Neurovasculature of the upper limbs

The arteries of the upper limb arise from the subclavian artery, a branch of the aortic arch. At the outer border of the 1^st rib, the subclavian artery continues as the axillary artery, which is the main artery of the axillary fossa. At the inferior border of the teres major, the axillary artery continues as the brachial artery, the main artery of the arm. The brachial artery divides at the cubital fossa into the radial and ulnar arteries, the main arteries of the forearm and hand. The venous system of the upper limbs can be divided into a superficial and deep venous system. The cephalic vein, basilic vein, and medial antebrachial vein comprise the superficial venous system, which drains into the deep venous system. The deep veins accompany the arteries of the upper limbs and drain into the axillary vein; this continues as the subclavian vein and drains into the superior vena cava. The upper limb is innervated by nerves of the brachial plexus, a somatic neural network formed by the anterior branches of the spinal nerves C5–T1. The musculocutaneous, axillary, radial, ulnar, and median nerves are the most important sensorimotor nerves of the upper limb.

The upper limb is supplied by the axillary artery, which receives blood from the thoracic aorta via the subclavian artery and its branches.

Axillary artery ^[1][2]

• Origin: continuation of the subclavian artery at the outer border of the 1^strib
• Course
  • Continues as the brachial artery at the outer border of the teres major
  • Divided into 3 parts by the overlying pectoralis minor muscle
    • 1^st part: proximal to the pectoralis minor
    • 2^nd part: inferior to the pectoralis minor
    • 3^rd part: distal to the pectoralis minor
• Anatomical relations: In the axilla, it lies lateral to the axillary vein and is bordered inferiorly by the brachial plexus cords.
• Area of supply: lateral thoracic wall, upper limb, and axilla

Branches of the axillary artery

Scapular anastomosis ^[2]

• Definition: an anastomosis between the branches of the first part of the subclavian artery and the third part of the axillary artery that provides collateral circulation to the arm in case of occlusion or injury to the axillary or subclavian arteries

Brachial artery ^[1][2]

• Origin: continuation of the axillary artery at the inferior border of the teres major
• Course
  • Passes from the medial aspect of the humerus to the anterior aspect of the arm
  • Terminates at/just below the cubital fossa by bifurcating into the radial and ulnar arteries
• Anatomical relations
  • Close location to the humerus allows blood pressure and pulse measurement.
  • The median nerve lies laterally and the ulnar nerve lies medially at the teres major border.
• Area of supply: coracobrachialis, biceps, and triceps brachialis muscles along with the elbow joint and overlying skin

The brachial artery can be compressed proximally against the medial humerus to stop bleeding in the distal arm.

The deep artery of the arm ensures collateral circulation through the elbow anastomosis in case of proximal brachial artery injury. Disruption of the brachial artery distal to the origin of the deep artery of the arm is associated with a greater degree of ischemia of the upper limb.

Radial artery

• Origin: terminal branch of the brachial artery
• Course
  • Begins at/just below the cubital fossa
  • Passes deep to the brachioradialis
  • Descends along the ventrolateral aspect of the forearm, dorsally at the wrist
  • Pierces the first dorsal interosseous muscle to enter the palm
  • Anastomoses with branches of the ulnar artery to form the carpal arches
• Anatomical relations
  • Running laterally at the forearm and its location at the wrist allows for pulse and heart rate measurement.
  • The radial artery courses dorsally at the wrist and passes through the anatomical snuffbox.
• Area of supply: supplies the elbow, wrist, hand, and the posterolateral aspect of the forearm

The Allen test evaluates patency of the collateral circulation to the hand through the radial and ulnar arteries.

Ulnar artery

• Origin: terminal branch of the brachial artery
• Course
  • Begins at/just below the cubital fossa
  • Descends along the ulnar (medial) aspect of the forearm
  • Passes superficial to the flexor retinaculum at the wrist
  • Courses through the Guyon canal to enter the hand
  • Anastomoses with branches of the radial artery form the carpal arches
• Anatomical relations
  • Separated by the pronator teres muscle from the median nerve
  • At the Guyon canal, it passes along with the ulnar nerve
• Area of supply: supplies the medial forearm, wrist and hand

Anastomosis within the hand

• Dorsal carpal arch: formed by an anastomosis between the dorsal carpal branch of the radial artery and the dorsal carpal branch of the ulnar artery
• Palmar carpal arch: an anastomosis between the palmar carpal branch of the radial artery and the palmar carpal branch of the ulnar artery
• Superficial palmar arch: formed by the distal ulnar artery and the superficial palmar branch of the radial artery
• Deep palmar arch: formed by the distal radial artery and the deep palmar branch of the ulnar artery

Overview ^[1]

• The upper limbs have a superficial and deep venous system that eventually drains into the superior vena cava.
• The superficial veins lie within the subcutaneous tissues and drain into the deep venous system.
• The deep veins lie deep to the fascia, accompanying the arteries of the upper limb as venae comitantes.
• Venous valves ensure the unidirectional flow of blood toward the heart.

