Ulnar Tunnel Syndrome (Guyon's Canal)

Anatomical Boundaries

Guyon's canal (ulnar tunnel) is a fibro-osseous tunnel at the wrist where the ulnar nerve enters the hand.

Three Anatomical Zones

The Shea and McClain classification (1969) divides Guyon's canal into three zones based on ulnar nerve branching anatomy. This determines clinical presentation.

Zone 2 is most common (50% of cases) because pisotriquetral ganglion cysts preferentially compress the deep motor branch as it curves around the hook of hamate.

Specific Motor Deficits by Zone

Zone 1 and Zone 2 Motor Deficits (deep motor branch affected):

• Interossei (palmar and dorsal): Cannot spread or adduct fingers
• Lumbricals 3 and 4: Contributes to clawing
• Adductor digiti minimi: Hypothenar wasting
• Flexor digiti minimi brevis: Weak small finger flexion
• Opponens digiti minimi: Weak small finger opposition
• Flexor pollicis brevis (deep head): Usually minimal impact

SPARED in Guyon's canal compression:

• Adductor pollicis: Branches off BEFORE Guyon's canal (no Froment's sign)
• Flexor carpi ulnaris: Motor branch proximal in forearm
• FDP ring and small: Motor branch proximal in forearm
• Dorsal ulnar cutaneous nerve: Branches 5-8cm proximal to wrist

Mechanisms of Compression

Distinguishing from Other Ulnar Neuropathies

Critical to localize lesion: proximal forearm vs elbow vs wrist.

Key Differentiating Features for Guyon's:

1. NO Froment's sign (adductor pollicis spared)
2. NO dorsal hand sensory loss (dorsal ulnar cutaneous branches proximal)
3. NO FCU or FDP weakness (motor branches in forearm)
4. May have pure motor OR pure sensory deficit (zone-dependent)
5. Elbow asymptomatic (no cubital tunnel tenderness or Tinel's)

Shea-McClain Classification (1969)

Key Points:

• Zone 2 is most common (50% of cases)
• Zone 2 = Pure motor = Pathognomonic presentation
• Zone determines imaging and surgical approach

Classification by Etiology

Space-Occupying Lesions (60%):

• Ganglion cyst (85-90% of masses)
• Lipoma, neurofibroma
• Ulnar artery aneurysm

Bony/Traumatic (30%):

• Hook of hamate fracture
• Pisotriquetral arthritis
• Distal radius malunion

Vascular (5%):

• Hypothenar hammer syndrome
• Ulnar artery thrombosis

Chronic Pressure (5%):

• Cycling (handlebar palsy)
• Wheelchair use
• Occupational tool use

Clinical Assessment

History:

• Onset (acute vs gradual)
• Hand dominance and occupation
• Trauma history (fall on hand, hook of hamate fracture)
• Cycling, tool use, wheelchair use
• Palpable mass in hypothenar region
• Weakness vs numbness (zone localization)

Symptom Patterns by Zone:

• Zone 1: Motor weakness + hypothenar numbness
• Zone 2: Motor weakness ONLY (no sensory symptoms)
• Zone 3: Hypothenar numbness ONLY (no weakness)

Physical Examination

Inspection:

• Hypothenar wasting (Zone 1 or 2)
• Interosseous wasting (dorsal hand)
• Claw deformity of ring/small fingers
• Visible or palpable mass

Palpation:

• Hook of hamate tenderness (fracture)
• Palpable ganglion cyst (may be subtle)
• Tinel's sign over Guyon's canal
• Allen's test (ulnar artery patency)

Motor Testing:

• Interosseous function: Finger spread/adduction (Wartenberg's sign)
• Froment's sign: Should be NEGATIVE (adductor spared)
• Hypothenar strength: Abduction and opposition of small finger
• FCU and FDP ring/small: Should be normal (localize to wrist)

Sensory Testing:

• Hypothenar eminence (superficial branch)
• Ulnar 1.5 digits palmar surface (small finger + ulnar ring)
• Dorsal ulnar cutaneous: Should be NORMAL (branches proximal to wrist)

Imaging and Electrodiagnostics

Nerve Conduction Studies

Motor NCS:

• Stimulate ulnar nerve at wrist, record hypothenar (ADM)
• Compare wrist-to-hypothenar latency with normal side
• Prolonged distal latency in Guyon's compression
• May have reduced amplitude if severe

Sensory NCS:

• Test superficial sensory branch
• Abnormal in Zone 1 and 3, normal in Zone 2
• Dorsal ulnar cutaneous should be normal (localizes to wrist)

EMG:

