Peripheral Nerve Entrapment and Injury in the Upper Extremity

SARA L. NEAL, MD, MA, and KARL B. FIELDS, MD, Moses Cone Health System, Greensboro, North Carolina

http://www.aafp.org/afp/2010/0115/p147.pdf

  • Risk factors for nerve injury: superficial position of the nerve, long course of travel, location in area of high likelihood of trauma, narrow path in body canal
  • Most common nerve injury: carpal tunnel ~ 3% of general population, 5-15% in industrial setting
  • 3 categories of nerve injury
    • Neurapraxia - least severe, focal damage of myelin fibers (days to weeks for recovery)
    • Axonotmesis - more severe, injury axon itself (months for recovery), may not fully recover
    • Neurotmesis - complete disruption of axon, little likelihood of regrowth

Shoulder and Arm

  • Axillary Nerve:
    • Quadrilateral Space Syndrome - MOI: often from a traumatic shoulder dislocation, upward pressure from improper crutch use, repetitive overload, or damage during Shoulder Arthroscopic Surgery
    • Symptoms include - arm fatigue with overhead activity, paresthesias of superior and lateral arm - weakness in  shoulder abduction and external rotation
  • Brachial Plexus Injury: “stinger” -
    • MOI: more common in football with a direct blow
    • Symptoms: acute onset of paresthesia in upper arm. More circumferential than in a dermatomal pattern for differential diagnosis between nerve root impingement
    • Differential Diagnosis: from C/S by unilateral, no point tenderness in neck, often return to sport within 15 minutes if symptoms dissipate
  • Long thoracic nerve:
    • MOI: Often from an acute blow to the shoulder or repetitive traction on the nerve (ex:  swimming, tennis)
    • Symptoms: Diffuse shoulder and neck pain, scapular winging, weakness of forward elevation of the arm
  • Spinal accessory nerve:
    • MOI: Often from trauma to the Trapezius or traumatic shoulder dislocation
    • Present with generalized weakness and pain in shoulder. Affected side often sags and patient often unable to shrug shoulder
  • Suprascapular nerve:
    • MOI: Repetitive overhead loading, certain GH labral tears and cyst formation.
    • Symptoms: May only affect infraspinatus depending on site of lesion (Suprascapular notch). Weakness in shoulder ER, weakness in arm elevation from 90-180 degrees elevation.

Forearm and Elbow

  • Median nerve:
    • Pronator teres syndrome - pronator teres compresses nerve on anterior forearm, can mimic carpal tunnel. Aching in the forearm with the elbow extended. Paresthesias in the thumb and 1st two fingers may be present.
    • Differential Diagnosis: Normal forearm sensation, but sensory loss is present over the thenar eminence which is not present in carpal tunnel. Tinel’s and Phalen’s at wrist should be negative
  • Radial nerve injury:
    • Radial Tunnel Syndrome: Forearm pain exacerbated by repetitive forearm pronation for radial tunnel syndrome - superficial branch is involved
      • Almost identical pain presentation to Lateral Epicondylalgia - main difference in location of origin of pain; tendon ECRB vs anterior radial neck
    • Posterior Interosseous Nerve - if motor weakness is present, with extension of the wrist
    • Ulnar nerve at the elbow: Cubital Tunnel Syndrome
      • Very superficial, may cause paresthesia of 4th and 5th digits. Motor weakness may occur but is a symptom later in the progression. Weak digit abduction, thumb abduction, and weak pinch grip

Hand and Wrist

  • Median Nerve: Carpal Tunnel - most common, paresthesias of thumb, index and long finger. Positive findings hypalgesia and abnormal Katz hand diagram
  • Radial nerve: Handcuff Neuropathy - compression wound around the wrist. Numbness on the back of the hand - motor function intact
  • Ulnar Nerve - Cyclist’s palsy - compression of ulnar nerve, often against the handlebars. Paresthesia in 4th and 5th digit - weakness is less common as motor branch is less superficial

Diagnostic Testing for Nerve Injury

  • Plain radiograph - Often used first, used to rule out other diagnosis
  • MRI - Rarely needed initially but may show muscle atrophy in specific muscles from nerve injury. Normal MRI does not rule OUT a nerve injury
  • Diagnostic Ultrasound - Less expensive and able to see anatomic entrapment but is limited by lack of standardization and differences in interpretation
  • EMG - Records the electrical activity of the muscle, looking for denervation
  • Nerve Conduction Studies - Assess the integrity of sensory and motor nerves within areas of injury, presents as slowing of conduction speed.    
    • Ability confirm carpal tunnel Sensitivity: 85%, Specificity: 95%

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