Describe In Detail About Brachial Plexus Along With Its Clinical Anatomy. 10 mark

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Brachial Plexus — Detailed Description with Clinical Anatomy

1. Introduction

The brachial plexus is a somatic nerve plexus formed by the anterior rami of spinal nerves C5, C6, C7, C8, and most of T1. It originates in the neck, passes laterally and inferiorly over the first rib, and enters the axilla to provide the entire motor and sensory innervation of the upper limb.

— Gray's Anatomy for Students, p. 858

2. Formation and Components

The plexus is organized into five sequential levels: Roots → Trunks → Divisions → Cords → Branches

A useful mnemonic: "Robert Taylor Drinks Cold Beer"

Brachial Plexus — Major components in the neck and axilla (Gray's Anatomy for Students)

Schematic of the brachial plexus — Roots to terminal nerves

2.1 Roots (Anterior Rami)

Formed by the anterior rami of C5–C8 and T1
Emerge between the anterior and middle scalene muscles (interscalene space)
Receive gray rami communicantes from the cervical sympathetic trunk carrying postganglionic sympathetic fibers
Lie posterior and superior to the subclavian artery in the posterior triangle of the neck
Prefixed plexus: C4 contributes; Postfixed plexus: T2 contributes (anatomical variants)

— THIEME Atlas of Anatomy, p. 381

2.2 Trunks

Three trunks cross the base of the posterior triangle above the clavicle:

Trunk	Root Contributions	Position
Superior (Upper)	C5 + C6	Superior in the neck
Middle	C7 alone	Intermediate position
Inferior (Lower)	C8 + T1	Lies on rib I, posterior to subclavian artery

— Gray's Anatomy for Students, p. 858

2.3 Divisions

Each trunk divides into an anterior and posterior division behind the clavicle — giving 6 divisions total.

Anterior divisions → supply anterior (flexor) compartments
Posterior divisions → supply posterior (extensor) compartments
No peripheral nerves arise directly from the divisions

2.4 Cords

The divisions reunite to form three cords, named by their relationship to the second part of the axillary artery:

Cord	Composition	Position
Lateral cord	Anterior divisions of upper + middle trunks (C5–C7)	Lateral to axillary artery
Medial cord	Anterior division of inferior trunk (C8–T1)	Medial to axillary artery
Posterior cord	All three posterior divisions (C5–T1)	Posterior to axillary artery

— Gray's Anatomy for Students, p. 859

3. Branches of the Brachial Plexus

Brachial Plexus — Branches from roots to terminal nerves, with axillary artery relationship (Gray's Anatomy for Students)

3.1 Branches from the Roots (Supraclavicular)

Nerve	Origin	Segments	Supplies
Dorsal scapular nerve	C5 root	C4, C5	Rhomboid major, rhomboid minor, levator scapulae
Long thoracic nerve	C5–C7 roots	C5–C7	Serratus anterior
Small muscular branches to neck	C5–C8	—	Scalenes, longus colli
Contribution to phrenic nerve	C5 root	C5	Diaphragm (partial)

3.2 Branches from the Trunks (Supraclavicular)

Only the superior trunk gives branches:

Nerve	Segments	Supplies
Suprascapular nerve	C5, C6	Supraspinatus, infraspinatus
Nerve to subclavius	C5, C6	Subclavius

3.3 Branches from the Lateral Cord (Infraclavicular)

Nerve	Segments	Motor Supply	Sensory Supply
Lateral pectoral nerve	C5–C7	Pectoralis major	—
Musculocutaneous nerve	C5–C7	Coracobrachialis, biceps brachii, brachialis	Lateral cutaneous nerve of forearm
Lateral root of median nerve	C5–C7	(contributes to median nerve)	—

