High Yield Overview

ULNAR NERVE ANATOMY

The Musician's Nerve (Fine Motor Control)

C8-T1Root Origin

MedialCord Origin

IntrinsicFunction

CubitalKey Danger Zone

KEY ZONES

Axilla

PatternMedial Cord, medial to artery

TreatmentRarely compressed

Arcade of Struthers

PatternHiatus in medial intermuscular septum (8cm proximal to elbow)

TreatmentRelease

Cubital Tunnel

PatternOsborne's Ligament (most common compression)

TreatmentRelease +/- Transposition

Guyon's Canal

PatternWrist compression (Handlebar Palsy)

TreatmentRelease

Critical Must-Knows

Originates from Medial Cord (C8-T1)
Passes POSTERIOR to Medial Epicondyle
Enters forearm between two heads of FCU
Supplies all intrinsics EXCEPT LOAF (Lumb 1/2, Opponens, AbdPB, FlexPB)
Sensory to medial 1.5 fingers

Examiner's Pearls

"
Ulnar Paradox: High lesions claw LESS than low lesions (FDP paralysis)
"
Froment's Sign tests Adductor Pollicis (Ulnar), compensation by FPL (Median/AIN)
"
Struthers Arcade is in the ARM (Ulnar), Struthers Ligament is Supracondylar (Median)
"
Martin-Gruber Anastomosis: Median → Ulnar communication in forearm

Clinical Imaging

Imaging Gallery

Ulnar nerve anatomy at the elbow. The ulnar nerve courses posterior to the intermuscular septum and adjacent to the triceps. It passes posterior to the medial epicondyle before entering into the cubit — Ulnar nerve anatomy at the elbow. The ulnar nerve courses posterior to the intermuscular septum and adjacent to the triceps. It passes posterior to thCredit: Open-i / NIH via Open-i (NIH) (Open Access (CC BY))

Normal anatomy of the ulnar nerve in the cubital tunnel. Axial protondensity–weighted image demonstrates normal ulnar nerve (black arrow) in thecubital tunnel. The cubital tunnel is bordered by the me — Normal anatomy of the ulnar nerve in the cubital tunnel. Axial protondensity–weighted image demonstrates normal ulnar nerve (black arrow) in thecubitaCredit: Sampath SC et al. via Sports Health via Open-i (NIH) (Open Access (CC BY))

Cadaveric dissection of the right posterior elbowNote the ulnar nerve (crossing pin) as it travels deep into the ligament of Osborne seen here as a triangular connective tissue joining the proximal ul — Cadaveric dissection of the right posterior elbowNote the ulnar nerve (crossing pin) as it travels deep into the ligament of Osborne seen here as a trCredit: Open-i / NIH via Open-i (NIH) (Open Access (CC BY))

Critical Exam Concepts

The Ulnar Paradox

"High lesion = Less Clawing." In a high lesion (elbow), the FDP to the ring/little fingers is paralyzed, so the IP joints do not flex, masking the claw deformity. In a low lesion (wrist), FDP is intact, causing unopposed flexion of IP joints → Severe Clawing.

Froment's Sign

Tests Adductor Pollicis. Patient asked to hold paper between thumbs. If Adductor is weak (Ulnar), patient flexes IPJ (FPL - Median) to compensate. This is a positive sign.

Cubital Tunnel Floor

The floor is the MCL (Ulnar Collateral Ligament). Transposition is often indicated if the nerve subluxes or the bed is irregular (arthritic osteophytes).

Wartenberg's Sign

Abducted Little Finger. Due to weakness of Palmar Interossei (Adduction) and unopposed action of EDM (Radial) and Abductor Digiti Minimi (Ulnar - but often spared or less affected relative to mechanics). Note: Wartenberg's Syndrome is Radial sensory, Wartenberg's Sign is Ulnar motor.

