Lecture Notes: The Shoulder Joint (Glenohumeral Joint)

Overview

• Type of Joint: Ball and socket joint.
• Components:
  • Head of the humerus.
  • Glenoid cavity of the scapula.
• Characteristics:
  • Freely moving joint.
  • Sacrifices stability for movement.
  • Requires reinforcement for stability.

Ligaments Reinforcing the Joint

• Primary Ligament: Coracohumeral ligament.
  • Connects the coracoid process of scapula to the humerus.
  • Supports the weight of upper limbs.
• Other Ligaments: Glenohumeral ligaments (3).
  • Weak and part of the articular capsule.
• Glenoid Labrum:
  • Fibrocartilage that deepens the glenoid cavity.
  • Covers only 13% of the humeral head.
  • Provides limited stability, similar to a golf ball on a tee.

Tendons and Muscles

• Key Tendon: Tendon of the long head of the biceps.
  • Travels through intertubercular sulcus of the humerus.
  • Secures humerus into the glenoid cavity.
• Rotator Cuff Muscles:
  • Subscapularis: Largest and strongest.
    • Originates in the subscapular fossa of the scapula.
    • Interacts with the greater tubercle of the humerus.
  • Supraspinatus:
    • Originates in the supraspinous fossa.
    • Interacts with the tubercle of the humerus.
  • Infraspinatus and Teres Minor.
• Function: Provide range of motion and stability.
  • Rotator cuff injuries common in sports like baseball due to circumduction strain.

Structural Weaknesses

• Anterior Weakness:
  • Relies mainly on coracohumeral ligament.
• Inferior Weakness:
  • Fewer muscles on the inferior side.
  • Results in frequent dislocations when humerus moves forward and downward.

Conclusion

• The shoulder joint allows significant movement but requires reinforcement due to its inherent instability.
• Understanding the role of ligaments, tendons, and muscles is crucial to addressing common injuries and maintaining shoulder health.