NERVE REPAIR PRINCIPLES
Biology and Technique
Injury Types (Seddon/Sunderland)
Critical Must-Knows
- Wallerian Degeneration occurs distal to the injury site.
- Regeneration proceeds at ~1mm/day (or 1 inch/month).
- Tension-free repair is the single most important surgical principle.
- Primary repair is preferred if clean and no gap.
- Grafts (Autograft) are the Gold Standard for gaps.
- Conduits are acceptable for small gaps (less than 2cm) in small diameter nerves.
Examiner's Pearls
- "Motor End Plates die after 12-18 months ('Time is Muscle').
- "Sensation can recover years later (though quality diminishes).
- "The most common cause of failure is tension at the repair site.
Clinical Imaging
Imaging Gallery
The Trap: 'Wait and See'
The Problem
Uncertain Diagnosis In closed injuries, it's hard to tell Axonotmesis from Neurotmesis. Waiting 3-6 months is standard.
The Exception
Open Injuries If there is a penetrating wound and a deficit, Assume the nerve is CUT. Do NOT wait. Explore early.
| Feature | Neurapraxia | Axonotmesis | Neurotmesis |
|---|---|---|---|
| Pathology | Myelin Block | Axon cut / Sheath intact | Complete Transection |
| Wallerian Degen | No | Yes | Yes |
| Tinel's | No (or at site) | Yes (Moves distal) | Yes (Stays at site) |
| Recovery | Hours to Weeks | Months (1mm/day) | None without surgery |
| Surgery | No | No | Yes |
My Axon Endo Peri EpiSunderland Classification
Memory Hook:Layers breached from inside out.
TIPSSurgical Principles
Memory Hook:Tips for nerve repair.
SAMSDonor Nerves
Memory Hook:SAMS nerves.
Overview
Wallerian Degeneration: The process where the distal axon segment disintegrates and is cleared by macrophages/Schwann cells, creating a tube for the new axon to grow into. Bands of Bungner: The columns of Schwann cells that guide the regenerating axon.
Peripheral nerve injury creates a race between axonal regeneration and end-organ atrophy.
Pathophysiology
Wallerian Degeneration
Following nerve transection, the distal segment undergoes Wallerian degeneration—a coordinated destruction and clearance process:
Timeline:
- 0-24 hours: Axoplasm granulates, neurofilaments fragment
- 24-48 hours: Calcium influx triggers cytoskeletal breakdown
- Days 3-7: Schwann cells dedifferentiate and proliferate
- Weeks 2-4: Macrophages infiltrate and phagocytose myelin debris
- Weeks 4-8: Complete clearance creates "empty tubes" for regeneration
Molecular Events:
- c-Jun activation in Schwann cells: Master transcription factor for dedifferentiation
- Myelin breakdown: Cholesterol-rich debris must be cleared before regeneration
- Neurotrophic factor release: NGF, BDNF, GDNF guide regenerating axons
Axonal Regeneration
The proximal stump forms a growth cone—a specialized structure that navigates toward target tissues:
Growth Cone Function:
- Filopodia (finger-like projections) sample the environment
- Respond to chemoattractants (neurotrophins) and repellents (semaphorins)
- Require intact endoneurial tubes for successful guidance
Rate of Regeneration:
- Standard rate: 1 mm/day (1 inch/month)
- Faster in children, slower in elderly
- Faster proximally, slower distally
- Calculate expected recovery: Distance to target ÷ 1mm/day + latent period (1 month)
End-Organ Atrophy
Motor End Plate Degeneration:
- Begin to atrophy at 3-6 months
- Irreversible changes by 12-18 months
- Cannot be reinnervated after permanent fibrosis
- This is the "biological clock" that limits proximal repairs
Sensory Receptors:
- More resilient than motor end plates
- Can recover even years after injury
- Quality diminishes over time (never normal 2-point discrimination)
Factors Affecting Regeneration
| Factor | Better Outcome | Worse Outcome |
|---|---|---|
| Age | Children | Adults greater than 60 |
| Level | Distal | Proximal |
| Mechanism | Sharp cut | Crush/avulsion |
| Timing | Early repair | Delayed repair |
| Gap | Direct repair | Long graft |
| Nerve | Pure motor/sensory | Mixed nerve |
Anatomy
Wallerian Degeneration
- Starts: 24-48 hours post-injury.
