Ch._16-17_Axilla_and_Brachial_Plexus_and_Scapular_Region--2025__1_

Axilla and Brachial Plexus Overview

• Axilla (Armpit):

  • Base: hairy skin, fat, and axillary fascia.

  • Apex: formed by the posterior border of the clavicle, superior border of the scapula, and Rib 1.

  • Anterior Wall: pectoralis major and minor.

  • Posterior Wall: comprises latissimus dorsi, teres major, and subscapularis muscles.

  • Medial Wall: Ribs 1-4, intercostal, and serratus anterior muscles.

  • Lateral Wall: intertubercular groove of the humerus.

Brachial Plexus Structure

• Nerves:

  • Comprises roots (C5-T1), trunks, divisions, cords, and branches.

  • Mnemonic: "Robert Taylor Drinks Cold Beer" helps remember the sequence.

• Cord Relationships:

  • Lateral, Medial, and Posterior cords are named based on their relationship with the axillary artery.

  • Five terminal branches: Musculocutaneous, Axillary, Radial, Median, and Ulnar nerves (Mnemonic: "MARMU").

Anatomy of the Brachial Plexus

• Nerve Roots:

  • Emerge from C5-T1, passing between anterior and middle scalene muscles above Rib 1.

  • Trunks form after roots unite.

• Divisions:

  • Each trunk divides into anterior and posterior divisions behind the clavicle.

• Terminal Branches:

  • Peripheral nerves arise from cords, providing innervation to upper limb structures.

Injury Mechanisms of the Brachial Plexus

• Types of Injuries:

  • Superior neck injuries: caused by forceful lateral neck flexion.

  • Inferior neck injuries: result from extreme forceful abduction of the upper extremity (UE).

  • FOOSH injuries (Falling on Outstretched Hand): common in various accidents and sports.

  • Birth-related injuries (e.g., Erb's Palsy): involve damage to the 5th, 6th, and 7th cervical nerve roots.

• Consequences:

  • Superior trunk injuries can lead to loss of elbow flexion, inability to abduct the arm, and sensory loss in the C5-C6 dermatome (Waiter’s tip deformity).

  • Inferior trunk injuries can cause paralysis of wrist and finger flexors, inability for fine motor movements, and numbness along the C8-T1 dermatome.

Specific Brachial Plexus Nerve Innervations

• Axillary Nerve:

  • Muscular innervation: deltoid and teres minor.

  • Sensory distribution: lateral shoulder.

  • Clinical loss includes loss of shoulder abduction and weak shoulder external rotation.

• Musculocutaneous Nerve:

  • Innervates coracobrachialis, biceps, and brachialis.

  • Clinical loss results in loss of elbow flexion when supinated and weak supination.

• Radial Nerve:

  • Innervates triceps, anconeus, brachioradialis, and dorsal wrist extensors.

  • Clinical manifestation: wrist drop due to loss of extension of the wrist and fingers.

• Median Nerve:

  • Innervates pronators, wrist and finger flexors (radial side), and thumb muscles.

  • Clinical loss results in inability to perform thumb opposition and wrist pronation ("ape hand").

• Ulnar Nerve:

  • Innervates flexor carpi ulnaris, medial half of flexor digitorum profundus, and intrinsic hand muscles.

  • Clinical loss includes loss of ulnar deviation and claw hand appearance.

Scapular Region Anatomy

• Scapula Overview:

  • Flat triangular bone with borders: superior, medial (vertebral), lateral (axillary).

  • Costal surface overlies Ribs 2-7.

  • Key structures include the spine (level of T3), acromion, and glenoid cavity.

• Muscle Categories:

  • Extrinsic muscles (attach axial to appendicular skeleton): Trapezius, Latissimus Dorsi, Levator Scapulae, Rhomboids.

  • Intrinsic muscles (attach scapula to humerus): Deltoid, Supraspinatus, Infraspinatus, Teres muscles, Subscapularis.

• Rotator Cuff:

  • Composed of four muscles: Supraspinatus, Infraspinatus, Teres Minor, Subscapularis (mnemonic: "SITS").

  • Provides stabilizing function to the glenohumeral joint.

• Clinical Considerations:

  • Scapular fractures are rare but indicate severe trauma.

  • Lymphatic drainage from the scapular region to axillary and supraclavicular lymph nodes.