Mid-facial trauma is more common in clinical practice. Because it involves the frontal bone, zygomatic bone, nasal sieve orbital bone, maxilla and other parts, with many sinus cavities and complex structures, the depressed fracture of the midface is one of the most complicated fracture sites of the face, and its repair and reconstruction is still a difficult point in the treatment of craniomaxillofacial trauma. Clinical manifestations and pathogenesis: Since the anatomical structure of the bony contour of the midface is complex, the bone blocks are irregular in shape and closely connected with each other, a complex fracture of multiple bone blocks often occurs after the impact of external force, and the soft tissue deformity of the face is combined. 1, frontal bone deformity: frontal bone fracture is common in the supraorbital rim, and is mostly accompanied by frontal sinus injury. The frontal sinus is the main component of the frontal bone part of the midface, and frontal sinus fractures account for 5-15% of facial fractures [1]. Because of the proximity to the anterior cranial fossa, dura mater, sieve plate, and frontal lobe of the brain, frontal sinus fractures often affect these tissues. Early interbrow hematoma, bruising, twisted pronation of local tissues, and cerebrospinal fluid leakage should be highly suspicious of frontal sinus injury. Late frontal fracture mainly shows obvious depressed deformity, including collapse of nasal root, and frontal sinusitis, cerebrospinal fluid leakage and meningitis, intracranial or orbital abscess may also occur in a few patients. 2, nasal sieve deformity: due to the special location of the nasal bone, which is the most prominent structure of the face, nasal bone fractures are the most common among facial trauma fractures and also rank third among all fractures [2, 3]. While the nasal bone and sieve bone are closely connected, nasal bone fractures are mostly accompanied by sieve bone rupture. The destruction of the bony scaffolding structure of the nasal sieve fracture leads to the collapse of the nasal root and dorsum, resulting in the shortening of the nasal height and the upturning of the nasal tip, forming a “pig nose” deformity, which can lead to significant changes in the patient’s appearance, and if timely and effective treatment is not provided in the early stage, it is very difficult to reconstruct later. In addition, nasal sieve fractures often damage the medial canthus, resulting in soft tissue deformity, medial canthus displacement, bilateral asymmetry, and widened medial canthus spacing. Also, some patients may damage the nasolacrimal duct, leading to tearing, dacryocystitis, and pus accumulation in the lacrimal sac. 3.Orbital bone fracture: Orbital bone fracture is one of the common fractures in facial trauma, it can exist alone or combined with other parts of the fracture. It is mainly a depression type fracture of the orbital wall. The orbital bone is adjacent to the maxillary sinus and septal sinus, and its depressed fracture leads to the increase of bony volume in the orbit and the herniation of ocular contents into the sinus cavity, resulting in the sunken eyeball. Diplopia is another complication of orbital fracture, which occurs due to entrapment of the intraocular muscles, local tissue ischemia, hematoma, and nerve injury. Orbital bone fractures can also cause paralysis of the infraorbital nerve and tearing with nasolacrimal duct obstruction. If the orbital tip is injured, it may also cause temporary or permanent blindness. 4, zygomatic bone deformity: zygomatic bone is an important structure that determines the width, prominence and vertical height of the three-dimensional contour of the midface, which is easily damaged in trauma. After zygomatic fracture, most of them are displaced outward and downward due to muscle pulling, which is manifested as zygomatic maxillary depression, local abnormal protrusion, reverse eye deformity, orbital horizontal misalignment downward, and if the rostral prominence of mandible is pressed, it will cause dental closure. There may also be infraorbital nerve palsy, diplopia, and lower lid ectropion. 5, maxillary deformity: the maxilla is an important part of the mid-facial contour, and its injury is usually bilateral, and the fracture level varies. It shows an increase in the transverse diameter of the face, midface depression, discoid facial features, and antimandibularity, and may also damage the temporomandibular joint and present with restricted mouth opening. Severe maxillary fractures may present with nasal airway obstruction and open-mouth breathing. Auxiliary examinations and diagnosis: 1. X-ray: X-ray examination has become one of the routine auxiliary examinations for facial fractures due to its inexpensive and other characteristics. A complete facial imaging examination should include: (1) Frontal and lateral head position: to show the proportion and