Mechanism of the inverted supinator reflex. A clinical and neurophysiological study.

The inverted supinator reflex sign was analysed in two patients by recording the response of the finger flexor muscles of the forearm to tapping of the styloid process of the radius before and after procain infiltration of these muscles. It was found that the response persisted despite the block. The findings support the concept that the underlying mechanism is increased alpha motoneurone excitability below the level of the lesion; however, a possible contribution of the dynamic muscle spindles could not be excluded.