Scapular Morphometry Informs Suprascapular Nerve Injury Risk During Reverse Shoulder Arthroplasty: A Cadaveric Study

Area of Science:

• Orthopedic Surgery
• Anatomy
• Biomechanical Engineering

Background:

• Reverse shoulder arthroplasty (RSA) requires secure glenoid baseplate fixation.
• Peripheral screw insertion during RSA risks suprascapular nerve (SSN) injury.
• Existing safe zones for screw placement may not account for individual scapular anatomy.

Purpose of the Study:

• To determine if described safe zones for RSA screw placement correlate with scapular morphometry.
• To assess if common screw positions during RSA confer differential SSN risk.
• To investigate the relationship between scapular dimensions and SSN proximity during screw insertion.

Main Methods:

• Dissection of 20 cadaveric shoulders to measure safe zones and scapular dimensions.
• Simulated RSA baseplate fixation with varying superior and posterior screw positions.
• Analysis of cortical breach and SSN proximity, correlating findings with scapular morphometry.

Main Results:

• The superior safe zone significantly correlated with scapular dimensions (r = 0.78-0.86).
• All superior screws remained intraosseous; no significant SSN proximity difference was noted for posterior screws.
• Posterior cortical breach occurred in 50% of cases, associated with shorter scapular spine length (p = 0.027).

Conclusions:

• Scapular dimensions predict the superior safe zone, indicating anatomical scalability.
• Posterior safe zone is not predicted by scapular dimensions, but shorter spines increase breach risk.
• Scapular morphometry may inform preoperative RSA planning, but requires prospective validation.