Peripheral Nerve Flashcards
1
Q
What is the mnemonic for the terminal branches of the brachial plexus from top to bottom?
A
MARMU
Musculocutaneous Axillary Radial Median Ulnar
See: https://www.youtube.com/watch?v=gTas7ijp0YE
2
Q
Which nerves come off the roots of the brachial plexus?
A
- Dorsal Scapular (C5)
2. Long Thoracic Nerve (C5, C6, C7)
3
Q
Which nerves come off the trunks of the brachial plexus?
A
- Suprascapular (C5, C6)
- Nerve to subclavian (C5, C6)
Both come off the superior trunk. No other trunks give rise to nerve branches.
4
Q
Which nerves come off the divisions of the brachial plexus?
A
None
5
Q
Which nerves come of the cords off the brachial plexus?
A
Lateral Cord:
1. Lateral Pectoral (C5, C6, C7)
Posterior Cord (smallest, little contribution from T1):
- Upper Subscapular (C5-T1)
- Middle Subscapular (C5-T1)
- Lower Subscapular (C5-T1)
Medial Cord:
- Medial Pectoral Nerve (C8, T1)
- Medial Brachia-cutaneous (C8, T1)
- Medial Antebrachial cutaneous (C8, T1)
6
Q
Suprascapular nerve innervates which muscles?
A
Supraspinatus and infraspinatus muscles
the most proximal muscles innervated by the brachial plexus
7
Q
The cords are named lateral, posterior and medial in relation to what anatomic structure?
A
Axillary artery
8
Q
The lateral cord, which forms the lateral head of the median nerve carries which modalities?
A
Sensory and Motor (2 muscles only: pronator teres and flexor carpi radialis)
ALL SENSORY FUNCTION OF MEDIAN NERVE COMES FROM THE LATERAL CORD
9
Q
The medial head of the median nerve carries all motor function and no sensory and arises from what cord?
A
Medial cord
Medial cord is pure motor
10
Q
The roots and trunks lie in which triangle of the neck?
A
The posterior triangle
Between the posterior border of the SCM and the clavicle
11
Q
The cords lie where?
A
In the axilla
12
Q
The divisions lie where?
A
Below the medial 2/3 of the clavicle (between the clavicle and the 1st rib)
13
Q
What is the longest component of the brachial plexus?
A
The cords
14
Q
The brachial plexus divides into its terminal branches where?
A
The lower axilla
15
Q
How can you divide the brachial plexus surgically?
A
Supraclavicular - Roots and Trunks
Infraclavular - Divisions, Cords and Branches
16
Q
Trauma is most likely to affect which part of the brachial plexus?
A
The upper plexus (upper trunk or lateral cord)
ie. Erb’s palsy (waiter’s tip)
17
Q
Non-traumatic pathologies are more likely to affect which part of the brachial plexus?
A
The lower plexus (ie. Pancoast tumour or thoracic outlet syndrome, Klumpke’s palsy)
18
Q
Describe brachial plexitis
A
Stereotyped clinical syndrome characterized by acute onset of pain in the shoulder and upper arm followed by weakness then atrophy of variable severity. It predominately affects the upper arm and shoulder.
19
Q
The phrenic nerve arises from the phrenic nucleus at C3-C5, what does it do?
A
- Carries sensory fibres from the diaphragm, pericardium and pleura
- Motor innervation of the unilateral diaphragm
3.
20
Q
The phrenic nerve is commonly involved in which neurologic conditions?
A
- ALS
- Diabetes
- Mediastinal radiation
- Sarcoid
- TB
- Lyme disease
- Acute and chronic inflammatory demyelinating polyneuropathies
21
Q
The long thoracic nerve (C5, C6, C7) does what?
A
Supplies:
1. Serratus anterior (Winged scapula)
Can be injured by heavy backpacks or mastectomy surgery
22
Q
The dorsal scapular nerve (C5) does what?
A
Supplies:
1. Rhomboid muscles (lateral displacement of vertebral border of scapula and lateral displacement of the inferior border of the scapula)
23
Q
The suprascapular nerve (C5, C6) does what?