Feature	Key Detail	Clinical Significance
Origin	Medial Cord (C8-T1)	Lower Trunk Plexopathy mimics Ulnar nerve
Elbow	Cubital Tunnel	#1 Compression site
Forearm	FCU + FDP (Medial 1/2)	Flexion of wrist/digits 4,5
Wrist	Guyon's Canal	#2 Compression site
Measurements	Arcade of Struthers (8cm)	Proximal to medial epicondyle

Mnemonic

HILAHand Intrinsics (Ulnar Supplied)

Hypothenar muscles

ADM, FDM, ODM

Interossei

Dorsal (Abduct) & Palmar (Adduct)

Lumbricals

Medial two (3 and 4)

Adductor Pollicis

Key muscle for Froment's

Memory Hook:Ulnar nerve is HILA-rious (supplies the HILA muscles).

Mnemonic

LOAFExceptions (Median Supplied)

Lumbricals (Lateral)

1 and 2

Opponens Pollicis

Thenar

Abductor Pollicis Brevis

Thenar

Flexor Pollicis Brevis

Superficial head

Memory Hook:Median nerve supplies the LOAF, Ulnar supplies the rest.

Mnemonic

ULNARClaw Hand Causes

Ulnar nerve palsy

Classic cause

Leprosy

Thickened nerve

Neuritis

Viral/Autoimmune

Amyotrophy

Diabetic/Neuralgic

Radiculopathy

C8/T1

Memory Hook:Differential diagnosis for clawing.

Overview and Function

Functional Summary

The Ulnar Nerve is the nerve of fine manipulation. It powers the intrinsic muscles that allow for grip strength, pinch, and complex finger movements. "Power Grip" relies heavily on ulnar-innervated intrinsic function to stabilize the MCP joints.

Motor Innervation Summary

Forearm: Flexor Carpi Ulnaris (FCU), FDP (Ring, Little).
Hypothenar: Abductor Digiti Minimi, Flexor Digiti Minimi, Opponens Digiti Minimi.
Hand: Palmar Interossei (3), Dorsal Interossei (4), Lumbricals (3, 4), Adductor Pollicis, Deep head FPB.

Total: 1.5 Forearm muscles + Most Hand Intrinsics.

The profound impact of this innervation is seen in the 'Intrinisic Minus' hand.

Neurovascular

Axilla & Arm Course

Origin:

Terminal branch of Medial Cord (C8, T1).
Often receives C7 fibers (from Lateral Cord).
Lies medial to axillary and brachial arteries.

Arm:

Runs in anterior compartment initially.
At mid-arm, it pierces the Medial Intermuscular Septum to enter the posterior compartment.
Arcade of Struthers: A band of fascia approx. 8cm proximal to medial epicondyle. A potential compression site (esp after transposition).
Runs distally towards the groove behind the medial epicondyle.

This proximal course is relatively safe from compression.

Classification Systems

McGowan Classification (Cubital Tunnel)

Standard formatting for grading compression neuropathy.

Grade	Clinical Findings	Prognosis
Grade I	Mild lesions, Paresthesia, No motor weakness	Good prognosis with conservaive/surgical
Grade II	Intermediate, Weakness of intrinsics, Wasting maybe absent	Good outcome likely
Grade III	Severe, Profound weakness, Atrophy, Clawing	Guaarded prognosis, permanent deficit common

Clinical Assessment

Inspection

Wasting: Hypothenar eminence and First Dorsal Interosseous (dorsum of webspace).
Clawing: Hyperextension of MCPJ and Flexion of IPJ (Ring/Little).
Wartenberg's Sign: Little finger sits abducted.

Provocation Tests

Tinel's: Tap over cubital tunnel and Guyon's canal.
Elbow Flexion Test: Patient flexes elbow fully, wrist extended. Hold 60s. Reproduction of symptoms (+ve).
Scratch Collapse Test: Sensitivity controversial.

Froment's Sign

Patient grasps paper between thumbs.
Positive: Flexion of IPJ (FPL) to compensate for weak Adductor Pollicis.
Jeanne's Sign: Hyperextension of MCPJ during pinch (instability).

Sensory Sparing

Dorsal ulnar sensation SPARED in Guyon's canal / Wrist lesions.
LOST in Cubital Tunnel / High lesions.

