You Asked for It
November 2004

Hello Sharon,

I am an Occupational Health Nurse. I’ve recently been working with a client who was having arm/wrist symptoms likely related to repetitive computer use. He had a workplace ergonomic assessment and changes were made. He was recently assessed by an orthopedic specialist who also suggested that his symptoms may also, in part, be related to his workplace truck tires. He apparently uses “Good Year Work Horse” truck tires on his vehicle and the specialist commented that vibration associated with his tires may be contributing to some of his symptoms. I was just wondering if you might have any information or could direct me to any other sources that may be able to provide any feedback about vibration from tires. (i.e.: Do tires with more tread (more rugged tires) cause greater vibration, etc?) Any feedback you might have would be appreciated.

Thank you. Angie

Response:

Hmm... unusual

I would expect that the more rigid the tire, the higher the frequency of vibration. I don't know of any studies looking specifically at tires though in relation to MSI. Vibration basically fools the muscles into thinking that they are contracting by sending erroneous signals through the nerves. If the limb is immobilized, the worker will counter contract to stabilize because he thinks it is moving. If the limb is mobile, the muscle will contract causing motion at the joint. Again, the worker will have to counter contract to maintain the correct position. This may contribute to muscle fatigue and tendon irritation.

I have worked with people who had Carpal Tunnel Syndrome who were sensitive to vibration. Many of them have found that vibration damping gloves were very effective. These have a dense, flexible foam in the palm (under the brand Viscolas or Sorbothane in the past) and can be found at safety supply shops. Because gloves reduce tactility (and therefore increase grip force requirements), I usually suggest getting the fingerless version.

st

Hello,

My chiropractor carries a mouse to help with carpal tunnel. It's called a Zero Tension Mouse. I'd like to invest in one if it is worthwhile, but at $89 I'm reluctant to do so without a review by someone who would know how to evaluate it. Would you review it for your newsletter?

Larissa

Response:

Good Afternoon Larissa,

While I haven't had the opportunity to try this product myself, my colleague at the WCB did a semiempirical study with it using some of the staff there who had CTS, tendonitis and / or myofascial pain. Simply put, he found that those workers who infrequently used the mouse found there was some benefit, but intensive users developed anterior rotator cuff strains or pain from having to stabilize the movement of the hand via the shoulder. Essentially this is because muscles designed for gross motor movements are being used to control a task that involves fine motor movements. This can be alleviated slightly by ensuring there is support for the arm via an arm rest.

The other problem was that the position of the scroll wheel on top of the mouse requires frequent use of the thumb extensor muscles, not only to reposition the thumb (as instructed) from beside the scroll wheel to on top of it, but also the action of scrolling with the thumb requires you to pull back on the thumb. The thumb is designed to be pulled into the fist and then relax back to the neutral position, not be actively contracted to pull back. After a short period of scrolling, the workers in the WCB "study" found irritation to the thumb extensor muscles. He reported that workers experienced symptoms in the wrist, forearm/elbow and shoulder after an average trial period of 4.9 days (among 4 staff).

While there is merit to a supported semi-supinated (i.e. thumb higher than the fingers) mouse design, I am not convinced that this particular design will be entirely effective. One of the other issues that I have concern with is that there is no left handed version available. In our society we over use the right hand, which is one of the primary reasons why there is such a high incidence of injuries since the implementation of the mouse. Even with a better mouse design, unless some of the work load is transferred to the left hand, the tissues of the right hand will continue to be fatigued and injured. (Because the left hand is used to a lesser extent, it is less likely to develop an injury with the addition of the mouse to it’s work load).

Also, I understand that the only scientific studies done on this product had a sample of one - Dr. Leahy. This is a highly biased study. Even in his promotional material he states that it will be difficult to learn to relax the upper arm, shoulder and upper back muscles. Given the type of movements required (controlling the mouse from the shoulder) this is almost impossible. As such, I would expect that although the hand and lower arm muscles may be able to relax as he suggests, the work load is simply being transferred to other joints.

My colleague at the WCB has had better success with the Evoluent VerticalMouse2 (from ergocanada.com). He says it is quite sensitive but had to decrease the tracking speed (1000 dpi). It is also only available for the right hand.

st

Feedback

Good Morning Sharon,

On behalf of Ergonomic Solutions, we would like to thank you for your candid comments about the Zero Tension Mouse. In your article you had mentioned an alternative vertical mouse, the Evoluent. I would like to let you know that we also carry this mouse, retailing it for $109.00. With being a retailer for a Canadian market, but more specifically an Alberta market, we offer it without charging PST. As you are aware, we have an excellent return policy of 30 days to give the individual an opportunity to determine if it will provide them comfort.

Also, the manufacture of the Evoluent Mouse have advised us that they are in production of a left handed version they anticipate distribution, hopefully, by the end of 2004.

I always appreciate the opportunity to read your articles and get your feedback on various equipment.

Have a great day....Teresa

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