A
Supplies:
- Supraspinatus
- Infraspinatus
Note: runs posteriorly through the suprascapular notch (beneath the supra scapular ligament) to innervate the supraspinatus muscle, wraps around the glenoid process and travels inferiorly to innervate the infraspinatus.
24
Q
The axillary nerve (C5, C6) does what?
A
Supplies:
- Deltoid muscle
- Teres minor
- Sensory to the skin over the deltoid
Runs around humeral head (circumflex artery) through the quadrangular space then divides into anterior and posterior branches.
25
The musculocutaneous nerve (C5, C6, C7) does what?
Supplies:
1. Coracobrachialis
2. Biceps brachii
3. Brachialis (part)
4. Sensation of the lateral forearm from elbow to thenar eminence
Travels in the groove between the deltoid and the pectoralis. At the elbow, pierces the deep fascia lateral to the biceps tendon and continues as the lateral antebrachial cutaneous nerve.
26
Describe the track of the median nerve in the arm.
1. Lateral and medial cords form the median nerve at the brachial plexus.
2. The medial and lateral divisions fuse to form 1 trunk which travel together in the upper arm without splitting down to the elbow.
3. At the elbow, branches from the lateral division are given off to innervate the pronator teres and flexor carpi radialis.
4. The main trunk passes through two heads of the pronator teres beneath an aponeurosis connecting the two heads of the flexor digitorum superficialis (potential entrapment).
5. Distal to the pronator teres, the nerve gives off the Anterior Interosseous Nerve which runs along the interosseous membrane and innervates the median head of the flexor digitorum profundus, the flexor pollicis longus, and the pronator quadratus.
6. The main trunk of the median nerve continues down the forearm giving branches to palmaris longus and flexor digitorum superficialis.
7. The main nerve crosses from the distal forearm to the hand through the carpal tunnel.
8. 5-8cm proximal to the wrist, the palmar cutaneous branch comes off the main trunk, travels in its own passage in the transverse carpal ligament, and provides sensation to the thenar eminence. IT DOES NOT TRANSVERSE THE CARPAL TUNNEL.
9. Distal to the tunnel, the median nerve gives off the recurrent thenar motor branch, which curves backwards and radially to innervate abductor pollicis brevis, opponens pollicis, and the lateral head of the flexor pollicis brevis.
10. The nerve ends by giving terminal branches to the 1st and 2nd lumbricles and provides sensation to the 1st, 2nd, 3rd, and medial half of the 4th fingers.
See: http://www.medianmusic.com/MedianNerve.html
27
The anterior interosseous nerve has no sensory cutaneous branches.
True or False?
TRUE!
It only supplies motor to 3 muscles:
1. flexor digitorum profundus
2. flexor pollicis longus
3. pronator quadratus
28
Describe the boundaries of the carpal tunnel.
The wall and floor are formed by the carpal bones.
The roof is formed by the transverse carpal ligament.
The transverse carpal ligament evolves from the antebrachial fascia at the level of the wrist crease and extends 4-6cm distally.
29
What are the 10 components of the carpal tunnel?
4 tendons of flexor digitorum superficialis
4 tendons of flexor digitorum profundus
1 tendon of flexor pollicis longus
1 median nerve
30
What is the differential diagnosis for Carpal Tunnel Syndrome?
1. C6 Radiculopathy
2. Upper brachial plexopathy
3. Proximal median neuropathy
4. Thoracic outlet syndrome
5. Anterior interosseous syndrome
31
Describe the features of anterior interosseous nerve paralysis.
Inability to flex the distal phalanx of the thumb (flexor pollicus longus) or index finger (flexor digitorum profundus). So instead of making a circle with their thumb and index finger, they make a triangle.
32
Differentiate between C6 radiculopathy and carpal tunnel syndrome.
Neck and shoulder pain, weakness of C6 innervated muscles, reflex changes, sensory loss restricted to the thumb.
33
Describe the track of the ulnar nerve in the arm.
