Lower Limb Nerve Injuries

• The peripheral nervous system (PNS) includes all neural structures outside the brain and spinal cord.
• The PNS includes sensory receptors, peripheral nerves, associated ganglia, and efferent motor endings.
• The PNS links to the outside world by receiving and responding to stimuli via afferent and efferent nerves
• Peripheral nerves are supported and covered by three connective tissue layers: endoneurium, perineurium, and epineurium.
• Endoneurium surrounds each axon and is the innermost layer.
• Perineurium surrounds groups of neurons (fascicles) and is the middle layer.
• Epineurium surrounds the entire nerve and is the outermost layer.
• Myelinated nerves are larger in diameter and have an extra membrane for electrical insulation, speeding nerve impulse conduction.
• Unmyelinated nerves are smaller in diameter and lack the extra membrane, resulting in slower conduction time.

Terminology

• Neuropathy: functional disturbance and/or pathological change in nerve function.
• Neuralgia: Pain in the distribution of nerves generally in the absence of objective signs/structural damage to nerve.
• Neuritis: Inflammation of the nerve.
• Neuroma: Overgrowth of nerve cells.
• Radiculitis: Inflammation of a spinal nerve root.
• Radiculopathy: Compression of a nerve root, causing numbness and/or weakness.
• Polyradiculopathy: Affecting more than 1 nerve root.
• Plexopathy: Disorder involving one of the major neural plexuses – cervical, brachial, or lumbosacral.
• Fasciculation: Spontaneous contraction of muscle fibers in denervated tissue.
• Flaccidity: Paralysis in which muscle tone is lacking in the affected muscles, and tendon reflexes are decreased or absent.
• Atrophy: Decrease in size or wasting away of a body part or tissue.
• Double Crush Syndrome: Nerve compressed or injured in more than one location, like median nerve compression at the carpal tunnel and pronator teres.
• Peripheral nerves serve motor, sensory and autonomic functions, so neuropathies present differently based on the affected nerve type.

Motor Neuropathy

• Results in weakness, flaccid paralysis, atrophy, and decreased reflexes.

Sensory Neuropathy

• Results in paresthesias (tingling, prickling), dysesthesias (abnormal sensation), pain, and numbness.

Autonomic Neuropathy

• Results in hypotension (BP), anhidrosis (reduced sweating), diaphoresis (excessive sweating), diarrhea/constipation.

Mixed Neuropathy

• Presents as a combination of any of the above.

Nerve Injuries

• Neuropraxia involves compression of a nerve with no structural damage to the axon or distal tissue.
• In neuropraxia, the endo, peri & epineurium are intact, and the axon is preserved.
• Neuropraxia involves some myelin loss (segmental demyelination), reducing action potential conduction.
• Neuropraxia often follows nerve compression, causing mild ischemia of the nerve fiber.
• Neuropraxia results in mild weakness up to paresis/paralysis, without atrophy, and full recovery.
• Axonotmesis involves damage to the axon, but the epi, peri & endoneurium remain intact.
• Wallerian Degeneration, or axonal degeneration distal to the lesion, occurs
  • Results in paresis/paralysis, with atrophy
• Axonotmesis often occurs after severe or prolonged compression, and prognosis for recovery is variable.
• Neurotmesis is complete severance of the axon and disruption of the endo, peri & epineurium.
• Wallerian Degeneration, or axonal degeneration distal to the lesion, occurs
• Neurotmesis often occurs after gunshot or stab wounds, or avulsion injuries.
• Neurotmesis requires surgical intervention for any neural re-growth.
• Neurotmesis results in paresis/paralysis, with atrophy, and recovery is incomplete.
• Peripheral nerves can regenerate even if the axon is damaged if the cell body is intact.
• In axonotmesis, the intact endoneurial tube provides a good pathway for nerve regeneration.
• Compression on a nerve causes myelin breakdown, exposing the axon and stimulating remaining Schwann cells to reproduce and form more myelin.
• Axonal Degeneration/Wallerian Degeneration
  • The degeneration of an axon distal to a site of lesion.
  • The segment between the nerve cell body and the site of injury remains intact.
  • Proximal and distal ends of the endoneurium are surgically attached for better outcomes.
  • The axon continues to re-grow until it reaches a muscle or sensory receptor.

Causes of Peripheral Nerve Lesions

• Compression: Internal (bony callus, tight muscles, tumor, edema) or External (crutches, casts).
• Trauma: Crush injuries, severance (knife, bullet), industrial accidents, or birth trauma.
• Systemic Disorders: Leprosy
• Systemic Edematous Conditions: Pregnancy, hypothyroidism, diabetes, kidney & heart conditions.

Common Symptoms of Peripheral Nerve Lesions

• Edema: Occurs due to injury-related inflammation, and persists if autonomic nerve fibers are damaged.
• Altered tissue health: Results from loss of autonomic function, causing changes to skin, hair, and nails (trophic changes).
• Altered motor function: Flaccid paralysis and muscle wasting within 3 weeks, fibrillation of denervated tissue a few weeks post-injury, and diminished deep tendon reflexes.
• Holding patterns: Limb positions such as wrist drop or claw hand may be present, depending on severity.
• Contractures: Develop due to unopposed antagonist muscles.
• Pain: Can develop into Causalgia or RSD (Reflex sympathetic dystrophy).

