Median Nerve

Original Editor - Daniele Barilla 

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Description

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 interroseous artery. 

Root

C5-C6-C7-C8-T1

From

lateral and medial cords of the 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 
  

Function

Motor

Muscular branch

• all the superficial muscles on the front of the forearm except the flexor carpi ulnaris

Volar interosseous branch

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

Sensory

Palmar branch

It pierces the volar carpal ligament, and divides into:

• lateral branch

skin over the ball of the thumb;

communicates with the volar branch of the lateral antibrachial cutaneous nerve.

• medial branch

skin of the palm;

communicates with the palmar cutaneous branch of the ulnar. 

Assessment

Neuro exams

Signs of a median nerve lesion include weak pronation of the forearm, weak flexion & radial deviation of wrist, with thenar atrophy & inability to oppose or flex the thumb;
- sensory distribution includes thumb, radial 2 1/2 fingers, and 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 

Neuro dynamics

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