1. Continuation of the medial cord of the brachial plexus.
2. As it exits the thoracic cavity, it passes through the axilla, to the upper arm, lying medial to the brachial artery in a common neurovascular sheath with the median nerve and the medial brachial and medial antebrachial cutaneous nerves.
3. At the level of the coracobrachialis, the ulnar nerve leaves the sheath and pierces the medial inter muscular septum to gain the posterior compartment of the arm.
4. The nerve then descends towards the elbow in a groove alongside the medial head of the triceps in a sheath (arcade of Struthers).
5. After piercing the medial inter muscular septum, the nerve slants distally and medially and then transverses the retroepicondylar groove (aka ulnar groove) between the medical epicondyle and the olecranon process.
6. It then passes beneath the humeroulnar aponeurotic arcade, which is a dense aponeurosis joining the humerus and ulnar heads of origin of flexor carpi ulnaris, which typically lies 1-2cm distal to a line connecting the medial epicondyle and olecranon process.
7. After passing under the HUA, the nerve runs through the belly of the flexor carpi ularis.
8. Then exits through the deep flexor pronator aponeurosis, lining the deep surface of the muscle 4 - 6 cm beyond the medial epicondyle and then runs distally toward the wrist.
9. The ulnar palmar cutaneous branch arises in the mid-distal forearm. It enters the hand superficial to Guyon's canal and supplies sensation to the skin of the hypothenar eminence.
10. The large, dorsal ulnar cutaneous branch, leaves the main trunk 5-10 cm proximal to the wrist, to wind posteriorly and emerge on the dorsal surface of the wrist to provide sensation to the dorsal ulnar surface of the hand and small finger.
11. The ulnar nerve enters the hand through Guyon's canal.
12. As it emerges from the canal, a branch is given to palmaris brevis and then the nerve branches into the superficial terminal sensory divisions and deep palmar divisions.
13. The deep branches innervate the interosseous muscles and break up into terminal branches upon reaching the adductor pollicis and 1st dorsal interossei.
14. The deep head of the flexor pollicis bravis is usually supplied by a short twig from the terminal branch to the adductor pollicis.
34
Describe the boundaries of Guyon's canal.
Proximal Floor - flexor retinaculum/flexor carpal ligament
Distal floor - piso-hamate ligament
Roof - volar carpal ligament
Laterally - hook of hamate
Medially - flexor carpi ulnaris tendon and pisiform
35
What are the sites of entrapment of the ulnar nerve?
1. Retroepicondylar groove (Ulnar Groove)
| 2. Humeroulnar aponeurotic arcade (Cubital tunnel syndrome)
36
List the muscles innervated by the ulnar nerve (proximally to distally).
1. Flexor carpi ulnaris
2. Flexor digitorum profundus (digits 3 and 4)
3. Abductor, opponens, and flexor digiti minimi
4. 3rd and 4th lumbircals
5. Dorsal and palmar interossei
6. Adductor pollicis
7. Flexor pollicis brevis (medial head)
37
List the muscles innervated by the median nerve (proximally to distally)
1. Pronator teres
2. Flexor carpi radialis
3. Flexor pollicis longus (AIN)
4. Flexor digitorum profundus (AIN)
5. Pronator quadratus
6. Flexor digitorum superficialis
7. Palmaris longus
8. Abductor pollicis brevis
9. Opponens pollicis
10. Flexor pollicis brevis (lateral head)
11. 1st and 2nd lumbricals
38
List the muscles innervated by the radial nerve (proximally to distally)
1. Triceps
2. Brachioradialis
3. Extensor carpi radialis longus
4. Extensor carpi radialis brevis
5. Supinator (PIN)
6. Extensor carpi ulnaris (PIN)
7. Extensor digitorum (PIN)
8. Extensor digiti minimi (PIN)
9. Extensor pollicis longus (PIN)
10. Extensor pollicis brevis (PIN)
11. Extensor indicis (PIN)
12. Abductor pollicis longus (PIN)
39
What leads to Saturday night palsy?
