CHAPTER: Brachial Plexus
TOPIC: Formation and Components of the Brachial Plexus
SUBTOPIC: Definition and Overview
The brachial plexus is a network of nerves formed by the anterior primary rami (ventral rami) of the lower four cervical and first thoracic spinal nerves — C5, C6, C7, C8, and T1 — with minor contributions from C4 and T2 in some individuals. It innervates the entire upper limb.
The plexus consists of five sequential components:
| Component | Number | Location |
|---|---|---|
| Roots | 5 | Neck — between scalenus anterior and scalenus medius |
| Trunks | 3 | Posterior triangle of neck |
| Divisions | 6 (3 anterior + 3 posterior) | Behind the clavicle |
| Cords | 3 | Axilla — around the axillary artery |
| Branches | 5 terminal + collateral | Axilla and arm |
SUBTOPIC: Roots
- Constituted by the anterior primary rami of C5, C6, C7, C8, and T1
- Located in the neck, deep to scalenus anterior
- Emerge in the gap between scalenus anterior (anterior) and scalenus medius (posterior)
- C4 and T2 make minor contributions in some individuals
Prefixed plexus: C4 contribution is large; T2 is often absent; plexus shifted one segment upward.
Postfixed plexus: T1 contribution is large; T2 is always present; C4 is absent; C5 is reduced in size; plexus shifted one segment downward.
SUBTOPIC: Trunks
Three trunks are formed in the posterior triangle of the neck, in the cleft between scalenus medius (behind) and scalenus anterior (in front):
| Trunk | Formed by |
|---|---|
| Upper trunk | C5 + C6 roots |
| Middle trunk | C7 root alone |
| Lower trunk | C8 + T1 roots |
SUBTOPIC: Divisions
Each of the three trunks divides into an anterior and a posterior division — six divisions in total.
- Lie behind the clavicle
- Anterior divisions supply the anterior (flexor) compartment of the limb
- Posterior divisions supply the posterior (extensor) compartment of the limb
SUBTOPIC: Cords
Three cords are named by their relationship to the second part of the axillary artery (the part lying posterior to pectoralis minor):
| Cord | Formed by | Position relative to axillary artery |
|---|---|---|
| Lateral cord | Anterior divisions of upper trunk + middle trunk | Lateral side |
| Medial cord | Anterior division of lower trunk alone | Medial side |
| Posterior cord | Posterior divisions of all three trunks | Posterior |
SUBTOPIC: Sympathetic Contribution
Sympathetic fibres for the upper limb are derived from spinal segments T2–T6:
- Preganglionic fibres travel via white rami communicantes to the sympathetic chain
- They ascend and synapse in the middle cervical, inferior cervical, and first thoracic (stellate) ganglia
- Postganglionic fibres re-enter the brachial plexus roots via grey rami communicantes
- Functions: vasomotor (constrict skin arterioles), sudomotor (sweat secretion), pilomotor (arrector pili)
TOPIC: Branches of the Brachial Plexus
SUBTOPIC: Supraclavicular Branches — From Roots
| Branch | Root Value | Supply |
|---|---|---|
| Long thoracic nerve (nerve to serratus anterior; Bell’s nerve) | C5, C6, C7 | Serratus anterior |
| Dorsal scapular nerve (nerve to rhomboids) | C5 | Rhomboideus major, rhomboideus minor, levator scapulae (partly) |
| Branches to scaleni and longus colli | C5–C8 | Scalene muscles, longus colli |
| Contribution to phrenic nerve | C5 | Diaphragm (minor contribution) |
SUBTOPIC: Supraclavicular Branches — From Trunks
Both named trunk branches arise from the upper trunk only. The middle and lower trunks give no named branches.
| Branch | Root Value | Supply |
|---|---|---|
| Suprascapular nerve | C5, C6 | Supraspinatus, infraspinatus |
| Nerve to subclavius | C5, C6 | Subclavius |
SUBTOPIC: Erb’s Point
Erb’s point is the region of the upper trunk where six nerves meet:
- Ventral ramus of C5 root
- Ventral ramus of C6 root
- Suprascapular nerve (from upper trunk)
- Nerve to subclavius (from upper trunk)
- Anterior division of upper trunk
- Posterior division of upper trunk
Injury at Erb’s point produces Erb’s paralysis (upper plexus injury).
