Which of the following statements about the biomechanics of reverse total shoulder arthroplasty is true?

• A. RTSA uses a reversed ball-and-socket to rely on the deltoid, changing center of rotation.
• B. RTSA preserves native glenoid cavity and rotator cuff.
• C. RTSA does not modify center of rotation.
• D. RTSA is only for patients with intact rotator cuffs.

Answer: (B)

The key idea is that a reverse total shoulder arthroplasty changes how the joint moves by swapping the roles of the ball and socket. By placing a ball on the glenoid side and a cup on the humeral side, the design shifts the center of rotation medially and slightly distally. This realignment lengthens and tensionens the deltoid, making it the primary driver of shoulder elevation when the rotator cuff is damaged or nonfunctional. Because of this, the procedure doesn’t preserve the native glenoid cavity or the rotator cuff; the glenoid is modified with a glenosphere and the rotation relied on by the joint is achieved through the deltoid rather than the intact cuff. The center of rotation is indeed changed, and the operation is specifically useful in cases with a deficient rotator cuff, not only when the cuff is intact. That’s why the statement describing the reversed ball-and-socket design that relies on the deltoid and alters the center of rotation is the true one.