Compression of the radial nerve at the Spiral Groove (posterior mid shaft of humerus)
40
What's the most common site of Ulnar Nerve entrapment?
Head of flexor carpi ulnaris at the ulnar groove
41
What is the most common site of Radial Nerve entrapment?
Between the heads of the supinate at the elbow.
42
The Lumbar portion of the lumbosacral plexus originates from which roots?
L1-L4 (anterior primary rami) and lies in or just anterior to the posts muscle
43
The lumbosacral trunk arises from?
L4-L5
44
What does the lumbosacral trunk do?
It joins the lumbar plexus and the sacral plexus
45
Sacral plexus arises from which roots?
S1-S3
46
The lumbosacral plexus spans which roots?
L1 - S3 continuously
47
The sacral portion of the LSP lies where?
Lateral pelvic wall between the piriformis and major vessels
48
The major motor nerves which arise from the LSP are?
1. Femoral n.
2. Obturator n.
3. Sciatic n. (branches tibial and common perineal)
4. Superior gluteal n.
5. Inferior gluteal n.
6. Pudendal n.
49
The major sensory branches of the LSP are?
1. Saphenous n. (continuation of femoral n.)
2. Iliohypogastric n.
3. Ilioinguinal n.
4. Genitofemoral n.
5. Lateral femoral cutaneous n.
50
What is the course of the lateral femoral cutaneous nerve?
Arises from the lumbar plexus, courses around the pelvic brim and exits beneath the inguinal ligament adjacent to the anterior superior iliac spine (ASIS).
51
What pathologies can affect the LSP?
1. Diabetes (Most common)
2. Neoplasms
3. Retroperitoneal hemorrhage
4. Post-radiation plexopathy
52
What is diabetic amyotrophy (diabetic lumbosacral rediculoplexus neuropathy)?
Syndrome of pain proximal bilaterally and very asymmetrical weakness and weight (muscle) loss.
53
Describe the femoral nerve.
1. Largest nerve in the LSP
2. Formed within the psoas muscle
3. Arises from the _posterior_ divisions of the anterior primary rami of L2-L4
4. Leaving the covering of the psoas it then runs between the psoas and the iliacus muscles
5. It exits the pelvis beneath the inguinal ligament lateral to the femoral vessels
54
What does the femoral nerve supply (motor and sensory)?
Motor
1. Psoas
2. Iliacus
3. Sartorius
4. Pectineous
5. Quadriceps
Sensory
1. Anterior femoral cutaneous n.
2. Medial femoral cutaneous n.
3. Saphenous n. (terminating branch) - supplies medial aspect of leg and foot
55
What are causes of femoral nerve neuropathy?
1. Pelvic tumours
2. Psoas abscess/hematoma
3. Fractures of pelvis or upper femur
4. Aneurysms of the femoral artery
5. Penetrating wounds
6. Diabetic mononeuropathy
7. Labour (lithotomy position)
8. Pelvic surgery
56
Describe the obturator nerve.
1. Arises from the lumbar plexus _anterior_ division of the anterior primary rami of L2-L4.
57
What does the obturator nerve innervate?
Motor
1. Adductors of the thigh
2. Gracilis
3. Obturator
Sensory
1. Superomedial aspect of the thigh
58
Describe the lateral femoral cutaneous nerve (LFCN).
1. Arises from the _posterior_ divisions of anterior primary rami of L2-L3.
2. Supplies sensation to anterior lateral aspect of thigh.
59
What is Meralgia Paresthetica?
Pain, paresthesia and sensory loss in the distribution of the LFCN
60
What is the site of entrapment of the LFCN?
1. Under or through the inguinal ligament just medial to ASIS
2. Where it pierces the fascia lata
61
What are the risk factors of Meralgia Paresthetica?
1. Weight gain
2. Pregnancy
3. Ascites
4. Trauma
5. Belt pressure
6. Diabetes
62
Describe the sciatic nerve.
