Median Nerve

THE MEDIAN NERVE

• A key landmark in the upper arm is the

palpable space posterior to the biceps

muscle ; the median nerve lies in close

apposition to the brachial artery and ulnar

nerve within this space.

• At the level of the elbow, one can divide the

antecubital fossa into thirds, and the

median nerve lies roughly at the junction of

the medial and middle third.

• If the wrist is flexed, there are 1 or 2 creases that are

exaggerated.

• The creases mark the proximal boundary of the carpal tunnel.

• If the thumb and fifth finger are apposed, the longitudinal

plane between the thenar and hypothenar muscles will be

exaggerated . The median nerve at the wrist can be readily

found at the intersection of the latter crease and the wrist

crease.

• The course of the nerve then can be traced in the forearm by

joining the longitudinal crease at the wrist with the junction of

the medial and middle thirds of the antecubital fossa.

Formed by C5 to C7 roots from lateral cord of brachial plexus

C8 and T1 roots from medial cord

From the axilla, it enters the arm at inferior margin of teres major

Passes vertically down the medial side of ant compartment of arm

Proximally, it is immediately lateral to brachial artery

Distally, it crosses to medial side of brachial artery & lies anterior to elbow joint

Covered & protected anteriorly in distal part of cubital fossa by the bicipital aponeurosis

Leaves cubital fossa by passing between ulnar & humeral heads of pronator teres + humero – ulnar & radial heads of flexor digitorum superficialis

No branch in arm, 1 branch to pronator teres in forearm, which may originate from nerve immediately proximal to elbow joint

In forearm, it continues a straight linear course distally down in the fascia on deep surface of FDS muscle

Branches to superficial & intermediate layers of forearm, originating medially from nerve just distal to elbow joint:

• Largest branch: ant interosseous nerve

Origin: between 2 heads of pronator teres

Pass distally down forearm with ant interosseous artery

Motor innervation to deep muscles e.g. FPL, lat ½ FDP & PQ

Terminates: articular branches to joints of distal forearm & wrist

1. Small branch: palmar cutaneous branch

Origin: distal forearm, proximal to flexor retinaculum

Passes superficially in hand

Innervates skin over base and central palm

Sensory innervation to skin over thenar eminence

Proximal to the wrist, the median nerve moves lateral to the muscle, becoming more superficial in position and lying between tendons of PL & FCR

From the forearm, it passes through the carpal tunnel deep to the flexor retinaculum & enters the palm of the hand where it divides into

1.Recurrent 2.Palmar digital branches

Recurrent branchOrigin: lateral side of median nerve near

distal margin of flexor retinaculum, curves around its margin

Pass proximal over FPB, then pass between FPB & abductor pollicis brevis to end in the opponens pollicis

Motor Innervation to 3 thenar muscles

Palmar digital nervesCross palm deep to palmar aponeurosis &

superficial palmar arch & enters the digits Sensory Innervation to palmar skin surfaces

of lat 3½ digits + dorsal cutaneous regions of distal phalanges of same digits

Distal nerves also supply motor innervation to the lateral 2 lumbricals

MEDIAN NERVELESIONS

Common Sites Affected & Causes

Axilla:

crutch compression

missle injury

anterior shoulder dislocation

Upper Arm: stab wounds +/- brachial artery injury

sleep palsy: near pectoralis major tendon

# of shaft of humerus

Elbow:

supracondylar # of humerus

fracture of medial epicondyle

injection injury

after elbow dislocation

Just Distal to Elbow:

pronator teres syndrome

In the Forearm:

anterior interosseous syndrome

fractures of forearm bones

In the Carpal Tunnel:

carpal tunnel syndrome

# & dislocations about the wrist

Damage to the median N generally results in

weakness of abduction & opposition of thumb

weakness of forearm pronation

deviation of wrist to ulnar side on wrist flexion

weakness of flexion of distal phalanx of thumb & index finger

wasting of thenar muscles

sensory loss is variable but most marked on index & middle fingers.

Examination of Median Nerve

High median nerve injuries, in the proximal forearm or above, lead to loss of:

wrist flexion strength,

ulnar deviation of the wrist,

thumb opposition,

flexion of the thumb, index & long finger interphalangeal joints.

When making a fist, the ring and small fingers flex while the long and index tend to stay straight. This is known as the pointing test.


The patient’s hand is placed on a flat surface with palm facing upwards. The examiner holds his finger above palm. The patient is asked to raise his thumb & try to touch examiner’s finger. This is a test for Abductor Pollicis Brevis.

Another test may be performed to check for strength of Flexor Pollicis Longus in thumb & Flexor Digitorum Profundus in index. The patient is asked to try to flex the appropriate distal joint while the examiner supports the phalanx proximal to it. Weakness of these 2 muscles indicates a lesion proximal to the wrist.


In low median nerve injuries the fingers are still able to flex, but thumb opposition is often lost.

