Brachial plexus clinical correlations

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Brachial Plexus - Clinical Correlations

Anatomy Overview

The brachial plexus is formed by the anterior rami of C5-T1, passing between the anterior and middle scalene muscles before entering the axilla. Its organization follows a consistent pattern:

Brachial Plexus - Major Components in the Neck and Axilla

Fig. 7.52 - Gray's Anatomy for Students: Brachial plexus components including roots, trunks, divisions, and cords in the neck and axilla

Level	Structure	Composition
Roots	Anterior rami	C5, C6, C7, C8, T1
Trunks	Superior	C5 + C6
	Middle	C7 alone
	Inferior	C8 + T1
Divisions	Anterior + Posterior	From each trunk
Cords	Lateral	Anterior divisions of superior + middle trunks
	Medial	Anterior division of inferior trunk
	Posterior	All three posterior divisions

The cords are named for their relationship to the axillary artery. Terminal branches arise from the cords: musculocutaneous (lateral cord), axillary and radial (posterior cord), and median (lateral + medial cords) and ulnar (medial cord).

Brachial Plexus Schematic - Roots to Terminal Branches

Miller's Review of Orthopaedics: Complete brachial plexus schematic from C5-T1 roots to terminal nerves

Pre-Trunk Branches (Supraclavicular)

These arise proximal to the trunks and are clinically important because their injury helps localize the lesion level:

Nerve	Origin	Muscle	Clinical sign
Dorsal scapular n.	C5 root	Rhomboids	Winging of scapula (with serratus palsy)
Long thoracic n.	C5, C6, C7 roots	Serratus anterior	Winging of scapula - the vertebral border becomes prominent
Suprascapular n.	Upper trunk (C5, C6)	Supraspinatus, Infraspinatus	Shoulder abduction and external rotation weakness
Nerve to subclavius	Upper trunk (C5, C6)	Subclavius	Clinically silent

Classic Plexus Injury Syndromes

1. Erb's Palsy (Erb-Duchenne) - Upper Trunk Injury (C5, C6)

Mechanism: Forcible widening of the angle between the neck and shoulder. Occurs in:

Difficult delivery (head pulled while shoulder is arrested) - commonest obstetric injury, 0.4-4% of live births
Fall of a load on the shoulder
Motorcycle accidents; forced shoulder depression

Structures damaged: Superior trunk (C5, C6) - suprascapular nerve, musculocutaneous nerve, and axillary nerve are most affected.

Deformity - "Waiter's tip" / "Policeman's tip" position:

Arm hangs adducted and internally rotated at the shoulder (deltoid + supraspinatus weakness)
Elbow extended (loss of biceps/brachialis)
Forearm pronated (loss of supinator)
Wrist and fingers are in slight flexion (extensors are weakened)

Motor losses:

Deltoid (axillary n.) - abduction of arm above 15°
Supraspinatus/infraspinatus (suprascapular n.) - abduction initiation, external rotation
Biceps/brachialis (musculocutaneous n.) - elbow flexion
Brachioradialis - weakened

Reflexes lost: Biceps jerk (C5, C6), brachioradialis reflex

Sensory loss: Lateral aspect of arm and forearm (C5, C6 dermatomes)

Obstetric Erb's palsy prognosis: Over 90% resolve by 3 months. Biceps function is the key prognostic indicator. Surgical plexus reconstruction is considered at 3 months if no spontaneous recovery. - Miller's Review of Orthopaedics, p. 156; Bradley and Daroff's Neurology, p. 2870

2. Klumpke's Palsy - Lower Trunk Injury (C8, T1)

Mechanism: Forcible hyperabduction of the arm (e.g., catching a support while falling, birth traction with arm over head). Less common than Erb's palsy.

Structures damaged: Inferior trunk (C8, T1) → medial cord → ulnar nerve and medial head of median nerve are primarily affected.

Deformity - "Claw hand" (Main en griffe):

Hyperextension at metacarpophalangeal joints
Flexion at proximal and distal interphalangeal joints
Due to paralysis of intrinsic hand muscles (interossei and lumbricals)
The flexor digitorum profundus and superficialis are intact, but unopposed - they pull the IP joints into flexion; the absent intrinsics cannot extend the IP joints

Motor losses:

All intrinsic muscles of the hand (interossei, hypothenar, thenar - especially abductor pollicis brevis)
Flexors of the wrist and fingers may be affected in severe cases

Reflexes lost: Finger jerk; triceps jerk may be affected if C8 root is involved

Sensory loss: Medial aspect of the forearm and hand (C8, T1) - ulnar 1.5 digits and medial forearm

Horner's syndrome: When T1 root is avulsed, sympathetic fibers (which travel with T1 gray rami communicantes to the stellate ganglion) are disrupted → ipsilateral ptosis, miosis, enophthalmos, and anhidrosis - S Das Manual of Clinical Surgery, p. 127; Schwartz's Principles of Surgery, p. 1876

