J Oral Maxillofac
Surg
50:1048-1051,1992
Facial Nerve Function Following Temporomandibular Joint Surgery Using the Preauricular Approach SIMON WEINBERG, DDS, FRCD(C), FICD,* AND BOHDAN KRYSHTALSKYJ, BSc, DDS, MRCD(C)t Sixty-eight patients (83 temporomandibular joints) consecutively operated on who had a variety of temporomandibular joint operations using a preauricular approach were assessed for facial nerve function following surgery. Nine patients (10.84%) showed signs of facial nerve injury in which the temporal and zygomatic branches were involved. The incidence of facial nerve injury was greater in patients who had undergone previous temporomandibular joint surgery (17.64%) than in patients with previously unoperated joints (9%). Normal facial nerve function returned in 9 to 14 weeks except in one patient who showed a mild deficit of the zygomatic branch at 20 weeks. The nature and duration of the surgical procedure did not correlate with facial nerve injury. Scarring of tissues as a result of previous temporomandibular joint surgery may significantly increase the risk of facial nerve injury during subsequent temporomandibular joint surgery. preauricular approach, House et al3 reported a 15% incidence of facial nerve injury. Dolwick and Kretzschmar4 reported a 32% incidence of facial nerve involvement after their modified preauricular approach in which a separate skin flap was not developed. By altering the dissection technique Hall et al5 were able to decrease the incidence of facial nerve injury from 25% to 1.7%. This study was undertaken to determine the incidence of facial nerve injury following a variety of TMJ surgical procedures using the preauricular approach.
The ability to preserve the functional integrity of the facial nerve is a critical measure of success in temporomandibular joint (TMJ) surgery. However, in spite of the development of a myriad of surgical approaches to the TMJ, the facial nerve is always at risk for damage and the resulting impairment of frontalis and/or orbicularis oculi muscle function constitutes a relevant and distressing complication of TMJ surgery. According to Keith,’ the incidence of facial nerve injuries resulting from TMJ surgery ranges from 1% to 25%. The nerve injuries are mainly transient in nature, usually resolving within 6 months. Dingman et al2 reported an incidence of 55% following surgery through the preauricular approach. In their modified
Materials and Method Sixty-eight patients (83 joints) who consecutively underwent TMJ surgery were assessed for facial nerve injury. The sample consisted of 62 women and 6 men between the ages of 19 and 62 years. Fifty-three patients had unilateral surgery and 15 patients had bilateral surgery. Thirteen patients had had unilateral TMJ surgery once before and two had previous bilateral surgery on three occasions. The surgery was carried out by the same surgeon using a preauricular approach as described by Weinberg and Kryshtalskyj6~’ and Weinberg.8 The surgical procedures consisted of discoplasty and eminoplasty, 49 patients (60 joints); discoplasty, eminoplasty, and high condylar shave, 8 patients ( 10
Received from the Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. * Professor; Chief, Department of Oral and Maxillofacial Surgery, The Doctors Hospital, Toronto, Ontario, Canada. t Associate StaE, Chief, Department of Oral and Maxillofacial Surgery, Queensway Genera1 Hospital, Toronto, Ontario, Canada. Presented at the 38th Annual Meeting of the Canadian Association of Oral and Maxillofacial Surgeons, Ottawa, Ontario, May 199 1. Address correspondence and reprint requests to Dr Weinberg: Department of Oral and Maxillofacial Surgery, The Doctors Hospital, 340 College St, No. 465, Toronto, Ontario, MST3A9 Canada. 0 1992 American
Association
0278-2391/92/501
O-0005$3.00/0
of Oral and Maxillofacial
Surgeons
1048
1049
WEINBERG AND KRYSHTALSKYJ
joints); discectomies without placement of implants, 6 patients (6 joints): implant removal, eminoplasty, and high condylar shave, 2 patients (2 joints); and gap arthroplasty, 3 patients (5 joints). General anesthesia was administered to all patients and the duration of the surgical procedures was between 48 and 76 minutes per TMJ. Facial nerve function was initially assessed in the operating room as the patient regained consciousness and again 1 day after surgery. Facial nerve injury was deemed to have occurred if the patient was unable to raise the eyebrow or wrinkle the forehead (temporalis branch), or to completely close the eyelids (zygomatic branch). Patients were similarly examined weekly by the same surgeon for the assessment of facial nerve function. Results Nine of the 68 patients or 9 of 83 TMJs (10.84%) showed signs of facial nerve dysfunction following TMJ surgery. This included 3 of 15 patients (3 of 17 TMJs) (17.66%) who had undergone previous TMJ surgery. Of the 53 patients who had TMJ surgery for the first time 6, or 9%, had facial nerve involvement (6 of 66 TMJs). There were no cases of bilateral facial nerve injury. Table 1 shows the facial nerve branches that were injured and the time taken for the patient to recover from the injury. The temporal branch was involved in 7 of the 9 patients who showed signs of facial nerve damage; two patients had damage to the zygomatic branch. Of these two patients, one had three previous operations and the other had TMJ surgery once before. By the 14th postoperative week, normal function had returned in 8 of the 9 affected patients. One patient showed significant improvement, but still had mild involvement of the zygomatic branch 20 weeks after surgery. Six patients who showed signs of facial nerve injury shortly after regaining consciousness exhibited normal Table 1. Facial Nerve Branches Injured and lime to Recovery
