Median Nerve

Original Editor - Wendy Walker and Daniele Barilla

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Anatomy

Figure.1 Median Nerve Course and Supply

The Median Nerve begins in the axillary region with the root of median nerves situated in the anterior rami of C5-T1. Median and lateral cords of the brachial plexus are merged and extended as the median nerve. Uniting either in front of or lateral to that vessel. Its fibers are derived from the sixth, seventh, and eighth cervical and first thoracic nerves. As it descends through the arm, it lies at first lateral to the brachial artery; about the level of the insertion of the Coracobrachialis it crosses the artery, usually in front of, but occasionally behind it, and lies on its medial side at the bend of the elbow, where it is situated behind the lacertus fibrosus (bicipital fascia) and is separated from the elbow-joint by the brachialis.

In the forearm, it passes between the two heads of the pronator teres and crosses the ulnar artery, but is separated from this vessel by the deep head of the pronator teres. It descends beneath the flexor digitorum sublimis, lying on the flexor digitorum profundus, to within 5 cm. of the transverse carpal ligament; here it becomes more superficial and is situated between the tendons of the flexor digitorum sublimis and flexor carpi radialis. In this situation, it lies behind, and rather to the radial side of the tendon of the palmaris longus, and is covered by the skin and fascia. It then passes behind the transverse carpal ligament into the palm of the hand. In its course through the forearm, it is accompanied by the median artery, a branch of the volar interosseous artery. 

Figure.2 Median Nerve

Nerve Roots

C5-C6-C7-C8-T1

• C5 to C7 Roots from Lateral Cord of Brachial Plexus
• C8 and T1 Roots from Medial Cord of Brachial Plexus

Nerve Branches

With the exception of the nerve to the pronator teres, which sometimes arises above the elbow-joint, the median nerve gives off no branches in the arm. There are a few vascular branches of the median nerve that supply to the brachial artery, and articular branches of the median nerve innervate the elbow joint as it passes in front of the elbow.

Table.1 Branches of Median Nerve in Forearm

Branches in Forearm	Muscle Supplied by
Muscular Branch	All the superficial muscles on the front of the forearm except the Flexor Carpi Ulnaris Pronator Teres Palmaris Longus Flexor Digitorum Superficialis Flexor Carpi Radialis
Anterior Interosseus Nerve (AIN)	Anterior Interosseus Nerve supplies Flexor Pollicis Longus Radial part of Flexor Digitorum Profundus This branch runs on interosseous membrane with the anterior interosseous artery supplying; Pronator Quadratus It terminates by giving articular branches to the distal radioulnar, radiocarpal and carpal joints.

Table.2 Branches of Median Nerve in Hand

Branches in Hand	Muscle Supplied by
Cutaneous Nerve	Cutaneous nerve supplies the proximal aspect of the palm. This branch does not enter the carpal tunnel and is hence spared in carpal tunnel syndrome.
Palmar Digital Nerves	The two common Palmar Digital nerves First of which supplies the radial two lumbricals. The second runs between the ring and middle finger, and divides into digital nerves that provide sensation to certain areas of the hand.
Recurrent Branch (‘Million Dollar Nerve’ )	Recurrent Branch supplies the muscles of the Thenar Eminence Flexor Pollicis Brevis Abductor Pollicis Brevis Opponens Pollicis

Nerve Function

Motor function of the median nerve are mainly flexor aspect of forearm, hand, and thumb, with motor function outlined in the above table. Sensory innervation to the dorsal aspect of the distal first two digits of the hand is supplied by median nerve.

Sensory Function

• The skin of the palmar and dorsal aspect of lateral three to three and half palm
• The skin of palmar and dorsal aspect of thumb
• The skin of adjacent sides of respective digits.
• The skin of center of the palm

Figure.3 Median Nerve Sensory Innervation

Clinical Relevance

The Median Nerve can be compressed at many points along its course to the wrist. Depending on the site of injury and the symptoms, the syndrome is known by various names. There are three entrapment syndromes involving the medial nerve or its branches with the most well-known and frequent form of Median Nerve Entrapment known as Carpal Tunnel Syndrome (CTS).

Carpal Tunnel Syndrome

Carpal Tunnel Syndrome is a common condition that causes a tingling sensation, numbness and sometimes pain in the hand and fingers. These sensations usually develop gradually and start off being worse during the night. They tend to affect the thumb, index finger, and middle finger. Other symptoms of carpal tunnel syndrome include:

• Pins and Needles (Paraesthesia)
• Thumb Weakness
• Dull ache in the hand or arm

Anterior Interosseous Syndrome

Anterior Interosseous Syndrome is a pure motor neuropathy, as the anterior interosseous nerve contains no sensory fibers; dull forearm pain is however sometimes mentioned by patients.

Typically, patients fail to make an “O K Sign", as flexion of the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger, are impaired.

Another sensitive test is the Pinch Test: a patient with anterior interosseous syndrome will also not be able to pinch a sheet of paper between the thumb and index finger, instead of clamping the sheet between theextended thumb and index fingers, akin to a tong rather than a clamp. The weakness of pronator quadratus manifests itself in pronation weakness with a flexed elbow.

