Shoulder from book

Overview of Shoulder Anatomy

• Myopic Viewpoint: Common misconception of shoulder anatomy as simply the ball and socket of the humerus and scapula.

• Complexity of the Shoulder: Assessment must begin at the thoracic spine.

Thoracic Spine and Its Role

• Structure: Consists of 12 vertebrae, each with an articulating rib.

• Movement Variability: Influences shoulder mechanics.

• Convexity: Apexes at the sixth thoracic vertebrae.

Scapula

• Definition: Irregularly shaped bone resting on ribs, housing head of the humerus.

• Joint Formation: Functions as the socket for the glenohumeral joint.

• Mobility and Stability: Essential for shoulder function, making it a temperamental bone.

Scapulohumeral Rhythm

• Key Concept: Relationship between scapulothoracic and glenohumeral joints.

• Movement Contribution: 2/3 from humeral head movement, 1/3 from scapular movement on rib cage.

• Range of Motion Implications: Lack of scapular mobility can restrict shoulder motion.

Scapular Mechanics

Lower Resolution Model

• Muscle Actions: Focus on strength to enhance scapular movement.

• Key Movements:

  • Elevation: Shoulder blade moves up (Upper trapezius, levator scapula).

  • Depression: Shoulder blade moves down (Lower trapezius).

  • Protraction: Shoulder blades pushed away from spine (Serratus anterior).

  • Retraction: Shoulder blades pulled towards spine (Middle trapezius, rhomboids).

Higher Resolution Model

• Instantaneous Axis of Rotation: Defines scapular movements, blending four binary movements into upward and downward rotation.

• Breathing Influence: Breathing mechanics expand and express the rib cage, critical for shoulder function.

Coracoid Process

• Definition: Anterior prominence on scapula, attachment site for several muscles.

• Importance: Contributes to coracoacromial arch for shoulder stability.

Acromioclavicular Joint (AC Joint)

• Definition: Joint between acromion process of scapula and clavicle.

• Stability: Provides structural integrity via the trapezoid and conoid ligaments.

• Injury: AC joint separations are graded by severity, identifiable by a gap above the clavicle.

Clavicle

• Role: Links anterior shoulder girdle; articulates with acromion and sternum.

• Movement: Minor rotations that are crucial for shoulder function.

Shoulder Joints Overview

• Four Major Joints:

  • Glenohumeral Joint: Greatest freedom of range, relies on functional stability.

  • Acromioclavicular and Sternoclavicular Joints: Stability for the shoulder structure.

  • Scapulothoracic Joint: Largest by surface area, complex due to muscle and breathing dynamics.

Scaption

• Definition: Angle of humerus relating to scapula movement and rib cage shape.

• Variation: Neutral shoulder position differs among individuals due to rib cage shape.

Rotator Cuff Overview

• Components: Comprised of supraspinatus, infraspinatus, teres minor, subscapularis.

• Roles: Stabilization of glenohumeral joint, often overlooked except when injured.

Individual Muscles of the Rotator Cuff

• Supraspinatus: Initiates shoulder abduction.

• Infraspinatus: External rotator, crucial during shoulder stabilization.

• Teres Minor: Assists with external rotation during arm elevation.

• Subscapularis: Internal rotation powerhouse, critical at various abduction degrees.

Rethinking Rotator Cuff Function

• Action vs Function: Strength in isolation vs functional stability in integration.

• Training Focus: Emphasizes shoulder flexion/extension rather than isolated actions.

Serratus Anterior

• Functionality: Protraction of the shoulder blade, essential for scapular stability.

• Importance of Balance: Need for both retraction and protraction cues in training:

  • Overemphasis on retraction can hinder scapular stability.

Winged Scapula

• Definition: Inferior angle protrudes from rib cage due to muscle instability.

• Interventions: Focus on serratus anterior training coupled with proper breathing mechanics.