Type of TMJ No previous surgery (66) Previous surgery ( 17)
Facial Nerve Branch Injured
Recovery Time
Temporal branch (6)
9- 14 weeks
Temporal branch (1) Zygomatic branch (2)
IO weeks One at 14 weeks, second patient (3rd surgery) had mild nerve deficit at 20 weeks
facial nerve function the day after surgery. There was no instance in which the early diagnosis of normal facial nerve function was followed by signs of facial nerve deficit. A x2 test with P = .05 revealed that there was a significant difference in the incidence of facial nerve damage between patients with previous TMJ surgery and those having surgery for the first time, 17.64% compared with 9%, respectively (P = .05). Discussion The variety of approaches that have been described for surgery of the TMJ share a common objective: adequate exposure ofjoint structures and maximum protection of the facial nerve. Maximum protection of the facial nerve requires meticulous surgical dissection and a thorough knowledge and heightened awareness of the regional anatomy. In his classic studies of 100 cadaver heads, Callander’ found eight major variations of the distribution of the facial nerve. Similarly McCormack et al” and Davis et al’ ’ have demonstrated six different patterns of facial nerve distribution. Of interest is the fact that of the six variations, there is distal branching in four of the patterns that can allow for more than one pathway of innervation of the frontalis muscle. Hall et al5 speculate that because of this branching, the most distal branch of the facial nerve that crosses the zygomatic arch could possibly be cut 63% of the time without loss of frontalis function. Similarly, Baker and Conley” have found that the temporal branch has many branches of its own. They found five to seven branches on average. One of these branches leads to the frontal region, 2 to the orbital region, 3 to the zygomatic region, and 2 to the buccal region. They postulated that complete transection of the temporal branch would result in permanent paralysis or incomplete recovery of forehead movement. This was due to the fact that 15% of the fibers to the brow have no connection with other branches of the ipsilateral or contralateral facial nerve. The temporal branch, in particular, as well as the zygomatic branch of the facial nerve, are especially vulnerable to injury during TMJ surgery. These nerves lie in a condensation of superficial fascia, temporalis fascia, and periosteum, and may be injured by any dissection technique that attempts to violate the integrity of this region. In their classic article, Al Kayat and Bramley13 stressed the clinical importance of this dangerous area of fusion over the zygomatic arch and they have shown that the temporal branch of the facial nerve lies within this area of tissue condensation on average 2 cm from the anterior concavity of the external auditory canal, with a range of 0.8 cm to 3.5 cm. Of particular importance is the fact that in more than one half of their samples the nerve was less than 2 cm away. Pitanguy and Ramos14 revealed that the direction of
1050 the temporofacial branches in 20 cadaver facial halves was constant, with the course and vector being on a line located 0.5 cm below the tragus of the ear, in the direction of the eyebrow and passing 1.5 cm above the lateral extremity of the eyebrows. They also noted that the insufficiency of the superficial muscular and aponeurotic system (SMAS) at the level of the lateral border of the frontalis muscle renders the temporal branches of the facial nerve more vulnerable to injury. To minimize the chance of temporal branch damage, DeCastro-Correia and Zani” proposed external landmarks. They postulated that the temporal branch is likely the most superficial of the five facial nerve branches, and may be found in a triangle bounded by the earlobe, lateral brow, and highest frontal crease. RudolphI found the average depth of the temporal branch of the facial nerve to be 9.1 k 2.8 mm from the parotid edge and the zygomatic branch to be 9.2 + 2.2 mm from this edge. He further indicated that the dangerous area in which nerve branches become superficial is the distal temporal region, 5 cm from the parotid border and 2.3 + 0.6 mm deep. This corresponds to the supraorbital bony ridge above the lateral orbit. On the other hand, the zygomatic branch was found to be well