The Pectoral Girdle Consists Of The

The pectoral girdle, also known as the shoulder girdle, serves as the crucial bony structure that connects the upper limb to the axial skeleton, enabling a wide range of movements essential for daily activities. Understanding the components, functions, and clinical significance of the pectoral girdle is fundamental for anyone studying anatomy, physiology, or related healthcare fields.

Anatomy of the Pectoral Girdle

The pectoral girdle is composed of two bones: the clavicle (collarbone) and the scapula (shoulder blade). These bones articulate with each other and with the sternum and humerus, forming a complex that supports and facilitates upper limb movement.

1. Clavicle

The clavicle is a long, slender, S-shaped bone that lies horizontally across the anterior aspect of the thorax, just superior to the first rib. It is the only bony connection between the upper limb and the axial skeleton.

• Structure: The clavicle has two ends:

  • Sternal end: This is the medial end, which articulates with the manubrium of the sternum at the sternoclavicular joint.
  • Acromial end: This is the lateral end, which articulates with the acromion process of the scapula at the acromioclavicular joint.

• Features: The clavicle has several important features:

  • Superior surface: Relatively smooth.
  • Inferior surface: Marked by grooves and ridges for muscle and ligament attachments, including the conoid tubercle for the conoid ligament.

• Function: The clavicle performs several critical functions:

  • Bracing the shoulder: It acts as a brace, holding the shoulder joint away from the thorax to allow for free movement of the upper limb.
  • Transmitting forces: It transmits forces from the upper limb to the axial skeleton.
  • Protecting underlying structures: It protects the underlying neurovascular structures, such as the subclavian artery and vein, and the brachial plexus.

2. Scapula

The scapula is a flat, triangular bone located on the posterior aspect of the thorax, overlying the second to seventh ribs. It is highly mobile, allowing for a wide range of shoulder movements.

• Structure: The scapula has several borders, angles, and processes:

  • Borders:
    • Superior border: The shortest and thinnest border.
    • Medial border (vertebral border): Runs parallel to the vertebral column.
    • Lateral border (axillary border): Extends towards the axilla.
  • Angles:
    • Superior angle: Located at the junction of the superior and medial borders.
    • Inferior angle: Located at the junction of the medial and lateral borders.
    • Lateral angle: Contains the glenoid cavity.
  • Processes:
    • Spine of the scapula: A prominent ridge that runs across the posterior surface of the scapula.
    • Acromion: A flattened, expanded process at the lateral end of the spine, which articulates with the clavicle.
    • Coracoid process: A hook-like process projecting anteriorly from the superior border of the scapula.

• Features: The scapula also includes several important features:

  • Glenoid cavity (glenoid fossa): A shallow, pear-shaped depression on the lateral angle that articulates with the head of the humerus to form the glenohumeral (shoulder) joint.
  • Supraspinous fossa: Located superior to the spine of the scapula.
  • Infraspinous fossa: Located inferior to the spine of the scapula.
  • Subscapular fossa: A large, concave depression on the anterior surface of the scapula.

• Function: The scapula's primary functions include:

  • Muscle attachment: It provides a large surface area for the attachment of numerous muscles that control shoulder and arm movements.
  • Articulation: It articulates with the humerus at the glenohumeral joint, contributing to shoulder joint stability and mobility.
  • Scapulothoracic movement: It glides along the posterior ribcage, allowing for protraction, retraction, elevation, depression, and rotation of the shoulder.

Joints of the Pectoral Girdle

Several joints are associated with the pectoral girdle, each contributing to the overall movement and stability of the shoulder complex.

1. Sternoclavicular (SC) Joint

The sternoclavicular joint is where the sternal end of the clavicle articulates with the manubrium of the sternum and the first costal cartilage. It is the only direct bony connection between the pectoral girdle and the axial skeleton.

• Type of Joint: Synovial, saddle-shaped joint.
• Ligaments: The SC joint is supported by several ligaments, including:
  • Anterior and posterior sternoclavicular ligaments: Reinforce the joint capsule anteriorly and posteriorly.
  • Interclavicular ligament: Connects the sternal ends of the clavicles and the manubrium.
  • Costoclavicular ligament: Connects the clavicle to the first rib and cartilage.
• Movements: The SC joint allows for elevation, depression, protraction, retraction, and rotation of the clavicle, which in turn affects the movement of the scapula and upper limb.