- Process: Calcium influx leads to Cytoskeleton breakdown leads to Axon and Myelin digestion.
- Clearance: Macrophages clear debris (takes weeks).
The distal stump must be cleared before the new axon can enter.
This latent period is why early repair doesn't mean immediate regeneration.
Classification Systems
Immediate Repair (less than 24-48 hours)
- Indications: Sharp, clean lacerations.
- Pros: Anatomy is clear, no retraction, single procedure.
- Cons: Emergency setting (maybe less optimal team).
Standard of care for clean glass/knife injuries.
Clinical Assessment
History
- Mechanism: Sharp vs Blunt vs Traction.
- Time: Duration since injury.
- Age: Patient age (prognostic).
Examination
- Motor: Test individual muscles (MRC grade).
- Sensory: Light touch, 2PD (Static/Moving).
- Tinel's: Percuss over nerve. Distal advancement sign of regeneration.
Investigations
Nerve Conduction Studies
- Timing: Wait 3-4 weeks for Wallerian degeneration to complete (otherwise distal stump conducts).
- Findings: Denervation potentials (Fibs/Positive Sharp Waves) in muscle.
A baseline study at 3-4 weeks is standard for monitoring.
Management Algorithm
Autografts (Gold Standard)
- Indication: Any gap that cannot be closed without tension.
- Donor: Sural (calf), MABC (arm), LABCN (forearm).
- Technique: Cable grafting (multiple strands).
- Pros: Contains Schwann cells + basal lamina.
- Cons: Donor site morbidity (numbness).
Must reverse the graft direction if using Sural nerve (valves).
Surgical Technique
Epineurial Repair
- Standard: For most digital/peripheral nerves.
- Suture: 8-0, 9-0, or 10-0 Nylon.
- Goal: Align surface vessels (vasa nervorum) to ensure rotational alignment.
- Technique: 2-4 sutures in the epineurium. Avoid entering the fascicles.
Faster and less inflammatory than fascicular repair.
The key is to avoid tension which causes ischemia.
Nerve Transfers
Concept: "Rob Peter to Pay Paul". Using a redundant or expendable proximal nerve branch to reinnervate a critical distal target.
- Goal: Bypass the injury site and reduce regeneration distance.
- Example:
- Oberlin Transfer: Ulnar fascicle to Biceps (for Musculocutaneous injury).
- AIN to Ulnar: For high ulnar nerve palsy.
- Spinal Accessory to Suprascapular: For Brachial Plexus injury.
Advantage: Converts a high level injury into a low level injury (faster recovery).
Complications
- Neuroma: Painful lump at repair site (failed regeneration).
- CRPS: Pain syndrome.
- Failur of Motor Recovery: Atrophy.
- Cold Intolerance: Permanent symptom in almost all nerve injuries.
- Mismatch: Sensory axon growing into motor tube (wasted).
- Cross-talk: Synkinesis (rare in peripheral, common in facial nerve).
Postoperative Care
- Splint: Protective position (relieve tension).
- Motion: Protected gliding (controlled active motion) to prevent adhesion.
- Wean Splint: Gradual extension.
- Desensitization: Texture exposure.
- Sensory: Discriminative training (Dellon).
- Motor: Biofeedback / Mirror therapy.
Neural plasticity plays a huge role in outcome.
Prognosis
- Factors:
- Age: The most important factor. Children regenerate excellently. Adults greater than 60 poorly.
- Level: Distal is better than Proximal.
- Type: Sharp cut better than Crush/Avulsion.
- Gap: Tension kills repair.
