Updated: 4/9/2022

Peripheral Nerve Injury & Repair

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  • Summary
    • Peripheral nerve injuries encompass a range of reversible and irreversible impairments determined by injury level, axonal disruption, and time to treatment.
    • Diagnosis can be made based on clinical examination and confirmed with EMG/NCS.
    • Treatment can involve observation, repair, tendon transfers or nerve grafting depending on the acuity, degree of injury, and mechanism of injury.
  • Epidemiology
    • Incidence
      • major peripheral nerve injury sustained in 2% of patients with extremity trauma
      • nerve injuries account for approximately 3% of injuries affecting the upper extremity and hand
    • Demographics
      • males = females
    • Risk factors
      • penetrating injuries
      • displaced fractures
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • stretching injury
          • 8% elongation will diminish nerve's microcirculation
          • 15% elongation will disrupt axons
          • examples
            • "stingers" refer to neurapraxia from brachial plexus stretch injury
            • suprascapular nerve stretching injuries in volleyball players
            • correction of valgus in TKA leading to common peroneal nerve palsy
        • compression/crush
          • fibers are deformed
            • local ischemia
            • increased vascular permeability
          • endoneurial edema leads to poor axonal transport and nerve dysfunction
          • fibroblasts invade if compression persists
            • scar impairs fascicular gliding
          • chronic compression leads to Schwann cell proliferation and apoptosis
          • 30mm Hg can cause paresthesias
            • increased latencies
          • 60 mm Hg can cause complete block of conduction
        • laceration
          • sharp transections have a better prognosis than crush injuries
          • continuity of nerve disrupted
            • ends retract
            • nerve stops producing neurotransmitters
            • nerve starts producing proteins for axonal regeneration
      • pathophysiology
        • presynaptic terminal & depolarization
          • electrical impulse transmitted to other neurons or effector organs at presynaptic terminal
          • resting potential established from an unequal distribution of ions on either side of the neuron membrane (lipid bilayer)
          • action potential transmitted by depolarization of resting potential
          • caused by influx of Na across membrane through three types of Na channels
            • voltage gate channels
            • mechanically gated channels
            • chemical-transmitter gated channels
        • regeneration process after transection
          • distal segment undergoes Wallerian degeneration (axoplasm and myelin are degraded by phagocytes)
          • existing Schwann cells proliferate and line endoneurial basement membrane
          • proximal budding (occurs after 1 month) leads to sprouting axons that migrate at 1mm/day to connect to the distal tube
        • variables affecting regeneration
          • contact guidance with attraction to the basal lamina of the Schwann cell
          • neurotropism
          • neurotrophic factors (factors enhancing growth and preferential attraction to other nerves rather than other tissues)
        • functional recovery during regeneration (in order)
          • sympathetic activity
          • pain
          • temperature sensation
          • touch
          • proprioception
          • motor function
          • motor function is the first to be lost and the last to recover
      • pathobiology
        • Schwann cells proliferate and trophic factors are upregulated to promote regeneration
      • pathoanatomy
        • involvement of the axon, myelin, and supporting connective tissues influence regeneration potential
          • myelin disruption typically occurs before axon disruption
          • axonal disruption leads to distal degeneration, requiring regeneration or repair to regain function
            • neuronal connective tissue structure provides a framework for regeneration
              • endoneurium
              • perineurium
              • epineurium
    • Associated conditions
      • predictable nerve injuries arise from certain fracture patterns and clinical scenarios
        • axillary nerve
          • anterior shoulder dislocation
        • radial nerve
          • distal 1/3 humeral shaft (Holstein-Lewis) fractures
          • prolonged compression along the humerus while intoxicated (Saturday night palsy)
          • extension-type supracondylar humerus fracture
        • ulnar nerve
          • distal humerus ORIF
          • improper positioning on OR table
          • flexion-type supracondylar humerus fracture
        • anterior interosseus nerve
          • extension-type supracondylar humerus fracture
        • sciatic nerve
          • posterior hip dislocation
        • common peroneal nerve
          • correction of valgus alignment during a total knee arthroplasty
        • superficial peroneal nerve
          • percutaneous plating of tibial fractures (holes 11-13)
  • Anatomy
    • Blood supply
      • extrinsic vessels
        • run in loose connective tissue surrounding nerve trunk
      • intrinsic vessels
        • plexus lies in epineurium, perineurium, and endoneurium
