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Radial Nerve Anatomy

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Radial Nerve Anatomy

Comprehensive guide to the anatomy, course, branches, and clinical correlations of the Radial Nerve

complete
Updated: 2025-12-20
High Yield Overview

RADIAL NERVE ANATOMY

The Great Extensor Nerve of the Upper Limb

C5-T1Root Origin
PosteriorCord Origin
ExtensorFunction
SpiralKey Danger Zone

KEY ZONES

Axilla
PatternCompression affects triceps + extensors (Crutch Palsy)
TreatmentRemove compression
Spiral Groove
PatternTriceps spared, wrist drop present (Saturday Night Palsy)
TreatmentObservation (good prognosis)
Elbow
PatternPIN compression (Arcade of Frohse)
TreatmentRelease
Wrist
PatternSuperficial sensory compression (Wartenberg)
TreatmentRelease/Avoidance

Critical Must-Knows

  • Originates from Posterior Cord (C5-T1)
  • Passes through Triangular Interval to enter Spiral Groove
  • Pierces Lateral Intermuscular Septum 10cm proximal to lateral epicondyle
  • Divides into Superficial (Sensory) and Deep (PIN) at lateral epicondyle
  • PIN enters Supinator via Arcade of Frohse

Examiner's Pearls

  • "
    Triceps is usually SPARED in humeral shaft fractures (innervation is proximal)
  • "
    ECRL is innervated by Radial Nerve proper (before division)
  • "
    ECRB is often innervated by Radial Nerve proper or PIN
  • "
    Mobile Wad = BR, ECRL, ECRB

Clinical Imaging

Imaging Gallery

Dissection showing the variation of radial nerve (DL: deltoid; LoHT, LtHT and MHT: Long, lateral and medial head of triceps brachii, respectively; 1: radial nerve; 2, 3, 4: branches to LoHT, LtHT and
Click to expand
Dissection showing the variation of radial nerve (DL: deltoid; LoHT, LtHT and MHT: Long, lateral and medial head of triceps brachii, respectively; 1: Credit: Yogesh A et al. via J Neurosci Rural Pract via Open-i (NIH) (Open Access (CC BY))
The branches of the brachial plexus on the left side. AN, axillary nerve; CNA, medial cutaneous nerve of the arm; CNF, medial cutaneous nerve of the forearm; DM, deltoid muscle; I, inferior; L, latera
Click to expand
The branches of the brachial plexus on the left side. AN, axillary nerve; CNA, medial cutaneous nerve of the arm; CNF, medial cutaneous nerve of the fCredit: Viswanathan U et al. via Anat Cell Biol via Open-i (NIH) (Open Access (CC BY))
a Representative image showing the LAFF design with the lateral intermuscular septum as the central axis and the lateral condyle at the inferior trisection point of flap. The flap had the shape of an
Click to expand
a Representative image showing the LAFF design with the lateral intermuscular septum as the central axis and the lateral condyle at the inferior triseCredit: Yang XD et al. via Head Face Med via Open-i (NIH) (Open Access (CC BY))
Dissection of right arm showing the additional slip of triceps brachii (AS) taking origin from MIS and lower part of medial border of humerus joining the other heads of triceps brachii. UN passing thr
Click to expand
Dissection of right arm showing the additional slip of triceps brachii (AS) taking origin from MIS and lower part of medial border of humerus joining Credit: Swamy R et al. via Ann Med Health Sci Res via Open-i (NIH) (Open Access (CC BY))

Critical Exam Concepts

The Septum Danger Zone

10cm Rule: The nerve pierces the lateral intermuscular septum approximately 10cm proximal to the lateral epicondyle. This is the danger zone in lateral approaches to the humerus.

Holstein-Lewis Fracture

Distal Third Spiral Fracture: High risk of radial nerve entrapment or injury as the nerve is tethered by the septum at this level.

Triceps Sparing

Differentiating Lesions: High lesions (Axilla) affect Triceps. Mid-shaft lesions (Spiral Groove) SPARE Triceps. This distinguishes Crutch Palsy from Saturday Night Palsy.