Differential Diagnosis

Condition	Differentiating Features	Key Test
C8 Radiculopathy	Neck pain, All medial hand muscles affected (incl Median)	Spurling's Test / MRI Neck
Lower Trunk Plexopathy	T1 fibers affected (AP loss), Horner's Syndrome (sometimes)	Chest X-Ray (Pancoast)
Thoracic Outlet Syndrome	Vascular signs, Positional provocation	Adson's Test / Doppler
MND (ALS)	Painless wasting, Fasciculations, Hyperreflexia	EMG (Widespread denervation)

Investigations

Radiology

X-rays: Check for bone spurs, cubitus valgus deformity, supracondylar spur (rare), or hook of hamate fracture (Guyon).
Ultrasound: Cross-sectional area over 10mm² suggests compression. Can see nerve instability (subluxation) in real-time.
MRI: Space-occupying lesions (ganglion cystic in Guyon's).

Advanced imaging is reserved for atypical cases or recurrences.

Management Strategy

Non-Operative Management

Indication: Mild symptoms (McGowan I), intermittent paresthesia.
Night Splinting: Prevents elbow flexion over 45 degrees. Keep arm straight-ish.
Activity Modification: Avoid resting elbows on tables, headset use.
NSAIDs: Adjunct.
Success: ~50% effective in mild cases.

Patient compliance is key to conservative success.

Surgical Technique: Decompression

In Situ Decompression

Op Tech: In Situ Decompression

IncisionPosteromedial Approach

Curvilinear incision over cubital tunnel, centered on epicondyle. Protect MABCN (Medial Antebrachial Cutaneous Nerve) crossing the field.

ReleaseStructures Released

Distal: Aponeurosis of FCU (two heads).
Tunnel: Osborne's Ligament (Roof).
Proximal: Arcade of Struthers and Medial Intermuscular Septum.

CheckStability Check

Flex elbow. Does nerve sublux? If yes → Transpose. If no → Close.

MABCN Injury

The MABCN branches cross the surgical field. Injury causes painful neuroma and numbness over the olecranon/posterior proximal forearm.

Room Setup & Logistics

Preparation Checklist

Position: Supine, Arm board, Tourniquet high on arm
Anesthesia: General or Regional (Block)
Equipment: Loupes/Microscope (optional but recommended), Nerve stimulator
Instruments: Basic plastic set, Tenotomy scissors, Vessel loops

Clinical Handoff

Phase	Action	Goal
Pre-Op	Mark incision, Confirm symptoms side	Avoid wrong site
Intra-Op	Identify MABCN, Release all 5 sites	Complete decompression
Post-Op	Soft dressing, Early ROM	Prevent stiffness

Complications

Complication	Cause	Management
MABCN Neuroma	Surgical trauma	Excision / Burying
Persistent Symptoms	Incomplete release (septum/FCU)	Revision Decompression
Nerve Subluxation	Excessive release anteriorly	Transposition
Medial Epicondyle Pain	Destabilized origin	Physio / Repair

Rehabilitation

Decompression: Early motion. Soft dressing. Avoid direct pressure.
Transposition: Immobilize 1-2 weeks to allow position to stabilize, then ROM.
Strengthening: Start at 6 weeks.

Rehabilitation Protocol

Phase	Timeframe	Goals	Precautions
Phase 1 (Protection)	0-2 Weeks	Wound healing, Edema control, Nerve gliding	Avoid resisted flexion
Phase 2 (Mobility)	2-6 Weeks	Full ROM, Scar management, Isometrics	No heavy lifting
Phase 3 (Strength)	6-12 Weeks	Progressive strengthening, Work hardening	Monitor for recurrence

Outcomes

Sensory recovery typically precedes motor.
Motor recovery: Unpredictable in severe cases (McGowan III). "Time is muscle." Intrinsic atrophy acts as a poor prognostic sign.
Intrinsic function may not fully return in elderly or long-standing cases (over 1 year).

Factors Influencing Recovery

Age: Patients over 50 years have poorer outcomes.
Duration: Symptoms over 1 year correlate with incomplete recovery.
Severity: Pre-operative muscle atrophy is difficult to reverse.
Site: Distal lesions (wrist) reinnervate faster than proximal (elbow), but intrinsic demand is high.

Expect paresthesia resolution first, then strength. Sensation may take months.