SUBTOPIC: Infraclavicular Branches — From Lateral Cord
| Branch | Root Value | Supply |
|---|---|---|
| Lateral pectoral nerve | C5, C6, C7 | Pectoralis major (clavicular head) |
| Musculocutaneous nerve | C5, C6, C7 | Coracobrachialis, biceps brachii, brachialis; lateral cutaneous nerve of forearm |
| Lateral root of median nerve | C5, C6, C7 | Unites with medial root to form median nerve |
SUBTOPIC: Infraclavicular Branches — From Medial Cord
| Branch | Root Value | Supply |
|---|---|---|
| Medial pectoral nerve | C8, T1 | Pectoralis major (sternocostal head) and pectoralis minor |
| Medial cutaneous nerve of arm | T1 | Skin of medial side of arm |
| Medial cutaneous nerve of forearm | C8, T1 | Skin of medial side of forearm |
| Medial root of median nerve | C8, T1 | Unites with lateral root to form median nerve |
| Ulnar nerve | C7, C8, T1 | See Ulnar Nerve topic |
SUBTOPIC: Infraclavicular Branches — From Posterior Cord
| Branch | Root Value | Supply |
|---|---|---|
| Upper subscapular nerve | C5, C6 | Subscapularis (upper part) |
| Thoracodorsal nerve (nerve to latissimus dorsi) | C6, C7, C8 | Latissimus dorsi |
| Lower subscapular nerve | C5, C6 | Subscapularis (lower part) and teres major |
| Axillary nerve | C5, C6 | Deltoid, teres minor; skin over lower deltoid |
| Radial nerve | C5, C6, C7, C8, T1 | See Radial Nerve topic |
SUBTOPIC: Five Terminal Nerves — Summary
| Nerve | Origin | Root Value |
|---|---|---|
| Musculocutaneous | Lateral cord | C5, C6, C7 |
| Median | Lateral cord + medial cord | C5, C6, C7, C8, T1 |
| Ulnar | Medial cord | C7, C8, T1 |
| Radial | Posterior cord | C5, C6, C7, C8, T1 |
| Axillary | Posterior cord | C5, C6 |
The median nerve is the only terminal nerve formed from two cords.
SUBTOPIC: Segmental Control of Upper Limb Movements
| Movement | Spinal Segments |
|---|---|
| Adduction of shoulder | C5 |
| Abduction of shoulder | C5, C6 |
| Flexion of elbow | C5, C6 |
| Extension of elbow | C6, C7 |
| Flexion of wrist and fingers | C8, T1 |
| Small muscles of hand | T1 |
TOPIC: Relations of the Brachial Plexus
SUBTOPIC: Supraclavicular Part — Relations in the Neck
The roots and trunks lie in the posterior triangle of the neck:
- Roots emerge between scalenus anterior (anteriorly) and scalenus medius (posteriorly)
- Trunks occupy the cleft between scalenus medius (behind) and scalenus anterior (in front)
- The plexus passes over the first rib to enter the axilla through the cervico-axillary canal
| Direction | Relation |
|---|---|
| Anteriorly | Skin, platysma, investing fascia, sternocleidomastoid |
| Posteriorly | Scalenus medius, serratus posterior superior |
| Medially | Scalenus anterior (separates roots from subclavian artery) |
| Superiorly | Subclavian artery (runs between the scalene muscles, medial to the plexus) |
The subclavian vein lies anterior to scalenus anterior, separated from the brachial plexus by that muscle.