3. Complete Brachial Plexus Injury (C5-T1)

Rarest and most severe type
Flail arm: total loss of motor function in the upper limb
Complete sensory loss
Associated with high-velocity trauma (motorcyclists)
Horner's syndrome indicates root avulsion at T1

Individual Nerve Injury Correlations

Axillary Nerve (C5, C6) - Posterior cord

Common causes: Anterior shoulder dislocation, fracture of the surgical neck of humerus, intramuscular injections in the deltoid (quinine), direct blows to the lateral shoulder

Deficits:

Deltoid paralysis → loss of arm abduction beyond 15° and forward flexion
Teres minor paralysis → loss of external rotation
Sensory loss: "Regimental badge area" - lateral aspect of the proximal arm

Test: Ask patient to abduct the arm against resistance. Look for flattening of the shoulder contour.

Musculocutaneous Nerve (C5, C6, C7) - Lateral cord

Common causes: Coracobrachialis entrapment, penetrating injuries

Deficits:

Biceps and brachialis paralysis → loss of elbow flexion (most powerful in supination)
Coracobrachialis weakness
Sensory loss: Lateral forearm (lateral cutaneous nerve of the forearm)

Radial Nerve (C5-T1) - Posterior cord

Classic injury site - Spiral groove of humerus (mid-shaft humeral fracture or "Saturday night palsy"):

Deficits:

Wrist drop - inability to extend the wrist; the hand hangs limp in flexion at the wrist
Loss of finger and thumb extension (extensor digitorum, extensor pollicis longus/brevis)
Weakened elbow flexion in the mid-prone position (brachioradialis)
Triceps is spared in spiral groove injuries (triceps branch arises more proximally)

Axillary injury (above spiral groove, e.g., crutch palsy): Triceps weakness is added to the above picture.

Posterior interosseous nerve (deep branch): No sensory loss; only finger drop (cannot extend MCPJs); wrist can still be extended (radial wrist extensors are spared because they arise before the nerve enters the radial tunnel).

Sensory loss: Dorsum of hand and lateral 3.5 digits (superficial radial nerve)

- Schwartz's Principles of Surgery, p. 1876

Median Nerve (C6-T1) - Lateral + Medial cords

Carpal tunnel (most common entrapment site):

Night pain, waking from sleep, shaking the hand for relief
Thenar wasting (abductor pollicis brevis)
Positive Tinel's and Phalen's tests
Sensory loss: Lateral 3.5 digits (palm side)

Anterior interosseous nerve syndrome (pure motor branch):

Loss of flexor pollicis longus + flexor digitorum profundus to index and middle fingers
"OK sign" failure - patient cannot make a precise pinch (the distal phalanges extend instead of flexing, producing a flattened pinch)

High median nerve injury (above elbow, e.g., supracondylar fracture):

All above + loss of wrist flexion (flexor carpi radialis)
Partial loss of finger flexion (FDP to ring/little = intact, supplied by ulnar)
"Pointing index" / "Pope's blessing" deformity: When trying to make a fist, the index and middle fingers remain relatively extended because their FDP is non-functional, but the ring and little fingers flex normally

Sensory loss: Lateral palm, lateral 3.5 digits including tips of index and thumb (critical for fine sensation)

Ulnar Nerve (C8, T1) - Medial cord

Common injury sites:

Medial epicondyle / cubital tunnel (most common entrapment)
Guyon's canal at the wrist

Deficits:

Claw hand - particularly pronounced in ring and little fingers (ulnar two digits); less severe than Klumpke's because the lumbricals to index and middle fingers (supplied by median nerve) still function → "ulnar paradox" (low ulnar lesion produces a worse claw than high ulnar lesion, because high lesion also paralyzes FDP to ring/little, partially equalizing finger IP flexion force)
Hypothenar wasting (abductor digiti minimi, opponens digiti minimi)
First dorsal interosseous wasting (visible in the first web space)
Loss of finger abduction/adduction (all interossei)
Froment's sign: Patient compensates for paralyzed adductor pollicis by flexing the IP joint of the thumb (flexor pollicis longus, median nerve) when gripping a piece of paper

Sensory loss: Medial 1.5 digits and medial palm; at elbow level the dorsum of the hand is also affected

Special Clinical Syndromes

Pancoast Tumor (Superior Sulcus Tumor)

An apical lung tumor that invades the lower trunk of the brachial plexus from below.

Pancoast's Syndrome:

Insidious onset of pain in the upper arm / medial forearm
Sensory disturbance in the medial forearm and hand (C8, T1 distribution)
Weakness and atrophy of intrinsic hand muscles (lower trunk involvement)
Ipsilateral Horner's syndrome - ptosis, miosis, enophthalmos, anhidrosis (pressure on the stellate ganglion / sympathetic chain)
Distension of veins of the face, neck and thorax (superior vena cava compression in advanced disease)

Key point: Pancoast tumor invades the lower trunk (C8-T1). Contrast with radiation-induced plexopathy (which tends to affect the upper trunk, C5-C6, after treatment of breast or lung cancer). - S Das Manual, p. 413; Harrison's 22E, p. 3658

Thoracic Outlet Syndrome (TOS)

Mechanism: Compression of the lower trunk of the brachial plexus (or subclavian vessels) at the thoracic outlet - between the clavicle and first rib, or by a cervical rib.

