Human Anatomy Week 9 - Shoulder and Pectoral Region (Notes)

Overview of the Shoulder

• Clavicle:
  • Only bone with true articulation with the axial skeleton.
  • S-shaped bone with convexities on both ends.
  • Allows for greater shoulder elevation.
• Scapula:
  • Plays a crucial role in shoulder mobility and stability.
  • Has three distinct areas: superior, inferior, and spine.
  • No direct joint attachment to the posterior thorax.
• Humerus:
  • Forms the glenohumeral joint.
  • Head of humerus articulates with the glenoid fossa.
  • Surgical neck is a common fracture location.
• Surface Projections:
  • Spine of scapula, medial border, inferior angle, clavicle, acromion process, coracoid process, and greater tuberosity of humerus are palpable landmarks.

Anatomical Spaces at the Shoulder

• Triangular Space:
  • Located between teres minor, teres major, and long head of triceps.
  • Passes circumflex scapular artery.
• Triangular Interval:
  • Bounded by the long head of triceps, teres major, and lateral head of triceps.
  • Located between radial nerve and profunda brachial artery.
• Quadrangular Space:
  • Has four sides: teres minor, long head of triceps, teres major, and shaft of humerus.
  • Passes axillary nerve and posterior circumflex artery.
• Triangle of Auscultation:
  • Located between trapezius, latissimus dorsi, and rhomboid major.
  • Allows for clear auscultation of lung sounds.
• Clavipectoral Triangle:
  • Located between clavicle and deltoid.
  • Useful for palpating the coracoid process.

Sternoclavicular and Acromioclavicular Joints

• Sternoclavicular (SC) joint:
  • Saddle joint, but functions like a ball and socket.
  • Has an articular disc dividing the joint.
  • Supported by multiple ligaments: anterior SC ligament, interclavicular ligament, Costoclavicular ligament.
• Acromioclavicular (AC) Joint:
  • Synovial planar joint.
  • Contains the Acromioclavicular, Coracoclavicular, Trapezoid and Conoid Ligaments.
  • Susceptible to separation.
• Scapulothoracic Joint:
  • Not a true joint, but a functional relationship between the scapula and thoracic cage.

Glenohumeral Joint

• Structure:
  • Ball and socket joint with a shallow glenoid fossa.
  • Relies heavily on ligaments and muscles for stability.
  • Capsule is loose, allowing for greater range of motion.
• Movements:
  • Flexion/extension, abduction/adduction, external/internal rotation, horizontal abduction/adduction.
• Scapulothoracic Rhythm:
  • Combined movement of glenohumeral and scapulothoracic joints are needed for full shoulder movement overhead.
• Capsule and Ligaments:
  • Superior, middle, and inferior glenohumeral ligament, coracohumeral ligament, coracoacromial ligament, supraspinatus muscle.
  • Posterior side: labrum, fibrous joint capsule, biceps tendon.
• Cavity:
  • Large synovial cavity encases the joint and the biceps tendon.
• Bursae:
  • Subacromial (subdeltoid) bursa and subscapularis bursa.
  • Both are prone to inflammation.

Muscles Connecting to the Spine

• Posterior Muscles:
  • Trapezius, levator scapula, rhomboids, latissimus dorsi.
• Trapezius:
  • Originates from the skull, ligamentum nuchae, and C7-T12 processes.
  • Inserts on clavicle, acromion, and scapular spine.
  • Actions: elevation, depression, upward rotation.
• Latissimus Dorsi:
  • Originates from T7-12 processes, thoracolumbar fascia, ribs 8-12, and indirectly from the ilium.
  • Inserts at the humerus.
  • Actions: extension, adduction, medial rotation.
• Levator Scapula:
  • Originates from C1-C4 transverse processes.
  • Inserts on the medial border of the scapula.
  • Actions: elevation, downward rotation, inferior glenoid tilt.
• Rhomboid Major & Minor:
  • Originate from C7-T5 spinous processes.
  • Insert on medial border of scapula to the inferior angle.
  • Actions: retraction, downward rotation.

Muscles Connecting to Thoracic Wall

• Anterior Muscles:
  • Pectoralis major, pectoralis minor, serratus anterior, subclavius, sternocleidomastoid.
• Pectoralis Major:
  • Originates from clavicle and sternum.
  • Inserts at the humerus.
  • Actions: adduction, flexion, extension, medial rotation.
• Pectoralis Minor:
  • Originates from ribs 3-5.
  • Inserts on coracoid process of scapula.
  • Actions: protraction, downward rotation, depression.
• Serratus Anterior:
  • Originates from ribs 1-8.
  • Inserts on the medial border of scapula.
  • Actions: protraction, upward rotation, stabilization.
• Subclavius:
  • Depresses and stabilizes clavicle.
• Sternocleidomastoid:
  • Not directly related to the shoulder; it acts on the neck.

Scapular Stability

• Serratus anterior stabilizes the scapula
• Serratus anterior originates on ribs 1-8 and inserts on the medial border of the scapula
• It pulls the medial border down and forward, causing upward rotation
• It also pulls the medial border toward the spine and rib cage, stabilizing the scapula on the back
• Gravity and muscles downwardly rotate the scapula

Pectoral Fascia

• Covers the pectoralis major muscle
• Continuous with the fascia of the abdominal wall and the axillary region

Clavipectoral Fascia

• Deep to the pectoral fascia
• Contains the costocoracoid membrane
• Costocoracoid membrane connects the subclavius, clavicle, and pec minor to the axillary fascia
• Nerves and blood vessels pass through this fascia
• Contains the lateral pectoral nerve, cephalic vein, and thoracoacromial artery
• Contains the suspensory ligament of the axilla which connects the pec minor and axillary fascia

Intrinsic Shoulder Muscles

• Teres major
  • Originates on the inferior angle of the scapula
  • Inserts on the humerus' medial lip of the intertubercular groove
  • Action: adducts and medially rotates the arm
  • Nerve: lower subscapular nerve C5, C6
• Deltoid
  • Originates on the lateral ⅓ of the clavicle, acromion, and scapular spine
  • Inserts on the deltoid tuberosity of the humerus
  • Action:
    • Clavicular fibers: flex and medially rotate the arm
    • Acromial fibers: abduct the arm
    • Spinal fibers: extend and laterally rotate the arm
  • Nerve: axillary nerve C5, C6

Subacromial And Subdeltoid Bursae

• Found deep to the deltoid muscle
• Inflammation can cause pain over the supralateral point of the shoulder

Rotator Cuff

• Supraspinatus
  • Originates on the scapular supraspinous fossa
  • Inserts on the superior facet of the greater tubercle of the humerus
  • Action: initiates arm abduction and helps hold the humeral head in the glenoid fossa
  • Nerve: suprascapular nerve C4, C5, C6
• Infraspinatus
  • Originates on the scapular infraspinous fossa
  • Inserts on the middle facet of the greater tubercle of the humerus
  • Action: laterally rotates the arm, holds the humeral head in the glenoid fossa
  • Nerve: suprascapular nerve C5, C6
• Teres minor
  • Originates on the middle lateral border of the scapula
  • Inserts on the inferior facet of the greater tubercle of the humerus
  • Action: laterally rotates the arm, holds the humeral head in the glenoid fossa
  • Nerve: axillary nerve C5, C6
• Subscapularis
  • Originates on the subscapular fossa
  • Inserts on the lesser tubercle of the humerus
  • Action: adducts and medially rotates the arm, holds the humeral head in the glenoid fossa
  • Nerve: upper and lower subscapular nerves C5, C6, C7