What is a primary reason for indicating a CA humeral head instead of an RTSA?

The decision to indicate a companion humeral head (CA) instead of a reverse total shoulder arthroplasty (RTSA) is often influenced by deltoid insufficiency. The deltoid muscle plays a crucial role in shoulder stabilization and function, particularly in the context of reverse arthroplasties, which rely heavily on the deltoid for movement. If the deltoid muscle is insufficient or has poor functionality, the mechanics of a reverse total shoulder can be compromised, potentially leading to suboptimal outcomes such as instability or inadequate strength.

In contrast, the companion humeral head replaces the articulating surface without requiring the same reliance on the deltoid for joint function. This option may be preferable in patients with significant deltoid insufficiency, where a more traditional shoulder prosthesis can provide better stability and functionality.

Considering the other factors, while age, bone density, and previous shoulder surgeries can play roles in surgical decisions, they do not specifically highlight the same immediate impact on the necessity of deltoid function as an indication for choosing between CA and RTSA.