1. From its origin, has tibial (medial) and peroneal (lateral) divisions.
2. Arises from the lower part of the lumbar plexus and fuses with parts of the sacral plexus.
3. Usually exits the pelvis beneath the piriformis muscle through the greater sciatic foramen
4. The nerve courses in close proximity to the posterior aspect of the hip joint and then enters the thigh
5. Through its course in the thigh innervates the hamstrings and some innervation to the adductor magnus
63
What nerves exit the pelvis through the greater sciatic foramen?
1. Sciatic nerve
2. Superior gluteal nerve
3. Inferior gluteal nerve
The piriformis can compress here
64
The sciatic nerve is a sheath which carries what?
The peroneal and tibial nerves
65
Where do the common peroneal and tibial nerves divide?
At the level of the knee
66
What is the only portion of the hamstring which is innervated by the common peroneal nerve?
Short head of the biceps femoris (otherwise, hamstrings are all tibial)
67
Describe the course of the common peroneal nerve.
After the bifurcation within the popliteal fossa, it moves laterally around the fibular head and then descends towards the foot.
68
Describe the course of the tibial nerve.
Descends in the midline within the popliteal fossa down the posterior aspect of the leg to innervate the gastrocnemius and soleus. In its proximal course, it gives a sural communicating branch which joins its fellow from the common peroneal nerve to form the sural nerve.
Distally, it travels posterior to the medial malleolus under the flexor retinaculum (forming the roof of the tarsal tunnel). The tibial nerve terminates by dividing into: 1. medial and 2. lateral plantar nerves (supplying the abductors and short flexors of the toes and sensation to sole).
69
How is the sural nerve formed?
By two branches which come off the common peroneal and the tibial nerves after the bifurcation in the popliteal fossa.
70
Describe the sural nerve.
After its formation, it moves lateral as it runs distally and then pierces the deep fascia to emerg into a superficial position at about 15cm proximal to the lateral malleolus.
Then it curves around the lateral malleolus to supply the skin of the lateral foot.
71
How do you differentiate a lesion of the sciatic nerve vs. the common peroneal nerve by EMG?
If EMG demonstrates abnormalities in the short head of the biceps femoris, lesion is in the sciatic nerve not the common peroneal.
72
What is piriformis syndrome?
Compression of the sciatic nerve by the piriformis muscle as it exits the pelvis at the greater sciatic foramen. The existence of this syndrome is controversial.
73
Sciatic nerve compression externally such as having a heavy wallet in your back pocket is termed what?
Pistol packers palsy
74
What are the roots of the common peroneal nerve?
L5 major, less from L4 and S1 (L4, L5, S1)
75
Describe the peroneal nerve after it bifurcates from the sciatic in the popliteal fossa.
1. Gives off a branch to the sural nerve and a branch forming the lateral cutaneous nerve of the calf.
2. Winds around the fibular head.
3. Pierces the peroneus longs muscle and divides into the superficial and deep branches.
76
What muscles are supplied by the superior branch of the peroneal nerve?
1. Peroneus longus
2. Peroneus brevis
Terminates as a sensory branch which supplies the dorsum of the foot.
77
What muscles are supplied by the deep branch of the peroneal nerve?
1. Tibialis anterior
2. Peroneus tertius
3. Peroneus longus
4. Short toe extensors
Supplies sensation to the webbed space between the 1st and 2nd toes.
78
An accessory peroneal nerve arises in what percentage of the population?
20% (a branch from the superficial peroneal, passing behind the lateral malleolus and innervates the lateral portion of the extensor digitorum brevis)
79
Features of common peroneal neuropathy at the fibular head include?
1. Weakness of dorsiflexion of the foot and toes
2. Weakness of ankle eversion
Foot Drop
80
Differentiate between common peroneal neuropathy at the fibular head and L5 radiculopathy.
L5 Radiculopathy - back and leg pain with weakness of foot inversion, +SLR, depressed medial hamstring reflex
Common peroneal neuropathy - absence of pain, weak foot eversion
81
What forms the tibial nerve?
The anterior division of the anterior rami of L4-S2 (some say L4-S3)
82
The tibial nerve supplies what?
