Ulnar deviation occurs when your wrist is bent outward in the direction of your little finger. On tradtional keyboards the span of your shoulders exceeds the contiguous width of the home row of keys. In order to position your hands over the home row it is necessary to bring your hands together in front of your body with your wrists deviated. This constricts the blood flow through your wrist and also requires sustained muscle tension which further reduces blood flow to the muscles. The median nerve runs through the carpal tunnel in your wrist, ulnar deviation reduces the size of this tunnel and pressure on this nerve. Ulnar deviation is among the most common and potentially damaging keyboard postures.

Solution
The contoured keyboard addresses the issue of ulnar deviation by separating the left and right key wells positioning your arms approximately at shoulder width and with wrists straight reducing ulnar deviation and abduction.