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BRACHIAL PLEXUS FOR EMERGENCY MEDICINE DETAIL , AND BREAK

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🧠 BRACHIAL PLEXUS — Emergency Medicine Deep Dive

📍 OVERVIEW

The brachial plexus is a somatic nerve network formed from the anterior rami of C5–C8 and T1, occasionally with contributions from C4 (prefixed) or T2 (postfixed). It originates in the neck between the anterior and middle scalene muscles, crosses over the first rib, and enters the axilla — supplying all motor and most sensory innervation to the upper limb.
Gray's Anatomy for Students, p. 858–861

🏗️ STRUCTURE: The "RTDC" Memory System

The plexus has 4 sequential levels — Roots → Trunks → Divisions → Cords → Branches
Mnemonic: "Robert Taylor Drinks Cold Beer" (Roots, Trunks, Divisions, Cords, Branches)

LEVEL 1 — ROOTS (Anterior Rami)

RootExits Between
C5Between anterior & middle scalene
C6Between anterior & middle scalene
C7Between anterior & middle scalene
C8Between anterior & middle scalene
T1Over rib I, posterior to subclavian artery
Each root receives gray rami communicantes from the sympathetic trunk (carries postganglionic sympathetic fibers). This is clinically important — T1 root injury → Horner syndrome (ptosis, miosis, anhidrosis, enophthalmos).

LEVEL 2 — TRUNKS (3)

TrunkFormed ByPosition
Superior (Upper)C5 + C6Superior
MiddleC7 aloneMiddle
Inferior (Lower)C8 + T1Posterior to subclavian artery, on rib I
The trunks cross the base of the posterior triangle of the neck.
Gray's Anatomy for Students, p. 858

LEVEL 3 — DIVISIONS (6 total)

Each trunk splits into anterior and posterior divisions.
  • Anterior divisions → supply anterior (flexor) compartments
  • Posterior divisions → supply posterior (extensor) compartments
  • No named nerves arise directly from divisions

LEVEL 4 — CORDS (3)

Named by their position relative to the axillary artery (2nd part):
CordOriginContributionsPosition
Lateral cordAnterior divisions of superior + middle trunksC5, C6, C7Lateral to axillary artery
Medial cordAnterior division of inferior trunkC8, T1Medial to axillary artery
Posterior cordAll 3 posterior divisionsC5–T1 (all)Posterior to axillary artery

🔱 BRANCHES (The 5 Terminal Nerves + Pre-terminal Branches)

Brachial Plexus Schematic - Terminal nerves, cords, divisions, trunks and roots labeled
Fig. 7.53 Brachial Plexus — Schematic (A) and relationship to axillary artery (B). Gray's Anatomy for Students, p. 860

FROM THE ROOTS

NerveRootsMuscles
Dorsal scapular nerveC5Rhomboid major & minor
Long thoracic nerveC5, C6, C7Serratus anterior
Contribution to phrenic nerveC5Diaphragm (partial)
EM pearl: Long thoracic nerve injury → winged scapula (serratus anterior paralysis). Seen in blunt chest trauma, backpack compression, or radical neck dissection.

FROM THE TRUNKS (Superior trunk only)

NerveRootsMuscles
Suprascapular nerveC5, C6Supraspinatus, Infraspinatus
Nerve to subclaviusC5, C6Subclavius

FROM THE LATERAL CORD

NerveNotes
Lateral pectoral nervePectoralis major
Musculocutaneous nerve (C5–C7)Coracobrachialis, biceps, brachialis → becomes lateral cutaneous nerve of forearm
Lateral root of median nerveJoins medial root to form median nerve

FROM THE MEDIAL CORD

NerveNotes
Medial pectoral nervePectoralis minor + major
Medial cutaneous nerve of armSkin, medial arm
Medial cutaneous nerve of forearmSkin, medial forearm
Medial root of median nerveJoins lateral root → median nerve
Ulnar nerve (C8, T1)Terminal branch

FROM THE POSTERIOR CORD

NerveRootsKey Targets
Upper subscapular nerveC5, C6Subscapularis (upper)
Thoracodorsal nerveC6–C8Latissimus dorsi
Lower subscapular nerveC5, C6Subscapularis (lower), teres major
Axillary nerveC5, C6Deltoid, teres minor, lateral cutaneous nerve of arm
Radial nerveC5–T1All posterior compartment muscles of arm + forearm
Gray's Anatomy for Students, p. 860–861

📊 COMPLETE PLEXUS DIAGRAM

Brachial Plexus - Major components in neck and axilla
Fig. 7.52 Brachial Plexus. Major components in neck and axilla. Gray's Anatomy for Students, p. 858

