## Clinical Scenario

A 45-year-old cyclist presents with weakness of finger abduction and wasting of the hypothenar eminence but NORMAL sensation in the little finger. Where is the most likely site of ulnar nerve compression?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A Cubital tunnel

B Guyon canal Zone 1

C Guyon canal Zone 2

D Guyon canal Zone 3

E Arcade of Struthers

Reveal Answer Pattern

**Correct Pattern:** `FFTFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | FALSE | | C | TRUE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "Cubital tunnel"

**Why this is INCORRECT:** Understanding the clinical presentation: 1. **Cubital tunnel compression**: - **Proximal ulnar nerve lesion** - At elbow level - Would affect sensation - Dorsal ulnar cutaneous branch involved - Opposite presentation 2. **Expected findings**: - **Sensory loss** in little finger - Dorsal hand numbness - Motor AND sensory deficit - Not pure motor - Key difference 3. **Motor findings**: - Hypothenar wasting: YES - Interossei weakness: YES - ADM weakness: YES - Similar motor pattern - But sensation affected 4. **Sensory distribution**: - **Dorsal ulnar cutaneous** nerve - Branches proximal to wrist - Before Guyon canal - Supplies dorsal hand - Would be affected 5. **Clinical distinction**: - Cubital tunnel: motor + sensory - Guyon canal: can be pure motor - Key exam point - Different levels - Critical differentiation **Clinical Pearl**: The dorsal ulnar cutaneous nerve branches from the main ulnar nerve approximately 5-8cm proximal to the wrist (before entering Guyon canal). This is why cubital tunnel syndrome affects dorsal hand sensation while Guyon canal compression Zone 2 (deep motor branch only) spares sensation entirely.

### Option B: FALSE ✗

FALSE "Guyon canal Zone 1"

**Why this is INCORRECT:** Understanding Guyon canal zones: 1. **Zone 1 anatomy**: - **Proximal Guyon canal** - Before nerve bifurcation - Main ulnar nerve affected - Both branches compressed - Mixed lesion 2. **Zone 1 compression findings**: - **Motor AND sensory deficit** - Superficial branch affected - Deep branch affected - Complete presentation - Not pure motor 3. **Sensory involvement**: - **Superficial branch** supplies sensation - Palmar little finger - Ulnar half ring finger - Would be numb - Contradicts scenario 4. **Clinical presentation**: - Hypothenar wasting: YES - Interossei weakness: YES - **Sensory loss: YES** - Not matching scenario - Wrong zone 5. **Common causes**: - Ganglion cyst - Hook of hamate fracture - Ulnar artery thrombosis - Cyclist handlebar pressure - Mixed deficit expected **Clinical Pearl**: Zone 1 compression is the most common Guyon canal syndrome location (approximately 40% of cases). It affects the main ulnar nerve before bifurcation, causing BOTH motor weakness (hypothenar, interossei) AND sensory loss (palmar little and ulnar ring finger), distinguishing it from the pure motor deficits of Zones 2 and 3.

### Option C: TRUE ✓

TRUE "Guyon canal Zone 2"

**Why this is CORRECT:** Understanding Zone 2 compression: 1. **Zone 2 anatomy**: - **Deep motor branch ONLY** - After nerve bifurcation - Around hook of hamate - Pure motor compression - Sensory branch spared 2. **Zone 2 boundaries**: - Distal to bifurcation - Proximal to hypothenar muscles - Deep motor branch isolated - Superficial branch free - Critical anatomical point 3. **Motor deficit pattern**: - **Hypothenar wasting: YES** - **Interossei weakness: YES** - All deep branch muscles - Complete motor involvement - Matches scenario 4. **Sensory preservation**: - **NORMAL sensation** - Superficial branch intact - Palmar sensation preserved - Key diagnostic feature - Matches scenario perfectly 5. **Clinical causes**: - Hook of hamate fracture - Ganglion cyst (deep) - Chronic cyclist pressure - Occupational compression - Common mechanism 6. **Muscles affected**: - ADM (abductor digiti minimi) - FDM (flexor digiti minimi) - ODM (opponens digiti minimi) - All interossei (palmar and dorsal) - Adductor pollicis - Deep head FPB **Clinical Pearl**: Zone 2 compression produces a pure motor deficit affecting ALL ulnar intrinsic muscles while preserving sensation completely. This is pathognomonic for deep motor branch compression and distinguishes it from more proximal lesions. The cyclist in this scenario likely has chronic handlebar compression at the hook of hamate level.

### Option D: FALSE ✗

FALSE "Guyon canal Zone 3"

**Why this is INCORRECT:** Understanding Zone 3 anatomy: 1. **Zone 3 location**: - **Superficial branch ONLY** - Distal Guyon canal - Pure sensory compression - Motor branch spared - Opposite presentation 2. **Zone 3 compression findings**: - **Pure sensory deficit** - NO motor weakness - NO wasting - Normal strength - Contradicts scenario 3. **Sensory distribution affected**: - Palmar little finger - Ulnar half ring finger - Superficial branch territory - Numbness only - No weakness 4. **Motor preservation**: - **Normal hypothenar bulk** - **Normal interossei function** - Deep branch intact - Strength preserved - Not matching 5. **Clinical rarity**: - Least common zone - Approximately 15% cases - Usually from direct trauma - Pure sensory pattern - Easily distinguished **Clinical Pearl**: Zone 3 compression is the rarest form of Guyon canal syndrome, causing isolated sensory loss in the palmar aspect of the little finger and ulnar half of the ring finger WITHOUT any motor deficit. The patient would have normal grip strength, normal hypothenar bulk, and intact interossei function - the opposite of this clinical scenario.

### Option E: FALSE ✗

FALSE "Arcade of Struthers"

**Why this is INCORRECT:** Understanding the Arcade of Struthers: 1. **Anatomical location**: - **Medial arm** - 8cm proximal to medial epicondyle - Intermuscular septum - Far from wrist - Proximal lesion 2. **Arcade anatomy**: - Fascial band - From medial head triceps - To intermuscular septum - Ulnar nerve passes through - Uncommon compression site 3. **Expected findings**: - **Motor AND sensory deficit** - Dorsal ulnar cutaneous affected - FCU weakness (unique sign) - FDP to ring/little weakness - Proximal compression pattern 4. **Clinical presentation**: - Sensory loss: YES - Dorsal hand numbness - Proximal muscle weakness - FCU involved (test at wrist) - Not matching scenario 5. **Differentiation**: - More proximal than cubital tunnel - FCU weakness key finding - Not isolated to hand - Sensation always affected - Wrong level **Clinical Pearl**: The Arcade of Struthers is an inconsistent fascial structure present in 70% of individuals. When it causes compression, FCU weakness distinguishes it from cubital tunnel syndrome (where FCU is typically spared because its nerve branches arise proximal to the area of compression in the cubital tunnel). Any arcade compression would affect sensation, ruling it out in this pure motor scenario.

