Upper limb nerve injuries

Question 1

How is lower motor neuron lesion differentiated from upper motor neuron lesion?

Answer 1

Any lesion between where nerve starts in motor cortex + where it synapses at anterior horn cell -> UMN.
Anything from anterior horn cell out -> LMN.
Damage to anterior horn cells within spinal cord -> LMN

Question 2

What are the features of upper motor neuron lesions?

Answer 2

Held in flexed posture if chronic
Increased tone
Pyramidal weakness (flexor muscles stronger than extensors)
Brisk reflexes
Sensory level

Question 3

What are the features of lower motor neuron lesions?

Answer 3

Wasting / fasciculations
Flaccid tone
Weakness in either a myotomal distribution or a peripheral nerve distribution.
Reduced reflexes
Dermatomal or peripheral nerve distribution of sensory loss.

Question 4

What are the 3 anatomical regions for localising lesions?

Answer 4

Roots
Brachial plexus
Peripheral nerve

Question 5

What is a dermatome?

Answer 5

Area of skin supplied by nerve fibres originating from single dorsal nerve root.
There’s considerable overlap of innervation between adjacent dermatomes + considerable anatomical variation.

Question 6

The nerve roots C5-T1 are responsible for which muscle action?

Answer 6

C5: shoulder abduction
C6: elbow flexion
C7: elbow extension, wrist extension + flexion
C8: finger extension + flexion 
T1: finger abduction

Question 7

What are the reflexes and which nerves are they conveyed by?

Answer 7

Biceps reflex –> C5 reflex, musculocutaneous nerve.
Supinator jerk –> C6 reflex, radial nerve.
Triceps jerk –> C7 reflex, radial nerve.
Finger jerk –> C8 reflex, median + ulnar nerve.

Question 8

When are reflexes depressed?

Answer 8

Lower motor neuron lesions

Question 9

What are the consequences of nerve root impingement?

Answer 9

Pain –> radiates / aggravated by neck movement, sensory loss, weakness, reflex loss.
Flexibility of cervical spine protects from fractures or dislocation but may be injury to neural structures –> hyper flexion / extension.

Question 10

What are the types of nerve plexus injuries and which one has the best prognosis?

Answer 10

Avulsion -> tearing of nerves from attachment at spinal cord, surgical repair.
Rupture -> tearing of nerves but not from attachment to spinal cord, surgical repair.
Neuroma -> tumour / growth of nerve tissue from axon or myeloma, surgical repair.
Neurapraxia -> axons remain intact, but myelin damage cause interruption of impulse down nerve fibre, good prognosis.

Question 11

What is a sign of cervical root avulsion?

Answer 11

Flail arm

Question 12

What are the types of brachial plexus injury?

Answer 12

Trauma -> Erb-Duchenne type paralysis: avulsion of C5, C6 roots. Klumpke paralysis: avulsion of C8, T1 roots.
Cancer -> lung cancer: pancoasts tumour, radiotherapy
Inflammatory -> brachial neuritis.
Structural -> thoracic outlet syndrome.

Question 13

What is Erb’s palsy and which muscles does it affect?

Answer 13

Upper plexus palsy, C5/C6 innervated muscles, superior trunk of brachial plexus, adults -> blow to shoulder.
Weak muscles -> biceps (flexes arm), brachioradialis (flexes arm in semi-prone position), deltoid (abducts arm),
supraspinatus (abducts arm), supinator (externally rotates arm).
Arm can’t be elevated, abducted, external rotated, flexed at elbow.
Fingers unimpaired, hand works but arm doesn’t.

Question 14

What is Klumpke’s palsy?

Answer 14

Clutching for object when falling from height -> inferior trunk plexus injury of C8/T1.
Involves trunk that supplies median + ulnar nerves.
Can’t flex wrist or fingers.
Weakness of all small muscles of hand, sensory loss of hand + inner border of forearm.
May lead to a claw hand, arm works, hand doesn’t.

Question 15

What is metastatic brachial plexopathy?

Answer 15

Pancoast tumour –> infiltration of lower brachial plexus
Pain in shoulder girdle + inner arm.
Ipsilateral horners syndrome.

Question 16

What is radiation induced brachial plexopathy?

Answer 16

Mean 6 yrs post radiation
Treatment for breast, lung cancer + lymphoma
Pain not consistent feature
Predilection for upper brachial plexus

Question 17

What is idiopathic brachial neuritis (Parsonage – Turner Syndrome) and how is it treated?