- Delay: Repair within 3 months is best.
- Outcome: Normal 2PD is rarely achieved in adults (~6-10mm is good).
Evidence Base
Tension Effects
- Pioneered the use of nerve grafts
- Demonstrated that tension causes ischemia and fibrosis
- Grafts had better outcomes than tensioned primary repair
Conduits vs Grafts
- Comparison of conduit vs autograft for digital nerves
- Conduits equal to grafts for gaps less than 2cm
- Grafts superior for gaps greater than 2cm
Early Mobilization
- Meta-analysis
- Early active motion vs immobilization
- No difference in rupture rate
- Better functional recovery with early motion
Sensory Re-education
- Described the protocol for sensory re-education
- Early phase (perception) vs Late phase (discrimination)
- Significant improvement in functional outcome
Nerve Transfers
- Described Ulnar to Musculocutaneous transfer
- Restored elbow flexion in C5/6 avulsion
- Changed the paradigm of brachial plexus reconstruction
Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: The Gap
"You are exploring a cut median nerve at the wrist. The ends are retracted. You cannot approximate them without flexing the wrist 45 degrees. What do you do?"
Scenario 2: The Old Injury
"A patient presents 18 months after a laceration to the Ulnar nerve at the forearm. They have no sensation and no intrinsics (Claw hand). They want surgery."
Scenario 3: The Neuroma
"A patient has a painful stump neuroma after a digital nerve injury. It's Tinel positive."
MCQ Practice Points
Biology
Q: At what rate does a nerve regenerate? A: Approximately 1mm per day (or 1 inch per month).
Technique
Q: What is the maximum gap suitable for a nerve conduit in a digital nerve? A: Generally accepted as less than 2cm (some say 3cm maximum).
Prognosis
Q: What is the most significant predictor of poor outcome in adults? A: Increasing Age (especially greater than 60).
Anatomy
Q: Which structure guides the regenerating axon? A: The Basal Lamina of the Schwann Cell (Bands of Bungner).
Timing
Q: What is the critical time limit for motor recovery after nerve injury? A: 12-18 months - after this time, motor end plates undergo irreversible fibrosis and atrophy, so muscle recovery is not possible.
Australian Context
Peripheral nerve injuries in Australia commonly result from occupational accidents, particularly in the manufacturing, construction, and agricultural sectors. WorkCover claims for nerve injuries represent a significant burden on state compensation systems, with average claim costs exceeding $50,000 for complete nerve transections requiring surgical repair.
Referral Pathways:
- Complex nerve injuries are referred to major Hand Surgery Units including Sydney Hand Hospital, St Vincent's Melbourne, Princess Alexandra Brisbane, and Royal Perth Hospital
- Regional and remote injuries require transfer for microsurgical expertise
- Telehealth consultations assist in initial assessment and transfer decisions
Hand Therapy Services:
- DVA and WorkCover fully fund hand therapy rehabilitation
- Medicare provides limited rebates for allied health under CDM items
- Early therapy involvement is critical for desensitization and protected mobilization
Antibiotic Prophylaxis (eTG):
- Open nerve injuries: First-generation cephalosporin (Cephalexin 500mg QID for 5 days)
- Heavily contaminated wounds: Add metronidazole for anaerobic coverage
- Tetanus prophylaxis required for all open injuries
High-Yield Exam Summary
Principles
- •Tension-Free Repair
- •Clean Preparation
- •Microsurgical alignment
- •Early protected motion
Timing
- •Primary: Less than 48 hours - best outcomes, clean wounds
- •Delayed: 2-3 weeks - contaminated/crushed injuries
- •Secondary: Greater than 3 months - if recovery plateau
- •Nerve regeneration rate: 1mm/day (1 inch/month)
- •Advanced Tinel sign indicates regeneration progress
Options
- •1. Primary Repair
- •2. Nerve Conduit (Gap less than 2cm)
- •3. Nerve Autograft (Gap greater than 2cm)
- •4. Nerve Transfer