Facial Nerve Injury Following TMJ Surgery and its Management by Electrical Stimulation-A Case Study

The temporomandibular (TMJ) joints are multipart structures containing muscles, ligaments, bones and neurovascular bundle. Surgery for TMJ disorders represents a significant risk of facial nerve damage that can result in facial weakness affecting patients’ mental health, ability to communicate and self-image. This case report examined the effect of electrical stimulation in the treatment of facial palsy. A 15 year old male patient with a left sided facial palsy came with the history of TMJ surgery exactly at 7th day after surgery. The patient was functionally assessed by House Brackmann method, neurologically evaluated by strength duration (SD) curve and graded by Sunderland’s classification of peripheral nerve injury. The SD curve was plotted at 0 week and then at 1st and 2nd week after subjecting the patient to electrical stimulation, facial massage and ‘Y’ shaped facial adhesive strap. The prognosis of the patient shows the shift of the SD curve to the left which indicates near normal complete re-innervations after treating with electrical stimulator for a month. It was concluded that electrical stimulation may improve the facial paralysis and decrease the psychosocial influence on the patient.


INTRODUCTION
Temporomandibular joint (TMJ) disorders are characterized by the incidence of pain, clicking sound and restricted mouth opening (1) .TMJ disorders include disease, derangement, degeneration, hypo mobility, hyper mobility, benign/malignant tumors and trauma.
Epidemiological studies have shown that, adolescents and young adults, reported clicking sounds during energetic movement of the mandible This is an Open Access article licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (https://creativecommons.org/licenses/by-nc-sa/4.0/ ), which permits unrestricted Non Commercial use, distribution and reproduction in any medium, provided the original work is properly cited.
Published by Oriental Scientific Publishing Company © 2017 (2) .The universal causes of clicking sound are neuromuscular incoordintion of lateral pterygoid muscle, dislocation and derangement of the articular disc.However, the etiology of clicking is divisive; it is not known whether it's due to undisruptive situation (3)(4) or due to internal derangement of the TMJ (5)(6) .
Despite the surgical management of TMJ disorders, there are possible complication which comprise internal bleeding, disease, auriculotemporal (ATN) nerve syndrome, ear pathology, parotid gland tumor, (12) and damage to the facial or VII cranial nerve (7)(8)(9)(10)(11)(12) .The facial nerve is mixed cranial nerve comprising both sensory and motor components.The motor branch arise from pons while the sensory branch arise from the nervus intermedius and emerge from the brainstem and enters petrous part of the temporal bone into the internal auditory meatus and forms the geniculate ganglion prior to entry into the facial canal.After passing through the canal, it comes out through the stylomastoid foramen and runs throughout substance of the parotid gland and divides into five terminal branches.It has an important function on facial aesthetics by enabling the movements of mimic muscles, and it is the most damaged nerve among the cranial nerves after leaving the central nervous system (13) .Eating, drinking and speaking difficulties are observed in peripheral facial nerve damages, as well as difficulties in expressing the feelings.
The nerve supplies the muscles of facial expression, the posterior belly of the digastric muscle, the stylohyoid muscle, and the stapedius muscle developing from hyoid arch.It provides secretomotor supply to the submandibular and sublingual salivary glands.
The temporal and zygomatic branches of the facial nerve are highly susceptible for damage during TMJ surgery (14) .The functional integrity of facial nerve should be preserved during TMJ surgery (15) .There are many factors that could contribute to the injury of the temporal and zygomatic branches of the facial nerve (16) .These nerves lie in a confluence of superficial fascia, temporalis fascia, and periosteum, and may be damaged during surgical approach.Undue retraction causes compression and/or stretching of nerve fibres resulting in neuropraxia which forms the basis for the nerve injuries associated with TMJ surgery (17) .
Treating facial paralysis in early period with a multidisciplinary approach is important for speeding up the recovery process (18) .In addition to medical therapy, thermal heat modalities, electrical stimulation, exercise and massage are physical therapy methods of which the effectiveness were shown (18) .

Aim and Objective
The aim of the present study is to detect the facial nerve injury following TMJ surgery and its prognosis by electrical stimulation with the case report.

MATERIALS AND METHODS
A 15 year old male patient with a left sided facial paralysis came to the hospital with the history of TMJ surgery exactly at 7 th day after surgery.After receiving informed consent from the parents of the patient, the neurological signs of the patient were assessed at 0, 1 & 2 weeks by the following methods: i) Functional assessment ii) Strength -Duration Curve

Functional assessment
The patient was functionally assessed by a.
Sunderland's classification ( Table -2) The House-Brackmann method is the conventional method for the clinical assessment of facial nerve function.It is prejudiced and sporadic, prone to inter-observer disparity.

