Peripheral Nerve Injury

Anatomy of the peripheral nerve 

 

Endoneurium 

- loose collagenous matrix

- surrounds the individual nerve fibers within the fascicle

 

Perineurium 

- thin, dense connective tissue sheath that surrounds each fascicle

 

Epineurium 

- a loose meshwork of collagen  and elastin fibers 

- provides a supportive and protective framework for the fascicles

- collagen fibers in the epineurium are thicker than those in the endoneurium / perineurium

 

Definition

 

Neuropraxia

- focal demyelination 2° ischaemia

- full recovery by 3 months

 

Axonotmesis

- axon disrupted

 

Neurotmesis

- nerve division

 

Seddon & Sunderland  Grading

 

1st Degree / Neuropraxia

- localised conduction block leading to segmental demyelination

- axons are not injured

- remyelination and recovery < 3 months, no Tinel's

 

2nd Degree / Axonotemesis

- axonal injury with distal segment Wallerian degeneration

- full recovery

- nerve fibres regenerate 1 mm per day

- but > 3 months, advancing Tinel's

 

3rd Degree / Endoneurium disrupted

- incomplete recovery due to fibrosis

- advancing Tinel's

 

4th Degree / Perineurium divided / Epineurium intact

 

Nerve is in continuity but complete block due to scar

 

Poor prognosis

- perineurium disrupted

- becomes filled with scar

- no recovery, no Tinel's

- no SNAP, denervation potential

- no rennervation at 3/12 (polyphasic AP)

 

Often needs repair 

 

5th Degree / Epineurium divided

- 100% divided / neurotmesis

 

6th Deg (added by Susan McKinnon)

- neuroma in continuity

- mixed recovery

 

Injury Response 

 

Wallerian Degeneration

 

Axon dies distally

- remains intact for 3/24 (until stores depleted)

 

Schwann cell proliferation and macrophage ingrowth

- clear distal stump of axoplasm & myelin

- prepares way for new axon 

 

Axon Regeneration

 

Axon sprouts enter distal endoneural tubes

- 1-2 mm/day

- survive if contact an end organ

- sprouts often enter wrong tube & wrong end organs

- some axons fail to cross repair site & form neuroma

 

Axon Guidance 

 

1. Directional Neurotropic Cues 

- target releases tropic factor

 

2. Survival Neurotropic Cues 

- tube supports correct axon

 

3. Mechanical Alignment 

- worst

 

4. Contact Recognition 

- path selection based on surface

 

Sensory Fibres

 

Survive years of degeneration

- sensory return order

- pinprick / moving touch / constant touch / vibration

 

Muscle Fibres

 

Myofibrils atrophy without nerve

- 50% in 2/12

- fibrotic by 12/12

- need to repair < 9/12

 

Neuromuscular Junction

 

Receptor dispersal over 12 months

- needs to be re-innervated prior to 12 months

 

Receptor becomes more sensitive to ACh

- spontaneous fibrillation start Day 10 

- significant EMG changes > 2/52 

 

Neuronal Response

 

Cell body dies if very proximal axon injury

- 2° ion leakage

- if neurone survives body & nucleolus enlarges

- regenerative proteins produced

- responsible for delay in nerve recovery / regeneration

 

Mechanism Injury

 

1. Open wounds

 

2. Compression

- pressures > 30 mmHg impair venular epineural flow

- retards axonal transport

- alteration in intraneural BV permeability

- leads to nerve function deterioration 

- relative to length of compression & absolute pressure 

 

Tourniquet

- UL 200 mmHg / Max 90 min

- LL 300 mmHg/ Max 120 min

 

3. Traction

 

4.  Thermal 

 

5.  Irradiation Neuritis

 

6.  Injection

 

Recovery Assessment

 

EMG

 

Denervation

- 3 weeks

- fibrillation potentials

- positive sharp waves 

- spontaneous AP

 

Reinnervation

- polyphasic AP  

 

Tinel's Sign

 

Percuss along the nerve

- transient tingling in nerve distribution not at injury site

- indicates axonal sprouts progressing along tube that haven't remyelinised

- response fades proximally secondary to progressive myelinization

 

Sweat Test

 

Sympathetic fibres very resistant to injury

- sweat preservation 

- 20+ magnification lens 

 

Management

 

Outcome Factors 

 

General

- age of patient / most important / < 30 best prognosis

- level of injury (proximal worse than distal)

- health of patient

- time delay to repair

- pure sensory nerves do better than mixed nerves

 

Local

- cut or crush

- single or double level

- surgeon factors

- nil gap, no tension on repair

 

Contraindications to Repair

 

Noncompliant patient

Elderly

Hopeless outcome

Insignificant nerve eg SRN -> surgery to avoid neuroma

Insufficient skills

 

Types of Repair

 

1.  Direct

 

Epineurium repair without tension

 

Primary repair

- best chance of fascicular matching / best fit

- minimal retraction & gap formation

- historically best results

- 8/0 or 9/0 nylon

 

Fascicular Repair

 

Not usually indicated except

- distal 1/3 forearm median nerve

- distal 1/3 forearm ulna nerve

- sciatic nerve in thigh

 

Approach

 

Median nerve

- release PT and FDS radial insertion

- can transpose anterior to pronator and FDS

 

Results

 

Rujis et al Plastic Recon Surg 2005

- meta-analysis

- age > 40 / proximal lesions / delay to repair poor prognostic indicators

 

2.  Nerve Grafting 

 

Indications

- gaps > 2.5 cm

 

Options

- cable graft

- vascularised graft

 

Cable graft

 

Graft options

- Sural / MCNF / LCFN / Saphenous

 

Vascularised graft

 

Technique

- mobilise on BV pedicle

 

Advantage

- faster recovery

 

3.  Neural tubes

 

Description

- absorbable synthetic tubes

- epineurium sutured to each end of tube

- nerve fibrils grow into and along tubue

 

Advantage

- tension free repair

 

Results


Aberg et al J Reconst Plast Aesthet Surg 2009

- RCT of epineural repair v tube in sharp distal median and ulna nerve injures

- no difference between two groups

 

3. Nerve Transfer 

 

4. Neuroma 

 

Resect, diathermy & bury nerve end deeply in good tissue not bone