displacement of various parts of the face, while the lateral position can show the plane of frontal sinus and temporal bone. (2) Fasciotomy: it can show the frontal sinus, maxillary sinus, zygomatic bone and zygomatic arch, which can help the diagnosis of fracture in these areas. (3) Chin apex position: it helps to determine the displacement of zygomatic arch fracture. (4) Orbital bone tomography: it helps in the diagnosis and preoperative evaluation of orbital rim, orbital wall, and zygomatic fractures. However, the facial skeletal contour is complex, and X-rays sometimes cannot reflect the facial fracture very exactly, and the fracture and displacement of some fine structures cannot be responded, thus affecting the preoperative judgment. 2.CT scan: CT can get clear imaging information by scanning the craniofacial tomography. In the case of the midface, the combined use of sagittal and coronal scans can better show the injury of each paranasal sinus and the fracture displacement, especially for the diagnosis of orbital wall fractures [4]. Three-dimensional reconstruction can compensate for the inability of CT to show holistic, comminuted fractures and bone fragment defects, and provide an intuitive, three-dimensional reconstruction of the facial skeletal scaffold from the whole, which helps in preoperative evaluation and surgical design. 3.MRI: Nuclear magnetic scanning is less used in craniomaxillofacial trauma. For fracture repair, CT can reflect the bone better, but MRI is useful for showing soft tissue, brain tissue and nerve damage. Imaging plays a large role in the diagnosis and treatment of facial fractures, but this does not neglect the need for a thorough physical examination. A thorough history taking, careful physical examination and complete ancillary examinations are the most effective methods to understand the patient’s specific situation and make a clear diagnosis. The treatment of depressed fractures of the midface is still a difficult task. Knowledge of the anatomical features of the functional areas of the face, accurate preoperative diagnosis and prediction of surgical outcome, early treatment, and stable and accurate repositioning and fixation of the skeletal brace are the keys to the success of surgery. 1.Surgical approach: The choice of surgical approach after craniofacial trauma determines the success of surgery and postoperative effect to some extent. The principle is not only to facilitate the full exposure of the fracture end during the operation and facilitate the repositioning and fixation, but also to make the incision concealed as much as possible. (1) Scalp coronal incision: It is one of the most commonly used approaches for craniomaxillofacial trauma repair due to its advantages of open field and concealed postoperative scar. It can fully reveal the frontal bone, supraorbital rim and lateral orbital rim, zygomatic bone and nasal bone. (2) Inferior lid margin incision: It is very helpful to reveal fractures of the orbitozygomatic region and maxilla, especially for the inferior orbital rim, inferior orbital wall, medial orbital wall and lateral orbital wall. (3) Intraoral vestibular incision: a 5-mm incision on the buccal side of the upper lip of the vestibular groove in the oral cavity with a concealed wound that can fully reveal the maxilla, zygoma, and part of the orbital rim. Care should be taken to avoid injury to the parotid ducts with this approach. (4) Local incision: For patients with open soft tissue injury, the injury site or the site of late scar formation can be chosen as the access, which can better reveal the trauma site and also repair the soft tissue and the remaining scar. For large injury area and complex facial depression fracture, multiple combined surgical approaches are often required to obtain good surgical results. 2, repair of frontal sinus injury: open frontal sinus injury, must be carefully cleared. Bone flap grafting and sinus cavity filling are crucial in the treatment and are known as the “gold standard” [6-8]. If the trauma is intracranial, osteotomy of the posterior frontal sinus wall and endonasal fistula of the frontal sinus are required [12, 13]. In closed fractures, fractures of the anterior wall of the frontal sinus without damage to the frontal nasal canal are mainly focused on repairing the frontal contour, and the bone mass can be removed, reconditioned and fixed. Fixation can be done with wires, titanium plates or absorbable plates. However, due to the thin subcutaneous tissue of the frontal area, any metal plate fixation can be touched after surgery, and even some of them can be seen after the postoperative edema disappears. Therefore, some advocate the use of absorbable materials for fixation here [11]. If the bone is broken and beyond repair, the contour of the anterior frontal sinus wall can be reconstructed with an autologous cranial outer plate or artificial material instead. Recently, endoscopic