    • Nerve structure
      • epineural sheath
        • surrounds peripheral nerve
      • epineurium
        • surrounds a group of fascicles to form peripheral nerve
        • functions to cushion fascicles against external pressure
      • perineurium
        • connective tissue covering individual fascicles
        • primary source of tensile strength and elasticity of a peripheral nerve
        • provides extension of the blood-brain barrier
        • provides a connective tissue sheath around each nerve fascicle
      • fascicles
        • a group of axons and surrounding endoneurium
      • endoneurium
        • loose fibrous tissue covering axons
        • participates in the formation of Schwann cell tube
      • myelin
        • made by Schwann cells
        • insulates axons to increase conduction velocity
          • conduction occurs at nodes of Ranvier
      • neuron cell
        • cell body - the metabolic center that makes up < 10% of cell mass
        • axon - primary conducting vehicle
        • dendrites - thin branching processes that receive input from surrounding nerve cells
        • Nerve fiber types
        • Fiber Type
        • Diameter (uM)
        • Myelination
        • Speed
        • Example
        • A
        • 10-20
        • heavy
        • fast
        • touch
        • B
        • < 3
        • moderate
        • medium
        • autonomic nervous system (ANS)
        • C
        • < 1.3
        • none
        • slow
        • pain
  • Classification
    • Seddon Classification
      • neurapraxia
        • same as Sunderland 1st degree, "focal nerve compression"
        • nerve contusion or stretch leading to reversible conduction block without Wallerian degeneration
        • pathophysiology
          • usually caused by local ischemia
          • histopathology shows focal temporary demyelination of the axon (axon remains intact)
          • endoneurium remains intact
        • electrophysiologic studies
          • nerve conduction velocity slowing or a complete conduction block
          • no fibrillation potentials
        • prognosis
          • recovery prognosis is excellent
      • axonotmesis
        • same as Sunderland 2nd-4th degree
        • incomplete nerve injury more severe than neurapraxia
        • pathophysiology
          • axon and myelin sheath disruption leads to focal conduction block with Wallerian degeneration
          • variable degree of connective tissue disruption
        • electrophysiologic studies
          • fibrillations and positive sharp waves on EMG
        • prognosis
          • unpredictable recovery
      • neurotmesis
        • encompasses Sunderland 5th degree
        • complete nerve division with disruption of endoneurium
        • pathophysiology
          • all connective tissues disrupted
          • focal conduction block with Wallerian degeneration
        • electrophysiologic studies
          • fibrillations and positive sharp waves on EMG
        • prognosis
          • no recovery unless surgical repair performed
          • neuroma formation at proximal nerve end may lead to chronic pain
        • Seddon Classification
        • Seddon Type
        • Myelin intact
        • Endoneurium intact
        • Wallerian Degeneration
        • Reversible
        • Neuropraxia
        • No
        • Yes
        • No
        • Reversible
        • Axonotmesis
        • No
        • Variable
        • Yes
        • Variable
        • Neurotmesis
        • No
        • No
        • Yes
        • Irreversible
    • Sunderland Classification
      • 1st degree
        • same as Seddon's neurapraxia (loss of myelin sheath)
      • 2nd degree
        • included within Seddon's axonotmesis
        • intact endoneurium, perineurium and epineurium
      • 3rd degree
        • included within Seddon's axonotmesis
        • endoneurium injured with endoneurial scarring
        • intact perineurium and epineurium
        • most variable degree of recovery
      • 4th degree
        • included within Seddon's axonotmesis
        • endoneurium and perineurium injured
        • intact epineurium
        • nerve in continuity but at the level of injury there is complete scarring across the nerve
        • unsatisfactory regeneration
        • may lead to neuroma-in-continuity
      • 5th degree
        • same as Seddon's neurotmesis
        • completely severed or transected nerve involving all layers
        • regeneration not possible without repair
          • Sutherland Classification
          • Grade
          • Axon
          • Endoneurium 
          • Perineurium
          • Epineurium
          • I
          • Intact
          • Intact
          • Intact
          • Intact
          • II
          • Disrupted
          • Intact
          • Intact
          • Intact
          • III
          • Disrupted
          • Disrupted
          • Intact
          • Intact
          • IV
          • Disrupted
          • Disrupted
          • Disrupted
          • Intact
          • V
          • Disrupted
          • Disrupted
          • Disrupted
          • Disrupted
  • Studies
    • Nerve conduction studies
      • Electromyography (EMG)
      • Nerve conduction velocity (NCV)
    • EMG
      • assesses function at the neuromuscular junction
      • often the only objective evidence of a compressive neuropathy (valuable in workers' compensation patients with secondary gain issues)