protected and lying deep within the facial fat as it exits the parotid gland. RudolphI also found that there was no zygomatic branch that crossed over the prominence of the zygoma. Furthermore, the zygomatic branch was found to have many anastomoses between branches. Baker and Conley” have concurred that because of these anastomoses, paralysis of the orbicularis oculi muscles is more unusual after one of the branches is cut, and if so, function usually recovers within 1 year. Mitz and Peyronie” have further suggested that the following anatomic factors may explain injury to the facial nerve: a thin subcutaneous musculoaponeurotic system (SMAS), a superficial lobe of the parotid gland that is short and does not protect the nerves, and a surgical dissection that is carried too far forwards. In light of the measurements of Al Kayat and Bramley,r3 the safest way to approach the glenoid fossa and articular eminence at the subperiosteal plane and avoid injury to the temporofacial outflow of the facial nerve is to operate within the safety of the pocket formed by the splitting of the outer layer of the temporalis fascia. The facial nerve branches are superficial to this plane and they may be protected at this level by gentle anterior retraction. To gain adequate exposure of the glenoid fossa and articular eminence, the periosteum over the zygomatic root should be incised vertically no further than 5 mm anterior to the most anterior concavity of the external auditory meatus. The increased incidence of facial nerve injury in patients who have undergone previous TMJ surgery may be explained by the fact that surgical scarring leads to
FACIAL NERVE
FUNCTION
AFTER
TMJ
SURGERY
fibrosis and distortion of the fascial layers and significantly increases the difficulty of establishing precise tissue planes during the dissection. The usual fat-occupying “safe pocket” that is formed by the splitting of the outer layer o’fthe temporalis fascia may no longer be identifiable in the patient with multiple operations because it is often obliterated by dense fibrous connective tissue. In these circumstances, after the development of a layered skin flap, the dissection should be deepened directly to the temporalis muscle to ensure the establishment of a fascial plane that is deep to the branches of the facial nerve. Excessive or heavy-handed retraction causes compression and/or stretching of nerve fibers resulting in neurapraxia; this may be responsible for a significant number of nerve injuries associated with TMJ surgery. Because densely scarred tissues are difficult to retract without creating considerable tension, a precisely layered surgical dissection should be done to minimize retraction forces. Incisions that are deepened directly to the outer layer of temporalis fascia without adequate undermining of fascial layers create a thick, immobile layer of tissue that is difficult to retract without causing excessive tissue tension. Facial nerve injury may also be caused by inadvertent suture ligation of facial nerve branches, particularly during wound closure. Care must be exercised during wound closure to avoid taking deep blind bites with the suture needle. The use of electrocautery in deep sites that are potentially close to facial nerve branches, or within the parotid gland, also should be avoided. Furthermore, one should avoid crushing or clamping tissue indiscriminately, particularly during episodes of brisk bleeding. Excessive swelling and/or hematoma formation may result in transient facial nerve injury. Corticosteroids should be used to reduce swelling and nerve sheath edema, and the establishment of good hemostasis before a layered wound closure to obliterate dead space and minimize hematoma formation. Occasionally a pressure dressing consisting of fluffed gauze and an elastic gauze bandage is recommended. The wound should be drained only if oozing persists before skin closure or if dead space cannot be adequately eliminated. If nerve damage should occur, one should determine which nerves are affected and whether microsurgical repair may be indicated. If the choice is simply to observe the situation, serial testing by electroneurography and electromyography may help in determining whether the affected muscles have the capability of rehabilitating themselves spontaneously. Conservative palliative management includes physiotherapy, exercises, reassurance, and the establishment of close rapport between surgeon and patient. Baker and Conley” have also suggested that if electrical test-
1051
WEINBERG AND KRYSHTALSKYJ
Table 2. Possible Causes of Facial Nerve Injury in TMJ Surgery Preoperative palsy from previous surgery Trauma from heat of electrocoagulation Local anesthesia injected in immediate nerve area Deep ligatures or plication sutures Crushing by forceps or clamps Excessive retraction and traction Nerve transection Hematoma or edema in nerve sheath Inflammation and infection Distortion of the normal anatomy by adhesions from previous TMJ surgery
References I. Keith DA: Surgery Of The Temporomandibular Joint: Success, 3.