techniques have been attempted to repair frontal sinus fractures [12, 13], but its ineffectiveness in detecting damage to the posterior wall of the frontal sinus and the frontal nasal canal, as well as its inadequacy in fixation and repair of complex fractures, have limited the promotion of this technique. Injuries to the frontal canal are common in frontal sinus injuries, and it has been reported that frontal canal injuries account for 55% of all frontal sinus fractures [11]. Therefore, preoperative and intraoperative examination of the patency of the frontal nasal canal should not be neglected. In patients with frontal canal injury, repair of the frontal form alone is not sufficient and requires filling of the shaped sinus cavity. During the filling of the sinus cavity, all mucosa must be removed, the sinus wall smoothed and bone fragments embedded in the frontal nasal canal. The fillings in question can be of various types, the more commonly used being autologous materials: fat, muscle, cartilage, bone, cranial periosteal flaps and allogeneic materials: silicone, hydroxyapatite, methyl isobutyrate and even bone wax [14-20]. Since allogeneic tissues are not resistant to infection and are also not conducive to tissue repair and reconstruction, more and more physicians are now advocating the use of autologous tissue fillings. For nondisplaced fractures of the posterior wall of the frontal sinus, no special treatment is required. If there is cerebrospinal fluid leakage, conservative treatment can be started. 30° lying position helps the dura mater to heal spontaneously, and if there is still cerebrospinal fluid leakage after 4 days, lumbar puncture can be performed to drain the cerebrospinal fluid, thus lowering the cranial pressure and reducing cerebrospinal fluid leakage. If conservative treatment is not effective after 10 days, craniotomy is required to repair the dura mater. For fractures with posterior wall displacement, if there is no damage to the frontal nasal canal and cerebrospinal fluid leakage, the frontal sinus can be preserved or the sinus cavity can be filled, depending on the situation. If there is damage to the frontal nasal canal or a dural tear, frontal sinus tamponade or cranialization of the frontal sinus is required. Cranial cavitation of the frontal sinus involves removing the posterior wall of the frontal sinus, opening the sinus cavity, scraping the mucosa of the frontal sinus while smoothing the bone, occluding the frontal nasal canal and filling the canal opening with a frontal muscle flap. In this way, the frontal sinus will soon be filled with cerebrospinal fluid-filled meninges. 3. repair of nasal dorsal collapse and scaffold reconstruction: nasal fractures have the highest proportion of facial fractures, but their treatment is not satisfactory. in a follow-up of their treated patients after 3 months, Rohrich et al. found that 14-50% of patients required secondary surgical treatment [21]. Many of these could have been avoided with early and comprehensive diagnosis and perfect treatment [22]. The best timing for surgery is generally considered to be before the edema after trauma, i.e., 3-6 hours, or after the edema has partially subsided, i.e., 3-10 or 14 days [21, 23, 24]. This is because tissue edema can not only mask the fracture displacement but also affect the fracture repositioning. In contrast, early treatment is required for some emergencies, such as localized hematoma, open injuries, and large facial fractures. The aim of surgery is to restore the length of the nose and the position of the septum. A “bird-like” incision in the nasal vestibule is usually used. After fully exposing the septal cartilage, the displaced septal cartilage needs to be repositioned in the pear bone groove and fixed with sutures. For severe septal fractures, septoplasty or submucosal resection is required to achieve good repositioning. If the nasal dorsum is severely collapsed and cannot be repositioned, reconstruction of the nasal dorsum can be performed at the same time. Generally, autologous bone such as the outer plate of the skull and iliac bone is used as the scaffold for reconstruction. We generally prefer cranial external plates with good strength and curve, and two to three cranial external plates are superimposed as needed until the desired height is reached, and the scaffold is fixed to the frontal nasal eminence with a miniature titanium plate at the nasal root [23]. A large proportion of nasal dorsal collapse is associated with injury and displacement of the medial canthal ligament, the treatment of which is directly related to the overall postoperative outcome. Therefore, medial canthopexy fixation is essential. If there is a fracture fragment attached to the medial canthal ligament, the fracture fragment is fixed with a wire through the nasal bone along with the medial canthal ligament, and if the medial canthal ligament is completely separated from the fracture fragment, a hole is made above the posterior lacrimal fossa and a fine wire is fixed through the nasal bone [25]. 