3.4 Branches from the Medial Cord (Infraclavicular)

Nerve	Segments	Motor / Sensory Supply
Medial pectoral nerve	C8, T1	Pectoralis major and minor
Medial cutaneous nerve of arm	C8, T1	Skin of medial arm
Medial cutaneous nerve of forearm	C8, T1	Skin of medial forearm
Ulnar nerve	C7–T1	Intrinsic hand muscles, flexor carpi ulnaris, medial FDP; medial 1½ digits
Medial root of median nerve	C8, T1	(contributes to median nerve)

3.5 Branches from the Posterior Cord (Infraclavicular)

Nerve	Segments	Motor / Sensory Supply
Upper subscapular nerve	C5, C6	Subscapularis (upper)
Thoracodorsal nerve	C6–C8	Latissimus dorsi
Lower subscapular nerve	C5, C6	Subscapularis (lower), teres major
Axillary nerve	C5, C6	Deltoid, teres minor; skin over deltoid (upper lateral arm)
Radial nerve	C5–T1	All posterior compartment muscles of arm and forearm; skin on posterior arm, forearm, dorsum of hand

The median nerve is formed by union of the lateral root (from lateral cord) and medial root (from medial cord) — these form an "M" shape over the third part of the axillary artery.

— Gray's Anatomy for Students, p. 865

4. Relations & Surface Anatomy

In the neck: Roots lie between anterior and middle scalene muscles; trunks are in the posterior triangle
At the clavicle: Divisions pass posterior to the clavicle and subclavius muscle
In the axilla: Cords surround the axillary artery — lateral, posterior, and medial cords named accordingly
The musculocutaneous nerve pierces the coracobrachialis muscle — a useful landmark for cord identification in the axilla

— THIEME Atlas of Anatomy, p. 381

5. Clinical Anatomy

5.1 Erb–Duchenne Palsy (Upper Plexus Injury: C5, C6)

Mechanism: Forced separation of head and shoulder (e.g., shoulder dystocia at birth, motorcycle fall widening the cervicohumeral angle, fall on outstretched hand).

Muscles paralysed: Deltoid, supraspinatus, infraspinatus, biceps brachii, brachioradialis (C5, C6-innervated muscles).

Classic posture — "Waiter's Tip" deformity:

Arm hangs adducted and medially rotated (deltoid, supraspinatus paralysed)
Forearm pronated and extended (biceps, brachioradialis paralysed)
Wrist flexed

Sensory loss: Lateral aspect of arm and forearm (C5, C6 dermatomes) Reflex loss: Biceps and brachioradialis reflexes absent

Prognosis: Best prognosis of all brachial plexus injuries; >90% recover without surgery.

— Miller's Review of Orthopaedics 9th Ed., p. 260; Bradley & Daroff's Neurology, p. 2870

5.2 Klumpke's Palsy (Lower Plexus Injury: C8, T1)

Mechanism: Forced abduction of the arm above the head (e.g., grasping a branch during a fall, forceps delivery in breech presentation).

Muscles paralysed: Intrinsic hand muscles (interossei, lumbricals, thenar, hypothenar), flexor carpi ulnaris, medial FDP.

Classic posture — "Claw Hand":

Hyperextension of MCPJs with flexion of IPJs — due to loss of intrinsic hand muscles
More severe in the ring and little fingers (ulnar paradox not fully applicable here)

Associated finding: If T1 sympathetic fibers are involved → Horner syndrome (ptosis, miosis, anhidrosis, enophthalmos) due to damage to preganglionic sympathetic fibers at T1.

Prognosis: Poor; associated with Horner syndrome carries worst prognosis.

— Miller's Review of Orthopaedics 9th Ed., p. 260; The Harriet Lane Handbook, 23rd Ed.

5.3 Total Brachial Plexus Palsy (C5–T1)

Complete flaccid paralysis of the entire upper limb ("flail arm")
Total sensory loss below the shoulder
Absent all upper limb reflexes
Horner syndrome present
Worst prognosis

5.4 Long Thoracic Nerve Injury (C5–C7 roots)

Cause: Axillary lymphadenectomy (breast cancer surgery), heavy backpack, stab wounds.

