Anatomy Answer 2

This is the smaller terminal branch of sciatic nerve. it extends from the superior angle of the fossa to the lateral angle, along the medial border of biceps femoris. Continuing downwards & forwards, it winds around the posterolateral aspect of the neck of the fibula, pierces the peroneus longus & divides into superficial and deep peroneal nerves.

• Formed by: Axons from L4, L5, S1 & S2 roots
• Course of axons
  
  • Through popliteal fossa: Separates from sciatic nerve in upper fossa
  • Behind head & along fibula: Covered only by skin & subcutaneous tissue
  • Behind peroneus longus muscle (fibular tunnel): In anterior compartment of leg
  • Emerge from fibular tunnel: Nerve divides into superficial & deep branches
• Branches
  
  • Common peroneal in popliteal fossa: Sensory
  • Superficial peroneal
    
    • Motor
      
      • Peroneus brevis
    • Cutaneous sensory:
      
      • Lower leg: Anterolateral
        
      • Foot: Dorsum, except between 1st 2 toes
  • Deep peroneal
    
    • Motor branches in leg
      
      • Tibialis anterior
      • Extensor hallucis & digitorum longus
        
      • Peroneus tertius
        
    • Lateral terminal branch in foot
      
      • Extensor digitorum brevis
        
        • May also be innervated by accessory deep peroneal from superficial peroneal (28%)
      • Cutaneous: Skin between 1st & 2nd toes

• Weakness: Dorsiflexion & eversion of foot; Extension of toes
• Sensory loss: Anterolateral lower leg; Dorsum of foot & toes

• L5 root
• Lumbosacral trunk or plexus
• Sciatic nerve: Lateral trunk

• External compression: Especially with weight loss
  
  • Altered consciousness: Coma, Anesthesia, Sleep & Bed rest
  • Positional: Crossed legs; Squatting
• Trauma: Blunt; Traction; fractures
• Entrapment
  
  • Masses: Ganglia; Baker's cyst...
  • Fibular tunnel
• Mononeuropathy in systemic disorder
  
  • HNPP
  • Vasculitis
  • Diabetes mellitus
  • Leprosy
• Deep peroneal
  
  • Anterior compartment syndrome
  • At ankle
    
    • External copmpression
    • Weak: Extensor digitorum brevis
• Superficial peroneal
  
  • Peroneal compartment syndrome
  • Local trauma
  • Compression of sensory branch when traversing deep fascia of lower leg

Category: AIIMS Nov 2006 MCQs