Finger Extension

Tenodesis Effect: Do not be fooled by 'extension' caused by wrist flexion. Isolate the MCP joints to test EDC.

FeatureKey DetailClinical Significance
OriginPosterior Cord (C5-T1)Shoulder dislocation can injure it
CourseSpiral Groove of HumerusVulnerable in shaft fractures (10-15%)
MotorALL Extensors of Arm/ForearmLoss = Wrist Drop
SensoryDorsal Hand (Webspace 1)Autonomous zone for testing
BifurcationAnterior to Lateral EpicondyleSplits into SRN (Sensory) + PIN (Motor)
Mnemonic

BESTBranches in the Arm

B
Brachioradialis
First branch in anterior compartment
E
Extensors
ECRL (and often ECRB)
S
Supinator
Branch from PIN
T
Triceps
Branches in axilla and spiral groove

Memory Hook:The Radial nerve is the BEST nerve for extension.

Mnemonic

BRECOrder of Innervation (Mobile Wad)

B
Brachioradialis
Proximal
R
Radial nerve proper
Source
E
ECRL
Distal to BR
C
Capsule/ECRB
Variable

Memory Hook:Break-fast is the first meal (Brachioradialis first).

Mnemonic

PL PSensory Branches (Proximal to Distal)

P
Posterior cutaneous (Arm)
Axilla
L
Lower lateral cutaneous
Spiral Groove
P
Posterior cutaneous (Forearm)
Spiral Groove

Memory Hook:People Love Pasta (3 branches before the hand).

Overview and Function

Functional Summary

The Radial Nerve is the nerve of extension. It extends the elbow, wrist, and fingers. It also supinates the forearm (when elbow is extended). Loss of function results in the classic "Wrist Drop".

Motor Innervation Summary

  • Arm: Triceps (Long, Lateral, Medial heads), Anconeus.
  • Lateral Epicondyle: Brachioradialis, ECRL, ECRB (variable).
  • Forearm (PIN): Supinator, EDC, EDM, ECU, APL, EPB, EPL, EIP.

These muscle groups represent the ordered motor recovery.

Sensory Distribution

  • Posterior Cutaneous Nerve of Arm: Posterior arm.
  • Lower Lateral Cutaneous Nerve of Arm: Lateral aspect of lower arm.
  • Posterior Cutaneous Nerve of Forearm: Strip down middle of posterior forearm.
  • Superficial Radial Nerve: Dorsal aspect of thumb, index, middle, and radial half of ring finger (proximal to PIP joints). Autonomous zone: First dorsal webspace.

This sensory map is crucial for localizing lesion levels.

Neurovascular

Origin and Proximal Course

Origin:

  • Continuation of the Posterior Cord of the Brachial Plexus.
  • Roots: C5, C6, C7, C8, (T1).
  • Lies posterior to the axillary artery.

The Triangular Interval:

  • The nerve exits the axilla entering the posterior compartment through the Triangular Interval.
  • Boundaries: Teres Major (superior), Long Head Triceps (medial), Humerus (lateral).
  • Contents: Radial Nerve + Profunda Brachii Artery.

Spiral Groove:

  • Winds around the humerus in the spiral groove (musculospiral groove) between lateral and medial heads of triceps.
  • Passes medial to lateral.
  • Innervates: Triceps (Lateral and Medial heads), Anconeus.

The spiral groove is the classic site for "Saturday Night Palsy".

Distal Arm and Elbow

Transition to Anterior:

  • Pierces the Lateral Intermuscular Septum approx. 10cm proximal to the lateral epicondyle.
  • Moves from Posterior → Anterior Compartment.
  • Lies between Brachialis (medial) and Brachioradialis (lateral).

Innervation Order:

  1. Brachioradialis
  2. ECRL
  3. ECRB (Variable - can be PIN)

Bifurcation:

  • Anterior to the lateral epicondyle (level of radiocapitellar joint).
  • Splits into:
    1. Superficial Radial Nerve (SRN): Purely sensory.
    2. Posterior Interosseous Nerve (PIN): Purely motor.

