The Z-Axis Shoulder Joint - A New Concept

Abstract

It is difficult for a shoulder amputee to do anything while sitting at a desk or table with the elbow tucked in against the side. For useful work the elbow needs to move forward 30-45 degrees and out 30-45 degrees to a position of function. These moves require a well designed shoulder joint. Conventional friction joints are constrained to move about an abduction axis followed by a forward flexion axis with both motions against gravity. An ideal shoulder moves 'out' away from vertical and then locks. It then swings forward or back around the vertical Z axis with no gravitational constraint. Such a joint places the forearm in a convenient location for useful work.