- Clinical science
Peripheral nerve injuries include a variety of conditions in which one or more peripheral nerves are damaged, leading to neurological deficits distal to the level of the lesion. Possible causes include systemic diseases (e.g., diabetes, autoimmune disease) and localized damage (e.g., trauma, compression, tumors). Peripheral nerve injuries may occur as isolated neurological conditions or, more commonly, in association with soft tissue, vascular, and/or skeletal damage. Patients with peripheral nerve injury may present with sensory deficits, loss of motor function, or a combination of both. Diagnosis is based on clinical evaluation, imaging techniques (x-ray, CT/MRI), and electrodiagnostic examination (e.g., nerve conduction study, EMG). Observation and conservative treatment (e.g., activity modification, splinting, electrical stimulation) are indicated in most closed injuries, which have a high rate of spontaneous recovery. Patients with open injuries or long disease courses may require surgical treatment. Recovery from peripheral nerve injury is often incomplete and patients may experience chronic pain.
Classification of peripheral nerve injury is useful for determining the prognosis and choosing a treatment strategy.
- Compression injury; causing temporary disruption of nerve conduction
- The whole nerve remains structurally intact.
- Good prognosis with complete recovery of nerve function
- The axon is damaged but the perineurium and epineurium remain intact.
- Leads to central chromatolysis
- Definition: the reaction of a neuronal cell body in response to an axonal injury
- Swelling of the neuronal body
- Dispersion of the Nissl bodies
- Displacement of the nucleus to the periphery
- Function: These changes reflect an increase in protein synthesis in an effort to restore the integrity of the damaged axon.
Results in Wallerian degeneration
- Definition: an active neuronal degeneration process in response to axonal injury
- Initially retained electrical excitability of axonal membrane distal to the injury, lasting up to 36 hours
- Progressive degeneration of distal segment cytoskeleton with dissolution of axonal membrane
- Degradation of residual myelin sheath by macrophages and Schwann cells
- The proximal stump either stays in place or retracts slightly; ultimately, the stump will sprout regenerative nervous fibers that, ideally, reinnervate the distal tissues.
- Regeneration is significantly more efficient in the peripheral nervous system than in the central nervous system.
- To clear axonal debris and prevent scarring
- Facilitate targeted reinnervation of tissues previously innervated by that axon before injury
- Good chance of at least partial recovery
- Complete nerve transection
- Connective sheath damage
- The chances of recovery are very poor without surgical repair.
- Traumatic neuroma: benign, painful nodular thickening caused by nerve regeneration at the site of different forms of nerve injury
- Injury to the upper trunk of the brachial plexus (C5–C6)
- Weakness of muscles in the C5 and C6 myotomes → flexed wrist with an extended forearm and internally rotated and adducted arm (waiter's tip posture)
- Asymmetric Moro reflex in infants (absent or impaired on the affected side)
- Sensory loss in the C5 and C6 dermatomes (thumb and lateral surface of the forearm and arm)
- Injury to the lower trunk of the brachial plexus (C8–T1)
- Weakness of muscles in the C8 and T1 myotomes (intrinsic hand muscles) → total claw hand (persistent flexion of the interphalangeal joints and extension of the metacarpophalangeal joints in the hand)
- Absent grasp reflex in infants
- Sensory loss in the C8 and T1 dermatomes (little finger and medial surface of the forearm and arm)
- Preganglionic if injury occurs proximal to the white ramus communicans
- Decreased peripheral pulses if subclavian vessels are compressed by a Pancoast tumor or cervical rib (see )
Peripheral nerve injuries in the upper extremity
|Injured nerve||Nerve roots||Common causes||Motor deficits||Sensory deficits|
|Axillary nerve injury|| |
|Musculocutaneous nerve injury|| || |
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Peripheral nerve injuries in the cervicothoracic region
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"C3, 4, 5 keeps the diaphragm alive"
|Superior gluteal nerve injury|| || || |
|Inferior gluteal nerve injury|| || |
|Lateral femoral cutaneous nerve injury (meralgia paresthetica)|| || |
|Obturator nerve injury|| || |
|Sciatic nerve injury|| || |
|Tibial nerve injury|| || |
|Common peroneal nerve injury|| |
|Sural nerve lesion|| || || |
- Electrodiagnostic studies
- Observation and expectant management in closed injuries of the nerve, which have a high rate of spontaneous recovery
- Activity modification (e.g., avoid sports or activities that increase likelihood of further nerve injury)
- Splinting: prevents stiffness and contractures of joints; supports residual nerve functionality and reinnervation
- Electrical stimulation: supports the regeneration of the proximal axons and reinnervation of the denervated muscles after surgical nerve repair
- Drug therapy: treatment of chronic neuropathic pain following peripheral nerve injury (e.g., gabapentin); used in combination with surgical treatment to enhance remyelination and motor regeneration (e.g., lithium)
- Analgesia: infiltration with local anesthetics
- Open, non-contaminated, sharp injuries; concomitant vascular injuries → immediate surgical exploration and repair
- Open, contaminated injuries; postreduction palsy → early surgical exploration and repair (within 3 weeks)
- Patients without clinical or electromyographic signs of spontaneous recovery → delayed surgical exploration and repair (within 3 months)
- Nerve repair (neurorrhaphy): reconstruction of nerve continuity
- Tendon transfer: A tendon from a sufficiently powerful muscle is redirected towards another tendon in order to restore its motion and function.
- Nerve transfer: An intact healthy nerve is redirected towards a denervated nerve in order to restore the innervation of its target organ.