Shoulder Anatomy: Ligaments Connecting the Humerus and Scapula

What are the ligaments between the humerus and scapula?

The primary ligaments connecting the humerus and scapula are the three Glenohumeral Ligaments (Superior, Middle, Inferior) and the Coracohumeral Ligament, all of which play a crucial role in providing static stability to the highly mobile glenohumeral (shoulder) joint.

Understanding the Glenohumeral Joint

The shoulder joint, anatomically known as the glenohumeral joint, is a classic ball-and-socket synovial joint. It is formed by the articulation of the spherical head of the humerus (upper arm bone) and the shallow, pear-shaped glenoid fossa of the scapula (shoulder blade). This anatomical configuration allows for an extraordinary range of motion, making the shoulder the most mobile joint in the human body.

However, this extensive mobility comes at the expense of inherent stability. Unlike the hip joint, where the femoral head fits deeply into the acetabulum, the glenoid fossa provides only a limited bony constraint for the humeral head. Consequently, the shoulder joint relies heavily on a combination of static and dynamic stabilizers to maintain its integrity and prevent dislocation. Ligaments are the primary static stabilizers, providing passive restraint to excessive movement.

Primary Ligaments Connecting Humerus and Scapula

The key ligaments directly linking the humerus and scapula are integral thickenings of the fibrous joint capsule, strategically positioned to limit specific movements and maintain the congruence of the articular surfaces.

• Glenohumeral Ligaments (GHLs) These three distinct bands are thickenings of the anterior (front) aspect of the joint capsule and are crucial for anterior and inferior stability.

  • Superior Glenohumeral Ligament (SGHL):
    • Origin: Superior aspect of the glenoid rim and the base of the coracoid process (scapula).
    • Insertion: Anatomical neck of the humerus, superior to the lesser tubercle.
    • Function: Primarily resists inferior translation of the humeral head, especially when the arm is adducted. It also helps limit external rotation and adduction.
  • Middle Glenohumeral Ligament (MGHL):
    • Origin: Anterior aspect of the glenoid rim (scapula), just inferior to the SGHL.
    • Insertion: Anterior aspect of the anatomical neck of the humerus, medial to the lesser tubercle.
    • Function: Resists anterior translation of the humeral head, particularly when the arm is abducted to approximately 45-60 degrees and externally rotated.
  • Inferior Glenohumeral Ligament Complex (IGHLC):
    • This is the most significant and robust of the glenohumeral ligaments, providing critical stability, especially when the arm is abducted above 90 degrees. It is often described as having three distinct parts:
      • Anterior Band: Strongest component, resisting anterior translation of the humeral head when the arm is abducted and externally rotated.
      • Posterior Band: Resists posterior translation of the humeral head when the arm is abducted and internally rotated.
      • Axillary Pouch: The hammock-like inferior portion that supports the humeral head when the arm is abducted.
    • Origin: Anterior and inferior glenoid rim (scapula).
    • Insertion: Anatomical neck of the humerus.
    • Function: Together, the IGHLC limits anterior, posterior, and inferior translation of the humeral head, especially at higher degrees of abduction. It is the primary restraint against anterior-inferior dislocation.

• Coracohumeral Ligament (CHL) This broad, strong band lies superior to the joint capsule and is distinct from the glenohumeral ligaments.

  • Origin: Base and lateral border of the coracoid process (scapula).
  • Insertion: Divides into two bands, inserting onto the greater and lesser tubercles of the humerus.
  • Function: Provides superior support to the joint, resisting inferior translation of the humeral head, especially with the arm adducted. It also limits external rotation. The CHL forms the roof of the rotator interval, an important area of the shoulder.

Other Related Ligaments (Indirect but Important for Shoulder Stability)

While not directly connecting the humerus and scapula to each other, the following ligament is crucial for the overall stability and function of the shoulder complex and is often discussed in this context due to its proximity and role in humeral mechanics.

• Transverse Humeral Ligament: This ligament spans across the intertubercular (bicipital) groove on the proximal humerus, connecting the greater and lesser tubercles. Its primary function is to retain the long head of the biceps brachii tendon within this groove, preventing its displacement during arm movements. While it doesn't directly connect the scapula and humerus, its integrity is vital for the dynamic stability provided by the biceps tendon within the shoulder joint.

Functional Significance of These Ligaments

These ligaments work in a coordinated fashion to provide static stability to the glenohumeral joint. They act as passive restraints, becoming taut at the end ranges of motion to prevent excessive translation or rotation of the humeral head relative to the glenoid fossa. Their specific orientations allow them to limit different movements:

• Anterior Stability: Primarily provided by the MGHL and the anterior band of the IGHLC, especially during abduction and external rotation.
• Inferior Stability: Largely maintained by the SGHL and the coracohumeral ligament, particularly when the arm is adducted. The axillary pouch of the IGHLC also contributes significantly during abduction.
• Posterior Stability: The posterior band of the IGHLC is the main ligamentous restraint against posterior displacement.

It is crucial to remember that while ligaments provide essential static stability, the dynamic stability of the shoulder joint is primarily provided by the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) and the long head of the biceps. The interplay between these static and dynamic stabilizers is fundamental to healthy shoulder function.

Clinical Relevance and Injuries

Given their critical role in joint stability, these ligaments are frequently involved in shoulder injuries.

• Dislocations and Subluxations: The glenohumeral ligaments, especially the IGHLC, are commonly injured during shoulder dislocations (when the humeral head completely separates from the glenoid) or subluxations (partial separation). Anterior-inferior dislocations are the most common, often tearing or stretching the anterior band of the IGHLC and potentially detaching it from the glenoid rim (Bankart lesion).
• Ligamentous Laxity: Chronic stretching or inherent looseness of these ligaments can lead to shoulder instability, making an individual more prone to recurrent dislocations or subluxations.
• Adhesive Capsulitis (Frozen Shoulder): While primarily characterized by inflammation and fibrosis of the joint capsule, this condition involves a thickening and contracture of the capsule and its associated ligaments, significantly restricting shoulder range of motion.

Conclusion

The ligaments connecting the humerus and scapula—namely the Superior, Middle, and Inferior Glenohumeral Ligaments and the Coracohumeral Ligament—are indispensable components of shoulder anatomy. They serve as the primary static stabilizers of the glenohumeral joint, working in concert to limit excessive movement and maintain the delicate balance between the shoulder's remarkable mobility and its essential stability. Understanding their individual functions and collective contribution is fundamental for anyone involved in exercise science, rehabilitation, or the comprehensive care of the musculoskeletal system.