Shoulder Girdle

Shoulder Girdle Overview

  • Instructor: Dr. Chris Ramos

  • Institution: Arizona State University

Anatomy of the Shoulder Girdle

  • Key Components:

    • Subacromial space

    • Acromioclavicular (AC) joint

    • Glenohumeral joint: main joint of the shoulder

    • Scapulothoracic joint: functional joint; not a true synovial joint

    • Sternoclavicular (SC) joint

Shoulder Girdle Joints

  • Sternoclavicular Joint (SC):

    • Description: Joint between the sternum and clavicle.

    • Joint Type: Saddle joint.

  • Acromioclavicular Joint (AC):

    • Description: Joint between the clavicle and acromion process.

    • Joint Type: Gliding joint.

  • Scapulothoracic Joint:

    • Description: Occurs where the anterior scapula meets the posterior rib cage.

    • Nature: Functional joint; not a true synovial joint.

    • Mechanism of Movement: Completely dependent on movement at the SC and AC joints; no ligaments present, requires dynamic support from muscles.

Ligaments Supporting the Joints

  • Sternoclavicular Joint:

    • Costoclavicular ligament (posterior fibers)

    • Anterior sternoclavicular ligament

    • Interclavicular ligament

    • Fibrous capsule: stabilizes the joint.

  • Acromioclavicular Joint:

    • Stabilization: Fibrous capsule, acromioclavicular ligament, and coracoclavicular ligament.

    • Coracoclavicular ligament parts:

    • Trapezoid ligament

    • Conoid ligament

Movements of the Shoulder Girdle

  • The shoulder girdle can be simplified to exhibit six possible movements:

    1. Protraction (abduction) - movement forward in the transverse plane.

    2. Retraction (adduction) - movement backward in the transverse plane.

    3. Elevation - upward movement in the frontal plane.

    4. Depression - downward movement in the frontal plane.

    5. Upward Rotation - rotation of the scapula in the frontal plane.

    6. Downward Rotation - counter-rotation of the scapula in the frontal plane.

  • Joint Mechanism: The SC joint acts as a pivot point for the clavicle and scapula to move around.

Anatomy of the Vertebrae

  • Cervical Vertebrae: 7 in total (C1-C7)

  • Thoracic Vertebrae: 12 in total (T1-T12)

  • Lumbar Vertebrae: 5 in total (L1-L5)

  • Sacrum: 5 fused vertebrae.

  • Coccyx: 4 fused vertebrae.

  • Vertebral Structure Components:

    • Spinous processes

    • Facets

    • Lamina

    • Foramen

    • Transverse processes

Anatomy of the Scapula

  • Features of the scapula include:

    • Acromion

    • Coracoid process

    • Glenoid cavity

    • Supraspinous fossa

    • Infraspinous fossa

    • Subscapular fossa

  • Anatomy notes:

    • Coracoid process location and function

    • Glenoid cavity for humeral articulation.

Muscles Associated with Shoulder Girdle Movement

  • Upper Trapezius:

    • Origin: External occipital protuberance, superior nuchal line, ligamentum nuchae.

    • Insertion: Clavicle (posterior lateral ⅓), acromion process.

    • Action: Elevate scapula; rotation and retraction of scapula; extend neck; contralateral head rotation.

  • Middle Trapezius:

    • Origin: C7, T1-T3 (spinous processes).

    • Insertion: Acromion process (medial margin), scapular spine (superior).

    • Action: Retract (adduct) scapula; upwards rotation; elevate scapula.

  • Lower Trapezius:

    • Origin: T4-T12 (spinous processes).

    • Insertion: Scapular spine (base).

    • Action: Retract (adduct) scapula; depress scapula; upwards rotation.

  • Levator Scapulae:

    • Origin: C1-C4 (transverse processes).

    • Insertion: Medial border of scapula (between spine & superior angle).

    • Action: Elevate scapula; downwards rotation of scapula.

Common Injuries and Impairments

  • Injuries: Most common injuries involve muscles of the shoulder joint rather than the shoulder girdle, but impairments can affect function and cause pain.

  • Separated Shoulder:

    • Definition: A true injury of the shoulder girdle, different from shoulder dislocation (which involves separation of humerus from scapula).

    • Involved Structures: Damage (usually a tear) to ligaments holding scapula to clavicle.

    • Key Ligaments:

    • Superior Acromioclavicular Ligament: Connects acromion process to clavicle.

    • Trapezoid and Conoid Ligaments: Connect clavicle to coracoid process.

Muscle Dynamics and Imbalances

  • Muscle Imbalance Types:

    • Elevators vs. depressors

    • Upward vs. downward rotators

    • Retractors vs. protractors

Shoulder Girdle Stability

  • Static Stability:

    • Bony Architecture: Integrity and design of bones supporting the joints.

    • Static Stability: Stability provided by ligaments.

  • Dynamic Stability: Support provided by muscle contractions and interactions during movement.