Ch 29 & 30 Peripheral nerves and entrapment neuropathies Flashcards
(101 cards)
1
Q
How do you classify motor and sensory nerves?
A
A alpha - large extrafusal motor fibres A Beta - Large sensory carrying crude touch, pressure and vibration sense A gamma - small intrafusal motor fibres A delta - fast pain, fine touch B pre ganglionic autonomic C pain, post ganglionic autonomic
2
Q
What is the conduction velocity in 1A fibres?
A
120m/s
3
Q
What is the conduction velocity in C fibres?
A
2m/s
4
Q
All post-ganglionic autonomic fibres are which category?
A
C fibres
5
Q
What is the difference between fasciculations and fibrillation?
A
Fasciculations are coarse muscle contractions that are visible to the naked eye, whereas fibrillations are not visible and require EMG to detect;
6
Q
What muscles does the dorsal scapular nerve innervate?
A
rhomboids levator scapulae Dorsal scapula nerve C (3 for LS) 4, 5 Root
7
Q
Which nerve innervates serratus anterior?
A
Long thoracic C5-7 Root
8
Q
What is the function of supraspinatous?
A
shoulder abduction 15-30 degrees
9
Q
What nerve innervates Supraspinatous?
A
suprascapular C4-6 Superior trunk
10
Q
All 3 trunks in the brachial plexus form which cord?
A
Posterior
11
Q
Which nerve innervates abductor pollicis longus?
A
Posterior interosseus nerve C7,8
12
Q
Which nerve innervates extensor digitorum?
A
Posterior interosseus nerve C7,8
13
Q
What root levels supply Posterior interosseus nerve?
A
C7,8
14
Q
Which peripheral nerve innervates brachioradialis?
A
Radial C5,6
15
Q
Which peripheral nerve innervates biceps brachii?
A
Musculocutaenous C5,6 Lateral cord
16
Q
How do you differentiate brachioradialis motor function from biceps brachii?
A
Biceps tested with hands supinated brachioradialis with thumbs pointing up (pronated)
17
Q
Which muscle in the upper limb receives innervation from all 3 trunks?
A
Triceps (C6,7,8)
18
Q
Which muscles are innervated by anterior interosseous nerve?
A
Radial part of FDP (1+2) Flexor pollicis longus pronator quadratus
19
Q
What sign do you look for with AIN palsy?
A
OK sign
20
Q
What muscles does the median nerve innervate?
A
LOAF Pronator teres, flexor carpi radialis, FDS
21
Q
Which muscle controlling thumb movement is innervated by ulnar nerve?
A
adductor pollicis
22
Q
Which thumb movement is innervated by radial nerve?
A
extension (extensor pollicis brevis and longus)
23
Q
What is the function of superficial peroneal nerve?
A
Foot eversion and plantar flexion (innervates peroneus longus)
24
Q
What is the function of tibial nerve?
A
knee, ankle and toe flexion and ankle inversion
25
Which muscle inverts the ankle?
Posterior tibialis
26
What is the motor function of deep peroneal?
ankle dorsiflexion toe extension
27
Which nerves form the roots of the brachial plexus?
Ventral rami of C5-T1
28
What do the dorsal rami of the brachial plexus supply?
paraspinal muscles
29
Fibrillation potentials on EMG indicate what?
Motor axon loss
30
When is the H reflex used?
Suspected S1 radiculopathy
31
What is a Martin-Gruber anastamosis?
Anastamosis between median and ulnar nerves in the forearm Classification based on the origin from the median nerve: Type a (47.3%) from the branch to the superficial forearm flexor muscles, Type b (10.6%) from the common trunk, and Type c (31.6%) from the anterior interosseous nerve. Pattern II was a duplication of Type c (10.5%)
32
What is Richie-Cannieu anastamosis?
Motor connections from median to ulnar in the palm. Found in 70% of patients.
33
Medical conditions associated with entrapment neuropathies?
Diabetes Acromegaly Hypothyroidism RA PMR Gout
34
What is the mechanism of entrapment in hypothyroidism?
Glycogen deposition in Schwann cells
35
How would you treat occipital neuralgia?
Non surgical options Analgesia (NSAIDs, neuropathic agents) TENS machine Botox Occipital nerve injections (can be done at trigger points at nuchal line or C2 nerve root blocks) Surgical options decompression at C1/2 OCF in cases of AAS If idiopathic - ONS Occipital neurectomy
36
Where are the 2 most common sites of median nerve entrapment?
1. Carpal tunnel syndrome 2. Pronator teres syndrome
37
Why is sensation to the palm in tact in CTS?
Palmar cutaneous branch of median nerve comes off 5.5cm proximal to the styloid process of the radius and travels over the TCL.
38
What is the difference between struthers ligament and struthers arcade?
Struthers Arcade is a normal finding (and in closer proximity to the ulnar nerve) Struthers ligament bridges between medial epicondyle and supracondylar process (an anatomical variant in 0.7-2.7% population)
39
Commonest peripheral nerve entrapment
CTS
40
What proportion of patients with median or ulnar neuropathy also have a cervical radiculopathy?
