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Repetitive Strain Injury (RSI) &
Work-Related Upper Limb Disorder (WRULD)

RSI and the MouseBean® Hand Rest by David Tibbs MS, FRCS. Consulting Surgeon. Oxford.

Repetitive Strain Injury (RSI). A variety of conditions nowadays are included under the non-specific terms of RSI or WRULD, that is to say, a painful, and possibly disabling condition in or near the wrist, and associated with an occupation involving prolonged or repeated manipulation of the hand or wrist. However, each of these various states is distinct and has its own particular occupational associations. In the case of the computer mouse, RSI is quite often attributed to its use and the Carpal Tunnel Syndrome is the usual variety found here.

There are many other possible causes for Carpal Tunnel Syndrome but here we are only concerned with it in relation to the prolonged use of a computer mouse and its prevention or relief by a device specifically designed for this purpose. Let us first consider the ways in which the median nerve becomes involved to cause this syndrome.

What is Carpal Tunnel Syndrome?
The hand is a miracle of compact engineering. It can grip or manipulate with power and delicacy and is provided with a nerve system giving a remarkable array of sensors governing its use and protection. Its scope of activity is greatly enhanced by the wide range of wrist movement, giving virtually a universal joint.

The real power in the hand comes from the forearm muscles and is transmitted by strong tendons to the digits. To permit free movement at the wrist, these tendons are channelled through a narrow tunnel, the carpal tunnel, centrally situated at the base of the hand, and allowing a sliding movement of the tendons in every position of the wrist. The tunnel is shared by a large nerve, the median nerve, which is some 5mm across and responsible for receiving sensation from the thumb and the first three fingers and also controlling some of the small muscles in the hand (especially the thumb) which give the fine adjustment movements. The nerve is nourished by an artery and vein running along its length. Compression of this nerve and its blood supply is the basic cause of the syndrome.

[Two other nerves, the ulnar and the radial, are responsible for supplying the remainder of the hand but these nerves enter it by different routes and are not prone to the same stresses.]

The carpal tunnel has unyielding walls of bone and is roofed over by a very tough ligament. It acts as a pulley, centralising the direction of pull by the tendons in any position of the wrist. The tendons are lubricated by synovial sheaths which can become inflamed by excessive use. The nerve and tendons are uneasy companions in the tunnel. The tunnel is a tight fit and the median nerve can be compressed when the strong tendons alongside it are tensed. The tendency to compression of the nerve is accentuated by use of the wrist in a bent position during which the limits of tolerance may be reached. In the working hand, the most favourable position is for the wrist to be relatively straight, and the least favourable is with the wrist bent strongly backwards.

Another factor giving the median nerve a hard time is its central alignment in front of the tendons, giving it an exposed position on the front surface of the wrist (it is the first structure to be divided if the wrist is slashed in a suicide attempt). In this way, the nerve is vulnerable to external pressure just before it enters the carpal tunnel. This occurs when the wrist and base of the hand (and weight of the arm) are rested heavily on a flat surface, especially if the nerve is made prominent by a backward bending of the wrist. This happens all too easily when using a mouse and the arm is tiring from prolonged use.

The Manifestations of Carpal Tunnel Syndrome
The symptoms arise from distress in the median nerve. In the early stages there is tingling in the thumb and first three fingers. This is soon replaced by numbness in the same area. On ceasing to use the mouse, the symptoms will subside in a few minutes but are a clear warning of compression causing distress in the median nerve. Unless the method of using the mouse is altered, the symptoms will occur with increasing frequency and severity, often accompanied by weakness of the small muscles at the base of the thumb which can affect its control of gripping and fine movements. Eventually, use of the mouse has to be abandoned and recovery usually occurs slowly, although some loss of sensation and muscle control may persist. At this stage, surgical operation to open up the tunnel (by dividing the strong ligament spanning over it) may be the only way of restoring full use. The condition should not be allowed to progress this far.

There are considerable variations in the dimensions and proportions of the wrist structures, and for this reason, some people are much more likely to sustain median nerve compression. Nevertheless, all users would be wise to find ways to ease the stresses on this nerve by any simple device that spares it from the unfavourable factors described above. The MouseBean® Hand Rest offers a good solution.

Engineered for Comfort and Protection

The MouseBean® Hand Rest
The inventor, John Crocker, set out to provide a device with the following features:

  • It would support the hand and weight of the arm on a sliding device fully able to move with the mouse.
  • The surface on which the base of the hand rested was to be well cushioned but with a space between the cushions to spare the line of the vulnerable median nerve from any external pressure.
  • The hand would be supported with the wrist in a near-straight position.
  • Finger movement for fine adjustment of the mouse position, or when pressing its buttons, should be easily possible without raising the hand, and, when required, wide movement of the mouse is easily permitted by sliding the device over the mouse pad.

The final version was developed from a series of devices and was christened the MouseBean® Hand Rest. It has been tried by a number of full-time mouse users, including some who were known to be prone to carpal tunnel syndrome.

Read the Surgeon's Report

Copyright © 2000 D Tibbs. All rights reserved. Used with permission.

National Press

Daily Telegraph
"Overuse of the fingers with a bent wrist can lead to inflammation of the protective tendon sheath and the risk of repetitive strain injury. Another potential risk is carpal tunnel syndrome, which triggers painful tingling in three of four fingers – usually at night. This nifty gadget worked first time for me and I became an instant fan; it moves easily about the mousemat and I am glad my niggling pain did not have time to get worse."


Simon (Web Developer)
"Before I started using the MouseBean Hand Rest I was coming home from work with sore hands/wrists and a weakened forearm. The day I started using this device I started to notice the change; now the pain has gone in my mousing hand and work is no longer painful. Every mouse should be equipped with one of these amazing pieces of equipment."

Tips for Safer Working

Take regular breaks. Short breaks, even for a few seconds, can help to reduce the risk of some types of cumulative trauma. If you work under pressure and find it hard to remember to take a break, then download and install a simple Rest Break Timer (see our links page). You'll soon grow to enjoy a quick stretch every so often and the minor interruption is a very small price to pay for feeling more relaxed.

Sit Properly. Get yourself a good chair and make sure it is properly adjusted to suit your body height and desk height. Your elbows should be about level with the desk and you should have plenty of leg room to avoid static postures.

We're Listening

Please email us with your experiences. We are always interested to hear your views on computer-related problems, especially in the hand, wrist and arm.



Comments or Technical Problems -
All material is Copyright © MouseBean Ltd 2002/2003. All rights reserved worldwide.
MouseBean is a registered trade mark of J Crocker.
The MouseBean® Hand Rest is a Registered Design (2104424). UK and International Patents Pending.