What is the Glenoid Bone?
The glenoid is the shallow, cup-shaped socket portion of the scapula (shoulder blade) that articulates with the humeral head to form the glenohumeral joint. 1
Anatomical Structure
The glenoid serves as the articular surface on the scapula where the ball of the humerus sits, forming the shoulder's ball-and-socket joint. 1 This bone is relatively small with limited surface area for fixation, which becomes clinically relevant during surgical procedures. 2
Key Structural Features:
- Cup-shaped morphology that provides a shallow socket for the humeral head 2
- Subchondral bone layer at the surface, with underlying cancellous (spongy) bone 3
- Two bony pillars that approach the glenoid: one directed inferiorly near the lateral margin and another directed superiorly into the scapular spine 2
- The "bare area" - a central region of maximum concavity on the glenoid joint surface 3
Bone Quality and Strength Distribution
The glenoid demonstrates significant variation in bone strength across its surface. 3 At the proximal subchondral level, bone strength averages 66.9 MPa, with higher peak values measured posteriorly, superiorly, and anteriorly to the bare area. 3 Bone strength decreases dramatically with depth: 25% reduction at 1mm below the subchondral plate and 70% reduction at 2mm depth. 3
The cortical shell contributes approximately 31% to total glenoid strength, while the cancellous bone shows strong anisotropy with an average ratio of 5.2. 3
Clinical Significance
In Shoulder Arthroplasty:
Adequate glenoid bone stock is essential for successful shoulder replacement. 1 Hemiarthroplasties are specifically recommended when patients have deficient glenoid bone stock, as they avoid the need for glenoid component fixation. 1
Common Pathological Conditions:
- Glenoid erosion occurs in 20.6% of hemiarthroplasties from the unresurfaced glenoid wearing against the prosthetic humeral head 1
- Glenoid loosening represents the most common complication (14.3%) in total shoulder arthroplasties 1, 4
- Glenoid bone loss can occur with shoulder instability, particularly in posterior instability cases, requiring bone grafting procedures when severe 5, 6
In Reverse Shoulder Arthroplasty:
The glenoid surface receives a metal ball component (glenosphere) attached to a baseplate, fundamentally altering the joint's center of rotation. 1, 4 This design reduces the risk of glenoid loosening compared to standard total shoulder arthroplasty. 1