Median-nerve

Adductor pollicis

REF: http://en.wikipedia.org/wiki/Median_nerve, Gray’s anatomy, 39^th edition, P 931,932 See chart of previous question for explanation

Median nerve.

Cubital fossa

-This area is clinically important for venepuncture  and for blood pressure  measurement. It is an imaginary triangle with borders being:

* Laterally, the medial border of brachioradialis  muscle

* Medially, the lateral border of pronator teres muscle

* Superiorly, the intercondylar  line, an imaginary line between the two condyles of the humerus

* The floor is the brachialis & supinator muscle

* The roof is the skin and fascia of the arm and forearm

– Contents of cubital fossa (lateral to medial) are: Radial nerve, Biceps tendon, Artery and Median nerve.

Motor nerve supply of Median nerve in the hand:

Thenar muscles which include

1. Flexor pollicis brevis
2. Opponens pollicis
3. Abductor pollicis

Carpal tunnel syndrome is caused by the compression of the median nerve at wrist and is most common type of nerve entrapment syndrome.

 This is usually due to excessive use of the hands and occupational exposure to repeated trauma.

Infiltration of the transverse carpal ligament with amyloid (as occur in multiple myeloma) or thickening of connective tissue in rheumatoid arthritis, acromegaly, amyloidosis, mucopolysaccharidosis and hypothyroidism are less common cause of the syndrome.

It is not uncommon for the condition to make its appearance during pregnancy.

Perilunate dislocation

Carpel tunnel syndrome is due to compression ofmedian nerve.

Ref: Harrison’s Internal Medicine, 14th Edition, Page 2467; Essential Orthopedics By J Maheswari, 2nd Edition, Page 257

Median nerve innervates the thenar muscles and the skin over it. The likely condition is  Carpal Tunnel Syndrome.

The median nerve enters the hand through the carpal tunnel, deep to the flexor retinaculum along with the tendons of flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus.

The median nerve supplies the surface of the lateral palm, the palmar surface of the first three digits and the distal dorsal surface of the index and middle fingers (including the nail beds). Therefore, prior to performing surgery in this area, it is essential to anesthetize a branch of this nerve (possibly a proper digital branch) to eliminate pain sensation around the nail bed of the index finger.

Pollex means Thumb, which means strong in latin. There are four short muscles of thumb (pollex), they are abductor pollicis brevis, opponens pollicis, flexor pollicis brevis and adductor pollicis. The first three of these muscles form the thenar eminence. All these muscles are supplied by median nerve except for adductor pollicis which is innervated by ulnar nerve.

Median nerve (C6–T1): Provides most of the innervation to the anterior forearm, excluding one and one half muscles, the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus muscle, which are innervated by the ulnar nerve. The median nerve continues into the hand to innervate the thenar eminence and lumbricals 1 and 2. It provides cutaneous innervation to the medial palmar side of the hand and the palmar surface of digits 1 through 3 and half of digit 4.

• Superficial branch of ulnar nerve and ulnar artery
• Tendon of palmaris longus
• Palmar cutaneous branch of median nerve
• Origin of the thenar muscles

• Median nerve
• Tendons of flexor digitorum superficialis
• Tendon of flexor digitorum profundus
• Tendon of flexor pollicis longus
• Ulnar bursa and radial bursa

A i.e. Radial nerve injury cause anaesthesia over anatomical snuff box; C i.e. Ulnar nerve injury cause claw hand; B i.e. Index finger anesthesia is caused by median nerve injury 

All Correct – A,B, C, 

D i.e. Adductor pollicis

Injury or compression of median nerve at wrist (eg carpel tunnel syndrome) can be tested by

1.      Pen test for loss of action of Abductor pollicis brevis

2.      Ape thumb deformity Q (adducted posture of thumb)

3.      Loss of opposition & abduction of thumb Q (d/ t wasting of thenar muscles)

4.      Sensory loss – lateral 3¹/2 of digits & 2/3 palm (autonomous zone is tip of index & tniddle finger)

Abductor pollicis longus is supplied by posterior interosseous nerve (br. of radial nerve)Q; so abduction of thumb is not completely lost.

A, B, C,  i.e. Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis, & First lumbricals

B i.e. Median Nerve

A i.e. Medial Nerve 

D i.e. All of the above 

C i.e. Median nerve

• Anterior interosseous nerve is the most commonly injured nerve with loss of motor- power to flexor pollicis longus & deep flexor to the index finger in extension type supracondylar fractureQ
• Over all involvement of peripheral nerve in fracture supracondylar humerus is AIN > median nerve > radial nerve > ulnar nerveQ

A i.e. Median nerve

B i.e. Lunate

The median nerve controls the coarse movements of the hands, as it supplies most of the long muscles of the front of the forearm a nd therefore called the ‘labourer’s nerve’.

The median nerve is formed from parts of the medial and lateral cords of the brachial plexus

The median nerve is the only nerve that passes through the carpal tunnel.

Innervation

• Upper Arm

No motor innervation.

• Forearm

It innervates most of the flexors in the forearm except flexor carpi ulnaris and the medial two digits of flexor digitorum profundus, which are supplied by the ulnar nerve.

Unbranched, the median nerve supplies the following muscles:

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

The anterior interosseus branch supplies the following muscles:

• Lateral (radial) half of flexor digitorum profundus muscle
• Flexor pollicics longus muscle
• Pronator quadratus Hand.

In the hand, the median nerve supplies motor innervation to the 1st and 2nd lumbricals and the muscles of the thenar eminence of the hand by a recurrent thenar branch.