🚨 INJURIES — EMERGENCY MEDICINE BREAKDOWN

CLASSIFICATION: Seddon & Sunderland

SeddonSunderlandPathologyPrognosis
NeuropraxiaGrade IMyelin injury only, axon intact, conduction blockFull spontaneous recovery (days–weeks)
AxonotmesisGrade IIAxon + myelin disrupted, endoneurium intactRecovery by regeneration (1 mm/day)
AxonotmesisGrade IIIAxon + endoneurium disrupted, perineurium intactIncomplete recovery likely
AxonotmesisGrade IVAll except epineurium disruptedPoor recovery without surgery
NeurotmesisGrade VComplete nerve divisionNo recovery without surgical repair
EM pearl: Grades III–V require surgical referral. Surgical repair ideally within 1–2 months to prevent irreversible denervation changes.
  • Rockwood and Green's Fractures in Adults, 10th Ed., 2025

INJURY PATTERN 1 — ERB-DUCHENNE PALSY (Upper Trunk: C5–C6)

Mechanism:
  • Adults: fall from motorcycle, weight on shoulder, shoulder-neck angle forcefully widened
  • Neonates: shoulder dystocia, difficult delivery
Roots injured: C5, C6 (±C4)
Muscles paralyzed: Deltoid, biceps, brachialis, brachioradialis, supinator
Classic posture: "Waiter's tip" / "Policeman taking a tip"
  • Arm: adducted + internally rotated
  • Elbow: extended
  • Forearm: pronated
  • Wrist: flexed
Sensory loss: Lateral arm and upper lateral forearm (C5, C6 dermatomes)
Prognosis: Best prognosis of all brachial plexus injuries. Most common type (~90% of neonatal injuries).
S. Das Manual of Clinical Surgery, 13th Ed., p. 140; Miller's Review of Orthopaedics, 9th Ed., p. 260

INJURY PATTERN 2 — KLUMPKE'S PALSY (Lower Trunk: C8–T1)

Mechanism:
  • Forceful hyperabduction of arm (grabbing overhead support during a fall, breech delivery with arms raised)
Roots injured: C8, T1
Muscles paralyzed: Intrinsic hand muscles (lumbricals, interossei, thenar, hypothenar)
Clinical finding: Claw hand — combined features of median + ulnar nerve palsy
Sensory loss: Medial forearm, hand, medial 1.5 fingers
Horner Syndrome (ptosis, miosis, enophthalmos, anhidrosis): Present when T1 root is involved — sympathetic fibers to face travel with T1
Prognosis: Poor; <2% of neonatal cases
S. Das Manual of Clinical Surgery, 13th Ed., p. 140

INJURY PATTERN 3 — TOTAL PLEXUS PALSY (C5–T1)

  • Complete flaccid paralysis of the entire upper limb
  • Anaesthesia of the whole upper limb (sparing upper arm skin via C3–4)
  • Horner syndrome present (T1 involvement)
  • Worst prognosis
  • Occurs only in severe high-energy trauma

NERVE INJURY CLASSIFICATION TABLE (Emergency Quick Reference)

Injury TypeRootsPostureKey DeficitHorner?
Erb-DuchenneC5–C6Waiter's tipNo shoulder abduction, no elbow flexionNo
KlumpkeC8–T1Claw handNo intrinsic hand musclesYes (if T1)
Total plexusC5–T1Flail armComplete paralysis + anaesthesiaYes

🏥 EMERGENCY MEDICINE CLINICAL SCENARIOS

1. Shoulder Dislocation (Infraclavicular Plexus Injury)

Anterior shoulder dislocation is the most common EM cause of brachial plexus injury in adults. The infraclavicular plexus (cords level) is at risk.
  • Axillary nerve (C5–C6) most commonly injured: loss of deltoid function + patch of sensory loss over lateral arm ("regimental badge area")
  • Test axillary nerve before and after reduction: sensation over lateral deltoid
  • Musculocutaneous nerve may also be injured (loss of biceps)
  • [Rockwood and Green's Fractures, 2025] documents this as the most common nerve injury with shoulder dislocation
EM Action: Always document distal neurovascular exam before and after reduction. Check deltoid sensation, grip, biceps function.

