Management of IAN and LN Damage following Oral and Maxillofacial Surgery

1. Neurosensory Sensory Deficit
post mandibular surgery
20/03/17

3. Contents
• Background Revision of
• Rates of NSD in OMFS
• Lingual Nerve Anatomy
• Preoperative evaluation of Third Molars
• Avoiding Injuries in Third Molar Surgery
• When Injury Occurs
• Immediate Management
• NST
• Mx Protocol
• Medical Mx
• Microsurgical Repair

4. Neurosensory Deficits (NSD)
• Third Molars (White Paper)
• IAN: 1%
• Lingual N: 0.5%
• High risk wisdom teeth (Rood/Shehab)
• 12% if 3 x high risk criteria present
• 30% (greater than 3mm loss of IAN cortical bone on CBCT)
• Orthognathics
• BSSO alone: 13% (Collela)
• BSSO + Genio: 40% (Boloux)
• BSSO: >31 years: 20%, 20-30yrs: 15%, <19: 10%
• Fracture mandible (Zuniga)
• Pre-ORIF: 54%
• Post-ORIF: 73%

5. Preoperative Evaluation
• Age (>35)
• Type of Impaction (Horizontal, DA)
• Operator experience
• Presence of Rood and Shehab criteria : Shadow across the root of
impacted molar, deviation or deflection of IAN canal, interruption of
the white line of IAN canal
• If above -> CBCT (CBCT is not to be done as routine)
• Criteria +ve is predictive of loss of cortication on CBCT (>50%)
• CBCT: decortication of canal for greater than 3mm
• Remember OPGs can be distortion of size.
• Implants should be atleast 2mm away from canal

6. Lingual Nerve Anatomy (Benninger 2013)
• On MRI: 10% above alveolar crest, and 25% contacting lingual plate
• Crosses on average 13.2mm for distolingual cost of third molar before
it turns medial, and goes 7.3mm below crest on average.

7. Avoiding Injuries
• Risk Stratification as described
• Technique (Experience (Jerjes 2010), GA, Force)
• NSAIDs (Diclofenac), ? Dexamethasone
• Stay buccal on relieving incisions.
• Lingual flaps increase temporary LN Paraesthesia ? But unchanged
long-term
• Assess for IAN once extracted tooth
• Remember Coronectomy, Orthodontic extrusion options

8. When Injury occurs 1
• Most injuries occult i.e. you notice during the review
• Two options in OR when injury noticed:
1) Repair primarily using microsurgery (primary repair),
2) Tag ends with nylon or polypropylene (for secondary repair).
Either way give NSAIDs, and steroids

9. When Injury Occurs 2 (Assessment)
• Take Baseline neurosensory
assessment
• Is it sensory deficit or pain?
• If deficit (paraesthesia,
hypoesthesia or anaesthesia)?
• Clinical Examination is stepwise as
per Right--------------------------------
• If pain, is it on stimulation or
spontaneous. SOCRATES, and VAS
• Clinical exam in dysesthesia
involves testing all fibre sizes
without stepwise progression-----
(Two point: IAN <4mm, LN <3mm)
Wooden end of cotton swab, von Frey
Dental Needle
Aɑ, Aβ fibres (5-12um)
Aβ fibres (4-8um)
A𝛿, C fibres (0.2- 5 um)

10. Testing and Management
• Who to Image? What image?
• OPG?
• CBCT if suspicion of mechanical
injury
• MRI for Lingual nerve (3T)
• Always Monitor for 3 months
• 75% improve
• If Improving, continue to
monitor monthly until
improvement ceases, or
12months passes,
Central Peripheral
1 week,
1 month,
2 months

11. Is it really a long term problem?

12. Medical Management of post-traumatic
Trigeminal Neuralgia
• Based on Benoliel 2012
• Can be used alone or as an
adjunct following
microsurgical procedure
• When used alone have up to
30% success rate in pain
reduction

13. Classification

14. Microsurgical Repair
Indications Contraindications
• Observed Nerve Transection
• No improvement in hypoesthesia for 3 months
• Development of pain caused by nerve entrapment
or neuroma formation
• Presence of foreign body
• Progressively worsening hypoesthesia or
dysesthesia
• Intolerable hypoesthesia
• Central neuropathic pain
• Improving Sensory function
• Acceptable hypesthesia
• Metabolic neruopahty
• Excessive time following surgery (?12mos
?24mos?)*
• Not fit for surgery
*Meyer 1992 – 90% recovery if <3mos, 10%>12mos

15. Nerve Repair
• IAN Approaches
• Can be done vestibular (oral) or cutaneous approach based on position of
nerve
• Requires decortication of the nerve(can be difficult)
• LN Approaches
• Paralingual approach(smaller incision, direct, but may have retraction of ends)
• Lingual sulcus approach (larger incision, less chance of retraction of ends)

16. Surgical Options
• Primary Neurorraphy
• Should be done where possible
• Needs to be tension free (<25g) which
may require Proximal exploration of LN,
or decortication of IAN to MN for extra
laxity
• ?Use of vein or grafts as adjunct (but not
to bridge gap – Pogrel 2001 shows poor
results)
• Graft
• Indication is continuity defect that can
not be repaired primarily without
tension.
• Sural and GAN are most popular grafts
Nerve Diameter Shape Fasciles
IAN 2.4mm Round 18-21
LN 3.2mm Round 15-18
GAN 1.5mm Ovoid 8-9
Sural 2.1mm Flat 11-12
Other Graft Options:
Allopastic Tubules e.g. gortex ( no good evidence)
Skeletal Muscle
Vein Grafts (may be acceptable for gaps <5mm)

17. Pogrel 2002 Robinson 2000 (LN ONLY) Strauss 2006 Bagherei 2010(LN)
Bagheri 2012 (IAN)
• 28/51 had improvement
• Procedures done <10weeks
post injury appeared to have
better improvement*
• IAN slightly better than LN
• Little correlation between
subjective and objective
testing.
• No one developed
dysesthesia as a result of
surgery (one worsened
dysesthesia)**
• 30% improvement in
Dysasthesia, but no one
becomes pain free
• Symptoms most likely to
benefit are Anaesthesia, and
tongue biting.
• Is it worthwhile? Median
score 7(0-10), Zuniga 2.5(0-
4)
• Lots of controv cf other
studies (timing, fibre size
improvement etc)
• 35% had significant
improvement
• 90% had some improvement
• Pain and A-delta fibres
return before other larger
nerves (3mos v 12mos)
• Functional improvement in
IAN 81%,
• Improved Outcome with Age
<51, Time b/w trauma and
surgery 12mo.
• Functional improvement in
LN 91%
• Improvement in outcomes
with Age<45, Time b/w
trauma and surgery
(5.8%/mo, drop off 9mo)
Outcomes

18. 10 Things I Have learnt.
1. NSD of IAN and LN are uncommon
2. Most (75%) recover with time
3. Risk Stratification allows appropriate counselling, and surgical planning
4. When Injury happens it can significant impact on patient lives.
5. Structured History and exam are important to follow mx protocol
6. Centrally mediated pain syndromes are difficult to treat with poor outcomes.
7. Microneurosurgical outcomes depend on what we are testing. Subjective
recovery may not be as good as Objective Recovery.
8. Subjective outcomes are (probably more important indicator for surgery and
measure of outcome).
9. 50% of surgical patients are going to have good outcomes with another 40%
have some improvement.
10. Most patients are happy they had surgical intervention