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 bone represents the articular surface on the scapula where the shoulder joint is formed. 1 Key structural features include:
- Small size with limited surface area for prosthetic fixation, which becomes particularly challenging in revision surgery with large bony defects 2
- Cup-shaped morphology that provides the socket for the ball-and-socket shoulder joint 2
- Two substantial bony pillars that approach the glenoid: one directed inferiorly near the lateral margin and another directed superiorly into the scapular spine, both outlined by three cortices and oriented to the circle formed by the rim of the inferior glenoid quadrants 2
Bone Quality and Strength Distribution
The glenoid demonstrates specific biomechanical properties critical for surgical planning:
- Subchondral bone strength averages 66.9 MPa at the proximal level, with higher peak values measured posteriorly, superiorly, and anteriorly to the "bare area" (the area of maximum concavity) 3
- Rapid strength decline with depth: strength decreases by 25% at 1mm below the subchondral plate and by 70% at 2mm depth 3
- Cortical shell contribution: the cortical bone contributes approximately 31% to total glenoid strength 3
- Strong anisotropy: the cancellous bone shows an average anisotropy ratio of 5.2, with elastic modulus varying from approximately 100 MPa at the bare area to 400 MPa at the superior glenoid 3
Dimensional Characteristics
CT scan measurements provide standardized dimensions:
Clinical Significance in Shoulder Arthroplasty
The glenoid bone stock is a critical determinant in surgical decision-making:
- Deficient glenoid bone stock is an indication for hemiarthroplasty rather than total shoulder arthroplasty, as it requires shorter operative time and avoids the technical challenges of glenoid component fixation 1
- Glenoid loosening represents the most common complication of total shoulder arthroplasty at 14.3%, making bone quality assessment essential 1
- Glenoid component placement requires attachment to the glenoid surface, with reverse arthroplasty using a glenosphere (round metal ball) attached to a baseplate along this surface 1
Common Pitfall
The most critical error is underestimating glenoid bone loss or quality preoperatively. Erosion of the unresurfaced glenoid occurs in 20.6% of hemiarthroplasties, emphasizing the importance of thorough preoperative bone stock assessment. 1 CT imaging should be used to evaluate glenoid dimensions and bone quality when planning shoulder arthroplasty. 4