--- ### Exam Tip

**High-Yield Points for Guyon Canal Zones:** - **Zone 1**: Proximal to bifurcation - Main ulnar nerve compressed - Motor + Sensory deficit - Most common (40%) - Example: Ganglion, ulnar artery aneurysm - **Zone 2**: Deep motor branch ONLY - **Pure motor deficit** (hypothenar + interossei) - **NORMAL sensation** (superficial branch intact) - Around hook of hamate - Example: Hook fracture, cyclist's palsy - **Zone 3**: Superficial branch ONLY - Pure sensory deficit - Normal motor function - Least common (15%) - Example: Direct trauma - **Key Teaching**: "If sensation is normal but motor is gone, think Zone 2. If sensation is gone but motor is normal, think Zone 3. If both are gone, think Zone 1 or more proximal." - **Cyclist presentation**: Chronic handlebar pressure → Zone 2 compression at hook of hamate level

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

## Clinical Scenario

What is the PRIMARY origin of the abductor digiti minimi muscle?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A Hook of hamate

B Pisiform bone

C Flexor retinaculum

D Fifth metacarpal base

E Triquetrum

Reveal Answer Pattern

**Correct Pattern:** `FTFFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | TRUE | | C | FALSE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "Hook of hamate"

**Why this is INCORRECT:** Understanding hypothenar muscle origins: 1. **Hook of hamate anatomy**: - **Volar projection** of hamate - Palpable in palm - Important bony landmark - Multiple attachments - Not ADM origin 2. **Muscles from hook of hamate**: - **Flexor digiti minimi (FDM)** - **Opponens digiti minimi (ODM)** - Transverse carpal ligament - Flexor retinaculum - NOT abductor 3. **ADM different origin**: - **Pisiform bone** (primary) - Pisohamate ligament - FCU tendon continuation - More ulnar location - Distinct attachment 4. **Clinical significance**: - Hook fractures common - Cyclist's injury - Affects FDM/ODM - Deep motor branch at risk - ADM usually spared initially 5. **Anatomical relationships**: - Hook ulnar to ADM - Different muscle layer - Guyon canal landmark - Zone 2 compression site - Important distinction **Clinical Pearl**: The hook of hamate is the origin for flexor digiti minimi and opponens digiti minimi, but NOT abductor digiti minimi. Hook fractures (common in golfers, baseball players, and racquet sports) typically present with pain in the hypothenar eminence and may cause ulnar nerve deep branch compression, affecting all hypothenar muscles despite ADM not originating from the hook.

### Option B: TRUE ✓

TRUE "Pisiform bone"

**Why this is CORRECT:** Understanding ADM origin: 1. **Pisiform as PRIMARY origin**: - **Main bony attachment** - Sesamoid bone in FCU tendon - Most ulnar carpal bone - Volar surface - Classic teaching 2. **Pisiform anatomy**: - Pea-shaped bone - Within FCU tendon - Articulates with triquetrum - Palmar prominence - Easily palpable 3. **Additional origins**: - **Pisohamate ligament** - **Pisometacarpal ligament** - Flexor retinaculum (minor) - FCU tendon continuation - Composite origin 4. **Functional significance**: - Provides mechanical advantage - Leverage for abduction - Pisiform acts as pulley - FCU-ADM continuity - Coordinated action 5. **Clinical relationships**: - Pisiform fractures rare - Pisotriquetral arthritis - May cause ulnar-sided pain - ADM wasting in chronic cases - Excision affects ADM function 6. **Embryological connection**: - FCU tendon insertion - Sesamoid development - Muscle-tendon-bone unit - Integrated structure - Phylogenetic significance **Clinical Pearl**: The pisiform bone serves as both the insertion of FCU and the origin of ADM, creating a functional muscle-tendon-bone-muscle unit. Pisiform excision for pisotriquetral arthritis can theoretically weaken ADM function, though this is rarely clinically significant as the muscle also has substantial fascial and ligamentous origins.

### Option C: FALSE ✗

FALSE "Flexor retinaculum"

**Why this is INCORRECT:** Understanding the flexor retinaculum: 1. **Flexor retinaculum anatomy**: - **Transverse carpal ligament** - Roof of carpal tunnel - Ulnar to radial attachment - Multiple muscle origins - Minor ADM contribution only 2. **Primary flexor retinaculum origins**: - **Thenar muscles** (APB, FPB, OP) - Palmaris brevis (superficial) - Some hypothenar fibers - NOT primary ADM origin - Secondary attachment 3. **ADM relationship**: - **Some fibers** from retinaculum - Minor contribution - Not PRIMARY origin - Supplementary attachment - Pisiform is main 4. **Clinical distinction**: - Carpal tunnel release - Divides flexor retinaculum - Thenar muscles affected - ADM largely unaffected - Different compartment 5. **Anatomical accuracy**: - Question asks PRIMARY origin - Pisiform is correct answer - Retinaculum is accessory - Exam precision required - Key distinction **Clinical Pearl**: While some ADM fibers may arise from the flexor retinaculum, this is NOT the primary origin. The pisiform bone is the main origin point. This distinction matters clinically because carpal tunnel release (division of flexor retinaculum) may theoretically affect thenar muscle origins but does not significantly impact ADM function.

### Option D: FALSE ✗

FALSE "Fifth metacarpal base"

**Why this is INCORRECT:** Understanding metacarpal attachments: 1. **Fifth metacarpal base**: - **NOT ADM origin** - Different muscle attachments - Carpometacarpal joint - Ligamentous connections - Wrong location 2. **Muscles at 5th MC base**: - **Opponens digiti minimi** (primary) - ECU tendon insertion (base) - Dorsal interossei (shaft) - Palmar interossei (shaft) - NOT abductor 3. **ADM course**: - Origin: pisiform - Insertion: proximal phalanx - Superficial in hypothenar - Does NOT attach to metacarpal - Distinct anatomy 4. **Opponens vs Abductor**: - **Opponens**: hamate → 5th MC shaft - **Abductor**: pisiform → proximal phalanx - Different functions - Different layers - Easy to confuse 5. **Functional implications**: - ADM: abducts little finger - ODM: opposes little finger - Different actions - Complementary muscles - Separate anatomy **Clinical Pearl**: The fifth metacarpal base is the insertion of opponens digiti minimi, NOT the origin of abductor digiti minimi. This is a common exam trap. Remember: ADM is the most superficial hypothenar muscle (pisiform to proximal phalanx), while opponens is the deepest (hook of hamate to entire 5th metacarpal shaft).