Motor
1. The long head of biceps femoris
2. Semimembranosus
3. Semitendinosus
4. Gastrocnemius
5. Popliteus
6. Soleus
7. Plantaris
8. Tibialis posterior
9. Flexor digitorum longus
10. Hallicus longus
Sensory
1. Sensation from posterolateral aspect of leg and ankle
2. Sural nerve territory
3. Calcaneal nerve supplies sensation to the posterior and medial aspect of the plantar surface of the heel
4. Medial and lateral plantar nerves supply the medial and lateral aspects of the plantar surface of the foot
83
What are features of tibial neuropathy?
1. weakness of plantar flexion or inversion of foot
2. weakness of flexion or abduction of the toes
3. Loss of ankle reflex
Uncommon since nerve is located deep
84
Sites of entrapment of the tibial nerve.
1. By the tendinous arch at the origin of the soleus muscle
2. Fibrous band between the heads of the gastrocnemius muscle.
3. At the tarsal tunnel, compression by the flexor retinaculum behind the medial malleolus (tarsal tunnel syndrome)
85
In the cervical spine, what is the relationship of the exiting nerve roots to the vertebral artery as they exit the foramen?
Nerve roots run posterior to the vertebral artery in the C-Spine
86
What are the attachment points of the Scalenus anterior muscle?
Anterior tubercle of the transverse processes (C3-C6) and the inner border first rib (minority to second rib).
87
What are the attachment points of the Scalenus medius muscle?
Largest of 3 muscles. Posterior tubercle of the transverse process (C2-C7) and the upper surface of the first rib between the tubercle and subclavian groove.
88
What is the relationship of the subclavian vein, artery and lower trunk of the brachial plexus to the scalenus anterior muscle?
Anteriorly to posteriorly ---> Vein, Muscle, Artery, Lower Trunk
89
What are the fascial planes of the neck from superficial to deep?
Superficial investing, pretracheal, prevertebral
http://body-disease.com/wp-content/uploads/2013/02/Transverse-section-of-the-neck-at-the-level-of-C6.jpg
90
Describe the supraclavicular incision to the trunks of the brachial plexus.
An incision is made posterior and inferior to the ear, behind the SCM and in front of the Trapezius, downward to the middle of the clavicle. Then, the incision is taken laterally along the superior border of the clavicle.
91
Describe the utility of the phrenic nerve in the supraclavicular approach to the trunks of the brachial plexus.
The phrenic nerve sits on top of the scalenus anterior muscle and following it superiorly, will lead directly to the upper trunk of the brachial plexus.
92
Describe the contents of the triangular space medial and inferior to the scalenus anterior muscle.
The boundaries are longus colli medially, scalenus anterior laterally, and subclavian artery inferiorly. The contents of this triangle are: 1) stellate ganglion 2) vertebral artery 3) Thyrocervical vessels 4) suprapleural membrane and 5) pleura
93
What are the epineurium, mesoneurium, perineurium, and endoneurium?
Epineurium - external nerve sheath, made of connective tissues with abundant collagen, elastic fiber, abundant blood vessels and protects nerve against compression.
Mesoneurium/Paraneurium - Attached to the epineurium and contains capillaries which give blood supply to the nerve. It's traversed by vascular channels. It allows nerves to glide between tissue planes during physiological movement.
Perineurium - directly around each fascicle constituted by perineurial cells in between circular, oblique, and longitudinal strands of collagen fibres. It is the "Blood-Nerve Barrier". In trauma, fibroblasts within the perineurium form neuromas as a futile attempt at repair.
Endoneurium - provides connective tissue support for the nerve fibres. It surrounds each myelinated fibre and groups of unmyelinated fibres.
94
How much stretch can a nerve withstand?
About 12% is viable
At 16% ischemia occurs
At 8% venous congestion occurs
95
What is neurapraxia?
"Nerve not working". A focal conduction block but distal conduction is preserved. Denotes a nonfunctional nerve condition because of a focal, electrophysiologic conduction block with minimal macroscopic or microscopic anatomic disturbance of a nerve.