2. Clavicle Fractures (Supraclavicular Plexus)

  • Displaced mid-shaft clavicle fractures can injure the supraclavicular plexus (trunks level)
  • Usually neuropraxia/axonotmesis — most recover
  • Check suprascapular nerve function (shoulder abduction + external rotation)
  • Also risk of subclavian vessel injury — always palpate distal pulses

3. High-Energy Polytrauma (Root Avulsion)

  • Common with motorcycle accidents (head forced away from shoulder during impact)
  • Nerve roots can be avulsed from the spinal cord — these are preganglionic injuries (worst type, no spontaneous recovery)
  • Associated with ipsilateral Horner syndrome, phrenic nerve palsy (C5 root), hemidiaphragm paralysis
  • MRI cervical spine for pseudomeningoceles (indicative of root avulsion)
  • [Grainger & Allison's Diagnostic Radiology] emphasizes avulsion occurs in polytrauma with traction force

4. Pancoast Tumor (Neoplastic Plexopathy)

  • Apical lung tumor (superior sulcus) invades the lower trunk (C8–T1) from below
  • Presents as:
    • Progressive hand weakness and wasting
    • Horner syndrome (sympathetic chain involvement)
    • Severe shoulder and medial arm pain
    • ± venous distension (SVC/subclavian vein compression)
  • EM red flag: unilateral hand weakness + Horner + shoulder pain in a smoker = Pancoast until proven otherwise
  • Confirmed with chest X-ray (apical mass) → CT chest
Harrison's Principles of Internal Medicine, 22nd Ed., 2025; S. Das Surgery, p. 140

5. Thoracic Outlet Syndrome (TOS)

  • Compression of the brachial plexus (and/or subclavian vessels) between the clavicle and first rib
  • Neurogenic TOS: lower trunk (C8–T1) most common → ulnar nerve-type pain, hand intrinsic wasting
  • Vascular TOS: subclavian artery/vein compression → arm ischemia, Raynaud's
  • EM presentation: effort thrombosis (Paget-Schroetter syndrome) — young athlete with arm swelling and pain

6. Parsonage-Turner Syndrome (Brachial Neuritis)

  • Sudden severe shoulder/arm pain followed by rapid motor deficits
  • Often post-viral, post-vaccination, or idiopathic
  • Affects individual nerve components, especially suprascapular nerve (infraspinatus, supraspinatus)
  • Mimics rotator cuff injury or cervical radiculopathy in the ED
  • No sensory level; MRI of brachial plexus shows enhancement in acute phase
Neuroanatomy through Clinical Cases, 3rd Ed.

🔑 EMERGENCY EXAM QUICK GUIDE

NerveRootTest
AxillaryC5, C6Deltoid contraction + lateral arm sensation
MusculocutaneousC5–C7Biceps contraction + lateral forearm sensation
RadialC5–T1Wrist/finger extension; posterior forearm sensation
MedianC6–T1Thumb opposition ("OK sign"); thenar wasting; palmar sensation
UlnarC8, T1Finger abduction ("spread fingers"); hypothenar wasting; little finger sensation

🔴 RED FLAGS IN THE ED

FindingThink
Flail arm + Horner after motorcycle crashRoot avulsion / total plexus injury
Waiter's tip after delivery/shoulder fallErb-Duchenne palsy (C5–C6)
Claw hand + Horner + medial arm painKlumpke's palsy / Pancoast tumor
Deltoid weakness after shoulder reductionAxillary nerve injury
Sudden shoulder pain + weak arm, no traumaParsonage-Turner syndrome
Young athlete with arm swelling + subclavian veinEffort thrombosis (TOS)
Winging of scapula after chest traumaLong thoracic nerve injury

📐 NERVE REGENERATION — EM PROGNOSTIC PEARLS

  • Nerve regenerates at approximately 1 mm/day after axonotmesis
  • Hofmann-Tinel sign (distal tingling on tapping) tracks regeneration front
  • Surgical repair must ideally occur within 1–2 months to maximize functional recovery
  • After brachial plexus injury: may take 12–18 months for axons to reinnervate distal targets
  • Lack of biceps function at 6 months = poor prognosis marker in birth palsy
  • Horner syndrome = T1 root involvement = poor prognosis
Rockwood and Green's Fractures in Adults, 10th Ed., 2025; Miller's Review of Orthopaedics, 9th Ed.
Sources:
  • Gray's Anatomy for Students (4th Ed.), pp. 858–861
  • S. Das — A Manual on Clinical Surgery (13th Ed.), p. 140
  • Rockwood and Green's Fractures in Adults (10th Ed., 2025)
  • Miller's Review of Orthopaedics (9th Ed.), p. 260
  • Harrison's Principles of Internal Medicine (22nd Ed., 2025)
  • Harriet Lane Handbook (23rd Ed.), p. 664
  • Grainger & Allison's Diagnostic Radiology
  • Bradley and Daroff's Neurology in Clinical Practice
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