4, repair of orbitozygomatic fracture deformity and ocular entropion: the zygomatic complex, due to its special structure, has multiple fracture sites mainly: zygomatic arch, zygomatic-frontal junction, zygomatic maxillary pillar, and infraorbital rim. The choice of incision is also affected by the fracture at different sites. A fracture of the suprazygomatic pillar can be treated with an oral vestibular incision, a fracture of the infraorbital rim can be treated with a lower lid margin incision, and a complex fracture of the zygomatic arch requires a coronal incision. Usually we combine 2-3 incisions to better visualize the fracture site and reposition for fixation. Displacement of the orbitozygomatic fracture not only affects the symmetry of the face, but also causes an increase in the intraorbital volume and sunken eyeball. Therefore, good repositioning and strong internal fixation are the main focus of treatment for orbitozygomatic fractures and are a prerequisite for correction of intraocular invagination. There are many studies on the treatment of orbital wall burst fractures, and most physicians consider severe fractures, intraocular invagination, and manifestations of extraocular muscle entrapment to be important surgical indications. For the timing of surgery, it is generally considered [26-28] to be preferable within two weeks, so as to avoid post-traumatic fibrous adhesions affecting the surgical outcome. However, some patients have elevated vagal excitability and oculocardiac reflex manifestations such as bradycardia, heart block, nausea, vomiting or syncope due to the impaction of ocular contents, which may have serious consequences and therefore require early surgical treatment. The main goal of treatment of orbital wall burst fractures is to reconstruct the bony orbital wall and restore the intraorbital volume, while the trapped ocular contents must be returned into the orbit. We generally use an inferior lid margin incision, which provides excellent exposure of the infraorbital wall, the vast majority of the medial and lateral orbital walls, without the need for a medial canthal secondary incision. Because the orbital wall bone is very thin, most cannot be repositioned and requires biomaterial filling to achieve the surgical goal. Autologous cartilage, cranial outer plates, iliac bone, ribs, de-antigenized allograft bone, titanium, silicone, porous polyethylene, ceramics and many others can be used as filler materials. In our experience porous polyethylene has good results for repairing the orbital wall, and recently, Yaremchuk et al [29] reported a 9-month postoperative follow-up of 64 patients with orbital wall fractures and found no displaced or infected patients. 5. Reconstruction of deformity in the maxillary fracture area: fractures are classified according to Le Fort, and midfacial Le Fort fractures mostly co-exist as type I and II. The main purpose of surgical treatment is to correct the occlusal jaw relationship and improve the facial appearance mainly. Among all surgical procedures for maxillary fractures, restoration of the occlusal-mandibular relationship is the most fundamental and requires a complete fracture reduction. In principle, the unstable bone is fixed on the stable bone, and the small bone is fixed on the large bone, while multiple points of fixation are required according to the specific shape. If there is a comminuted fracture that cannot be repositioned, early bone grafting treatment is required. In patients with advanced secondary deformity, due to the majority of comminuted fractures in the nasal orbital region, it is very difficult to perform the classical Le fort II osteotomy and reset. Le fort I osteotomy and reset is feasible, where the receding maxilla is re-osteotomized and moved forward, and after performing intermaxillary ligation, the position of the maxilla is determined through the position of the mandible, and finally fixed to the repositioned lateral facial brace with a small splint. After the operation, the intermaxillary ligature was loosened to further determine the occlusal relationship and to check for any mouth opening restriction. Postoperatively, intermaxillary elastic traction was applied for 6-8 weeks [30]. Repair of midface fractures is a complex procedure, and differences in the timing of surgery and surgical approach can affect the long-term outcome of the procedure. In general, the surgical outcome of early surgery is significantly better than late treatment. This is because post-traumatic fibrous adhesions and deformed healing of the fracture site are important reasons for the surgical outcome. The treatment requires not only to reconstruct the function as much as possible, but also to restore the facial shape to the maximum extent.