Ulnar Nerve Palsy
The Musician's Nerve
Levels
Critical Must-Knows
- The Ulnar Nerve supplies ALL interossei and the Adductor Pollicis.
- Ulnar Paradox: High lesions claw LESS than low lesions because FDP to ring/little is paralyzed.
- Froment's Sign tests the Adductor Pollicis (Patient uses FPL to hold paper).
- Cubital Tunnel Syndrome is the 2nd most common compression neuropathy.
Examiner's Pearls
- "Wartenberg's Sign: Persistent abduction of the little finger (3rd Palmar Interosseous weak, EDM unopposed).
- "Jeanne's Sign: Hyperextension of Thumb MCPJ (FPB deep head weak).
- "Duchenne's Sign: The 'Claw Hand' (Hyperextension MCPJ, Flexion IPJ).
Exam Essentials
The Paradox
High vs Low Paradox Examiners love asking why a high lesion looks "better" (less clawing). Answer: "Because the FDP to the ring and little fingers is also paralyzed, removing the deforming flexor force at the IPJs."
Incision Safety
MABC Danger During cubital tunnel approach, watch out for the Medial Antebrachial Cutaneous (MABC) nerve crossing the field. Injury causes painful neuroma and numbness over the olecranon.
| Feature | High (Cubital Tunnel) | Low (Guyon's Canal) |
|---|---|---|
| Sensory Loss | Volar + Dorsal ulnar hand | Volar only (Usually) |
| FDP Function | Weak/Absent (Ring/Little) | Intact |
| Clawing | Mild (Paradox) | Severe |
| Tinel's | At Elbow | At Wrist |
AFIOMuscles Supplied (Hand)
Memory Hook:All Fine Interossei Owe (the ulnar nerve).
U-L-N-A-RGuyon's Canal Contents
Memory Hook:Anatomy of the canal.
SAM-FODecompression Sites (Elbow)
Memory Hook:Sites of compression.
Overview
Ulnar Nerve Palsy: Compression or injury of the ulnar nerve leading to intrinsic muscle weakness and sensory loss.
The ulnar nerve is the nerve of fine movement and power grip. Its loss is devastating for manual dexterity.
Anatomy
Course of the Nerve
- Arm: Descends medial to brachial artery. Pierces medial intermuscular septum (Arcade of Struthers).
- Elbow: Passes behind Medial Epicondyle (Cubital Tunnel). Enters forearm between two heads of FCU (Osborne's Ligament).
- Forearm: Deep to FCU. Gives off Dorsal Cutaneous Branch (5cm prox to wrist).
- Wrist: Enters Guyon's Canal (superficial to Flexor Retinaculum).
The Dorsal Cutaneous Branch is key to localizing the lesion (High vs Low). Knowing the course aids exposure.
Pathophysiology
Sites of Compression
Cubital tunnel (elbow): Most common site
- Between medial epicondyle and olecranon
- Osborne ligament forms roof
- Nerve stretched with elbow flexion
- Traction and compression combine to cause injury
Guyon canal (wrist):
- Between hook of hamate and pisiform
- May be compressed by ganglion, fracture, or ulnar artery aneurysm
- Motor and sensory branches divide within canal
Mechanism of Nerve Injury
Compression:
- External pressure reduces intraneural blood flow
- Initially affects large myelinated fibers (sensory first)
- Prolonged compression causes axonal degeneration
- Schwann cell damage leads to demyelination
Traction:
- Nerve elongates with elbow flexion
- Cubital tunnel pressure increases 6-fold in flexion
- Chronic traction leads to fibrosis and adhesions
Double crush phenomenon:
- Compression at one site sensitizes nerve to compression at another
- Cervical radiculopathy may coexist with cubital tunnel syndrome
- Always examine entire upper extremity
Progression of Injury
Seddon classification applies:
- Neurapraxia: Demyelination, complete recovery expected
- Axonotmesis: Axon damage, recovery depends on distance to target
- Neurotmesis: Complete disruption, requires repair
Classification
McGowan Classification (Cubital Tunnel)
- Grade I (Mild): Sensory symptoms only (intermittent paresthesia). No weakness.
