The zygomatic bone is located in the middle third of the face and determines the three-dimensional structure of the facial contour, i.e., the horizontal width, anterior prominence, and vertical height of the midface. Because of its prominent position, it is one of the most vulnerable sites for fracture in head and facial trauma. The zygomatic bone is closely related to the anatomical adjacency of adjacent bones, and a fracture of the zygomatic bone, especially if caused by high velocity direct violence, will inevitably lead to fracture of adjacent bones. The orbital and maxillary bones are most closely related to the zygomatic bone anatomically and are therefore most frequently involved. Based on the above, there are different terms to express these fractures, including: zygomatic complex fracture, orbitozygomatic maxillary fracture, zygomatic maxillary complex fracture, zygomatic lateral orbital complex fracture, and orbitozygomatic fracture. The term orbitozygomatic fracture is mostly used in the current literature. The orbitozygomatic fracture is not fixed by timely repositioning or improper treatment in early stage for various reasons, and when the swelling subsides, the deformity of the fracture segment due to deformity healing, resorption, and scar contracture pulling causes deformity of the orbitozygomatic bone and adjacent organs and soft tissue structures in later stage, which is called secondary deformity of the orbitozygomatic fracture and seriously affects the facial appearance and function.
Anatomical features of the orbitozygomatic region
The orbitozygomatic bone is extremely close in anatomical relationship, and the zygomatic bone itself is one of the important components of the outer, lower orbital rim, and its own position is extremely important in maintaining the normal anatomical form of the orbital bone and orbital volume.
1, Normal anatomy of the zygomatic bone
The zygomatic bones are located on both sides of the middle third of the face and play an important role in maintaining the width, prominence and vertical height of the face. The zygomatic bone can be divided into two parts: the zygomatic body and the zygomatic arch, which are connected to the frontal bone, the temporal bone, the pterygoid bone, and the maxilla by the sutures of the domicile (Figure 2). The zygomatic arch maintains the forward projection of the zygomatic body, and its position between the zygomatic process of the temporal bone and the anterior zygomatic body determines the anterior-posterior, vertical, and horizontal position of the zygomatic bone in relation to the skull base, constituting the lateral facial scaffold, which is closely related to the medial facial scaffold composed of the frontal bone, the orbital bone, the nasal sieve bone, and the anterior maxillary pillar, and the breakage of the lateral facial scaffold directly affects the position of the medial facial scaffold connected by the zygomatic arch [1, 14]. The accurate repair of the zygomatic arch is of great importance in the repair of 1/3 fractures and orbitozygomatic fractures in complex type faces.
Starting from the lacrimal fossa of the maxilla, outward through the zygomatic body to the zygomatic prominence of the temporal bone constitutes the transverse facial arch, and the accurate repair of the transverse arch is extremely important to maintain the anterior prominence of the zygomatic bone and facial symmetry, while the height of the zygomatic arch determines the width of the face. The deep and superficial layers of the deep temporal fascia attach to the outer edge of the frontal eminence of the zygomatic bone and the upper edge of the zygomatic arch [15]. The chewing muscle attaches to the lower edge of the zygomatic arch. The former is important for maintaining the position of the zygomatic bone, while the latter is the most important deformogenic force leading to the displacement of the zygomatic fracture after trauma.
2.Traumatic anatomical characteristics of zygoma
The deformation displacement after zygomatic fracture is directly related to the size and direction of the traumatic force and the pulling of the chewing muscle. Fractures caused by moderate force mostly occur in the separation of the zygomatic bone from the adjacent bone at the suture connection, which is called Zygomatic Complex fracture or Three Pillar Fracture. Severe violence can result in multiple fractures of the entire zygomatic bone, i.e., comminuted fractures. The fracture of the zygomatic complex may result in multiple axial rotational displacements in addition to upward, downward, anterior, and lateral translations. In the repair of orbitozygomatic fracture deformity, it is important to understand the normal anatomical position of the zygomatic bone and its displacement in different quadrants after fracture to guide the accurate anatomical repositioning after osteotomy.
3. Biomechanical structure of the orbitozygomatic bone and adjacent maxillofacial bones
Understanding the biomechanical structure of the maxillofacial skeleton is an important guide to the selection of osteotomy reconstruction and fixation sites for secondary deformities of the orbitozygomatic bone. Light transmission studies of dry skulls revealed that the middle 1/3 of the facial bones are composed of thin and unevenly thickened bone plates. The thicker parts are called buttresses (or Pillars). The pillars of the maxillofacial region include the vertical and horizontal pillar systems, through which the facial skeleton is constructed as a solid whole to resist a significant degree of violence.
