Carpal Tunnel and Wrist extensors Flashcards
Name the Extensor Tendon Compartments of the Wrist
The extensor tendon compartments of the wrist are six tunnels which transmit the long extensor tendons from the forearm into the hand
They are located on the posterior aspect of the wrist. Each tunnel is lined internally by a synovial sheath and separated from one another by fibrous septa.
Compartment 1
The first extensor compartment is located on the lateral (radial) aspect of the wrist. It transmits two tendons:
Extensor pollicis brevis
Abductor pollicis longus
These tendons form the lateral border of the anatomical snuffbox.
De Quervains tendosynovitis refers to inflammation of the tendons within which extensor compartment?
Compartment 1
De Quervain’s tenosynovitis is inflammation of the tendons within the first extensor compartment of the wrist, resulting in wrist pain and swelling. It is most common in women between the ages of 30-50, especially in those with occupations or hobbies involving repetitive movements of the wrist.
Patients with De Quervain’s tenosynovitis will often complain of pain near the base of the thumb with an associated swelling (secondary to thickening of the tendon sheath). Movements involving grasping or pinching are particularly painful and difficult.
Conservative management of De Quervain’s tenosynovitis involves lifestyle advice (avoiding repetitive actions) and a wrist splint. Steroid injections will reduce swelling and relieve pain in most cases, and can be repeated several times if a good response is observed.
For those failing to respond to conservative management, surgical decompression of the extensor compartment can be performed under local or general anaesthetic.
Borders
As the snuffbox is triangularly shaped, it has three borders, a floor, and a roof:
Ulnar (medial) border: Tendon of the extensor pollicis longus.
Radial (lateral) border: Tendons of the extensor pollicis brevis and abductor pollicis longus.
Proximal border: Styloid process of the radius.
Floor: Carpal bones; scaphoid and trapezium.
Roof: Skin.
The anatomical snuffbox (also known as the radial fossa), is a triangular depression found on the lateral aspect of the dorsum of the hand. It is located at the level of the carpal bones, and best seen when the thumb is extended.
In the past, this depression was used to hold snuff (ground tobacco) before inhaling via the nose – hence it was given the name ‘snuffbox’.
Contents
The main contents of the anatomical snuffbox are the radial artery, a branch of the radial nerve, and the cephalic vein:
Radial artery – crosses the floor of the anatomical snuffbox, then turns medially and travels between the heads of the adductor pollicis muscle.
The radial pulse can be palpated in some individuals by placing two fingers on the proximal portion of the anatomical snuffbox.
Superficial branch of the radial nerve – found in the skin and subcutaneous tissue of the anatomical snuffbox. It innervates the dorsal surface of the lateral three and half digits, and the associated area on the back of the hand.
Cephalic vein – arises from the dorsal venous network of the hand and crosses the anatomical snuffbox to travel up the anterolateral aspect of the forearm.
Clinical Relevance: Scaphoid Fracture
The scaphoid bone of the hand is the most commonly fractured carpal bone – typically by falling on an oustretched hand (FOOSH).
In a fracture of the scaphoid, the characteristic clinical feature is pain and tenderness in the anatomical snuffbox.
The scaphoid is at particular risk of avascular necrosis after fracture because of its so-called ‘retrograde blood supply’ which enters at its distal end. This means that a fracture to the middle (or ‘waist’) of the scaphoid may interrupt the blood supply to the proximal part of the scaphoid bone rendering it avascular.
Patients with a missed scaphoid fracture are likely to develop osteoarthritis of the wrist in later life.
Compartment 2
The second extensor compartment contains the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis.
This compartment is separated from compartment 3 by Lister’s tubercle – a bony prominence of the distal aspect of the radius.
Compartment 3
Compartment three conducts the extensor pollicis longus tendon – this forms the medial border of the anatomical snuffbox.
Posterior compartment of the forearm and hand Deep and Superficial compartments
Compartment 4
The 4th extensor compartment of the wrist transmits the tendons of the extensor digitorum and extensor indicis.
Compartment 5
Compartment five contains the extensor digiti minimi tendon, which travels into the little finger.
Compartment 6
The sixth compartment is the located on the medial (ulnar) aspect of the wrist. It conducts the tendon of the extensor carpi ulnaris.
Structures that pass through the carpal tunnel
Ten structures pass through the carpal tunnel, most of them flexor tendons (not the muscles themselves):
flexor digitorum profundus (four tendons)
flexor digitorum superficialis (four tendons)
flexor pollicis longus (one tendon)
Median nerve between tendons of flexor digitorum profundus and flexor digitorum superficialis
The flexor carpi radialis (one tendon), is often incorrectly stated to travel within the carpal tunnel. More precisely, it travels within the fibers of the flexor retinaculum which forms the roof of the carpal tunnel, rather than running inside the tunnel itself.
