Median Nerve in Carpal Tunnel

  • In Section 8 the median nerve is in the carpal tunnel with nine flexor tendons.
  • The median nerve is positioned volar radially in the carpal tunnel dorsal to the palmar fascia and transverse carpal ligament.
  • Proximal to the carpal tunnel the median nerve is dorsal to the FDS muscle.
  • At the wrist crease the median nerve is dorsal to the palmaris longus.
  • The common terminal branches of the median nerve are the motor branch to the thenar muscles, the radial and ulnar digital nerves to the thumb, the radial digital nerve to the index, the common digital nerve in the index/long web space, and the common digital nerve in the long/ring web space, and finally the motor nerve to the first two lumbrical muscles.
Diagrams & Photos
  • Median nerve and its branches.
    Median nerve and its branches.
  • The palmar fascia has been released from the palmaris longs and reflected distally showing the transverse carpal ligament (yellow lines).
    The palmar fascia has been released from the palmaris longs and reflected distally showing the transverse carpal ligament (yellow lines)
  • Open carpal tunnel showing the median nerve and its motor branch two the thenar muscles.
    Open carpal tunnel showing the median nerve and its motor branch two the thenar muscles.
  • Nerve with axons enclosed in endoneurium (1); Fascicle enclosed in perineurium (2); Fascicular groups enclosed in connective tissue called internal epineurium (3); Internal epineurium (4); External epineurium (5); Epineural blood vessels (6).
    Nerve with axons enclosed in endoneurium (1); Fascicle enclosed in perineurium (2); Fascicular groups enclosed in connective tissue called internal epineurium (3); Internal epineurium (4); External epineurium (5); Epineural blood vessels (6).
Key Points
  • The carpal tunnel is formed by the carpal bones and the transverse carpal ligament.
  • The radial side of the carpal tunnel is formed by the distal scaphoid and the trapezial ridge. The dorsal part is formed by the scaphoid, lunate, capitate, and hamate. The ulnar side is formed by the hook of hamate and pisiform.
  • The motor branches to the first two lumbrical muscles are branches of the index radial digital nerve and index/long common digital nerve.
  • On ultrasound the median nerve averages 6-10 mm wide at the entrance to the carpal tunnel.
  • In Section 9 the palmar cutaneous branch of the median nerve originates from the radial edge of the median nerve approximately 6 cm. proximal to the wrist flexion crease.
Anatomy References
Anatomic Abbreviations
Hand Surgery Resource Anatomy Diagnostic Guide (Chapter)