### Option E: FALSE ✗

FALSE "Triquetrum"

**Why this is INCORRECT:** Understanding triquetrum anatomy: 1. **Triquetrum location**: - **Ulnar proximal carpal row** - Pyramidal shape - Articulates with pisiform - Hamate distally - Not muscle origin 2. **Triquetrum attachments**: - **Carpal ligaments primarily** - Lunotriquetral ligament - Triquetrohamate ligament - Ulnar collateral ligament - NO major muscle origins 3. **Pisiform vs Triquetrum**: - **Pisiform articulates WITH triquetrum** - Pisotriquetral joint - Common arthritis site - Separate bones - Different functions 4. **Clinical confusion**: - Anatomically adjacent - May confuse on exam - Pisiform is anterior - Triquetrum is deeper - Important distinction 5. **Fracture patterns**: - Triquetrum: dorsal chip fractures - Pisiform: rare direct trauma - Different mechanisms - Different presentations - ADM affected by pisiform injury **Clinical Pearl**: The triquetrum does NOT give origin to any major hand muscles. It is primarily a carpal bone with ligamentous attachments. The pisiform (which articulates with the triquetrum at the pisotriquetral joint) is the origin of ADM. Pisotriquetral arthritis can cause ulnar-sided wrist pain that may be confused with FCU tendinitis or ulnar nerve compression.

--- ### Exam Tip

**High-Yield Points for ADM Origin:** - **PRIMARY Origin**: Pisiform bone (sesamoid in FCU tendon) - **Secondary Origins**: - Pisohamate ligament - Pisometacarpal ligament - Minor fibers from flexor retinaculum - **Hypothenar Muscle Origins**: - **ADM**: Pisiform → proximal phalanx (most superficial) - **FDM**: Hook of hamate → middle phalanx (middle layer) - **ODM**: Hook of hamate → 5th MC shaft (deepest layer) - **Common Exam Traps**: - Hook of hamate is for FDM and ODM, NOT ADM - 5th metacarpal base is ODM insertion, NOT ADM origin - Flexor retinaculum is minor, NOT primary origin - **Key Teaching**: "Pisiform is the Primary origin of the Abductor (both start with P-A). The hook is for Flexors and Opponens." - **Clinical correlation**: Pisiform excision may weaken ADM; hook of hamate fracture affects FDM/ODM more directly

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

## Clinical Scenario

Which nerve supplies the abductor digiti minimi muscle?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A Superficial branch of ulnar nerve

B Deep branch of ulnar nerve

C Median nerve

D Anterior interosseous nerve

E Posterior interosseous nerve

Reveal Answer Pattern

**Correct Pattern:** `FTFFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | TRUE | | C | FALSE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "Superficial branch of ulnar nerve"

**Why this is INCORRECT:** Understanding ulnar nerve branching: 1. **Superficial branch anatomy**: - **Sensory branch ONLY** - Bifurcates in Guyon canal - Supplies palmar sensation - Little and ring fingers - NO motor function 2. **Superficial branch territory**: - **Palmar cutaneous** innervation - Palmar little finger - Ulnar half ring finger - No muscle supply - Pure sensory 3. **Muscle innervation**: - Superficial branch: ZERO muscles - Only sensory distribution - Does NOT supply ADM - Wrong branch - Common exam trap 4. **ADM innervation**: - **Deep motor branch** required - All hypothenar muscles - All interossei - Motor function only - Different branch 5. **Clinical significance**: - Zone 3 compression - Pure sensory deficit - Normal ADM function - Normal strength - Numbness only **Clinical Pearl**: The superficial branch of the ulnar nerve is purely sensory and does NOT supply any muscles. It provides sensation to the palmar aspect of the little finger and ulnar half of the ring finger. Zone 3 Guyon canal compression affects this branch, causing numbness WITHOUT weakness - the opposite of what deep motor branch injury produces.

### Option B: TRUE ✓

TRUE "Deep branch of ulnar nerve"

**Why this is CORRECT:** Understanding deep motor branch anatomy: 1. **Deep branch as MOTOR branch**: - **Pure motor function** - Bifurcates in Guyon canal - Supplies ALL ulnar intrinsics - No sensory component - Key anatomical fact 2. **Deep branch course**: - **Passes around hook of hamate** - Travels deep in palm - Between hypothenar muscles - Across deep palmar arch - Vulnerable to compression 3. **Muscles supplied by deep branch**: - **All hypothenar muscles**: - Abductor digiti minimi (ADM) - Flexor digiti minimi (FDM) - Opponens digiti minimi (ODM) - **All interossei** (palmar and dorsal) - **Adductor pollicis** - **Deep head of FPB** - **Lumbrical 3 and 4** 4. **Clinical significance**: - Zone 2 compression - Pure motor deficit - Sensation preserved - Hook of hamate fracture - Cyclist's palsy 5. **Examination findings**: - Hypothenar wasting - Weak finger abduction/adduction - Positive Froment sign - Wartenberg sign - Normal sensation (key) 6. **Anatomical relationships**: - First branch to ADM - Then FDM and ODM - Then deep into palm - Sequential innervation - Proximal-to-distal pattern **Clinical Pearl**: The deep motor branch of the ulnar nerve supplies ALL ulnar-innervated intrinsic hand muscles. It is purely motor with NO sensory component. ADM is typically the first muscle branch as the nerve enters the hypothenar eminence, which is why isolated deep branch injuries still affect ADM despite it being the most superficial hypothenar muscle.