SUBTOPIC: Infraclavicular Part — Relations in the Axilla
The brachial plexus enters the axilla through the apex (cervico-axillary canal) together with the axillary artery, enclosed within the axillary sheath.
Relation of cords to parts of the axillary artery:
| Part of Axillary Artery | Cord Relations |
|---|---|
| First part (medial to pectoralis minor) | All three cords lie posteriorly |
| Second part (posterior to pectoralis minor) | Cords in their named positions — lateral, medial, posterior |
| Third part (lateral to pectoralis minor) | Cords give terminal branches that surround the artery |
Relations of the infraclavicular plexus to axillary walls:
| Axillary Wall | Nerve Relation |
|---|---|
| Anterior wall (pectoralis minor) | Lateral and medial pectoral nerves |
| Posterior wall (subscapularis, teres major, latissimus dorsi) | Subscapular nerves, thoracodorsal nerve, axillary nerve |
| Medial wall (serratus anterior) | Long thoracic nerve descends on the medial wall |
| Lateral wall (humerus) | Musculocutaneous nerve pierces coracobrachialis |
SUBTOPIC: Axillary Sheath
- A prolongation of the prevertebral fascia from the neck into the axilla
- Encloses the brachial plexus and the axillary artery together as a continuous fascial compartment
- Local anaesthetic injected into this sheath for brachial plexus block can spread up toward the scalene muscles
SUBTOPIC: Structures at Risk During Axillary Surgery
During axillary lymph node dissection (e.g., for breast cancer):
| Structure | Consequence of Injury |
|---|---|
| Intercostobrachial nerve | Anaesthesia or dysaesthesia along medial arm |
| Long thoracic nerve | Winging of scapula |
| Thoracodorsal nerve | Weakness of latissimus dorsi; impaired adduction and medial rotation of arm |
| Thoracodorsal artery | Bleeding |
SUBTOPIC: Cervical Rib and Thoracic Outlet Syndrome
A cervical rib arising from C7 may compress the lower trunk (C8, T1) as it passes over the rib. This produces:
- Neurological features of lower trunk compression — weakness and wasting of intrinsic hand muscles, sensory loss along medial forearm and hand (Klumpke-type distribution)
- Vascular compromise of the subclavian artery
Together these constitute thoracic outlet syndrome.
TOPIC: Intercostobrachial Nerve
SUBTOPIC: Origin, Course, and Clinical Relevance
The intercostobrachial nerve is the lateral cutaneous branch of the second intercostal nerve. It is not a branch of the brachial plexus.
Course:
- Pierces the lateral thoracic wall
- Crosses the axilla
- Supplies skin of the medial side of the arm and the axillary floor
- Communicates with the medial cutaneous nerve of the arm (from the medial cord of the brachial plexus)
Clinical relevance:
- Lies within the axilla during axillary lymph node dissection for breast cancer
- Division produces anaesthesia or dysaesthesia (often a burning or numb sensation) along the medial upper arm
- Enlargement of central axillary lymph nodes (e.g., in cancer) can compress this nerve, causing pain along the inner border of the arm
TOPIC: Axillary Nerve
SUBTOPIC: Origin and Course
Origin: Posterior cord of the brachial plexus (C5, C6)
Course:
- Arises in the axilla at the lower border of subscapularis
- Passes posteriorly through the quadrangular space with the posterior circumflex humeral artery
- The quadrangular space is bounded by: teres minor (above), teres major (below), long head of triceps (medially), surgical neck of humerus (laterally)
- Winds around the surgical neck of the humerus
- Divides into anterior and posterior branches deep to deltoid
- Intimately related to the medial aspect of the surgical neck of the humerus, just inferior to the shoulder joint capsule
SUBTOPIC: Branches, Motor Supply, and Sensory Supply
Posterior branch:
- Motor to teres minor (carries a pseudoganglion)
- Motor to posterior part of deltoid
- Continues as the upper lateral cutaneous nerve of the arm — sensory to skin over the lower half of deltoid (the regimental badge area)
Anterior branch:
- Motor to deltoid (anterior and middle parts)
- Small cutaneous branches through the muscle
Articular branch: To the shoulder joint
SUBTOPIC: Axillary Nerve Injury