To test motion, ask the patient to move thumb and fifth digit so that the finger tips touch and attempt to flex the wrist.

Damage is indicated by numbness, tingling and pain in the palm and fingers, weak thumb movements and proper flexion of the wrist.


APE HAND (no thumb opposition): a deformity marked by thumb movements being limited to flexion and extension in the plane of the palm due to the inability to oppose and limited abduction of the thumb.

The recurrent (thenar) branch of the median nerve supplying the thenar muscles lies subcutaneously and may be severed by relatively minor lacerations involving the thenar eminence.

Severence of this nerve paralyzes the thenar muscles, and the thumb loses much of its usefulness.


MEDIAN NERVEENTRAPMENTSYNDROMES

Carpal Tunnel Syndrome

disorder characterised by compression of the median nerve at the wrist

Causes:

congenital predisposition – carpal tunnel is smaller

trauma / injury to the wrist that cause swelling, e.g. sprain / fracture

mechanical problems in wrist joint

repeated use of vibrating hand tools

development of cyst / tumor in the canal

fluid retention during pregnancy / menopause, overactivity of pituitary gland, obesity, hypothyroidism, rheumatoid arthritis, diabetes, work stress – predispose to CTS

in some cases – cause unknown

Signs & Symptoms:

numbness in the distribution of median nerve

burning, tingling, swollen & a prickly pin-like sensation over the palmar surface of the hand, & into the thumb, forefinger, middle finger, & half of the ring finger, esp. at night

with continued nerve compression – may experience muscle weakness, resulting in decreased grip strength

some people – unable to tell between hot & cold by touch

eventually – muscle atrophy, esp. muscles at the base of thumb

if left untreated - may eventually result in permanent weakness, loss of sensation, or even paralysis of the thumb and fingers

RED SHADED AREAS NORMALLY AFFECTED BY SYMPTOMS OF CARPAL TUNNEL SYNDROME


Treatment:Conservative

resting of affected hand & wrist for at least 2 weeks

immobilisation of wrist in a splint to avoid further damage from twisting / bending (specially designed carpal tunnel wrist support)

Medications:

NSAIDS, e.g. aspirin, ibuprofen

pain relievers

orally administered diuretics (“water pills”) – to decrease swelling

corticosteroids or the drug lidocaine can be taken orally or injected directly into the wrist

Physiotherapy:

cool packs – reduce swelling

stretching & strengthening exercises (small weights to do flexion & extension – use of theraband may also be considered)

Surgical

done in most severe cases of CTS

recommended if symptoms last for 6 months

involves cutting the ligament crossing the wrist, thus providing more room to the median nerve & decreasing compression


Note: if underlying causes of CTS are diabetes / arthritis / ….. – these conditions should be treated 1st

Examination: wrist is examined for tenderness, swelling, warmth &

discoloration

each finger is tested for sensation

muscles at the base of the hand are examined for strength & signs of atrophy

routine lab tests & X-rays – reveal diabetes, arthritis & factures

Diagnosis: EMG – to determine severity of damage to median nerve

ultrasound imaging – to show impaired movement of median N

MRI – to show anatomy of wrist (but NOT really useful in diagnosing CTS)

Tests:

Phalen’s (wrist flexion) Test

• performed by holding the patient’s wrist in maximum flexion for 1 minute. A positive test is indicated by tingling in the thumb, index finger, and middle finger and lateral half of the ring finger

Tinel’s Sign• performed by briskly tapping over the carpal tunnel at the wrist. A positive test causes tingling or paraesthesia into the thumb, index finger and middle and lateral half of the ring finger( median N distribution). Tingling or paraesthesia must be felt distal to the point of pressure for a positive test

Tests:

Carpal Compression Test

a relatively new test

the supinated wrist is held in both hands & direct even pressure is applied over the median N in the carpal tunnel for up to 30 secs.

production of the pt’s symptoms is considered to be a positive test for the carpal tunnel syndrome


also known as pronator syndrome

more common in women

involves entrapment (compression / pinching) of the median nerve by the pronator teres muscle

can also include median nerve compression by other structures in the elbow, e.g. ligament of Sruthers / bicipital aponeurosis

Pronator Teres Syndrome

depending on the site of entrapment – 2 types of symptoms may occur:

1. compression of median nerve at / just above the elbow – leads to weakness of pronator teres muscle (rare occurrence & more commonly seen in children)

2. entrapment of median nerve at the pronator muscle itself – the median nerve passes between the superficial & deep heads of the muscle & can become entrapped due to edema & hypertrophy (enlargement) of the muscle

Note:Entrapment at the pronator teres muscle does not involve the muscle since its nervous innervation comes from a point more proximal than the muscle itself, thus sparing it.

Neuropathies (nerve loss) at either site will involve both sensory and motor deficits on the flexor (palmar) side of the forearm.

