1. Nerve Injury and Repair
Mike Lehoang, MD
Clinical Professor
Department of Orthopaedic Surgery
University of Southern California

2. Overview History of nerve repair Anatomy of the peripheral nerve
Nerve degeneration and regeneration
Techniques for direct repair and grafting
Factors affecting outcome after repair
Rehabilitation after nerve repair
I will start the talk today with an overview of the history of nerve repair, the anatomy of the peripheral nerve, nerve degeneration and regeneration. I will then go over the different techniques for direct repair and grafting. Finally we will discuss the factors affecting the outcome after repair is done and rehabilitation of the patient after surgery.
I will start the talk with the history of the nerve repair, then go over the anatomy of the peripheral nerve, nerve degeneration

3. Goals Evaluate patients with peripheral nerve injury
Establish diagnosis
Formulate plan of treatment
When we see a patient with peripheral nerve injury, our goals are to thoroughly evaluate the patient to come up with a correct diagnosis. Once this is done, we can then formulate a plan of treatment.

4. History Chalic: Cut nerves restored by sutures (1300’s)
Cruishank: Nerve regeneration (1700’s)
Waller: Degeneration axon distal stump (1800’s)
Tinel: Sign of regenerating axons (1915)
Seddon: Classification of nerve injuries ( WW2)
Sunderland: Expand classification and mapping on
internal architecture of nerves ( WW2)
Milesi: Results after nerve grafting (1970’s)
As early as the 2nd Century A.D., it was thought that nerve regeneration was impossible. However, in the 1300s, Guy de Chalic wrote that cut nerve had been so well restored by sutures and other remedies that afterward one could not believe they had been cut . Scientific interest in nerve regeneration began in the 1700s with the work of Cruishank . Waller demonstrated the proximal source of the regenerating axons in his description of the dying off of the axon in the distal nerve stump in frog glossopharyngeal nerves ( Wallerian degeneration). During both WW1 and WW2, Tinel described the irritability of the regenerating nerve and the presence of a “Tinel’s sign.” Seddon provided an anatomic classification of nerve injuries during WW2, late expanded by Sunderland of Australia. In the 1970’s, Milesi reported on the results after nerve grafting.

5. Anatomy Axons Endoneurium Fascicles Perineurium Epineurium Mesoneurium
The axons are single nerve fibers, much like the “wiring” of the nerve. The endoneurium exists between individual axons. Many axons form groups called fascicles. The fascicles are surrounded by perineurium. The whole nerve is surrounded by epineurium.

6. Epineurium Ext covering Loose connective tissue Amount variable
Epineurial fibroblast
The epineurium is the external covering of the nerve. It is a loose connective tissue encasing the nerve and also dividing fascicles groups. The amount of epineurium is variable from nerve to nerve as well as along the course of an individual nerve. Epineurial fibroblasts are involved in the inflammatory response and proliferate in response to injury. This can cause 2-3 mm thickening of a nerve in response to chronic inflammation

7. Perineurium Surrounds fascicles Extension blood brain barrier
Limits diffusion
If absent, nerve
does not function
Resist traction
The perineurium is an extension of the blood brain barrier, controlling the environment within a fascicle. The perineurium surrounds the nerve fascicle. Removal of the perineurium results in loss of nerve function. The perineurium resists longitudinal traction and provides the elastic properties of peripheral nerve

8. Endoneurium Collagenous packing around axons Form Schwann cell tube
The endoneurium is collagenous packing tissue that separates axons within the perineurium. Endoneurium participates in the formation of the Schwann cell tube.

9. Fascicles Unit of nerve structure Groups of axons surrounded
by perineurium
Fascicular groupings:
mono, oligo, polyfascicular
Functional groupings and
topographical groupings
The fascicle is the smallest unit of nerve structure which can be surgically manipulated. It consists of groups of axons surrounded by perineurium. Fascicular grouping varies from nerve to nerve with mono, oligo or polyfascicular grouping. Functional groupings of motor and sensory fibers and groupings corresponding to topographical distribution become more defined moving from proximal to distal along the course of a nerve.