      • characteristic findings
        • denervation of muscle
          • fibrillations
          • positive sharp waves (PSW)
          • fasciculations
        • neurogenic lesions
          • fasciculations
          • myokymic potentials
        • myopathies
          • complex repetitive discharges
          • myotonic discharges
    • NCV
      • assesses large myelinated fibers
      • focal compression and demyelination leads to
        • increase latencies (slowing) of NCV
          • distal sensory latency of > 3.2 ms are abnormal for CTS
          • motor latencies > 4.3 ms are abnormal for CTS
        • decreased conduction velocities less specific that latencies
          • velocity of < 52 m/sec is abnormal
        • motor action potential (MAP) decreases in amplitude
        • sensory nerve action potential (SNAP) decreases in amplitude
  • Treatment
    • Nonoperative
      • observation with sequential EMG
        • indications
          • neuropraxia (1st degree)
          • axonotmesis (2nd degree)
          • gunshot wounds affecting brachial plexus
            • assess extent of recovery over 3 months
        • outcomes
          • variable recovery depending on degree of injury
          • most nerve deficits that present after a closed fracture or dislocation will resolve with observation alone
    • Operative
      • direct muscular neurotization
        • indications
          • transected unrepairable nerve ending at risk of forming neuroma
          • plan for integrated prosthesis
        • outcomes
          • degree of functional recovery varies
          • decreases neuroma formation
          • promising results with targeted muscle reinnervation (TMR) for amputees
      • surgical repair
        • indications
          • neurotmesis (3rd-5th degree)
          • early surgical exploration: penetrating trauma, iatrogenic injury, vascular injury, progressive deficits
            • exception: gunshot wounds affecting brachial plexus may be observed
          • 1-3 weeks after gunshot injury with confirmed neurotmesis
            • allows time for zone of injury to be declared
        • outcomes
          • variable and dependent on multiple factors (i.e., patient age, level of injury, type of injury, time to repair, etc.)
            • fascicular repair outcomes are similar to epineurial repair
            • best recovery when performed within 7-14 days of injury
          • reinnervation and sensory re-education may take several years
      • nerve grafting
        • indications
          • gaps that prevent tension-free direct repair
        • outcomes
          • variable and dependent on multiple factors (i.e., patient age, level of injury, type of injury, time to repair, etc.)
          • quality of nerve recovery drops with gaps >5mm
      • nerve transfer
        • indications
          • proximal nerve injury
            • goal to deliver new axons and stimulus before degeneration of motor endplates and irreversible muscle damage
            • priority is to restore shoulder abduction/external rotation, elbow flexion, and finger function
          • loss of shoulder abduction and external rotation
            • spinal accessory nerve (CN XI) to suprascapular nerve
          • loss of shoulder abduction and flexion
            • Leechavengvong procedure: triceps motor branch of radial nerve to axillary nerve
          • loss of elbow flexion
            • Oberlin transfer: FCU motor branch to upper trunk/musculocutaneous nerve
        • outcomes
          • potentially similar outcomes as tendon transfer for irreparable proximal nerve injuries
      • tendon transfer
        • indications
          • return of function through nerve regeneration is not expected
        • outcomes
          • better with age <30 and more distal locations due
          • improved in children due to neuroplasticity
          • one grade of motor strength loss is expected following transfer
  • Techniques
    • Observation with sequential EMG
      • technique
        • 'active surveillance' daily or weekly by the same surgeon
          • exploration indicated if no functional recover after 3 months
        • functional splinting
        • rehabilitation focusing on sensory reeducation and prevention of joint contracture
    • Direct muscular neurotization
      • technique
        • insert proximal nerve stump into nearby muscle belly
    • Surgical repair
      • Epineurial repair
        • approach
          • primary repair of the epineurium
          • requires resection of proximal neuroma and distal glioma to healthy fascicles
          • alignment aided by epineurial blood vessels
        • technique
          • resect zone of injury until "mushrooming" of the fascicles is observed
          • repair should be tension free in well-vascularized wound bed
            • tensioned closures compromise perfusion; inhibit Schwann cell activation and regeneration; and cause scar formation
          • length can be gained with nerve transposition and neurolysis
      • Fascicular repair
        • approach
          • similar to epineural repair, but also repair the perineural sheaths (individual fascicles are approximated under a microscope)
            • theoretically provides more accurate alignment of axons over epineurial repair
        • technique
          • fascicular matching
