IMG_0033

Axilla and Brachial Plexus

Definition of Axilla

• The axilla, also known as the armpit, is a concave area located at the junction of the arm and trunk.

• Components:

  • Base: Formed by hairy skin, subcutaneous fat, and axillary fascia.

  • Apex: Bounded by:

    • Posterior border of the clavicle

    • Superior border of the scapula

    • Rib I

  • Anterio Wall: Formed by the pectoralis major and minor muscles.

  • Posterior Wall: Composed of:

    • Lateral parts of latissimus dorsi

    • Teres major

    • Subscapularis muscles

  • Medial Wall: Made up of ribs I to IV and intercostal and serratus anterior muscles.

  • Lateral Anterior Wall: The intertubercular groove of the humerus.

• Structural Support: Provided by the lateral rib cage, clavicle, and scapula.

Brachial Plexus

• Definition: A complex network of nerves originating from the anterior rami of spinal nerves C5 to T1.

• Location: Enclosed with the axillary artery and vein within the axillary sheath (extension of cervical fascia).

• Components: Comprised of nerve roots, trunks, divisions, cords, and branches.

Composition of Brachial Plexus

• Roots: Emerging from the intervertebral foramina of lower cervical vertebrae, situated between the anterior and middle scalene muscles.

• Trunks:

  • Superior trunk: Formed by C5, C6.

  • Middle trunk: Formed by C7.

  • Inferior trunk: Formed by C8, T1.

Nerve Branches

• From Roots:

  • Dorsal scapular nerve (to levator scapulae, rhomboids)

  • Long thoracic nerve (to serratus anterior)

• From Trunks:

  • Suprascapular nerve

  • Subclavian nerve

Divisions and Cords

• Divisions: Each trunk splits into anterior and posterior divisions.

• Cords: The divisions form:

  • Lateral cord: Anterior divisions of superior and middle trunks.

  • Medial cord: Anterior division of the inferior trunk.

  • Posterior cord: Posterior divisions of all three trunks.

Nerve Supply from Cords

• Lateral Cord:

  • Lateral pectoral nerve (becomes musculocutaneous nerve)

• Medial Cord:

  • Medial pectoral nerve

  • Medial cutaneous nerve of arm

  • Medial cutaneous nerve of forearm

• Posterior Cord:

  • Superior subscapular nerve

  • Thoracodorsal nerve

  • Inferior subscapular nerve

Terminal Nerves of Brachial Plexus

• Main Terminal Branches:

  • Musculocutaneous nerve (C5-C7)

  • Axillary nerve (C5-C6)

  • Radial nerve (C5-T1)

  • Median nerve (C6-T1)

  • Ulnar nerve (C7-T1)

Arteries of the Axilla

• Axillary Artery: A continuation of the subclavian artery, bifurcates into 3 parts related to the pectoralis minor muscle.

  • First Part: Runs between rib I and pectoralis minor, branches into superior thoracic artery.

  • Second Part: Posterior to pectoralis minor, branches into thoracoacromial artery and lateral thoracic artery.

  • Third Part: Extends to the lower border of teres major with branches:

    • Subscapular artery

    • Anterior and posterior circumflex humeral arteries.

Veins and Lymphatics

• Axillary Vein: Located medially to the axillary artery, becomes the subclavian vein at rib I.

• Lymphatic Drainage: Includes five groups of lymph nodes:

  • Pectoral nodes (drain chest wall, mammary glands)

  • Humeral nodes (drain upper limb)

  • Subscapular nodes (drain back muscles)

  • Central nodes (drain lateral quadrants of the breast)

  • Apical nodes (drain other axillary nodes & structures in the neck).

Clinical Correlations: Brachial Plexus Injuries

• Types of Injuries: Superior and inferior trunk injuries

• Superior Trunk Injury:

  • Caused by forceful neck flexion and shoulder depression.

  • Causes inability to flex the arm, abduct, and supinate forearm.

• Inferior Trunk Injury:

  • Due to extreme abduction of the upper limb.

  • Leads to paralysis or weakness of fingers.

Assessment and Treatment of Brachial Plexus Injury

• Diagnosis: Confirmed via electrical stimulation and imaging techniques.

• Prognosis: Poor if complete avulsion occurs; some restoration of function is possible with injury management.

Mnemonics**

• Brachial Plexus Structure: Really Thirsty? Drink Cold Beer (Roots, Trunks, Divisions, Cords, Branches)

• Terminal Nerves: MARMU (Musculocutaneous, Axillary, Radial, Median, Ulnar)

Scapular Region

Overview

• Definition: Superior posterior surface of the trunk defined by muscles that attach to the scapula.

• Muscle Groups:

  • Extrinsic Muscles: Connect axial to appendicular skeleton (trapezius, latissimus dorsi, levator scapulae).

  • Intrinsic Muscles: Attach scapula to humerus (deltoid, rotator cuff muscles).

Anatomy of Scapula

• Bony Landmarks:

  • Borders: Superior, medial, lateral

  • Angles: Inferior angle, lateral angle

  • Spine: Divides the scapula posterior surface into supraspinous fossa (above) and infraspinous fossa (below).

Muscles of the Scapular Region

• Superficial Extrinsic Muscles:

  • Trapezius and latissimus dorsi connect trunk to upper limb.

• Deep Extrinsic Muscles:

  • Levator scapulae, rhomboid major, and rhomboid minor elevate/retract scapula.

• Intrinsic or True Muscles:

  • Deltoid (three parts), supraspinatus, infraspinatus, teres minor, teres major, subscapularis, all contributing to shoulder movements.

Nerve Supply

• Sensory Innervation: From medial branches of posterior rami of cervical nerves C4-C8 and thoracic nerves T1-T6.

• Motor Innervation:

  • From brachial plexus branches including dorsal scapular nerve, suprascapular nerve, etc.

Arteries and Veins

• Blood Supply: Formed by scapular anastomosis via multiple arteries.

• Venous Drainage: Corresponds to arterial drainage into axillary or subclavian veins.

Clinical Relevance

Scapular Fracture

• Often due to high-velocity injuries; associated with other serious injuries (e.g., pneumothorax).

• Symptoms: Extreme upper back pain, difficulty lying comfortably, respiratory symptoms.

• Assessment: Immediate evaluation includes airway, breathing, circulation checks.

• Treatment: Conservatively with immobilization, pain control, or surgical repair if necessary.

Shoulder Complex

Joints of the Shoulder

• Types of Joints:

  • Sternoclavicular joint (saddle-type),

  • Acromioclavicular joint (plane-type),

  • Glenohumeral joint (ball-and-socket).

Glenohumeral Joint Anatomy

• Components: Head of humerus articulating with glenoid cavity; supported by rotator cuff muscles.

• Nerve Supply: Suprascapular, axillary, and subscapular nerves.

Clinical Correlations

• Rotator Cuff Tears: Caused by repetitive overhead movements or trauma. Symptoms include pain and limited range of motion.

• Acromioclavicular Joint Injuries: Common due to downward forces; treated with conservative methods or surgical stabilization based on injury severity.