3.
4.
5.
6.
7.
ing shows that the chronaxaxial levels remain high for more than 3 months, it is most likely that there will be no return of movement of the affected structures. If the nerve damage is left unrepaired by microsurgery, then the persistent muscle paralysis will result in frontalis and/or orbicularis oculi muscle atrophy and permanent ptosis of the brow and upper eyelid. Six of our patients (six joints) who showed facial nerve deficit on regaining consciousness had normal facial nerve function the following day. This can be explained by the fact that we routinely infiltrate the preauricular soft tissues with 4 to 6 mL of 0.5% MarCaine (Winthrop Laboratories, Aurora, Ontario, Canada) with 1:200,000 epinephrine before skin incision. This local anesthetic solution may block facial nerve conduction for 5 to 12 hours. Table 2 summarizes the potential causes of facial nerve injury related to TMJ surgery. In patients who have had previous TMJ surgery, a slight modification in the surgical dissection may offer additional protection to the facial nerve.
8. 9.
10.
I I. 12. 13.
14.
Ii.
16. 17.
Failure And Complications Of Temporomandibular Joint Surgery. Boston, MA. Blackwell Scientific, 1988, pp 272,282 Dingman RO, Dingman DL, Lawrence RA: Surgical correction of lesions of the temporomandibular joints. Plast Reconstr Surg 55335, 1975 House LR, Morgan DH, Hall WP: Clinical evaluation of TMJ arthroplasties with insertion of articular eminence prosthesis on ninety patients. Laryngoscope 87: I 182. 1977 Dolwick MF. Kretzschmar DP: Morbidity associated with the preauricular and perimeatal approaches to the temporomandibular joint. J Oral Maxillofac Surg 40:699. 1982 Hall MB. Brown RW, Lebowitz MS: Facial nerve injury during surgery of the temporomandibular joint: A comparison of two dissection techniques. J Oral Maxillofac Surg 43:20. 1985 Weinberg S: Eminectomy and meniscorhaphy for internal derangements of the temporomandibular joint-Rationale and operative technique. Oral Surg 57:24 1. I984 Weinberg S. Cousens G: Meniscocondylar plication: A modified operation for surgical repositioning of the ectopic temporomandibular joint meniscus. Oral Surg 63:393. 1987 Kryshtalskyj B, Weinberg S: Surgical correction of internal derangements of the TMJ. Oral Health 78:5: 19. 1988 Callander N: Callander surgical anatomy, In Anson BJ, Maddock WC feds): Anatomia Quirurgica. Barcelona. Salyat Editores, 1956, p 133 MCCormack LJ. Cauldwell EW, Anson BJ: The surgical anatomy of the facial nerve. Surg Gynecol Obstet 80602. I945 Davis RA, Anson BJ, Budinger JM, et al: Surgical anatomy of the facial nerve and parotid gland based upon a study of 350 cervico-facial halves. Sum Gvnecol Obstet 102:385. 1956 Baker DC, Conley J: Avoid&g facial nerve injuries in’rhytidectomy. Plast Reconstr Surg 64:78 1. 1979 Al-Kayat A, Bramley P: A modified preauricular approach to the temporomandibular joint and malar arch. Br J Oral Surg 17:91. 1979 Pitanguy I, Ramos AS: The frontal branch of the facial nerve: The importance of its variations in face lifting. Plast Reconstr Surg 38:4:352. 1966 De Castro-Correia P. Zani R: Surgical anatomy of the facial nerve as related to ancillary operations in rhytinectoplasty. Plast Reconstr Surg 52:549. 1973 Rudolph R: Depth of the facial nerve in face lift dissections. Plast Reconstr Surg 85537, 1990 Mitz V, Peyronie M: The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg 58:1:80, 1976
Surg
50:1048-1051,1992
Facial Nerve Function Following Temporomandibular Joint Surgery Using the Preauricular Approach SIMON WEINBERG, DDS, FRCD(C), FICD,* AND BOHDAN KRYSHTALSKYJ, BSc, DDS, MRCD(C)t Sixty-eight patients (83 temporomandibular joints) consecutively operated on who had a variety of temporomandibular joint operations using a preauricular approach were assessed for facial nerve function following surgery. Nine patients (10.84%) showed signs of facial nerve injury in which the temporal and zygomatic branches were involved. The incidence of facial nerve injury was greater in patients who had undergone previous temporomandibular joint surgery (17.64%) than in patients with previously unoperated joints (9%). Normal facial nerve function returned in 9 to 14 weeks except in one patient who showed a mild deficit of the zygomatic branch at 20 weeks. The nature and duration of the surgical procedure did not correlate with facial nerve injury. Scarring of tissues as a result of previous temporomandibular joint surgery may significantly increase the risk of facial nerve injury during subsequent temporomandibular joint surgery. preauricular approach, House et al3 reported a 15% incidence of facial nerve injury. Dolwick and Kretzschmar4 reported a 32% incidence of facial nerve involvement after their modified preauricular approach in which a separate skin flap was not developed. By altering the dissection technique Hall et al5 were able to decrease the incidence of facial nerve injury from 25% to 1.7%. This study was undertaken to determine the incidence of facial nerve injury following a variety of TMJ surgical procedures using the preauricular approach.