The Leash of Henry

The recurrent radial artery vessels ("Leash of Henry") overlie the nerve at the level of the bifurcation and must be ligated during the Henry approach.

Forearm Course

Posterior Interosseous Nerve (PIN):

  • Passes beneath the Arcade of Frohse (proximal edge of Supinator). Or supinator arch.
  • This is the most common site of compression.
  • Winds around radial neck within substance of Supinator.
  • Emerges in posterior compartment to innervate extensor muscles.
  • Terminates as a sensory twig to the wrist capsule.

Superficial Radial Nerve (SRN):

  • Runs deep to Brachioradialis in the forearm.
  • In distal third, it emerges posteriorly between BR and ECRL tendons ("Wartenberg's Point").
  • Becomes subcutaneous and divides into dorsal digital nerves.

Injury here leads to Wartenberg's Syndrome (purely sensory).

Classification Systems

Injury Levels & Patterns

LevelMotor LossSensory LossEponym
Axilla (High)Triceps, Wrist Ext, Finger ExtPost Arm, Forearm, Dorsal HandCrutch Palsy / Saturday Night (High)
Spiral Groove (Mid)Wrist Ext (Weak), Finger ExtPost Forearm, Dorsal Hand (Triceps Sparing)Saturday Night Palsy / Humeral #
Elbow (Low/PIN)Finger Ext, Thumb Ext (ECRL preserved → radial deviation)None (PIN is motor)PIN Syndrome
Wrist (Distal)NoneDorsal WebspaceWartenberg Syndrome

Clinical Assessment

Motor Testing

  • Triceps: Extend elbow against resistance (abduct shoulder to eliminate gravity).
  • Brachioradialis: Flex elbow in neutral rotation.
  • ECRL/B: Extend wrist (check for radial deviation).
  • EDC: Extend MCP joints (block wrist extension).
  • EPL: Retropulsion of thumb (lift thumb off table palm down).

Sensory Testing

  • Autonomous Zone: First dorsal webspace.
  • Any loss proximal suggests higher lesion.

Trick Movements

Patients with radial nerve palsy can appear to extend the wrist using finger flexion (tenodesis effect). Always isolate the joint being tested.

Investigations

Radiological Assessment

  • Plain X-rays: Humeral shaft fracture (Holstein-Lewis), Radial head fracture/dislocation.
  • Ultrasound: Can visualize nerve continuity in Holstein-Lewis fractures (nerve entrapped in callus?).
  • MRI: For soft tissue masses (lipoma, ganglion) compressing PIN.

Reliable imaging confirms the diagnosis.

EMG / NCS

Indications:

  • Assessing continuity in closed injuries (wait 3-4 weeks for Wallerian degeneration signs).
  • Monitoring recovery (looking for re-innervation potentials).
  • Differentiating PIN syndrome from Radial Tunnel Syndrome.

Timing: Baseline study immediately is of limited value. 3-4 weeks is optimal for first assessment.

Management of Palsy

Treatment Algorithm

Management Algorithm for Humeral Shaft Palsy

AcuteAssessment

Closed injury? Open? Check nerve function. Most are neurapraxia (85-90% recovery).

3-4 WeeksEMG Study

If no clinical recovery. Look for fibrillation potentials (denervation).

3-4 MonthsExploration vs Tendon Transfer

If no recovery by 3-4 months (and no advancing Tinel's), consider exploration + nerve graft OR tendon transfers.

LateTendon Transfers

Jones transfer (PT to ECRB, FCU to EDC, PL to EPL).

Tendon Transfers

The classic Jones Transfer for radial nerve palsy:

  1. Pronator Teres → ECRB (Restore Wrist Ext)
  2. FCU (or FCR) → EDC (Restore Finger Ext)
  3. Palmaris Longus → EPL (Restore Thumb Ext)

Surgical Approaches

Posterior Approach to Humerus

Indication: Distal 1/3 fractures, Exploration of Radial Nerve.

technique:

  • Midline posterior incision.
  • Identify interval between Long and Lateral heads of Triceps (proximal).
  • Or split Triceps midline (distal).
  • Identify Nerve: In spiral groove with Profunda Brachii artery.
  • Trace distally through lateral intermuscular septum.

