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Core
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 - cervico-axillary canal (the passage between the root of the neck and the axilla), bounded by the lateral border of the first rib, the clavicle, and the superior border of the scapula
- Lateral wall - intertubercular groove of the humerus (the groove at the upper end of the humerus that holds a tendon of the biceps)
- Anterior wall - pectoralis major (the large chest muscle) and pectoralis minor (a smaller chest muscle beneath it)
- Posterior wall - subscapularis, teres major and latissimus dorsi (three muscles that join the scapula or the back to the humerus)
- Medial wall - thoracic wall (the ribs and the muscles between them) and serratus anterior (the muscle on the side of the ribcage)
The axilla contains the following key nerves, blood vessels and lymph nodes:
- Axillary artery
- Axillary vein
- Axillary lymph nodes
- Brachial plexus
Knowing the contents helps locate the axillary lymph nodes. These nodes may contain metastases (spread of cancer) from malignant tumours, including breast cancer, or enlarge reactively (swell as a normal response) to infection. Infection-related node enlargement is not metastasis.
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 (a forearm muscle on the thumb side)
- Medial border - lateral border of pronator teres (a forearm muscle that turns the palm downwards)
- Superior border - an imaginary line between the two epicondyles of the humerus (the bony bumps on either side of its lower end)
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 clinically important. For example, the brachial artery can be felt by palpating medial to the biceps tendon. This is useful when taking blood pressure or testing peripheral pulses. The superficial fascia (the layer of connective tissue under the skin) of the roof contains the median cubital vein, a common site for venepuncture (taking blood or placing a cannula). The vein lies superficial to the bicipital aponeurosis (a flat sheet of tendon that spreads from the biceps tendon across the fossa) and is separate from the deep contents of the fossa.
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 travel through it from the anterior forearm into the palm of the hand.
There are two borders forming the tunnel:
- Carpal arch - a curved groove formed by the carpal bones (the small bones of the wrist). Laterally it is formed by the tubercles (small bony bumps) of the scaphoid and trapezium, two bones on the thumb side of the wrist. Medially it is formed by the hook of the hamate and the pisiform, two bones on the little-finger side.
- 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 (the deep finger-bending muscle)
- Four tendons of flexor digitorum superficialis (the superficial finger-bending muscle)
- Tendon of flexor pollicis longus (the muscle that bends the thumb)
- Median nerve
Compression of the median nerve in the tunnel can cause carpal tunnel syndrome (numbness, tingling and pain in the hand), so knowing the anatomy of the tunnel helps explain the condition.
Diagram - Transverse section illustrating the carpal 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 (a muscle that straightens the thumb)
- Lateral border - tendons of abductor pollicis longus and extensor pollicis brevis (two thumb muscles that move the thumb away from the palm and straighten it)
- Proximal border - styloid process of the radius (the bony point at the wrist end of the radius)
- Roof - skin
- Base - scaphoid and trapezium (two carpal bones on the thumb side of the wrist)
Contents include:
- Radial artery
- Radial nerve (superficial branch)
- Cephalic vein (a superficial vein that runs up the arm from the thumb side of the hand)
Knowing the contents and boundaries of the anatomical snuffbox is important. For example, localised pain to this region could indicate a fracture of the scaphoid. Scaphoid fractures can be missed at first on examination and X-ray, and the bone is at particular risk of avascular necrosis (death of bone because its blood supply is lost), so the injury must be diagnosed quickly.
Diagram - The green triangle highlights the location of the anatomical snuffbox (also known as the radial fossa)
Public Domain Image by Grant, John Charles Boileau [Public domain]
Guyon's canal, or the ulnar canal, carries the ulnar nerve and artery into the hand. It occupies the proximal hypothenar region (the fleshy pad on the little-finger side of the palm). The canal extends from the proximal border of the pisiform (a small wrist bone on the little-finger side) to the hook of the hamate (a hook-shaped bump on another wrist bone), where the hypothenar muscles begin. The hook of the hamate marks the lateral side of the canal.
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
The canal matters clinically because of Guyon's canal syndrome, also called 'Handlebar' palsy. This is an ulnar neuropathy (damage to the ulnar nerve) at the wrist, caused by compression of the nerve in the canal.
For Pathologies and Conditions of the Upper Limb, check out our four articles on the conditions of the Shoulder and Clavicle, Arm, Elbow, and Forearm and Wrist.
Reviewed by: Dr. Marcus Judge
Edited by: Dr. Maddie Swannack
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