(1) By pressure of the end of the stump in the socket (in amputations low down with a palmar flap—for example, in disarticulation at the wrist joint).
(2) By pressure of the top of the forearm socket on the enlargement of the forearm below the elbow.
(3) By pressure of the inner side of the upper edge of the armlet against the axilla.
But, in actual work, thrusting movements are nearly always made with the elbow bent to a right angle or almost so, then the pressure transmitted through the forearm piece is borne almost entirely by the steels of the armlet.
3. Resistance to Rotation.—A well-adjusted artificial arm cannot rotate on the limb because—
(1) The forearm is elliptical in section and not circular, this is specially so in the lower third.
(2) Flexion of the elbow is only possible if the artificial joint is in the same plane as the axis of the elbow joint—that is, the sagittal plane.
(3) The axillary strap of the shoulder attachment prevents rotation.
