Nerve injury

Question 1

Riche Cannieu anastomosis

Answer 1

Ulnar motor nerve to median nerve communication in the hand

77% in cadaver

Question 2

Marinacci communication

Answer 2

Reverse Martin Gruber communication or Marinacci communication in which ulnar nerve fibers cross over to median nerve

5-17% patients

Question 3

Sources of nerve graft

Answer 3

1. Sural nerve graft
2. Medial and lateral antebrachial cutaneous nerve
3. Distal sensory end of posterior interosseous nerve
4. Dorsal radial sensory nerve

Question 4

Sensory versus motor versus mixed nerve grafts which achieves better regeneration?

Answer 4

Motor or mixed nerve grafts achieve better regeneration across the repair.

Question 5

Martin Gruber anastomosis

Answer 5

Crossover of median nerve or anterior interosseous nerve fibers to the ulnar nerve in proximal forearm

Incidence - 5-34% cadaveric studies and high as 57% in electrophysiologic studies.

Question 6

Importance of Martin Gruber anastomosis

Answer 6

Intrinsic muscles that are normally innervated by the ulnar nerve may be innervated by median nerve.

Or intrinsic muscles normally supplied by median nerve may still receive median nerve innervation but via the median to ulnar nerve cross over.

This variant requires additional crossover in the palm from ulnar nerve to thenar muscles.

High ulnar nerve injury if it occurs above Martin Gruber anastomosis may present with numbness in ulnar nerve distribution of hand but intact function of hand intrinsic muscles.

Question 7

Clinical tests for radial nerve function

Answer 7

1. Extrinsic motor - Wrist extension
2. Intrinsic motor - None
3. Sensory - Dorsal first web space

Question 8

Clinical tests for Median nerve function

Answer 8

1. Extrinsic motor - Profundus index finger
2. Intrinsic motor - Abductor pollicis brevis
3. Sensory - Pulp of index finger

Question 9

Clinical tests for Ulnar nerve function

Answer 9

1. Extrinsic motor -Profundus small finger
2. Intrinsic motor - First Dorsal interosseous
3. Sensory - Pulp of small finger

Question 10

Quick intraoperative landmarks used to match fascicles during end to end neurorrhaphy

Answer 10

1. Vascular markings within the epineurium
2. Size and grouping of fascicles especially at a more distal location

Question 11

Types of nerve repair

Answer 11

1. Primary nerve repair - Sharp, limited crush mechanism, clean wound bed, two ends are easily juxtaposed.
2. Nerve graft - Large gap needs to be repaired. 4 - 5 cm gap in upper arm, 1 cm gap in a digital nerve.
3. Vascularised nerve graft - ensure survival of graft, hasten regeneration in burns or irradiated tissue with poor vascularity.
4. Conduits indicated in patients in whom a small nerve gap is present but no autologous nerve is available or donor defect not warranted.
5. Nerve transfer - Ends will not approximate, no vascularised bed, graft not possible, proximal portion of nerve not intact, distal portion of nerve intact.

Question 12

Classification of nerve repairs

Answer 12

1. Primary repair - Nerve repair within first few days
2. Delayed primary repair - Nerve repair between 2-7 days
3. Secondary repair - Repair after 7 days

Question 13

Is primary repair better than secondary repair ?

Answer 13

Yes.

Delayed repair or secondary repair preferred until wound is clean
1. Significant crush injury,
2. Highly contaminated wound bed,
3. Questionable viability of nerve because of vascular supply,
4. Infection

Question 14

Best method for surgical nerve repair

Answer 14

Simple epineurial repair with several interrupted 9-0 or 10-0 nylon sutures through epineurium under microscope control.

No advantage of fascicular or grouped fascicular repair over simple epineurial repair.

Question 15

What cases of nerve injury will you explore immediately?

Answer 15

Nerve injury with open wounds
eg. Sharp laceration exception gunshot wound which is associated with indirect heat and shock effects.

Question 16

How to manage a closed nerve injury?