Special Scenarios

Ulnar Tunnel Syndrome

Causes: Ganglion cyst (most common - 50%), Hook breakdown (Golfer), Ulnar Artery Aneurysm (Hammer syndrome), Cyclist Palsy.

Akahori Classification

Zone	Location	Contents	Symptoms
Zone 1	Proximal to bifurcation	Motor + Sensory	Muscle weakness + Sensory loss (digits)
Zone 2	Distal to bifurcation (Around hook)	Deep Motor Branch	Motor weakness ONLY (Claw hand)
Zone 3	Distal (Superficial)	Superficial Sensory Branch	Sensory loss ONLY (No motor deficit)

Treatment: Decompression of tunnel, address pathology (remove cyst).

Anatomical knowledge of these zones aids in localizing the lesion.

Evidence Base

Simple Decompression vs Transposition

Zlowodzki et al. • Hand (2007)

Key Findings:

Meta-analysis of randomized controlled trials
No significant difference in outcomes scores
Complication rate lower in simple decompression

Clinical Implication: Simple decompression is the gold standard for primary cases without subluxation.

Limitation: Heterogeneous studies.

Endoscopic Release results

Watts et al. • J Hand Surg (2000)

Key Findings:

Minimal incision technique
Fast recovery, less scar pain
Higher risk of nerve injury/incomplete release in learning curve

Clinical Implication: Good option for experienced surgeons.

Limitation: Learning curve.

Ultrasound Diagnostic Criteria

Beekman et al. • Radiology (2004)

Key Findings:

Nerve area over 10mm² is diagnostic
Ratio of tunnel area to proximal area over 1.5
High sensitivity and specificity

Clinical Implication: Ultrasound is a reliable first-line investigation.

Limitation: Operator dependent.

Prognostic Factors

Dellon • Hand Clin (2002)

Key Findings:

Age over 50 associated with poorer outcome
Duration over 1 year associated with incomplete recovery
Muscle atrophy is the strongest negative predictor

Clinical Implication: Operate early before atrophy sets in.

Limitation: Review / Expert Opinion.

Submuscular Transposition Outcomes

Le Reste et al. • Orthop Traumatol Surg Res (2010)

Key Findings:

Effective for revision cases (failed decompression)
Significant improvement in 80% of recurrent cases
Longer recovery time

Clinical Implication: Procedure of choice for revision surgery.

Limitation: Retrospective.

Ulnar Nerve Vivas

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: The Claw Hand

EXAMINER

"A patient presents with clawing of the ring and little fingers. Explain the mechanism and the 'Ulnar Paradox'."

EXCEPTIONAL ANSWER

Clawing is caused by paralysis of the lumbricals and interossei (ulnar innervated). These muscles normally flex the MCPJs and extend the IPJs. When paralyzed, the Extensor Digitorum (Radial - unopposed) hyperextends the MCPJs, and the FDP (Ulnar - if intact) flexes the IPJs, creating the claw. The 'Ulnar Paradox' refers to the finding that high lesions (elbow) cause LESS clawing than low lesions (wrist). In high lesions, the FDP is also paralyzed, so the IPJs remain relaxed (less deformed). In low lesions, the FDP is intact and unopposed, pulling the IPJs into severe flexion, worsening the claw.

KEY POINTS TO SCORE

Intrinsic minus hand

Hyperextension of MCP (EDC)

Flexion of IP (FDP)

Ulnar Paradox mechanism

COMMON TRAPS

✗Failing to explain the role of FDP

✗Confusing with Benedict's Hand (Median)

LIKELY FOLLOW-UPS

"What is the Bouvier test?"

"How do you reconstruct a claw hand?"

VIVA SCENARIOStandard

Scenario 2: Cubital Tunnel Decompression

EXAMINER

"You are performing a cubital tunnel decompression. What are the key sites of compression you must release?"

EXCEPTIONAL ANSWER

There are 5 potential sites, from proximal to distal: 1. The Arcade of Struthers (hiatus in medial septum, 8cm proximal). 2. The Medial Intermuscular Septum (nerve passes through it). 3. The Cubital Tunnel Retinaculum / Osborne's Ligament (between epicondyle and olecranon). 4. The Flexor-Pronator Aponeurosis / Fascia of FCU (nerve enters between two heads). 5. Deep flexor-pronator aponeurosis. A complete release addresses all tethering points. I would also assess for nerve subluxation after release.

