Editing Nerve injury

== Anatomy ==

* Subunit of the peripheral nerve is the axon
* Axons surrounded by endoneurium and grouped into fascicles
* Fascicles encapsulated by perineurium, and groups of fascicles are surrounded by interfascicular epineurium
* Motor endplates within muscle will irreversably degenerate after 12 months, and after this point the muscle cannot be reinnervated

== Classification of nerve injuries ==

* Open - laceration
* Closed - overstretching, blunt, compressive trauma
* Neuropraxia
** focal or segmental demyelination with preservation of axon continuity
** Functional recovery expected as the myelin heals
** Expected to take up to 6 weeks to recover
** No surgical intervention required
* Axonotmesis
** Axonal injury with preservation of the endo and epineurial sheath
** Axon will die back to nearest node of Ranvier, and then regrow at rate of 1mm/day through the distal endoneurial tubes
** Axons distal to the injury will undergo Wallerian degeneration - this process commences in 72-96 hours, and after this time period the distal axons will irreversably degrade, so repair should be undertaken within this period where it is going to be attempted
** Range of recovery - can be complete, can be minimal. Depends on degree of damage to surrounding structures and resulting scar tissue.
** Spontaneous recovery is likely in Sunderland II or III, but not in IV
* Neurotmesis
** Complete transection of all neural structures
** Surgical intervention required

== Indications for repair ==

* Early (3 days)
** Suspected transection with sharp injuries
*** Any nerve deficits are likely to represent Sunderland V or VI
** Acute nerve compression resulting from vascular or bony injuries, especially in the vicinity of a closed compartment
* Subacute (3 weeks)
** Blunt or ragged injuries (chainsaw, propeller blades)
*** Some would advocate for still treating those injuries within 3 days
**** Can combine repairs with other procedures
**** Technical challenges of dealing with scarring can be avoided
**** Probably reasonable to explore early, and if nerve is found to be in continuity, can observe it for a few months (intra-op nerve testing would not be helpful because Wallerian degeneration has not yet occurred)
*** These injuries represent neurotmesis (Sunderland V or VI)
*** Delaying repair allows Wallerian degeneration to begin occurring, better defining the zone of injury
*** Nerve endings can be resected back to healthy tissue, which would be difficult to evaluate in early setting
* Delayed (3 months)
** Lesions-in-continuity (stretch injuries, contusive injuries, gunshot wounds)
*** Hard to predict which path the nerve injury will follow, and whether it will resolve or require repair
*** Continue non-op for nerves showing signs of recovery or partial lesions (90% of nerves that recover will do so within 4 months) and intervene if no evidence of clinical or electrical recovery
*** Delay also allows intra-op nerve testing to distinguish between recovering lesions (Sunderland II or III) and non-recovering (Sunderland IV)
* Late (>1 year)
** Salvage procedure - delayed presentation or no/incomplete recovery
*** Nerve repair and reconstruction typically does not work well

== Operative principles ==

* Excellent exposure - identify the normal nerve, before carrying dissection forward or back
* Tourniquet up for no longer than 30 mins if intra-operative nerve stimulation is planned
* Really there are two things you are likely to find: neuroma in continuity, or nerve stumps
* Neuroma-in-continuity: 
** Intra-operative nerve action potentials will be helpful, because inspection/palpation does not predict histology or outcomes, and can determine recovery before that recovery is seen either clinically or via electromyogram
** If NAP is present across a lesion, don't resect - probably better off with neurolysis alone
** If no NAP, probably needs resection and surgical repair
* Nerve stumps
** Nerve repair or reconstruction is indicated
* Microsurgery should be used to repair
** Sharply remove neuroma and scar tissue, until normal fascicular structures are seen (this pattern is called les yeux d'escargot - snail's eyes)
** Divide protruding fascicles until they lie flush with epineurial sheath - ensure no overlapping of fascicles
** End to end repair or interpositional grafting - 8-0, 9-0 or 10-0 suture should be used
** Tension-free
** Ensure the suture only connects epineurium, and not fascicles - will lead to intraneural neuroma
** Often only two or three interrupted sutures required
** Fibrin glue may be used to reinforce the suture line
* Neurolysis
** Releasing scar tissue surrounding the injured nerve
** Indicated for neuroma in continuity, with intact NAP conduction
* Nerve graft
** Most frequent source is sural nerve
** Suture in reversed orientation, which ensures that axons will not be lost to small side branches in the nerve graft

== Timing of repair ==

* 3+1 rule



[[Category:Skin, soft tissue and wounds]]