Summary Peripheral nerve injury is a relatively common condition that encompasses a range of reversible and irreversible impairments determined by injury level, axonal disruption, and time to treatment. Diagnosis is typically clinical with a combination of known injury with a nerve deficit. Advanced imaging such as ultrasound or MRI may be used to characterize nerve morphology after injury; however, EMG/NCS is a mainstay of evaluating both nerve injury and nerve recovery. Surgical exploration is confirmatory for traumatic nerve injuries. Treatment may involve observation, primary repair, nerve reconstruction with grafting, tendon transfers, nerve transfers, or a combination thereof depending on acuity, degree of injury, nerve quality, and mechanism of injury. Epidemiology Incidence 16.9 per 100,000 per year peripheral nerve injury sustained in 2.6% of upper extremity trauma and 1.2% of lower extremity trauma nerve injuries account for approximately 3% of injuries affecting the upper extremity and hand Demographics males (80%) >> females younger in age, average age of 32-39 Risk factors penetrating and/or high energy trauma crush injuries significantly displaced fractures Etiology Pathophysiology mechanism of injury stretching injury login to view 6 more bullets compression/crush login to view 10 more bullets laceration login to view 5 more bullets pathophysiology presynaptic terminal & depolarization login to view 7 more bullets regeneration process after transection login to view 3 more bullets variables affecting regeneration login to view 3 more bullets functional recovery during regeneration (in order) login to view 7 more bullets 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 login to view 6 more bullets Associated conditions predictable nerve injuries arise from certain fracture patterns and clinical scenarios axillary nerve login to view 1 more bullet radial nerve login to view 3 more bullets ulnar nerve login to view 3 more bullets anterior interosseus nerve login to view 2 more bullets sciatic nerve login to view 1 more bullet common peroneal nerve login to view 1 more bullet superficial peroneal nerve login to view 1 more bullet 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 login to view 1 more bullet 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 login to view 3 more bullets electrophysiologic studies login to view 2 more bullets prognosis login to view 1 more bullet axonotmesis same as Sunderland 2nd-4th degree incomplete nerve injury more severe than neurapraxia pathophysiology login to view 2 more bullets electrophysiologic studies login to view 1 more bullet prognosis login to view 1 more bullet neurotmesis encompasses Sunderland 5th degree complete nerve division with disruption of endoneurium pathophysiology login to view 2 more bullets electrophysiologic studies login to view 1 more bullet prognosis login to view 2 more bullets 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 Sunderland 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 Imaging Ultrasound (High-resolution ultrasound) Indication: neuropathy from entrapment/compression or trauma may help localize entrapment, nerve ends in lacerations, neuromas Findings: may help localize entrapment, nerve ends in lacerations, neuromas real time dynamic evaluation better assessment of superficial nerves Compliments electrodiagnostic studies MRI/MRN (Magnetic resonance neurography) Indication: traumatic nerve injury, particularly brachial plexus injuries Findings: similar to ultrasound better detection of muscle denervation better as assessment of deeper structures better static resolution than ultrasound Studies Electrodiagnostic 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 login to view 3 more bullets neurogenic lesions login to view 2 more bullets myopathies login to view 2 more bullets NCV assesses large myelinated fibers focal compression and demyelination leads to increase latencies (slowing) of NCV login to view 2 more bullets decreased conduction velocities less specific that latencies login to view 1 more bullet motor action potential (MAP) decreases in amplitude sensory nerve action potential (SNAP) decreases in amplitude Treatment Nonoperative observation with sequential EMG indications login to view 4 more bullets outcomes login to view 2 more bullets Operative direct muscular neurotization indications login to view 2 more bullets outcomes login to view 3 more bullets surgical repair indications login to view 5 more bullets outcomes login to view 4 more bullets nerve grafting indications login to view 1 more bullet outcomes login to view 2 more bullets nerve transfer indications login to view 15 more bullets outcomes login to view 3 more bullets tendon transfer indications login to view 1 more bullet Key tendon transfers login to view 25 more bullets outcomes login to view 3 more bullets Techniques Observation with sequential EMG technique 'active surveillance' weekly by the same surgeon login to view 2 more bullets 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 login to view 3 more bullets technique login to view 4 more bullets Fascicular repair approach login to view 2 more bullets technique login to view 6 more bullets complications login to view 1 more bullet 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 login to view 6 more bullets acellular/decellular allograft login to view 3 more bullets conduits login to view 7 more bullets 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 login to view 5 more bullets 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 login to view 1 more bullet select synergistic donor and recipient login to view 1 more bullet set appropriate excursion login to view 5 more bullets 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 login to view 4 more bullets operative login to view 3 more bullets 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 login to view 1 more bullet distal level of injury login to view 2 more bullets sharp transections and stretch injuries login to view 1 more bullet negative older age proximal level of injury crush injuries repair delay login to view 1 more bullet 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