Glenohumeral Joint

Structure and Actions

Overview

• The glenohumeral joint is a synovial joint.
• Formed by the articulation of two bones wrapped in a synovial membrane and bathed in synovial fluid.
• Type: Ball and socket joint, allowing movement in multiple directions.
• Most flexible synovial joint with the greatest range of motion in the body.

Components

• Ball: Head of the humerus.
• Socket: Glenoid cavity.
• Only one-third of the humeral head articulates with the glenoid cavity at a time.
  • Implications: Flexibility (high), Stability (low).
  • Analogy: Golf ball on a tee (glenoid cavity as tee, humeral head as golf ball).

Support Structures

Glenoid Labrum

• Acts like a bowl, stabilizing the joint like a golf ball in a bowl.
• Made of fibrocartilaginous ring.
• Increases the depth of the glenoid cavity by about 50%.
• Provides a suction effect to adhere the humeral head to the socket.
• Important attachment site for the biceps tendon.

Joint Capsule

• Surrounds the glenohumeral joint.
• Functions:
  • Contains articular cartilage to prevent bone-on-bone contact.
  • Periosteum continues to form the joint capsule.
  • Produces synovial fluid to lubricate the joint.
  • Intracapsular negative pressure helps maintain articulation.
  • Axillary fold allows flexibility but increases dislocation risk, especially inferiorly.

Ligaments

• Coracohumeral Ligament: Connects coracoid process to humerus; stabilizes the humeral head.
• Coracoacromial Ligament: Connects coracoid process to acromion; prevents upward dislocation.
• Coracoclavicular Ligament: Connects coracoid process to clavicle; anchors the clavicle and facilitates articulation with the scapula.
  • This articulation is crucial for linking the upper limb to the axial skeleton.

Actions

Movement Types

• Flexion: Arm moves forward.
• Extension: Arm moves backward.
• Abduction: Arm moves away from midline.
• Adduction: Arm moves toward midline.
• Medial (Internal) Rotation: Humerus rotates medially.
• Lateral (External) Rotation: Humerus rotates laterally.

Views

• Lateral View: Demonstrates flexion, extension, abduction, adduction, medial and lateral rotation.
• Anterior View: Illustrates medial rotation and lateral rotation.