Upper Limb Nerve Lesions

• Nerve lesions can occur due to trauma, compression, ischemia, or inflammation

Upper Limb Nerve Lesions

• Axillary Nerve:
  • Injury typically results from shoulder dislocation or fracture of the surgical neck of the humerus
  • Leads to paralysis of the deltoid and teres minor muscles, causing weakness in abduction and external rotation of the arm
  • Sensory loss may occur over the lateral aspect of the shoulder (regimental badge area)
• Musculocutaneous Nerve:
  • Often injured due to penetrating trauma or forceful traction injuries
  • Results in weakness of elbow flexion (biceps brachii, brachialis) and supination (biceps brachii)
  • Sensory loss occurs along the lateral aspect of the forearm
• Radial Nerve:
  • Can be damaged in the axilla (e.g., from crutches – "crutch palsy"), mid-humerus fractures, or compression in the forearm (e.g., supinator entrapment)
  • High radial nerve injury (axilla) causes paralysis of the triceps brachii, brachioradialis, wrist extensors, and finger extensors, leading to wrist drop
  • Sensory loss occurs over the posterior aspect of the arm and forearm, as well as the dorsal aspect of the hand (excluding the digits)
  • If the radial nerve is compressed more distally (e.g., in the supinator muscle), wrist drop may occur, with sparing of triceps function
• Median Nerve:
  • Can be injured at the elbow (e.g., supracondylar fracture) or at the wrist (carpal tunnel syndrome)
  • High median nerve injury (elbow) causes weakness of forearm pronation, wrist flexion, and finger flexion of the lateral digits (digits 1-3)
  • Results in an inability to oppose the thumb (ape hand deformity) and sensory loss over the palmar aspect of the lateral hand and digits 1-3
  • Carpal tunnel syndrome: Compression of the median nerve in the carpal tunnel leads to sensory disturbances (numbness, tingling) in the median nerve distribution and weakness/atrophy of the thenar muscles; Phalen's test and Tinel's sign can help diagnose this
• Ulnar Nerve:
  • Vulnerable to injury at the elbow (cubital tunnel syndrome) or wrist (Guyon's canal)
  • High ulnar nerve injury (elbow) causes weakness of wrist flexion and adduction, finger flexion of digits 4-5, and intrinsic hand muscle weakness (interossei, adductor pollicis, hypothenar muscles)
  • Results in claw hand deformity (digits 4-5), inability to abduct or adduct the fingers, and sensory loss over the medial aspect of the hand and digits 4-5
  • Injury at Guyon's canal will spare the dorsal cutaneous branch; therefore, it will present with motor deficits and sensory loss over the palmar side of digits 4-5 only

Lower Limb Nerve Lesions

• Sciatic Nerve:
  • Can be injured by hip dislocation, intramuscular injections, or compression
  • Results in weakness of knee flexion (hamstrings) and all movements below the knee (foot and ankle)
  • Sensory loss occurs over the posterior aspect of the thigh, lateral aspect of the leg, and the entire foot (except for the saphenous nerve distribution)
• Femoral Nerve:
  • Can be damaged by pelvic fractures, hematomas, or compression
  • Causes weakness of knee extension (quadriceps femoris) and hip flexion (iliopsoas, sartorius)
  • Sensory loss occurs over the anterior and medial aspects of the thigh and medial aspect of the leg (saphenous nerve)
• Obturator Nerve:
  • Often injured during pelvic surgery or due to compression
  • Leads to weakness of hip adduction (adductor muscles)
  • Sensory loss may occur over the medial aspect of the thigh
• Common Peroneal (Fibular) Nerve:
  • Vulnerable to injury at the fibular neck (e.g., from leg casts, crossing legs)
  • Causes weakness of ankle dorsiflexion (tibialis anterior), foot eversion (peroneal muscles), and toe extension
  • Leads to foot drop and a steppage gait
  • Sensory loss occurs over the anterior and lateral aspects of the leg and the dorsum of the foot
• Tibial Nerve:
  • Can be injured in the popliteal fossa or at the ankle (tarsal tunnel syndrome)
  • Causes weakness of ankle plantarflexion (gastrocnemius, soleus), foot inversion (tibialis posterior), and toe flexion
  • Results in an inability to stand on tiptoes
  • Sensory loss occurs over the plantar aspect of the foot
  • Tarsal tunnel syndrome: Compression of the tibial nerve in the tarsal tunnel leads to sensory disturbances (numbness, tingling) in the tibial nerve distribution

Examination Techniques

• Motor Testing:
  • Assess muscle strength using the standard 0-5 scale
  • Look for specific movements affected to determine nerve involvement
• Sensory Testing:
  • Test light touch, pain, temperature, and vibration sensation
  • Map out areas of sensory loss to determine the distribution of nerve damage
• Reflex Testing:
  • Assess deep tendon reflexes (e.g., biceps, triceps, brachioradialis, knee, ankle)
  • Changes in reflexes (diminished or absent) can indicate nerve or muscle dysfunction
• Specific Tests:
  • Phalen's Test: For carpal tunnel syndrome, hold the wrists in forced flexion
  • Tinel's Sign: Tap over a nerve to elicit tingling sensations
  • Trendelenburg Test: To assess hip abductor weakness (superior gluteal nerve)

Nerve Regeneration

• Peripheral nerves can regenerate, but the process is slow (approximately 1 mm per day)
• Recovery depends on the extent and location of the injury
• Complete transection of a nerve may require surgical repair

Important Considerations for Diagnosis

• Mechanism of Injury: Understand how the injury occurred
• Pattern of Weakness: Identify specific muscle groups affected
• Sensory Deficits: Map the distribution of sensory loss
• Associated Symptoms: Consider pain, paresthesia, and autonomic changes

Clinical Scenarios & Questions

• A patient presents with weakness in shoulder abduction and sensory loss over the lateral shoulder after a shoulder dislocation; the axillary nerve is most likely injured
• A patient reports difficulty flexing their elbow and supination of their forearm; they also have sensory loss along the lateral forearm; the musculocutaneous nerve is most likely injured
• A patient presents with wrist drop after a mid-shaft humerus fracture; the radial nerve is most likely injured
• A patient presents with numbness and tingling in their thumb, index finger, and middle finger, as well as weakness of thumb abduction; they report symptoms worsen at night; the median nerve is likely affected, and they likely have carpal tunnel syndrome
• A patient has clawing of the 4th and 5th digits and weakness in finger adduction/abduction; they also have sensory loss over the medial aspect of the hand; the ulnar nerve is most likely injured
• A patient is unable to extend their knee and has sensory loss over the anterior thigh; the femoral nerve is most likely injured

Common Nerve Entrapment Syndromes

• Carpal Tunnel Syndrome: Median nerve compression at the wrist
• Cubital Tunnel Syndrome: Ulnar nerve compression at the elbow
• Peroneal Nerve Entrapment: Common peroneal nerve compression at the fibular neck
• Tarsal Tunnel Syndrome: Tibial nerve compression at the ankle
• Nerve injuries lead to specific motor and sensory deficits, understanding the anatomy will help ascertain which nerve is injured