Answer 16

Closed nerve injury includes direct blow, traction injuries, clinical course is followed closely.

Wait till 6-8 weeks, if clinical recovery does not occur, nerve conduction and electromyographic studies are obtained for baseline evaluation. Follow up till 12 weeks and repeat electrical studies.

If improvement in clinical course is seen by 12 weeks, continue conservative management. If no sign of recovery either clinically or electrodiagnostic testing, operative intervention is warranted. Type of surgical procedure varies from neurolysis to nerve grafting or nerve transfer depending on the grade of injury and distance of injury from end organ.

Question 17

What is the best way to treat peripheral nerve injuries resulting in segmental loss of continuity?

Answer 17

Motor nerve gap that cannot be primarily repaired, autogenous nerve grafts harvested from appropriate donor sites is gold standard.

Cadaveric nerve grafts have been recently commercially available.
1. Limits upto 7 cm in length - cadaveric nerve graft used
2. More than 7 cm in length defect - Autogenous nerve graft used
3. Upto 6 cm defect in motor nerve defect - Vein or conduits have been used in experimental studies.
4. For long nerve gaps - Nerve transfer is better alternative.
5. Maximum length of nerve grafts used successfully > 15 cm

Sensory nerve gaps upto 3 cm length can be repaired with vein grafts and artificial conduits.

Massive loss of nerve segments - transplanted nerves can be used for grafting, especially in whom limited amount of autogenous nerve available such as children and amputees.

Donor nerves can be preserved in cold University of Wisconsin solution for 7 days to reduce antigenicity before transplant. Recipient and donors must be blood type compatible, HLA compatibility not necessary.

Immunosuppression is required until there is evidence of regeneration across the graft into native distal nerve.

Question 18

When to use motor nerve transfer instead of nerve graft?

Answer 18

1. Brachial plexus injuries in which only very proximal or no nerve is available for grafting
2. High proximal injuries that require a long distance for regeneration
3. To avoid scarred areas where there is high likelihood that critical structures may be injured.
4. Major limb trauma with segmental loss of nerve tissue
5. As alternative to nerve grafting when time from injury to reconstruction is prolonged
6. Partial nerve injuries with a defined functional loss
7. Spinal cord root avulsion injuries
8. Nerve injuries where level of injury is uncertain such as radiation trauma and multiple level nerve injury

Question 19

Is motor nerve transfer better than tendon transfer?

Answer 19

Not always.
Nerve injuries that occur more than 12 months earlier or that need to regenerate over long distances will have poor results and should be treated with tendon transfers. The advantage of tendon transfers is the immediate results seen soon after surgery.

Injuries that are amenable to nerve transfers do better because -
1. Nerve transfer can restore motor and sensory function
2. Multiple muscle groups can be restored with a single nerve transfer
3. Insertion and attachments of the muscle are not disrupted, so original muscle function and tension is maintained.

Question 20

What are nerve transfers?

Answer 20

Nerve transfer uses uninjured proximal nerve to power an injured distal nerve and may restore motor function or sensory function. Motor nerve transfers are designed by selecting donor nerves that supply nonessential muscles or muscles with redundant fibre innervation and that are synergistic with recipient motor nerve.

Example - Transfer of redundant flexor carpi radialis fascicles of the medial nerve and redundant flexor carpi ulnaris fascicles of ulnar nerve to the biceps brachii and brachial branches of musculocutaneous nerve for elbow flexion recovery.

Question 21

Do all proximal motor nerve injuries result in permanent loss of function?

Answer 21

No. Excellent recovery is possible across long distances under certain circumstances. Early primary repair of sharp transections that maintain motor and sensory topography by excellent coaptation along anatomic landmarks on the epineurium results in good recovery of function.

Nerve repairs in children tend to have good outcomes even with nerve grafts because of enhanced nerve regeneration capacity, shorter distances and possibly greater central plasticity.

Protective sensibility and improved muscle function are possible after long nerve grafts when meticulous micro technique is used and sensory/motor topography is correct.