The rest of the intrinsic muscles of the hand are supplied by the ulnar nerve.

Injury

• Injury of this nerve at a level above elbow joint results in loss of pronation and a decrease in flexion of the hand at the wrist joint.
• In the hand, thenar muscle are paralysed and atrophy with in time. Opposition and flexion movements of thumb are lost, and thumb and index finger are arrested in adduction and hyperextension position. This appearance is referred as ape hand deformity.

In addition, in palmar side of the hand sensation of lateral part of hand, first three fingers and lateral half of the f our t h finger and in dorsal side sensation of distal S! portion of first three fingers and lateral half of distal S! portionof fourth finger is lost.

The flexor retinaculum stretches across the front of the wrist and converts the concave anterior surface of the hand into an osteofascial tunnel, the carpal tunnel, for the passage of:

• The median nerve
• Flexor tendons of the thumb (flexor pollicis longus and fingers) (flexor digitorum superficialis and profundus).
• Radial and the ulnar bursa

It is attached medially to the pisiform bone and the hook of the hamate and laterally to the tubercle of the scaphoid and the trapezium bones.

The attachment to the trapezium consists of superficial and deep parts and forms a synovial-lined tunnel for passage of the tendon of the flexor carpi radialis.

The lower border is attached to the palmar aponeurosis.

Ans. D: Median Nerve

Supracondylar humerus fracture:

• Most common < 10 years, peak age 5-8 years
• Constitutes 80% of all pediatric distal humerus fractures
• 2:1 males to female ratio

Classificatio:

• Extension type: Extension type accounts for 90-98% of all supracondylar fractures
• Flexion type

Gartland Classification is commonly used to classify extension type of injuries:

I: Nondisplaced

IIA: displaced, posterior cortex intact; rotationally stable, intact posterior cortex acts like a hinge

IIB: displaced, posterior cortex intact; rotationally unstable

III: completely displaced, no cortical contact, most often a medial periosteal sleeve intact when medially displaced and vice-versa

Management:

i. Closed Reduction is done for type I and type II fractures. Closed reduction is not attempted in type III fractures. Assessing adequacy of reduction:

• Jones view: hyperflexion shoot through elbow
• Baumann’s Angle: comparison to uninjured side, difference of more than 5degrees is unacceptable
• Anterior Humeral Line

Type III fracture:

• Increased swelling and soft tissue injury
• Proper neurovascular and compartment assessment
• Closed reduction and percutaneous pinning is the management of choice, 2 pins may achieve stability

Neurologic Injury:

• 5-19% of supracondylar farctures
• More in type III supracondylar fractures
• Median nerve 52% (especially posteromedial displacement)
• Radial nerve: 28%
• Most are neuropraxic injuries
• Motor Recovery may take 7-12 weeks
• Sensory recovery may take nearly 6 months

Ans. C i.e. Median nerve

Ans. A: Ulnar and median nerve

Claw hand deformity is manifested by flattening of the transverse metacarpal arch and longitudinal arches, with hyperextension of MCP joints and flexion of the PIP and DIP joints;

This deformity is produced by imbalance of the intrinsic & extrinsics:

i. Intrinsic muscles must be markedly weakened or paralyzed to produce claw deformity;

Long extensor muscles hyperextend the MCP joint, & long flexor muscles flex the PIP and DIP joints; weakness of the

long flexors (as in high palsy) actually decreases claw fingers;

In ulnar nerve palsy, only the medial two fingers develops clawing while all the four fingers develop clawing in combined median and ulnar nerve palsy.

Ans. is ‘b’ i.e., Median nerve

• Anterior interosseous nerve is a branch of median nerve.
• Anterior interosseous artery is a branch of ulnar artery.

Ans. is ‘c’ i.e., Median nerve

• Pronation of the forearm is by two muscles pronator teres and pronator quadratus. These two muscles are supplied by median nerve. Thus injury to median nerve produces inability to pronate forearm.
• The median nerve is also called labourer’s nerve. The median nerve arises by two roots, one from the lateral cord (C5,6,7) and the other from the medial cord (C8, T1). The various muscles supplied by median nerve are : ‑

1) In the forearm

• All the flexor muscles of the forearm, except the flexor carpi ulnaris and the medial half of flexor digitorum profundus to the ulnar two fingers. These muscles are : –

1. Pronater teres
2. Flexor digitorum superficialis
3. Flexor pollicis longus
4. Flexor carpi radialis
5. Flexor digitorum profundus (lateral half)
6. Pronator quadratus
7. Pulmaris longus

2) In hand

• Median nerve supplies : –

1. Thenar muscles (except adductor pollicis) – Flexor pollicis brevis, opponens pollicis and abductor pollicis brevis. Adductor pollicis is supplied by ulnar nerve.
2. First two lumbricals

Hand muscles supplied by median nerve are :-

i) Thenar muscles (except adductor pollicis) :- Flexor pollicis brevis, opponens pollicis and abductor pollicis brevis. Adductor pollicis is supplied by ulnar nerve.

ii) First two lumbricals.

Hand muscles supplied by ulnar nerve are :‑

1) Superficial terminal branch : It supplies palmaris brevis and skin of palmar surface of medial 1% fingers.

2) Deep terminal branch : It supplies adductor pollicis, all interossei, medial two (3^rd & 4^th)lumbricals and all hypothenar muscles except palmaris brevis (i.e. abductor digiti minimi, flexor digiti minimi, opponens digiti minimi).

 Median nerve

Ans. is ‘b’ i.e., Weakness of Adductor pollicis

Adductor pollicis is supplied by ulnar nerve.