Shoulder Girdle

INTRODUCTION TO THE SHOULDER GIRDLE

  • In this document, we will explore the anatomy and functional movements of the shoulder girdle as explained by Brandon Snyder, DHSC.

OBJECTIVES OF STUDYING THE SHOULDER GIRDLE

  • Understand the following:
    • Bony features of the shoulder girdle.
    • Muscles associated with the shoulder girdle.
    • Shoulder girdle movements, including their planes and axes of rotation.
    • Antagonists of shoulder girdle muscles.

MOVEMENTS OF THE SHOULDER GIRDLE

  • The shoulder girdle's movements can be described in relation to the scapula, which acts around the sternoclavicular joint.

Axis of Rotation

  • The axis of rotation for the shoulder girdle is the sternoclavicular joint.

Types of Movements

  1. Abduction (Protraction):

    • Description: Lateral movement of the scapula away from the spinal column.
    • Example: Reaching for an object located in front of the body; bar ascent during the bench press.

  2. Adduction (Retraction):

    • Description: Medial movement of the scapula toward the spinal column.
    • Example: Pinching the shoulder blades together; bar descent during the bench press.

  3. Elevation:

    • Description: Superior movement of the shoulder girdle.
    • Example: Shrugging the shoulders during clean pulls.

  4. Depression:

    • Description: Inferior movement of the shoulder girdle.
    • Example: Movement during the 'Farmer's walk'.

  5. Upward Rotation:

    • Description: Rotation that turns the glenoid fossa upward, moving the inferior angle superiorly and laterally away from the spinal column.
    • Example: During jumping jacks.

  6. Downward Rotation:

    • Description: Returns the scapula to the fundamental anatomical position.
    • Example: During jumping jacks.

  7. Lateral Tilt:

    • Description: Rotation of the scapula around a longitudinal axis; the medial border moves posteriorly while the lateral border moves anteriorly.
    • Importance: This movement occurs during abduction; bar ascent during benchmark exercises.

  8. Medial Tilt:

    • Description: The return movement from lateral tilt.
    • Example: Bar descent during the bench press.

BONES AND LANDMARKS OF THE SHOULDER GIRDLE

COMPONENTS OF THE SHOULDER GIRDLE

  • The shoulder girdle consists of two main bones:
    • Scapula: A flat, triangular bone that provides anatomical features important for movement.
    • Clavicle: A long bone that connects the arm to the body, articulating with the sternum at the manubrium.

MANUBRIUM

  • The manubrium connects the axial skeleton to the appendicular skeleton and provides articulation for the clavicles with the sternum.

ANTERIOR SCAPULA LANDMARKS

  • Coracoid Process: A process on the scapula that serves as an attachment point for muscles and ligaments.
  • Acromion Process: The apex of the scapula, forming a joint with the clavicle.
  • Glenoid Fossa (Cavity): A shallow cavity that receives the head of the humerus, forming the glenohumeral joint.
  • Medial & Lateral Borders: The edges of the scapula.
  • Inferior & Superior Angles: The angles formed at the corners of the scapula's triangular shape.

POSTERIOR SCAPULA LANDMARKS

  • Spine of Scapula: The prominent ridge that runs across the posterior surface.
  • Infraspinatus and Supraspinatus Fossae: These depressions on the scapula serve as attachment sites for muscles.
  • Glenoid Cavity: Reiterated as the site of articulation for the head of the humerus.

JOINTS OF THE SHOULDER GIRDLE

TYPES OF JOINTS

  1. Sternoclavicular (SC) Joint:

    • Type: Arthrodial joint allowing sliding and gliding movement; multiaxial.
    • Movements include protraction, retraction, elevation, and depression of the scapula.

  2. Acromioclavicular (AC) Joint:

    • Type: Arthrodial joint that allows gliding and rotational motion accompanying movements of the shoulder girdle.
    • Ligamentous Support: Includes coracoclavicular ligaments (trapezoid and conoid) along with superior and inferior acromioclavicular ligaments.

  3. Scapulothoracic (ST) Articulation:

    • Definition: The articulation of the scapula over the thorax.
    • Characteristics: Not a true synovial joint; it lacks conventional synovial features and ligamentous support, relying instead on muscles for stabilization.
    • Movements facilitated: Abduction, adduction, upward and downward rotation, elevation, and depression.