Management Guidelines for Peripheral Nerve Injury Recovery

• Acute Phase: Focus on healing and preventing complications through immobilization (time dictated by MD) and splinting/bracing to prevent deformities.
• Recovery Phase: Emphasize retraining and re-education when reinnervation occurs, including motor retraining (holding muscle in shortened position), desensitization (stroking skin with different textures), and discriminative sensory re-education (object identification with/without visual cues).
• Chronic Phase: Focus on training compensatory function when recovery plateaus with significant physical deficits, and splint/brace wearing may continue.

Muscle Weakness

• Neurogenic weakness is distal to proximal, fasciculations may be present, reflexes are diminished, and sensory signs/symptoms may be present.
• Myogenic weakness is proximal to distal, no fasciculations, reflexes are often preserved and no sensory signs.

Precautions & Treatment Considerations for Regenerating Lesions

• Do not traction a regenerating nerve.
• Treat edema with elevation, nodal pumping & drainage techniques, proximal to the edge of the edema.
• Use segmental techniques proximal to the lesion, applied at right angles to the direction of the regenerating nerve.
• Consider "blocking" with the ulnar border of the hand, just proximal to the lesion, to prevent drag on the healing tissue.
• Avoid work on lesion site until regeneration has passed (approx. 2 weeks post-trauma or 3 weeks post-surgery).
• Treat flaccid or weakened muscles distal to the lesion with light strokes & gentle compressions.
• PROM can be used to affect joints in the direction that shortens the affected tissue & nerve.
• Treatment of nerve compression/entrapment (neuropraxia) is different from treatment for nerve injuries (axonotmesis, neurotmesis).
• Neuropraxia (non-degenerative condition) presents with paresthesia, dysesthesia, pain, mild weakness, and nerve palpation is indicated.
• Axonotmesis/Neurotmesis (degenerative condition) is indicated when there is atrophy, flaccidity, significant weakness/paresis/paralysis, sensory loss, and palpation of the nerve is not indicated.
• Simple compressions or entrapments without tissue damage require releasing compression at the compression site for treatment.
• The precautions apply to degenerative conditions.

Assessment Considerations

• Acute injuries and regenerating tissue must be handled with extreme caution, and MD/Neurologist confirmation is needed for movement assessment & treatment.
• Palpation: Compare bilaterally for muscle bulk (atrophy), sweating (anhidrosis/diaphoresis), and edema.
• ROM testing: Avoid actions that traction/stretch a regenerating nerve; ROM testing can be used on the affected muscles.
• PROM: Can be used with a regenerating nerve to assess contracture of unopposed antagonistic muscles, as long as the motion does not traction or stretch the regenerating nerve.
• AAROM Can be used with minimal assistance provided by a therapist.
• Deep Tendon Reflexes diminish with a partial lesion (hyporeflexia); hyperreflexia may be indicative of an upper motor neuron lesion.
• Sensory Testing: Dysfunction appears in the affected nerve's normal function. Types of sensory testing include deep & light touch, 2 point discrimination, piloerector response and temperature.

Nerve Root Compression vs. Peripheral Nerve Lesion

• Nerve root compression causes altered sensation in a dermatome pattern

• Assess the corresponding myotome to determine muscle function

• Nerve roots are part of the PNS.

• Cutaneous nerves are C-fibers that respond to thermal, mechanical, and chemical stimuli, producing dull, diffuse, aching, burning, and delayed pain.

• During palpation: consider the nerve's referral pattern

• Nerves may feel like tight bands/wires/nodules in tissue

• If a nerve is compressed/tractioned/suffering a chemical imbalance, it may become swollen due to intraneural edema.

• The key points for muscles and skin for the various cranial and spinal nerves include

• Cranial Nerve 5

• Cranial Nerve 7

• Brachial Plexus

• Median Nerve

• Radial Nerve

• Ulnar Nerve

• Lateral Femoral Cutaneous Nerve

• Obturator Nerve

• Sciatic Nerve

• Tibial Nerve

• Common Fibular Nerve

• The following symptoms are caused by cutaneous nerve damage

• Pain (dull, ache, sharp, bright)

• Numbness, tingling, prickling, and loss of sensation

• The following symptoms are caused by motor nerve damage

• Weakness, paresis, and paralysis of innevated muscles

• Atrophy, flacidity dependong on the length and severity

• Key clinical findings for common nerve distributions include

• Cranial Nerve 5

• Cranial Nerve 7

• Brachial Plexus

• Median Nerve

• Radial Nerve

• Lateral Femoral Cutaneous Nerve

• Obturator Nerve

• Sciatic Nerve

• Tibial Nerve

• Common Fibular Nerve

This quiz assesses your knowledge of potential nerve injuries in the lower limb. Questions cover nerve damage resulting from surgery, strains, or fractures and their corresponding symptoms such as muscle weakness, altered sensation, and foot drop.