### Option C: FALSE ✗

FALSE "Median nerve"

**Why this is INCORRECT:** Understanding median nerve territory: 1. **Median nerve muscles**: - **Thenar muscles** (not hypothenar) - Abductor pollicis brevis - Opponens pollicis - Superficial head FPB - Lumbricals 1 and 2 2. **Thenar vs Hypothenar**: - **Thenar**: median nerve - **Hypothenar**: ulnar nerve - Opposite sides of hand - Easy distinction - Different eminences 3. **Median nerve course**: - Through carpal tunnel - Radial side of hand - Does NOT reach hypothenar - Different distribution - Separate territory 4. **Clinical presentations**: - Median: thenar wasting, APB weakness - Ulnar: hypothenar wasting, ADM weakness - Opposite patterns - Different examinations - Clear distinction 5. **Anatomical boundaries**: - Median: radial 3.5 digits - Ulnar: ulnar 1.5 digits - No overlap in motor - Distinct territories - Exam fundamental **Clinical Pearl**: Median nerve supplies THENAR muscles (thumb side), while ulnar nerve supplies HYPOTHENAR muscles (little finger side). This is a fundamental anatomical principle. In carpal tunnel syndrome (median nerve compression), patients have weak thumb opposition and thenar wasting, NOT hypothenar involvement. Confusing median and ulnar territories is a basic exam error.

### Option D: FALSE ✗

FALSE "Anterior interosseous nerve"

**Why this is INCORRECT:** Understanding anterior interosseous nerve: 1. **AIN anatomy**: - **Branch of median nerve** - Pure motor branch - Arises in proximal forearm - Descends on interosseous membrane - NO hand muscles 2. **AIN muscle supply**: - **Flexor pollicis longus (FPL)** - **Flexor digitorum profundus** (index, middle) - **Pronator quadratus (PQ)** - All FOREARM muscles - NO intrinsic hand muscles 3. **AIN vs hand intrinsics**: - AIN: extrinsic flexors - Deep motor branch ulnar: intrinsics - Different compartments - Different functions - Different nerve territories 4. **AIN syndrome presentation**: - Weak pinch (FPL and FDP) - Cannot make "OK" sign - Normal sensation - Normal hand intrinsics - Forearm pathology 5. **Anatomical location**: - Forearm only - Does NOT enter hand - Ends at PQ - No carpal tunnel passage - Separate from hypothenar **Clinical Pearl**: The anterior interosseous nerve (AIN) is a pure motor branch of the MEDIAN nerve that supplies deep forearm flexors (FPL, FDP index/middle, PQ) but does NOT innervate any intrinsic hand muscles. AIN syndrome presents with weak pinch grip (inability to make "OK" sign) but normal sensation and normal hand intrinsic function - completely different from ulnar nerve pathology.

### Option E: FALSE ✗

FALSE "Posterior interosseous nerve"

**Why this is INCORRECT:** Understanding posterior interosseous nerve: 1. **PIN anatomy**: - **Branch of radial nerve** - Pure motor branch - Arises at elbow (arcade of Frohse) - Posterior compartment forearm - NO hand muscles 2. **PIN muscle supply**: - **All finger/thumb extensors** - Extensor digitorum communis (EDC) - Extensor indicis proprius (EIP) - Extensor digiti minimi (EDM) - Extensor pollicis longus/brevis - Abductor pollicis longus 3. **PIN vs ulnar nerve**: - PIN: extensors (dorsal) - Ulnar: intrinsics (palmar) - Different compartments - Different functions - Opposite territories 4. **PIN syndrome presentation**: - Finger drop - Cannot extend fingers at MCP - Normal wrist extension (ECRL/ECRB) - Normal sensation - No hypothenar involvement 5. **Radial nerve anatomy**: - Superficial branch: sensory - Deep branch (PIN): motor - Forearm extensors only - Does NOT enter hand - No intrinsic innervation **Clinical Pearl**: The posterior interosseous nerve (PIN) is the deep motor branch of the RADIAL nerve, supplying all finger and thumb extensors in the posterior forearm. PIN syndrome causes finger drop (weak MCP extension) but does NOT affect hand intrinsics, sensation, or wrist extension. It has no relationship to hypothenar muscles, which are ulnar nerve territory.

--- ### Exam Tip

**High-Yield Points for ADM Innervation:** - **Nerve Supply**: Deep motor branch of ulnar nerve (C8, T1) - **Ulnar Nerve Branching in Guyon Canal**: - **Superficial branch**: Sensory ONLY (palmar little and ring finger) - **Deep motor branch**: Motor ONLY (all ulnar intrinsics) - **Deep Motor Branch Supplies**: - All hypothenar muscles (ADM, FDM, ODM) - All interossei (palmar and dorsal) - Adductor pollicis - Deep head FPB - Lumbricals 3 and 4 - **Common Exam Traps**: - Superficial branch is sensory only - does NOT supply ADM - Median nerve supplies thenar (NOT hypothenar) - AIN is median branch for forearm flexors (NOT hand intrinsics) - PIN is radial branch for forearm extensors (NOT hand intrinsics) - **Key Teaching**: "Deep motor branch supplies ALL ulnar intrinsics. Superficial branch supplies ZERO muscles (sensory only)." - **Clinical correlation**: Zone 2 Guyon compression → deep branch → motor deficit with normal sensation

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

## Clinical Scenario

A patient with ulnar nerve palsy at the elbow demonstrates a positive Wartenberg sign (abducted little finger at rest). Why is the little finger abducted despite the ADM also being ulnar-innervated and weak?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A The ADM is spared in cubital tunnel syndrome

B The EDM (radial nerve) abducts the little finger unopposed when interossei are weak

C The little finger extensors are hypertonic

D The ADM is stronger than the interossei

E The median nerve takes over abduction function

Reveal Answer Pattern

**Correct Pattern:** `FTFFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | TRUE | | C | FALSE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "The ADM is spared in cubital tunnel syndrome"

**Why this is INCORRECT:** Understanding cubital tunnel compression: 1. **ADM is NOT spared**: - **Ulnar nerve affected** - All ulnar intrinsics weak - ADM included in deficit - Hypothenar wasting present - Opposite claim 2. **Cubital tunnel findings**: - **Hypothenar wasting** (ADM, FDM, ODM) - Interossei weakness - Clawing (ring and little) - Sensory loss - ADM definitely affected 3. **Wartenberg sign mechanism**: - NOT due to ADM sparing - Due to interossei weakness - EDM (radial nerve) unopposed - Different explanation - Misunderstanding of pathology 4. **Pattern of weakness**: - All ulnar muscles weak - FCU may be spared (proximal branches) - FDP to ring/little affected - Intrinsics ALL affected - No selective sparing 5. **Clinical presentation**: - Hypothenar atrophy visible - Weak ADM on testing - Cannot abduct little finger forcefully - Wartenberg occurs DESPITE weakness - Paradoxical finding **Clinical Pearl**: ADM is NOT spared in cubital tunnel syndrome - all ulnar intrinsics including ADM are weakened. The Wartenberg sign occurs not because ADM is functional, but because the palmar interossei (which normally adduct the little finger) are weak, allowing EDM (extensor digiti minimi, innervated by radial nerve) to pull the finger into abduction unopposed.