Careful dissection preserves the nerve.

Anterolateral Approach

Indication: Mid/Proximal shaft, PIN decompression.

Technique:

  • Interval: Brachioradialis (Radial N) and Brachialis (Musculocutaneous N).
  • Nerve identified between these muscles.
  • CAUTION: Nerve pierces septum 10cm proximal to elbow. Don't strip too vigorously proximally on the lateral side.

Protection of the nerve is paramount.

Henry Approach (Volar)

Indication: PIN Decompression / Radius Fixation.

Technique:

  • Interval: BR (Radial) and FCR (Median).
  • Identify Superficial Radial Nerve under BR.
  • Follow proximally to bifurcation.
  • Ligate Leash of Henry.
  • Identify PIN entering Supinator.
  • Supinate forearm to move PIN away from incision site.

This approach gives excellent exposure of the radius.

Complications

ComplicationCausePreventionManagement
NeuromaInjury to SRNProtect Wartenberg's pointBury nerve end
Iatrogenic InjuryPlate fixation (humerus/radius)Identify and protectExplore/Repair
Failure to recoverNeurotmesisEarly exploration if openTendon transfers
Radial Tunnel SyndromeDynamic compressionRelease arcadeDecompression

Recovery and Rehab

Splinting

Dynamic Splinting: Use a dynamic extension splint (outrigger) to prevent flexor contractures and assist function while waiting for nerve recovery.

Physiotherapy

Maintain passive ROM of all joints. Prevent stiffness. Strengthen substitute muscles.

Outcomes and Prognosis

  • Humeral Shaft Compressive Palsy: 90% spontaneous recovery.
  • Holstein-Lewis: High rate of recovery, but some advocate early exploration if caused by spiral distal fracture (nerve may be encased).
  • Post-operative Palsy: If nerve was seen intact, observation. If nerve integrity unknown, consider exploration.

Special Topics and Variants

Wartenberg's Syndrome

Compression of Superficial Radial Nerve (SRN).

  • Site: Between Brachioradialis and ECRL tendons during pronation (scissoring effect).
  • Symptoms: Pain/Paresthesia in dorsal thumb/webspace. +ve Tinel's.
  • DDx: De Quervain's (Finkelstein test distinguishes).

Surgical release is rarely needed but effective.

Radial Tunnel Syndrome

Pain vs Palsy.

  • PIN Syndrome: Motor palsy (finger drop, radial deviation). Painless.
  • Radial Tunnel Syndrome: Pain in proximal forearm. No motor weakness. controversial diagnosis. Resembles Tennis Elbow but pain is 4cm distal to epicondyle.

Conservative management is the mainstay.

Evidence Base

Shao et al. - Radial Nerve Palsy in Humeral Shaft Fractures

1
Shao et al. • J Bone Joint Surg Br (2005)
Key Findings:
  • Systematic review of radial nerve palsy management
  • Overall recovery rate 88%
  • Spontaneous recovery in 92% of closed fractures
  • Recovery in 71% of secondary palsies (post-manipulation)
Clinical Implication: Expectant management is appropriate for most closed humeral shaft fractures with radial nerve palsy.
Limitation: Systematic review of heterogeneous studies.

Tendon Transfers for Radial Nerve Palsy

4
Chuinard • J Hand Surg (1990)
Key Findings:
  • Detailed the PT to ECRB transfer
  • FCU to EDC provides strong finger extension
  • PL to EPL restores independent thumb extension
  • Excellent functional outcomes reported
Clinical Implication: Standard algorithm for irreversible nerve injury.
Limitation: Review article / Technique description.

