Anatomy of the Shoulder Joint

Overview

• The shoulder joint is a complex joint involving multiple bones, ligaments, muscles, and movements.
• It includes a ball-and-socket joint, specifically called the glenohumeral joint, which provides a wide range of motion.

Bones Involved

1. Sternum
2. Clavicle (collarbone)
3. Scapula (shoulder blade)
   • Coracoid Process: Anterior projection.
   • Acromion: Extends laterally over the shoulder joint.
   • Glenoid Fossa/Cavity: Concave part that articulates with the humerus.
4. Humerus
   • Forms the ball component of the ball-and-socket joint.

Ligaments

• Acromioclavicular Ligament: Connects acromion to clavicle.
• Sternoclavicular Ligament: Connects sternum to clavicle.
• Coracoacromial Ligament: Connects coracoid to acromion.
• Coracoclavicular Ligament: Connects coracoid to clavicle.
• Coracohumeral Ligament: Connects coracoid to humerus.
• Glenohumeral Ligaments (Superior, Middle, Inferior): Connect humerus to glenoid cavity.
• Joint Capsule: Surrounds joint, holds synovial fluid and provides some stability.

Joint Characteristics

• Type: Synovial joint with a joint capsule and synovial fluid for lubrication.
• Cartilage: Articular cartilage is present on both the head of the humerus and the glenoid cavity to reduce friction.

Rotator Cuff Muscles

1. Infraspinatus: Located below the spine of the scapula; rotates the shoulder back.
2. Teres Minor: Works with infraspinatus to laterally rotate the humerus.
3. Supraspinatus: Located above the spine of the scapula; abducts the arm, works with deltoid.
4. Subscapularis: Located on the anterior side; rotates shoulder anteriorly.

Functions of Rotator Cuff Muscles

• Stabilization: Provides structural support.
• Concavity Compression: Helps in efficient lifting and movement of the shoulder.
• Movement: Facilitates abduction and rotation of the arm.

Additional Muscles

• Biceps Brachii: Originates from the scapula and aids in flexing the arm; involves two heads.
  • One head connects to coracoid process.
  • The other head threads through the subscapularis tendon.

Common Injuries

• Torn Rotator Cuff: Often affects the supraspinatus muscle; can lead to pain and reduced mobility.

Recap of Key Structures

• Bones: Clavicle, Scapula (acromion, coracoid, glenoid fossa), and Humerus.
• Ligaments: Acromioclavicular, Sternoclavicular, Coracoacromial, etc.
• Muscles: Rotator cuff muscles and biceps brachii.
• Functions: Stability, efficient movement, and support.