Critical Glenoid Bone Loss in Posterior Shoulder Instability

Area of Science:

• Orthopedic surgery
• Biomechanics
• Shoulder instability research

Background:

• The critical amount of posterior glenoid bone loss for shoulder instability is not well-defined.
• Critical bone loss signifies when an isolated labral repair is insufficient for stability.

Purpose of the Study:

• To determine the critical size of posterior glenoid bone defects.

Main Methods:

• A controlled laboratory study using eleven cadaveric shoulders.
• A custom robot applied a 50-N compressive force to the glenohumeral joint.
• Measured posterior humeral head translation force and lateral displacement with varying posterior glenoid defect sizes (10% to 40%).

Main Results:

• Increasing osseous defect size reduced posterior displacement force and lateral displacement.
• A posterior glenoid defect of 20% or more, even with reverse Bankart repair, showed significantly lower peak force (13 ± 9 N) compared to isolated repair (22 ± 10 N).
• Lateral displacement was significantly less with a 20% defect and repair (0.61 ± 0.57 mm) versus isolated repair (1.6 ± 0.78 mm).

Conclusions:

• Posterior glenoid bone defects of 20% or greater result in persistent shoulder instability following isolated reverse Bankart repair.
• Shoulders with posterior glenoid defects ≥20% may require bony restoration procedures for glenoid reconstruction.