35. Nerve injuries to the upper limb

Question 1

Why is there injury to the radial nerve in a mid shaft humeral fracture?

Answer 1

The radial nerve runs in the radial (or spiral) groove on the posterior surface of the shaft of the humerus. It is closely associated with the bone and may therefore be injured in a mid-shaft humeral fracture

Question 2

Will the patient still be able to actively extend their elbow when radial nerve is injured?

Answer 2

Yes. Extension of the elbow will either be normal or only mildly compromised. The nerve supply to the long and lateral heads of triceps is given off prior to the radial nerve entering the spiral groove. The nerve supply to the medial head of triceps is given off in the spiral groove, but this is generally proximal to the fracture and thus is unaffected. Anconeus is paralysed but this has only a minor role in elbow extension.

Question 3

If a patient has radial nerve injury, In what position will a their wrist and fingers be when the wrist is pronated? Why?

Answer 3

The wrist and fingers will be flexed. Injury to the radial nerve in the radial groove will result in paralysis of brachioradialis and all extensor muscles of the wrist and fingers. This injury results in “wrist drop” (i.e. inability to actively extend the wrist) and inability to actively extend the fingers. The wrist and fingers are flexed when the forearm is pronated because of unopposed flexor muscles and gravity.

Question 4

What is the likely distribution of sensory impairment in radial nerve injury?

Answer 4

The posterior cutaneous nerve of the arm branches from the radial nerve above the spiral groove, so is unaffected. The lower lateral cutaneous nerve of the arm and posterior cutaneous nerve of the forearm branch high in the spiral groove and are also usually unaffected. The paraesthesia is therefore usually in the distribution of the superficial branch of the radial nerve

Question 5

In an injury to the median nerve in the arm, above the level of the elbow (high median nerve injury), which muscles will be affected?

Answer 5

paralysis of pronator teres, flexor carpi radialis, palmaris longus and flexor digitorum superficialis as well as all
of the other muscles supplied by the median nerve in the forearm and hand. In the anterior forearm, both pronators are weak and the flexors of the wrist are paralysed except for flexor carpi ulnaris and the ulnar half of flexor digitorum profundus (both supplied by the ulnar nerve).

Question 6

Does the median nerve give off and muscular branches to the arm?

Answer 6

The median nerve gives off no muscular branches to the muscles of the arm

Question 7

In a patient with high median nerve injury, in what position will their forearm be?

Answer 7

The forearm will be supinated (due to the unopposed action of supinator [radial nerve] and biceps brachii [musculocutaneous nerve]). Flexion of the wrist is weak and is often accompanied by adduction, due to the pull of flexor carpi ulnaris

Question 8

How does high median nerve injury affect the thumb?

Answer 8

In the hand, flexion of the thumb is very weak or absent as FPL is paralysed but the deep head of FPB may have some residual innervation from the ulnar nerve. Opposition (opponens pollicis) and palmar abduction (APB) of the thumb are absent

The interphalangeal joint and MCPJ of the thumb will be extended (due to unopposed action of EPL) and the thumb will be adducted (due to unopposed action of adductorpollicis). Lateral (external) rotation of the thumb occurs due to loss of opponens pollicis (which usually medially rotates the thumb). In long standing lesions, there will be wasting of the thenar eminence.

Question 9

How does high median nerve injury affect the fingers?

Answer 9

FDS will be paralysed to all four fingers and FDP will be paralysed to the index and middle fingers. The radial two lumbricals (to the index and middle fingers) will also be paralysed but the MCPJs can still flex a little due to the action of the interossei.

Question 10

What happens when a patient with high median nerve injury attempts to make a fist?

Answer 10

When the patient attempts to make a fist, the ring and little fingers will flex into the palm normally as FDP and the lumbricals are still intact to these digits. However, the index and middle fingers will remain fully extended

Question 11

What is the name given to the appearance of the hand when trying to make a fist in a patient with high median nerve injury?

Answer 11

Hand of Benediction

Question 12

When is the Hand of benediction seen in high median nerve injuries?

Answer 12

It is only seen when the patient attempts to make at fist and is not present at rest.

Question 13

In patients with high median nerve injuries, what may develop in the long term?

Answer 13

in long-standing lesions an Ape Hand Deformity may develop at rest.