Ultrasound vs EMG for Radial Nerve

3
Bodner et al. • Ultrasound Med Biol (2001)
Key Findings:
  • Ultrasound correctly identified nerve pathology in 88% of cases
  • Useful for differentiating entrapment vs tear
  • Can visualize nerve continuity in humeral fractures
Clinical Implication: Ultrasound is a valuable early screening tool before waiting 3 weeks for EMG.
Limitation: Operator dependent.

Holstein-Lewis Fracture Incidence

3
Ekholm et al. • J Bone Joint Surg Am (2006)
Key Findings:
  • Overall radial nerve palsy rate 11.8% in humeral fractures
  • Distal third fractures had HIGHER risk (22%)
  • Spiral fractures of distal third (Holstein-Lewis) had highest risk
Clinical Implication: Distal third spiral fractures warrant higher vigilance for nerve entrapment.
Limitation: Retrospective study.

Early Exploration Outcomes

4
Sotereanos et al. • J Orthop Trauma (1999)
Key Findings:
  • Advocated early exploration for high-energy injuries or open fractures
  • Nerve often lacerated or interposed in these cases
  • Primary repair yields better results than delayed grafting
Clinical Implication: High energy mechanism may justify early exploration rather than observation.
Limitation: Small case series.

Anatomy Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Humeral Shaft Fracture

EXAMINER

"A patient presents with a mid-shaft humeral fracture and a wrist drop. Describe the anatomy of the radial nerve relevant to this injury."

EXCEPTIONAL ANSWER
The radial nerve originates from the posterior cord (C5-T1). In the axilla, it gives branches to the long and medial heads of the triceps. It enters the spiral groove of the humerus via the triangular interval, running with the profunda brachii artery. In the spiral groove, it lies directly against the bone, making it vulnerable to fractures. At this level, it supplies the lateral and medial heads of the triceps. It pierces the lateral intermuscular septum approx 10cm proximal to the lateral epicondyle to enter the anterior compartment. A fracture at the mid-shaft (Spiral Groove) typically causes a wrist drop but spares the triceps (innervated proximally). This is a key clinical sign.
KEY POINTS TO SCORE
Posterior Cord Origin
Spiral Groove with Profunda Brachii
Pierces Lateral Septum 10cm proximal to elbow
Triceps spared in mid-shaft fractures
COMMON TRAPS
✗Thinking triceps is paralyzed (it's spared)
✗Forgetting the artery (Profunda Brachii)
✗Not mentioning the septum piercing
LIKELY FOLLOW-UPS
"What is a Holstein-Lewis fracture?"
"When would you explore this nerve?"
VIVA SCENARIOStandard

Scenario 2: PIN Syndrome

EXAMINER

"Describe the course of the Posterior Interosseous Nerve and the potential sites of compression."

EXCEPTIONAL ANSWER
The PIN is the deep motor branch of the radial nerve. It arises anterior to the lateral epicondyle. It passes between the two heads of the supinator muscle. The proximal edge of the superficial head of the supinator is thickened in 30% of people, forming the Arcade of Frohse, the most common site of compression. Other compression sites include the Leash of Henry (radial recurrent vessels) and the fibrous edge of ECRB. The PIN supplies the extensors of the wrist and fingers (ECRB, EDC, EDM, ECU, APL, EPB, EPL, EIP). Compression leads to finger drop and inability to extend the thumb, but wrist extension is preserved (ECRL spared) though often with radial deviation.
KEY POINTS TO SCORE
Deep motor branch
Arcade of Frohse (Supinator edge) is key site
Leash of Henry is another site
Supplies all extensors except ECRL/BR
Radial deviation of wrist in palsy
COMMON TRAPS
✗Confusing PIN syndrome with Radial Tunnel Syndrome (Pain vs Palsy)
✗Forgetting ECRL is spared
LIKELY FOLLOW-UPS
"What is the Arcade of Frohse?"
"How do you test for PIN function?"
VIVA SCENARIOChallenging

Scenario 3: Wartenberg Syndrome

EXAMINER

"A patient has paresthesia over the dorsal thumb and index finger. Differentiate Wartenberg's Syndrome from De Quervain's Tenosynovitis."