### Option B: TRUE ✓

TRUE "The EDM (radial nerve) abducts the little finger unopposed when interossei are weak"

**Why this is CORRECT:** Understanding Wartenberg sign mechanism: 1. **Normal finger position balance**: - **Extensors** (EDC, EDM) pull radially - **Palmar interossei** adduct fingers - **Balance maintains alignment** - Fingers rest together - Equilibrium state 2. **EDM anatomy**: - **Extensor digiti minimi** - Innervated by **posterior interosseous nerve** (radial) - Extends little finger at MCP - Pulls with **radial vector** - Creates abduction force 3. **Palmar interossei role**: - **Third palmar interosseous** key muscle - Adducts little finger - Ulnar nerve innervation - **Counteracts EDM pull** - Maintains finger position 4. **Wartenberg sign pathophysiology**: - Ulnar nerve palsy - **Palmar interossei weak** - Cannot counteract EDM - **EDM pulls unopposed** - Little finger abducts at rest 5. **Clinical significance**: - **Specific for ulnar nerve palsy** - Seen at rest (not active movement) - Worsens with finger extension - Improves with finger flexion - Diagnostic sign 6. **Paradox explained**: - ADM also weak (ulnar) - But ADM abducts in different plane - EDM abduction is different vector - Interossei loss is KEY - Not ADM sparing **Clinical Pearl**: Wartenberg sign is the involuntary abduction of the little finger at rest in ulnar nerve palsy. It occurs because the palmar interossei (which normally adduct the little finger) are paralyzed, allowing EDM (radial nerve innervation) to pull the finger into abduction unopposed. This is a PASSIVE finding, not active ADM function. Both ADM and interossei are weak, but loss of the third palmar interosseous is the critical deficit.

### Option C: FALSE ✗

FALSE "The little finger extensors are hypertonic"

**Why this is INCORRECT:** Understanding muscle tone in nerve palsy: 1. **No hypertonicity**: - **Normal muscle tone** - Not spastic paralysis - Not upper motor neuron - Peripheral nerve injury - Flaccid paralysis pattern 2. **Lower motor neuron lesion**: - **Ulnar nerve is LMN** - Causes weakness/flaccidity - NOT hypertonicity - Reduced tone if anything - Opposite claim 3. **Wartenberg mechanism**: - **Balance disruption** - NOT increased extensor tone - Normal EDM function - Weak interossei - Imbalance not hypertonicity 4. **Clinical findings**: - Muscles NOT tight - No resistance to passive movement - No spasticity - Hypotonic if anything - Wasting present 5. **Hypertonicity conditions**: - Upper motor neuron lesions - Stroke, spinal cord injury - NOT peripheral nerve - Different pathology - Wrong mechanism **Clinical Pearl**: Wartenberg sign is NOT due to hypertonic extensors. It results from normal EDM function acting unopposed by weak palmar interossei - a BALANCE issue, not a tone issue. Peripheral nerve injuries cause flaccid (hypotonic) paralysis, not spastic (hypertonic) paralysis. Confusing these mechanisms suggests misunderstanding of upper vs lower motor neuron pathology.

### Option D: FALSE ✗

FALSE "The ADM is stronger than the interossei"

**Why this is INCORRECT:** Understanding muscle strength relationships: 1. **ADM is NOT stronger**: - **Both supplied by ulnar nerve** - Both equally affected - Similar weakness pattern - No differential strength - False comparison 2. **Cubital tunnel syndrome**: - **All ulnar muscles weak** - ADM weak - Interossei weak - No selective sparing - Uniform deficit 3. **Wartenberg mechanism misunderstanding**: - NOT about ADM strength - About **interossei weakness** - About **EDM being unopposed** - Different muscle (radial nerve) - Wrong comparison 4. **Clinical testing**: - ADM: weak abduction - Interossei: weak adduction/abduction - Similar degree of weakness - Both demonstrate atrophy - Parallel deficits 5. **Actual strength relationship**: - Interossei normally strong - ADM relatively weaker - But BOTH affected equally in palsy - Relative strength irrelevant - Wrong focus **Clinical Pearl**: In ulnar nerve palsy, ADM is NOT stronger than the interossei - both are equally weak as they share the same nerve supply (deep motor branch of ulnar nerve). Wartenberg sign reflects loss of the third palmar interosseous (which normally adducts the little finger), allowing radial nerve-innervated EDM to pull the finger into abduction. It is not a comparison of ADM vs interossei strength.

### Option E: FALSE ✗

FALSE "The median nerve takes over abduction function"

**Why this is INCORRECT:** Understanding nerve territories: 1. **Median nerve territory**: - **Thenar muscles only** - Radial side of hand - Does NOT reach little finger - No hypothenar innervation - Wrong territory 2. **No median compensation**: - Cannot "take over" function - Different anatomical location - No muscle substitution - Separate territories - Anatomically impossible 3. **Wartenberg sign pathology**: - **Radial nerve** (EDM) involved - NOT median nerve - Radial pulls unopposed - Median plays no role - Wrong nerve 4. **Nerve substitution principles**: - Nerves cannot "take over" - Fixed anatomical innervation - No neuroplasticity at this level - Muscle reinnervation different - Fundamentally incorrect 5. **Clinical reality**: - Median supplies thumb - Ulnar supplies little finger - Radial supplies extensors - Clear separation - No crossover **Clinical Pearl**: Median nerve does NOT and CANNOT "take over" abduction function of the little finger in ulnar palsy. Median nerve supplies thenar muscles on the thumb side of the hand and has no anatomical pathway to innervate hypothenar muscles. Wartenberg sign is caused by unopposed action of EDM (radial nerve), not median nerve compensation - this would be a fundamental anatomical error.