(1) The vertical pillar system of the face
The vertical pillars of the face include four:
(1) Anteriorly, the Naso-Frontal buttress, which runs anteriorly through the cuspids and the maxillary alveolar ridge along the outer edge of the plagiocephalic foramen and upward through the anterior tear ridge on the medial side of the orbit and the maxillary nasal eminence to above the medial orbital rim.
②Laterally, the zygomatic buttress (Zygomatic buttress). From the alveolar ridge above the maxillary first molar upward along the lateral orbital rim to the zygomatic process of the frontal bone and along the temporal process of the zygomatic bone through the zygomatic arch to the temporal bone.
(iii) Posteriorly, the pterygo-maxillary buttress, which runs from the maxillary eminence and the pterygo-plate to the skull base.
(iv) Mandibular buttress, from the mandibular body, the mandibular ascending branch, and the condyle to the temporomandibular joint fossa at the base of the skull.
(2) The horizontal pillar system of the face [19]: the frontal bone, including the upper part of the horizontal pillar composed of the superior orbital rim on both sides; (2) the inferior orbital rim and the nasal bone on both sides constitute the middle part of the horizontal pillar; (3) the palatine bone and the maxillary alveolar ridge constitute the lower part of the horizontal pillar.
The vertical and horizontal pillars of the maxillofacial skeleton are like the reinforced concrete framework in architecture, which plays a role in linking and reinforcing the maxillofacial skeleton. When a fracture occurs in the maxillofacial bone, the fracture and displacement of the struts often occur. These struts provide important reference marks for the accurate repositioning of the jaw fracture repair, and they are also the selected sites for strong internal fixation with small splints. The orientation of the splint must be consistent with the stress direction of the struts in order to obtain accurate and reliable fixation.
The main clinical manifestations and pathogenesis of secondary deformity of orbitozygomatic fracture
1. Concave deformity of the maxillary zygomatic area
Depending on the cause of the injury, secondary depression deformities of different degrees may occur. The typical deformities are outward displacement of the zygomatic complex, protrusion of the zygomatic arch, depression of the zygomatic maxilla, widening of the affected side, and downward displacement of the zygomatic prominence, with obvious asymmetry of the bilateral sides.
2. Eye inversion and subluxation
The secondary deformity of orbitozygomatic fracture is often accompanied by different degrees of ocular invagination. When the eyeball is posteriorly displaced by more than 5 mm, it can become obvious that the eye is sunken. There are many theories of the pathogenesis, including: (1) herniation of the orbital fat into the maxillary sinus. (ii) Increased bony volume of the orbital bone due to fracture displacement. (iii) Fat atrophy or necrosis. (iv) Posterior displacement of the eye due to scar pulling of the retrobulbar tissue. (5) Insertional obturation or fibrosis of the extraocular muscles. There is a consensus that post-traumatic entropion is the result of an imbalance between the orbital contents and the bony volume of the orbital bone. Under normal conditions, the specific three-dimensional morphology and size of the orbital bones play a role in limiting the morphological position of the orbital contents and maintaining the normal anterior protrusion of the eye. When an orbital zygomatic fracture occurs, in addition to the common orbital floor fracture, it is often accompanied by fractures of the medial and lateral orbital walls. The displacement of the fracture fragment not only leads to an increase in the bony volume, but also changes the normal morphology of the orbital contents. Intraocular invagination can be corrected by “retrieving” the “off track” orbital contents and repositioning them within the normal anatomic definition of the orbital bone. In addition to the aforementioned intraocular invagination, fracture collapse of the infraorbital rim and orbital floor may be accompanied by varying degrees of downward displacement of the eye.
3.Adjacent soft tissue deformity
All orbitozygomatic fractures are accompanied by different degrees of adjacent soft tissue deformities, such as facial scarring, soft tissue defects, internal and external canthal displacement, etc. Especially if the injury is accompanied by severe facial contusions and avulsions, it often leads to serious facial deformities, which makes treatment more difficult.
4.Functional disorders
Including ① diplopia, reduced or complete loss of visual acuity, and related dysfunction due to extraocular muscle imbalance; ② restricted mouth opening; ③ numbness or reduced sensation in the infraorbital area; ④ frontal muscle paralysis or paresis.
