An elbow joint prosthesis having a metal humeral component, the head of which has flanges forming a recess in which a U-shaped plastic insert is nested. A boss projecting anteriorly from the head portion of a metal ulnar component is received within the insert with latero-medial clearance for laxity. A tubular plastic sleeve is received in axle holes in the ulnar boss and the legs of the plastic insert, and an axle spanning the flanges of the humeral component and extending through the sleeve bore connects the ulnar component to the humeral component for articulation. Clearance between the sleeve and the axle hole of the ulnar boss provides laxity up to nominal limits, beyond which elastic deformation of plastic at contact areas of the sleeve and insert restrains rotational and angular motions under supination, pronation and varus-valgus angulation of the arm, absorbing energy in the process. Lateral and medial protuberances on the proximal portion of the humeral head enhance support of the humeral component in strong bone of the distal humerus at the border of the olecranon depression.