Which statement best differentiates reverse total shoulder arthroplasty from anatomic total shoulder arthroplasty?

• A. RTSA relies on the rotator cuff; Anatomic TSA relies on the deltoid.
• B. RTSA relies on the deltoid and changes center of rotation; Anatomic TSA relies on native rotator cuff.
• C. Both are identical in indications.
• D. Anatomic TSA uses reversed ball-and-socket.

Answer: (B)

The main distinction lies in how the joint mechanics are restored. A reverse total shoulder reverses the ball-and-socket geometry so the glenoid side bears a ball and the humeral side has a socket. This configuration medializes and lowers the center of rotation, which makes the deltoid the primary driver of arm elevation and provides stability when the rotator cuff is deficient. Anatomic total shoulder preserves the native ball-and-socket anatomy and relies on a functional rotator cuff to center the humeral head on the glenoid; without a working rotator cuff, the anatomic design cannot compensate as RTSA can. So the best statement captures that RTSA depends on the deltoid and changes the center of rotation, while anatomic TSA relies on the native rotator cuff.