Etiology and characteristics of secondary deformity of orbitozygomatic fracture
The main causes of secondary deformities of orbitozygomatic fractures are the lack of timely and effective treatment or improper treatment. The main causes include the following:
1. Early surgical treatment of orbitozygomatic fractures is delayed due to the presence of other fatal injuries, such as severe craniocerebral injuries. It is now recognized that the best time to operate for orbitozygomatic fracture is after the vital signs are stable at the time of injury. At this time, surgery is not only less difficult and less costly, but if treated properly the results are far better than those of second-stage surgery, and it is possible to reconstruct the “pre-injury appearance” (Preinjury appearence), if delayed to more than 3w, the fibrous healing of the bone break occurs or even bony healing, the surgery becomes more difficult and the results are hardly comparable to those of first-stage treatment.
2, due to the serious craniofacial swelling at that time, the examination is not careful and comprehensive and misdiagnosis or omission occurs, which is another cause of secondary deformity of orbitozygomatic fracture.
3, Improper treatment. For unstable fractures with displacement, incision and reliable internal fixation were not taken at that time, resulting in inappropriate repositioning or unreliable fixation after repositioning, and secondary displacement after surgery due to muscle pulling or scar contracture, resulting in deformity of varying degrees at a later stage.
4.Surgical complications. Despite the use of advanced techniques and tools in the early stage, some patients still have deformities of varying degrees secondary to the severity of the injury at the time and require further revision after surgery.
Diagnosis of secondary deformity of orbitozygomatic fracture
Secondary deformities of the orbitozygomatic fracture have distinctive features. It is not difficult to determine the orbitozygomatic fracture, but for the design and implementation of the surgical plan, further ancillary tests must be done.
1. Radiographs
X-rays should become a routine adjunct to the examination of secondary deformities of the orbitozygomatic fracture. The most commonly used are the tile position and the chin apex position. The tile position helps to diagnose the fracture of the maxilla, maxillary sinus, orbital floor, infraorbital rim, zygomatic bone and zygomatic arch, and to understand the deformity healing of the zygomatic bone and whether there is herniation of the orbital contents into the maxillary sinus, and also helps to observe whether there is fracture of the nasal bone and supraorbital rim. The fracture displacement of the zygomatic arch can be determined by the chin-top position [9]. The fractures of the orbital wall can be roughly understood by orbital tomography, but to accurately diagnose the fractures of each orbital wall, axial and coronal CT examinations of the orbital bone are required, because some fractures that do not appear serious on the X-ray can actually occur in the deeper part of the orbit, including the posterior part of the orbital floor, the superior part of the orbital wall, and even the lateral wall of the orbit. The fracture may be more severe in the deep part of the orbit, including the posterior part of the orbital floor, the superior part of the orbital wall, and even the lateral wall of the orbit [10].
2. CT examination
CT scans, especially the thin axial and coronal tomography provided by high-resolution CT, can usually identify all major deformities of the traumatized orbital bone, including fractures of the orbital wall and the displacement of intraorbital soft tissues into the adjacent anatomical space, providing a reliable basis for the etiological diagnosis and surgical design of intraocular invagination. In the last decade or so, CT imaging has been widely used to study the pathogenesis of post-traumatic entropion and has made significant progress. [7,8]
3.Three-dimensional reconstruction
Three-dimensional reconstruction has been successfully used for the diagnosis and surgical design of various congenital craniomaxillofacial deformities and post-traumatic deformities. Compared with planar CT scanning imaging, three-dimensional reconstruction imaging has the characteristics of intuitive and three-dimensional, and the deformed displacement of the orbitozygomatic fracture can be understood at a glance, which helps the design and implementation of surgery. Although 3D CT is highly intuitive, it still has its limitations for the diagnosis of orbital fractures, as it cannot understand the displacement of the intraorbital soft tissues, while the thin orbital floor and intraorbital wall often make 3D reconstructive imaging of this region very difficult.
4. Adequate visualization of the fracture site
For severe orbitozygomatic fractures secondary to deformity, the surgical approach is mostly made through a coronal scalp incision, a sublash margin incision of the lower lid, and an intraoral gingivobuccal sulcus incision. In individual patients with significant trauma scar on the zygomatic surface of the infraorbital rim, an incision can also be made through the scar to access the infraorbital rim, orbital floor, and zygomatic maxillary surface without the need for a separate submasculature incision.
