Major Nerves of Upper Limb

• The upper limb is supplied by five major peripheral nerves, all of which arise from the brachial plexus.
• These nerves provide motor innervation to the muscles and sensory innervation to the skin and joints of the upper limb.
• The five major nerves of the upper limb are:
  • Axillary nerve
  • Musculocutaneous nerve
  • Radial nerve
  • Median nerve
  • Ulnar nerve

Axillary Nerve

• The axillary nerve is one of the terminal branches of the posterior cord of the brachial plexus.
• It is also known as the circumflex nerve because it winds around the surgical neck of the humerus.
• The root value of the axillary nerve is C5 and C6..

Beginning

The axillary nerve arises from the posterior cord of the brachial plexus.

Course and relations

In the Axilla

• The axillary nerve originates from the posterior cord of the brachial plexus.
• It passes posterolateral to the third part of the axillary artery.
• It lies on the anterior surface of the subscapularis muscle.

In the Quadrangular Space

• The axillary nerve leaves the axilla by passing through the quadrangular space.
• It is accompanied by the posterior circumflex humeral artery and vein.

Relations of the Quadrangular Space

• Superior: Subscapularis muscle and the capsule of the shoulder joint
• Inferior: Teres major muscle
• Lateral: Surgical neck of the humerus
• Medial: Long head of the triceps brachii muscle

Termination

• In quadrangular space, axillary nerve divides into anterior and posterior branches Within the quadrangular space, the axillary nerve divides into:
  • Anterior branch
  • Posterior branch

Branches

Articular Branch

• The axillary nerve gives an articular branch to the shoulder joint.

Anterior Branch

• The anterior branch accompanies the posterior circumflex humeral vessels.
• It winds around the surgical neck of the humerus deep to the deltoid muscle.
• It supplies:
  • Deltoid muscle
  • Skin over the anteroinferior part of the deltoid region

Posterior Branch

• The posterior branch winds around the posterior border of the deltoid muscle.
• It supplies:
  • Teres minor muscle
  • Posterior part of the deltoid muscle
• The nerve to the teres minor contains a pseudoganglion, which has no functional significance.
• The posterior branch continues as the upper lateral cutaneous nerve of the arm.
• The upper lateral cutaneous nerve supplies the skin over the lower half of the deltoid region.

Musculocutaneous Nerve

• The musculocutaneous nerve is the main motor nerve of the anterior compartment of the arm.
• It supplies all the muscles in the front of the arm.

Beginning

• The musculocutaneous nerve arises from the lateral cord of the brachial plexus.

• The root value of the musculocutaneous nerve is C5–C7.
• It contains fibers from the ventral primary rami of the fifth, sixth, and seventh cervical spinal nerves.

Termination

• The musculocutaneous nerve terminates by continuing as the lateral cutaneous nerve of the forearm, approximately 2 cm above the elbow.

Course

• The musculocutaneous nerve arises from the lateral cord of the brachial plexus in the lower part of the axilla.
• It pierces the coracobrachialis muscle, which is an important identifying feature.
• It then descends downward and laterally between the biceps brachii and brachialis muscles.
• About 2 cm above the elbow, it emerges lateral to the tendon of the biceps brachii, pierces the deep fascia, and continues as the lateral cutaneous nerve of the forearm.

Relations

In the Lower Part of the Axilla

• Anterior: Pectoralis major muscle
• Posterior: Subscapularis muscle
• Medial: Axillary artery
• Lateral: Coracobrachialis muscle

In the Upper Part of the Arm

• The musculocutaneous nerve lies within the substance of the coracobrachialis muscle after piercing it.

In the Middle Part of the Arm

• The nerve lies between the biceps brachii and brachialis muscles.
• It pierces the deep fascia approximately 2 cm above the elbow joint.

Branches and distribution

Muscular Branches

• The musculocutaneous nerve supplies the following muscles:
  • Coracobrachialis
  • Biceps brachii
  • Brachialis (mainly its large medial part)

Cutaneous Branch

• The terminal lateral cutaneous nerve of the forearm supplies the skin over the lateral aspect of the forearm.