Question 14

Describe the appearance of the Ape Hand Deformity

Answer 14

Deformity with thenar wasting in a high median nerve lesion. The thumb can still be actively flexed by FPB at the MCPJ due to the ulnar nerve supply to the deep
head. (You can tell this is a high lesion as FPL is paralysed with absent flexion of the IPJ of the thumb)

Question 15

In patients with high median nerve injury, how is sensation affected?

Answer 15

The patient will have sensory loss in the whole of the region supplied by the median nerve

Question 16

Give an example of an injury that can lead to high median nerve injury?

Answer 16

supracondylar fracture of the humerus

Question 17

How may the median nerve be injured at the wrist?

Answer 17

The median nerve may be injured at the wrist by a penetrating injury (e.g. from broken glass) or by compression in the carpal tunnel.

Question 18

What is the difference between high and low median nerve injury?

Answer 18

The presentation differs from the high median nerve injury in that the innervation to the muscles of the common flexor origin at the medial epicondyle (pronator teres, flexor carpi radialis, palmaris longus, and flexor
digitorum superficialis) is intact, as is the innervation to flexor digitorum profundus.
The palmar cutaneous branch of the median nerve, supplying the skin over the thenar eminence, will be spared

Question 19

Which are the muscles that are paralysed in low median nerve injury?

Answer 19

(remember LOAF):
 lumbricals to the index and middle fingers
 opponens pollicis
 abductor pollicis brevis
 flexor pollicis brevis (superficial head)

Question 20

What is the deformity that results with low median nerve injury? How does it look?

Answer 20

Ape Hand Deformity - after the muscles have atrophied.

The thenar eminence is flattened, and the thumb is adducted and externally (laterally) rotated

Question 21

Describe the branches of the ulnar nerve

Answer 21

• The ulnar nerve does not supply any muscles in the arm.
• At the level of the elbow, it gives off a branch to flexor carpi ulnaris, which originates from the common flexor origin on the medial epicondyle and from the ulna.
• In the forearm it supplies the ulnar half of flexor digitorum profundus (to the ring and little fingers) and gives off the palmar cutaneous branch (ulnar border of the palm) and the dorsal (posterior) cutaneous branch (ulnar border of
  the dorsum plus dorsum of ulnar 1½ digits as far distally as the DIPJ). T

Question 22

In a patient with ulnar nerve injury at the wrist, which muscles might be affected?

Answer 22

In the hand, the ulnar nerve supplies the muscles of the hypothenar eminence: adductor pollicis, the deep head of flexor pollicis brevis, the interossei, the lumbricals to the ring and little finger, palmaris brevis, and gives off palmar digital branches to the ulnar 1½ digits. Hence, if the nerve is damaged at the wrist, all of these functions may be impaired.

Question 23

What may lead to ulnar nerve injury at the wrist?

Answer 23

a laceration or by compression in Guyon’s canal

Question 24

What might long standing injury to the ulnar nerve at the wrist lead to?

Answer 24

‘claw hand’.

The claw affects the little and ring fingers of the hand. These fingers are hyperextended at the metacarpophalangeal (MCP) joint, and flexed at both the
proximal and distal interphalangeal (IP) joints.

Question 25

In a low ulnar claw, Why are the MCPJs of the ring and

little fingers hyperextended and the IPJs flexed?

Answer 25

• The 3rd and 4th lumbrical muscles, acting on the ring and little fingers, are supplied by the ulnar nerve and hence are paralysed, whereas those to the index and middle fingers are supplied by the median nerve and are intact. (The interossei to all fingers are paralysed so are not the differentiating factor between the digits).
• The lumbrical muscles flex the digits at the metacarpophalangeal joints (MCPJ) and extend the digits at the interphalangeal joints (IPJ) via the dorsal extensor
  expansion.
• In ‘ulnar claw’, the MCPJs are hyperextended due to unopposed extension from extensor digitorum in the posterior compartment of the forearm.
• The proximal and distal IP joints are flexed due to unopposed flexion from the long flexor muscles (FDS and FDP respectively) in the anterior compartment of
  the arm.
• The extensor muscle (extensor digitorum) cannot extend the IP joints as their energy is dissipated in hyperextending the MCP joints.

