Case Study: Nerve Repair Surgery
It’s Time to Rethink Nerve injuries and Nerve Repair
Injuries to the peripheral trigeminal nerve, most specifically the inferior alveolar nerve and the Lingual nerve are rarely repaired. These injuries cause patients considerable clinical and psychosocial problems, most of which are minimized and de-emphasized or ignored by our profession. All of us are guilty of this. There are 1.4 million injuries to the trigeminal nerve each year and the vast majority go untreated. Why? The simple answer is the cure has always been worse than the disease. Now there are options that are game changing.
In the past, the protocol for witnessed and unwitnessed injury to the lingual and inferior alveolar nerve has been observation, neurosensory testing (NST) and…. cross your fingers and hope it gets better. The reason for this may relate back to a study done in 1986 that inferred that 80% of all lingual nerve injures and 90+ percent of all inferior alveolar nerve injuries spontaneously recovered. (1.) This attitude of “observe and hope” has permeated through dentistry for decades. It has been reinforced and defended for many reasons. Here are the roadblocks to repairing a known nerve injury:
- Lingual and inferior alveolar nerve repair outcomes are poor.
- Nerve repair surgery is hard.
- Nerve repair requires micro-neurosurgical training in order to be successful.
- Additional donor site morbidity. Getting the donor nerve graft requires surgery to harvest the sural nerve. More surgery, more risk and a new area of numbness in the calf and foot.
- Nerve degeneration occurs after a nerve injury. This process can be extensive over time with central nervous system ramifications.
- No diagnostic imaging is available to determine where the nerve is injured or how bad the injury really is.
With the exception of # 5, all of the reasons given above for not repairing lingual and inferior alveolar nerve injuries are no longer so problematic. This is not 1986. Crossing our fingers and hoping for the best is not the answer…. it’s time to rethink nerve injuries and repair.
Recent advances in nerve grafting have significantly increased the success rate of nerve repair for the inferior alveolar and lingual nerve. A new bio technology company named AxoGen has developed a proprietary process to treat donated nerve tissue that greatly increases the regrowth of nerve fibers through the preserved nerve tubules of the graft. With AxoGen nerve grafting protocols and their proprietary cadaveric nerve graft, success rates for early nerve repair of witnessed nerve injuries has increased significantly. Return of Functional Sensory Recovery has been documented over 80% and in some studies reaching 93% when the injury is repaired within the first three months of damage. (2, 3) Figure 1 and 2.
Time remains the enemy in treating nerve injuries. The treatment algorithm for timing has changed considerably. In the past, treatment of nerve injuries went something like the illustration in Figure 3 and 4. This illustration is a little exaggerated but hopefully the point is made. Valuable time is lost following the old “wait and see” approach. Even the use of neurosensory testing to determine the “progression” of perceived changes in numbness has been challenged. In a landmark article by Zuniga, he concludes, “NST (neurosensory testing) results are not reliable in the first month in inferior alveolar nerve injuries and the first three months after lingual nerve injury because of postoperative changes and the inability of the patients and or physicians to reproduce the sensory response.” (4)
While in the past most experts agreed that better outcomes were achieved if inferior alveolar nerve injuries and lingual nerve injuries were repaired within a 3 month window, that timeline is being shortened drastically. This is because we know that persistent nerve damage and later repairs leads to poorer surgical outcomes, more neuropathic pain and troublesome oral dysfunction. Because of AxoGen’s advances in nerve grafting techniques and their new Avance ™ cadaveric nerve grafts that are more successful and easier to place, the old patient management timeline has been revised so that, in known or witnessed nerve injuries, sensory improvement is determined within the first four weeks and if improvement is not seen, the nerve injury is repaired nearer the two month window. (5, 6)
Earlier diagnosis and management are essential to improve outcomes. If a patient has total anesthesia for just 2 months, it is extremely unlikely that they will ever have total recovery from the nerve injury without intervention. (5) If a patient has partial or altered sensation for 4 months (that includes paresthesia, burning or stabbing pain), it is extremely unlikely they will see any further resolution of their symptoms without intervention. (5)
The Avance cadaveric nerve graft developed by AxoGen in combination with their proprietary porcine nerve wraps and nerve connectors makes for a simplified surgical approach to nerve repair. It yields a much greater return of Functional Sensory Recovery.
Functional Sensory Recovery has been shown to approach approaches 90% within the first 12 months postoperatively in a study by Zuniga, reported in the Journal of Oral Surgery in 2017. (7) AxoGen’s technique has been described as “plug and play.” Figure 5 shows a nerve graft prepared for insertion into a lingual nerve defect created by removing the damaged section of the nerve. Figure 5 demonstrates the insertion of the graft using the connectors to position the proximal and distal nerve segments next to the graft. Suturing the graft in place and attaching the connectors to the proximal and distal segments is accomplished with 7.0 monofilament suture. Magnification loops are all that is needed.
Permanent injury to the inferior alveolar nerve during third molar surgery happens .25 to 8.4% of the time. While lingual nerve injuries are less common, injury to this nerve has higher consequences in terms of oral dysfunction and pain. These numbers are considered low by some experts since many nerve injuries go unreported. The incidence of nerve injuries is on the rise possibly because of an increase in dental implant surgery by both generalists and specialists. Still, tooth extractions account for 60% of all nerve injuries in the lower jaw.
The percentage of cases of trigeminal nerve injury that are repaired is low owing to the reasons stated earlier in this report. New nerve grafting techniques and new cadaveric nerve grafts are changing the dynamics of this by making repairs easier and more predictable. Success rates have increased dramatically for witnessed nerve injuries repaired right away and for nerve injuries that are repaired late as well. The success of repair has also increased because of new imaging techniques using Magnetic Resonance Neurography. MRN can identify damage to a nerve as early as 21 days after injury. (8) MRN can aid in identification of the injured area along the nerve paths of both the lingual and inferior alveolar nerves.
Employing the advances outlined in this report, the majority of lingual and inferior alveolar nerve injuries can be repaired more easily and with better expectations of Functional Sensory Recovery.
Nerve injuries happen to all who practice our craft. Ignoring them or trivializing them is a thing of the past. It’s in our patients’ best interest to rethink nerve injuries and nerve repair using AxoGen’s Avance™ donor nerve grafts and nerve connectors with a fresh look at accelerating the timeline from injury to repair.
Bibliography upon request.