Overview

Passageway on the palmar side of the wrist that connects the forearm to the hand.
The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue

Carpal Bones

Some Lovers Try Positions That They Can’t Handle

Superficial: Flexor retinaculum
Flexor retinaculum:
- Medial attachment – Hook of Hamate and Pisiform
- Lateral attachment – Scaphoid tubercle and Trapezium
Deep: Carpal bones
- Medial/Ulnar Border: Lateral surface of Hamate
- Lateral/Radial Border: Medial surface of Trapezium

Long flexor tendons of the fingers and thumb (9 tendons in total)
- Flexor Digitorum Superficialis (FDS) tendons lie in 2 separate rows – middle and ring finger tendons anterior to index and little finger tendons
- Flexor Digitorum Profundus (FDP) tendons lie in one row deeply with only tendon to index finger separate from the others
  - All 8 tendons of FDS and FDP share common flexor sheath
    - Sheath does not invest them completely but is reflected from their radial sides where arterial supply gain access – it is as if the tendons have been invaginated into the sheath from the radial side
- Tendon of Flexor Pollicis Longus (FPL) lies in its own synovial sheath
Median Nerve
- Passes deep to flexor retinaculum between FDS to the middle finger and Flexor Carpi Radialis tendon

Figure: Left carpal tunnel, looking distally towards the palm

Flexor Carpi Radialis (FCR), Flexor Carpi Ulnaris (FCU) and Palmaris Longus (PL) tendons travel outside the carpal tunnel but in close contact with it
- FCR - At lateral end of tunnel, enclosed in its own synovial sheath, the tendon runs in the groove within the groove on the Trapezium
- FCU – Tendon inserts into pisiform
- PL – Continues with palmar fascia and inserts into flexor retinaculum

Nerves at Risk During Carpal Tunnel Release

Palmar Branch of Median Nerve
- Enters palm superficial to flexor retinaculum
Recurrent Branch of Median Nerve
- Comes off median nerve distal to flexor retinaculum
- Curls proximally around distal border of flexor retinaculum to supply thenar muscles

Symptoms:
- Impaired sensation over 3 and a half digits on the lateral/thumb side of the hand
- In late cases: wasting and weakness of the thenar muscles
NOTE: No sensory loss over thenar eminence ⇒ this area supplied by palmar branch of the median nerve which enters the palm superficial to the flexor retinaculum ⇒ escapes compression
Must be distinguished from median nerve injury at a higher level
If higher level ⇒ Palmar cutaneous branch affected and weakness of relevant flexor muscles, e.g. FPL, becomes notable

Carpal Tunnel Release
Incision site: The intersection of the Kaplan cardinal line and the radial border of the 4th ray ending at the wrist crease
Kaplan cardinal line = line drawn from the apex of the 1st web space (between thumb and index finger) toward the ulnar side of the hand, parallel with the proximal palmar crease.