• Denervation in ulnar intrinsics (Zone 1 and 2)
• First dorsal interosseous and ADM most sensitive
• Adductor pollicis should be normal (supplied proximal to Guyon's)

Common Presentation Patterns

Scenario 1: Cyclist with Pure Motor Deficit

• 35-year-old cyclist, 3-month history
• Weak grip, difficulty with fine motor tasks
• Interosseous wasting, Wartenberg's sign
• Normal sensation in hand
• No Froment's sign
• Diagnosis: Zone 2 compression (likely ganglion)
• Workup: MRI shows pisotriquetral ganglion

Scenario 2: Baseball Player with Hypothenar Pain

• 22-year-old baseball catcher
• Hypothenar pain after foul tip
• Tenderness over hook of hamate
• Interosseous weakness, hypothenar numbness
• Diagnosis: Hook of hamate fracture (Zone 1)
• Workup: CT shows hamate fracture with displacement

Scenario 3: Tool User with Pure Sensory Loss

• 50-year-old carpenter
• Hypothenar numbness, no weakness
• Abnormal Allen's test (no ulnar artery flow)
• Diagnosis: Zone 3 (ulnar artery thrombosis)
• Workup: Doppler ultrasound shows ulnar artery occlusion

Essential Investigations Summary

Mandatory Before Surgery:

• NCS confirms wrist-level slowing (not elbow)
• Imaging to identify treatable cause

Detailed Investigation Approach

Nerve Conduction Studies:

• Wrist-to-hypothenar latency prolonged
• Dorsal ulnar cutaneous nerve NORMAL (key!)
• Compare with contralateral side
• EMG: Denervation in intrinsics, ADM

Imaging Protocol:

• Start with plain films + carpal tunnel view
• CT if hamate fracture suspected
• MRI for soft tissue mass
• Ultrasound: Dynamic assessment, Doppler for artery

Special Tests:

• Allen's test: Ulnar artery patency
• Angiography: If hypothenar hammer syndrome suspected

Non-Operative Management

Indications:

• Mild symptoms, short duration (less than 3 months)
• No muscle wasting
• Idiopathic (no mass lesion on imaging)
• Occupational cause with modifiable activity

Treatment Protocol:

1. Activity Modification:

• Avoid repetitive hypothenar pressure
• Padded gloves for cyclists
• Ergonomic tool handles
• Wheelchair cushion padding

2. Splinting:

• Wrist splint in neutral position
• Night splint (6-8 weeks)
• Reduces pressure in Guyon's canal
• Evidence limited but low risk

3. NSAIDs:

• Short course (2-4 weeks)
• Anti-inflammatory effect
• Minimal evidence for nerve compression

4. Therapy:

• Nerve gliding exercises
• Strengthening when symptoms improve
• No evidence for benefit but commonly prescribed

Outcomes:

• 30-40% improve with conservative treatment
• Best results in idiopathic, occupational causes
• Poor results if ganglion or structural lesion present

Guyon's Canal Release

Indications:

• Ganglion cyst or other mass lesion
• Progressive motor weakness
• Muscle atrophy present
• Failed conservative treatment (3 months)
• Hook of hamate fracture nonunion

Patient Position:

• Supine, arm on hand table
• Tourniquet on upper arm
• Hand supinated

Surgical Approach:

Incision:

• Longitudinal incision along ulnar border of hypothenar
• Starts 1cm proximal to wrist crease
• Extends 3-4cm distally into palm
• Radial to FCU tendon, ulnar to thenar crease

Superficial Dissection:

1. Incise skin and subcutaneous fat
2. Identify and protect palmar cutaneous branch of ulnar nerve (small sensory branch)
3. Expose palmaris brevis muscle

Identify Neurovascular Structures:

1. Incise palmaris brevis longitudinally
2. Identify ulnar artery (RADIAL to nerve - do not injure!)
3. Identify ulnar nerve (ULNAR to artery)
4. Follow nerve distally to bifurcation

Decompress Zones:

1. Zone 1: Release palmar carpal ligament proximal to wrist crease
2. Follow nerve distally, identify bifurcation into motor and sensory branches
3. Zone 2: Follow deep motor branch as it curves around hook of hamate
4. Release all fibrous tissue compressing motor branch
5. Zone 3: Follow superficial sensory branch distally, release any constricting tissue

Address Pathology:

• Ganglion cyst: Excise completely, trace to joint origin
• Hook of hamate fracture: Excise hook fragment (do NOT attempt fixation)
• Ulnar artery thrombosis: Ligate or resect thrombosed segment
• Pisohamate ligament: Release if compressing nerve

