What is the main purpose of the trunnion in shoulder arthroplasty systems like the Univers II and Apex?

The trunnion plays a critical role in shoulder arthroplasty systems such as the Univers II and Apex by functioning as the connection point between the humeral head and the stem. This connection is essential for the overall stability and biomechanical function of the prosthetic shoulder joint. By securely attaching the humeral head to the stem, the trunnion helps to ensure proper alignment and load distribution during various arm movements.

In the context of shoulder arthroplasty, a well-designed trunnion can contribute to improved rotational stability and an optimal range of motion for the patient, enabling a more natural function post-surgery. While there are other components involved that may assist with stabilization, adjustment of inclination, or healing, the primary importance of the trunnion lies in its role as the linkage between the prosthetic components, thereby forming the foundation of the prosthetic shoulder joint.