The ability to preserve the functional integrity of the facial nerve is a critical measure of success in temporomandibular joint (TMJ) surgery. However, in spite of the development of a myriad of surgical approaches to the TMJ, the facial nerve is always at risk for damage and the resulting impairment of frontalis and/or orbicularis oculi muscle function constitutes a relevant and distressing complication of TMJ surgery. According to Keith,’ the incidence of facial nerve injuries resulting from TMJ surgery ranges from 1% to 25%. The nerve injuries are mainly transient in nature, usually resolving within 6 months. Dingman et al2 reported an incidence of 55% following surgery through the preauricular approach. In their modified
Materials and Method Sixty-eight patients (83 joints) who consecutively underwent TMJ surgery were assessed for facial nerve injury. The sample consisted of 62 women and 6 men between the ages of 19 and 62 years. Fifty-three patients had unilateral surgery and 15 patients had bilateral surgery. Thirteen patients had had unilateral TMJ surgery once before and two had previous bilateral surgery on three occasions. The surgery was carried out by the same surgeon using a preauricular approach as described by Weinberg and Kryshtalskyj6~’ and Weinberg.8 The surgical procedures consisted of discoplasty and eminoplasty, 49 patients (60 joints); discoplasty, eminoplasty, and high condylar shave, 8 patients ( 10
Received from the Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. * Professor; Chief, Department of Oral and Maxillofacial Surgery, The Doctors Hospital, Toronto, Ontario, Canada. t Associate StaE, Chief, Department of Oral and Maxillofacial Surgery, Queensway Genera1 Hospital, Toronto, Ontario, Canada. Presented at the 38th Annual Meeting of the Canadian Association of Oral and Maxillofacial Surgeons, Ottawa, Ontario, May 199 1. Address correspondence and reprint requests to Dr Weinberg: Department of Oral and Maxillofacial Surgery, The Doctors Hospital, 340 College St, No. 465, Toronto, Ontario, MST3A9 Canada. 0 1992 American
Association
0278-2391/92/501
O-0005$3.00/0
of Oral and Maxillofacial
Surgeons
1048
1049
WEINBERG AND KRYSHTALSKYJ
joints); discectomies without placement of implants, 6 patients (6 joints): implant removal, eminoplasty, and high condylar shave, 2 patients (2 joints); and gap arthroplasty, 3 patients (5 joints). General anesthesia was administered to all patients and the duration of the surgical procedures was between 48 and 76 minutes per TMJ. Facial nerve function was initially assessed in the operating room as the patient regained consciousness and again 1 day after surgery. Facial nerve injury was deemed to have occurred if the patient was unable to raise the eyebrow or wrinkle the forehead (temporalis branch), or to completely close the eyelids (zygomatic branch). Patients were similarly examined weekly by the same surgeon for the assessment of facial nerve function. Results Nine of the 68 patients or 9 of 83 TMJs (10.84%) showed signs of facial nerve dysfunction following TMJ surgery. This included 3 of 15 patients (3 of 17 TMJs) (17.66%) who had undergone previous TMJ surgery. Of the 53 patients who had TMJ surgery for the first time 6, or 9%, had facial nerve involvement (6 of 66 TMJs). There were no cases of bilateral facial nerve injury. Table 1 shows the facial nerve branches that were injured and the time taken for the patient to recover from the injury. The temporal branch was involved in 7 of the 9 patients who showed signs of facial nerve damage; two patients had damage to the zygomatic branch. Of these two patients, one had three previous operations and the other had TMJ surgery once before. By the 14th postoperative week, normal function had returned in 8 of the 9 affected patients. One patient showed significant improvement, but still had mild involvement of the zygomatic branch 20 weeks after surgery. Six patients who showed signs of facial nerve injury shortly after regaining consciousness exhibited normal Table 1. Facial Nerve Branches Injured and lime to Recovery
Type of TMJ No previous surgery (66) Previous surgery ( 17)
Facial Nerve Branch Injured
Recovery Time
Temporal branch (6)