10. Vascularity Segmental contributions Longitudinal plexus
Allows mobilization without devascularization
Limits
Nerves receive segmental contributions to a longitudinal plexus which courses along the length of the nerve. The extensive interconnection of the plexus allows for significant mobilization of a nerve from its tissue bed without causing compromising its vascularity. While the nerve can be extensively mobilized without causing ischemia, there may be limits to mobilization, as animal studies have demonstrated adverse effects on outcome of repaired median nerve when more than 5 cm of nerve is mobilized about the site of transaction

11. Motor Unit Single motor neuron and its axonal projection
Multiple muscle fibers innervated by a single axon ( )
Muscle fibers/axon: innervation ratio
The motor unit consists of a single motor neuron and its axonal projection. Multiple muscle fibers may be innervated by a single axon, ranging from 100 to The innervation ratio is the ratio of muscle fibers to one axon.

12. Nerve injury Classification : neuropraxia, axonotmesis, neurotmesis
Seddon
neuropraxia, axonotmesis, neurotmesis
Sunderland: 5 types
1: myelin
2: axon
3: endoneurium
4: perineurium
5: epineurium
Classification of nerve injuries is very important because it helps during communication and in predicting the recovery. During WW2 Seddon classified nerve injury into three types that provide adequate information concerning the injury: neuropraxia, axonotmesis, and neurotmesis. In neuropraxia, there is local myelin damage and the axons are preserved, there is no degeneration and full recovery is to be expected. In axonotmesis, the axons are disrupted, there is degeneration but the neural tube is intact. In neurotmesis, there is complete loss of neural continuity. This was expanded by Sunderland, both expanding and refining the anatomic description of the injury. In type 1, only myelin is involved, type 2 axon, type 3, the endoneurium, type 4 the perineurium and type 5 the epineurium.

13. Wallerian Degeneration
Each nerve fiber: regenerating unit
After injury, axons undergo changes
Distal Schwann cell “tubes” cleared
Axon proximal to injury:
Multiple sproutings:
Collateral sprouts
Terminal sprouts
Each nerve fiber represents a regenerating unit. After division, axons undergo a series of changes described as Wallerian degeneration. The distal Schwann cell “tubes” are cleared creating a path for axon regeneration. Wallerian degeneration occurs mostly in the distal stump, and to a lesser extent in the proximal stump. The axon proximal to the injury gives out multiple sprouts: the collateral spouts from outside the basal lamina and the terminal spout form inside the basal lamina.

14. Growth Cone Most distal part of regenerating axon
Continous sampling of
environment
Rate of growth: 1-2mm/day
Innervation specificity:
motor and sensory axons
regenerating in the correct regions
This is the most distal part of the regenetating axon, it is capable of continously sampling the environment in which it grows and may change direction in minutes. The axon rate of growth is approximately 1-2mm/day. The ability of the motor or sensory axons to regenerate in the correct region relates to innervation specificity.

15. Growth Cone Motor-sensory specificity aided by correct orientation
at time of repair
Motor nerve preferentially
innervate motor pathways
(Brushart, 1993)
The motor-sensory specificity is aided by correct orientation at the time of nerve repair. However, motor nerves will preferentially innervate motor pathways and can “prune” themselves if the initial path of regeneration is incorrect.

16. Specific muscle testing
Median nerve (intrinsic): thumb palmar abduction
Median nerve (extrinsic): all FDS, FPL, FDP index
Ulnar nerve (intrinsic):1st dorsal interosseus, abductor digiti minimi
Ulnar nerve (extrinsic): FDP little finger, FCU
Radial nerve: wrist extension, MP joint extension
A quick review of the patient examination to identify the nerve injured.
To test the intrinsic of the median nerve, ask the patient to palmarly abduct the thumb
To test the extrinsic median nerve, check all the FDS, FPL, FDP of the index
For the intrinsic of the ulnar nerve, check the 1st dorsal interosseus, the abductor digiti minimi.
For the extrinsic ulnar nerve, check the FDP to the little finger and the FCU
And for the radial nerve, check for wrist extension and MP joint extension

17. Sensory evaluation Pin prick, light touch: not helpful
Best: two point discrimination
Innervation density testing
Useful for nerve regenerating
testing
Not useful for compressive
neuropathy
For digital sensory evaluation, the most objective information possible is obtained. Information related to “pin prick” and “ light touch” sensation is usually not helpful. The two point discrimination is the standard method of evaluation.
For the median nerve, check the pulp of the thumb and index
For the ulnar nerve, check the pulp of the small finger
For the radial nerve, check the first web space
For the palmar cutaneous median nerve, check the thenar eminence
For the dorsal cutaneous ulnar nerve, check the dorsal ulnar hand
And for the digital nerve,check both the radial and ulnar aspects of the finger.