Causes: Fracture of the surgical neck of humerus; inferior dislocation of the shoulder; improper injection into the upper deltoid
Effects:
- Paralysis of deltoid → loss of shoulder abduction from 15° to 90°
- Flattening of the shoulder contour (loss of deltoid bulk; greater tubercle becomes prominent)
- Sensory loss over the regimental badge area (lower half of deltoid)
TOPIC: Musculocutaneous Nerve
SUBTOPIC: Origin and Course
Origin: Lateral cord of the brachial plexus (C5, C6, C7)
Course:
- Arises in the axilla
- Pierces coracobrachialis (supplying it)
- Runs between biceps brachii (anterior) and brachialis (posterior) in the arm, supplying both
- Emerges lateral to the biceps tendon at the elbow
- Continues as the lateral cutaneous nerve of the forearm
SUBTOPIC: Motor and Sensory Supply
Motor: Coracobrachialis, biceps brachii, brachialis
- Biceps brachii: powerful supinator of the forearm (when elbow flexed); flexor of forearm; weak flexor of shoulder
- Brachialis: principal flexor of the forearm
- Coracobrachialis: weak flexor and adductor of arm
Sensory: Lateral cutaneous nerve of the forearm → lateral aspect of the forearm (anterior and posterior surfaces)
SUBTOPIC: Musculocutaneous Nerve Injury
Effects:
- Loss of forearm flexion (brachialis and biceps paralyzed; brachioradialis supplied by radial nerve remains intact for weak flexion)
- Loss of forearm supination
- Loss of biceps jerk (C5, C6)
- Sensory loss over lateral forearm
TOPIC: Radial Nerve
SUBTOPIC: Origin and Course
Origin: Posterior cord of the brachial plexus (C5, C6, C7, C8, T1) — the largest nerve of the brachial plexus
Course:
| Segment | Path | Branches given |
|---|---|---|
| Axilla | Posterior to third part of axillary artery; anterior to posterior axillary wall | Posterior cutaneous nerve of arm; nerves to long head and medial head of triceps |
| Arm — spiral groove | Between long and medial heads of triceps; then in the spiral (radial) groove of humerus with profunda brachii artery | Lateral head of triceps; lower lateral cutaneous nerve of arm; posterior cutaneous nerve of forearm; anconeus |
| Anterior compartment of arm | Pierces lateral intermuscular septum; runs between brachioradialis and brachialis | Brachioradialis; extensor carpi radialis longus (ECRL); small part of brachialis |
| Cubital fossa | Divides at the level of the lateral epicondyle into superficial and deep branches | — |
| Deep branch (posterior interosseous nerve) | Passes through supinator into posterior compartment of forearm | ECRB, supinator, all remaining extensors of forearm |
| Superficial branch | Deep to brachioradialis; emerges at the wrist | Dorsum of lateral two-thirds of hand; dorsal surface of lateral 3½ digits (excluding nail beds) |
SUBTOPIC: Motor and Sensory Supply
Motor supply:
- Back of arm: triceps (all three heads), anconeus
- Anterior compartment of arm: brachioradialis, ECRL, small part of brachialis
- Back of forearm (via posterior interosseous nerve): ECRB, supinator, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, extensor indicis
Sensory supply:
- Posterior cutaneous nerve of arm — back of arm
- Lower lateral cutaneous nerve of arm — lower lateral arm
- Posterior cutaneous nerve of forearm — back of forearm
- Superficial terminal branch — dorsal lateral two-thirds of hand; dorsal lateral 3½ digits (excluding nail beds)
- Autonomous sensory area: first web space on dorsum of hand
SUBTOPIC: Radial Nerve Injury — Axilla (Crutch Palsy)
Cause: Pressure of the crutch top on the radial nerve in the axilla
Effects:
- Paralysis of triceps → loss of elbow extension
- Wrist drop — loss of wrist extension (paralysis of wrist extensors)
- Loss of finger extension
- Loss of supination with elbow extended
- Sensory loss over back of arm, back of forearm, lateral dorsum of hand, and lateral 3½ digits
SUBTOPIC: Radial Nerve Injury — Spiral Groove (Saturday Night Palsy)
Causes:
- Midshaft fracture of humerus (radial nerve lies in direct contact with bone in the spiral groove)
- Prolonged pressure on the nerve from an arm draped over a chair back (classically in intoxication)
Important anatomical point: The injury occurs distal to the origin of the branches to the long and medial heads of triceps → elbow extension is preserved (or only mildly weak).
