Humeral component retroversion in reverse total shoulder arthroplasty: a biomechanical study

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Anatomy

Background:

• Reverse total shoulder arthroplasty (RT SA) improves function and reduces pain in patients with rotator cuff deficiency.
• Determining optimal humeral component positioning is crucial for RT SA success.

Purpose of the Study:

• To investigate the impact of varying degrees of humeral retroversion on muscle force requirements during scaption.
• To evaluate the effect of humeral retroversion on shoulder range of motion, including internal and external rotation.

Main Methods:

• Six cadaveric shoulders underwent CT imaging and dissection.
• RT SA was implanted with 0°, 20°, 30°, and 40° of humeral retroversion.
• Shoulders were tested on a simulator to measure muscle forces for scaption and analyzed using 3D models for range of motion.

Main Results:

• No significant differences in muscle forces for 30° or 60° scaption were observed across all retroversion angles.
• Increased retroversion improved impingement-free external rotation but decreased internal rotation.
• Humerus rotation around the glenosphere was unencumbered above 60°.

Conclusions:

• Humeral retroversion in RT SA does not alter muscle force demands for scaption.
• 0° to 20° of retroversion optimizes internal rotation for arm-at-side activities.
• This range limits side-arm external rotation but does not affect elevated arm external rotation.