🎯 Pathology

• the carpal tunnel is a narrow passageway in the wrist formed by the flexor retinaculum (a dense band of fibrous tissue) superiorly, and the carpal bones inferiorly

• carpal tunnel syndrome occurs when there is increased pressure within the carpal tunnel leading to compression of the median nerve

• the median nerve is one of the structures that passes through the carpal tunnel

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💡 Risk factors

• while underlying risk factors (below) have been identified, the exact cause is unknown

• risk factors include:

  • ​female (ten times more common than males)

  • rheumatoid arthritis

  • fluid retention (e.g. pregnancy)

  • diabetes

  • acromegaly

  • lunate dislocation

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💫 Structures that pass through the carpal tunnel

• 9 tendons and 1 nerve

  • tendons

    • flexor digitorum superficialis (x4)

    • flexor digitorum profundus (x4)

    • flexor pollicis longus (x1)

  • nerve

    • median nerve

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⚡️ Nerve supply of the median nerve

• nerve roots

  • C5-T1

• course

  • runs alongside the brachial artery and medial to the biceps brachii tendon in the cubital fossa

  • it enters the hand through the carpal tunnel

• nerve supply

  • motor

    • forearm

      • all muscles in the anterior compartment except flexor carpi ulnaris and the medial half of flexor digitorum profundus

    • hand: ‘LOAF’ muscles

      • Lateral 2 lumbricals

      • Opponens pollicis

      • Abductor pollicis brevis

      • Flexor pollicis brevis

  • sensory

    • skin over the lateral palm from the thumb to the lateral half of the ring finger

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🩺 Clinical features

• pain, numbness and tingling especially at night

• the first 3.5 digits are usually affected

• these symptoms may ascend to the proximal forearm

• shaking the affected hand may relieve symptoms

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🕵️‍♂️ Investigations

• examination and special tests

  • weak abduction —> due to weakness of abductor pollicis brevis

  • wasting of the thenar eminence

• special tests

  • Phalen’s test: wrist flexion (touch dorsum of both hands together) for 60 seconds induces symptoms of tingling and numbness

  • Tinel’s test: tapping at the wrist induces paraesthesia

• electrophysiology (e.g. nerve conduction studies)

  • slower conduction of nerve impulses in motor and sensory neurons in the median nerve passing across the wrist

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💆‍♂️ Management

• mild to moderate symptoms

  • 6 week trial of either:

    • corticosteroid injections

    • wearing wrist splints at night (favourable if temporary risk factors contributing are present)

• Severe symptoms

  • surgical decompression of the flexor retinaculum (connective tissue superior to the median nerve) as this helps reduce pressure on the nerve

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🧲 High-yield tips​

• carpal tunnel syndrome is the most common mononeuropathy (accounts for 90% of all neuropathies)

• it is also the most common entrapment neuropathy