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Anatomy · Joints & cartilage

Carpal tunnel

Nine tendons and a nerve

Upper limb · palmar wrist

The carpal tunnel is a narrow passage on the palm side of the wrist. Its floor and sides are the curved arch of the carpal bones and its roof is the tough flexor retinaculum (transverse carpal ligament). Through it pass the median nerve and nine flexor tendons, and swelling within it squeezes the nerve, causing carpal tunnel syndrome.

How to spot them

  • ▸Floor and walls: the arch of the carpal bones, with the scaphoid and trapezium on the thumb side and the pisiform and hook of the hamate on the little-finger side
  • ▸Roof: the flexor retinaculum, a strong band bridging the two sides of the arch
  • ▸Contents: median nerve plus four flexor digitorum superficialis, four flexor digitorum profundus and one flexor pollicis longus tendon
  • ▸The ulnar nerve and artery lie outside it, in Guyon's canal

What to know

A passage under a strong band on the palmar wrist that carries the median nerve and nine tendons

Carpal tunnel — the flexor retinaculum forms the roof.

Squeezing of the median nerve there causes tingling in the thumb, index and middle fingers, worse at night

Carpal tunnel — carpal tunnel syndrome.

A compression syndrome that spares the skin over the ball of the thumb, because the nerve's palmar cutaneous branch leaves before the passage

Carpal tunnel — the palmar cutaneous branch runs superficial to the retinaculum.

Tapping over the nerve at the wrist causes tingling, Tinel's sign; wrist flexion for a minute reproduces the symptoms, Phalen's test

Carpal tunnel — two clinical tests.

Surgical division of its roof relieves the pressure on the nerve

Carpal tunnel — carpal tunnel release.

Key ideas

  • A rigid box with a fixed volume: any swelling (tenosynovitis, fluid retention in pregnancy, fracture) raises the pressure on the soft median nerve.

Quick-fire facts

  • •It contains the median nerve and nine tendons: four of flexor digitorum superficialis, four of flexor digitorum profundus and one of flexor pollicis longus.
  • •The flexor carpi radialis tendon runs in its own sheath through the retinaculum, not in the tunnel proper.
  • •Symptoms: numbness, tingling and pain in the thumb, index, middle and half of the ring finger.
  • •It is more common in women; associated with pregnancy, diabetes, hypothyroidism, rheumatoid arthritis and repetitive work.
  • •The thenar branch of the median nerve can be involved, causing weakness of thumb abduction and wasting of the thenar eminence in late disease.
  • •Treatments include a wrist splint at night, steroid injection and surgery (NHS).
  • •The ulnar nerve does not pass through it: it runs through Guyon's canal.

Drill it — 7 cards

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Sources