Peripheral Nerve Injury

a) Anatomy of a peripheral nerve:

A peripheral nerve is made up of several components which work together to transmit signals between the CNS to the periphery. The anatomy of a typical peripheral nerve can be divided into the following structures:

  1. Nerve fibers: the elongated cells that carry electrical signals along the length of the nerve. Nerve fibers are classified as either sensory or motor, depending on the type of signals they carry..
  2. Epineurium: This is the outermost layer of the nerve, composed of dense connective tissue that encases the entire nerve and protects it from injury.
  3. Perineurium: This layer is located within the epineurium and surrounds individual fascicles of nerve fibers. It is composed of specialized cells that help maintain the integrity of the fascicles and regulate the flow of substances into and out of the nerve.
  4. Endoneurium: This is the innermost layer of the nerve, consisting of delicate connective tissue that surrounds individual nerve fibers within each fascicle.
  5. Schwann cells: These are specialized cells that wrap around individual nerve fibers and provide support, insulation, and assistance with nerve regeneration.
  6. Blood vessels: Peripheral nerves require a rich blood supply to function properly, and blood vessels are present throughout the nerve to provide oxygen and nutrients to the nerve fibers and other cells.

Together, these structures form the complex anatomy of a peripheral nerve, allowing it to carry signals between the CNS and the body with remarkable speed and precision.

b) Classification & diagnosis of peripheral nerve injuries:

Classification of Nerve Injuries:

By Seddon(1943) into 3 groups:

  1. Neuropraxia– →Physiological disruption of impulse transmission,
    →Minor contusion/compression of a peripheral nerve; preserved axis cylinder ; minor oedema or breakdown of myelin sheath locally.
    Recovery is complete in a few days/weeks.
  2. Axonomesis– →Injury to axon; distal wallerian degeneration; Preservation Schwann cell & Endoneurial tubes
    Spontaneous regeneration with good functional recovery.
  3. Neurotmesis– →The complete anatomical severance of nerve &/or extensive avulsion or crushing
    →The axon, Schwan cell & endoneurial tube- completely disrupted
    →Perineurium & Epineurium- varying degree of injury & disruption
    Usually no expectation of spontaneous recovery.

By Sunderland (1951) into 5 degrees: more clinical application- with each degree of injury, more anatomical disruption & decreasing prognosis.

  1. 1st degree injury (I): →Physiological disruption of impulse conduction along the axon; No anatomical disruption, & no wallerian degeneration.
    →Injury similar to Neuropraxia of Seddon
    Motor > Sensory (Proprioception, touch, temperature, & pain in that order)
    →Proprioception & Motor- last to return.
    →Simultaneous return of motor function in the proximal & distal muscles – No “Motor-march”
    →No Tinel sign, as no axonal damage or regeneration.
    Recovery- spontaneous & complete in days to weeks.
  2. 2nd degree injury (II):  →Disruption of axon & wallerian degeneration distal to the injury & proximal degeneration upto one/more nodes.
    →Endoneurial tube maintained- a perfect anatomical course for regeneration
    →Complete neurological deficit (Motor, Sensory & Autonomic)
    →Motor reinnervation in a progressive manner- from proximal to distal- “Motor march”.
    →Advancing Tinel sign at a rate of 1 inch/month
    →Good functional return.
  3. 3rd degree injury (III) : →Both the axons & endoneurium- disrupted; Perineurium preserved.
    →Complete neurological deficit
    Motor-march from proximal to distal & an advancing Tinel sign +nt.
    →No complete recovery of neural function as against 2nd degree injury & more time needed for the recovery.
  4. 4th degree injury (IV) : →Disruption of the axon & endoneurium,; some of the endoneurium & some of the perineurium intact—– no complete severance of the entire nerve trunk.
    →Retrograde degeneration more severe
    →Nerve continuity maintained by scar tissue- prevents proximal axons from entering the distal endoneurial tubes; axonal sprouts exit through defects & wander in surrounding tissues.
    →Prognosis of functional recovery is poor, & needs surgery.
  5. 5th degree injury (V) : → complete transection of the nerve with variable distance between neural stumps.
    →Injury only in open wounds & can be identified at early surgical exploration
    →Prognosis is poor & need surgery.
    →Appropriate surgery needed to gain any significant functional return.

6th degree injury (VI):  (by Mackinnon) – Mixed injuries→ the nerve trunk is partially severed & the remaining part has 4th degree, 3rd degree, 2nd degree or even 1st degree injury.
→A neuroma-in-continuity +nt.
→The recovery pattern is mixed
→If surgery is done to correct 4th & 5th degree components, it can cause loss of function of lesser degree injured fascicles.

c) Algorithm for management of radial nerve palsy:

Radial nerve palsy is a condition that results from damage to the radial nerve, which controls movement of the muscles in the forearm and wrist. The following algorithm outlines a general approach to the management of radial nerve palsy:

  1. Confirm the diagnosis: The diagnosis of radial nerve palsy is typically made based on a combination of clinical examination and imaging studies. It is important to confirm the diagnosis before proceeding with treatment.
  2. Determine the extent of the injury: The severity and extent of the nerve damage will guide the choice of treatment. Mild injuries may require only observation and physical therapy, while more severe injuries may require surgical intervention.
  3. Initiate physical therapy: Physical therapy is an essential component of the management of radial nerve palsy. It can help to maintain muscle strength and prevent muscle atrophy. A physical therapist will design a rehabilitation program that is tailored to the individual patient’s needs.
  4. Consider surgical intervention: In cases of severe nerve damage, surgical intervention may be necessary to repair or reconstruct the nerve. The decision to proceed with surgery will depend on the extent of the injury and the patient’s overall health status.
  5. Manage pain: Pain management is an important part of the management of radial nerve palsy. Pain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), may be used to control pain.
  6. Monitor progress: Regular follow-up appointments with a healthcare provider are essential to monitor progress and adjust the treatment plan as needed.
  7. Educate the patient: It is important to educate the patient about the condition and the expected course of treatment. The patient should be informed about the potential risks and benefits of various treatment options, as well as the importance of adherence to the rehabilitation program.

Overall, the management of radial nerve palsy is a multifaceted process that requires a collaborative effort between healthcare providers and the patient. Treatment should be tailored to the individual patient’s needs and guided by evidence-based practice.

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