Closure:

• Ensure hemostasis (critical near ulnar artery)
• Skin closure with 4-0 nylon interrupted sutures
• Soft bulky dressing
• Wrist splint in neutral (optional, 1-2 weeks)

Hook of Hamate Fracture Treatment

Fracture Classification:

• Type I: Tip avulsion
• Type II: Base fracture
• Type III: Comminuted

Treatment Algorithm:

Acute Fracture (less than 4 weeks):

• Non-displaced: Trial of immobilization (4-6 weeks)
  • Short arm cast with ulnar gutter
  • Success rate only 30-50%
  • Nonunion common due to poor blood supply
• Displaced: Primary excision recommended
  • Union rare even with prolonged immobilization
  • Early excision prevents nerve compression

Chronic Nonunion or Delayed Presentation:

• Symptomatic: Hook excision (treatment of choice)
• Asymptomatic: Observation acceptable if incidental finding

Hook of Hamate Excision Technique

Indications:

• Symptomatic nonunion
• Displaced acute fracture
• Chronic fracture with ulnar neuropathy

Approach:

• Same incision as Guyon's canal release
• Identify and protect ulnar nerve and artery
• Expose hook of hamate
• Use small osteotome or rongeur to remove hook fragment
• Remove all fragments, smooth edges with rasp
• Ensure no sharp edges remain (risk of flexor tendon rupture)

Postoperative:

• Soft dressing, early motion
• Avoid forceful gripping for 6 weeks
• Return to sport 8-12 weeks

Outcomes:

• 90-95% pain relief
• Grip strength returns to 85-90% of normal
• Nerve symptoms resolve in 80-90% if present

Postoperative Protocol

Week 0-2: Protection Phase

• Bulky soft dressing
• Finger ROM exercises immediately
• Wrist mobilization gentle
• Suture removal 10-14 days

Week 2-6: Active Motion

• Remove dressing/splint
• Active wrist and finger ROM
• Light activities of daily living
• Avoid forceful gripping

Week 6-12: Strengthening

• Progressive grip strengthening
• Return to work (light duty)
• Therapy for stiffness if needed

Month 3-6: Full Recovery

• Return to full activities
• Sport-specific training
• Final assessment of nerve recovery

Expected Outcomes

Prognostic Factors:

Motor Recovery:

• Sensory recovery faster than motor (3-6 months vs 6-12 months)
• Intrinsic strength improves but may not return to baseline if chronic atrophy
• Clawing resolves in 90%
• Grip strength improves 30-50%

Sensory Recovery:

• Numbness resolves in 95%
• Dysesthesias may persist for 3-6 months
• Protective sensation returns first (1-2 months)

Guyon's Canal Decompression Summary

Patient Setup:

• Supine, arm on hand table
• Tourniquet, hand supinated
• Loupe magnification recommended

Incision:

• Longitudinal along ulnar hypothenar border
• 1cm proximal to wrist crease, 3-4cm distally

Key Steps:

1. Identify ulnar artery (RADIAL to nerve) - protect first
2. Identify ulnar nerve
3. Follow nerve to bifurcation
4. Release all three zones as needed
5. Excise ganglion/pathology to origin

Technical Details

Surgical Dissection:

• Incise palmaris brevis longitudinally
• Identify and protect palmar cutaneous branch
• Trace nerve from proximal to distal through all zones

Zone-Specific Decompression:

• Zone 1: Release palmar carpal ligament
• Zone 2: Follow deep motor branch around hamate hook
• Zone 3: Release superficial branch compression

Pathology-Specific:

• Ganglion: Trace to pisotriquetral joint origin
• Hamate fracture: Excise hook (NOT ORIF)
• Artery aneurysm: Ligation or resection

Closure:

• Meticulous hemostasis (near ulnar artery)
• 4-0 nylon skin closure
• Soft dressing, splint 1-2 weeks optional

Problems and Management

Intraoperative Complications:

Early Postoperative (0-6 weeks):

• Hematoma (2-3%): Risk near ulnar artery

  • Prevention: Meticulous hemostasis, consider drain
  • Management: Evacuate if symptomatic, compressive dressing

• Infection (less than 1%): Rare with clean technique

  • Antibiotics, washout if severe
  • Risk to nerve recovery if deep

• Wound dehiscence: Incision in mobile area of palm

  • Prevention: Careful closure, immobilize 1-2 weeks
  • Management: Local wound care, may need re-closure

Late Complications (greater than 6 weeks):

Unusual Presentations

Hypothenar Hammer Syndrome:

