Glenohumeral Joint

The glenohumeral joint is the primary joint of the shoulder, formed by the articulation between the head of the humerus and the glenoid cavity of the scapula. It is a synovial ball-and-socket joint and is the most mobile joint in the human body, allowing a wide range of motion in multiple planes. However, this mobility comes at the cost of reduced stability, making it prone to dislocations.

Structure

The joint comprises two main articulating surfaces:

• Humeral head: Hemispherical structure forming the ball of the joint.
• Glenoid cavity: Shallow, pear-shaped depression on the lateral angle of the scapula. It is deepened by a fibrocartilaginous rim called the glenoid labrum.

Joint Capsule

• Loose fibrous capsule that allows for a wide range of motion.
• Attaches medially to the scapular neck and laterally to the anatomical neck of the humerus.
• Inferior part is weakest and most distensible—site of potential dislocation.

Ligaments

• Glenohumeral ligaments (superior, middle, inferior): Thickenings of the anterior capsule; stabilize the joint during specific movements.
• Coracohumeral ligament: From the coracoid process to the greater tubercle; supports the superior aspect of the joint.
• Transverse humeral ligament: Bridges over the intertubercular groove, holding the tendon of the long head of the biceps brachii in place.

Labrum and Bursae

• Glenoid labrum: Fibrocartilaginous ring that deepens the glenoid cavity and increases joint stability.
• Subacromial bursa: Lies between the acromion and the supraspinatus tendon; reduces friction during abduction.
• Subscapular bursa: Communicates with the joint cavity; located between the subscapularis tendon and the joint capsule.

Location

The glenohumeral joint is located between the lateral angle of the scapula (glenoid cavity) and the proximal end of the humerus. It lies deep to the deltoid muscle and anterior to the scapular spine.

Function

• Mobility: Allows flexion, extension, abduction, adduction, medial and lateral rotation, and circumduction of the upper limb.
• Range of motion: The most mobile synovial joint in the body, essential for upper limb function and overhead activities.
• Force transmission: Transmits mechanical forces from the upper limb to the trunk during activities like lifting or throwing.

Development

The humeral head and glenoid cavity begin ossifying during fetal development. The glenoid labrum forms postnatally as part of the fibrous capsule. Growth plates of the proximal humerus fuse between ages 17 and 20, while scapular ossification centers mature throughout adolescence.

Clinical Significance

• Shoulder dislocation: Most commonly occurs in the anterior direction due to the shallow glenoid and lax inferior capsule.
• Rotator cuff injuries: Damage to the supraspinatus, infraspinatus, teres minor, or subscapularis can compromise joint stability and movement.
• SLAP lesion: Tear of the superior labrum from anterior to posterior, often seen in overhead athletes.
• Frozen shoulder (adhesive capsulitis): Characterized by thickening of the capsule and restricted movement.
• Osteoarthritis: Degenerative changes may affect the glenohumeral joint, leading to pain and stiffness in older adults.