KEY POINTS TO SCORE

Arcade of Struthers

Medial Septum

Osborne's Ligament

FCU Fascia

Subluxation check

COMMON TRAPS

✗Missing the FCU fascia (common cause of failure)

✗Forgetting to check for subluxation

LIKELY FOLLOW-UPS

"When would you transpose?"

"What nerves are at risk?"

VIVA SCENARIOStandard

Scenario 3: Guyon's Canal

EXAMINER

"A cyclist complains of numbness in the little finger but has normal grip strength. Localization?"

EXCEPTIONAL ANSWER

This is likely a Zone 3 lesion in Guyon's Canal. Zone 3 (distal) contains only the Superficial Sensory Branch. Zone 2 (around the hook of hamate) contains the Deep Motor Branch - compression here causes weakness without numbness. Zone 1 (proximal) contains both. The sparing of grip strength (intrinsics) and isolated sensory loss suggests distal compression, often external (handlebars).

KEY POINTS TO SCORE

Zone 1: Mixed

Zone 2: Motor

Zone 3: Sensory

Cyclist's Palsy

Differential from Cubital Tunnel (Dorsal branch spared)

COMMON TRAPS

✗Assuming all Guyon's lesions have weakness

✗Not checking dorsal sensation (spared in Guyon's)

LIKELY FOLLOW-UPS

"What is the most common cause of compression here?"

"Anatomy of the canal walls?"

VIVA SCENARIOStandard

Scenario 4: MABCN Injury

EXAMINER

"Post-operatively, your patient complains of numbness over the medial proximal forearm and pain when resting the elbow on a table. What has happened?"

EXCEPTIONAL ANSWER

This is an injury to the Medial Antebrachial Cutaneous Nerve (MABCN). It often crosses the surgical field during decompression. Injury leads to a painful neuroma and anesthesia in its territory (medial forearm/olecranon). It is distinct from the ulnar nerve (hand sensation). Management involves initial desensitization, but established neuromas may require excision and burying into muscle.

KEY POINTS TO SCORE

MABCN Anatomy

Differentiation from Ulnar nerve symptoms

Neuroma prevention

Surgical landmarks

COMMON TRAPS

✗Confusing with medial cord plexopathy

✗Dismissing as 'normal post-op pain'

LIKELY FOLLOW-UPS

"How do you prevent this intra-operatively?"

"What is the treatment for a painful neuroma?"

MCQ Practice Points

Martin-Gruber

Q: What is the most common anomaly of upper limb innervation? A: Martin-Gruber Anastomosis. (Median to Ulnar in forearm). Occurs in 15-20% of people.

First Dorsal Interosseous

Q: Which nerve innervates the First Dorsal Interosseous? A: Ulnar Nerve (Deep branch). It abducts the index finger. Weakness causes a positive Wartenberg's Sign (abducted pinky - wait, that's ADM) - Weakness of 1st DI leads to weak pinch.

Adductor Pollicis

Q: Which muscle is tested by Froment's Sign? A: Adductor Pollicis. It is the only hypothenar/thumb muscle supplied by the Ulnar nerve (besides deep head of FPB).

Guyon's Canal Zones

Q: What distinguishes Zone I from Zone II injury at Guyon's Canal? A: Zone I (proximal to bifurcation) causes mixed motor and sensory loss. Zone II (deep branch only) causes pure motor weakness of interossei with sparing of hypothenar sensation.

Elbow Flexion Test

Q: What is the positive finding in the elbow flexion test for cubital tunnel syndrome? A: Paresthesias in the ring/small fingers within 60 seconds of holding the elbow maximally flexed with the wrist extended.

Australian Context

Guidelines: Cubital tunnel decompression is one of the most common hand procedures in Australia.
Workers Compensation: Common claim in repetitive manual tasks.
Tumors: Ganglions in Guyon's canal should be excised.

This section highlights local practice patterns.