Articular Branches

• The musculocutaneous nerve gives articular branches to:
  • Shoulder joint
  • Elbow joint

Radial Nerve

• The radial nerve, also known as the musculospiral nerve, is the main nerve of the posterior compartment of the arm and forearm.
• It also provides sensory innervation to the dorsum of the hand.
• The radial nerve is the continuation of the posterior cord of the brachial plexus.
• It is the largest terminal branch of the brachial plexus.
• The radial nerve has a root value of C5–T1.
• It contains fibers from the ventral primary rami of C5, C6, C7, C8, and T1 spinal nerves.

Beginning

• The radial nerve arises as the continuation of the posterior cord of the brachial plexus.
• It originates behind the third part of the axillary artery in the lower part of the axilla.

Course and relations

In the Axilla

• The radial nerve passes posterior to the axillary artery.
• It continues for a short distance behind the upper part of the brachial artery.

In the Arm

• The radial nerve enters the posterior compartment of the arm through the lower triangular space (triangular interval) together with the profunda brachii artery.
• It descends downward and laterally within the radial groove of the humerus.
• It pierces the lateral intermuscular septum to enter the anterior compartment of the arm.
• In the anterior compartment, it lies deep to the brachioradialis and extensor carpi radialis longus muscles.

In the Forearm

• Just below the lateral epicondyle of the humerus, the radial nerve divides into:
  • Superficial branch
  • Deep branch (posterior interosseous nerve)

Branches

Branches in the Axilla

• Muscular branches to:
  • Long head of triceps brachii
  • Medial head of triceps brachii
• Posterior cutaneous nerve of the arm, which supplies the skin over the posterior aspect of the arm.

Branches in the Radial Groove

• Muscular branches to:
  • Lateral head of triceps brachii
  • Medial head of triceps brachii
    • The branch to the medial head is also called the ulnar collateral nerve because it lies close to the ulnar nerve.
  • Anconeus muscle (through the branch to the medial head of the triceps)
• Cutaneous branches:
  • Lower lateral cutaneous nerve of the arm
  • Posterior cutaneous nerve of the forearm

Branches in the Lower Part of the Arm

• Muscular branches to:
  • Brachialis (lateral part)
  • Brachioradialis
  • Extensor carpi radialis longus
• Articular branch to the elbow joint

Terminal Branches

Superficial Branch

• The superficial branch is purely sensory.
• It supplies:
  • The lateral half of the dorsum of the hand
  • The dorsal surface of the lateral 3½ digits (except the distal phalanges)

Deep Branch (Posterior Interosseous Nerve)

• The deep branch pierces the supinator muscle.
• It continues as the posterior interosseous nerve.
• It supplies all the remaining muscles of the posterior compartment of the forearm.

Posterior Interosseous Nerve

• The posterior interosseous nerve is the continuation of the deep branch of the radial nerve.
• It is the principal motor nerve of the posterior compartment of the forearm.

Beginning

• The posterior interosseous nerve begins as the deep branch of the radial nerve in the cubital fossa.
• It arises deep to the brachioradialis muscle.

Course and Relations

• The nerve leaves the cubital fossa by entering the substance of the supinator muscle.
• It passes through the supinator to enter the posterior compartment of the forearm.
• In the posterior compartment, it descends deep to the superficial extensor muscles.
• It reaches the dorsum of the wrist by passing deep to the extensor retinaculum through the fourth extensor compartment.

Termination

• Near the wrist, the posterior interosseous nerve exhibits a pseudoganglion.
• It terminates by supplying the:
  • Wrist joint
  • Intercarpal joints

Branches

Muscular Branches

Before Piercing the Supinator

• Extensor carpi radialis brevis
• Supinator

Within the Supinator

• Supinator

After Emerging from the Supinator

• Extensor digitorum
• Extensor digiti minimi
• Extensor carpi ulnaris
• Abductor pollicis longus
• Extensor pollicis longus
• Extensor pollicis brevis
• Extensor indicis

Articular Branches

• The posterior interosseous nerve supplies the:
  • Wrist joint
  • Distal radioulnar joint
  • Intercarpal joints
  • Intermetacarpal joints

Median Nerve

• The median nerve, also known as the laborer’s nerve, is the main nerve of the forearm.
• It is called the laborer’s nerve because it supplies most of the muscles responsible for the powerful and precise movements of the forearm and thumb.
• The median nerve is formed by the union of the lateral root (from the lateral cord) and the medial root (from the medial cord) of the brachial plexus in the lower part of the axilla.
• The median nerve, also known as the laborer’s nerve, is the main nerve of the forearm.
• It is called the laborer’s nerve because it supplies most of the muscles responsible for the powerful and precise movements of the forearm and thumb.
• The median nerve is formed by the union of the lateral root (from the lateral cord) and the medial root (from the medial cord) of the brachial plexus in the lower part of the axilla.