Effects:
- Wrist drop (principal feature) — loss of wrist extension
- Loss of finger extension
- Loss of supination with elbow extended
- Sensory loss restricted to a small area over the dorsum of the hand between the first and second metacarpals (first web space)
SUBTOPIC: Radial Nerve Injury — Elbow (Radial Tunnel Syndrome)
Cause: Entrapment of the deep branch (posterior interosseous nerve) at the radial tunnel — Arcade of Frohse, fibrous bands, tendinous edge of ECRB, or radial recurrent vessels
Effects:
- Loss of extension of wrist and fingers
- No wrist drop — ECRL is supplied proximal to the division (before the nerve enters the radial tunnel) and remains intact
- Pain over the extensor aspect of the forearm
TOPIC: Median Nerve
SUBTOPIC: Origin and Course
Origin: Two roots — lateral root from the lateral cord (C5, C6, C7) and medial root from the medial cord (C8, T1). The roots unite in front of the third part of the axillary artery in a Y-shaped arrangement. The median nerve is the only terminal nerve of the brachial plexus formed from two cords.
Course:
| Segment | Key points |
|---|---|
| Axilla | Lateral to third part of axillary artery; no branches |
| Arm | No branches; crosses the brachial artery from lateral to medial at mid-humerus |
| Cubital fossa | Medial to brachial artery; gives branches to superficial flexors of forearm |
| Forearm | Passes between the two heads of pronator teres; gives off the anterior interosseous nerve |
| Wrist | Passes deep to the flexor retinaculum through the carpal tunnel; the palmar cutaneous branch is given off proximal to the wrist and passes superficial to the flexor retinaculum |
| Palm | Divides into the recurrent (thenar) branch and palmar digital branches |
SUBTOPIC: Motor and Sensory Supply
Motor — forearm:
- All superficial flexors except flexor carpi ulnaris: flexor carpi radialis, palmaris longus, flexor digitorum superficialis
- Via anterior interosseous nerve: flexor pollicis longus, lateral half of flexor digitorum profundus, pronator quadratus
Motor — hand (LOAF muscles):
- Lumbricals 1st and 2nd
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis (superficial head)
Sensory:
- Palmar aspect of lateral two-thirds of hand and lateral 3½ digits including nail beds
- Palmar cutaneous branch → skin over thenar eminence (passes superficial to flexor retinaculum — spared in carpal tunnel syndrome)
- Autonomous sensory area: pulp of the index finger
SUBTOPIC: High Median Nerve Injury (Above Elbow)
Deformity — Benediction attitude / Pope’s blessing hand:
When the patient attempts to make a fist:
- Index and middle fingers remain extended (lateral half of FDP is paralyzed; these fingers cannot flex at the DIP joints)
- Ring and little fingers flex normally (medial half of FDP supplied by ulnar nerve is intact)
The hand in attempted fist-making resembles a hand giving a blessing.
