The functional significance of the fifth metacarpus and hypothenar in two useful grips of the hand.

Abstract

Two useful grips for daily living and professional life concerning the two ulnar fingers, designated the "locking grip" and the "supporting grip," are presented. Flexion of the fifth metacarpus was recorded by an electrogoniographic method together with an electromyogram of the hypothenar muscles during formation of the two grips. For the locking grip the flexed position of the fifth metacarpus was shown to be the functional basis of the hypothenar muscles, especially the abductor digiti minimi, operating on the proximal phalanges of the little finger, thus giving full strength to the grip together with the ulnar hand flexor. For the supporting grip the flexed metacarpus enables the stretched little finger to prop up an ordinary plate and hold it horizontally. After immobilization of the ulnar fingers as a result of trauma or in the after care of cases of entrapments of the ulnar nerve, there often arise difficulties in restoring the two grips, mostly because of the atrophy of the hypothenar. A simple method, based on the statements above, of reactivating an atrophic hypothenar and exercising the fingers is suggested. A functional positioning of the fifth metacarpus and ulnar fingers during immobilization to favor the rehabilitation of the two grips is also recommended.