Result: Serratus anterior paralysis → Winging of scapula (medial border of scapula lifts away from chest wall on pushing against a wall).

— THIEME Atlas of Anatomy, p. 382

5.5 Axillary Nerve Injury (C5, C6 — Posterior cord)

Cause: Fracture of surgical neck of humerus, anterior shoulder dislocation, improper use of crutches.

Result:

Deltoid paralysis → inability to abduct arm beyond 15° (first 15° by supraspinatus)
Loss of sensation over the "regimental badge" area (skin over deltoid)
Quadrangular space syndrome (compression in quadrilateral space)

5.6 Radial Nerve Injury (C5–T1 — Posterior cord)

Cause: Fracture of mid-shaft of humerus ("Saturday night palsy"), axillary compression.

Result: Wrist drop — inability to extend the wrist and fingers (posterior compartment muscles paralysed); sensory loss over anatomical snuffbox and dorsum of hand (C7 territory).

5.7 Musculocutaneous Nerve Injury (C5–C7 — Lateral cord)

Cause: Coracobrachialis piercing, anterior shoulder dislocation.

Result: Weak flexion and supination of forearm; sensory loss over lateral forearm.

5.8 Thoracic Outlet Syndrome (TOS)

The brachial plexus must traverse several anatomically narrow passages where it is vulnerable to compression:

Type	Site of Compression	Cause
Scalene syndrome (Cervical rib syndrome)	Interscalene space	Cervical rib or fibrous band; present in ~1% of population
Costoclavicular syndrome	Space between 1st rib and clavicle	Drooping shoulders, clavicular fracture
Hyperabduction syndrome	Under pectoralis minor / coracoid process	Arm raised above head
Backpack paralysis	Direct plexus compression	Chronic heavy shoulder loads

Clinical features: Pain radiating down the arm (ulnar side predominant), paresthesias, circulatory impairment.

— THIEME Atlas of Anatomy, p. 382

5.9 Brachial Plexus Injury in Adults — Classification by Level

Level of Injury	Structure Affected	Typical Cause
Preganglionic (avulsion)	Root avulsed from spinal cord	High-speed trauma (motorcycle); poorest prognosis; no Tinel sign
Postganglionic (rupture)	Root or trunk torn outside cord	Blunt trauma, traction
Cord/division level	Glenohumeral dislocation	Shoulder dislocation

Preganglionic avulsion: no possibility of spontaneous recovery; requires nerve grafting/transfer
Electrodiagnostic studies (EMG/NCS) + MRI/CT myelography used to map extent

— Gray's Anatomy for Students, p. 867

5.10 Neonatal Brachial Plexus Palsy — Summary

Type	Roots	Deformity	Prognosis
Erb–Duchenne	C5–C6	Waiter's tip	Best (~90% resolve)
Klumpke	C8–T1	Claw hand + Horner	Poor
Total palsy	C5–T1	Flail arm	Worst

Causes: Large neonate, shoulder dystocia, forceps delivery, breech position. Management: Passive ROM exercises; surgical reconstruction considered if no recovery by 3–6 months.

6. Summary Table — The Brachial Plexus at a Glance

Component	No.	Location	Nerve Roots
Roots	5	Interscalene space	C5–T1
Trunks	3	Posterior triangle (above clavicle)	C5–T1
Divisions	6	Behind clavicle	C5–T1
Cords	3	In axilla (around 2nd part of axillary artery)	Lateral (C5–C7), Medial (C8–T1), Posterior (C5–T1)
Terminal branches	5 major	Axilla and arm	Musculocutaneous, Median, Ulnar, Radial, Axillary

Sources: Gray's Anatomy for Students (pp. 858–867) | THIEME Atlas of General Anatomy and Musculoskeletal System (pp. 381–382) | Miller's Review of Orthopaedics 9th Ed. | Bradley and Daroff's Neurology in Clinical Practice | The Harriet Lane Handbook 23rd Ed.

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