Neuropathies of the Upper Limb

Question 1

What are the main causes of nerve damage?

Answer 1

disease

drugs and toxins

trauma

Question 2

polyneuropathy

Answer 2

when disease, drugs, and toxins affect many nerves at the same time symmetrically on both sides of the body

Question 3

mononeuropathy

Answer 3

when trauma affects only one nerve at a time on one side

Question 4

What are the ways a nerve can be physically damaged?

Answer 4

cut by penetrating wounds (gunshot or stab wounds) and fractures

compressed against a bone by a hard outside object

compressed by swelling in an osseofibrous tunnel

stretched by dislocation or excessive movement at a joint

Question 5

What are the oucomes of an injured nerve?

Answer 5

muscles and skin supplied lose their innervation

results in complete or incomplete paralysis

anasthesia (numbness)

Question 6

complete paralysis

Answer 6

no movement is detectable because all of the muscles that produce the movement have lost their innervation

Question 7

incomplete paralysis

Answer 7

not all muscles that produce the movement have lost their innervation

therefore the patient can move, but the movement is weak or paretic (paresis)

Question 8

What is the difference between the course and distribution of a nerve?

Answer 8

course indicates where the nerve has been injured - only those muscles and skin areas distal to the site of injury will be affected

distribution indicates what muscles and skin have been affected by injury

Question 9

What causes Erb-Duchenne palsy?

Answer 9

upper brachial plexus injury

caused by traction or tear of the upper trunk (C5 and C6)

in the adult a blow to the shoulder producing excessive separation of neck and shoulder

in the newborn during delivery by pulling on the head when the arm is caught in the birth canal

Question 10

What is the result of injury of the upper brachial plexus (C5, C6)?

Answer 10

results in waiter’s tip position:

• loss of arm flexion, abduction, and lateral rotation (biceps, deltoid, supraspinous, infraspinatus, teres minor)
• loss of forearm flexion and weakness of supination (biceps, brachialis, brachioradialis)
• weakness of wrist extension (wrist extensors are innervated in part by C6)
• the limbs hang by the side in medial rotation and pronation, the hand is flexed

Question 11

Describe the location of the C5 and C6 dermatomes.

Answer 11

lateral side of the arm, forearm, and hand

Question 12

What is the cause of Klumpke’s palsy?

Answer 12

lower brachial plexus injury

caused by traction or tear of the lower trunk (C8 and T1)

in the newborn, a forceful upward pull of the shoulder during birth by pulling on the arm when the head is caught in the birth canal

in the adult, when grasping something to break a fall

Question 13

What is the effect of low brachial plexus injury?

Answer 13

paralysis of the distal limb muscles (C8, T1 myotomes) primarily affects intrinsic hand muscles innervated by the median and ulnar nerves

results in Klumpke’s total claw hand

Question 14

What dermatomes are affected by a lower plexus injury?

Answer 14

anesthesia in the C8 and T1 dermatomes along the medial side of the arm, forearm, and hand

Question 15

Klumpke’s total claw hand

Answer 15

caused by loss of flexion of the MCP joints (interossei and lumbricals) and loss of extension of the PIP and DIP joints (lumbricals) in the fingers, and paralysis of the thenar and hypothenar muscles

the unopposed actions of the long extensors and flexors pull the MCP joints of all digits into hyperextension and the IP joints

Question 16

What is the function of the interossei and lumbricals?

Answer 16

in addition to adducting (PAD) and abducting (DAB) the finger, the interossei also flex the MCP joints

the lumbricals extend the PIP and DIP joints and assist the interossei in flexing the MCP joints

Question 17

What can cause proximal lesions of the medial nerve?

Answer 17

fractures of the supracondylar humerus

Question 18

What causes pronator syndrome?

Answer 18

produced by compression of the nerve as it lies between the two heads of pronator teres

penetrating wounds

Question 19

What is the most common cause of distal lesions?

Answer 19

carpal tunnel syndrome - produced by repetitive hand and finger movements that lead to swelling of the long flexor tendons and their synovial sheaths that compress the nerve

Question 20

What muscles does the median nerve innervate?

Answer 20

all of the flexor forearm muscles except for the half innervated by the ulnar nerve

LOAF mnemonic:

L = 1st and 2nd lumbricals

O = opponens pollicis

A = abductor pollicis brevis

F = flexor pollicis brevis (superficial head)

Question 21

What is ape hand? What causes it?

Answer 21

both proximal and distal lesions

caused by loss of thumb opposition (flexion and abduction) with atrophy of the thenar eminence

thumb remains extended and adducted

Question 22

Where are the sensory changes in the presence of a median nerve injury?

Answer 22

on the dorsal and palmar surfaces of the thumb, index, middle, and lateral half of the ring fingers and adjacent portion of the palm

Question 23

What is Pope’s blessing (hand of benediction)? What causes it?

Answer 23

proximal leasions lead to the inability to flex the second and third digits due to paralysis of the FDS and the lateral half of the FDP

also weakness of wrist flexion - when the wrist is flexed it deviates to the ulnar side

loss of pronation and the hand is supinated

Question 24

What produces median claw hand of digits 2 and 3?

Answer 24

distal lesions

caused by weakness of flexion in MCP joints and loss of extension in the PIP and DIP joints of the index and middle fingers

unopposed actions of the long flexors (FDS and the lateral half of the FDP) and extensors (ED, EI) pull the MCP joints of the index and middle fingers into extension and the IP joints into flexion

Question 25

What causes proximal lesions of the ulnar nerve?