9- 14 weeks
Temporal branch (1) Zygomatic branch (2)
IO weeks One at 14 weeks, second patient (3rd surgery) had mild nerve deficit at 20 weeks
facial nerve function the day after surgery. There was no instance in which the early diagnosis of normal facial nerve function was followed by signs of facial nerve deficit. A x2 test with P = .05 revealed that there was a significant difference in the incidence of facial nerve damage between patients with previous TMJ surgery and those having surgery for the first time, 17.64% compared with 9%, respectively (P = .05). Discussion The variety of approaches that have been described for surgery of the TMJ share a common objective: adequate exposure ofjoint structures and maximum protection of the facial nerve. Maximum protection of the facial nerve requires meticulous surgical dissection and a thorough knowledge and heightened awareness of the regional anatomy. In his classic studies of 100 cadaver heads, Callander’ found eight major variations of the distribution of the facial nerve. Similarly McCormack et al” and Davis et al’ ’ have demonstrated six different patterns of facial nerve distribution. Of interest is the fact that of the six variations, there is distal branching in four of the patterns that can allow for more than one pathway of innervation of the frontalis muscle. Hall et al5 speculate that because of this branching, the most distal branch of the facial nerve that crosses the zygomatic arch could possibly be cut 63% of the time without loss of frontalis function. Similarly, Baker and Conley” have found that the temporal branch has many branches of its own. They found five to seven branches on average. One of these branches leads to the frontal region, 2 to the orbital region, 3 to the zygomatic region, and 2 to the buccal region. They postulated that complete transection of the temporal branch would result in permanent paralysis or incomplete recovery of forehead movement. This was due to the fact that 15% of the fibers to the brow have no connection with other branches of the ipsilateral or contralateral facial nerve. The temporal branch, in particular, as well as the zygomatic branch of the facial nerve, are especially vulnerable to injury during TMJ surgery. These nerves lie in a condensation of superficial fascia, temporalis fascia, and periosteum, and may be injured by any dissection technique that attempts to violate the integrity of this region. In their classic article, Al Kayat and Bramley13 stressed the clinical importance of this dangerous area of fusion over the zygomatic arch and they have shown that the temporal branch of the facial nerve lies within this area of tissue condensation on average 2 cm from the anterior concavity of the external auditory canal, with a range of 0.8 cm to 3.5 cm. Of particular importance is the fact that in more than one half of their samples the nerve was less than 2 cm away. Pitanguy and Ramos14 revealed that the direction of
1050 the temporofacial branches in 20 cadaver facial halves was constant, with the course and vector being on a line located 0.5 cm below the tragus of the ear, in the direction of the eyebrow and passing 1.5 cm above the lateral extremity of the eyebrows. They also noted that the insufficiency of the superficial muscular and aponeurotic system (SMAS) at the level of the lateral border of the frontalis muscle renders the temporal branches of the facial nerve more vulnerable to injury. To minimize the chance of temporal branch damage, DeCastro-Correia and Zani” proposed external landmarks. They postulated that the temporal branch is likely the most superficial of the five facial nerve branches, and may be found in a triangle bounded by the earlobe, lateral brow, and highest frontal crease. RudolphI found the average depth of the temporal branch of the facial nerve to be 9.1 k 2.8 mm from the parotid edge and the zygomatic branch to be 9.2 + 2.2 mm from this edge. He further indicated that the dangerous area in which nerve branches become superficial is the distal temporal region, 5 cm from the parotid border and 2.3 + 0.6 mm deep. This corresponds to the supraorbital bony ridge above the lateral orbit. On the other hand, the zygomatic branch was found to be well protected and lying deep within the facial fat as it exits the parotid gland. RudolphI also found that there was no zygomatic branch that crossed over the prominence of the zygoma. Furthermore, the zygomatic branch was found to have many anastomoses between branches. Baker and Conley” have concurred that because of these anastomoses, paralysis of the orbicularis oculi muscles is more unusual after one of the branches