To investigate the common complications of mandibular angle hypertrophy osteotomy by intraoral approach and its prevention and management. Methods From July 2007 to August 2012, 121 cases of intraoral approach mandibular angle hypertrophy osteotomy were summarized, of which 75 cases underwent chin surgery at the same time (including 61 cases of horizontal osteotomy chinoplasty, 9 cases of Medpor prosthesis chin augmentation, and 5 cases of mandibular angle osteotomy sandwich chinoplasty), 19 cases of high zygomatic bone and zygomatic arch lowering at the same time, and 3 cases of buccal fat pad removal at the same time. Through symptom analysis and clinical follow-up of the patients with complications, the causes of complications were analyzed, effective preventive measures were identified, and the management methods of different complications were summarized. Results Among the 121 patients, 56 patients had orofacial lip injury, 42 patients had numbness of orofacial lip and mandibular chin skin, 28 patients had hematoma in the operative area, 15 patients had infection in the operative area, 9 patients had second mandibular angle, 6 patients had asymmetry on both sides of the face, and 2 patients had accidental fracture after the operation. Conclusion: Intraoral approach for mandibular angle hypertrophy osteotomy requires a detailed treatment plan before surgery, requires strict compliance with surgical operation standard and the principle of aseptic operation during surgery, and gives negative pressure drainage and reliable compression bandage after surgery to try to avoid the occurrence of serious complications [1], and some of the complications can still obtain satisfactory results after appropriate treatment. Mandibular angle shape is an important anatomical standard guiding the width and shape of the lower 1/3 of the face, and mandibular angle hypertrophy will lead to a wide lower part of the face with a square or even trapezoidal shape, which is seriously incompatible with the aesthetic standard of melon face and goose egg face that is highly respected by the people in China. Mandibular angle hypertrophy deformity in the West is mostly biting muscle hypertrophy, and in the Eastern ethnic groups are mostly bony hypertrophy. With the continuous development and improvement of surgical techniques, the introduction of new advanced instruments, the advantages of intraoral approach without skin scarring, and the improvement of consumption level and people’s awareness, more and more young people choose to improve the facial contour of the jaw angle hypertrophy plastic surgery for employment, dating, and stargazing reasons. As the number of patients continues to rise and the number of surgeries continues to increase, various surgical complications also increase and are highly valued, and serious complications can even lead to the death of the patient. Therefore, to understand and analyze the causes of surgical complications, to develop appropriate preventive measures and to give reasonable treatment after the occurrence is the basis of the success of the operation. 1, bed data From July 2007 to August 2012, 121 cases of mandibular angle hypertrophy osteotomy were performed by intraoral approach, 109 female patients and 12 male patients; the age was from 18 to 40 years old, and the average age was 24.6 years old. All patients underwent intraoral approach osteotomy for mandibular angle hypertrophy, of which 75 cases underwent chin surgery, 19 cases underwent high zygomatic bone and zygomatic arch reduction surgery, and 3 cases underwent buccal fat cushion removal surgery at the same time.Among the 121 patients, there were 56 cases of lip injuries, 42 cases of lip and mandibular-chin skin numbness, 28 cases of hematomas in the surgical area, 15 cases of infections in the surgical area, 9 cases of the second jaw angle, 6 cases of facial asymmetry, and 6 cases of the second mandibular angle. There were 9 cases of second mandibular angle, 6 cases of facial asymmetry, and 2 cases of accidental fracture. 2, Surgical methods 2.1, Anesthesia: all patients were given general anesthesia by transnasal intubation, and controlled hypotensive anesthesia was given during the operation. 2.2 Incision: The mucoperiosteum was incised along the lateral gingivo-buccal groove from the proximal middle of the mandibular second premolar to the anterior edge of the mandibular ascending branch. 