Peripheral Nerve Injuries and Palsies

Article Last Updated:22/06/2026

Peripheral Nerve Injuries and Palsies

Peripheral nerve injuries and palsies cause characteristic patterns of motor weakness, sensory loss and reflex changes depending on the affected nerve. This article summarises high-yield upper and lower limb peripheral nerve anatomy, brachial plexus injuries, and common peripheral nerve palsies including median, ulnar, radial, femoral, sciatic, common peroneal and tibial nerve lesions.

Disclaimer:

The anatomy of peripheral nerves is based on standard textbook descriptions. However, exact nerve root values, sensory territories and muscle innervation patterns can vary slightly between sources and between individuals.

Upper Limb

Normal Anatomy

Upper limb motor and sensory innervation is mainly supplied by the brachial plexus, formed from the anterior rami of C5–T1 nerve roots.

Major branches of the brachial plexus:

Nerve	Nerve root	Motor supply	Sensory supply
Axillary nerve	C5-C6	Deltoid Teres minor	Lateral shoulder and upper arm (“regimental badge” area)
Musculocutaneous nerve	C5-C7	BBC: Biceps brachii Brachialis Coracobrachialis	Lateral forearm
Median nerve	C5-T1	Most anterior forearm flexors and pronators (apart from FCU and medial half FDP) LOAF thenar muscles Lateral 2 lumbricals Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis	Palmar aspect of the lateral 2/3 of the hand (palm and 1st-3.5th finger) Dorsal aspect of the lateral fingers (1st-3.5th finger) (but not the lateral hand, which is innervated by the radial nerve)
Ulnar nerve	C8-T1	Hand intrinsic muscles (apart from LOAF thenar muscles) FCU Medial half FDP	Palmar and dorsal aspect of 3.5-5th finger (medial half of the ring finger + whole little finger)
Radial nerve	C5-T1	Posterior arm (triceps brachii and anconeus) Supinators Brachioradialis Posterior forearm extensors	Dorsal aspect of the lateral hand (proximal aspect of the 1st-3.5th finger) (not the finger itself, which is innervated by the median nerve) Posterior aspect of the arm and forearm
Long thoracic nerve	C5-C7	Serratus anterior	n/a (pure motor nerve)
Thoracodorsal nerve	C6-C8	Latissimus dorsi
Suprascapular nerve	C5-C6	Supraspinatus Infraspinatus
Subscapular nerve	C5-C6	Subscapularis

Upper Limb Nerve Injuries and Palsies

Brachial Plexus Injuries

Erb palsy

Affects the upper trunk of the brachial plexus (usually involving C5-C6)

Commonly caused by excessive lateral traction on the neck (increase in the angle between the neck and the shoulder)

Birth trauma (e.g. shoulder dystocia, breech deliveries)
Falling off a motorcycle or horse and landing on the shoulder while the head is pushed to the opposite side

Presentation:

“Waiter’s tip” posture – due to paralysis of specific muscle groups
- Arm adduction
- Arm internal rotation
- Forearm pronation
- Elbow extension
- Wrist and digit flexion (mimicking a waiter subtly asking for a tip)
Motor and reflex deficits
- Absent Moro reflex on the affected side (in neonates)
- Loss of shoulder abduction + elbow flexion + forearm supination
- Reduced / absent biceps reflex
- Normal hand movement and grip strength (unlike in Klumpke palsy)
Sensory deficit
- Lateral arm and forearm

Klumpke palsy

Affects the lower trunk of the brachial plexus (usually involving C8-T1)

Commonly caused by hyperabduction of the upper limb (increase in the angle between the arm and trunk)

Birth trauma (e.g. shoulder dystocia, breech deliveries)
Traumatic injuries (e.g. falling from a height and instinctively reaching out to grab an object, violently catching the body’s full weight by 1 arm)
Non-traumatic compressions (rare)
- Pancoast tumours
- Cervical ribs (thoracic outlet syndrome)

Presentation:

“Claw hand”
- MCP joint hyperextension
- IP joint flexion
- Most obvious in the ring and little fingers
Motor and reflex deficits
- Loss of grip strength
- Paralysis of intrinsic hand muscles
- Preserved shoulder and elbow movement (unlikely in Erb palsy)
Sensory deficit
- Medial forearm and hand
Ipsilateral Horner’s syndrome (as T1 sympathetic fibres run closely to the inferior trunk)
- Ptosis (drooping eyelid)
- Miosis (constricted pupil)
- Anhidrosis (lack of sweating)