Overview

The nerves of the upper limb are derived from the brachial plexus.

• Course and composition of the brachial plexus
  • Five roots, which are the anterior branches of C5–T1 spinal nerves that merge within the posterior triangle of the neck to form the trunks.
  • Three trunks (upper, middle, lower) pass through the scalene triangle, between the anterior and middle scalene muscles
  • Six divisions
    • Formed beneath the clavicle as each trunk splits into an anterior and posterior division
    • The divisions then pass into the axillary fossa.
  • Three cords (lateral, posterior, and medial)
    • Formed by the merging of the divisions within the axillary fossa
    • The cords lie posterior to the axillary artery.
  • Terminal branches arise from the cords and innervate the upper limb, back, and superior thoracic wall.
• Functional significance
  • Motor innervation: all upper limb and shoulder muscles except for the trapezius, which is supplied by the spinal accessory nerve
  • Sensory innervation: the axilla and the upper limb except for the medial portion of the arm, which is supplied by the intercostobrachial nerve

Brachial plexus

• Definition: a somatic neural network derived from C5–T1 spinal nerves, from which the peripheral nerves of the upper limb arise
• Composition: The brachial plexus is composed of roots, trunks, divisions, cords, and branches (proximal to distal).

“Rugby Teams Drink Cool Beer!”: Roots, Trunks, Divisions, Cords, Branches (order of the brachial plexus divisions)

Roots

• Anterior (ventral) divisions of C5–T1
• The roots merge in the posterior triangle of the neck to form the trunks.
• The dorsal scapular nerve and long thoracic nerve arise from the roots of the brachial plexus.

Trunks

• The roots form three trunks that are located in the neck:
  • Upper trunk of the brachial plexus (C5 and C6): The suprascapular and subclavian nerve originate here.
  • Middle trunk of the brachial plexus (C7)
  • Lower trunk of the brachial plexus (C8 and T1)
• The trunks course through the scalene triangle (together with the subclavian artery) and the base of the posterior triangle of the neck to enter the axillary fossa.

Divisions

• Each trunk divides into an anterior and posterior division that enters the axillary fossa.
• All three posterior divisions innervate the extensor compartment of the arm and forearm (i.e., the posterior compartment).
• All three anterior divisions innervate the flexor compartment of the arm and forearm (i.e., the anterior compartment).

Cords

• The cords and proximal portions of their branches lie in the axillary fossa.
• There are three cords, which are named according to their position in relation to the axillary artery:
  • Lateral cord of the brachial plexus: formed by the anterior divisions of upper and middle trunks
  • Medial cord of the brachial plexus: formed by the anterior division of the lower trunks
  • Posterior cord of the brachial plexus: formed by the posterior divisions of all three trunks

Branches ^[2]

Branches are the peripheral nerves that arise from each of the cords of the brachial plexus. The five most clinically significant branches of the brachial plexus are the musculocutaneous, axillary, median, radial, and ulnar nerves.

Lateral cord of the brachial plexus

Medial cord of the brachial plexus

Branches from the medial and lateral cords form the median nerve.

Posterior cord of the brachial plexus

Disorders

• Upper brachial plexus palsy (Erb palsy)
• Lower brachial plexus palsy (Klumpke palsy)
• Peripheral nerve injuries
• Suprascapular nerve injury
• Dorsal scapular nerve injury (lateral winging of the scapula)
• Long thoracic nerve injury (medial winging of the scapula)
• Musculocutaneous nerve injury
• Median nerve palsy
• Carpal tunnel syndrome
• Pronator teres syndrome
• Anterior interosseous nerve syndrome
• Ulnar nerve palsy
• Cubital tunnel syndrome
• Guyon canal syndrome
• Thoracodorsal nerve injury
• Axillary nerve injury
• Radial nerve palsy
• Radial tunnel syndrome
• Deep vein thrombosis
• Thoracic outlet syndrome
• Thrombophlebitis
• Axillary artery injury
• Axillary artery thrombosis
• Axillary artery aneurysm

Procedures

• Site for intravenous access or cannulation, especially the median cubital and cephalic veins
• Brachial arterial pressure: site for measuring blood pressure
• Pectoral nerve block
• Brachial plexus block