--- ### Exam Tip

**High-Yield Points for Wartenberg Sign:** - **Definition**: Involuntary abduction of little finger at rest in ulnar nerve palsy - **Mechanism**: - Palmar interossei (especially 3rd PI) weak/paralyzed - EDM (radial nerve via PIN) pulls unopposed - Creates radial deviation of little finger - PASSIVE finding, not active - **Key Anatomy**: - **EDM**: Posterior interosseous nerve (radial) - INTACT - **Palmar interossei**: Deep motor branch ulnar - PARALYZED - Balance lost → abduction at rest - **Clinical Significance**: - Specific for ulnar nerve palsy - Present at rest - Worsens with extension - Improves with flexion (FDP weak but still pulls) - **Common Exam Traps**: - ADM is NOT spared (it's also weak) - NOT due to ADM being stronger - NOT hypertonicity of extensors - Median nerve plays NO role - EDM (radial) is the unopposed muscle - **Key Teaching**: "Wartenberg sign = Weak interossei allow EDM (radial nerve) to pull little finger into abduction. NOT due to strong ADM or median compensation." - **Related sign**: Froment sign (thumb IP flexion due to weak adductor pollicis)

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

## Clinical Scenario

Where does the abductor digiti minimi insert?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A Ulnar side of proximal phalanx base only

B Middle phalanx of little finger

C Ulnar side of proximal phalanx base AND ulnar edge of extensor expansion

D Fifth metacarpal shaft

E Distal phalanx of little finger

Reveal Answer Pattern

**Correct Pattern:** `FFTFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | FALSE | | C | TRUE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "Ulnar side of proximal phalanx base only"

**Why this is INCORRECT:** Understanding ADM insertion complexity: 1. **Dual insertion pattern**: - **Proximal phalanx: YES** - **Extensor expansion: ALSO** - Not single insertion - Composite attachment - Incomplete answer 2. **Proximal phalanx attachment**: - Ulnar (medial) side - Base of proximal phalanx - Primary insertion - But NOT only site - Partial truth 3. **Why expansion matters**: - **Contributes to extension** - Links to extensor mechanism - Functional significance - Not just MCP action - Important addition 4. **Similar muscle pattern**: - Like thenar muscles - Like dorsal interossei - Dual insertion common - Anatomical principle - Standard pattern 5. **Clinical implications**: - MCP abduction (phalanx) - IP extension assistance (expansion) - Complete function - Both components needed - Full answer required **Clinical Pearl**: While the proximal phalanx insertion is the PRIMARY attachment of ADM, stating "only" is anatomically incorrect. The muscle also sends fibers to the ulnar edge of the extensor expansion (extensor hood), which allows ADM to contribute to IP extension in addition to MCP abduction - similar to the pattern of dorsal interossei and thenar muscles.

### Option B: FALSE ✗

FALSE "Middle phalanx of little finger"

**Why this is INCORRECT:** Understanding phalangeal attachments: 1. **ADM does NOT insert on middle phalanx**: - **Proximal phalanx base**: correct - **Extensor expansion**: correct - Middle phalanx: WRONG - Different muscle - Wrong level 2. **Middle phalanx insertions**: - **Central slip** (extensor digitorum) - **FDS** (flexor digitorum superficialis) - NOT intrinsic muscles - Extrinsic tendons - Different category 3. **ADM function**: - MCP abduction - MCP flexion (minor) - IP extension (via expansion) - NOT middle phalanx action - Wrong attachment 4. **Confusion source**: - FDM goes more distal - But still NOT middle phalanx - May confuse muscles - Different hypothenar muscle - Still wrong 5. **Anatomical hierarchy**: - Intrinsics → proximal phalanx - Extrinsics → middle/distal phalanx - General principle - ADM follows pattern - Fundamental anatomy **Clinical Pearl**: Intrinsic hand muscles (including ADM) primarily insert on the proximal phalanges and extensor expansions, NOT on middle or distal phalanges. Middle phalanx insertions are reserved for extrinsic tendons like FDS (palmar side) and the central slip of the extensor mechanism (dorsal side). This is a consistent anatomical pattern.

### Option C: TRUE ✓

TRUE "Ulnar side of proximal phalanx base AND ulnar edge of extensor expansion"

**Why this is CORRECT:** Understanding complete ADM insertion: 1. **Dual insertion anatomy**: - **Primary**: Ulnar side proximal phalanx base - **Secondary**: Ulnar edge extensor expansion - Both components present - Complete description - Anatomically accurate 2. **Proximal phalanx insertion**: - **Ulnar (medial) aspect** - Base of bone - Provides lever for abduction - MCP joint action - Primary attachment 3. **Extensor expansion insertion**: - **Ulnar edge of hood** - Blends with extensor mechanism - Contributes to IP extension - Secondary function - Important component 4. **Functional significance**: - **Proximal phalanx**: MCP abduction - **Extensor hood**: IP extension assistance - Dual action capability - Complete muscle function - Coordinated movement 5. **Similar anatomical pattern**: - Like **dorsal interossei** - Like **palmar interossei** - Like **abductor pollicis brevis** - Standard intrinsic pattern - Consistent anatomy 6. **Clinical correlation**: - ADM weakness affects: - MCP abduction (primary) - IP extension (secondary) - Both functions impaired - Complete deficit - Comprehensive testing **Clinical Pearl**: ADM has a dual insertion typical of intrinsic hand muscles: (1) the ulnar side of the proximal phalanx base for MCP abduction, and (2) the ulnar edge of the extensor expansion for contribution to IP extension. This is why ulnar nerve palsy causes not only weak finger abduction but also contributes to claw deformity (weak IP extension from loss of intrinsic contribution to extensor mechanism).

### Option D: FALSE ✗

FALSE "Fifth metacarpal shaft"

**Why this is INCORRECT:** Understanding metacarpal vs phalangeal insertions: 1. **ADM does NOT insert on metacarpal**: - **Proximal phalanx**: correct - **Metacarpal shaft**: WRONG - Different bone - Different muscle - Wrong target 2. **Fifth metacarpal shaft insertion**: - **Opponens digiti minimi (ODM)** - Entire ulnar border - Deepest hypothenar muscle - Different function - Easy confusion 3. **Hypothenar muscle insertions**: - **ADM**: proximal phalanx + expansion - **FDM**: proximal phalanx (similar to ADM) - **ODM**: fifth metacarpal shaft - Clear distinction - Three different patterns 4. **Functional correlation**: - ODM on metacarpal → opposition - ADM on phalanx → abduction - Insertion determines action - Anatomical logic - Different movements 5. **Clinical testing**: - ODM: cup palm, rotate 5th MC - ADM: abduct little finger at MCP - Different examinations - Separate functions - Distinct muscles **Clinical Pearl**: The fifth metacarpal shaft is the insertion of opponens digiti minimi (ODM), NOT abductor digiti minimi (ADM). This is a common exam trap. ODM inserts along the entire ulnar border of the 5th metacarpal to rotate and oppose the little finger, while ADM inserts on the proximal phalanx to abduct it. Remember: metacarpal insertions = opposition; phalangeal insertions = abduction/flexion.