Answer 25

fractures of the medial epicondyle can cut the nerve the nerve can be compressed in the ulnar groove of the ulna or between the two heads of the flexor carpi ulnaris (**cubital tunnel syndrome**)

Question 26

What causes distal lesions of the ulnar nerve?

Answer 26

the nerve can be compressed or cut at the wrist in the tunnel of Guyon deep to the pisohamate ligament fracture of the hook of the hamate (falling onto an outstretched hand) can cut the nerve

Question 27

What muscles does the ulnar nerve innervate?

Answer 27

innervates one and a half of the flexor forearm muscles (flexor carpi ulnaris, medial half of flexor digitorum profundus) and all of the intrinsic hand muscles not innervated by med LOAF also supplies the skin on the dorsal and palmar surfaces of the medial side of the hand, the little finger, and the medial side of the ring finger

Question 28

What deficits are shared by both proximal and distal lesions?

Answer 28

loss of adduction (palmar interossei) and abduction (dorsal interossei) of the fingers with atrophy of the intermetacarpal spaces loss of thumb adduction (adductor policis) loss of PIP and DIP joint extension of the ring and little fingers (3rd and 4th lumbricals) sensory changes on the dorsal and palmar surfaces of the medial side of the hand and the medial one and a half fingers

Question 29

What produces ulnar claw hand of digits 4 and 5?

Answer 29

distal lesions of the median nerve loss of flexion of the MCP joints (interossei, 3rd and 4th lumbricals) loss of extension of the PIP and DIP joints of the ring and little fingers (3rd and 4th lumbricals) medial half of FDP is intact and along with the intact FDS (median nerve), extensor digitorum (ED) and extensor digiti minimi (EDM) (radial nerve) pull the MCP joints of the ring and little fingers into hyperextension and the IP joints into flexion clawing doe snot occur in digits 2 and 3 because the first and second lumbricals are intact

Question 30

What is the difference between ulnar nerve injury and median nerve injury in terms of physical phenotype?

Answer 30

ulnar nerve injury - the patient cannot fully extend the ring and little fingers median nerve injury - the patient is asked to flex the fingers but cannot fully flex the index and middle fingers

Question 31

What are the physiscal mainfestations of proximal lesions of the ulnar nerve?

Answer 31

results in paralysis of the forearm and hand muscles innervated by the ulnar nerve and differ from distal lesions in two ways - there is a **milder ulnar claw hand** of digits 4 and 5 because the **medial half of FDP is paralyzed** and cannot pull the DIP joints into flexion and the **long extensors pull the MCP joints into hyperextension** - there is **weakness of wrist flexion** (flexor carpi ulnaris), when the wrist is flexed it **deviates to the radial side** (median nerve innervated flexor carpi radialis)

Question 32

What does radial nerve injury result in?

Answer 32

fractures of the humeral shaft can cut the nerve compression of the nerve in the radial groove ("Saturdaay night palsy", "honeymoon palsy" and poorly fitting crutches) when the nerve is injured in the radial groove, the triceps is not completely paralyzed because only the medial head is affected

Question 33

What is Saturday night palsy?

Answer 33

falling asleep with one's arm hanging over the arm rest of a chair, compressing the radial nerve at the spiral groove

Question 34

What is honeymoon palsy?

Answer 34

another individual sleeping on and compressing one's arm overnight

Question 35

What is the role of the radial nerve?

Answer 35

innervates the muscles that extend the elbow (triceps), wrist, and MCP joints (posterior forearm muscles) supplies the skin on the posterior surface of the arm (posterior cutaneous nerve of the arm), forearm (posterior cutaneous nerve of the forearm) and radial half of the back of the hand (superficial radial nerve)

Question 36

What are the outcomes of a radial nerve injury?

Answer 36

paralysis of forearm extensor muscles causes a **wrist drop** and inability to extend the MCP joints anesthesia is limited to a small patch on the radial half of the dorsum of the hand because of overlap from adjacent cutaneous nerves

Question 37

What happens if the radial nerve is injured above the radial groove?

Answer 37

triceps will be paralyze and the patient will be unable to extend the elbow, wrist, and MCP joints all three joints are in a flexed position ("chicken wing")

Question 38

What causes injury of the axillary nerves (C5, C6)

Answer 38

fractures of the humeral surgical neck and can cut the nerve dislocations of the shoulder joints can stretch the nerve

Question 39

What happens when the axillary nerve is damaged?

Answer 39

loss of abduction (deltoid) and weakness of lateral rotation (teres minor) of the arm the rounded contour of the shoulder is lost there is anesthesia over the lateral surface of the shoulder

Question 40

What nerve is commonly injured during surgeries such as mastectomy or thoracic surgery?

Answer 40

long thoracic nerve (C6, C6, C7)

Question 41

What is the effect of injury to the long thoracic nerve?

Answer 41

paralysis of serratus anterior - causes loss of protraction and upward rotation of the scapula, which leads to winging of the scapula there is no sensory loss

Question 42

How is the musculocutaneous nerve usually injured?

Answer 42

by penetrating wounds in the axilla

Question 43

What are the effects of a damaged musculocutaneous nerve?

Answer 43

severe weakness of forearm flexion (brachialis, biceps) weakness of supination (biceps) and arm flexion (coracobrachialis, biceps) anesthesia on the lateral surface of the forearm (lateral antebrachial cutaneous nerve)