2.3 Surgical steps ① Subperiosteal stripping of soft tissues up to the lower edge of the mandible (decortication), fully revealing part of the mandibular body, mandibular angle area and the anterior edge of the ascending mandibular branch, the stripping of the whole process needs to be operated under the periosteum, to prevent damage to the soft tissues of the cheek. The wide osteotome was used to fully dissect the occlusal muscle attachment, and the curved hook periosteal peeler was used to peel off part of the internal pterygoid muscle attachment along the lower edge of the mandible. The oscillating saw was used to perform a curved osteotomy from the lower 1/3 of the posterior border of the ascending mandibular ramus to the mandibular first molar corresponding to the mandibular lower border, preserving a portion of the medial bone cortex to be broken with a curved bone chisel, and then the free bone segment was clamped with Kocher’s forceps to strip off the pterygoid muscle attachment connected to the free bone segment and then remove the bone segment intact. The second mandibular angle was trimmed and the osteotomy step was trimmed with a protective cover grinding head. (iii) In some patients, part of the outer plate of the bone can be split or part of the buccal fat pad can be removed according to the preoperative design. After the operation, stop bleeding thoroughly in the operation area, and place negative pressure drainage device and external elastic bandage with pressure. 3. Complications and treatment Related complication statistics (121 patients in total) Complications of mandibular angle surgery Number of cases Incidence rate Oral lip injury 56 46.3% Numbness in the operative area 42 34.7% Hemorrhage and hematoma 28 23.1% Infection in the operative area 15 12.3% Second mandibular angle 9 7.4% Asymmetry on both sides of the face 6 4.96% Accidental fracture 2 1.7% 3.1 Oral lip injury Transoral The transoral approach to mandibular angular hypertrophy osteotomy has become a mainstream procedure for mandibular angioplasty because of its advantage of leaving no surface scar, but the transoral approach also has its own defects, namely, a narrow field of operation. Transoral approach for mandibular angle hypertrophy osteotomy surgery requires pulling the angle of the mouth during the whole operation, and some operations can excessively pull the angle of the mouth, especially for patients with small clefts or involutional mandibular angle, which can easily lead to soft tissue strain of the lips and numbness of the angle of the mouth, and the emergence of vesiculation and ulcers in the angle of the mouth after the operation, and in some serious cases, the angle of the mouth can be asymmetric after the operation, and the angle of the mouth may be left with scar, etc. The operation is performed with a high-speed oscillating saw or a saw with a high speed or a saw with a high speed or a saw with high speed. If the soft tissues around the mouth are not protected during the operation of the high-speed rotating oscillating saw or grinding head, they may be burned or abraded by the rotating axis. In the above cases, erosion and hyperpigmentation in the corneal area are the most frequent, and soft tissue and nerve injuries caused by excessive pulling can be protected by applying erythromycin ointment around the mouth and lips during the operation and by using a polyethylene film sleeve to protect the perioral mucosa. After surgery, continue to rub to accelerate swelling and wound healing, can be given hormones or open mouth exercises, such injuries generally do not require special treatment, 1-3 months can be self-healing. 3.2 Numbness in the operation area Postoperative numbness in the operation area includes numbness in the mouth and lips, chin and soft tissues covering the mandible. The main cause is intraoperative injury to the inferior alveolar nerve vascular bundle or the chin nerve vascular bundle, and some patients may have numbness in the soft tissues of the perioral area due to excessive stretching of the mouth and lips during the operation. The main causes of injury to the inferior alveolar nerve are: ① the design of the mandibular angle osteotomy line is too high; ② the swinging saw is placed too high during osteotomy; ③ during the polishing process of the ball drill, the lower drill is too heavy and too deep; ④ the mandible is directly injured when it is cleaved to the outer plate. The main causes of damage to the chin neurovascular bundle are: ① intraoperative violent pulling; ② the ball drill grinding process involved in the tearing of the chin nerve; and ③ the mandibular angle osteotomy line is too far forward and downward to the chin foramen area. The height of the mandibular angle osteotomy line and the termination position of the osteotomy line at the lower edge of the mandible should be reasonably designed by CT and surface tomography before surgery, and the positioning should be done in the field of vision during the operation, and the saw should not be moved blindly. For patients who need to split the outer plate of the bone at the same time, the location of the inferior alveolar nerve and blood vessels should be localized by CT before the operation, and the bone chisel should be slightly buccal when splitting the bone to reduce the chance of damage to the inferior alveolar nerve. When polishing the bone surface, attention should be paid to the depth of the drill and the amplitude of swing, and the chin nerve should be protected. 