MID-WAY REVIEW QUESTIONS

  1. Movement Explanation: What is meant by the movement of the shoulder girdle?

    • Movements include protraction, retraction, upward rotation, downward rotation, elevation, depression, lateral tilt, medial tilt.

  2. Bony Structure Identification: What bones make up the shoulder girdle?

    • Scapula and clavicle.

  3. Joint Composition: What joints are present in the shoulder girdle?

    • Sternoclavicular, acromioclavicular, and scapulothoracic joints.

SHOULDER GIRDLE MUSCLES

  • The movement of the shoulder girdle relies on its associated muscles, which stabilize the scapula and allow for effective upper extremity movements.

MAJOR MUSCLES INVOLVED IN SHOULDER GIRDLE MOVEMENT

  • Five Key Muscles:
    1. Pectoralis Minor
    2. Serratus Anterior
    3. Trapezius
    4. Rhomboid
    5. Levator Scapulae
    6. Subclavius (not a prime mover)
  • All muscles originate from the axial skeleton and insert onto the scapula and/or clavicle.

ANTERIOR MUSCLES OF THE SHOULDER GIRDLE

  1. Pectoralis Minor:

    • Origin: Anterior surface of the 3rd to 5th ribs.
    • Insertion: Coracoid process of the scapula.
    • Movements: Abduction (protraction), downward rotation, and depression of the scapula.
    • Example movements include pushing movements like push-ups and bench press.

  2. Serratus Anterior:

    • Origin: Surface of the upper 9 ribs.
    • Insertion: Anterior aspect of the medial border of the scapula.
    • Movements: Abduction (protraction) and upward rotation of the scapula.
    • Important for push-ups and bench press activities.

  3. Subclavius:

    • Origin: Superior aspect of the 1st rib.
    • Insertion: Mid-portion of the inferior clavicle.
    • Movements: Depression and abduction (protraction) of the scapula.
    • Functions in stabilization and protection of the sternoclavicular joint; not a primary mover.

POSTERIOR MUSCLES OF THE SHOULDER GIRDLE

  1. Trapezius:

    • Comprised of upper, middle, and lower fibers that function collectively to stabilize and move the scapula.
    • Upper fibers:
      • Origin: Base of the skull; posterior ligaments of the neck.
      • Insertion: Posterior aspect of the lateral third of the clavicle.
      • Movements: Elevation of the scapula; example includes shrugging during clean pulls.
    • Middle fibers:
      • Origin: 7th cervical and upper 3 thoracic vertebrae.
      • Insertion: Medial border of the acromion process and above the scapular spine.
      • Movements: Elevation, adduction (retraction), and upward rotation; activities include rowing and shoulder abduction during jumping jacks.
    • Lower fibers:
      • Origin: 4th-12th thoracic vertebrae.
      • Insertion: Base of the scapula spine.
      • Movements: Adduction (retraction), depression, and upward rotation.

  2. Rhomboids:

    • Origin: Last cervical and first 5 thoracic vertebrae.
    • Insertion: Medial border of the scapula, below the scapular spine.
    • Movements: Elevation, adduction (retraction), and downward rotation.
    • Function as fixators of the scapula during shoulder joint extension and adduction.

  3. Levator Scapula:

    • Origin: Upper 4 cervical vertebrae.
    • Insertion: Medial border of the scapula.
    • Movements: Elevation and weak downward rotation/adduction; contributes to shrugging during clean pulls.

SUMMARY OF THE SHOULDER GIRDLE

  • Important bony features include the following:
    • Infraspinatus fossa, supraspinatus fossa, coracoid process, acromion process, glenoid fossa, lateral and medial borders, and spine of the scapula.
  • Key joints include the sternoclavicular joint, acromioclavicular joint, and scapulothoracic joint.
  • Movements of the shoulder girdle consist of:
    • Abduction (Protraction), Adduction (Retraction), Elevation, Depression, Upward Rotation, Downward Rotation, Lateral Tilt, Medial Tilt.
  • Primary muscles involved:
    • Anterior Muscles: Serratus anterior, pectoralis minor, subclavius.
    • Posterior Muscles: Trapezius, levator scapulae, rhomboid.

REVIEW QUESTIONS

  • Identify the major muscles involved in shoulder girdle movement.
  • Differentiate between anterior and posterior muscles.
  • State the origin, insertion, and actions of each muscle related to the shoulder girdle.

These comprehensive notes capture the critical details and concepts presented regarding the shoulder girdle, its movements, muscular attachments, and anatomical features for effective review and study.