Prevention of the Facial Nerve Injury
Facial Nerve Monitoring
Facial nerve monitoring has been a standard of practice for head and neck surgeons since the 1980s in order to minimize and prevent facial nerve injury. Monitoring can be defined into either “passive” or “active” forms. In the passive form, facial muscle movement is activated only by direct mechanical, stretch, or other nonelectrical stimulation of the facial nerve. As the simplest example, having a resident or a surgical assistant visually monitoring the face for twitching during a surgical approach to the TMJ is the simplest form of passive monitoring. A handheld device with a tip carrying low amplitude impulses to tissue in order to stimulate any nearby branch of the facial nerve is a common device applying passive monitoring in most TMJ surgeon’s practices. In the most advanced form of passive monitoring, electrodes placed near the orbicularis oculi and orbicularis oris muscles record electromyography (EMG) potentials that are audible to the surgeon when he or she approaches or encroaches on a branch of the facial nerve .
In active monitoring, the facial nerve itself is electrically stimulated with audible recordings of facial compound muscle action potentials (CAMP). The stimulation is delivered through either a monopolar or bipolar electrode with blunt tips. On bipolar stimulation, the current is confined to the tissue between the electrified tips allowing for a very specific stimulation. The same stimulus is created using monopolar tips, but it does not identify the nerve location with the same specificity .
These techniques are not fool proof and failure to stimulate the facial nerve could be from many sources including detached or incorrectly placed electrodes, a malfunction of the handheld stimulator, infiltration from local anesthetic paralyzing the nerve, pharmacological muscular paralysis from the induction of anesthesia, and even a muted speaker. Attempts should be made to avoid these errors by intraoperative checks of the monitor, communicating with the anesthesiologist, and being competent in the surgical anatomy and approach to the temporomandibular joint .