18. Sensory evaluation Median nerve: pulp thumb and index
Ulnar nerve: pulp of small finger
Radial nerve: first web space
Palmar cutaneous median nerve:
thenar eminence
Dorsal cutaneous ulnar nerve: dorsal ulnar hand
Digital nerve: radial and ulnar aspects digits
For digital sensory evaluation, the most objective information possible is obtained. Information related to “pin prick” and “ light touch” sensation is usually not helpful. The two point discrimination is the standard method of evaluation.
For the median nerve, check the pulp of the thumb and index
For the ulnar nerve, check the pulp of the small finger
For the radial nerve, check the first web space
For the palmar cutaneous median nerve, check the thenar eminence
For the dorsal cutaneous ulnar nerve, check the dorsal ulnar hand
And for the digital nerve,check both the radial and ulnar aspects of the finger.

19. Electrophysiologic testing
Not helpful in acute setting, helpful in later evaluation
Two types:
Nerve conduction velocity (NCV)
Electromyography (EMG)
The electrophysiologic testing is not useful in the acute setting but may be helpful in later evaluation. There are two types of electrophysiologic testing: the nerve conduction velocity and the electromyography.

20. Nerve Conduction Study
Measure speed nerve carries
information
Latency: time from stimulus
to recording
Since distance and time
are known, nerve conduction
velocity can be calculated (NCV)
This evaluation measures the speed with which a nerve carries information, the time measured from stimulus to recording is called the latency. Since distance and time are known, the nerve conduction velocity can be calculated.

21. Electromyography EMG: electrical activity of muscle
Small needle placed in
selected muscle and electrical
activity of muscle at rest and
with contraction is measured
The electromyogram measures the electrical activity of a muscle. A small needle is placed into the selected muscle and the electrical activity of the muscle at rest and with contraction is measured. The electrical activity is visualized as a wave form on an oscilloscope. The wave forms can be interpreted and provide information about the innervation of the muscle in question

22. Electromyography Electrical activity: visualized
as wave form on oscilloscope
Wave form provide information
about the innervation of the
muscle tested
The electromyogram measures the electrical activity of a muscle. A small needle is placed into the selected muscle and the electrical activity of the muscle at rest and with contraction is measured. The electrical activity is visualized as a wave form on an oscilloscope. The wave forms can be interpreted and provide information about the innervation of the muscle in question

23. Nerve Repair Guidelines to ensure good repair:
Appropriate personnel, equipment, magnification
Tension free repair
Be prepared to use free graft
Determine full extent of nerve injury
Be prepared to resect the scar to healthy nerve
There are some general guidelines to help ensure a good repair. These include the availability of appropriate equipment including personnel, magnification and instruments. It is desirable to have a tension free repair, which means you should be prepared to use nerve graft if necessary. Related to this is determining the extent of the initial injury. Additional nerve may have to be resected to reach a scar free area with normal fascicular anatomy

24. Nerve Repair Timing Primary Repair Delayed Primary Repair
Hours
Delayed Primary Repair
Up to 5-7 days
Secondary repair
Primary repair happens within hours of the injury. Delayed primary repair occurs within 5-7 days, and anything after that is secondary repair and nerve grafting.

25. Primary Nerve Repair Criteria
Clearly defined level of injury
Minimal wound contamination
Good tissue bed
Adequate equipment
Suitable patient
Primary repair can be done when there is a clearly defined level of injury, minimal wound contamination and a good tissue bed. If the conditions for repair are poor or the level of injury is not well demarcated, it is better to tack the nerve ends together to prevent retraction, close the skin and plan a delayed primary repair when conditions allow. Secondary repair under favorable conditions will give better results than primary repair under unfavorable ones.

26. Types of Nerve Repair Epineurial Group fascicular
Individual fascicular
There are three basic types of nerve repair. Epineurial, fascicular and group fascicular repairs.

27. Epineurial Repair Inspect external landmarks Inspect intraneural
topography
Serial section to healthy
fascicular tissue.
Use magnification
We should inspect external landmarks such as longitudinal blood vessels to aid in orientation. Inspect the intraneural topography for orientation. Serial section to healthy fascicular tissue. Determine this by direct inspection of the nerve with magnification.

28. Epineurial Repair Median nerve repair at the wrist level
This patient has a clean cut of the median nerve at the level of the wrist. The slide on the right shows the nerve after epineurial repair.

