Median Nerve

Original Editor - Wendy Walker and Daniele Barilla

Top Contributors - Daniele Barilla, Evan Thomas and Joao Costa

Description

Braplex.PNG
The Median Nerve extends along the middle of the arm and forearm to the hand. It arises by two roots, one from the lateral and one from the medial cord of the brachial plexus; these embrace the lower part of the axillary artery, 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. [1]

Video

Root

C5-C6-C7-C8-T1

From

C5 to C7 roots from lateral cord of brachial plexus

C8 and T1 roots from medial cord of brachial plexus

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. As it passes in front of the elbow, it supplies one or two twigs to the joint.

In the forearm its branches are:

  • muscular
  • volar interosseous
  • palmar

Variation

  • martin-gruber anastomosis;
  • bifid (high division) of median nerve: associated w/ a median artery. [2]

Function

Motor

Muscular branch

All the superficial muscles on the front of the forearm except the flexor carpi ulnaris

  • Pronator teres
  • Flexor carpi radialis
  • Flexor carpi sublimis
  • Anterior interosseous (motor)
  • Flexor pollicis longus
  • Flexor digitorum profundus to 2nd & 3rd fingers
  • Pronator quadratus

Volar interosseous branch

Deep muscles on the front of the forearm, except the ulnar half of the Flexor digitorum profundus

  • Abductor pollicis brevis
  • Opponens pollicis
  • Lumbricals: 1st & 2nd
  • ± Flexor pollicis brevis (also innervated by ulnar nerve)
Median Nerve Sensory
Median Nerve Sensory

Sensory

Palmar branch

It pierces the volar carpal ligament and divides into:

  • lateral branch (branch arises proximal to carpal tunnel)
    • skin over thenar eminence
    • communicates with the volar branch of the lateral antibrachial cutaneous nerve.


  • medial branch
    • skin of the palm, of thumb, 2nd, 3rd & lateral 1/2 of 4th finger
    • communicates with the palmar cutaneous branch of the ulnar. [1]

Clinical relevance

There are three entrapment syndromes involving the medial nerve or its branches:

  • Carpal Tunnel Syndrome
  • Anterior Interosseous Syndrome
  • Pronator Teres 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
  • a dull ache in the hand or arm [3]

Anterior Intraosseous Syndrome

AINS is a pure motor neuropathy, as the anterior interosseous nerve contains no sensory fibres; 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 is impaired.

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

AINS 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. [4]

Pronator Teres Syndrome

Due 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 PTS, however in this case symptoms worsen with elbow movements.

Pathology/Injury

Carpal Tunnel Syndrome is a condition which occurs due to pressure on the median nerve as it passes through the carpal tunnel

The median nerve is particularly vulnerable to damage at the elbow and wrist.

Injury at the elbow

Median N Hand of Benediction
Hand of Benediction

Most common injury = Supracondylar fracture of the humerus.

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

The forearm constantly supinated, and flexion is weak (often accompanied by adduction, because 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 paralysed, 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".

NB In lesions of the Ulnar Nerve the same posture occurs with the hand at rest, due to paralysis of the medial lumbricals. In these cases, it is known as the "ulnar claw".

Injury at the wrist

Most common injury =  Lacerations just proximal to the flexor retinaculum.

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

Sensory functions: 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.

Assessment

Neuro exams

Signs of a median nerve lesion include weak pronation of the forearm, weak flexion and radial deviation of wrist, with thenar atrophy and inability to oppose or flex the thumb;
- sensory distribution includes thumb, radial 2 1/2 fingers, and the corresponding portion of palm.
- w/ intact nerve, thumb can be pronated, lining up nails at or near 180 deg;
- w/ median nerve palsy, thumb can't be pronated & nail is < 100 deg [2]

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.[5]

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
  • Neurodynamic techniques
  • Functional massage
  • Carpal bone mobilization techniques
  1. Electrophysical therapy (EM)
  • Ultrasound therapy
  • Laser therapy

Both therapies had a positive effect on nerve conduction, pain reduction, functional status, and subjective symptoms in individuals with CTS. However, the results regarding pain reduction, subjective symptoms, and functional status were better in the MT group.[6]

Resources

[7]
[8]

See also

References

  1. 1.0 1.1 Gray, Henry. Anatomy of the human body. Philadelphia and New York: Lea & Febiger, 1825-1861
  2. 2.0 2.1 Wheeless' Textbooks of Orthopaedics, Medial Nerve http://www.wheelessonline.com/ortho/Median_nerve (accessed 7 april 2017)
  3. NHS choise. Carpal Tunnel Syndrome http://www.nhs.uk/Conditions/Carpal-tunnel-syndrome/Pages/Whatisit.aspx (last accessed 7 april 2017)
  4. Radiopaedia. Anterior interosseous nerve syndrome. https://radiopaedia.org/articles/anterior-interosseous-nerve-syndrome-1 (last accessed 7 April 2017)
  5. Special Tests. Orthopedic Testing Procedure http://special-tests.com/shoulder-tests/ultt/ (accessed 7 April 2017)
  6. Wolny T, Saulicz E, Linek P, Shacklock M, Mysliwiec A. Efficacy of Manual Therapy Including Neurodynamic Techniques for the Treatment of Carpal Tunnel Syndrome: A Randomized Controlled Trial. J Manipulative Physiol Ther. 2017.
  7. Kenhub. Median Nerve - Distribution, Innervation & Anatomy - Human Anatomy. Kenhub Available from: https://www.youtube.com/watch?v=-8iYxrZKAZU [last accessed 4/7/17]
  8. ehowhealt. Carpal Tunnel: Median Nerve Stretches for Relieving Carpal Tunnel Syndrome Pain. Available from: https://www.youtube.com/watch?v=PvXaBrZOeIw [last accessed 4/7/17]