TOPIC: Carpal Tunnel Syndrome
SUBTOPIC: Definition and Cause
Carpal tunnel syndrome is the most common entrapment neuropathy. It results from compression of the median nerve within the carpal tunnel, deep to the flexor retinaculum at the wrist.
Predisposing factors: Hypothyroidism, rheumatoid arthritis, pregnancy, obesity, acromegaly, repetitive wrist use
SUBTOPIC: Clinical Features
Sensory (early):
- Burning pain, tingling, and paraesthesia in the lateral 3½ fingers (median nerve distribution)
- Symptoms are characteristically worse at night and may wake the patient from sleep
- Thenar eminence sensation is preserved — the palmar cutaneous branch of the median nerve passes superficial to the flexor retinaculum and is not compressed
Motor (later):
- Weakness of thenar muscles (abductor pollicis brevis, opponens pollicis, flexor pollicis brevis)
Established (advanced):
- Ape thumb deformity (simian hand) — thumb is adducted and lies extended in the plane of the palm due to thenar muscle wasting; the patient cannot oppose the thumb
SUBTOPIC: Diagnostic Tests
Tinel’s sign: Tapping over the carpal tunnel at the wrist reproduces tingling or paraesthesia in the median nerve distribution.
Phalen’s test: Sustained passive wrist flexion for 60 seconds reproduces the symptoms.
TOPIC: Ulnar Nerve
SUBTOPIC: Origin and Course
Origin: Medial cord of the brachial plexus (C7, C8, T1)
Course:
| Segment | Key points |
|---|---|
| Axilla | Between axillary artery and axillary vein; no branches |
| Arm | No branches; runs medial to brachial artery; pierces medial intermuscular septum at mid-humerus; enters posterior compartment; descends to the groove behind the medial epicondyle |
| Medial epicondyle | Lies in the cubital tunnel (covered by a fibrous band between medial epicondyle and olecranon); palpable here (“funny bone”) |
| Forearm | Between the two heads of flexor carpi ulnaris; supplies FCU and medial half of FDP; gives dorsal cutaneous branch near wrist; gives palmar cutaneous branch near wrist |
| Wrist — Guyon’s canal | Lateral to the pisiform, medial to the ulnar artery; divides into superficial (sensory) and deep (motor) branches |
SUBTOPIC: Motor and Sensory Supply
Motor — forearm: Flexor carpi ulnaris (FCU) and medial half of flexor digitorum profundus (FDP) — supplying flexion of ring and little fingers at DIP joints
Motor — hand (all intrinsics except LOAF):
- Hypothenar muscles (abductor digiti minimi, flexor digiti minimi, opponens digiti minimi)
- 3rd and 4th lumbricals
- All interossei (4 dorsal + 3 palmar)
- Adductor pollicis
- Deep head of flexor pollicis brevis
Sensory:
- Palmar aspect of medial one-third of hand and medial 1½ fingers
- Dorsal aspect of medial one-third of hand and medial 1½ fingers (via dorsal cutaneous branch)
- Autonomous sensory area: pulp of the little finger
SUBTOPIC: Ulnar Nerve Injury at the Medial Epicondyle
Causes: Fracture of medial epicondyle; repetitive elbow leaning; cubital tunnel syndrome
Motor effects:
- Loss of FCU → wrist deviates radially on flexion
- Loss of medial half of FDP → ring and little fingers cannot flex at DIP joints
- Paralysis of all interossei, 3rd and 4th lumbricals, hypothenar muscles, adductor pollicis
Sensory loss: Medial 1½ fingers and medial palm (palmar and dorsal surfaces)
TOPIC: Claw Hand
SUBTOPIC: Ulnar Claw Hand (Partial Claw Hand)
Produced by ulnar nerve injury at the medial epicondyle.