2. Acromioclavicular (AC) Joint

The acromioclavicular joint is where the acromial end of the clavicle articulates with the acromion process of the scapula.

• Type of Joint: Synovial, plane joint.
• Ligaments: The AC joint is supported by:
  • Acromioclavicular ligaments: Superior and inferior ligaments that reinforce the joint capsule.
  • Coracoclavicular ligaments: Consisting of the conoid and trapezoid ligaments, which provide significant stability by connecting the clavicle to the coracoid process of the scapula.
• Movements: The AC joint allows for gliding and rotational movements between the clavicle and scapula, which are essential for full range of motion at the shoulder.

3. Glenohumeral (GH) Joint

The glenohumeral joint, commonly known as the shoulder joint, is where the head of the humerus articulates with the glenoid cavity of the scapula.

• Type of Joint: Synovial, ball-and-socket joint.
• Ligaments: The GH joint is supported by:
  • Glenohumeral ligaments: Superior, middle, and inferior ligaments that reinforce the anterior aspect of the joint capsule.
  • Coracohumeral ligament: Connects the coracoid process of the scapula to the greater tubercle of the humerus.
  • Transverse humeral ligament: Holds the tendon of the long head of the biceps brachii muscle in the intertubercular groove of the humerus.
• Movements: The GH joint is the most mobile joint in the human body, allowing for flexion, extension, abduction, adduction, internal rotation, external rotation, and circumduction.

4. Scapulothoracic Joint

The scapulothoracic joint is not a true anatomical joint because there are no direct bony connections. Instead, it is a physiological joint formed by the articulation of the anterior surface of the scapula with the posterior ribcage.

• Movements: The scapulothoracic joint allows for protraction, retraction, elevation, depression, upward rotation, and downward rotation of the scapula. These movements are critical for coordinating upper limb movements and maximizing reach and range of motion.

Muscles of the Pectoral Girdle

Numerous muscles attach to the pectoral girdle, controlling its position and movement. These muscles can be broadly categorized based on their primary actions.

1. Muscles that Move the Scapula

• Trapezius: A large, superficial muscle that extends from the occipital bone to the thoracic vertebrae and attaches to the scapula and clavicle. Its actions include elevation, depression, retraction, and rotation of the scapula.
• Rhomboids (Rhomboid Major and Rhomboid Minor): Located deep to the trapezius, these muscles originate from the thoracic vertebrae and insert on the medial border of the scapula. They retract and rotate the scapula.
• Levator Scapulae: Originates from the cervical vertebrae and inserts on the superior angle of the scapula. It elevates the scapula.
• Serratus Anterior: Originates from the ribs and inserts on the medial border of the scapula. It protracts and rotates the scapula upward, allowing for overhead movements.
• Pectoralis Minor: Located deep to the pectoralis major, it originates from the ribs and inserts on the coracoid process of the scapula. It protracts, depresses, and rotates the scapula downward.

2. Muscles that Move the Humerus (and indirectly affect the Pectoral Girdle)

• Deltoid: A large, triangular muscle that covers the shoulder joint and attaches to the clavicle, acromion, and spine of the scapula. It performs abduction, flexion, extension, and rotation of the humerus.
• Pectoralis Major: A large, fan-shaped muscle that originates from the clavicle, sternum, and ribs and inserts on the humerus. It performs adduction, internal rotation, and flexion of the humerus.
• Latissimus Dorsi: A broad, flat muscle that originates from the thoracic and lumbar vertebrae, ribs, and iliac crest and inserts on the humerus. It performs adduction, extension, and internal rotation of the humerus.
• Teres Major: Originates from the inferior angle of the scapula and inserts on the humerus. It performs adduction, extension, and internal rotation of the humerus.
• Rotator Cuff Muscles (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis): These muscles originate from the scapula and insert on the humerus. They provide stability to the glenohumeral joint and perform various rotational movements.