3.3 Hemorrhage and hematoma Because of the limited operating space and visual field of the intraoral approach, intraoperative injury to well-known blood vessels is the main cause of hemorrhage. Misinjured blood vessels are commonly found in the inferior alveolar nerve vascular bundle, chin nerve vascular bundle, facial artery and posterior mandibular vein. The second is bleeding when removing the biting muscle or removing the buccal fat pad, bleeding from the osteotomy section and bleeding when stripping the periosteal muscle. If the hemostasis is not sufficient after the blood vessels are damaged during the operation, obvious hematoma can appear in a short period of time after the operation, and in severe cases, the respiratory tract can be compressed, which can lead to serious consequences. The slow oozing of blood from the osteotomy section after the operation is the main reason for the long-term hematoma after the operation, which generally does not need special treatment, and it can be left to dissipate on its own after the localized pressure is put on the bone. Reasonable preoperative design of osteotomy line position, CT localization of important blood vessels, standardized intraoperative operation to ensure that the operation is carried out in a safe range, completed under the periosteum, the application of sawing and drilling with a protective cover, not blindly deep, timely and effective hemostasis operation, postoperative negative pressure drainage and pressure bandage is the key to prevent damage to important blood vessels caused by hemorrhage and postoperative hematoma formation. Bleeding from important well-known blood vessels often cannot be well hemostatized, and once there is a definite vascular injury, gelatin sponge, hemostatic gauze and pressure hemostasis should be filled immediately, and the operation should be terminated and the ipsilateral external carotid artery should be ligated if necessary. When removing the biting muscle or buccal fat pad, it is important to give adequate suture ligation and electrocoagulation to stop bleeding, otherwise, if there is more bleeding and poor drainage, it can compress the lateral wall of the pharynx and have serious consequences. When the osteotomy section oozes more, bone wax or other hemostatic materials can be given to fill in the spray to stop bleeding, and for the bleeding point formed after periosteal occlusal stripping, electrocoagulation should be given in time to stop bleeding. 3.4 Infection of the operative area cracking The most common reason for the appearance of postoperative infection at present is caused by hematoma secondary. Secondly, intraoral approach surgery is a contaminated incision surgery, which can cause postoperative wound infection and cracking if the principle of aseptic operation is not strictly observed, a large amount of debris produced by osteotomy or bone grinding is not cleaned up in time, oral hygiene is poorly maintained, and prophylactic antibiotic treatment is not given. Routine preoperative dental scaling, adequate intraoperative hemostasis, thorough rinsing of the surgical area, tight suture closure of the incision, placement of a negative pressure drainage device, postoperative oral care (dressing changes and mouthwash rinsing), routine prophylactic antibiotic treatment, and preoperative gastric tube for patients with implants can effectively prevent and avoid the occurrence of possible surgical wound infections and dehiscence. Intraoperative bone trauma bleeding surface, if the amount of blood seepage is not much, try not to use bone wax and other hemostatic materials coated, in order to reduce the occurrence of postoperative infection. If the hematoma secondary to fluid suppuration causes infection in the operation area and wound cracking, at the beginning stage, part of the suture can be removed from the operation area, and rubber drainage strips can be placed in the wound cavity to drain pus secretion, and when the pus exudate decreases and disappears, iodine imitation gauze can be placed in the wound cavity, and the wound can be changed every other day or every 2 days, and the wound can be healed gradually. 3.5 Second mandibular angle The appearance of the second mandibular angle is related to the surgeon’s proficiency in the operation and the choice of the operation. In the case of mandibular angle osteotomy, the smaller the angle of the patient’s mandibular angle or the larger the amount of bone to be removed from the mandibular angle in the case of multi-linear osteotomy and partially curved osteotomy, the more likely that the second mandibular angle will appear after the osteotomy. In some cases, the appearance of the second mandibular angle is not obvious, but the patient reports that the angularity is obvious when touching, which can cause psychological anxiety. The appearance of the second mandibular angle was significantly reduced after the change from a multilinear osteotomy to a curved osteotomy, but it still occurred. After the mandibular angle is removed during the operation, the operator and the assistant should touch