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Risk Factors and Sources of Injury > Ulnar Deviation When Using the Keyboard          
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Animation Showing Ulnar Deviation on a KeyboardUlnar Deviation When Using the Keyboard


What is Ulnar Deviation?

If one looks at the width of the shoulders of an adult and the width of the spacing of the hands when placed on the home row of a standard conventional keyboard, it is clear that the shoulders are wider.  To compensate for this, people are forced to bend their wrists outward (in the direction of the fifth finger) to type comfortably forming a 90° angle between the home row keys and their hands, and this bend is called ulnar deviation.

Ideally the hands should be in alignment with the forearm, so that a straight line can be drawn through the center of the forearm, your wrist, and through the third (middle) finger, with no 'bend' or lateral deviation at the wrist. The use of a thumb can also be a cause of ulnar deviation as it is shorter than the other digits, and as such people often rotate their hands outwards in order to make it easier for their thumb to reach keys.

Why is Ulnar Deviation a Risk Factor?

When adopting this position, blood flow is constricted through the wrist and this posture also requires sustained muscle tension which further reduces blood flow to the muscles. The median nerve runs through the carpal tunnel in the wrist, and when adopting a position of ulnar deviation the span of this tunnel is compressed and pressure on this nerve can lead to Carpal Tunnel Syndrome

How Much Ulnar Deviation is 'ok' and not a Risk Factor?


Every individual has different degrees of strength, dexterity, endurance and fatigue rates in the muscles in their hands.  For most individuals, a small amount of deviation will not cause any numbness, pain or discomfort.  However, maintaining a position which is non-neutral for extended periods of time may become more problematic, and with many individuals spending most of their working day on their keyboard, even a small amount of ulnar deviation can pose a risk factor.

What are the Symptoms of 'too much' Ulnar Deviation?

Symptoms to look for which indicate that the ulnar deviation in their workday has become a problem include pain, numbness or tingling in the fingers and weakness in the hand and fingers.

How can the Choice of Keyboard Help to Reduce Ulnar Deviation?

Adjustable Keyboards
which adjust so that they 'split' or 'splay' and Separated Keyboards can eliminate ulnar deviation by allowing the hand of the user to be perpendicular to the orientation of the keyboard without the need to bend their wrists outwards.  Also, since repetitive muscle use can cause inflammation and pressure on the median nerve (especially with keyboards which require higher force to press keys or more movement), keyboards which minimize range of movement and have a lighter touch can help reduce pressure on the median nerve.

What Other Strategies can be used to Reduce Ulnar Deviation?


Often individuals will adopt positions of ulnar deviation while they are asleep without being conscious of this movement.  The wearing of a wrist brace or support while sleeping can prevent accidental adoption of a position of ulnar deviation when one is supposed to be at rest.

To reduce awkward reach associated with multi-key combination keystrokes, a potential solution is to use Footswitches for the modifier keys (CTRL, ALT, SHIFT).

 

Last edited December 16th, 2013

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