Key feature - neurogenic TOS:

Weakness of all intrinsic hand muscles (not restricted to a single nerve distribution)
Sensory loss mainly in ulnar distribution (C8, T1 sensory fibers travel in the lower trunk, but median sensory fibers to the hand ascend through the middle trunk, which is spared)
Low-amplitude median and ulnar compound motor action potentials on EMG/NCS
Cervical rib may be present on imaging but is often asymptomatic

"Thoracic outlet syndrome is an overdiagnosed condition" - Bradley and Daroff's Neurology

Parsonage-Turner Syndrome (Neuralgic Amyotrophy / Immune-Mediated Brachial Plexus Neuropathy)

Hallmark: Acute, severe, burning shoulder pain lasting days to weeks, followed by weakness and sensory loss as the pain subsides.

Mechanism: Immune-mediated (can follow viral illness, surgery, vaccination, or occur idiopathically)

Pattern: Most commonly affects the upper trunk - suprascapular nerve (shoulder weakness), long thoracic nerve (winging of scapula), or axillary nerve. The phrenic and anterior interosseous nerves may also be affected.

Management: Empirical glucocorticoids for severe pain in the acute phase; physiotherapy for recovery. Attacks may recur (hereditary neuralgic amyotrophy - SEPT9 mutation). - Harrison's 22E, p. 3658

Obstetric Brachial Plexus Palsy

Feature	Erb's Palsy	Klumpke's Palsy
Roots	C5, C6	C8, T1
Mechanism	Shoulder dystocia, lateral neck traction	Arm forced over head
Frequency	Common (20x more frequent)	Rare
Deformity	Waiter's tip / policeman's tip	Claw hand
Reflexes lost	Biceps, brachioradialis	Finger jerk
Horner's	No	Yes (if T1 root avulsed)
Prognosis	>90% resolve by 3 months	Worse, incomplete recovery common
Prognostic marker	Biceps function recovery by 2-4 weeks	-

- Bradley and Daroff's Neurology in Clinical Practice, p. 2870; Miller's Review of Orthopaedics, p. 156

Long Thoracic Nerve Injury (C5, C6, C7 roots)

Causes: Carrying heavy loads on the shoulder, radical mastectomy, spontaneous (Parsonage-Turner)

Deficits: Paralysis of serratus anterior → winging of scapula (vertebral border of the scapula becomes prominent, especially when pushing against a wall)

Clinical test: Ask the patient to push against a wall with both arms extended - the medial scapular border lifts off on the affected side.

Summary Table - Nerve Injuries and Characteristic Signs

Nerve	Common cause	Motor deficit	Sensory loss	Classic sign
Axillary	Shoulder dislocation	Deltoid, teres minor	Lateral arm	"Regimental badge" area loss
Musculocutaneous	Coracobrachialis entrapment	Biceps, brachialis	Lateral forearm	Weak supinated elbow flexion
Radial (spiral groove)	Midshaft humerus #, Saturday night palsy	Wrist/finger extensors	Dorsum hand	Wrist drop; triceps intact
Radial (axillary)	Crutch palsy	+ Triceps	Dorsum hand	Wrist drop + triceps weakness
Median (wrist)	Carpal tunnel syndrome	Thenar (APB)	Lateral 3.5 digits	Thenar wasting, Tinel's/Phalen's
Median (elbow)	Supracondylar fracture	+FPL, FDP index/middle	Lateral palm + digits	Pointing index / Pope's blessing
Ulnar (elbow)	Cubital tunnel	Intrinsics, hypothenar	Medial 1.5 digits + dorsum	Claw hand, Froment's sign
Long thoracic	Carrying heavy loads	Serratus anterior	None	Winging of scapula
Upper trunk (C5-6)	Delivery, fall on shoulder	Deltoid, biceps, spinati	C5/6 dermatomal	Waiter's tip (Erb's palsy)
Lower trunk (C8-T1)	Hyperabduction, Pancoast	Intrinsic hand muscles	C8/T1 dermatomal	Claw hand ± Horner's

Sources:

Gray's Anatomy for Students, pp. 858, 1170
Schwartz's Principles of Surgery 11e, p. 1876
Miller's Review of Orthopaedics 9e, p. 156
Bradley and Daroff's Neurology in Clinical Practice, pp. 2869-2870
Harrison's Principles of Internal Medicine 22E, p. 3658
S Das Manual on Clinical Surgery 13e, pp. 127, 413

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