Peripheral Nerve Injury

Front 1

What is the role of Schwann cells in unmyelinated axons??

Back 1

1. Metabolic support for axons

Front 2

What is the endoneurium?

Back 2

1. Connective tissue layer wrapped around the individual axons

Front 3

What is the perineurium?

Back 3

1. Holds together groups of axons into fascicles

Front 4

What is the epineurium?

Back 4

1. Holds nerve fascicles together

2. Blood vessels run through this layer

Front 5

What is neurapraxia?

Back 5

1. Sunderland degree 1

2. Damage confined to Schwann cells and myelin

3. Myelination is re-established by proliferation of undamaged Schwann cells

Front 6

What is mild axonotmesis?

Back 6

1. Sunderland degree 2

2. Damage includes both axons and Schwann cells

3. Axonal damage results in Wallerian degeneration

4. Schwann cell damage results in demyelination

Front 7

What is the state of the endoneurium in mild axonotmesis?

Back 7

1. Intact

Front 8

What is axonotmesis?

Back 8

1. Sunderland degree 3

2. Damage to axons, Schwann cells, and endoneurium

3. Wallerian degeneration and loss of myelin occur

Front 9

What is the state of the perineurium in axonotmesis?

Back 9

1. Intact

Front 10

What is severe axonotmesis?

Back 10

1. Sunderland degree 4

2. Damage to all structures along with perineurium

3. Wallerian degeration and demyelination

4. Intact epineurium

Front 11

What is neurotmesis?

Back 11

1. Sunderland degree 5

2. Nerve is severed

3. Wallerian degeneration and demyelination

4. Damage to endoneurium, perineurium, and epineurium

Front 12

How close must nerve fibers be in order to repair them surgically?

Back 12

1. <5 mm

Front 13

What occurs 24-36 hours after injury in Wallerian degeneration?

Back 13

1. Axonal fragmentation begins in segment distal to injury site

2. Myelin begins to break down

3. TNFa and IL-1B are secreted and recruit macrophages

Front 14

What occurs 36-48 hours after injury in Wallerian degeneration?

Back 14

1. Fibroblasts detect TNFa and IL-1B--- produce GM-CSF

2. GM-CSF induces Schwann cells to proliferate and help clear degraded myelin

3. MCP-1 secreted by Schwann cells

Front 15

What are Bands of Bungler?

Back 15

1. Breakdown of myelin complete in 72 hours

2. Regeneration of Schwann cells occurs within 7 days

3. New Schwann cells align to form Bands of Bungner--- help to guide the regenerating axon to target tissue

Front 16

What occurs 48-72 hours after injury in Wallerian degeneration?

Back 16

1. Macrophages continue clearing myelin and axon gragments

2. New Schwann cells begin to align and form Bands of Bungner

3. Macrophages secrete IL-10 to suppress inflammation

Front 17

What occurs 3-7 days after injury in Wallerian degeneration?

Back 17

1. Bands of Bungner formed

2. NGF and BDNF released to induce axonal sprouting and guide axons to denervated sites

3. Macrophages begin to decline

Front 18

What occurs 7-21 days after injury in Wallerian degeneration?

Back 18

1. Inflammatory response has ended

2. Regrowth along bands of Bungner induced by NGF and BDNF

3. Regrowth can result in a return of function if not too extensive

Front 19

When can nerve regrowth occur with surgical intervention?

Back 19

1. Sunderland degree 3 or less

Front 20

When can nerve regrowth occur without surgical intervention?

Back 20

1. Sunderland 1 or 2

Front 21

What factors induce axonal sprouting?

Back 21

1. NGF

2. BDNF

Front 22

What is the rate of growth of neurites?

Back 22

1. 1-4 mm/d

Front 23

What does scar formation lead to in nerve injury?

Back 23

1. Block advancing neurites

2. Scar tissue must by surgically removed

Front 24

When is nerve debridement done?

Back 24

1. Prior to surgical reattachment of nerve ends

Front 25

What procedure is indicated if the nerve gap is <5 mm?

Back 25

1. Neurorrhaphy--- re-attach ends of severed nerves

2. Suture the epineurium or the perineurium

Front 26

What is the benefit of an epineural neurorrhaphy?

Back 26

1. Sutures are external

2. Do not interfere with recovery

3. Blood vessel alignment

Front 27

What method has the best outcome for fascicular alignment?

Back 27

1. Individual fascicular neurorrhaphy

2. Can increase scar formation with large number of sutures

Front 28

What are the advantage soft group fascicular repair?

Back 28

1. Better chance of good fascicular alignment

2. Slower

3. Doesn't show better clinical outcomes

Front 29

What is the gold standard nerve graft method?

Back 29

1. Autograft--- from own patient

2. Sural nerve commonly used---- cannot align fascicles

Front 30

What is an allograft?

Back 30

1. No additional surgical trauma

2. From a cadaver

Front 31

What are the drawbacks to nerve grafts?

Back 31

1. Undergo Wallerian degeneration

2. Double suture sites can increase scar formation

Front 32

What synthetic conduits can be used in a graft?

Back 32

1. Veins

2. Collagen

Front 33

What is the maximum gap length approved for collagen conduits?

Back 33

1. 3 cm

Front 34

What are the nonbiological conduits?

Back 34

1. Silicone

2. Does not degenerate--- additional surgery required

Front 35

What are the phases of conduit repair?

Back 35

1. Fluid phase--- accumulation of neurotrophic factors and ECM molecules

2. Matrix phase--- fibrin cable formation

3. Cellular phase-- Schwann cell migration, proliferation

4. Axonal phase-- growth of daughter axons

5. Myelination phase

Front 36

How good is conduit repair?

Back 36

1. Epineural--- gold standard

2. Conduit--- not so good---fascicle realignment difficult to achieve

3. Fascicle recovery not full, but better than nothing

Front 37

What is the role of exercise in nerve regeneration?

Back 37

1. Exercise enhances nerve regeneration

Front 38

What happens if you don't address a nerve injury?

Back 38

1. Loss of sensory and motor function

2. Development of a neuroma--- axons don't find their target

Front 39

What are the ssx of a neuroma?

Back 39

1. Intense, chronic pain at site of defect

Front 40

How do you tx a neuroma?

Back 40

1. Surgery

2. Nerve regeneration can be attempted

3. Nerve can be be buried in the muscle

Front 41

What leads to choric neuropathic pain in neuromas?

Back 41

1. Upregulation of NaV 1.3, 1.8, and 1.9 and CaV a2d

Front 42

What is the MOA of gabapentin?

Back 42

1. Block CaV a2d subunit