96
At what time point is muscle thought to be irreversibly degenerated/atrophic?
18 months
97
What is the time point where ideal reinnervation should occur?
1-3 months post injury, some success within 1 year, no success after 3 years.
98
What are neurotrophins?
Peripheral nerve growth factors
99
What order do nerve modalities recover after repair?
1. Pain
2. Touch
3. Motor
100
What is axonotmesis?
"Axons cut". Denotes a discontinuity of axons with intact guiding matrix. In this condition, the nerves outer appearance is in continuity, but the axons are ruptured and the distal axons degenerate. Because the ensheathing structures and the basal lamina of the Schwann cell are left intact, sprouting axons are left with a guiding matrix.
101
What is neurotmesis?
"Nerve cut". Denotes a nerve that may be severed or apart or that may still be in gross continuity but has severe disruption of the intramural connective tissue layers and axons.
102
What is the only nerve injury that absolutely requires repair for recovery to occur?
Neurotmesis
103
What are the stages of chronic nerve compression?
1. Edema and ischemia
2. Localized demyelination
3. Diffuse demyelination
4. Wallerian degeneration
104
What are the stages of acute nerve injury?
1. Neuronal (cell body) reaction
i. death - a minority of neurons die d/t unknown factors
- lack of end-organ trophic factors
ii. central chromatolysis
- alteration in function: from maintenance/synaptic transmission axonal repair/reconstruction
- Nissl substance disappears
- nucleus becomes eccentric
- cell body enlarges
2. Distal segment: Wallerian degeneration
- degenerative morph. & molecular changes in the distal nerve segment that affect axons, myelin, Schwann
cells, and endoneurial connective tissue which clears debris and prepares for axonal regeneration
i. axonal degeneration
- starts in hours (Ca-dependent proteolysis)
ii. myelin degradation & phagocytosis
- macrophages (mostly) and some Schwann cells
- may take several months
iii. Schwann cell proliferation (this proliferation under old basal lamina “bands of Bungner” is important for guiding regrowing axons)
- in response to macrophage cytokines, myelin debris, axonal membrane
- peaks at 3 days, declines over weeks
- then a second wave with axonal regeneration
iv. connective tissue changes
- Formation of bands of Bungner from basal lamina of endoneurial tubes
- in Grade 3 injury fibroblast proliferation with endoneurium disruption
3. Proximal segment
i. die-back - to at least next node of Ranvier
ii. regeneration - sprouts form within hours several per axon
- ends of the sprouts (growth cones) dilated with sER, mitoch., microtubules
- sample the environment
- tend to grow between Schwann cell and basal lamina
- affected by:
1. neuronal response to injury
2. - neurotrophic factors .eg., NGF (nerve GF), FGF, IGF-1, CNTF (ciliary neurotrophic factor), neurotrophin 3
3. - neurotropism ie. contact guidance (with basal lamina)
4. - inhibitory molecule esp. myelin-associated inhibitors in CNS “myelin breakdown products” (in PNS, myelin is quickly removed by macrophages and Schwann cells unlike CNS)
4. End-organ response
- denervation hypersensitivity
- atrophy of muscle
- over time, loses ability to receive nerve fiber input (about 2 yrs ( or 18 months) for muscle)
105
What are the Bands of Bungner and when do they occur?
Proliferating bands of Schwann cells which occur in the reparative phase of axonotmesis.
106
Which Sunderland classifications of injury get neuroma-in-continuity?
Grade III and IV (because the basal lamina is intact)
107
How do you manage an open injury where the nerve has a lesion in continuity?
medical management & follow-up with electrodiagnostics, clinical exam, imaging
108
How do you manage an open injury where the nerve is cut sharply?
if clean cut: perform end-to-end suture repair
109
How do you manage an open injury where the nerve is cut bluntly?
if ragged or contused ends or d/t blunt force trauma: delayed repair (wait 2-3 weeks) – place tag sutures on ends (to localize and to prevent retraction)
- allows demarcation of healthy stumps
- resect back to healthy fascicular pattern
- repair +/- nerve grafts
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What is the most common cause of a closed nerve injury?