the mandibular angle area together to feel the presence and position of the second mandibular angle, and the second mandibular angle can be trimmed with a lifting type grinding head with a protective cover, so that the second mandibular angle can be removed in general to ensure that the lower edge of the lower mandible has a natural streamline arc. 3.6 Asymmetry between two sides of the face Because most of the intraoral approach osteotomies for mandibular angular hypertrophy have a narrow field and need to be operated under semi-blind or blind vision, it is difficult to ensure that the amount of osteotomies on both sides of the mandibular angle is exactly the same [5], and although the surgeon locates the osteotomies by preoperative imaging, he still needs to rely on his experience to master the symmetry of the two sides of the osteotomies when he operates during the operation. Therefore, the surgeon often judged the gap between the two sides of the osteotomies based on the removed mandibular angle bone blocks for revision. The preoperative design of the osteotomy range by using spiral CT three-dimensional imaging is more intuitive and accurate than the early application of surface tomography, which improves the safety and accuracy of the surgery. In cases where part of the outer plate of the bone needs to be removed, part of the outer plate of the bone can be ground first to enlarge the field, which is more helpful to improve the accuracy of mandibular angle osteotomy. 3.7 Unintentional fracture Unreasonable design of intraoperative osteotomy line, violent cleavage of bone cortex before complete cleavage, and incorrect direction of bone cleavage are all reasons that lead to unintentional fracture of mandibular angle osteotomy. The most common situation is to split the bone when the medial plate has not yet been split, which may result in the problem of the lateral plate being split first and the medial plate still remaining. Once it occurs, it is quite tricky, and it can only be repaired by grinding off part of the medial plate as much as possible, but in most cases, part of the medial plate still remains, which affects the appearance of the operation. Inadequate osteotomy of the posterior border of the ascending mandibular ramus can also lead to an accidental fracture with upward extension of the fracture line into the neck of the condyle. If this occurs, intraoperative titanium plate fixation of the fracture is required. 4.Results: 121 patients underwent osteotomy for mandibular angle hypertrophy by intraoral approach, 56 patients had postoperative symptoms of lip and mouth injury such as lip and mouth swelling, pigmentation of the corners of the mouth, vesicles in the corners of the mouth, and inconsistency in the height of the corners of the mouth bilaterally, etc. Although the lip and mouth area was coated with ointment and the lip and mouth area was protected in the osteotomy process, the above symptoms still appeared in the postoperative period for the long duration of the operation and the excessive pulling and stretching in the operation, etc. This complication could only be alleviated, but now it is necessary to perform titanium plate fixation of the fracture area during operation. Complications can only be mitigated but cannot be completely avoided at this stage. Forty-two patients had numbness of the lips, chin, and mandibular skin. Although the inferior alveolar and chin nerves were properly protected during the operation, the pulling or touching of these sensory nerves by the retracting instruments still led to neurological or sensory abnormalities in the postoperative period, but most of them recovered on their own within 3 months after the operation. 28 patients had postoperative hematoma, and there was no hemorrhage due to injury of an important blood vessel. Adequate hemostasis and the application of external negative pressure drainage device could greatly reduce the postoperative hematoma and accelerate the swelling to subside. 15 patients had postoperative wound infection and cracking symptoms, of which 12 patients had pus secretion due to the obvious oozing from the operative area and untimely drainage, 2 patients had infection due to the excessive spacing of suture lines, 1 patient had infection due to the entry of food residue into the operative area, and 1 patient had a bladder infection due to the early postoperative bulging of the cheeks. One patient had a partially torn wound due to excessive intraoral tension as a result of the early postoperative gargling action. Nine patients who had a second mandibular angle during the operation were trimmed at the same time during the operation and had good postoperative results. 6 patients with facial asymmetry were trimmed twice during the operation and had good postoperative recovery of their facial appearance. 