· proposed in 1943
Neuropraxia
· conduction block due to ischaemia
· no interruption of axon or nerve fibre
· possible minor oedema or breakdown of the myelin sheath
· transmission of some impulses are physiologically interrupted
· power and discriminatory sensation lost
· pressure sense and sympathetic function lost
· electrical conduction in distal trunk persists
· no fibrillation potentials
· recovery is complete in a few days to a few weeks
Axonotmesis
· more significant injury with interruption of axon
· distal Wallerian degeneration occurs but Schwann cells and endoneural tubes preserved
· no distal conduction
· fibrillation potentials appear within 3 weeks
· loss of function of post-ganglionic sympathetic fibres
· red (vasodilation)
· dry (anhydrosis)
· spontaneous regeneration with good recovery can be expected
Neurotmesis
· complete anatomic severence of the nerve or extensive avulsing or crushing injury
· perineurium and epineurium are also disrupted to a varying degree
· significant spontaneous recovery cannot be expected
· proposed in 1951
· more readily applicable clinically
· each degree of injury suggests a greater anatomic disruption with its correspondingly altered prognosis
· anatomically each degree represents damage to
· myelin
· axon
· endoneurial tube and its contents
· perineurium
· entire nerve trunk
First degree
· conduction along the axon is physiologically interrupted but axon intact
· no wallerian degeneration
· spontaneous recovery in few days to few weeks
· corresponds to Seddon's neuropraxia
· motor function usually more profoundly affected than sensory function
· sensory affected as follows
· proprioception > touch > temperature > pain > sympathetic
· electrical excitability of the distal nerve is preserved
· characteristic simultaneous return of motor function in the proximal and distal musculature
· no wallerian " motor march"
Second degree
· disruption of the axon is evident with wallerian degeneration distal to the point of injury
· proximal degeneration for one or more nodal segments (more with greater severity of injury)
· motor reinnervation form proximal to distal "motor march"
· advancing Tinel sign at the rate of 1mm / day
· good functional return normally achieved
Third degree
· typical traction injury
· axon and endoneurial tube are disrupted
· preservation of the perineurium
· result is disorganization rather than disruption of the endoneurial tube
· complete return of neurological function does not occurr distinguishing this from a second degree injury
Fourth degree
· axon and endoneurial tube are disrupted
· some of epineurium and possibly also some perineurium are disrupted
· no advancing Tinel sign
· poor prognosis without surgical repair
· neuroma forms
Fifth degree
· nerve completely transected with a variable distance between neuronal stumps
· injury usually occurs in open wounds and usually identified at the time of early surgical exploration
Sixth degree (McKinnon)
· nerve trunk partially severed with the remaining intact part of the trunk sustaining second/ third/ or fourth degree injuries
· will go on to develop a neuroma in continuity with a mixed pattern of recovery
· two groups
· differentiated by presence of sympathetic changes
Conduction block
· corresponds to Seddon neuropraxia and Sunderland 1
· may be
· short-acting (eg. tourniquet)
· long-acting (eg. Saturday night palsy)
Degeneration
· corresponds to other groups
· may be
· favourable (Seddon axonotmesis and Sunderland 3)
· unfavourable (Seddon neurotmesis and Sunderland 4 & 5)
· axon dies distal to point of injury
· axon lacks synthetic capacity
· axon remains intact for several days
· until metabolic stores depleted
· remains excitable until then
· wallerian degeneration serves to clear distal stump of axoplasm and myelin
· prepares way for subsequent axon regeneration
· initiated by ingrowth of macrophages
· triggers proliferation of Schwann cells
· proliferation peaks at 3 days and continues for 2 weeks
· Schwann cells and macrophages clear tubes
· may survive years of degeneration
· no clear period of denervation after which useful sensation cannot be restored
· bare axon tips cf. sensory organs may be able to transduce sensory information
· return of sensation
· pinprick first to return
· then 30 cps vibration
· then moving touch
· constant touch and 256 cps vibration last to return
· myofibrils depend on interaction with their motor neurones for their normal function