### Option E: FALSE ✗

FALSE "Distal phalanx of little finger"

**Why this is INCORRECT:** Understanding distal phalanx attachments: 1. **ADM does NOT reach distal phalanx**: - **Proximal phalanx**: correct - **Distal phalanx**: WRONG - Too far distal - Wrong bone - Different muscles 2. **Distal phalanx insertions**: - **FDP** (flexor digitorum profundus) - **Terminal extensor tendon** - Extrinsic tendons only - NO intrinsic muscles - Fundamental principle 3. **Intrinsic vs Extrinsic pattern**: - **Intrinsics**: proximal phalanx level - **Extrinsics**: middle/distal phalanx - Consistent anatomy - Clear separation - Universal rule 4. **ADM course**: - Origin: pisiform - Insertion: proximal phalanx - Does NOT extend beyond - Short muscle - Limited reach 5. **Confusion possible with**: - FDP (ulnar nerve, but extrinsic) - Different compartment - Different function - Intrinsic vs extrinsic - Important distinction **Clinical Pearl**: NO intrinsic hand muscles insert on the distal phalanx - this is reserved exclusively for extrinsic tendons (FDP palmarly, extensor mechanism dorsally). Intrinsic muscles insert on proximal phalanges and contribute to the extensor expansion. This is a fundamental anatomical principle that helps distinguish intrinsic from extrinsic muscle actions.

--- ### Exam Tip

**High-Yield Points for ADM Insertion:** - **Complete Insertion**: - Ulnar side of proximal phalanx base (PRIMARY) - Ulnar edge of extensor expansion (SECONDARY) - **Functional Correlation**: - Proximal phalanx → MCP abduction - Extensor expansion → IP extension assistance - Dual action pattern - **Hypothenar Muscle Insertions**: - **ADM**: Proximal phalanx + expansion - **FDM**: Proximal phalanx (middle phalanx base, ulnar side) - **ODM**: Fifth metacarpal shaft (entire ulnar border) - **Common Exam Traps**: - "Only" proximal phalanx is INCOMPLETE (missing expansion) - Middle phalanx is for extrinsics (FDS, central slip) - Fifth metacarpal is ODM, NOT ADM - Distal phalanx is for extrinsics (FDP, terminal extensor) - **Key Teaching**: "Intrinsic muscles insert on PROXIMAL phalanges + extensor expansions. Extrinsic muscles insert on MIDDLE/DISTAL phalanges." - **Anatomical Pattern**: Similar to dorsal interossei, palmar interossei, and thenar muscles (dual insertion = bone + expansion)

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

## Clinical Scenario

Which structure forms the ulnar wall of Guyon canal?

## Answer Options

Select all statements that are **TRUE**. This is an X-Type question where each option is independently True or False.

A Hook of hamate

B Flexor retinaculum

C Pisiform bone and ADM origin

D Palmaris brevis

E Hypothenar fascia

Reveal Answer Pattern

**Correct Pattern:** `FFTFF` | Option | Answer | |:------:|:------:| | A | FALSE | | B | FALSE | | C | TRUE | | D | FALSE | | E | FALSE |

## Detailed Explanations ### Option A: FALSE ✗

FALSE "Hook of hamate"

**Why this is INCORRECT:** Understanding Guyon canal boundaries: 1. **Hook of hamate location**: - **RADIAL wall** of Guyon canal - NOT ulnar wall - Bony prominence - Medial (toward thumb) - Opposite side 2. **Guyon canal anatomy**: - **Radial (lateral) wall**: Hook of hamate - **Ulnar (medial) wall**: Pisiform + ADM - **Floor**: Pisohamate/pisometacarpal ligaments - **Roof**: Volar carpal ligament - Clear boundaries 3. **Hook as landmark**: - Zone 2 compression site - Deep motor branch passes around it - Important clinical structure - But radial wall - Wrong side for question 4. **Clinical significance**: - Hook fractures common - Compresses deep branch - Ulnar artery passes by - Not forming ulnar wall - Different anatomy 5. **Spatial relationships**: - Hook more radial - Pisiform more ulnar - Canal between them - Two opposite walls - Easy to confuse **Clinical Pearl**: The hook of hamate forms the RADIAL (lateral) wall of Guyon canal, while the pisiform and origin of ADM form the ULNAR (medial) wall. This is why hook of hamate fractures can compress the deep motor branch as it curves around the hook - the nerve is traveling from the ulnar side (pisiform) toward the radial side (hook) as it enters the hypothenar muscles.

### Option B: FALSE ✗

FALSE "Flexor retinaculum"

**Why this is INCORRECT:** Understanding carpal ligament anatomy: 1. **Flexor retinaculum vs volar carpal ligament**: - **Flexor retinaculum**: carpal tunnel roof - **Volar carpal ligament**: Guyon canal roof - Different structures - Often confused - Separate anatomy 2. **Flexor retinaculum location**: - **Forms carpal tunnel roof** - Deep to Guyon canal - Separates two spaces - Not Guyon wall - Different compartment 3. **Flexor retinaculum attachments**: - Scaphoid tubercle (radial) - Trapezium (radial) - Pisiform (ulnar) - Hook of hamate (ulnar) - Spans both sides 4. **Guyon canal roof**: - **Volar carpal ligament** (NOT retinaculum) - Superficial structure - Thin fibrous layer - Continuous with antebrachial fascia - Different layer 5. **Clinical distinction**: - Carpal tunnel release: divides retinaculum - Guyon release: different approach - Separate compartments - Different pathologies - Important differentiation **Clinical Pearl**: The flexor retinaculum (transverse carpal ligament) forms the roof of the CARPAL TUNNEL, not Guyon canal. Guyon canal is roofed by the volar carpal ligament (palmar carpal ligament), which is superficial to the flexor retinaculum. These are distinct anatomical structures - confusing them suggests misunderstanding of wrist compartment anatomy.

