Head extension effect in static posturography

The effect of head extension on the standing position has been studied by analysis of recordings made by static posturography type III (SPGIII), a set of six test of posturography for sensory interaction. The head extension effect in posturography was evaluated by comparing the results of testing with head extension on a stable platform and on foam rubber to testing with a normal head position. In normal subjects head extension increased the postural sway, but there was no more effect on foam rubber than on the stable platform. For patients with peripheral vestibular disorders the head extension effect on the measured postural sway was evaluated by the difference from the normal condition. This difference could be positive, zero, or negative on the stable platform as well as on foam rubber. In both patients and normal subjects, foam rubber had no more effect than the stable platform. The several types of results could be seen in each category of peripheral vestibular disorders. Only minor nuances could be observed: positive differences were more pronounced in benign paroxysmal positional vertigo, whereas negative ones were more obvious in unilateral vestibular deficits. These findings, moreover, deny that head extension in SPGIII should be considered a condition revealing vestibular dysfunction, as has been supposed. As head extension has an influence on the neck proprioceptor as well as on the position of the otoliths, its effect is ambiguous, which makes the interpretation rather difficult. A neck proprioceptive as well as an otolithic explanation appears to have some clinical support.