Common Upper Limb Peripheral Nerve Palsies

Affected peripheral nerve	Causes	Motor deficit	Sensory deficit
Axillary nerve	Anterior shoulder dislocation – most common Proximal humeral fracture Improper crutch use	Deltoid muscle involvement → impaired shoulder abduction beyond the initial 15 degrees Teres minor involvement → impaired external rotation Deltoid atrophy → flattening shoulder contour	Lateral aspect of the shoulder and upper arm (“Regimental badge”)
Musculocutaneous nerve	Hyperabduction / hyperextension of the arm (e.g. in football, heavy weightlifting) Anterior shoulder dislocation / humeral fracture	Impaired: Elbow flexion – most prominent Forearm supination (due to biceps brachii involvement) Impaired biceps reflex	Lateral forearm
Median nerve	High median nerve palsy (elbow and above) Supracondylar fracture of the humerus Elbow dislocations Pronator teres syndrome	Ape hand deformity Hand of Benediction Impaired wrist flexion and forearm pronation	Palmar aspect of the lateral 2/3 of the hand (palm and 1st-3.5th finger) Dorsal aspect of the lateral fingers (1st-3.5th finger)
Median nerve	Low median nerve palsy (wrist level) Carpal tunnel syndrome Wrist trauma / laceration Lunate bone dislocation	Ape hand deformity Hand of Benediction is NOT seen in low median nerve palsy. Wrist flexion and forearm pronation are also spared.	Palmar aspect of the lateral fingers (1st-3.5th finger) Dorsal aspect of the lateral fingers (1st-3.5th finger) The sensation of the central palm and thenar eminence is spared in low median nerve palsy (specifically if the damage is confined inside or distal to the carpal tunnel (e.g. carpal tunnel syndrome).
Ulnar nerve	High ulnar nerve palsy (at or above the elbow) Cubital tunnel syndrome Medial epicondyle fracture of the humerus	Less severe claw hand Loss of intrinsic hand function (finger abduction, adduction) Wasting of hypothenar eminence and interosseous spaces Impaired wrist flexion +ve Froment’s sign	Palmar and dorsal aspect of 3.5-5th finger (medial half of the ring finger + whole little finger)
Ulnar nerve	Low ulnar nerve palsy (wrist or hand level) Compression in the Guyon’s canal Hook of hamate fracture Wrist trauma / laceration	Severe claw hand Loss of intrinsic hand function (finger abduction, adduction) Wasting of hypothenar eminence and interosseous spaces +ve Froment’s sign Wrist flexion is spared	Palmar aspect of 3.5-5th finger (medial half of the ring finger + whole little finger) Dorsal aspect of the 3.5-5th finger is spared
Radial nerve	High lesion (axilla level): “Saturday night palsy” Improper crutch use Axillary dislocation / trauma	Impaired: Elbow extension (due to triceps involvement) Forearm supination Wrist extension → wrist drop Finger and thumb extension	Posterior arm Posterior forearm Dorsal hand and web space
	Mid-arm lesion (spiral groove level) Humeral shaft fracture “Honeymoon palsy” Prolonged tourniquet or cuff pressure	Impaired: Wrist extension → wrist drop Finger and thumb extension Elbow extension and forearm supination are spared	Dorsal hand and web space Sensation of the posterior arm and forearm is spared
	Low lesion (forearm / wrist level) PIN palsy Radial tunnel syndrome Radial head dislocation / fracture Superficial radial nerve palsy Wrist trauma / laceration Tight handcuffs or wristwatches	Impaired: Wrist extension Finger and thumb extension There is no true wrist drop	If PIN (a pure motor nerve) is affected → normal sensation If superficial radial nerve (sensory branch) is affected → web space only
Long thoracic nerve	Lymph node dissection Chest tube insertion Direct chest trauma (e.g. stab or gunshot wounds) Repetitive overhead sports (e.g. swimming, tennis, weight lifting)	Serratus anterior weakness → scapular winging deformity	n/a (long thoracic nerve is a pure motor nerve)
Thoracodorsal nerve	Lymph node dissection Chest tube insertion Direct chest trauma (e.g. stab or gunshot wounds)	Latissimus dorsi weakness → weakness in shoulder extension, adduction and internal rotation Patient would struggle with movements like pulling themselves up, climbing, rowing	n/a (thoracodorsal nerve is a pure motor nerve)
Suprascapular nerve	Fracture / dislocation of the scapula or clavicle Chronic stretching from repetitive overhead actions (e.g. volleyball, baseball pitching)	Supraspinatus weakness → impaired shoulder abduction of the first 15 degrees Infraspinatus weakness → impaired shoulder external rotation	n/a (suprascapular nerve is a pure motor nerve)
Subscapular nerve	Posterior shoulder dislocation Penetrating wounds to the back of the axilla	Subscapularis and teres major weakness → Impaired shoulder internal rotation +ve Lift-off test	n/a (subscapular nerve is a pure motor nerve)

Lower Limb

Normal Anatomy

Lumbar plexus (L1-L4):

Nerve	Nerve root	Motor supply	Sensory supply
Iliohypogastric nerve	L1 (+T12)	Internal oblique Transversus abdominis	Lateral gluteal region Skin over pubic bone
Ilioinguinal nerve	L1	Internal oblique Transversus abdominis	Upper medial thigh Root of penis / scrotum or labia majora
Genitofemoral nerve	L1-L2	Cremaster muscle (in males)	Genital branch: anterior scrotum / labia majora Femoral branch: upper anterior thigh
Lateral femoral cutaneous nerve	L2-L3	None (pure sensory)	Anterolateral thigh
Obturator nerve	L2-L4	Hip adductors	Medial thigh
Femoral nerve	L2-L4	Hip flexors (sartorius, iliacus, pectineus) Quadriceps femoris	Anteromedial thigh Medial leg (via the saphenous nerve)

