Carpal Tunnel

Description

A fibro-osseous canal on the palmar side of the wrist that serves as a passageway for tendinous structures and the median nerve between the forearm and anterior hand. It lies between the flexor retinaculum and the carpal bones.

Borders

• Roof (superficial): Flexor retinaculum
  • Thick fibrous band measuring 2-3 cm 
  • Attaches from the hook of hamate and pisiform medially
  • Attaches to the tubercle of the scaphoid and the ridge of the trapezium laterally
  • Proximal edge of the band corresponds to the distal dominant skin crease on the anterior wrist
  • Contains the flexor carpi radialis tendon (not located within the carpal tunnel itself)
• Medial (ulnar border): lateral surface of hamate
• Lateral (radial border): medial surface of trapezium
• Floor (deep): carpal groove formed by the palmar aspect of the carpal bones
  • hamate, pisiform, scaphoid, trapezium

Contents

Tendons

• Tendon of flexor pollicis longus (FPL)
  • Most lateral structure 
  • Surrounded by own synovial sheath
  • Runs in a groove on the trapezium
  • FPL flexes the interphalangeal joint of the distal phalanx of the thumb
• Four tendons of flexor digitorum superficialis (FDS)
  • Lie proximal to FDP in a row
  • FDS flexes the middle phalanges of the four fingers at the proximal interphalangeal joint
• Four tendons of flexor digitorum profundus (FDP)
  • Lie deep to FDS on one plane
  • FDP flexes hand and both interphalangeal joints
• The eight tendons of the FDS and FDP share a common sheath, which does not invest them completely.

Median nerve

• Divides into recurrent branch and palmar digital branch
  • Recurrent branch – thenar muscles (abductor pollicis, opponens pollicis, superficial head of the flexor pollicis brevis)
  • Palmar digital branch – palmar surface and fingertips of lateral three and a half digits, lateral two lumbrical muscles

Relations

• Medially: Guyon’s canal
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Variants

Nerve anomalies

• High bifurcation of median nerve
• Bifid median nerve
• Aberrant origin of motor branch of median nerve
• Transligamentous palmar cutaneous branch of median nerve
• Anomalous course of ulnar nerve
• Ulnar-to-median nerve connection (Marinacci communication)

Tendon anomalies

• Conjoint FPL and FDP II (Linburg-Comstock syndrome)

Vascular anomalies

• Persistent median artery
• Superficial ulnar artery

Muscle anomalies

• Presence of palmaris longus tendon within carpal tunnel
• Index lumbrical
• Flexor digitorum superficialis indicis