Carpal Tunnel
The carpal tunnel is an osseofibrous tunnel at the wrist formed by the carpal bones and flexor retinaculum. It transmits the median nerve and nine flexor tendons to the hand. Carpal tunnel syndrome, caused by median nerve compression, is the most common entrapment neuropathy.
Boundaries
superior
Not applicable (it's a tunnel)
inferior
Not applicable (it's a tunnel)
anterior
Flexor retinaculum (transverse carpal ligament)
posterior
Carpal bones forming a concave arch (scaphoid, trapezium laterally; triquetrum, hamate medially)
lateral
Scaphoid and trapezium tubercles
medial
Pisiform and hook of hamate
Contents
Tendons (9 total)
Nerve
Nerves
- • Median nerve
Vessels
- • No major vessels (ulnar artery and nerve pass through Guyon's canal, superficial to retinaculum)
Muscles
- • Flexor digitorum superficialis (tendons pass through)
- • Flexor digitorum profundus (tendons pass through)
- • Flexor pollicis longus (tendon passes through)
Clinical Relevance
- •Carpal tunnel syndrome: Median nerve compression causing numbness in lateral 3.5 digits, thenar weakness, positive Phalen's and Tinel's tests
- •Causes: Repetitive wrist motion, pregnancy, hypothyroidism, diabetes, rheumatoid arthritis, acromegaly
- •Treatment: Wrist splints, corticosteroid injection, surgical release of flexor retinaculum
- •Thenar atrophy: Late sign indicating chronic, severe compression
Study Tips
- ✓Contents: 9 tendons + 1 nerve = 10 structures through the tunnel
- ✓Median nerve is most superficial - first to be compressed
- ✓FDS tendons are superficial to FDP tendons (FDS "splits" around FDP at fingers)
- ✓Ulnar nerve and artery are NOT in carpal tunnel - they're in Guyon's canal
Carpal Tunnel FAQs
Common questions about this region
The palmar cutaneous branch of the median nerve arises proximal to the carpal tunnel and passes superficial to the retinaculum, so it is spared in carpal tunnel syndrome while the digital sensory branches are affected.
Phalen's test involves holding the wrists in maximum flexion for 60 seconds. Reproduction of numbness or tingling in the median nerve distribution (lateral 3.5 digits) suggests carpal tunnel syndrome due to increased pressure in the tunnel.