Question 22

Describe the functional anatomy of peripheral nerves

Answer 22

4 components -

1. Neurons - primary functional units of peripheral nerve are composed of cell bodies and axons. Cell bodies of motor axons are found in the anterior horn area of spinal cord and sensory cell bodies are found in the dorsal root ganglia of the spinal cord.
2. Connective tissues of the nerve - 3 layers
   a. Endoneurium connective tissue - found around individual axons.
   b. Perineurium connective tissue which surround fascicles.
   c. Epineurium connective tissue which runs between fascicles and around the outside of the nerve.
3. Schwann cells - Supply myelin for efficient electrical nerve conduction, appears to influence maturation and resting metabolism of axons.
4. End organs - Including motor endplates, sensory receptors, autonomic receptors transduce electrical activity into function.

Question 23

When does motor recovery appear to become refractory to reinnervation ?

Answer 23

Motor recovery becomes refractory to rein nervation after approximately 15-18 months of denervation.

Question 24

When does sensory recovery appear to become refractory to reinnervation ?

Answer 24

Sensory recovery has been described up to 20 years after initial denervation.

Question 25

Classification of nerve injuries

Answer 25

Seddon classification
1. Neuropraxia - Local conduction block at a discrete area along the course of the nerve; subsequently wallerian degeneration does not occur.
2. Axonotmesis - Direct axonal damage, Wallerian degeneration occurs distal to the site of injury.
3. Neurotmesis - Constitutes transection of a peripheral nerve

Sunderland classification
Expanded Seddon’s classification with grades of nerve injury from I to V.
Grade I - Neuropraxia - Complete recovery
Grade II - Axonotmesis - Complete recovery
Grade III to V - Neurotmesis - No recovery

Mackinnon described Grade VI - Neuroma in continuity

Question 26

Wallerian degeneration

Answer 26

Distal segment in a complete nerve injury undergoes series of degenerative changes collectively known as wallerian degeneration.

Gross changes of turbidity or coagulation seen even at the distal most end of neural tube after transaction.

Ground glass appearance represents remnants of degenerated myelin and axonal material after loss of axonal continuity.

Initial breakdown products of the axon and myelin are phagocytoses by macrophages and Schwann cells.

Eventually space originally occupied by myelinated axons is filled with columns of Schwann cell nuclei and their basement membranes.

Question 27

What are the bands of Bungner?

Answer 27

Collapsed columns of Schwann cells filling the distal segment of a complete nerve injury have characteristic band like appearance under electron microscopy; these columns are known as the bands of Bungner.

Question 28

What are the bands of Fontana?

Answer 28

Spiral bands surrounding the peripheral nerve. The irregular light and dark strips crossing the surface of unstretched nerves are due to the underlying undulations of the individual nerve fibers within the epineurial-perineurial sheaths.

May be responsible for keeping the proper fascicular structure, providing the elasticity of perineurium and tolerating stretching derformation.

Question 29

What is Tinel’s sign?

Answer 29

Percussion over the site of nerve injury or nerve repair elicits a tingling or electric shock-like sensation in the distribution of the injured nerve. This sensation represents leading edge of nerve regeneration.

Advancing Tinel’s sign after nerve repair implies successful nerve regeneration toward the target organ.

Tinel’s sign that does not advance with time may be due to extra-epineurial growth cones that have become misdirected outside the epineurial boundary at the level of the nerve repair.

Question 30

Is Tinel’s sign sensory or motor?

Answer 30

Although sensory in nature, Tinel’s sign is also found in regenerating motor nerves, probably because of presence of proprioceptive afferent fibers within all motor nerves.

Question 31

How fast do nerves regenerate?

Answer 31

1mm/day or 1 inch/month

Several studies have shown in advancing Tinel’s sign after nerve repair have reported a rate of recovery up to 2 mm /day.

Question 32

Drug that increases rate of axonal regeneration

Answer 32

Tacrolimus