Question 26

Are other muscles paralysed by an ulnar nerve lesion at the wrist responsible for the claw deformity?

Answer 26

The other muscles paralysed by an ulnar nerve lesion at the wrist (interossei, hypothenar muscles and adductor pollicis) are not responsible for the ‘claw’.

Question 27

Other than the claw deformity, what can be seen in a ulnar nerve injury at the wrist?

Answer 27

wasting of the interossei is seen as guttering between the metacarpals, and atrophy of adductor pollicis and the first dorsal interosseous leads to loss of the bulk of the first webspace of the hand. Atrophy of the hypothenar muscles leads to loss of the bulk of the hypothenar eminence

Question 28

How is sensation affected in ulnar nerve injury at the wrist?

Answer 28

Sensation is lost in the palmar aspect of the ulnar 1½ digits and the dorsum over the distal phalanges only.

Question 29

What is the difference between the hand of benediction and low ulnar claw?

Answer 29

Hand of benediction only occurs when trying to make a fist.

Low ulnar claw occurs even when at rest

Question 30

What might result in a high ulnar nerve lesion?

Answer 30

The ulnar nerve may be damaged at the elbow by a medial epicondylar fracture or by compression in the cubital tunnel.

Question 31

Which muscles might be affected in high ulnar nerve lesion?

Answer 31

In addition to the muscles in the hand discussed in the context of a low ulnar nerve lesion, this injury leads to paralysis of flexor carpi ulnaris, the ulnar half of flexor digitorum profundus (to the ring and little fingers) and loss of sensation in the dorsal and palmar cutaneous branches (in addition to the palmar digital nerves involved in a low ulnar nerve lesion)

Question 32

Why is the clawing seen with a high ulnar nerve lesion less pronounced than that seen with a low ulnar nerve lesion?

Answer 32

In high ulnar nerve lesion an ulnar claw will develop, but as flexor digitorum profundus is paralysed, there will not be any flexion at the DIPJ of the ring and little fingers.
The ulnar claw therefore only consists of hyperextension at the MCPJs and flexion at the PIPJs joints (intact FDS – median nerve supply). This produces a much less evident claw hand.

This is known as the ulnar paradox; you would expect a more proximal injury to produce a more pronounced deformity, but in fact the opposite occurs.

Question 33

How do you remember the muscles of the posterior forearm?

Answer 33

3 x 3 (+3)

3x muscles to the wrist: extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris

3x muscles to the fingers: extensor digitorum, extensor digiti minimi, extensor indicis

3x muscles to the thumb: abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis

+3: anconeus, supinator and brachioradialis

All innervated by the radial nerve

Question 34

How do you remember the action and innervation of brachioradialis?

Answer 34

Action: It’s the Beer Raising muscle!
Innervation: But Radial (Radial Nerve)
Why “But”? It is exceptional that this muscle is a flexor of the forearm but comes from the posterior compartment and therefore has radial nerve innervation.

Question 35

How do you remember the Muscles innervated by the median nerve in the hand?

Answer 35

L Lumbricals (1st and 2nd; to index and middle fingers)
O Opponens pollicis
A Abductor pollicis brevis
F Flexor pollicis brevis (superficial head)

Question 36

How do you remember the Action of the lumbricals?

Answer 36

‘L’ shape for Lumbricals
Flex MCPJ
Extend IPJ
This makes an ‘L’ shape with your hand.

Question 37

How do you remember the Action of the interossei?

Answer 37

PAD Palmar Adduct

DAB Dorsal ABduct

Question 38

How do you remember the Muscles of the thenar and hypothenar eminences?

Answer 38

Thenar:
O opponens pollicis
A abductor pollicis brevis
F flexor pollicis brevis

Hypothenar:
O opponens digiti minimi
A abductor digiti minimi
F flexor digiti minimi

Question 39

How do you remember the Carpal Bones?

Answer 39

“Trapezium is under the thumb”

“Sam Likes To Push The Toy Car Hard”:

4 proximal row, radial (lateral) to ulnar (medial):
Scaphoid, Lunate, Triquetrum, Pisiform

4 distal row, radial (lateral) to ulnar (medial)
Trapezium, Trapezoid, Capitate, Hamate