Glenosphere

The glenosphere is the spherical articulating component on the glenoid side of a reverse total shoulder arthroplasty (RTSA). It replaces the natural glenoid surface and works with the humeral cup to form the semi-constrained joint that allows shoulder motion when the rotator cuff is damaged or torn. The design and positioning of the glenosphere influence range of motion, stability, and impingement.

Most glenospheres are made from metal alloys such as cobalt-chromium and are available in a range of diameters to match patient anatomy. They attach to a glenoid baseplate and are secured by a combination of taper-fit interfaces and locking screws, depending on the system. Some designs feature an eccentric sphere or variable offsets to adjust the center of rotation, enable lateralization, or optimize deltoid tension and impingement risk. The interface between the glenosphere and baseplate is designed to be durable and to resist micromotion and wear.

In surgical practice, the size, offset, and positioning of the glenosphere are chosen to balance stability with range of motion. Inferior tilt and lateralization are common strategies to reduce scapular notching and spread forces more evenly through the glenoid. Glenosphere overhang can also be used to minimize impingement with the acromion during arm elevation. Improper selection or placement can lead to complications such as loosening, dislocation, or notching, which may affect function.

Historically, reverse shoulder designs evolved from earlier medialized concepts to include lateralized glenospheres aimed at improving range of motion and reducing impingement while maintaining stability. The glenosphere remains a central element of RTSA biomechanics and is chosen according to implant design and patient-specific factors.