Shoulder Girdle

Clavicle and Shoulder Joint Anatomy

• Clavicle: Connects the arm to the body, ensuring the proper alignment of the shoulder joint.

• Coraco-clavicular: Refers to the ligaments that connect the coracoid process of the scapula to the clavicle.

• Acromioclavicular joint (AC joint): The joint between the acromion of the scapula and the clavicle.

• Coraco-acromial ligament: Connects the coracoid process to the acromion, an important component for shoulder mechanics.

• Acromion: Bony prominence on the scapula that forms the highest point of the shoulder joint.

Overview of the Shoulder Joint

• Goals of Understanding the Shoulder Joint:
  • Identify important bones and bony features of the shoulder joint.
  • Understand the interaction between the shoulder girdle and shoulder joint during arm movements.
  • Comprehend the types of movement of the shoulder joint.
  • Identify major muscles involved in shoulder joint movements.

Functional Characteristics of the Shoulder Joint

• Range of Motion (ROM): The shoulder joint exhibits a large range of motion in various planes.
  • Implications: High ROM typically leads to increased laxity and potential instability in the shoulder.
  • General rule: Increased mobility in a joint typically correlates with decreased stability, especially in the shoulder.

Anatomical Structures and Landmarks

• Bones of the Shoulder Joint:

  • Scapula
  • Clavicle
  • Humerus

• Importance of Bony Landmarks: Understanding the specific bony structures is crucial for grasping the function of the shoulder joint.

Scapular Landmarks

• Major Features:
  • Glenoid Fossa: The socket for the shoulder joint.
  • Acromion: The bony structure that caps the shoulder.
  • Coracoid Process: A hook-like projection on the scapula.
  • Subscapular Fossa: The concave area on the anterior surface of the scapula.
  • Supraspinatus Fossa: Located above the spine of the scapula.
  • Infraspinatus Fossa: The area below the spine of the scapula.
  • Spine of Scapula: A prominent ridge on the posterior side.
  • Inferior and Superior Angles: The bottom and top angles of the scapula, respectively.
  • Medial and Lateral Borders: The inner and outer edges of the scapula.

Humeral Landmarks

• Major Features:
  • Greater Tubercle: A prominent bony structure for muscle attachment.
  • Lesser Tubercle: A smaller projection, also serving as an attachment point.
  • Head of Humerus: The ball that fits into the glenoid fossa of the scapula.
  • Neck of Humerus: The region below the head of the humerus.
  • Intertubercular Groove: The grooved area between the greater and lesser tubercles.
  • Deltoid Tuberosity: A roughened area for the deltoid muscle attachment.

Joint Characteristics

• Glenohumeral Joint: Commonly known as the shoulder joint, characterized by:
  • Type: Multiaxial ball-and-socket joint (Enarthroidal).
  • Movement: Flexibility across all planes, making it the most mobile joint in the body.
  • Stabilization Mechanism: Reinforced by ligaments and the glenoid labrum.

Glenoid Labrum

• Definition: A fibrocartilaginous ring attached to the rim of the glenoid fossa.
• Purpose: Enhances both the depth and size of the glenoid fossa.
  • Percentage Increases: Increases 75% in the superior-inferior diameter and 50% in the anterior-posterior diameter.

Glenohumeral Ligaments

• Major Ligaments:
  • Superior Glenohumeral Ligament: Provides support at the upper aspect of the joint.
  • Middle Glenohumeral Ligament: Provides stability on the anterior side.
  • Inferior Glenohumeral Ligament: Serves as the main stabilizer of the shoulder when the humerus is abducted, preventing dislocation.
  • Stability vs. ROM: While these ligaments provide stability, they are also lax enough to allow a significant range of motion.

Shoulder Joint Movements

• Flexion: Movement of the humerus straight anteriorly.
• Extension: Movement of the humerus straight posteriorly.
• Abduction: Upward, lateral movement of humerus away from the body.
• Adduction: Downward, medial movement of humerus toward the body.
• Internal Rotation: Medial movement of humerus toward the midline in a transverse plane.
• External Rotation: Lateral movement of humerus away from the midline in a transverse plane.