- Grade II (Moderate): Weakness of intrinsics. Wasting may be present. Constant numbness.
- Grade III (Severe): Profound weakness. Severe wasting. Paralysis.
Surgery is indicated for Grade II and III. Dellon's modification helps track recovery.
Clinical Signs
Froment's Sign: Screen for Adductor Pollicis weakness.
- Ask to hold paper between thumb and index (Key Pinch).
- Positive: IPJ flexes (FPL compensation). Jeanne's Sign: Hyperextension of MPJ during pinch (FPB weakness). Wartenberg's Sign: Persistent abduction of Little Finger.
- Mechanism: Weak 3rd Palmar Interosseous (can't adduct). Unopposed EDM (pulls into abduction). Duchenne's Sign (Claw):
- Hyperextension of MCPJs (unopposed EDC).
- Flexion of IPJs (unopposed FDP/FDS - lack of Lumbrical anti-gravity force).
Investigations
Nerve Conduction Studies (NCS):
- Slowing: Velocity less than 50 m/s across the elbow.
- Block: Conduction block (drop in amplitude) across elbow greater than 20 percent.
- EMG: Denervation potentials in ulnar muscles.
Imaging:
- Ultrasound: Can show nerve swelling (greater than 10mm^2 CSA) or subluxation.
- MRI: Useful for space-occupying lesions (tumors, ganglions in Guyon's).
Management Algorithm
Conservative Management
- Indications: Grade I (Sensory only), Mild symptoms.
- Splinting: Night splinting with elbow in 45 deg flexion (prevents max stretch).
- Activity: Avoid prolonged flexion (phone use).
- Glide: Nerve gliding exercises.
Success rate is roughly 50 percent for mild cases. Patient education is key.
Surgical Technique
Tendon Transfers for the "Claw Hand" (Anti-Claw)
-
Goal: Prevent MCP hyperextension (which allows EDC to extend IPJs).
-
Static: 'Lasso' procedures (Zancolli) - Capsulodesis.
-
Dynamic:
- Stiles-Bunnell / Brand: Use FDS (Middle or Ring) split into 2 slips. Pass through lumbrical canal. Insert into Lateral Bands.
- This restores the "intrinsic plus" position.
- Requires motor relearning.
- Fowler: EIP to Lateral Bands.
Steps for Stiles-Bunnell:
- Harvest FDS to Middle Finger.
- Split into two tails.
- Pass volar to transvere metacarpal ligament.
- Attach to Radial Lateral Bands of Ring and Little fingers.
- Tension with wrist in neutral and fingers in intrinsic plus.
This technique creates a dynamic tenodesis effect.
- Stiles-Bunnell / Brand: Use FDS (Middle or Ring) split into 2 slips. Pass through lumbrical canal. Insert into Lateral Bands.
Specific Details
Ulnar Nerve Transposition Technique:
- Incision posterior to medial epicondyle.
- Identify and protect MABC.
- Release Arcade of Struthers (ensure no kink).
- Release Cubital Tunnel retinaculum.
- Release FCU fascia (Osborne).
- Isolate nerve. Excision of Medial Intermuscular Septum is CRITICAL to prevent kinking when transposed.
- Move anteriorly. Secure with fascial sling or bury (submuscular).
Complications
MABC Neuroma
- Incidence: Common if incision is too anterior.
- Symptoms: Painful numbness over olecranon.
- Prevention: Find the nerve. Protect it.
The MABC is often mistaken for a vein.
Postoperative Care
- Soft dressing.
- Avoid hyperflexion.
- Immediate finger movement.
- Removal of sutures.
- Start nerve gliding.
- Strengthening exercises.
- Return to heavy work (if submuscular, may delay to 3 months).
Prognosis
- Outcome: Good for Grade I/II.