Mechanism:
- Interossei and 3rd and 4th lumbricals are paralyzed
- Paralysis of intrinsics removes the force that flexes the MCP joints and extends the IP joints
- Unopposed action of the long flexors and extensors produces the deformity
Deformity:
- Ring and little fingers: hyperextension at MCP joints + flexion at IP joints
- Index and middle fingers are relatively spared because their lumbricals (1st and 2nd) are supplied by the median nerve and remain functional
The claw is therefore partial (two fingers) — hence “ulnar claw hand.”
SUBTOPIC: Complete (True) Claw Hand
Produced by combined median and ulnar nerve injury.
Mechanism: All four lumbricals and all interossei are paralyzed. No intrinsic hand muscle remains to flex the MCP joints.
Deformity: Hyperextension at all four MCP joints + flexion at all IP joints — all four fingers clawed.
SUBTOPIC: Froment’s Sign
Test: The patient is asked to hold a sheet of paper (or card) between the thumb and index finger against the examiner’s pull.
Normal: Adductor pollicis (ulnar nerve) adducts the thumb to grip the paper; the thumb IP joint remains straight.
Positive sign: Adductor pollicis is paralyzed (ulnar nerve injury) → the patient compensates by flexing the distal phalanx of the thumb using flexor pollicis longus (median nerve) to maintain grip. The distal phalanx of the thumb visibly flexes.
Positive Froment’s sign indicates paralysis of adductor pollicis, confirming ulnar nerve injury.
TOPIC: Erb’s Paralysis
SUBTOPIC: Site, Mechanism, and Cause
Site: Upper trunk of the brachial plexus at Erb’s point (C5, C6; sometimes C7)
Mechanism: Forcible excessive increase in the angle between the head and the shoulder — separation of head and shoulder:
- Fall from a horse, landing on one shoulder
- Birth injury — excessive traction of the arm during difficult delivery
- Fall onto the shoulder from a height
- Arm position during anaesthesia (prolonged lateral tilt of head away from shoulder)
SUBTOPIC: Muscles Paralyzed and Deformity
Muscles paralyzed (C5 and C6): Deltoid, supraspinatus, infraspinatus, teres minor, biceps brachii, brachialis, brachioradialis, supinator, extensor carpi radialis longus
Deformity — Policeman’s tip / Waiter’s tip / Porter’s tip hand:
| Segment | Position | Cause |
|---|---|---|
| Arm | Adducted | Paralysis of deltoid and supraspinatus |
| Arm | Medially rotated | Paralysis of lateral rotators — supraspinatus, infraspinatus, teres minor |
| Elbow | Extended | Paralysis of biceps brachii and brachialis |
| Forearm | Pronated | Paralysis of biceps brachii (supinator action lost) |
The arm hangs limply by the side — adducted and medially rotated, with the elbow extended and forearm pronated.
SUBTOPIC: Sensory Loss, Reflexes, and Autonomic Signs
Sensory loss: Minimal — along the outer (lateral) aspect of the arm (C5, C6 distribution; regimental badge area)
Reflexes lost:
- Biceps jerk (C5, C6)
- Brachioradialis jerk (C5, C6)
Autonomic signs: Absent — sympathetic fibres travel via C8 and T1, which are unaffected in Erb’s paralysis
TOPIC: Klumpke’s Paralysis
SUBTOPIC: Site, Mechanism, and Cause
Site: Lower trunk of the brachial plexus (C8, T1; sometimes C7)
Mechanism: Hyperabduction of the arm — excessive upward pull on the arm:
- Clutching something with the hands after falling from a height
- Birth injury — extended arm in breech presentation
- Arm pulled upward into machinery
SUBTOPIC: Muscles Paralyzed and Deformity
Muscles paralyzed:
- All intrinsic muscles of the hand (T1) — interossei, lumbricals, thenar, hypothenar
- Ulnar flexors of wrist and fingers (C8) — flexor carpi ulnaris, medial half of flexor digitorum profundus
Deformity — Claw hand:
- Hyperextension at metacarpophalangeal joints (intrinsics paralyzed — no MP flexion)
- Flexion at interphalangeal joints (long flexors intact)
- Affects all four fingers (median nerve intrinsic supply — T1 fibres — is also interrupted)
SUBTOPIC: Horner’s Syndrome
Horner’s syndrome occurs when T1 is injured proximal to the white ramus communicans, interrupting the sympathetic fibres destined for the head and neck that leave the spinal cord through T1.
