Glenohumeral (GH) Joint

Overview

• Commonly referred to as the shoulder joint.
• Shoulder range of motion is a combination of shoulder girdle and GH joint movements.
• GH joint consists of the humeral head forming a joint space with the scapula.
• The joint space is called the glenoid fossa.
• Allows three degrees of freedom: flexion/extension, abduction/adduction, external/internal rotation, horizontal abduction/adduction.

Stability

• Stability relies on muscles, ligaments, and joint capsule.
• Key ligaments:
  • Coracohumeral ligament: forms the roof of the GH joint.
  • Glenohumeral ligament: includes superior and middle ligaments.
• Bursae: soft, cushiony structures surrounding ligaments and aiding movement.
  • Types: Subacromial bursa, subcutaneous acromial bursa, and subcoracoid bursa.

Shoulder Injury

• Shoulder pain leads to decreased movement, causing ligaments to tighten and bursae to become stiff.
• Overuse can cause damage to ligaments and bursae, leading to pain and potential development of a frozen shoulder.

Muscles Involved in Shoulder Movements

Abduction

• Supraspinatus: Pure shoulder abductor, effective up to ~90°.
• Middle Deltoid: Large muscle contributing to abduction, can cause impingement if not controlled.
• Long Head of Biceps: Assists in abduction when the arm is externally rotated.
• Muscle Cooperation: Supraspinatus initiates abduction, followed by the biceps, and deltoid takes over as movement progresses.

Adduction

• Pectoralis Major: Pulls humeral bone toward the body.
• Teres Major: Works from the back to pull the humeral bone towards the body.
• Latissimus Dorsi: Located below Teres Major, assists in pulling the humeral bone toward the body.

Flexion

• Anterior Deltoid: Primary mover for shoulder flexion.
• Pectoralis Major: Assists in shoulder flexion.
• Coracobrachialis: Helps in raising the shoulder.
• Long Head of Biceps: Assists in shoulder flexion.

Extension

• Posterior Deltoid: Brings the humeral bone backward.
• Teres Major: Helps in shoulder extension.
• Latissimus Dorsi: Assists in shoulder extension.

External Rotation

• Infraspinatus: Rotates the humeral head outward.
• Teres Minor: Assists in outward rotation.
• Posterior Deltoid: Contributes slightly to external rotation.

Internal Rotation

• Pectoralis Major: Contributes to internal rotation.
• Teres Major: Assists in internal rotation.
• Latissimus Dorsi: Helps in internal rotation.
• Anterior Deltoid: Contributes to internal rotation.
• Subscapularis: Located on the scapula and attaches to the humeral head, aiding in internal rotation.

Conclusion

• Understanding the origin and insertion of muscles helps in memorizing their function related to shoulder movements.