Procedure
The SD curve was plotted at 0 week and then the patient was subjected to electrical stimulation, facial massage and 'Y' shape facial adhesive strap.
A nineteen year old male patient with a left sided facial paralysis after TMJ surgery was assessed for neurological signs at 0, 1 & 2 weeks by the following methods in this case study.i) Functional assessment ii) Strength duration curve i) Functional assessment The House-Brackmann method was clinical assessment of facial nerve function.The following observations were made in the study (Table 3).

Strength duration curve
The graph represents the interdependence between the stimulus strength and the time required in activating the muscles.It also indicates the strength of impulses of various durations necessary to generate muscle contraction by joining the points that graphically represent the threshold value along the ordinate for various durations.This SD curve was plotted at 0, 1 and 2 weeks following postsurgical facial paralysis.

SD curve at 0 week
When all the nerve fibre supplying a muscle has degenerated, the strength duration produced is characteristic of complete denervation.For all impulses with duration of 100 ms or less the strength of the stimulus must be amplified each time the duration is reduced and no reaction is recorded to impulses of very short duration.The curve rises sharply and moves to the right than that of normally innervated muscle.The plotted SD curve showed that the facial nerve is at the state of 3 rd degree injury according to Sunderland's classification.(Figure 1) Bell's phenomenon Present The patient was then subjected to electrical stimulation using an electrical stimulator with diagnostic interrupted Galvanic current facility (Figure2), facial massage and "Y" shaped facial adhesive strap (Figure 3) to prevent the over stretching of the angle of the mouth.The current was passed to the patient through two small electrodes -Active electrode (nape of the neck) and Inactive electrode (motor points of the facial muscles).First the Faradic current was applied to the patient and observed for the contraction which was absent in this case.Next the galvanic current was applied after which the contraction was observed.This process was repeated for each length of the stimulus in turns, the magnitude being increased.The SD curve was plotted from the outcome of the investigation.

SD curve at 1 st week
SD curve plotted after 1 week shows the slight shift of the curve towards left which indicates the slight progression of the re-innervations after electrical stimulation (Figure 4).

SD curve at 2 nd week
Longer duration impulse -contraction was recorded with the stimulus of low intensity.As the impulses are shortened, some fibres respond less readily, so that a stronger stimulus was applied to produce a perceptible contraction and the curve rises steeply like that of the denervated muscle.
Shorter duration impulse -some fibres respond to a weaker stimulus than that necessary for the denervated fibres, so that the contraction of denervated fibres was not obtained and this part of the curve is similar to that of the innervated muscle.Thus the right side of the curve is similar to denervated muscle, the left side of the curve is similar to innervated muscle, and the bend is seen at the junction of the two (Figure 5).

Prognosis
The prognosis of the patient was assessed after treating with an electrical stimulator for a month.The SD curve plotted shows the shift of the curve to the left which indicates near normal complete re-innervations (Figure 6).

DISCUSSION
A male patient with a left sided facial paralysis came to the hospital with the history of TMJ surgery exactly at 7th day after surgery.The patient was functionally assessed by House Brackmann method, neurologically evaluated by strength duration curve and graded by Sunderland's classification of peripheral nerve injury.Choosing between the treatment methods is one of the impor tant points together with the paralysis diagnosis.The most efficient treatment strategy is still controversial (19) .The treatment may be planned with the determination of the disease period, actual lesion site and the exact degree of damage in the nerve.Physical methods are used in facial paralysis treatment along with medical therapy which include thermal therapies, electrical stimulation, exercise, massage, biofeedback and acupuncture therapy (20) .
In this case study the SD curve was plotted at 0 week and then at 1 st and 2 nd week after subjecting the patient to electrical stimulation, facial massage and 'Y' shaped facial adhesive strap.The prognosis of the patient was assessed after treating with electrical stimulator for a month.At 0 week no reaction was recorded to impulse of extremely small duration and the curve rises sharply and is further to the right than that of the normally innervated muscle.It also showed that the facial nerve is at the state of 3 rd degree injury according to Sunderland's classification.Studies on the successful results of the long-term electrical stimulation in sub acute and chronic period of facial paralysis were seen in literature (21)(22)(23)(24).
Alakram et al applied hot application, massage and exercise program to one group and electrical stimulation to the other in their study and reported that there were improvements in both groups which co-relates with our current case study (25)   .
The prognosis of the patient shows the shift of the SD curve to the left which indicates near normal complete re-innervations after treating with electrical stimulator for a month.The physical therapies like electrical stimulation, facial massage and facial strapping are important in terms of speeding-up the recovery process and decreasing the psychosocial influence on the patient.

CONCLUSIONS
The facial nerve injury is associated to the complexity implicated in TMJ surgery.The nerve lesion was shown to be temporary in nature.Care should be taken while doing TMJ surgery because of its varied complications one of which is facial nerve injury This case study proves that the patient display a near normal function of the facial nerve by subjecting patient to electrical stimulation, facial strapping and massage.
The plotting of strength duration curve indicates the strength of impulse of various duration required to produce contraction in a muscle.It is easy and consistent.It shows the percentage of denervation.It cannot indicate the site of nerve lesion.