High-Yield Exam Summary

Key Anatomy

•C8-T1 Origin
•Arcade of Struthers (8cm proximal)
•Osborne's Ligament (Cubital Tunnel)
•FCU Heads (Entry to forearm)
•Guyon's Canal (Pisohamate ligament)

Branches

•No branches in Arm
•Muscular: FCU, FDP (Medial 1/2)
•Dorsal Cutaneous: 5cm proximal to wrist (Spared in wrist lesions)
•Deep Branch: Motor to intrinsics
•Superficial Branch: Sensory to digits

Clinical Signs

•Froment's Sign (Thumb IP flexion)
•Wartenberg's Sign (Pinky abduction)
•Jeanne's Sign (Thumb MCP hyperextension)
•Duchenne's Sign (Clawing of ring/little)

Surgical Pearls

•Protect MABCN
•Release 5-8cm proximal (septum)
•Release FCU fascia distal
•Check for subluxation

Feature

Key Detail

Clinical Significance

Origin

Medial Cord (C8-T1)

Lower Trunk Plexopathy mimics Ulnar nerve

Elbow

Cubital Tunnel

#1 Compression site

Forearm

FCU + FDP (Medial 1/2)

Flexion of wrist/digits 4,5

Wrist

Guyon's Canal

#2 Compression site

Measurements

Arcade of Struthers (8cm)

Proximal to medial epicondyle

Axilla & Arm Course

Origin:

Terminal branch of Medial Cord (C8, T1).
Often receives C7 fibers (from Lateral Cord).
Lies medial to axillary and brachial arteries.

Arm:

Runs in anterior compartment initially.
At mid-arm, it pierces the Medial Intermuscular Septum to enter the posterior compartment.
Arcade of Struthers: A band of fascia approx. 8cm proximal to medial epicondyle. A potential compression site (esp after transposition).
Runs distally towards the groove behind the medial epicondyle.

This proximal course is relatively safe from compression.

Grade

Clinical Findings

Prognosis

Grade I

Mild lesions, Paresthesia, No motor weakness

Good prognosis with conservaive/surgical

Grade II

Intermediate, Weakness of intrinsics, Wasting maybe absent

Good outcome likely

Grade III

Severe, Profound weakness, Atrophy, Clawing

Guaarded prognosis, permanent deficit common

Condition

Differentiating Features

Key Test

C8 Radiculopathy

Neck pain, All medial hand muscles affected (incl Median)

Spurling's Test / MRI Neck

Lower Trunk Plexopathy

T1 fibers affected (AP loss), Horner's Syndrome (sometimes)

Chest X-Ray (Pancoast)

Thoracic Outlet Syndrome

Vascular signs, Positional provocation

Adson's Test / Doppler

MND (ALS)

Painless wasting, Fasciculations, Hyperreflexia

EMG (Widespread denervation)

Phase

Action

Goal

Pre-Op

Mark incision, Confirm symptoms side

Avoid wrong site

Intra-Op

Identify MABCN, Release all 5 sites

Complete decompression

Post-Op

Soft dressing, Early ROM

Prevent stiffness

Complication

Cause

Management

MABCN Neuroma

Surgical trauma

Excision / Burying

Persistent Symptoms

Incomplete release (septum/FCU)

Revision Decompression

Nerve Subluxation

Excessive release anteriorly

Transposition

Medial Epicondyle Pain

Destabilized origin

Physio / Repair

Phase

Timeframe

Goals

Precautions

Phase 1 (Protection)

0-2 Weeks

Wound healing, Edema control, Nerve gliding

Avoid resisted flexion

Phase 2 (Mobility)

2-6 Weeks

Full ROM, Scar management, Isometrics

No heavy lifting

Phase 3 (Strength)

6-12 Weeks

Progressive strengthening, Work hardening

Monitor for recurrence

Zone

Location

Contents

Symptoms

Zone 1

Proximal to bifurcation

Motor + Sensory

Muscle weakness + Sensory loss (digits)

Zone 2

Distal to bifurcation (Around hook)

Deep Motor Branch

Motor weakness ONLY (Claw hand)

Zone 3

Distal (Superficial)

Superficial Sensory Branch

Sensory loss ONLY (No motor deficit)