70%
41
Treatment of CTS?
Conservative - rest, neutral position splints Carpal tunnel injections Surgical decompression
42
What is Kaplan's cardinal line?
Runs from the base of the thumb web space to the hook of the hamate. The superficial palmar arch, which is vulnerable during carpal tunnel surgery, is distal to this line.
43
What are the 2 key branches of the median nerve coming off around the TCL?
Palmar cutaneous branch (usually proximal) recurrent motor branch (usually distal)
44
Where can the ulnar nerve be compressed?
1. Arcade of Struthers 2. Retroepicondylar groove 'ulnar groove' (between medial epicondyle and olecranon 3. Cubital tunnel - distal to ulnar groove between heads of FCU under 'Osborne's ligament' or cubital tunnel retinaculum 4. At the point of exit from the FCU 5. Guyon's canal at the wrist
45
What is Wartenberg's sign?
One of the earliest findings of ulnar nerve entrapment (abducted little finger due to weakness of the third palmar interosseous muscle--patient may complain that the little finger doesn’t make it in when they reach into their pocket)
46
What is Froment's sign?
grasping a sheet of paper between thumb and the extended index finger results in extension of the proximal phalanx of the thumb and flexion of the distal phalanx as a result of substituting flexor pollicis longus (which is spared since it is innervated by anterior interosseous nerve) for the weak adductor pollicis
47
How do you grade severity of ulnar nerve injury?
Stewart classification system 1 - mild - symptoms with no atrophy or weakness 2 - moderate - detectable sensory loss, mild atrophy, power 4 or 4+ 3 - severe - constant symptoms, moderate to marked atrophy and power \<4
48
What are the 2 most important parameters on EMG that predict a good outcome of treatment in ulnar nerve compression?
1. Preserved CMAP amplitude in ulnar hand muscles 2. Conduction block with slowed conduction velocity at elbow (as this suggests demyelination rather than axonal loss)
49
What do you expect to see on EMG for ulnar nerve compression at elbow?
1. NCV \<50m/sec across elbow 2. drop of \>10m/sec comparing below elbow to above elbow 3. CMAP drop \>20%
50
Would you do a simple decompression or transpose the ulnar nerve?
For most cases, simple decompression is recommended over transposition (similar success rate with lower complication rate). Possible exceptions include: bony deformity, nerve subluxation
51
How do you differentiate between radial nerve injury from posterior cord injury of the brachial plexus?
Deltoid and latissimus dorsi spared in radial nerve injury
52
What is Saturday night palsy?
Mid-upper arm compression on radial nerve from improper positioning of arm during sleep
53
How do you differentiate between radial nerve palsy and C7 radiculopathy?
Triceps will be weak in C7 radiculopathy
54
Non-entrapment cause of wrist drop and finger extensor weakness (usually bilateral)
lead poisoning
55
Site of compression of PIN in forearm
Arcade of Fröhse. PIN dives into supinator through this fibrous band.
56
2 main branches of radial nerve
PIN superficial radial nerve
57
Causes of isolated axillary nerve entrapment/injury
1. Shoulder dislocation 2. Sleeping in prone position with arms above the head 3. compression from thoracic harness 4. Injection injury in high posterior aspect of shoulder 5. compression in quadrilateral space (between neck of humerus, long head of triceps, teres major and minor)
58
How does suprascapular nerve entrapment present?
Shoulder pain Atrophy/weakness of supraspinatus and infraspinatus
59
Where is the site of suprascapular nerve entrapment?
suprascapular notch beneath the transverse suprascapular ligament.
60
What is Bernhardt-Roth syndrome?
Meralgia Paresthetica aka swashbuckler's disease
61
What roots comprise the lateral cutaenous nerve of thigh
L2, L3
62
Which nerve is most susceptible to acute compression palsy?
Common peroneal
63
What is the reliable test for damage to motor axons?
Sharp waves and fibrillation potentials occur 1 week - 12 months after damage. Reinnervation is associated with large motor units and polyphasic irregular muscle potentials which indicates chronic denervation.
64
What is the innervation of pronator teres?
Median nerve (C5-T1) - mostly from C6/7 roots
65
In EMG what is the interference pattern?
When the EMG during contraction fully obscures the baseline. Incomplete interference is seen with motor axon loss and is the earliest change seen with EMG
66
What are the EMG changes seen with radiculopathy?
\>day 0 = reduced interference pattern, fasciculation, prolonged H-reflex and reduced F-wave \>7 days = Fibrillation potentials and positive sharp waves in the paraspinal muscles \>14 days = Fibrillation potentials and positive sharp waves in the prox. limb muscles \>21 days = Fibrillation potentials and sharp waves in the distal limb muscles
67
What is a motor unit potential?
Sum of electrical activity from muscle fibres supplied by the same motor neuron
68
When do F-waves appear?
25-55ms. Measured in the muscle after the stimulation whilst CMAPs are after a few ms.
69
What is an F-wave?
