What’s the difference between a reverse total shoulder and a CTA prosthesis

This question is asked often. Here are the ‘cliff notes’.
Both are used to help manage the combination of shoulder arthritis and rotator cuff deficiency or rotator cuff tear arthropathy.
A CTA prosthesis is a resurfacing of the upper humerus that requires an intact coracoacromial arch for stability and active elevation of over 90 degrees before surgery.