Course and main relations

In the Axilla

• The median nerve is formed anterior to the third part of the axillary artery.
• It descends lateral to the artery and crosses anterior to the brachial artery from lateral to medial.

In the Arm

• The median nerve descends alongside the brachial artery without giving any major muscular branches.
• In the lower part of the arm, it lies medial to the brachial artery.

In the Cubital Fossa

• The median nerve lies medial to the brachial artery.
• It enters the forearm by passing between the humeral and ulnar heads of the pronator teres muscle.

In the Forearm

• The median nerve passes between the two heads of the pronator teres.
• At this level, it is separated from the ulnar artery by the deep head of the pronator teres.
• It then passes deep to the fibrous arch of the flexor digitorum superficialis.
• Approximately 5 cm proximal to the flexor retinaculum, the nerve becomes superficial and lies lateral to the tendons of the flexor digitorum superficialis.

At the Wrist

• The median nerve enters the palm by passing deep to the flexor retinaculum through the carpal tunnel.

In the Palm

• In the palm, the median nerve lies medial to the thenar muscles.
• It divides into medial and lateral terminal branches, which supply the thenar muscles, the first two lumbricals, and the lateral digits.

Branches

In the Axilla

• The median nerve gives no branches in the axilla.

In the Arm

• The median nerve normally gives no muscular branches in the arm.

In the Cubital Fossa

Muscular Branches

• Pronator teres
• Flexor carpi radialis
• Palmaris longus
• Flexor digitorum superficialis

In the Forearm

Anterior Interosseous Nerve

• The anterior interosseous nerve is the largest branch of the median nerve in the forearm.
• It supplies:
  • Flexor pollicis longus
  • Lateral (radial) half of the flexor digitorum profundus
  • Pronator quadratus
• It also provides articular branches to the:
  • Distal radioulnar joint
  • Wrist joint

Palmar Cutaneous Branch

• The palmar cutaneous branch arises proximal to the flexor retinaculum.
• It passes superficial to the flexor retinaculum.
• It supplies the skin over the thenar eminence and the lateral part of the palm.

Terminal Branches in the Palm

• The median nerve divides into medial and lateral branches.

Medial Branch

• The medial branch gives two common palmar digital nerves.

Lateral Common Digital Nerve

• Supplies the adjacent sides of the index and middle fingers.
• Supplies the second lumbrical muscle.

Medial Common Digital Nerve

• Supplies the adjacent sides of the middle and ring fingers.

Lateral Branch

Muscular Branch: Supplies the thenar muscles:

• Abductor pollicis brevis
• Opponens pollicis
• Superficial head of flexor pollicis brevis

Proper Digital Branches

• Gives three proper palmar digital nerves to:
  • Lateral side of the thumb
  • Medial side of the thumb
  • Lateral side of the index finger
• The branch to the lateral side of the index finger also supplies the first lumbrical muscle.

Carpal Tunnel Syndrome

• Carpal tunnel syndrome is the most common entrapment neuropathy of the median nerve.
• The carpal tunnel is an osseofibrous canal formed by the carpal bones posteriorly and the flexor retinaculum anteriorly.
• The carpal tunnel transmits:
  • The median nerve
  • The flexor tendons of the forearm
• Compression of the median nerve within the carpal tunnel produces carpal tunnel syndrome.

Clinical Features

Motor Deficits

• Paralysis of the thenar muscles results in an ape-like thumb deformity.
• The thumb becomes extended and adducted due to the inability to abduct, oppose, and flex the thumb effectively.
• Paralysis of the first and second lumbricals causes difficulty flexing the metacarpophalangeal joints of the index and middle fingers, producing a lag of these fingers while making a fist.

