresen, M. (1998), Musculoskeletal visual and psychosocial stress in VDU operators before and after multidisciplinary ergonomic interventions, Applied Ergonomics, 29, 335-354.

Acnowledgment:

The author wishes to thank Dick de Waard (University of Groningen, The Netherlands) who created the survey form that was placed on the web site of the Europe Chapter of the Human Factors and Ergonomics Society (HFES). Moreover, without his support, advice and assistance the web site survey would never have taken place.