Cubital Fossa - Boundaries, Contents, and Applied Aspects

Definition

Boundaries (2 Marks)

Contents - "MALT" mnemonic, lateral to medial (2 Marks)

1. Radial nerve - lies just deep to the brachioradialis muscle (under its lateral lip) and divides here into:
   • Superficial branch - continues deep to brachioradialis into the forearm
   • Deep branch - winds around the radius through the two heads of supinator to reach the posterior compartment
2. Biceps brachii tendon - central structure; passes to the radial tuberosity
3. Brachial artery - lies medial to the biceps tendon; normally bifurcates into radial and ulnar arteries at the apex of the fossa
4. Median nerve - lies immediately medial to the brachial artery; exits the fossa by passing between the ulnar and humeral heads of pronator teres

Memory aid: From lateral to medial - Radially Big Men (Radial nerve, Biceps tendon, brachial artery [B for Big], Median nerve)

• Median cubital vein - passes diagonally, connecting the cephalic vein (lateral) to the basilic vein (medial)
• Medial cutaneous nerve of the forearm (medially)
• Lateral cutaneous nerve of the forearm (laterally, terminal branch of musculocutaneous nerve)

Applied Aspects (1 Mark)

1. Venipuncture and IV cannulation: The median cubital vein in the roof of the cubital fossa is the most commonly used site for venous blood sampling and intravenous drug/fluid administration. The bicipital aponeurosis protects the underlying brachial artery and median nerve during venepuncture.
2. Blood pressure measurement: The brachial artery is auscultated in the cubital fossa when measuring blood pressure with a sphygmomanometer.
3. Brachial artery injury: A fracture of the lower end of the humerus (supracondylar fracture, especially in children) can injure the brachial artery inside the cubital fossa, leading to Volkmann's ischemic contracture due to compartment syndrome of the forearm.
4. Dialysis fistula: The brachial artery can be anastomosed to the cephalic vein at the elbow (within the cubital fossa region) to create an arteriovenous fistula for hemodialysis access.
5. Median nerve injury: Stab wounds or lacerations in the cubital fossa can damage the median nerve, causing weakness of pronation, wrist flexion, and loss of sensation over the lateral palm.

Q. Describe the boundaries and contents of the cubital fossa. Add a note on its applied anatomy. (5 Marks)

Cubital Fossa

Boundaries

• Superiorly (Base): An imaginary horizontal line drawn between the medial and lateral epicondyles of the humerus.
• Medially: The pronator teres muscle, arising from the medial epicondyle.
• Laterally: The brachioradialis muscle, arising from the lateral supraepicondylar ridge.
• Floor (Bed): Formed mainly by the brachialis muscle, with the supinator forming the lateral part of the floor.
• Roof: Formed by the deep fascia of the forearm, reinforced by the bicipital aponeurosis (lacertus fibrosus), covered externally by superficial fascia and skin.

Contents

1. Radial nerve - Lies just deep to the brachioradialis muscle, at the lateral margin of the fossa. Here, it divides into:
   • Superficial branch - Continues into the forearm deep to brachioradialis.
   • Deep branch - Winds around the neck of the radius through the two heads of supinator to reach the posterior compartment of the forearm.
2. Tendon of biceps brachii - The most central and easily palpable structure; passes to insert on the radial tuberosity.
3. Brachial artery - Lies medial to the biceps tendon. It bifurcates into the radial and ulnar arteries at the apex of the fossa. It is covered and protected by the bicipital aponeurosis anteriorly.
4. Median nerve - Lies immediately medial to the brachial artery. It exits the fossa by passing between the humeral and ulnar heads of pronator teres.

• Median cubital vein - The most important superficial structure; crosses the roof diagonally, connecting the cephalic vein (lateral) to the basilic vein (medial).
• Lateral cutaneous nerve of the forearm (lateral side of roof).
• Medial cutaneous nerve of the forearm (medial side of roof).

Note: The ulnar nerve does NOT pass through the cubital fossa. It passes posterior to the medial epicondyle.

Applied Anatomy

1. Venipuncture: The median cubital vein in the roof of the cubital fossa is the most commonly used site for drawing blood and intravenous cannulation. The bicipital aponeurosis protects the underlying brachial artery and median nerve during this procedure.
2. Blood pressure measurement: The brachial artery is palpated and auscultated in the cubital fossa when recording blood pressure with a sphygmomanometer.
3. Supracondylar fracture: A fracture of the lower end of the humerus (common in children) can injure the brachial artery, causing ischemia of the forearm muscles and leading to Volkmann's ischemic contracture.
4. Arteriovenous fistula for dialysis: The brachial artery can be surgically anastomosed to the cephalic vein at the elbow region to create an AV fistula for long-term hemodialysis access.
5. Median nerve injury: Penetrating wounds to the cubital fossa can damage the median nerve, resulting in weakness of pronation, loss of wrist flexion, and sensory loss over the lateral palm and digits.

• The triangular outline of the fossa with the base between the two epicondyles
• Pronator teres (medial border) and Brachioradialis (lateral border)
• Brachialis forming the floor
• Bicipital aponeurosis as the roof
• Contents in order - Radial nerve, Biceps tendon, Brachial artery, Median nerve (lateral to medial)
• Brachial artery bifurcating into radial and ulnar arteries at the apex
• Median cubital vein superficially in the roof

• Carpal Tunnel is covered in Chapter 10 (The Hand)
• It typically falls around pages 130-135 (varies slightly by edition - 8th edition has it near pg. 132)

• Flexor retinaculum (boundaries of the tunnel)
• Contents (9 tendons + median nerve)
• Carpal tunnel syndrome