Glenoid Cavity

The glenoid cavity, also known as the glenoid fossa, is a shallow, pear-shaped articular depression located on the lateral angle of the scapula. It serves as the socket for the head of the humerus, forming the glenohumeral joint, which is the main articulation of the shoulder. Despite being relatively shallow compared to other joint sockets, the glenoid cavity allows a remarkable range of motion and is stabilized by a combination of soft tissue structures.

Location

The glenoid cavity is situated on the lateral aspect of the scapula, just inferior to the acromion process and lateral to the coracoid process. It faces laterally, slightly anteriorly and superiorly, allowing articulation with the humeral head. The cavity is part of the scapula's lateral angle, between the superior and lateral borders.

Structure

• Shallow, oval or pear-shaped concavity measuring approximately 2.5–4.5 cm in vertical height and 2–3.5 cm in width.
• The superior portion is narrower than the inferior portion, giving it a teardrop appearance.
• The surface is lined with articular cartilage and surrounded by the glenoid labrum, a fibrocartilaginous ring that deepens the socket and improves stability.
• It is bordered superiorly by the supraglenoid tubercle and inferiorly by the infraglenoid tubercle, both serving as muscle attachment sites.

Function

• Articulation: Serves as the socket of the glenohumeral joint, allowing multi-axial movement of the upper limb.
• Stabilization: Works in concert with the glenoid labrum, rotator cuff muscles, and joint capsule to maintain the humeral head in position.
• Load distribution: Transmits and distributes forces from the upper limb into the axial skeleton through the scapula and clavicle.

Physiological Role(s)

• Enables a wide range of upper limb mobility, including flexion, extension, abduction, adduction, and rotation.
• Supports shoulder stability dynamically through muscular and ligamentous reinforcement.
• Acts as a shallow but adaptable socket to optimize the trade-off between mobility and joint congruity.

Relations

• Anterior: Subscapularis muscle and joint capsule.
• Posterior: Infraspinatus and teres minor muscles.
• Superior: Supraglenoid tubercle and long head of the biceps tendon.
• Inferior: Infraglenoid tubercle and origin of the long head of the triceps brachii.

Glenoid Labrum

• A fibrocartilaginous ring attached to the rim of the glenoid cavity.
• Increases the effective depth and surface area of the glenoid socket by approximately 50 percent.
• Serves as the attachment site for the long head of the biceps tendon superiorly and joint capsule along the circumference.
• Provides passive stabilization of the shoulder and resists translational forces of the humeral head.

Development

The glenoid cavity develops from the scapular ossification centers, which begin forming during the 8th week of gestation. It ossifies from membranous and cartilaginous precursors, with the articular surface developing in coordination with the proximal humerus. The glenoid labrum arises from mesenchymal tissue and matures into fibrocartilage after birth. Growth and shaping of the cavity are influenced by movement of the upper limb during development.

Clinical Significance

• Glenoid labrum tears: Damage to the labrum (such as SLAP lesions) can cause pain, instability, and clicking in the shoulder.
• Shoulder dislocation: The shallowness of the glenoid cavity makes the glenohumeral joint vulnerable to anterior dislocation, especially in athletes.
• Glenoid fractures: Result from direct trauma and may compromise shoulder stability, often requiring surgical fixation.
• Glenoid dysplasia: A congenital or developmental abnormality in which the glenoid cavity is underdeveloped, predisposing to chronic instability.

Imaging

• X-ray: Useful for identifying fractures, joint alignment, and gross structural abnormalities.
• CT scan: Provides detailed views of the bony contour and is helpful in assessing glenoid version and bone loss.
• MRI: Preferred for visualizing the glenoid labrum, soft tissue attachments, and evaluating internal derangement or labral tears.
• MR arthrogram: Highly sensitive for detecting labral injuries and capsular abnormalities by enhancing joint structures with contrast.

Anatomical Variations

• Glenoid version may vary between individuals and can be slightly anteverted or retroverted.
• The shape of the glenoid rim can be oval, pear-shaped, or comma-shaped, particularly in cases of bone loss.
• Congenital glenoid hypoplasia may lead to flattening of the socket and recurrent shoulder instability.