· after damage to the motor neurone the myofibrils atrophy and become more sensitive to acetyl choline
· appears 7 - 14 days post injury
· seen as spontaneous fibrillations
· significant EMG changes are not apparent for 2 weeks
· then spontaneous fibrillation potentials apparent awith onset of atrophic changes in muscle fibres
· atrophy of 50% - 70% muscle bulk within 2 months
· significant fibrosis by 12 months
· critical interval to repair about 9 months
· autonomic paralysis shows
· loss of sweating
· loss of pilomotor response
· vasomotor paralysis
· death of parent neurone may occur after axonotomy
· due to retrograde degeneration
· most common in proximal lesions in the young
· in those neurones that do not die, the following occurs
· neurone undergoes chromatolysis (dispersal of Nissl substance in cell body)
· cell body and nucleolus enlarges
· regenerative proteins rather than neurotransmitters produced
· sprouts formed that enter distal nerve stump
· regenerate through stump to contact and reinervate peripheral end organs
· sprouts regenerate at most distal remaining node of Ranvier
· 2-5 sprouts persist as axon collaterals
· those that contact an end organ survive while others are pruned away
· sprouts may enter separate and often unrelated Schwann cell tubes in distal nerve end and be led to different end organs
· sprouts of same axon may innervate different muscles or supply different cutaneous receptive fields
· axons begin to sprout within hours of injury
· permanent sprouts formed within 24 hrs
· distal progress of sprouts limited at site of transection
· 'scar delay' is about three weeks
· some axons fail to cross repair site and form neuroma
· other cross but only enter interfascicular epineurium
· most axons that reach the Schwann cell tube propagate along their inner surface
· at rate of 1-2 mm/day (slower toward periphery)
· there is heirarchy of specificity of axon regeneration
· firstly, there is preferential regeneration of axons towards nervous vs other forms of tissue
· due to neurotropism (directed regeneration up concentration gradient of substance diffusing from neural target)
· secondly, there is sensory/motor specificity
· due to neurotrophic (nutritive) support of motor axon collaterals that reinnervate old motor Schwann cell tubes
· thirdly, there is topographic specificity
· degree is proportional to accuracy of stump realignment
· finally, there is end-organ specificity
· reason unclear
Open wounds
· may be
· tidy
· untidy
Compression and traction
· traction more harmful
· effects of traction
· 6% stretch - disturbance of conduction
· 8% stretch - obstruction of venous flow
· 15% stretch - complete ischaemia
· severe stretch - rupture
Thermal injuries
· may be
· cold
· hot (eg. burns, PMMA)
Irradiation neuritis
· common in radiotherapy to
· axilla
· breast
Injection
· at risk are
· sciatic n
· brachial plexus
· nerves to shoulder
· nerves in front of elbow
Fractures and dislocations
· often have associated vascular injury
· vascular compromise affects nerve recovery
· exploration indicated in
· vascular injuries
· most dislocations
· widely displaced fractures with imperfect reduction
Pelvis and hip
· lumbosacral plexus at risk from fracture dislocations of pelvis
· sciatic nerve at risk from fracture dislocations of hip
Knee
· tibial nerve at risk from knee dislocations
· common peroneal nerve at risk from lateral plateau fractures
Elbow
· all nerves at risk from supracondylar fracture
· radial n most commonly injured
Shoulder
· from shoulder dislocations and fractures of proximal humerus
· range from isolated axillary palsy to brachial plexus palsies
Iatrogenic injuries
Tourniquet
· guidelines
· upper limb - 200 mg Hg for max of 90 min
· lower limb - 300 mg Hg for max of 120 min
· avoid tourniquet with
· fem-pop bypass
· atherosclerosis
Positioning
· lithotomy
· sciatic
· common peroneal
· prone
· ulnar
· lateral cutaneous n of thigh
· Trendelenberg
· brachial plexus
· lateral
· common peroneal
Surgical
· nerves at high risk
· accessory
· superficial radial
· common peroneal
· immediately after division
· EMG will demonstrate normal activity
· 5-10 days after injury
· early denervation changes begin
· 5-14 days
· positive sharp waves consistent with denervation seen
· 12 days
· denervation fibrillation potentials seen
· good prognostic sign if denervation potentials not seen by the end of the second week
· evidence of renervation seen when highly polyphasic motor unit potentials are seen on attempts at volitional activity