Antidromic motor neurone stimulation travels to the prox. horn and causes it to back fire. This then travels to the muscle causing a contraction in a delayed fashion. Amplitude is smaller and more variable depending on how many motor neurons are excited. It is useful for assessing proximal lesions in multiple nerve roots e.g. GBS/CIDP not isolated radiculopathy.
70
What is an H-reflex?
Stimulation of the tibial nerve generates a reflex arc (same as the ankle jerk) and causes gastrocnemius and soleus (triceps surae) activation. It is sensitive for S1 radiculopathy.
71
What causes multifocal demyelination?
Mononeuritis multiplex = paraproteinemia, diptheria and leptosy
72
What causes generalised demyelination?
GBD / CIDP / Lymphoma / Mulitple myeloma / Amiodarone
73
What causes multifocal axonopathy?
Diabetes Vasculitis HIV Sarcoid Amyloidosis Neoplasms
74
What causes generalised axonopathy?
Diabetes Alcohol Drugs Critical illness Multiple myeloma
75
What pattern of injury is seen in nerve entrapment?
Demyelination before axonal degeneration (on when severe)
76
What are the expected features of CTS?
Motor: Prolonged distal motor latencies (demyelination) with a reduced CMAP (axon loss) but normal conduction velocity between the elbow and the wrist. Sensory: Prolonged latencies (onset and peak) and slowed conduction velocity.
77
Where you measure radial nerve motor responses?
Needle or electrode over the extensor pollicus longus muscle (identified by extension of the thumb and palpating the muscle on the dorsal forearm). The radial nerve is stimulated at the lateral epicondyle.
78
What does the involvement of brachioradialis on EMG suggest?
Radial nerve injury proximal to the elbow (as the nerve branches to brachioradialis come off higher than the elbow)
79
In a suspected radial nerve injury, why test deltoid EMG?
As deltoid involvement (axillary nerve) would suggest a lesion of the posterior cord.
80
Why does radial nerve weakness / wrist drop cause weakness of grip?
Bow stringing effect - the hand flexors cannot work in a flexed position.
81
What does an absent radial nerve SNAP suggest?
That the main trunk of the radial nerve is affected not the PIN which is purely motor without a sensory component
82
What NCS/EMG changes occur with C6 radiculopathy?
Paraspinal muscles show acute denervation (telling you it is a radicular component). C5 muscles are unaffected i.e. rhomboids and supra/infraspinatus. Muscles with C6 input such as biceps, deltoid and brachioradialis will be weak.
83
How does a Martin-Gruber anastomosis present?
In patients with CTS, if they have a Martin-Gruber anastomosis, the prox latency is less than the distal latency. This is because the distal latency is slowed by demyelination at the carpal tunnel (because they have CTS). The proximal latency is short because the anastomosis allows the stimulation to travel along the ulnar nerve bypassing the slowing at the carpal tunnel and stimulates the thenar eminance.
84
What is the root supply to vastus lateralis?
Mostly L4 from the femoral nerve
85
What is the main root supply to tensor fascia lata?
Mostly L5 from the superior gluteal nerve (which also supplies gluteus medius and minimus)
86
Why would the CMAP for the common peroneal nerve be larger when stimulated at the knee than the ankle?
If there is an accessory deep peroneal nerve which would stimulated at the knee but not at the ankle.
87
What is the root supply to the adductors?
L2-4 via the obturator nerve
88
What root supply does the adductor reflex test?
L2-4
89
What root supplies inversion and eversion of the ankle?
L5. Inversion via the tibialis posterior (tibial nerve) and Eversion via peroneus longus/brevis (supfl. peroneal nerve)
90
What are the root values for wrist flexion and extension?
C6/7 - flexion C7/8 - extension
91
What are the root values for wrist extension?
C7/8
92
What is nerve supply to psoas?
L1-3 ventral rami
93
What nerve supplies sensation to the femoral triangle?
Genitofemoral nerve (L1/2)
94
Which part of the sciatic nerve forms the tibial nerve?
Ventral division (medial)
95
Which part of the sciatic nerve forms the common peroneal nerve?
Dorsal division (lateral)
96
What is the root supply to the pudendal nerve?
S2,3,4
97
How can you distinguish Guyon's canal from cubital tunnel compression?
Guyon's canal spares the dorsal sensation to the ulnar side of the hand (dorsal ulnar cut branch comes off 5 cm prox to Guyon's canal) and spares the ulnar innervated muscles in the forearm e.g. flex. carpi ulnaris.
98
Where does common peroneal nerve entrapment occur?
Fibular tunnel - due to a fibrous band on perneous longus
99
What is the difference between prox. and distal tibial tarsal tunnel syndrome?
Distal involves the medial and lateral plantar nerves causing chronic heel pain. Prox. compression occurs behind the medial malleolus and causes pain in the sole of foot and toes with clawing due to weakness of the foot intrinsics. Pain worse with dorsiflexion eversion test.
100
What is the inverted radial reflex?
Diminished brachioradialis reflex with reflex contraction of the fingers. Suggests C5/6 pathology
101
What levels do the reflexes in the upper limb test?
Biceps C5 Brachioradialis / supinator C6 Triceps C7