29. Group Fascicular Identify groups of fascicles Suture inner epineurium
surrounding groups of
fascicles
Repair external epineurium
Useful in ulnar nerve near wrist
dorsal sensory branch can be
separated from fascicles continuing
into the hand
In this technique, individual groups of fascicles can be identified. The inner epineurium surrounding the fascicular group is approximated in addition to the external epineurium. This technique is use useful in certain anatomical regions such as the ulnar nerve near the wrist. In this example, the dorsal sensory branch fascicles can commonly be separated from the fascicles continuing into the hand.

30. Single Fascicular Repair
Uncommon
Theoretically, better to align fibers
for appropriate nerve regeneration
Difficult to determine fascicular
alignment
Once aligned, less ability of
nerve to selectively regenerate
toward appropriate distal target
(preferential motor and
sensory regeneration)
The repair of single fascicles is uncommon. While fascicular alignment would theoretically better align fibers for appropriate nerve regeneration, it would be unusual to determine precise fascicular alignment with certainty. Once the fascicle has been aligned, there is less ability of the regenerating nerve to selectively regenerat toward an appropriate distal target (preferential motor or sensory regeneration)

31. Nerve Grafting Allows a gap in the periphery
nerve to be bridged so that
distal axon regeneration is poss.
Grafting Healthy nerve tissue for
short distance better than direct
repair of Injured neural tissue
Nerve grafting allows a gap in a peripheral nerve to be bridged so that distal axon regeneration is possible. Grafting healthy nerve tissue over a short distance is superior to direct repair of injured neural tissue. Therefore, the surgeon should not hesitate to use a nerve graft to avoid excessive tension at the repair site or the coaptation of injured tissue.

32. Nerve Grafting What is excessive tension
Nerve ends cannot be held by sutures at 180 degrees to each other
One 7-0 nylon draw the ends together without
tearing the epineurium
Gaps of cm should be grafted
We do nerve graft to avoid excessive tension, but what is excessive tension? In general, if the nerve ends cannot be approximated by sutures at 180 degrees to each other, then it is better to graft. Most authors use gaps of 2.5 – 4 cm as indication of nerve graft.

33. Donor Sites Sural nerve Posterior interosseus
Medial and lateral antebrachial
cutaneous
Do not use superficial radial nerve
The sural nerve is the workhorse of nerve grafts. The posterior interosseus nerve is easily accessible for digital nerve grafts. Local graft from the medial antebrachial cutaneous nerve can be conveniently harvested with little donor morbidity. The superficial radial nerve should not be used unless the parent nerve is irreparably damaged.

34. Conduits Other materials used to bridge the gap in the nerve: Veins
muscle tissue
artificial nerve tubes
There are other materials used to bridge the nerve gap, veins, muscle tissue, and artificial nerves. These nerve tubes are made of synthetic bioabsorble materials. Possible advantages from placing the nerve stumps within a nerve tube is that a chamber is provided separate from the surrounding tissues and the regenerating axons are better guided into the distal Schwann tubes.

35. Conduits Nerve tubes: synthetic tubes made of bioabsorbable materials.
Advantages: chamber for
nerve to grow separated
from the surrounding tissue
Regenerating axons better
guided into distal Schwann
tubes
Autogenous nerve grafts still
the mainstay for longer defects
There are other materials used to bridge the nerve gap, veins, muscle tissue, and artificial nerves. These nerve tubes are made of synthetic bioabsorble materials. Possible advantages from placing the nerve stumps within a nerve tube is that a chamber is provided separate from the surrounding tissues and the regenerating axons are better guided into the distal Schwann tubes.

36. Nerve Transfer Proximal stump hopelessly damaged
No continuity of proximal stump and spinal cord
Transfer of other nerves to the distal stump
Oberlin: One bundle from FCU to musculocutaneous for biceps function

37. Muscular neurotization
Distal stump hopelessly damaged
Direct implantation of nerves into the muscle

38. Tinel’s Sign Follow progress of nerve regeneration
Tinel’s: percuss along course of affected nerve form distal to proximal. When finger is over the regenerating nerve, patient will feel sensation of pins and needles into cutaneous distribution of nerve
Tinel sign is very useful in following the course of the nerve injury. To perform the Tinel’s test, the examiner lightly percusses along the course of the affected nerve from distal to proximal. When the finger percusses over the zone of regenerating fibers the patient will announce the sensation of pins and needles into the cutaneous distributin of the nerve.

