Peripheral Nerve Injury

Aka: Peripheral Nerve Injury, Peripheral Nerve Entrapment, Entrapment Neuropathy, Neuropraxia, Axonotmesis, Axonal Neuropathy, Neurotmesis, Compression Neuropathy, Compressive Neuropathy, Nerve Compression Syndrome

1. See Also
   1. Peripheral Neuropathy
   2. Overuse Syndromes of the Hand and Wrist
2. Definitions: Categories of Peripheral Nerve Injury
   1. Neuropraxia
      1. Least severe Peripheral Nerve Injury
      2. Myelin fibers surrounding the axon are injured focally
      3. Axon and connective tissue sheath remain unharmed
      4. Limited duration of injury (typically days to weeks)
   2. Axonotmesis
      1. Axon injury, but preserved connective tissue framework
      2. Risk of distal nerve degeneration
      3. Recovery over months to years and frequently incomplete nerve regeneration with residual deficit
   3. Neurotmesis
      1. Most severe Peripheral Nerve Injury and least common of the three nerve injury types
      2. Complete axon disruption, as well as disrupted connective tissue framework
      3. Normal regeneration of the nerve is uncommon and signficant persistent deficit is the norm
3. Pathophysiology
   1. Mechanisms of nerve injury
      1. Direct pressure
      2. Repetitive microtrauma
      3. Stretch-induced ischemia
      4. Compression-induced ischemia
   2. Degree of nerve injury may progress to nerve fibrosis with greater nerve injury
      1. Severity of injury mechanism
      2. Duration of exposure to compression or other mechanism
4. Causes: Upper Extremity
   1. Images
      1. 
      2. 
   2. Cervical Spine and Cervicobrachial (Axilla)
      1. Cervical Disc Disease
      2. Brachial Plexus Burner
   3. Shoulder
      1. Shoulder Band Syndrome (Reflex Sympathetic Dystrophy)
      2. Quadrilateral Space Syndrome (Axillary Nerve Injury)
      3. Long Thoracic Nerve Injury
         1. Injury: Direct blow to Shoulder or chronic repetitive overhead Shoulder traction (e.g. tennis, swimming, baseball)
         2. Symptoms: Diffuse Shoulder or Neck Pain with overhead activity
         3. Exam: Forward flexion weakness at Shoulder and Scapular winging
      4. Spinal Accessory Nerve Injury
   4. Humerus
      1. Radial Nerve Injury at the Humerus
         1. Radial Nerve may be compressed in axilla causing Saturday Night Palsy
         2. Mid-shaft Humerus Fracture may injure Radial Nerve
         3. Radial Nerve may be entrapped in radial groove
   5. Elbow and Forearm
      1. Cubital Tunnel (Ulnar Nerve, common)
      2. Radial Tunnel (and related Posterior Interosseus Nerve Syndrome)
   6. Wrist and Hand
      1. See Overuse Syndromes of the Hand and Wrist
      2. Carpal Tunnel Syndrome (Median Nerve, very common)
      3. Ulnar Tunnel Syndrome (Cyclist's Palsy)
      4. Handcuff Neuropathy (Radial Nerve)
5. Causes: Lower Extremity
   1. 
   2. Lumbar Spine and buttock
      1. Lumbar Disc Disease
      2. Piriformis Syndrome (Sciatica)
   3. Anterior Pelvis and thigh
      1. Ilioinguinal Nerve Compression
      2. Meralgia Paresthetica
      3. Obturator Nerve Compression
   4. Ankle and Foot
      1. Tarsal Tunnel
      2. Morton's Neuroma
6. Causes: Miscellaneous
   1. Images
      1. 
   2. Face
      1. Trigeminal Neuralgia
   3. Secondary Complications
      1. Compartment Syndrome
      2. Reflex Sympathetic Dystrophy
      3. Post-herpetic Neuralgia
7. History
   1. See Neuropathy
   2. Musculoskeletal Injury or Trauma to affected region
   3. Course of symptoms
   4. Provocative activities
8. Exam
   1. Musculoskeletal Exam of affected region
      1. Joint range of motion
      2. Specific joint exam for region
   2. Neurologic Exam
      1. See Motor Exam
      2. See Sensory Exam
      3. See Deep Tendon Reflex
9. Symptoms
   1. Burning pain
   2. Numbness
   3. Paresthesias
   4. Motor Weakness
10. Differential Diagnosis
    1. See Peripheral Neuropathy
    2. See Mononeuropathy
11. Imaging
    1. See Peripheral Neuropathy
    2. Modalities
       1. Ultrasound
          1. Real-time (point-of-care) evaluation of compression sites that reproduce symptoms
          2. Directed Corticosteroid Injection for certain compression neuropathies
       2. Magnetic Resonance Imaging (MRI)
          1. Identifies most likely sites and mechanisms of compression
          2. Identifies signs of muscle atrophy suggestive of muscle denervation
    3. Indications
       1. Severe weakness
       2. Multiple nerves involved
       3. Refractory course to 6-8 weeks of specific conservative therapy
12. Diagnostics: Electrodiagnostic Testing
    1. See Peripheral Neuropathy
    2. Modalities (typically performed together)
       1. Nerve Conduction Study
       2. Electromyography (EMG)
    3. Indications
       1. Localization of nerve lesion in atypical presentations
       2. Monitoring of nerve injury progression during management
       3. Presurgical planning
13. Management
    1. See Peripheral Neuropathy
    2. Initial conservative therapy is preferred for most non-Traumatic compression neuropathies
       1. Management is specific to the Neuropathy
    3. General conservative measures
       1. Patient Education regarding likely diagnoses and causative factors
       2. Relative rest with activity modification
       3. Consider bracing or Splinting (with care not to further compress underlying nerve)
       4. Consider physical therapy
    4. Surgical Management
       1. Indicated in refractory cases
       2. Lack of full resolution with surgery is common
       3. Surgical options depend on specific Neuropathy
          1. Nerve Decompression
          2. Surgical exploration for underlying cause
          3. Nerve transfer
14. References
    1. Neal (2010) Am Fam Physician 81(2): 147-55 [PubMed]
    2. Silver (2021) Am Fam Physician 103(5): 275-85 [PubMed]