2 patients with accidental fractures, 1 patient with a mandibular angle bone plate left behind after splitting of the outer plate of the mandibular angle bone, were trimmed at the same time during the operation, but had poor postoperative results in the lateral view, and 1 patient with condylar fracture in the process of splitting of the bone during the operation was treated immediately with a titanium plate during the operation. In one case, the condylar fracture occurred in the process of splitting the bone during the operation, and internal fixation with titanium plate and nail was performed immediately during the operation. 5. Discussion 5.1 Mandibular angle osteotomy requires subperiosteal operation During the surgical operation, complete periosteal stripping is required, i.e. “stripping”, complete stripping of the periosteum with very little bleeding, and osteotomies and bone grinding operations are completed under the periosteum, which can greatly reduce the chance of damage to the extra-mandibular arteries, the posterior vein, and other well-known blood vessels, and reduce intraoperative bleeding, as well as reduce the risk of damage to the external maxillary artery and the posterior vein. The field of operation is clear and clean, which reduces intraoperative bleeding and shortens the operation time, which in turn shortens the postoperative swelling period. 5.2 Removal or not of biting muscle At present, some scholars still advocate partial removal of biting muscle for patients with excessive biting muscle hypertrophy in order to correct the hypertrophy of soft tissues in the mandibular angle area. The process of mandibular angle hypertrophy plastic surgery itself includes the complete stripping of the bite muscle in the region of the bite muscle and the stripping of part of the wing muscle, the stripping of the bite muscle severed end of the postoperative period appeared to be atrophic, part of the loss of function, the muscle fibers are obviously narrowed, and there has been a thinning effect on the face. Intraoperative excision of the biting muscle can increase the amount of intraoperative bleeding, prolong the operation time, some cases due to insufficient intraoperative hemostasis caused by postoperative hematoma in the operative area, left and right soft tissue asymmetry of the face, and in severe cases, due to the excessive weakening of the descending jaw muscle group caused by the symptoms of restricted opening, retaining the biting muscle can avoid several complications, and at the same time, it will not have a greater impact on the postoperative facial morphology. 5.3 Removal of the buccal fat pad The more popular jaw angle plastic surgery includes partial removal of the buccal fat pad. The immediate effect of removing the buccal fat pad is better, and it can be used to slim down the face more substantially, which is the icing on the cake of bony surgery, but at the same time, there are also some disadvantages. The process of buccal fat pad removal increases the amount of bleeding during the operation. Inadequate hemostasis or failure to provide suture ligation to stop bleeding may result in the formation of postoperative buccal hematoma. Secondly, the lack of lubrication of the buccal fat pad may affect the muscle movement in the corresponding area. In the long term, the cheeks may become sunken and deformed, affecting the normal smile and accelerating the aging process. Therefore, the amount of buccal fat pad removed during surgery needs to be considered. At the present stage, the young group’s demand for appearance is increasing, and patients come to have jaw angle hypertrophy plastic surgery in an endless stream. Intraoral approach mandibular angle osteotomy has the absolute advantage of leaving no scar on the face, and it is respected by most patients and operators, and the improvement of the operator’s surgical skills, the shortening of the operation time, the use of new types of surgical instruments, and the cautious and gentle operation are all guarantees for avoiding and decreasing the emergence of the surgical complication. The improvement of surgical skills, shortening of surgical time, use of various new surgical instruments, and careful and gentle operation have all helped to avoid and minimize surgical complications. However, the emergence of various complications also reminds plastic surgeons to have a full understanding of various complications. Intraoral approach mandibular angle osteotomy surgery is surrounded by more important anatomical structures, the surgical operation field is restricted and the surgery is complicated and traumatic, which can cause a series of complications, therefore, clinicians need to attach great importance to the emergence of a variety of complications, precise design of the surgical program before the operation, make good use of three-dimensional helical CT and other imaging data, rigorous and gentle operation, careful postoperative care, to reduce the occurrence of complications, and to provide targeted care after complications occur. Targeted management of complications can reduce the pain suffered by patients and avoid possible medical disputes.