Re-engineering evolution

At the age of 92, William Shatner has shattered his shoulder upon being thrown from his horse. It's bad enough that he reports his doctors are recommending a "reverse shoulder replacement."

Apparently some bright soul noticed that the arrangement of the ball and socket in the shoulder is a vestigial design that is not the strongest option for an upright biped with a three-dimensional range of motion. If the shoulder is really toast and has to be replaced, it makes more sense for the new joint to have the ball on the torso and the socket on the top of the armbone.

In the new configuration, the center of rotation is moved downward (inferiorly) and inward (medially). The deltoid muscle (the large muscle covering the shoulder) gains a longer lever arm and better mechanical advantage in lifting the arm, while bypassing the often ruined (and irreplaceable) rotator cuff. The ball acts as a mechanical stop to prevent the humerus from sliding upward, converting the deltoid's pull into rotation and elevation rather than just shear forces. This makes for better overhead motion.

For now, at least, the improvement wouldn't be worth the trauma for someone suffering from garden-variety rotator cuff or arthritic trouble. Maybe someday, though, aspiring major-league pitchers will opt for it as a prophylactic upgrade.