· with progression of regeneration the more proximal nerves reveal evidence of electrical reinnervation
· elicited by gentle percussion of a finger or hammer along the course of an injured nerve
· transient tingling sign experienced by the patient in the distribution of the injured nerve rather than at the site
· test in a distal to proximal direction
· positive Tinel's sign is presumptive evidence that regenerating axonal sprouts that have not obtained complete myelinization are progressing along the endoneurial tube
· the response fades proximally because of progressive myelinization
· a Tinel's sign only occurs in Sunderland type 2 & 3 injuries
· sympathetic fibres among the most resistant to mechanical trauma
· preservation of sweating easily determined 20+ mag. lens (Kahn)
· iodine starch test
· turns normal sweat purple
· use of a Richter dermatometer
· resistance is increased with dry skin
· ie. autonomous area of nerve loss
· faradic stimulation of little use as normal muscles may fail to respond to this type of current
· galvanic stimulation of use in determining the chronaxy and strength-duration curves
· thin (atrophy)
· shiny (loss of creases)
· dry (loss of sweating)
· loss of fingerprint
· loss of wrinkling when waterlogged
· trophic ulcers
· weakness
· wasting
· more successful in children (? potential for CNS adaption)
· closing gap includes
· nerve mobilization
· nerve transposition
· nerve graft
· bone shortening
· nerve graft advised if after the nerve is mobilized the gap cannot be closed by flexing the limb to 90o
· excessive tension causes excess fibrosis and delays or retards regeneration
· affects motor more than sensory
· muscle end-plates undergo irreversible changes by 3 years
· Sunderland reported satisfactory reinnervation up to 12 months
· WWII observations for every 6 days delay loss of 1% maximum performance
· influence of delay in repair on sensory function remains unclear
· clinical impression that repair carried out beteen 7 - 18 days after injury gives return of satisfactory function (Kleinert)
· more proximal the injury the more incomplete the recovery
· important issues
· meticulous handling
· asepsis
· avoidance of tension
· suitable bed with minimal scar
· better results in specialised units
· indicated in open wounds where nerve likely to be divided
· contraindicated if conditions not optimal
· indicated in closed wounds where recovery not occurring in expected period
· primary repair is within hours of injury
· delayed primary repair is within first 5-7 days
· secondary repair is after one week
· primary repair is treatment of choice when conditions permit
· criteria
· sharp nerve transection
· minimal contamination
· viable bed
· absence of associated injuries that preclude good repair
· microscope, microsurgical equipment and experienced staff
· suitable patient (not drunk or suicidal)
Technique
· proximal and distal stumps identified and dissected out
· all damaged tissue removed
· stump surfaces trimmed perpendicularly
Epineurial suture
· stumps aligned using fascicular groups and vascular landmarks
· suture placed away from surgeon and then another placed 180o from first
· sutures placed in external epineurium just tight enough to produce contact
· 8/0 used for large peripheral nerve and tails left long to allow rotation
· 10/0 used for remaining sutures and for all sutures in smaller nerves
· 3rd and 4th sutures bisect distance between initial sutures
· further sutures used sparingly
Group fascicular suture
· matching fascicular groups dissected out for 3-4 mm
· groups trimmed and sutured through internal epineurium
Individual fascicular suture
· each fascicle dissected out and repaired
· one or two sutures used
· used to bridge gaps too large for direct suture
Technique
· no tension in graft
· routed through well-vascularised bed
Cable graft
· cutaneous nerve harvested
· sural
· medial cutaneous of forearm
· lateral cutaneous of thigh
· saphenous
· several strips used to approximate donor nerve diameter
Vascularised graft
· where multiple nerves injured
· one nerve can be used as graft for another
· mobilised on vascular pedicle and moved into defect
· ulnar nerve used for
· ulnar and median nerve injury
· brachial plexus lesion
Frozen muscle graft
· muscle snap frozen
· sutured into defect
· axons grow along myotubules
· healthy but easily dispensible nerve transferred and sutured to damaged nerve whose function is more important
· used in brachial plexus injuries
· donors include accessory and intercostal nerves