Shoulder Joint Muscles

Anterior Muscles

• Pectoralis Major:

  • Origin: Medial half of anterior clavicle, anterior surface of ribs 1-6, sternum.
  • Insertion: Intertubercular groove of humerus.
  • Actions: Internal rotation, adduction.

• Subscapularis:

  • Origin: Subscapular fossa.
  • Insertion: Lesser tubercle of humerus.
  • Actions: Internal rotation, adduction, extension.

• Coracobrachialis:

  • Origin: Coracoid process of scapula.
  • Insertion: Medial border of humeral shaft.
  • Action: Adduction.

Superior Muscles

• Deltoid (Three Parts):

  • Origins:
  • Anterior fibers: Anterior clavicle.
  • Middle fibers: Lateral acromion.
  • Posterior fibers: Inferior edge of scapular spine.
  • Insertion: All fibers insert into the deltoid tuberosity.
  • Actions: Abduction (all fibers), flexion (anterior).

• Supraspinatus:

  • Origin: Supraspinatus fossa.
  • Insertion: Greater tubercle of humerus.
  • Action: Abduction.

Posterior Muscles

• Latissimus Dorsi:

  • Origin: Posterior ilium, sacrum, lumbar and lower 6 thoracic vertebrae.
  • Insertion: Intertubercular groove of humerus.
  • Actions: Extension, adduction.

• Teres Major:

  • Origin: Posterior side of scapula on lateral border.
  • Insertion: Intertubercular groove.
  • Actions: Extension, adduction, internal rotation.

• Infraspinatus:

  • Origin: Medial aspect of infraspinatus fossa (below spine of scapula).
  • Insertion: Posterior side of greater tubercle (humerus).
  • Actions: External rotation, abduction, extension.

• Teres Minor:

  • Origin: Posterior on lateral border of scapula.
  • Insertion: Posteriorly on greater tubercle of humerus.
  • Action: External rotation, abduction, extension.

Understanding Shoulder Joint Concepts

• Key Questions:
  • What is another term for the shoulder joint?
  • What three bones serve as attachment sites for shoulder joint muscles?
  • Identify major bony landmarks of the humerus and scapula.
  • Describe the glenoid labrum and its purpose.
  • Identify the three shoulder joint ligaments and the one preventing dislocation.
  • Describe movements at the shoulder joint.
  • Name the anterior, superior, and posterior shoulder joint muscles along with their origin, insertion, and actions.

Rehabilitation and Injury Prevention

Exercises and Stretches

• Strengthening Exercises:

  • Pectoralis Major: Push-ups, bench press.
  • Subscapularis: Rope climbing, lat pull down.
  • Coracobrachialis: Bench press (horizontal adduction).
  • Deltoid: Shoulder press.
  • Supraspinatus: "Emptying the can" exercise.
  • Latissimus Dorsi: Lat pull down, rope climbing.
  • Infraspinatus and Teres Minor: External rotation against resistance.

• Stretching Exercises:

  • Pectoralis Major: External rotation and full shoulder extension.
  • Subscapularis: Externally rotate with the arm adducted.
  • Coracobrachialis: Extreme horizontal abduction.
  • Deltoid: Extreme horizontal adduction.
  • Supraspinatus: Adducting arm behind back while internally rotated.
  • Latissimus Dorsi: Extreme upward shoulder rotation against resistance.
  • Infraspinatus and Teres Minor: Stretch through internal rotation and horizontal adduction.

Rotator Cuff Injury

• Definition: Injury involving the rotator cuff muscles: Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis.

• Common Injuries:

  • Swimmer's Shoulder:
  • Caused by impingement, where rotator cuff muscles get pinched under the acromion due to inflammation.
  • Common among swimmers due to repetitive overhead strokes.
  • Can result from poor stroke techniques, unilateral breathing, or overuse.

• Pitchers: Susceptible to chronic rotator cuff injuries due to repetitive throwing actions.

  • Causes: Muscle imbalance and improper technique.

• Treatment Options:

  • Rehabilitation: Stretching and strengthening exercises.
  • Surgery: Considered for those not responding to physical therapy within 3-6 months, or for partial to full tears.