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This article will discuss four key areas within the upper limb:
- Cubital fossa
- Carpal tunnel
- Anatomical snuffbox
- Guyon's Canal
The axilla can be imagined as a pyramid, with the apex starting behind the lateral border of the first rib.
The borders are as follows:
- Apex – lateral border of the first rib, superior border of scapula
- Lateral wall – intertubecular groove of the humerus
- Anterior wall – pectoralis major
- Posterior wall – subscapularis, teres major, latissimus dorsi
The axilla contains the following key neurovasculature:
- Axillary artery
- Axillary vein
- Axillary lymph nodes
- Brachial plexus
Knowing the contents useful as it allows easy location of lymph nodes (important when considering potential metastases from cancers or infections in the thoracic region).
Diagram - Illustration showing the contents of the axilla.
Public Domain Image [Public domain]
This triangular region is found on the anterior side of the elbow.
The borders are as follows:
- Lateral border – medial border of brachioradialis
- Medial border – lateral border of pronator teres
- Superior border – an imaginary line between the condyles of the humerus
The contents are as follows (moving lateral to medial):
- Radial nerve
- Biceps tendon
- Brachial artery
- Median nerve
A way to remember the order of these structures is 'Really Need Beer To Be At My Nicest'.
Knowledge of the placement of contents within the cubital fossa is incredibly important. For example, the brachial artery can be felt by palpating medial to the biceps tendon – useful when taking blood pressure or testing peripheral pulses. The roof of the cubital fossa contains the medial cubital vein – a common site for venepuncture.
Diagram - The highlighted triangle locates the region of the cubital fossa
Creative commons source by CFCF [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
This is a small tunnel/passage located on the anterior wrist. Tendons and the median nerve pass through it to access from the anterior forearm to the palm of the hand.
There are two borders forming the tunnel:
- Carpal arch – formed laterally by the scaphoid and trapezium; medially by the hamate and pisiform.
- Flexor retinaculum – forms the roof of the carpal tunnel. It is a thick connective tissue that connects the medial and lateral edges of the arch.
The contents of the tunnel are as follows:
- Four tendons of flexor digitorum profundus (deep)
- Four tendons of flexor digitorum superficialis (superficial)
- Tendon of flexor pollicis longus
- Median nerve
Understanding the carpal tunnel is critical when understanding carpal tunnel syndrome and damage caused by compression of the median nerve.
Diagram - Transverse section illustrating the carpel tunnel and its contents
Creative commons source by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]
This is a small depression located on the posterior aspect of the hand, just proximal to the base of the thumb.
Borders forming the anatomical snuffbox:
- Medial border – tendon of extensor pollicis longus
- Lateral border – tendons of abductor pollicis longus and extensor pollicis brevis
- Proximal border – styloid process of the radius
- Roof – skin
- Base – Scaphoid and trapezium
- Radial artery
- Radial nerve (superficial branch)
- Cephalic vein
Understanding the contents and boundaries of the anatomical snuffbox are important! For example, localised pain to this region could indicate a fracture of the scaphoid, an injury that must be diagnosed quickly to avoid avascular necrosis of the bone.
Diagram - The green triangle highlights the location of the radial fossa
Public Domain Image by Grant, John Charles Boileau [Public domain]
Guyun's canal, or the ulnar canal, is a passageway for the ulnar artery and nerve to pass into the hand. It sits on top of the hypothenar eminence (the muscles of the little finger in the palm), just distal to the hook of hamate.
Borders of Guyon's canal include:
- Roof - palmar carpal ligament
- Floor - flexor retinaculum and hypothenar muscles
- Medial border - pisiform bone
- Lateral border - hook of hamate bone
It is a key anatomical feature due to Guyon's Canal Syndrome, or 'Handlebar' Palsy, which is radiculopathy in the ulnar nerve caused by compression in Guyon's canal.
Reviewed by: Dr. Marcus Judge
Edited by: Dr. Maddie Swannack