New Concepts for Posterior Shoulder Instability, Christian Gerber, M.D. | SDSI Shoulder Course 2023

www.sdsi-shoulder.com

Understanding Posterior Shoulder Instability: Causes, Anatomy, and Surgical Insights:

Posterior shoulder instability is categorized into dynamic (recurrent, often positional) and static (painful but without instability symptoms). Research indicates that hyperlaxity contributes to dynamic instability, and traditional treatments such as posterior-inferior capsule shift, glenoid osteotomy, and posterior bone block have shown limitations.

Key Findings on Posterior Instability:
Scapular Anatomy is Crucial: The acromion’s position and morphology significantly influence posterior instability, yet traditional B0 and B1 glenoid classifications have overlooked this factor.
Progression & Osteoarthritis: Static posterior subluxation is progressive, leading to eccentric osteoarthritis.
Acromial Morphology & Instability: Research shows that posterior acromial tilt, height, and coverage are systematically different in unstable shoulders. Patients with a posterior acromial height greater than 23mm have a 32x higher risk of posterior instability.
3D Analysis & Surgical Correction: Studies indicate that scapular osteotomies can correct acromial abnormalities and restore shoulder stability. Successful outcomes depend on precise execution, with improper correction leading to surgical failures.

Clinical Implications:
Posterior instability and eccentric osteoarthritis share similar acromial abnormalities.
The acromion serves as a secondary restraint, influencing posterior humeral escape.
Scapular corrective osteotomies show promising results in stabilizing the shoulder, reducing pain, and improving function.

Emerging studies reinforce that failed posterior reconstructions often exhibit distinct acromial abnormalities, further validating the role of scapular anatomy in treatment planning.