Carpal Tunnel Revision
The breadth of anatomy required for the FRCEM Primary is vast. The carpal tunnel is a common exam question. When revising anatomy it’s key to focus on the relevant details and not become focussed on minutiae. These summaries are designed around the RCEM Basic Sciences curriculum and contain the required level of detail.
The RCEM Basic Science Curriculum states the following as required knowledge:
Carpal tunnel: Its constituents: the separated tendons of the superficial flexors and the different arrangement of the deep tendon. Position of the median nerve in the tunnel.
The carpal tunnel is formed by a deep carpal arch and a superficial flexor retinaculum.
The deep carpal arch is formed medially by the pisiform and the hook of hamate, and laterally by the scaphoid and trapezium tubercles and forms the base of the carpal tunnel.
The flexor retinaculum is a fibrous band on the palmar side of the hand near the wrist which extends between these carpal bones and forms the roof of the carpal tunnel.
The carpal tunnel contains 9 flexor tendons and the median nerve.
The tendons within the carpal tunnel are:
- The 4 tendons of flexor digitorum profundus
- The 4 tendons of flexor digitorum superficialis
- The tendon of flexor pollicis longus
The tendon of the flexor carpi radialis tendon is sometimes listed, but this actually passes through the flexor retinaculum into the hand.
The 8 flexor digitorum tendons share a synovial sheath. The flexor pollicis longus sits within its own synovial sheath.
The median nerve is anterior to the tendons in the carpal tunnel.
The median nerve divides into 2 branches upon exiting the carpal tunnel
- the recurrent branch supplies the muscles of the thenar eminence
- the palmar digital nerves supply sensory innervation to the palmar aspect of the lateral three and half digits, and motor innervation to the lateral two lumbricals
The muscles of the hand supplied by the median nerve can be remembered using the mnemonic, “LOAF” for
- Lumbricals 1 & 2
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis.
The following video summarises carpal tunnel anatomy.
Clinical Considerations – Carpal Tunnel Syndrome
Compression of the median nerve within the narrow carpal tunnel can lead to carpal tunnel syndrome (CTS).
The patient reports pain and paraesthesia in the distribution of the median nerve in the hand i.e. the palmar aspect of the lateral three and half digits. Pain is often worse at night and can wake the patient. Pain may become progressively more persistent, and may radiate to the forearm and even the upper arm and shoulder. There may be weakness of hand grip and of opposition of the thumb and if left untreated, atrophy of the thenar muscles may occur.
There are 2 bedside clinical test that can be used to aid diagnosis:
Tinel’s test – tapping of the median nerve as it passes through the carpal tunnel results in pain in the median nerve distribution.
Phalen’s Manoeuvre – the wrist is held in flexion for 1 minute. Pain and paraesthesia in the median nerve distribution suggest a diagnosis of carpal tunnel syndrome.
CTS can be treated using local corticosteroid injections, wrist splints (holding the wrist in dorsiflexion) or ultimately surgical decompression.
Left untreated CTS can lead to wasting of the thenar muscles.