EXCEPTIONAL ANSWER
Both present with pain/symptoms over the radial styloid/dorsal thumb. Wartenberg's is a compression neuropathy of the Superficial Radial Nerve (SRN), typically as it emerges between Brachioradialis and ECRL. Symptoms are sensory (paresthesia, numbness) in the dorsal webspace. Tinel's sign over the nerve is positive. De Quervain's is a stenosing tenosynovitis of the first dorsal compartment (APL/EPB). Finkelstein's test (ulnar deviation with thumb in fist) is positive and creates sharp pain, but usually NO numbness. However, severe swelling in De Quervain's can compress the SRN, causing overlap.
KEY POINTS TO SCORE
Wartenberg = SRN Compression (Neuropathy)
De Quervain = Tendonitis (1st Compartment)
Tinel's positive in Wartenberg
Finkelstein's positive in De Quervain
Sensation altered in Wartenberg
COMMON TRAPS
✗Confusing the two (they coexist)
✗Thinking Wartenberg involves motor loss (SRN is sensory only)
LIKELY FOLLOW-UPS
"Where does the SRN emerge?"
"What is the autonomous zone of the radial nerve?"

MCQ Practice Points

Nerve Root Origin

Q: What is the primary root value of the Radial Nerve? A: C5-T1. It is the largest branch of the brachial plexus and receives fibers from all roots (continuation of posterior cord).

Septum Piercing

Q: Where does the radial nerve pierce the lateral intermuscular septum? A: 10cm proximal to the lateral epicondyle. This is a critical landmark for the anterolateral approach.

Tendon Transfer

Q: Which muscle is used to restore wrist extension in a radial nerve palsy? A: Pronator Teres. It is transferred to the ECRB tendon (PT → ECRB).

Arcade of Frohse

Q: What anatomical structure forms the Arcade of Frohse? A: The proximal fibrotendinous edge of the Supinator muscle.

Mobile Wad

Q: Which three muscles make up the Mobile Wad of Henry? A: Brachioradialis, ECRL, and ECRB.

Australian Context

Guidelines

  • Trauma Guidelines: Emphasize expectant management for closed humeral fractures with nerve palsy.
  • Testing: Standardized ASIA examination protocols.

Medicolegal

  • Iatrogenic Injury: Radial nerve injury during humerus plating is a known risk. Documentation of pre-op nerve status is mandatory.
  • Tourniquet Palsy: Radial nerve is vulnerable to tourniquet pressure.

High-Yield Exam Summary

Key Anatomy

  • •Posterior Cord (C5-T1)
  • •Triangular Interval (with Profunda Brachii)
  • •Lateral Intermuscular Septum (pierces 10cm proximal to elbow)
  • •Arcade of Frohse (Supinator edge) - PIN compression site
  • •Wartenberg's Point (Distal radius) - SRN emergence
  • •Lister's Tubercle - EPL turns around it (supplied by PIN)

Branches (Motor)

  • •Axilla: Long/Medial Triceps
  • •Spiral Groove: Lateral/Medial Triceps, Anconeus
  • •Elbow: Brachioradialis, ECRL, ECRB
  • •PIN: Supinator, EDC, EDM, ECU, APL, EPB, EPL, EIP

Clinical Signs

  • •Wrist Drop (High lesion)
  • •Finger Drop + Radial Deviation (PIN lesion)
  • •Triceps Sparing (Spiral Groove lesion)
  • •First Dorsal Webspace Numbness (Radial Nerve proper/SRN)
  • •Tinel's at Wartenberg's point (Wartenberg Syndrome)

Surgical Pearls

  • •Find nerve in interval between Brachialis and Brachioradialis (Anterior)
  • •Ligate 'Leash of Henry' (Radial Recurrent vessels)
  • •Supinate forearm to move PIN away from incision (Henry approach)
  • •Beware nerve 10cm proximal to lateral epicondyle in lateral plating
Quick Stats
Reading Time60 min
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