### Option C: TRUE ✓

TRUE "Pisiform bone and ADM origin"

**Why this is CORRECT:** Understanding Guyon canal ulnar wall: 1. **Ulnar wall anatomy**: - **Pisiform bone** (bony prominence) - **ADM muscle origin** (soft tissue) - Ulnar (medial) boundary - Forms lateral wall - Correct answer 2. **Pisiform as landmark**: - **Most ulnar carpal bone** - Easily palpable - Within FCU tendon - Proximal boundary - Key structure 3. **ADM origin from pisiform**: - **Creates muscular wall** - Distal to pisiform - Hypothenar eminence - Soft tissue boundary - Continuation ulnar wall 4. **Guyon canal boundaries review**: - **Ulnar wall**: Pisiform + ADM origin ✓ - **Radial wall**: Hook of hamate - **Floor**: Pisohamate/pisometacarpal ligaments - **Roof**: Volar carpal ligament - **Contents**: Ulnar nerve, ulnar artery 5. **Clinical significance**: - Pisiform fracture rare - ADM atrophy in compression - Ulnar wall pathology - Ganglion cysts here - Important relationships 6. **Anatomical continuity**: - FCU inserts → pisiform - Pisiform → pisohamate ligament - ADM arises → pisiform - Integrated structure - Functional unit **Clinical Pearl**: The ulnar wall of Guyon canal is formed by the pisiform bone proximally and the origin of ADM distally, creating a continuous ulnar boundary. This is clinically relevant because masses arising from this area (rare pisiform cysts, soft tissue tumors) can compress the ulnar nerve in Zone 1, causing combined motor and sensory deficits.

### Option D: FALSE ✗

FALSE "Palmaris brevis"

**Why this is INCORRECT:** Understanding palmaris brevis anatomy: 1. **Palmaris brevis location**: - **SUPERFICIAL** to Guyon canal - In subcutaneous tissue - Over hypothenar eminence - Not canal wall - Different layer 2. **Palmaris brevis anatomy**: - Small subcutaneous muscle - Ulnar nerve innervation (superficial branch) - Wrinkles hypothenar skin - Improves grip - Superficial structure 3. **Palmaris brevis attachments**: - Origin: ulnar border hand (skin, fascia) - Insertion: skin hypothenar eminence - Transverse orientation - Superficial to canal - No wall formation 4. **Layer relationships**: - Skin - Palmaris brevis - Volar carpal ligament (roof) - Guyon canal contents - Floor/walls 5. **Clinical significance**: - Innervated BEFORE Guyon canal - Superficial branch outside canal - May be spared in compression - Examination finding - Localization value **Clinical Pearl**: Palmaris brevis is a superficial muscle in the subcutaneous tissue ABOVE Guyon canal, not part of the canal walls. It is innervated by the superficial branch of the ulnar nerve before the nerve enters Guyon canal. In Guyon canal syndrome, palmaris brevis function is typically preserved (can still wrinkle hypothenar skin), helping distinguish it from more proximal ulnar nerve lesions.

### Option E: FALSE ✗

FALSE "Hypothenar fascia"

**Why this is INCORRECT:** Understanding fascial layers: 1. **Hypothenar fascia location**: - **OVER hypothenar muscles** - Superficial covering layer - Not canal boundary - Different structure - Wrong layer 2. **Fascial anatomy**: - Hypothenar fascia: superficial - Volar carpal ligament: Guyon roof - Deep fascia: around muscles - Multiple layers - Distinct functions 3. **Guyon canal walls specificity**: - **Bony structures**: pisiform, hamate - **Ligamentous structures**: pisohamate, volar carpal - **Muscular structures**: ADM origin - Not generic fascia - Defined anatomy 4. **Fascial confusion**: - Multiple fascial layers exist - Generic "fascia" too vague - Specific structures required - Anatomical precision - Exam expects detail 5. **Clinical relevance**: - Fascia not primary pathology - Bony/ligamentous structures matter - Compression sites specific - Not fascial release - Different treatment **Clinical Pearl**: While hypothenar fascia exists as a superficial covering layer over the hypothenar muscles, it is NOT the ulnar wall of Guyon canal. The canal has specific anatomical boundaries: bony (pisiform, hamate), ligamentous (volar carpal ligament), and muscular (ADM origin). Using "fascia" as an answer is too vague and anatomically imprecise for examination purposes.

--- ### Exam Tip

**High-Yield Points for Guyon Canal Anatomy:** - **Boundaries of Guyon Canal**: - **Ulnar (medial) wall**: Pisiform + ADM origin ✓ - **Radial (lateral) wall**: Hook of hamate - **Floor**: Pisohamate and pisometacarpal ligaments - **Roof**: Volar carpal ligament (NOT flexor retinaculum) - **Contents**: - Ulnar nerve (bifurcates into superficial and deep branches) - Ulnar artery - Ulnar vein - **Three Zones** (Shea and McClain): - **Zone 1**: Proximal, before bifurcation (motor + sensory) - **Zone 2**: Deep motor branch only (pure motor) - **Zone 3**: Superficial branch only (pure sensory) - **Common Exam Traps**: - Hook of hamate is RADIAL wall, NOT ulnar - Flexor retinaculum is carpal tunnel roof, NOT Guyon - Palmaris brevis is superficial TO canal, not wall - Generic "fascia" is too vague - **Key Teaching**: "Guyon canal ulnar wall = Pisiform + ADM. Radial wall = Hook. Roof = Volar carpal ligament. NOT flexor retinaculum." - **Clinical correlation**: Pisiform prominence forms proximal ulnar boundary; ganglion cysts arising here cause Zone 1 compression

--- ### Related Topic

📚 **Learn more**: [Hand Anatomy - Full Topic Review](/topics/hand/hand-anatomy)

--- ### References

- Shea JD, McClain EJ. Ulnar-nerve compression syndromes at and below the wrist. J Bone Joint Surg Am. 1969;51(6):1095-1103. PMID: 5805411 - Murata K, et al. Anatomy of the ulnar tunnel at the wrist. J Hand Surg Am. 2003;28(3):475-480. PMID: 12772107 - Gross MS, Gelberman RH. The anatomy of the distal ulnar tunnel. Clin Orthop Relat Res. 1985;(196):238-247. PMID: 4006007 - Depukat P, et al. Anatomy of Guyon's canal - a systematic review. Folia Med Cracov. 2014;54(2):81-86. PMID: 25628225

Abductor Digiti Minimi Anatomy

Abductor Digiti Minimi Anatomy