Initial glenoid component fixation in "reverse" total shoulder arthroplasty: a biomechanical evaluation

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Biomaterials Science

Background:

• Reverse shoulder prostheses improve function in rotator cuff arthropathy but face concerns of premature mechanical failure.
• Glenoid component loosening is a significant challenge impacting the longevity of these devices.

Purpose of the Study:

• To evaluate the initial glenoid component fixation of two uncemented reverse shoulder prostheses under physiologic loading.
• To determine how lateral offset and fixation method influence baseplate motion and component stability.

Main Methods:

• An in vitro study using polyurethane foam to simulate excellent glenoid bone stock.
• Testing two uncemented reverse shoulder prostheses: Delta III and Reverse Shoulder Prosthesis (RSP).
• Measuring baseplate motion in relation to lateral offset and peripheral screw fixation.

Main Results:

• Both lateral offset and peripheral screw type significantly affected baseplate motion.
• Motion for Delta III and RSP components (with 5.0-mm screws) remained below the 150 µm bone ingrowth threshold.
• RSP-neutral components demonstrated stable fixation despite a 69% greater moment at the interface compared to Delta III.

Conclusions:

• Uncemented reverse shoulder prosthesis fixation can achieve stability below critical thresholds for bone ingrowth.
• Lateral offset and screw fixation are key factors influencing glenoid component motion.
• Successful in vivo outcomes depend on surgical technique and patient bone stock.