The pectoral girdle, consisting of the clavicle and scapula, forms the foundation for upper limb movement. These bones work together to provide stability and a wide range of motion for the shoulder joint, allowing for complex arm movements essential in daily activities.

Understanding the structure and function of the pectoral girdle is crucial for grasping how our upper limbs move and interact with the rest of the body. From supporting arm movements to serving as attachment points for muscles, the clavicle and scapula play vital roles in our everyday lives.

Bones and Features of the Pectoral Girdle

Bones of pectoral girdle (also known as shoulder girdle)

• Clavicle
  • S-shaped bone connects upper limb to axial skeleton
  • Sternal end articulates with manubrium of sternum at sternoclavicular joint
  • Acromial end articulates with acromion process of scapula at acromioclavicular joint
  • Conoid tubercle and trapezoid line serve as attachment points for coracoclavicular ligament (stabilizes acromioclavicular joint)
• Scapula
  • Triangular, flat bone lies on posterior thoracic wall
  • Acromion process extends anteriorly from superior aspect of scapula and articulates with clavicle
  • Coracoid process projects anteriorly from superior border of scapula serves as attachment point for muscles (pectoralis minor, coracobrachialis) and ligaments (coracoclavicular, coracoacromial)
  • Glenoid cavity is shallow socket articulates with head of humerus to form glenohumeral joint (shoulder joint)
  • Spine of scapula is bony ridge runs horizontally across posterior surface serves as attachment point for muscles (trapezius, deltoid)

Pectoral girdle attachment and function

• Attachment to axial skeleton
  • Clavicle articulates with manubrium of sternum at sternoclavicular joint, only bony attachment of pectoral girdle to axial skeleton
  • Sternoclavicular joint allows for limited movement in all planes, providing stability to pectoral girdle
• Support for upper limb movement
  • Scapula and clavicle provide stable base for attachment of upper limb muscles (deltoid, rotator cuff)
  • Glenohumeral joint, formed by articulation of glenoid cavity of scapula and head of humerus, allows for wide range of motion in upper limb (flexion, extension, abduction, adduction, rotation)
  • Scapulothoracic "joint" is functional articulation between scapula and thoracic wall, allowing for smooth, coordinated movement of scapula during upper limb motion (elevation, depression, protraction, retraction)
  • Muscles attached to clavicle and scapula (trapezius, serratus anterior, pectoralis minor) help stabilize and position scapula during upper limb movement

Pectoral Girdle Movement and Muscles

• Scapular movement
  • Elevation, depression, protraction, retraction, and rotation
  • Facilitated by various muscles, including trapezius, rhomboids, and serratus anterior
• Clavicular movement
  • Elevation, depression, protraction, and retraction
  • Occurs in conjunction with scapular movement
• Pectoral girdle muscles
  • Include trapezius, rhomboids, levator scapulae, serratus anterior, and pectoralis minor
  • Work together to stabilize and move the shoulder complex

Injuries to clavicle and AC joint

• Clavicle fractures
  • Often result from direct trauma to shoulder or fall onto outstretched hand
  • Typically occur in middle third of clavicle
  • May cause visible deformity, pain, swelling, limited shoulder movement
  • Treatment depends on severity and location of fracture, ranging from immobilization with sling to surgical intervention (open reduction and internal fixation)
• Acromioclavicular (AC) joint injuries
  • Commonly caused by direct blow to top of shoulder or fall onto outstretched hand
  • Classified by degree of separation between acromion and clavicle
    1. Type I: Mild sprain of AC ligament with no separation
    2. Type II: Partial tear of AC ligament and coracoclavicular ligaments with slight separation
    3. Type III: Complete tear of AC and coracoclavicular ligaments with significant separation
  • Symptoms include pain, swelling, visible bump or step deformity at AC joint
  • Treatment ranges from rest and immobilization for mild injuries to surgical reconstruction for severe separations (Weaver-Dunn procedure, anatomic reconstruction with grafts)