Anterior interosseous syndrome can be confounded by the Martin-Gruber Anastomosis, present in up to 25% of the population: in these cases, the anterior interosseous nerve gives off branches to the ulnar nerve, creating atypical motor innervation patterns of the forearm and hand and thus effacing the typical clinical symptoms.

Pronator Teres Syndrome

Pronator Teres Syndrome is a result of the to the position of this muscle that sits over your median nerve, the pressure on the nerve can elicit pain while hindering your forearm movement. It occurs when your pronator teres muscle becomes tight or overworked, compressing the median nerve. Hammering, repeatedly using a screwdriver, cleaning fish can lead to overuse of the pronator teres. Symptoms include pain and reduced mobility. Carpal Tunnel Syndrome symptoms are often confused with pronator teres syndrome, however in this case symptoms worsen with elbow movements. Pronator Teres Syndrome test can be used for assessment of the syndrome.

Pathology and Mechanism of Injury

Figure.4 Carpal Tunnel Anatomy

Carpal Tunnel Syndrome is a condition that occurs due to pressure on the median nerve as it passes through the carpal tunnel. Because of anatomical structures arrangement at the wrist joint, the nerve become more prone to the injury at that level. The Carpal tunnel is formed by two layers, deep carpal arch and superficial flexor retinaculum. 9 tendons and median nerve pass through this tunnel. The wrist joint is the most functional joint and thus moves numerous times while doing many activities. This makes the median nerve at this level more vulnerable to injury.

Injury at the Elbow

Figure.5 Hand of Benediction

Most Common Associated Injury = Supracondylar Fracture of the Humerus.

This results in the flexors and pronators in the forearm being paralyzed, with the exception of the flexor carpi ulnaris and medial half of flexor digitorum profundus.

The forearm is constantly supinated, and flexion is weak and is often accompanied by adduction, as a result of the pull of the flexor carpi ulnaris.

Flexion at the thumb is also prevented, as both the longus and brevis muscles are paralysed.

Sensory Functions: Gives rise to the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand. 

The lateral two lumbrical muscles are paralyzed, and the patient will not be able to flex at the MCP Joints or extend at IP joints of the index and middle fingers.  So on trying to flex the fingers and thumb to make a fist, the 1st 3 digits remain in extension, and the posture is known as the "hand of benediction".

In lesions of the Ulnar Nerve the same posture occurs with the hand at rest, due to paralysis of the medial lumbricals, which is known as the "Ulnar Claw".

Injury at the Wrist

Most Common Associated Injury =  Lacerations just proximal to the Flexor Retinaculum.

Motor Function: Thenar muscles paralysed, as are the lateral two lumbricals. This affects the opposition of the thumb and flexion of the index and middle fingers.

Sensory Function: Same as an injury at the elbow.

Characteristic Signs: Same as an injury at the elbow, i.e. Hand of Benediction on attempting to make a fist.

Clinical Examination

Neuro Exam

Motor signs of a median nerve lesion include;

• Weak pronation of the forearm
• Weak flexion and radial deviation of wrist
• Thenar atrophy
• Inability to oppose or flex the thumb;

Sensory signs of a median nerve lesion include;

• sensory distribution includes thumb, radial 2 1/2 fingers, and the corresponding portion of palm.
  • with intact nerve, thumb can be pronated, lining up nails at or near 180 deg;
  • with median nerve palsy, thumb cannot be pronated & nail is < 100 deg 

Neurodynamics

Extending the elbow and wrist, two key components of the upper limb tension test, puts the median nerve under tension. Rotating the head and neck to the opposite side puts the nerve under increasing stretch. If the entrapment is in the inter scalene triangle then raising the arm above the head usually increases the response. The purpose is to test for C5, C6, C7 nerve roots and median nerve as the source of the patient’s painful shoulder and arm.
Upper Limb Tension Test 1 (ULTT1, Median Nerve Bias)

1. Shoulder Girdle Depression
2. Shoulder Joint Abduction
3. Forearm Supination
4. Wrist and Finger Extension
5. Shoulder Joint Laterally Rotated
6. Elbow Extension

Upper Limb Tension Test 2A (ULTT2A, Median Nerve Bias)

1. Shoulder Girdle Depression
2. Elbow Extension
3. Lateral Rotation of the whole Arm
4. Wrist, Finger and Thumb Extension

Treatment

1. Manual Therapy
   • Soft Tissue Mobilization
   • Splinting
   • Neurodynamic Techniques
   • Functional Massage
   • Carpal Bone Mobilization Technique
   • Corticosteroid injection
2. Electrophysical Therapy
   • Therapeutic Ultrasound
   • Laser Therapy
     

Both therapies had a positive effect on nerve conduction, pain reduction, functional status, and subjective symptoms in individuals with carpal tunnel syndrome. However, the results regarding pain reduction, subjective symptoms, and functional status were better in the manual therapy group.in cases of mild to moderate CTS, evidence supports the use of ultrasound-guided corticosteroid injections and night splints as part of the conservative management