Sensory Deficits

• There is loss of sensation over the lateral 3½ digits, including their palmar surfaces, nail beds, and dorsal distal phalanges.
• Patients commonly complain of pain, tingling, numbness, and paresthesia in the thumb, index finger, middle finger, and lateral half of the ring finger.

Autonomic Changes

• Compression of sympathetic fibers may produce vasomotor disturbances.
• The skin over the lateral 3½ digits may become dry because of reduced sweating.

Clinical Tests

Phalen’s Maneuver

• The patient is asked to maintain maximum wrist flexion for about 60 seconds.
• The test is positive if it reproduces pain, tingling, or numbness in the lateral 3½ digits.
• Wrist flexion increases pressure within the carpal tunnel, compressing the median nerve.

Durkan’s Test (Carpal Compression Test)

• Direct pressure is applied over the carpal tunnel for approximately 30 seconds.
• The test is positive if it reproduces pain or paresthesia in the distribution of the median nerve.

Causes

• The cause is idiopathic (unknown) in most patients.
• Other common causes include:
  • Repetitive occupational activities
  • Obesity
  • Pregnancy
  • Rheumatoid arthritis
  • Hypothyroidism
  • Inflammatory disorders

Treatment

• Physiotherapy and activity modification.
• Wrist splinting, particularly in a neutral position, to reduce pressure within the carpal tunnel.
• Surgical decompression by division of the flexor retinaculum in patients with persistent or severe symptoms.

Ulnar Nerve

• The ulnar nerve is a terminal branch of the medial cord of the brachial plexus.
• It has a root value of C7, C8, and T1.
• The ulnar nerve is commonly known as the “musician’s nerve” because it supplies most of the intrinsic muscles of the hand responsible for the fine movements of the fingers.

Course and Main Relations

In the Axilla

• The ulnar nerve arises in the lower part of the axilla.
• It descends between the axillary artery and the axillary vein.

In the Arm

• The ulnar nerve runs along the medial side of the brachial artery as far as the insertion of the coracobrachialis muscle.
• It pierces the medial intermuscular septum together with the superior ulnar collateral artery to enter the posterior compartment of the arm.
• It descends behind the medial epicondyle of the humerus, where it lies superficially and is vulnerable to injury.

In the Forearm

• The ulnar nerve enters the forearm by passing through the cubital tunnel, a gap between the humeral and ulnar heads of the flexor carpi ulnaris.
• It then descends vertically along the forearm.
• At the wrist, it passes superficial to the flexor retinaculum, lateral to the pisiform bone, and medial to the ulnar artery.

In the Palm

• At the distal border of the flexor retinaculum, the ulnar nerve divides into:
  • Superficial branch
  • Deep branch

Branches and Distribution

In the Axilla and Arm

• The ulnar nerve gives no branches in the axilla or arm.

In the Forearm

Muscular Branches

• Flexor carpi ulnaris
• Medial (ulnar) half of the flexor digitorum profundus

Articular Branch

• Elbow joint

Palmar Cutaneous Branch

• The palmar cutaneous branch arises just proximal to the wrist.
• It passes superficial to the flexor retinaculum.
• It supplies the skin over the hypothenar eminence.

Dorsal Cutaneous Branch

• The dorsal cutaneous branch arises approximately 7.5 cm proximal to the wrist beneath the flexor carpi ulnaris.
• It winds around the ulna to reach the dorsum of the hand.
• It supplies:
  • The proximal dorsal surface of the medial 2½ digits
  • The adjacent medial part of the dorsum of the hand

In the Palm

Superficial Branch

Muscular branch for palmaris brevis

Cutaneous Branches: The superficial branch gives two palmar digital nerves.

1. Medial Palmar Digital Nerve: Supplies the medial side of the little finger.
2. Lateral Palmar Digital Nerve: Divides into two branches supplying the adjacent sides of the ring and little fingers.

Deep Branch

Muscular Branches: The deep branch supplies:

• Hypothenar muscles
  • Abductor digiti minimi
  • Flexor digiti minimi brevis
  • Opponens digiti minimi
• Four palmar interossei
• Four dorsal interossei
• Third and fourth lumbricals
• Adductor pollicis

Articular Branches

• Intercarpal joints
• Carpometacarpal joints
• Intermetacarpal joints

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