• Chronic repetitive trauma to hypothenar
• Ulnar artery thrombosis or aneurysm
• May compress nerve (Zone 1 or 3)
• Presents with cold intolerance, pain, numbness
• Diagnosis: Doppler ultrasound or angiography
• Treatment: Vascular reconstruction or ligation + nerve decompression

Combined Carpal and Guyon's Tunnel:

• "Double crush" phenomenon
• Median nerve compression in carpal tunnel PLUS ulnar in Guyon's
• Presents with combined median/ulnar deficits
• Consider if hypothenar symptoms during CTR
• Treatment: Release both tunnels (can be simultaneous)

Pisotriquetral Arthritis:

• Degenerative arthritis of PT joint
• Osteophytes compress ulnar nerve
• Chronic wrist pain + ulnar neuropathy
• Imaging: Radiographs show PT arthritis
• Treatment: Pisiform excision + nerve decompression

Ulnar Artery Aneurysm:

• Pulsatile mass in Guyon's canal
• Compresses nerve (Zone 1)
• May thrombose → acute ischemia
• Diagnosis: Ultrasound with Doppler
• Treatment: Aneurysm excision + vascular reconstruction

When Primary Decompression Fails

Indications for Revision:

• Persistent or recurrent symptoms after 6+ months
• Incomplete initial decompression
• Recurrent ganglion cyst
• Nerve scarring in scar tissue

Preoperative Assessment:

• Repeat NCS to confirm persistent compression
• MRI to assess for recurrent mass or nerve scarring
• Exclude proximal lesion (cubital tunnel)

Revision Technique:

• Extended incision, careful dissection through scar
• Complete decompression of all three zones
• Neurolysis if nerve encased in scar
• Excise recurrent ganglion to joint origin
• Consider nerve wrapping (fat, vein) if extensive scarring

Outcomes:

• Less predictable than primary (60-70% success)
• Set realistic expectations
• Consider alternative diagnoses if second revision needed

Salvage Options:

• Tendon transfers for permanent motor deficit
• Nerve grafting if nerve defect
• Neuroma excision if intractable pain

Rehabilitation Protocol

Week 0-2: Protection

• Bulky soft dressing
• Finger ROM exercises immediately
• Suture removal 10-14 days

Week 2-6: Active Motion

• Remove splint, active wrist ROM
• Light ADLs permitted
• Avoid forceful gripping

Week 6-12: Strengthening

• Progressive grip strengthening
• Return to light duty work
• Sport-specific training begins

Return to Activity Guidelines

Office Work: 2 weeks Light Manual Work: 4-6 weeks Heavy Manual Work: 8-12 weeks Cycling/Golf: 8-12 weeks (hamate excision)

Monitoring:

• Clinical review at 2, 6, 12 weeks
• Assess motor recovery (intrinsic strength)
• Sensory recovery typically precedes motor
• Final NCS at 6 months if persistent symptoms

Outcome Summary

Good Prognostic Factors:

• Symptom duration less than 6 months
• No preoperative atrophy
• Identifiable and removable cause (ganglion)
• Younger patient age

Poor Prognostic Factors:

• Symptom duration greater than 12 months
• Severe muscle wasting
• Axonal loss on NCS
• Chronic arthritis or fibrosis

Recovery Timeline

Sensory Recovery:

• Protective sensation: 1-2 months
• Dysesthesias resolve: 3-6 months
• Full recovery: 95% by 6 months

Motor Recovery:

• Improvement begins: 2-4 months
• Maximum recovery: 6-12 months
• If severe atrophy: May not return to baseline
• Clawing resolves: 90% of cases

Key Evidence Summary

Shea-McClain Classification (1969):

• Landmark paper defining three anatomical zones
• Basis for all subsequent classification systems
• Guides surgical approach and prognostication

Ganglion Cyst as Primary Cause:

• Multiple case series: 78-91% of Zone 2 lesions
• Arise from pisotriquetral joint
• Complete excision to origin prevents recurrence

Hook of Hamate Management:

• Level IV evidence supports excision over ORIF
• Excision: 95% success, return to sport 10 weeks
• ORIF: 67% nonunion, conversion to excision common

Critical Appraisal

Level of Evidence:

• Mostly Level IV (case series, retrospective reviews)
• No randomized trials comparing surgical techniques
• Expert consensus guides management

NCS Localization Studies:

• 94% agreement between NCS and surgical findings
• Dorsal ulnar cutaneous nerve key differentiator
• Essential preoperative investigation

Outcomes Literature:

• Surgical success 89-92% across studies
• Better outcomes with shorter symptom duration
• Motor recovery less predictable than sensory