Sensory losses

include the thumb, index and middle fingers, and half the ring finger

typically involve all of the palm of the hand to the wrist

include numbness, tingling and / or “pins & needles” sensations along the palm of the hand and sometimes part way up the forearm

Motor losses

lead to loss of flexion (inability to make a tight fist) & opposition of the thumb & fingers involved

The exception to this is, as stated before, with involvement of the pronator teres muscle, which will make it difficult to pronate the arm

most significant feature – pain along median nerve axis – helped by rest & aggravated by activity

Median nerve is tender along its course in the forearm – patient may complain of aching discomfort & early fatigue of the muscles of the forearm


Examination:

Phalen & Tunnel tests are negative

pain upon palpation of origin ,muscle belly & insertion of pronator teres muscle

pain when pronating forearm against resistance

median nerve symptoms arise when the muscle belly of pronator teres muscle is deeply compressed

weakness of thenar muscles

Diagnosis: EMG (Note: if EMG does not confirm PTS but clinical evidence is

suggestive, then wait for 4-6 weeks before doing EMG once again)


Test:Pronator Teres Test

The patient stands with the elbow in 90 degrees of flexion. One hand is placed on his elbow for stabilization and the other hand grasps his hand in a handshake position. The patient holds this position as an attempt is made to supinate his forearm (forcing him to contract the pronator muscles).

While holding the resistance against pronation, the patient’s elbow is extended. If pain or discomfort is reproduced, there is a good chance of median nerve compression by the pronator teres.

Note: the patient should keep the elbow relaxed during the test, because holding the elbow firmly in flexion will NOT allow elbow extension.


Conservative

rest

Medications:

NSAIDS

Physiotherapy:

wrist immobilisation splint applied in 15 degrees dorsiflexion for 4-6 weeks

massage

ice

electrical stimulation

Surgical

exploration of the median nerve in the proximal forearm & release of all possible sites of compression – done in severe cases

Treatment:


Anterior Interosseous Syndrome

also known as Kiloh Nevin Syndrome

causes of compression include:

commonest – tendinous origin of the deep head of pronator teres

impingement of an enlarged bicipital tendon on the nerve

aberrant / thrombosed radial artery in mid-forearm

thrombosed ulnar artery

fascial band at the origin of flexor digitorum superficialis

in most cases – this syndrome is a complication of supracondylar fractures of the humerus in children

described in association with repetitive activities, e.g. throwing, racket sports & weight-lifting

characterised by a vague feeling of discomfort in the proximal forearm, which may mimic pronator teres syndrome

however, because the anterior anterosseus nerve is a pure motor division of the median nerve, there are no sensory complaints or deficits as in pronator teres syndrome


principal weakness: difficulty in moving index & middle fingers

weakness when turning the palm down against resistance

weakness in IP joint of thumb (FPL) & DIP joints of index & middle fingers (FDP) – this can be observed by the pitch attitude of the hand (normally, when an individual pinches something between the index finger & thumb, MP & IP joints of thumb & index finger are flexed, but with a nerve deficit, terminal phalanges of thumb & index finger are extended or hyperextended) – thus, frequent dropping of objects & difficulty in writing

Common Signs & Symptoms:


Diagnosis:

The patient is asked to pinch the tips of index finger & thumb together.

Normal – tip-to-tip pinch

Abnormal – pulp-to pulp pinch

Test is indicative of a positive sign for pathloogy to the anterior interosseus N

This finding is indicative for the entrapment of the ant interosseus N as it passes between the 2 heads of the pronator teres muscle.

1. Pinch Grip Test

2. Electroneurography however, these studies are difficult as the

3. EMG nerve is deep as are the muscles it supplies


Treatment:

Conservative

rest

use of splints

Medications:

NSAIDS

pain relievers

Physiotherapy:

cold – to relieve pain & reduce inflammation for acute & chronic cases (ice packs or ice massage are applied for 10-15 mins every 2-3 hours)

heat – heat packs or warm soaks may be used before performing stretching & strengthening exercises

Surgical

exploration of median nerve through an approach similar to that of pronator syndrome

includes release of bicipital aponeurosis, division of superficial & more or less to the deep heads of pronator teres muscle & ligation of crossing vessels


eMedicine- Hand, Nerve Compression Syndromes: Upper Extremity: Article by Bradon J Wilhelmi, MD

Last Updated, June 28, 2006http://www.emedicine.com/plastic/topic300.htm

Pain Management & Rehabilitation Centerhttp://www.painrehabcenter.com/view.php?SC=1

Carpal Tunnel Syndrome Fact Sheet: National Institute of Neurological Disorders and Stroke (NINDS)

Publication date November 2002.file:///G:/detail_carpal_tunnel.htm

Grays Anatomy For Students by Richard L. Drake, Wayne Volg and Adam W. M. Mitchell

References

Median Nerve

Documents

Transcript of Median Nerve