Stretch or compression
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What's the general management of closed injury?
- early surgery if worsening deficit d/t enlarging hematoma (or other compressive lesions such as callus (hardened part of skin or soft tissue due to irritation..))
- otherwise, follow with clinical exam, electrodiagnostics (EMG, NCS, SSEP), imaging
112
How is closed neuropraxia managed?
- can be diagnosed at 3 weeks based on EMG, NCS recovery seen (never any signs of denervation, so that's why the EMG is normal)
- will recover within weeks
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How is closed axonotmesis managed?
- can diagnose if PARTIAL nerve injury with DENERVATION on EMG
- variable recovery over weeks-months
114
Define nerve conduction study.
Stimulation of a nerve and recording of a response from a WELL DEFINED motor point.
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What's CMAP?
Compound Motor Action Potential - summation of a group of almost simultaneous action potentials from several muscle fibres in the same area.
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What is measured in a NCS?
Amplitude (in mV)
Duration
Distal motor latency (ie. conduction velocity)
Wave form
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What's a conduction block?
A reduction in the proximal CMAP amplitude of at least 20% compared with the distal amplitude.
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What's temporal dispersion?
A reduction in proximal CMAP amplitude compared with distal CMAP amplitude when the proximal duration increases by more than 20%.
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What do you see in motor neuron axon loss on NCS?
Decreased amplitude throughout the nerve regardless of location of stimulus.
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What do you in conduction block on NCS?
Decrease in amplitude when stimulating proximal to the lesion with restoration of amplitude when stimulating distal to the lesion.
121
What is SNAP?
Sensory nerve action potential (equivalent of CMAP)
| Like CMAP, also has you amplitude, duration, latency and wave form.
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What do you see in destructive lesions distal to the dorsal root ganglion of a sensory nerve?
Wallerian degeneration results in less axons firing and thus decreased amplitude.
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What do you see in demyelinating lesions distal to the dorsal root ganglion of a sensory nerve?
Increased latency/duration as well as possible amplitude changes.
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What do you see in lesions proximal to the dorsal root ganglion of a sensory nerve?
SNAP is completely normal however clinically the patient has sensory loss.
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What is distal latency?
Length of time from stimulation to response.
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What is conduction velocity?
Calculated by comparing the latencies between a more proximal and a more distal stimulation site.
Divide the distance between the two sites by the difference in the latencies (proximal to distal).
It is more commonly computed for motor conduction since it's easier to find two sites.
Cold will affect velocity.
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What do you see in demyelinating disease on NCS?
Increase duration, increase in distal latency, and amplitude can be normal or decreased.
In motor specifically, you see a decreased conduction velocity.
128
What do you see in conduction block on NCS?
Decreased amplitude. If complete, no stimulation possible above the lesion if incomplete decreased amplitude.
129
What do you see in axonal loss on NCS?
Decreased amplitude, normal distal latency, and normal duration.
130
What are some limitations of NCS?
1. Only good for determining velocities of large motor fibres only.
2. Wide range of normal values and these vary by age and temperature.
3. Lower limb conduction velocities are typically slower.
4. Proximal segments conduct faster than distal segments.
131
What is the H-Reflex in NCS?
Analogous to deep-tendon reflexes but using nerve stimulation on NCS. For example, the sensory stimulus results in a motor response. Mediated through the 1a fibres in the nerve. It can be recorded from the Soleus, Flexor Carpi Radialis and Quadriceps.
132
What are the three phases of EMG evaluation?
Insertional activity, spontaneous activity and voluntary activity.
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In a patient with demyelination what EMG changes would you find?
Spontaneous activity present
Voluntary (volitional) phase will show: increase in amplitude and duration (due to increased muscle acetylcholine receptors)
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In a patient with myopathy what EMG findings would you have?
Decrease in amplitude and duration in the voluntary (volitional) phase.