| Feature | Mechanism |
|---|---|
| Ptosis (partial drooping of upper eyelid) | Paralysis of superior tarsal muscle (Müller’s muscle) |
| Miosis (pupil constriction) | Paralysis of dilator pupillae |
| Anhydrosis (absent sweating on face and neck) | Loss of sympathetic sudomotor fibres |
| Enophthalmos (apparent recession of eyeball) | Paralysis of orbitalis muscle (Müller’s orbital muscle) |
| Loss of cilio-spinal reflex | Loss of sympathetic control |
Horner’s syndrome is present only when T1 is injured proximal to its white ramus communicans. If the injury is distal to this point, the sympathetic fibres are unaffected and Horner’s syndrome is absent.
SUBTOPIC: Sensory Loss and Vasomotor Changes
Sensory loss: Along the medial border of the forearm and hand (T1, C8 distribution)
Vasomotor changes:
- Skin in the area of sensory loss is warmer than normal — due to arteriolar dilation from loss of sympathetic vasoconstrictor tone
- Skin is drier than normal — due to absence of sweating from loss of sympathetic sudomotor activity
TOPIC: Erb’s Paralysis vs Klumpke’s Paralysis
| Feature | Erb’s Paralysis | Klumpke’s Paralysis |
|---|---|---|
| Nerve roots | C5 and C6 | C8 and T1 |
| Site of injury | Upper trunk — Erb’s point | Lower trunk |
| Cause | Head-shoulder separation; birth traction | Arm hyperabduction; upward pull |
| Muscles paralyzed | Deltoid, supraspinatus, infraspinatus, biceps, brachialis, brachioradialis, supinator, ECRL | All intrinsic hand muscles; FCU; medial half FDP |
| Deformity | Policeman’s/Waiter’s tip — arm adducted and medially rotated; elbow extended; forearm pronated | Claw hand — MP hyperextension and IP flexion, all four fingers |
| Sensory loss | Lateral aspect of arm (C5, C6) | Medial border of forearm and hand (T1, C8) |
| Reflexes lost | Biceps jerk; brachioradialis jerk | Finger flexion jerk |
| Autonomic signs | Absent | Present — Horner’s syndrome (if T1 injured proximal to white ramus) |
TOPIC: Winging of the Scapula
SUBTOPIC: Nerve, Cause, and Effects
Nerve injured: Long thoracic nerve (nerve to serratus anterior; Bell’s nerve) — root value C5, C6, C7
Cause:
- The long thoracic nerve arises from the posterior aspects of the C5, C6, and C7 roots in the neck, descends behind the brachial plexus, and runs along the lateral surface of serratus anterior. Its long, exposed course makes it vulnerable.
- Causes of injury: sudden downward pressure on the shoulder; carrying heavy loads on the shoulder; axillary lymph node dissection (most important surgical cause)
Serratus anterior function: Holds the medial border of the scapula against the thoracic wall; rotates the scapula upward (tilts glenoid upward) during overhead abduction.
Effects of paralysis:
- Winging of the scapula — the medial border of the scapula becomes prominent and lifts away from the thoracic wall. The rhomboids, now unopposed, pull the medial border medially and posteriorly.
- Winging is most visible when the patient pushes the outstretched arm against a wall.
- Loss of pushing, punching, and reaching-forward actions (protraction of scapula is lost)
- Arm cannot be raised beyond 90° — serratus anterior is required for the upward rotation of the scapula that is necessary for overhead abduction