Sacral plexus (L4-S4):

Nerve	Nerve root	Motor supply	Sensory supply
Superior gluteal nerve	L4-S1	Gluteus medius and minimus Tensor fasciae latae	None (pure motor)
Inferior gluteal nerve	L5-S2	Gluteus maximus	None (pure motor)
Posterior femoral cutaneous nerve	S1-S3	None (pure sensory)	Posterior thigh and popliteal fossa
Sciatic nerve: tibial division	L4-S3	Posterior thigh (hamstrings) Posterior leg compartment	Posterior leg Sole of the foot
Sciatic nerve: common peroneal division	L4-S2	Deep peroneal nerve: anterior leg compartment (tibialis anterior, extensor digitorum longus, extensor hallucis longus) Superficial peroneal nerve: lateral leg compartment (fibularis longus and brevis)	Deep peroneal nerve: web space between 1st and 2nd toe Superficial peroneal nerve: anterolateral leg and dorsum of the foot (apart from the web space)
Pudendal nerve	S2-S4	External anal sphincter Urethral sphincter muscles Levator ani	Perineum Posterior scrotum / labia Penis / clitoris

Lower Limb Nerve Injuries and Palsies

Common Lumbar Plexus Peripheral Nerve Palsies

Affected peripheral nerve	Causes	Motor deficit	Sensory deficit
Ilioinguinal nerve	Inguinal hernia repair Appendectomies Lower abdominal incisions (e.g. Pfannenstiel incision for C section) Direct blunt trauma to the lower abdomen	Weakness is rarely noticeable	Groin Upper medial thigh Scrotum / labia majora
Genitofemoral nerve	Tight clothing near the groin (esp. in obese individuals) Inguinal hernia repair Appendectomies	Loss of cremasteric reflex in males	Upper anterior thigh Scrotum / labia majora
Lateral femoral cutaneous nerve	Most commonly due to nerve entrapment under a tight inguinal ligament, risk factors include: Obesity Pregnancy Tight clothing / belts	n/a (pure sensory nerve)	Also known as meralgia paraesthetica: burning pain / tingling / numbness over the anterolateral thigh Symptoms are typically aggravated by prolonged standing / walking
Obturator nerve	Pelvic fractures Anterior hip dislocation Pelvic lymph node dissection Obturator hernia	Weakness of hip adduction Unstable gait – leg abducts during walking	Medial thigh
Femoral nerve	Hip replacement Pelvic / hip fractures Retroperitoneal haematoma	Impaired knee extension Impaired hip flexion Reduced or absent patellar reflex	Anteromedial thigh Medial leg (via saphenous nerve)

Common Sacral Plexus Peripheral Nerve Palsies

Affected peripheral nerve	Causes	Motor deficit	Sensory deficit
Sciatic nerve	Posterior hip dislocation Hip replacement IM injection error Piriformis syndrome	Impaired knee flexion Complete paralysis of all muscles below the knee Absent Achilles reflex	Entire leg and foot Posterior thigh
Common peroneal nerve	Proximal fibular fracture Prolonged lateral decubitus position (e.g. colonoscopy) Prolonged leg crossing Tight casts Knee splints	Impaired dorsiflexion → foot drop → high steppage gait Impaired toe extension Impaired eversion	Lateral leg Dorsum of the foot
Tibial nerve	Popliteal fossa trauma Posterior knee dislocation Tibial fracture Tarsal tunnel syndrome	Impaired plantarflexion → unable to stand on tiptoes Impaired toe flexion Impaired foot inversion Absent / reduced Achilles reflex	Sole of the foot
Superior gluteal nerve	IM injection error Posterior hip dislocation Pelvic fracture Posterior hip surgical approaches	Trendelenburg sign	n/a (pure motor)
Inferior gluteal nerve		Difficulty climbing stairs or standing from a seated position (due to impaired hip extension) Wasted, flattened buttock contour	n/a (pure motor)
Pudendal nerve	Cyclist’s syndrome Obstetric trauma Pelvic ring fracture Pelvic or retroperitoneal surgery	Weakness or loss of control over the external anal and urethral sphincters May lead to faecal or urinary incontinence	Perineum Posterior scrotum / labia Penis / clitoris

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Peripheral Nerve Injuries and Palsies

Peripheral Nerve Injuries and Palsies

Upper Limb

Normal Anatomy

Upper Limb Nerve Injuries and Palsies

Brachial Plexus Injuries

Common Upper Limb Peripheral Nerve Palsies

Lower Limb

Normal Anatomy

Lower Limb Nerve Injuries and Palsies

Common Lumbar Plexus Peripheral Nerve Palsies

Common Sacral Plexus Peripheral Nerve Palsies

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