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Carpal tunnel

The carpal tunnel is a narrow osteofibrous canal located on the palmar side of the wrist, found deep to the flexor retinaculum. The floor of the carpal tunnel is composed of the carpal bones, which is how it got its name.

The carpal tunnel serves as a passageway for structures passing between the anterior forearm and the hand. It transmits the median nerve and the tendons of the flexor pollicis longus, flexor digitorum superficialis and flexor digitorum profundus muscles

In some circumstances, the narrowing of the carpal tunnel can cause an entrapment of the median nerve, a common condition known as the carpal tunnel syndrome. 

In this article, we will explore the anatomy and functions of the carpal tunnel.

Key facts about the carpal tunnel
Definition Passageway found on anterior wrist for structures passing between anterior forearm and hand
Boundaries Floor: Carpal groove
Roof: Flexor retinaculum
Contents Flexor digitorum superficialis tendons
Flexor digitorum profundus tendons
Flexor pollicis longus tendon
Median nerve
Contents
  1. Boundaries
  2. Contents
  3. Clinical relations
    1. Carpal tunnel syndrome
  4. Sources
+ Show all

Boundaries

The floor of the carpal tunnel is formed by the carpal groove (or carpal arch), a deep arch formed by the palmar aspect of the carpal bones. This arch is bounded medially by the pisiform bone and the hook of the hamate, and laterally by the tubercles of the scaphoid and trapezium bones.

The roof of the carpal tunnel is formed by the flexor retinaculum (also known as transverse carpal ligament), a thick connective tissue ligament. This ligament bridges the space between the medial and lateral ends of the carpal arch, converting the arch into a tunnel.

Contents

The carpal tunnel contains the median nerve and nine tendons: four tendons of the flexor digitorum superficialis, the four tendons of the flexor digitorum profundus, and the tendon of the flexor pollicis longus.

The tendons are enveloped by synovial tendinous sheaths that allow free movement between them. The eight tendons of the flexor digitorum profundus and flexor digitorum superficialis are surrounded by a single synovial sheath, while the tendon of flexor pollicis longus is surrounded by its own synovial sheath. The flexor retinaculum holds all these tendons in place.

The flexor carpi radialis tendon does not pass through the carpal tunnel. It is enveloped by an individual synovial sheath and passes through its own tubular compartment within the lateral aspect of the flexor retinaculum. 

The ulnar artery, the ulnar nerve, and the tendon of the palmaris longus are anterior to the flexor retinaculum and do not pass through the carpal tunnel. The ulnar artery and nerve are contained within the so-called Guyon canal which is located superficial to the flexor retinaculum and deep to the palmar carpal ligament, a thickened portion of the antebrachial fascia on the anterior part of the wrist.

Carpal tunnel: want to learn more about it?

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