Clinical Significance

The pectoral girdle is susceptible to various injuries and conditions due to its complex anatomy and the wide range of movements it facilitates.

1. Fractures

• Clavicle Fractures: These are among the most common fractures, often resulting from falls onto an outstretched arm or direct blows to the shoulder. Symptoms include pain, swelling, and deformity at the fracture site. Treatment typically involves immobilization with a sling or figure-of-eight bandage.
• Scapula Fractures: These are less common due to the scapula's protected location and strong muscular attachments. They usually result from high-energy trauma, such as motor vehicle accidents. Treatment depends on the location and severity of the fracture and may involve immobilization or surgery.

2. Dislocations

• Sternoclavicular Joint Dislocation: This occurs when the sternal end of the clavicle is displaced from the manubrium. It can result from direct trauma to the shoulder or indirect forces transmitted through the upper limb. Treatment depends on the severity and direction of the dislocation.
• Acromioclavicular Joint Dislocation (Shoulder Separation): This occurs when the acromion of the scapula separates from the clavicle, usually due to a fall onto the shoulder. The severity of the dislocation is graded based on the degree of ligament damage. Treatment ranges from conservative management with a sling to surgical repair.
• Glenohumeral Joint Dislocation (Shoulder Dislocation): This is the most common type of joint dislocation, typically occurring anteriorly due to excessive external rotation and abduction. Symptoms include severe pain, deformity, and limited range of motion. Treatment involves reduction of the dislocation and immobilization.

3. Rotator Cuff Injuries

The rotator cuff muscles are prone to injury due to overuse, trauma, or age-related degeneration. Common rotator cuff injuries include tendinitis, tears, and impingement syndromes. Symptoms include pain, weakness, and limited range of motion. Treatment ranges from conservative measures, such as rest, ice, and physical therapy, to surgical repair.

4. Thoracic Outlet Syndrome (TOS)

Thoracic outlet syndrome is a condition characterized by compression of the neurovascular structures (brachial plexus and subclavian artery/vein) in the thoracic outlet, the space between the clavicle and the first rib. TOS can result from anatomical abnormalities, trauma, or repetitive movements. Symptoms include pain, numbness, tingling, and weakness in the upper limb. Treatment may involve physical therapy, medication, or surgery.

5. Scapular Dyskinesis

Scapular dyskinesis refers to abnormal movement or positioning of the scapula during shoulder movements. It can result from muscle imbalances, nerve injuries, or structural abnormalities. Symptoms include pain, weakness, and limited range of motion. Treatment focuses on addressing the underlying cause and restoring normal scapular mechanics through physical therapy.

Exercises for Pectoral Girdle Health

Maintaining the health and function of the pectoral girdle involves regular exercise and proper posture. Here are some exercises that can help strengthen the muscles of the shoulder and improve scapular stability:

• Scapular Squeezes: Sit or stand with good posture and squeeze the shoulder blades together, holding for a few seconds. This exercise strengthens the rhomboids and trapezius muscles.
• Rows: Use resistance bands or weights to perform rows, pulling the elbows back while squeezing the shoulder blades together. This exercise strengthens the back muscles and improves scapular retraction.
• Push-Ups: Perform push-ups to strengthen the chest, shoulder, and arm muscles. Focus on maintaining proper form and engaging the core muscles.
• Lateral Raises: Use light weights to perform lateral raises, lifting the arms out to the side. This exercise strengthens the deltoid muscles.
• External Rotations: Use resistance bands or weights to perform external rotations, rotating the arms outward. This exercise strengthens the rotator cuff muscles and improves shoulder stability.
• Wall Slides: Stand with your back against a wall and slide your arms up the wall, maintaining contact with the wall. This exercise improves scapular upward rotation and shoulder mobility.

Conclusion

The pectoral girdle is a complex and vital structure that connects the upper limb to the axial skeleton, enabling a wide range of movements. Understanding the anatomy, joints, muscles, and clinical significance of the pectoral girdle is essential for healthcare professionals and anyone interested in human anatomy and physiology. By maintaining good posture, engaging in regular exercise, and seeking prompt treatment for injuries, individuals can preserve the health and function of their pectoral girdle, ensuring optimal upper limb performance.