39. Tinel’s Sign
Strongly positive over lesion soon after injury indicates rupture or severance.
After successful repair: centrifugally moving Tinel is stronger than at suture line
After failed repair: Tinel sign at suture line stronger than at growing point
If the Tinel’s sign is strongly positive over the lesion soon after the injury, this indicates a rupture of severance of the nerve. If the repair is successful, the Tinel sign distal to the suture line will be stronger. If the repair fails, the Tinel sign will be stronger at the suture line than at the growing point.

40. Post op care 0-3 weeks Protect in splint
3 wks-3 months Progressive mobilization
. Prevent joint stiffness
. Gliding of nerve
3-6 months Strengthening
Vibratory return Sensory reeducation
Following nerve repair or grafting, the nerve is protected in a splint for 3 weeks. Gentle mobilization is then begun. It is as important to prevent joint stiffness as to allow gliding of the nerve to prevent adhesions and scarring in its tissue bed. Strengthening is begun after 3 monts. Sensory reeducation is started after the return of the vibratory sensation and after hyperesthesia has resoved.

41. Medical Research Council (MRC)
S-0 No sensation
S-1 Deep cutaneous pain in autonomous
region of nerve
S-2 Some return of superficial pain sensation
S-3 Return of tactile sensibility
S-3+ Some return of 2-point discrimination
S-4 Complete recovery
The British Medical Research Council developed a grading system to assess functional outcome and nowaday, most studies use a M3/S3 motor and sensory grade as a functional result where M3 indicates return of muscle function against resistance, and S3 represents return of some 2-point discrimination.

42. Medical Research Council (MRC)
M-0 No contraction
M-1 Perceptable contraction proximally
M-2 Perceptable contraction proximally and
distally
M-3 Motor power against resistance
M-4 Motor recovery to independent and
synergistic function
M-5 Complete recovery
Again, an M3 grading means the patient has some motor power against resistance

43. Factors influencing Repair Results
Technique
Age
Tension at Repair Site
Delay of surgery
Location of Injury
Nerve gap
Fascicular alignment
Concommitant injuries
These are the factors that are important in influencing the results of your repair. The technique, the age of the patient, the younger the better outcome, the tension at the repair site .Motor recovery is worse than sensory recovery with delay in surgery. Other factors are the severity and the location of the nerve injury.The shorter the distance over which the nerve must regenerate to reach the end organ, the more likely is the success of the repair. Other factor is the nerve gap. There is no difference between secondary repair and fascicular grafting if the graft length was less than 5 cm. The other factor influencing the repair is whether you were able to properly align the fascicles at the time of surgery and finally if the patient has associated injuries beside the nerve injury.

44. Outcome of Nerve Repair
Median: % M3 or S3 or >
Low Ulnar: % M3 or S3 or >
High Ulnar: 27% M3 or S3 or >
Radial: – 40% useful recovery
This is a study out of Finland, 60 to 80% of the patients with the median nerve repair achieved a grade M3 or S3 or better. Of the low ulnar nerve injured patients, 40% got M3 or S3 or better, and the high ulnar fare worse with only 27% got M3 or S3 or better recovery. They only reported 15 to 40% of the radial nerve got useful recovery. In this group the outcome was significantly affected by the presence of the associated injuries.

45. Rehabilitation after Nerve Repair
Rehabilitation: staged withdrawal of support while the patient reintegrates into normal life
Focus on three areas:
Initial immobilization to protect the repair
Mobilization of adjacent joints to promote normal longitudinal excursion of the nerve
Sensory re-education
Rehabilitation is a staged withdrawal of support while the patient reintegrates into normal life. We should focus on three areas: the initial immobilization to protect the repair, the mobilization of adjacent joints to promote normal longitudinal excursion of the nerve and finally the sensory reeducation .

46. Sensory Re-education
Progressive sensory stimuli introduced early in the recovery phase significantly improve sensory recovery
The sensory reeducation consists of introducing progressive sensory stimuli started early in the recovery phase. This was found to greatly improve the sensory recovery of the patient.

47. Summary
The most important factor in prognosis after injury to a nerve is the violence of that injury and the extent of damage to the limb
The most important factor in prognosis that the physician can control is the delay between injury and repair.
Good judgment is needed in the care of the patient with peripheral nerve injury to give the patient optimal results.
In summary, the most important factor is prognosis after an injury to a nerve is the violence of that injury and the extent of the damage to the limb. And the most important factor in prognosis that the physician can control is the delay between injury and repair. Good judgment is needed in the care of the patient with peripheral nerve injury to give the patient optimal results.

48. Thank You
It is nice to be back in Saigon again and see my friends. Thank you.