is cut, and if so, function usually recovers within 1 year. Mitz and Peyronie” have further suggested that the following anatomic factors may explain injury to the facial nerve: a thin subcutaneous musculoaponeurotic system (SMAS), a superficial lobe of the parotid gland that is short and does not protect the nerves, and a surgical dissection that is carried too far forwards. In light of the measurements of Al Kayat and Bramley,r3 the safest way to approach the glenoid fossa and articular eminence at the subperiosteal plane and avoid injury to the temporofacial outflow of the facial nerve is to operate within the safety of the pocket formed by the splitting of the outer layer of the temporalis fascia. The facial nerve branches are superficial to this plane and they may be protected at this level by gentle anterior retraction. To gain adequate exposure of the glenoid fossa and articular eminence, the periosteum over the zygomatic root should be incised vertically no further than 5 mm anterior to the most anterior concavity of the external auditory meatus. The increased incidence of facial nerve injury in patients who have undergone previous TMJ surgery may be explained by the fact that surgical scarring leads to
FACIAL NERVE
FUNCTION
AFTER
TMJ
SURGERY
fibrosis and distortion of the fascial layers and significantly increases the difficulty of establishing precise tissue planes during the dissection. The usual fat-occupying “safe pocket” that is formed by the splitting of the outer layer o’fthe temporalis fascia may no longer be identifiable in the patient with multiple operations because it is often obliterated by dense fibrous connective tissue. In these circumstances, after the development of a layered skin flap, the dissection should be deepened directly to the temporalis muscle to ensure the establishment of a fascial plane that is deep to the branches of the facial nerve. Excessive or heavy-handed retraction causes compression and/or stretching of nerve fibers resulting in neurapraxia; this may be responsible for a significant number of nerve injuries associated with TMJ surgery. Because densely scarred tissues are difficult to retract without creating considerable tension, a precisely layered surgical dissection should be done to minimize retraction forces. Incisions that are deepened directly to the outer layer of temporalis fascia without adequate undermining of fascial layers create a thick, immobile layer of tissue that is difficult to retract without causing excessive tissue tension. Facial nerve injury may also be caused by inadvertent suture ligation of facial nerve branches, particularly during wound closure. Care must be exercised during wound closure to avoid taking deep blind bites with the suture needle. The use of electrocautery in deep sites that are potentially close to facial nerve branches, or within the parotid gland, also should be avoided. Furthermore, one should avoid crushing or clamping tissue indiscriminately, particularly during episodes of brisk bleeding. Excessive swelling and/or hematoma formation may result in transient facial nerve injury. Corticosteroids should be used to reduce swelling and nerve sheath edema, and the establishment of good hemostasis before a layered wound closure to obliterate dead space and minimize hematoma formation. Occasionally a pressure dressing consisting of fluffed gauze and an elastic gauze bandage is recommended. The wound should be drained only if oozing persists before skin closure or if dead space cannot be adequately eliminated. If nerve damage should occur, one should determine which nerves are affected and whether microsurgical repair may be indicated. If the choice is simply to observe the situation, serial testing by electroneurography and electromyography may help in determining whether the affected muscles have the capability of rehabilitating themselves spontaneously. Conservative palliative management includes physiotherapy, exercises, reassurance, and the establishment of close rapport between surgeon and patient. Baker and Conley” have also suggested that if electrical test-
1051
WEINBERG AND KRYSHTALSKYJ
Table 2. Possible Causes of Facial Nerve Injury in TMJ Surgery Preoperative palsy from previous surgery Trauma from heat of electrocoagulation Local anesthesia injected in immediate nerve area Deep ligatures or plication sutures Crushing by forceps or clamps Excessive retraction and traction Nerve transection Hematoma or edema in nerve sheath Inflammation and infection Distortion of the normal anatomy by adhesions from previous TMJ surgery
References I. Keith DA: Surgery Of The Temporomandibular Joint: Success, 3.