            • topographical sketches can be used for visual alignment
            • electrical stimulation
              • proximal end: identifies sensory fascicles in awake patients
              • distal end: identifies motor fascicles in acute injuries, before significant Wallerian degeneration
            • histologic staining
        • complications
          • potentially increased scarring and damage to blood supply
    • Nerve grafting
      • approach
        • create tension-free repair by using a graft that is at least 10% longer than gap
        • ensure scar from nerve ends is completely resected
      • technique
        • autologous graft
          • nerve autografts harvested should result in the least morbidity possible
            • medial and lateral antebrachial cutaneous
            • posterior interosseus nerve terminal branches
            • sural
          • cabling can be used for donor-recipient size mismatch
        • acellular allograft
          • shown to be effective for gaps < 5cm
          • not as effective as autograft, but have shown promise for large defects unable to be bridged by autograft alone
        • conduits
          • made up of type 1 collagen
          • indications
            • defects up to 20 mm
              • allow coaptation ends without tension, typically small sensory nerves
              • synthetic polyglycolic acid, polycaprolactone, and collagen-based
              • collagen conduits allow nutrient exchange and accessibility to neurotrophic factors to the axonal growth zone during regeneration
      • complications
        • donor nerve neuroma formation
        • immune response and rejection of allograft
    • Nerve transfer
      • approach
        • redundant or non-essential nerve transferred to a nerve affected by a proximal injury
        • select donor motor nerves close to target muscles
      • technique
        • coaptation techniques
          • end-to-end
          • end-to-side
            • donor nerve attached to the recipient nerve through perineurial window
            • goal to "supercharge" damaged nerve by preservation of motor endplates until new axons can regenerate from more proximal injury
    • Tendon transfer
      • approach
        • maintain or restore passive joint mobility before tendon transfer
        • redundant or non-essential muscle-tendon unit transferred to restore a lost function
        • optimal to have one straight line of pull and transfer of muscle synergistic to lost function
        • one tendon transfer should perform one function
      • technique
        • select donor and recipient with similar power
          • power determined by cross-sectional area
        • select synergistic donor and recipient
          • i.e. wrist extensors and finger flexors
        • set appropriate excursion
          • can be adjusted with pulley or tenodesis effect
          • Smith 3-5-7 rule
            • 3 cm excursion - wrist flexors, wrist extensors
            • 5 cm excursion - EDC, FPL, EPL
            • 7 cm excursion - FDS, FDP
      • complications
        • adhesions, poor tendon gliding
  • Complications
    • Neuroma formation
      • incidence
        • true incidence unknown due to most being asymptomatic
        • up to 30% in amputees has been reported
      • treatment
        • non-operative
          • pharmacolgical (i.e., gabapentin, anticonvulsants, antidepressants, etc.)
          • local nerve distruction (i.e., injection of phenol or botulinum toxin, cautery, etc.)
          • rehabilitation
          • work modification
        • operative
          • resection
          • targeted muscle reinnervation (TMR)
  • Prognosis
    • Natural history of disease
      • pain is first modality to return
      • advancing Tinel sign is most reliable indication of recovery
      • nerve repair or reconstruction is unpredictable after 6 months
        • reinnervation by 18 months is the goal for muscle preservation
    • Prognostic variables
      • favorable
        • younger age
          • most important factor influencing success of nerve recovery (children have more favorable prognosis)
        • distal level of injury
          • second most important (the more distal the injury the better the chance of recovery)
          • peripheral nerve injuries include those affecting the Brachial Plexus
        • sharp transections and stretch injuries
          • have better prognosis than crush or blast injuries
      • negative
        • older age
        • proximal level of injury
        • crush injuries
        • repair delay
          • worse prognosis of recovery (time limit for repair is 18 months)
    • Prognosis with treatment
      • variable on several factors including injury location, age of patient, and type of injury
        • neurapraxia resolves with conservative measures
        • axonotmesis and neurotmesis may improve with repair, tendon transfers, and/or nerve transfers
        • the endoneurium must be intact for full recovery of an injured peripheral nerve
        • may lead to chronic neuropathic pain
Technique Guides (2)
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Questions (19)
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(OBQ18.155) A 36-year-old male injured his right arm after a fall. His injury radiograph is shown in Figure A. On physical examination, he was found to have a nerve injury. Which function is the last to return?