- Grade III: Recovery of intrinsics is unpredictable (often incomplete).
- Age: Older patients recover less motor function.
- Diabetes: Poor prognostic factor ("Double Crush").
Recurrence of symptoms after simple decompression forces a decision: Re-do decompression (if adhesions) or Transposition (if subluxation). Most surgeons opt for Submuscular Transposition in revision cases.
Evidence Base
Simple vs Transposition
- Meta-analysis of randomized trials
- No significant difference in outcome between simple decompression and subcutaneous transposition
- Transposition has higher complication rate (wound, etc)
Submuscular Transposition
- Excellent results for recurrent cubital tunnel
- Placing nerve in a fresh vascular bed
- Protect from trauma
Endoscopic Release
- Faster recovery, smaller scar
- Equal long term outcomes to open
- Higher risk of hematoma/nerve injury in learning curve
Supercharged End-to-Side
- AIN to Ulnar motor branch (SET) enhances recovery
- Babysits the intrinsic muscles while ulnar nerve regenerates
- Improved outcome in high ulnar nerve injuries
Splinting
- Night splinting effective for mild symptoms
- Reduces intraneural pressure
- Patients often poorly compliant
Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: The Claw Hand
"A 60-year-old man presents with a clawed ring and little finger. He has wasting of the first dorsal interosseous. Sensation is decreased on the volar small finger but NORMAL on the dorsum of the hand."
Scenario 2: Failed Decompression
"A patient had a simple decompression 6 months ago. Symptoms persisted and are now worse. There is snapping."
Scenario 3: The Musician
"A violinist complains of numbness in the small finger when playing. Symptoms resolve with rest."
MCQ Practice Points
Anatomy
Q: What structure forms the roof of the Cubital Tunnel? A: Osborne's Ligament (Arcuate ligament bridging the two heads of FCU).
Paradox
Q: Why is clawing less severe in high ulnar nerve palsy? A: Paralysis of the FDP to the ring/little fingers reduces the flexion moment at the IP joints.
Signs
Q: What muscle is being compensated for in Froment's Sign? A: Adductor Pollicis (Compensated by FPL).
Guyon's Canal
Q: What are the three zones of Guyon's Canal? A: Zone 1 (Mixed - motor and sensory), Zone 2 (Motor only - around hook of hamate), Zone 3 (Sensory only).
Wartenberg's Sign
Q: What causes Wartenberg's Sign (abducted little finger)? A: Weakness of the 3rd Palmar Interosseous (adductor) with unopposed EDM (abductor) action.
Nerve Course
Q: Where does the dorsal cutaneous branch of the ulnar nerve arise? A: Approximately 5cm proximal to the wrist. This helps differentiate high vs low lesions (intact in Guyon's Canal lesions).
Australian Context
- WorkCover: Common claim for desk workers (leaning on elbows).
- Guidelines: Funding models often differentiate between simple neurolysis and transposition (higher rebate for transposition).
- Referral: Hand Therapists in Australia are highly skilled in 'anti-claw' splinting.
High-Yield Exam Summary
Localization
- •Dorsal Sensation Intact = Wrist (Low)
- •Dorsal Sensation Lost = Elbow (High)
- •FDP Intact = Wrist (Low) to More Clawing
- •FDP Weak = Elbow (High) to Less Clawing
Compression Sites (SAM-FO)
- •Struthers (Arcade)
- •Arcade of Osborne
- •Medial Septum
- •Fascia
- •Osborne's Ligament
Signs
- •Froment: Adductor (Thumb IP Flex)
- •Wartenberg: 3rd Palmar (Little finger Abd)
- •Jeanne: FPB (Thumb MCP Ext)
- •Duchenne: Claw
Treatment Algorithm
- •Mild: Observation, Splinting, Activity Modification
- •Moderate: Simple Decompression vs Transposition
- •Severe: Anterior Transposition
- •Fixed Claw: Tendon Transfers