June 20, 2024

Peripheral Nerve Injury is an injury to peripheral nerves which may result in loss of motor function, sensory function, or both.

Anatomy of Peripheral Nerve

Epineurium: Connective tissue layers of the peripheral nerve which both muscle and runs between fascicles

Functions: Nourish and protects fascicles

Within and through epineurium:- Lie neutral fasciclesàeach surrounded by the peripheral sheath

Perineural layer:- Major contributor to nerve tensile strength

Endoneurium:-  Innermost loose collagen matrix within the fascicles

Axon runs through the endoneurium and is protected and nourished by this layer.

In nerve repair, fascicular matching is critical to the outcome

Nerve Cells in peripheral nerve injury
Nerve Cells

Blood Supply:

2 Major blood supply

  1. 1st lies superficial to nerve
  2. 2nd lies in interfascicular epineurium

1 Longitudinal system within endoneurium/perineurium

Segmental vascular supply is number of nutrient arteries that enter the nerve at the regular intervals

Endoneurium capillaries: functions as an extension of Blood-Brain Barriers (BBB)

Injury classification

Seddon and Sunderland Classification of Peripheral nerve injury
Seddon and Sunderland Classification of Peripheral nerve injury

Physiology of nerve degeneration

Axonal transaction

Cell body

  • Swells
  • Chromatolysis
    • Nissl granules(basophilic neurotransmitters)­­: Disperse and become eosinophilic
    • Change of priority form
  • Production of neurotransmitters to production of structural material for nerve regeneration (mRNAs, lipids, actins, tubulins, GPs)

Axons

Proximal Axons:

  • Traumatic degenerations at the zone of injury ( up to node of Ranvier) + Death of cell body can also occur

Distal Axons:

  • Wallerian degenerations initiated (48 -96 hr)
  • Myelin deterioration starts
  • Axon-disorganized
  • Schwann cell will proliferate and Phagocytes myelin +Axonal debris
Physiology of nerve Injury

Physiology of nerve regeneration

After Wallerian degeneration, Schwann cell of basal lamina persist creating a column of cells–>Bungner Band

Bungners band provides a supportive and growth-promoting environment

Tip of regenerating axons: Filopodia (finger-like projections) release protease (path to clear way to target organs and explore microenvironment)

Growth cone response to

  1. Neurotrophic factors
  2. Neurite-promoting factors
  3. Matrix forming precursors
  4. Metabolic and other factors

Distal Reinnervations:

  • Bone develop osteoporosis
  • Joint and soft will become fibrotic and stiff
  • Muscle ( atrophy / interstitial fibrosis) which is viable for 2 years

Neurorrhaphy

Historically wait for 3 weeks (conclusion of Wallerian degeneration)

Recently: Primary repair is associated with better functional results

Pre-requisites for primary repair

  • Clean wound
  • Good Vascular Supply
  • No crush components
  • Adequate soft tissue coverage

Skeletal Stability with minimal tension in the nerve

Techniques

  • Group Fascicular repair
    • Disadvantages of scarring and damage to blood supply due to additional dissection
  • Epi-neural Repair

Both functional outcomes are similar

Monofilament—Nylon (8-0) is used

Identification ( difference between motor and sensory)

  • Blue-SAb staining
  • Carbonic Anhydrase Staning
  • Cholinesterase staining

The sensory nerve is identified

Stain persists 35 days in the proximal stump, 9 days in the distal stump

According to time

  1. Primary Repair: within 6 – 8 hr of injury
  2. Delayed Primary Repair: between  – 18 days of injury
  3. Secondary Repair: After 18 days

Nerve grafting

Autograft (standard)

Cable:- multiple small caliper nerve grafts aligned in parallel to span a gap between the fascicular gap

Trunk:- Mixed motor-sensory whole nerve graft (poor functional result)

Vascular Nerve Graft

Common source:- Sural nerve

For most cases cable grafting ( easily obtainable, appropriate diameter, relatively dispensable)

Other Nerves:

Medial antebrachial cutaneous nerve

Lateral femoral cutaneous nerve

Superficial radial sensory nerve

Principle of treatment

Closed low energy injuries: Recovered Spontaneously

If

1. Nerve is seen to be divided and needs repair

2. Sharp cut type injury

3. Delayed in recovery and diagnosis in doubt

NERVE EXPLORATION

The divided nerve should be repaired as soon as possible (nerve ends are not retracted much, relative rotations are undisturbed, no fibrosis)

PRIMARY REPAIR

If closed injury left alone shows no sign of recovery

Patients present late or missed diagnosis

Failure of primary repair

DELAYED PRIMARY REPAIR

  1. Nerve ends slightly thickened/ soft: No resection
  2. Neuroma with no conduction on stimulation: Should be resected (nerve must be sutured without tension)

Tension-free gaps:

  • 2 cm in the median nerve
  • 4-5 cm in ulnar nerve
  • 6-8 cm in sciatic nerve
  • 1-2 cm in other nerves

Can be kept in limb in relaxing position

If not:

NERVE GUIDES

Collagen tubes, nano-engineered tubes, veins, silicon

If needs to bridge larger gaps

NERVE GRAFTING

Sural neve can be used to bridge up to 40 cm

In smaller diameter: cable grafting

In very proximal injury, root avulsions, distance for graft in long

NERVE TRANSFER

TENDON TRANSFER

BONY RECONSTRUCTION

Principle of Nerve Transfer:

  1. Sharply transecting the injured nerve ends to excise the zone of injury
  2. Nerve ends should display a good fascicular pattern
  3. The defect is measured: Appropriate length of graft is harvested for reconstruction with/out tension
  4. The graft is matched to corresponding fascicles and sutured to the injured nerve with an epineural suture
  5. If the injured Nerve has a large diameter relative to the nerve graft, several cable grafts are placed in parallel to reconstruct the nerve
  6. Fibrin glues can be used for cable graft (minimizing scar/hematoma)
  7. Placement of graft in reverse orientation in repair site (↓es chances of axonal dispersion through distal nerve branches)
  8. Well Vascularized Bed
  9. The graft should be 10%-20% longer than the gap to be filled, as it shortened with connective tissue fibrosis
  10. Limb immobilized (4 wks):- Graft repair site and graft itself regain some tensile strength.

See also: Nerve Injury Short Cases

See also: Brachial Plexus Injuries