QID: 213051

Pain sensation to the radial portion of the dorsum of the hand



Temperature sensation to the radial portion of the dorsum of the hand



Sensation of light touch to the radial portion of the dorsum of the hand



Wrist extension



Elbow extension



L 3 A

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(OBQ18.16) A 16-year-old male presents with a gunshot wound to his right upper arm. On examination, he has a wrist drop and reports loss of sensation in his radial nerve distribution. There is a 1.5cm entrance wound on the lateral aspect of the arm with a 6.8 cm stellate exit wound anteromedially. Figures A and B are the radiographs of the injury. The patient is taken to the operating room for fixation, and the radial nerve is found to be completely transected. When is the optimal timing for definitive nerve repair?

QID: 212912

At the time of initial debridement



At the time of definitive fracture fixation



After 3 months from the injury



After 1-3 weeks from the injury



Once a neuroma has formed on MRI



L 5 A

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(OBQ18.3) A 42-year-old male laborer sustains the injury shown in Figure A. He is taken to the operating room and found to have a partial laceration of the median nerve. Figure B shows a cross-sectional image of a nerve. Which of the following represents item D?

QID: 212899







Nerve fiber









L 1 A

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(OBQ13.24) Which statement most accurately describes the physiology of peripheral nerve regeneration following an axonotmesic lesion?

QID: 4659

The proximal nerve segment undergoes Wallerian degeneration



Axon growth occurs from the distal segment to proximal segment



Neurotrophic factors direct phagocytic activity



Proximal axon budding allows for antegrade (or distal) axon migration



Axoplasm and myelin are degraded distally predominantly by Schwann cells for the first 12 months following injury



L 3 B

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(OBQ13.9) Figure A shows a traumatic laceration of the distal forearm with a 5cm segmental median nerve defect. Which of the following repair or reconstruction techniques would allow for the best recovery of motor function?

QID: 4644

Autogenous venous nerve conduit



Collegen synthetic nerve conduit



Biodegradable polyglycolic acid



Processed nerve allograft



Nerve autograft



L 2 B

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(OBQ12.210) A 55-year-old male laborer comes in with a chief complaint of clumsiness with his right hand for the past 3 months including difficulty using a hammer while at work. He has had no injury to the right upper extremity. On physical examination, he has persistent small finger abduction/extension with finger extension and active adduction. An EMG is performed and demonstrates ulnar nerve conduction velocities of 31 m/sec (normal >52m/sec). The patient symptoms are most accurately described as:

QID: 4570

Axonotmesis with ischemia origin



Axonotmesis with myelin disruption



Neurapraxia with ischemia origin



Neurapraxia with endoneurium disruption






L 1 C

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(OBQ12.46) The patient sustains the injury seen in Figure A from a gunshot injury. The physical exam is notable for lack of sensation in his fourth and fifth digits as well as a positive Froment's sign. Which of the following factors has not been shown to be a significant prognostic indicator of functional recovery following nerve repair?

QID: 4406

Duration to time of repair



Repair level



Length of repair



Postoperative physical rehabilitation



Type of autograft used



L 4 C

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(OBQ09.268) You are seeing a 24-year-old male in the emergency room after he was involved in a knife fight. He has severed the common digital nerve to the index finger on his dominant hand, with an 8mm gap between nerve ends. In counseling him about repair, which of the following options is as good as autologous nerve grafting?

QID: 3081

Glycolide trimethylene carbonate conduit



Collagen conduit



Silicone sleeve



Primary end-to-end repair



Polyglycolic acid conduit



L 3 C

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(OBQ08.30) Which of the following nerves has the most favorable regenerative potential in restoring motor function after a graft repair within half a year after being injured?

QID: 416
















L 3 C

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(OBQ05.66) Axon regeneration almost always occurs following a Sunderland second-degree nerve injury because which anatomic structure is not injured?

QID: 952










Myelin sheath



Schwann cell



L 4 D

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(OBQ05.218) Vitamin B12 deficiency is a known cause of which the following?

QID: 1104

Inability to whistle



Peripheral sensory neuropathy



Increased deep tendon reflexes



Urinary retention






L 1 D

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(OBQ04.257) Which of the following peripheral nerve structures functions to cushion the nerve against external pressure?

QID: 1362
















L 3 D

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(OBQ04.248) Which of the following structures are slowly adapting skin receptors that detect pressure, texture, and low frequency vibration and are best evaluated by static two-point discrimination?

QID: 1353

Meissner's corpuscles



Pacinian corpuscles



Merkel's receptor



Free nerve endings



Ruffini corpuscles



L 1 C

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Evidence (29)
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