3.
4.
5.
6.
7.
ing shows that the chronaxaxial levels remain high for more than 3 months, it is most likely that there will be no return of movement of the affected structures. If the nerve damage is left unrepaired by microsurgery, then the persistent muscle paralysis will result in frontalis and/or orbicularis oculi muscle atrophy and permanent ptosis of the brow and upper eyelid. Six of our patients (six joints) who showed facial nerve deficit on regaining consciousness had normal facial nerve function the following day. This can be explained by the fact that we routinely infiltrate the preauricular soft tissues with 4 to 6 mL of 0.5% MarCaine (Winthrop Laboratories, Aurora, Ontario, Canada) with 1:200,000 epinephrine before skin incision. This local anesthetic solution may block facial nerve conduction for 5 to 12 hours. Table 2 summarizes the potential causes of facial nerve injury related to TMJ surgery. In patients who have had previous TMJ surgery, a slight modification in the surgical dissection may offer additional protection to the facial nerve.
8. 9.
10.
I I. 12. 13.
14.
Ii.
16. 17.
Failure And Complications Of Temporomandibular Joint Surgery. Boston, MA. Blackwell Scientific, 1988, pp 272,282 Dingman RO, Dingman DL, Lawrence RA: Surgical correction of lesions of the temporomandibular joints. Plast Reconstr Surg 55335, 1975 House LR, Morgan DH, Hall WP: Clinical evaluation of TMJ arthroplasties with insertion of articular eminence prosthesis on ninety patients. Laryngoscope 87: I 182. 1977 Dolwick MF. Kretzschmar DP: Morbidity associated with the preauricular and perimeatal approaches to the temporomandibular joint. J Oral Maxillofac Surg 40:699. 1982 Hall MB. Brown RW, Lebowitz MS: Facial nerve injury during surgery of the temporomandibular joint: A comparison of two dissection techniques. J Oral Maxillofac Surg 43:20. 1985 Weinberg S: Eminectomy and meniscorhaphy for internal derangements of the temporomandibular joint-Rationale and operative technique. Oral Surg 57:24 1. I984 Weinberg S. Cousens G: Meniscocondylar plication: A modified operation for surgical repositioning of the ectopic temporomandibular joint meniscus. Oral Surg 63:393. 1987 Kryshtalskyj B, Weinberg S: Surgical correction of internal derangements of the TMJ. Oral Health 78:5: 19. 1988 Callander N: Callander surgical anatomy, In Anson BJ, Maddock WC feds): Anatomia Quirurgica. Barcelona. Salyat Editores, 1956, p 133 MCCormack LJ. Cauldwell EW, Anson BJ: The surgical anatomy of the facial nerve. Surg Gynecol Obstet 80602. I945 Davis RA, Anson BJ, Budinger JM, et al: Surgical anatomy of the facial nerve and parotid gland based upon a study of 350 cervico-facial halves. Sum Gvnecol Obstet 102:385. 1956 Baker DC, Conley J: Avoid&g facial nerve injuries in’rhytidectomy. Plast Reconstr Surg 64:78 1. 1979 Al-Kayat A, Bramley P: A modified preauricular approach to the temporomandibular joint and malar arch. Br J Oral Surg 17:91. 1979 Pitanguy I, Ramos AS: The frontal branch of the facial nerve: The importance of its variations in face lifting. Plast Reconstr Surg 38:4:352. 1966 De Castro-Correia P. Zani R: Surgical anatomy of the facial nerve as related to ancillary operations in rhytinectoplasty. Plast Reconstr Surg 52:549. 1973 Rudolph R: Depth of the facial nerve in face lift dissections. Plast Reconstr Surg 85537, 1990 Mitz V, Peyronie M: The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg 58:1:80, 1976
