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Wrist Ulnar Deviation
Ulnar deviation occurs in the frontal plane. There is typically more joint range in the ulnar direction. Ulnar deviation is important in positioning the hand but far more important in its use as a power motion – as in hammering. The greater range coupled with the fact that the ECU possesses a greater moment arm for ulnar deviation than any other muscle for any other movement of the wrist verifies the importance and power of ulnar deviation.
While the ulnar deviators can be tested directly, they are more commonly tested with the wrist flexors and extensors. As with the other wrist muscles it is important to look for balance – is the person capable of pure wrist ulnar deviation or is an attempt at ulnar deviation accompanied by unwanted wrist flexion or wrist extension. This unwanted movement suggests damage to one of the pair of ulnar deviators. Loss of the dorsal ulnar deviator (ECU) would result in ulnar deviation with wrist flexion. Loss of FCU would result in unwanted wrist extension when trying to purely ulnarly deviate.