Answer 17

Aetiology not clear, infectious, post-infectious.
Severe pain over days. as pain diminishes, followed by weakness + wasting (motor>sensory).
Typically monophasic, rarely bilateral.
MRI -> thickening + enhancement.
NCS / EMG for prognostication.
Analgesia, physiotherapy, limited evidence for steroids

Question 18

What is thoracic outlet syndrome?

Answer 18

Variations in anatomy cause compression sites:
Between anterior + middle scalene muscles
Beneath clavicle in costoclarvicular space
Beneath tendon of pectoralis minor

Question 19

What are the features of neurogenic causes of thoracic outlet syndrome?

Answer 19

Paresthesia, numbness, weakness
Not localised to specific nerve distribution
Reproducibly aggravated by elevation or sustained use of arms or hands.

Question 20

What are the features of vascular causes of thoracic outlet syndrome?

Answer 20

Forearm fatigue within minutes of use.
Swelling, cyanosis
Collateral venous patterning over ipsilateral shoulder, chest wall + neck.
Rarely pain, pallor + coldness (arterial involvement).
Lower BP on affected arm, diminished distal pulses.

Question 21

How might the long thoracic nerve be injured?

Answer 21

Blows or pressure in posterior triangle of neck, radical mastectomy -> winged scapula.
Supplies serratus anterior -> pulls medial border of scapula to posterior thoracic wall + stabilises it.

Question 22

What are the 2 common sites of median nerve compression?

Answer 22

Wrist (Carpel tunnel syndrome -> thenar atrophy), elbow

Question 23

What does the median nerve innervate?

Answer 23

Hand muscles -> Lateral 2 lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (LOAF).

Question 24

What are the causes of carpal tunnel syndrome?

Answer 24

Diabetes, pregnancy, hypothyroidism, rheumatoid arthritis, repetitive strain

Question 25

Where does the anterior interosseous nerve arise from, what is it prone to, how may it be damaged?

Answer 25

Median nerve just above elbow.
Prone to compression between 2 heads of pronator teres.
Gripping tightly with forced pronation
Prolonged use of a screwdriver, careless blood taking

Question 26

What is anterior interosseous nerve syndrome?

Answer 26

Pure motor branch of median nerve.
Weakness in flexors of ip joint of thumb (flexor policis longus) + dip joints of index + middle fingers (flexor digitorum profundus).
Weakness of pronation

Question 27

What are the differences in sensory innervation of the median nerve in the forearm versus carpal tunnel?

Answer 27

Damage proximal to where palmar cutaneous branch comes off (forearm) -> damage to palm + fingers.
Distal in carpal tunnel -> tips of fingers also on dorsal side.

Question 28

What are the effects of a higher lesion in the upper limb of ulnar nerve palsy?

Answer 28

Paralysis of ulnar half of flexor digitorum profundus, interossei + lumbricals. ring + little fingers aren’t flexed, no claw.

Question 29

What are the effects of a lower lesion at the wrist of ulnar nerve palsy?

Answer 29

Flexion at DIP + PIP, interossei paralysed.

hyperextension at MCP, lumbricals paralysed.

Question 30

What are the sensory consequences of ulnar nerve lesions?

Answer 30

Lesion above dorsal cutaneous branch -> loss of sensation on 1.5 fingers + palm on dorsal + ventral side. Below dorsal cutaneous branch -> dorsum spared
Below palmar cutaneous branch -> palms spared

Question 31

What are the common causes of ulnar nerve damage?

Answer 31

Occupation, cycling, rheumatoid arthritis

Question 32

What is a sign of ulnar nerve palsy?

Answer 32

Weakness of adductor pollicis brevis -> Froment’s sign

Question 33

What is the best way to distinguish between C8 and the ulnar nerve?

Answer 33

Motor examination:

C8 -> all finger extensors (radial nerve), flexor digitorum profundus of index/middle (median nerve).

Question 34

Which muscles are affected in radial nerve palsy?

Answer 34

All extensors. radial nerve damage rarely causes extensive sensory loss. anatomical snuff box numbness.

Question 35

What is the purpose of nerve conduction studies?

Answer 35

Determines amplitude + velocity of peripheral nerve.
Axonal loss -> decrease in amplitude
Demyelination -> decrease in velocity
Needle EMG measures electrical activity of muscle during voluntary contraction. pattern helps distinguish lesion arising from nerve vs muscle.