(1) Scalp coronal incision: This approach can fully reveal the supraorbital rim, nasal bone, outer orbital rim, zygomatic arch and the upper part of the zygomatic body, and the scar is concealed, so it is the most commonly chosen incision. When using a coronal scalp incision, the key is to protect the frontal branch of the facial nerve from injury. During surgery, the incision should be deep under the capitellar tendon membrane, peeled on the surface of the periosteum, and when reaching the upper edge of the temporal muscle, care should be taken to lift the superficial temporal fascia along with the scalp, and peel downward between the superficial temporal fascia and the superficial layer of the deep temporal fascia, and when approaching the upper edge of the zygomatic arch, the temporal fat pad is visible. The frontal branch of the facial nerve can be properly protected by continuing to dissect downward within the superficial temporal fat pad to reveal the zygomatic arch.
(2) Trans-lid incision
Manson et al [15] proposed a lower eyelid flap approach via a submarginal incision in 1987. The incision is located 2-3 mm below the eyelash margin and extends outward to 8-10 mm beyond the outer canthus. The orbicularis oculi muscle is first dissected downward between the orbital septum and the infraorbital rim to 2-3 mm, then the periosteum is incised anterior to the infraorbital rim, and the subperiosteum is dissected to reveal the orbital floor, outer orbital rim, zygomatic bone, and upper maxillary component. When incising the periosteum of the infraorbital rim, the incision should be located anterior to the infraorbital rim to avoid damage to the orbital septum. The orbital septum is attached to the lateral part of the infraorbital rim in front of the infraorbital rim, and the periosteum must be cut below the septal attachment to avoid longitudinal shortening of the lower lid after surgery.
(3) Intraoral gingival-buccal sulcus incision approach
This approach was first used by Converse (1950) [9] and allows adequate exposure of the zygomatic bone, maxilla and infraorbital rim. Care was taken to protect the infraorbital neurovascular bundle and to avoid damaging the opening of the parotid duct. During the repositioning and fixation of the secondary deformity of the orbitozygomatic fracture, this incision allows the repositioning of the maxillary pillar of the zygomatic bone to be checked to prevent any remaining rotational displacement and to provide reliable fixation [10].
(4) Osteotomy of the orbitozygomatic bone
For healed orbitozygomatic fracture deformities, the design of the osteotomy approach is important for the reconstruction of facial symmetry and the correction of ocular entropion deformity. In cases where bony healing has not occurred between the broken ends of the bone due to a short post-injury period or soft tissue impaction, a simple approach is to make an incision along the fracture line. However, in cases where firm bony healing has occurred, a special osteotomy is required depending on the healing of the deformity.
In the repair of secondary deformities of the orbitozygomatic fracture, accurate repositioning of the zygoma helps to reconstruct the normal orbital volume. In normal conditions, the equator of the eye is located exactly in the plane from the outer edge of the orbit to the anterior edge of the cardboard of the inner orbital wall [10, 18], and after zygomatic fracture, external rotation displacement of the zygoma or fracture defect of the outer orbital wall can lead to a significant increase in the posterior lateral space of the equator of the eye. The orbital zygomatic bone fracture can effectively reduce the enlarged orbital cavity by osteotomy and repositioning, correcting the external rotation of the orbital wall, and repairing it with bone grafting in the external orbital wall, and then correcting the inward orbital deformity by deep intraorbital bone grafting.
(5) Strong internal fixation with a small splint
After osteotomy and reset of the secondary deformity of the orbitozygomatic fracture, reliable strong internal fixation must be used to ensure the stability of the postoperative reset. The purpose of strong internal fixation is: (1) to refix the fracture block in its normal anatomical position after osteotomy, and (2) to reconstruct the pre-traumatic load path of the maxillofacial skeleton before the injury [19]. To meet these two requirements, the correct fixation site and the correct orientation of the titanium plate must be selected. Usually the fixation sites are made at the zygomatic-frontal suture, zygomatic arch, infraorbital rim, and zygomatic-maxillary struts. At the same time, the direction of the splint must be consistent with the stress direction of the pillar, so that the splint is not easily fatigued and the titanium nail is not easily loosened to ensure the continuous and reliable fixation.
(6) Bone grafting and orbital wall repair and reconstruction
When the deformity of the orbit-zygomatic fracture heals and is repositioned by osteotomy, different degrees of defects are inevitably left at the fracture end, and the size of the bone defect is related to the degree of deformity displacement and the magnitude of the osteotomy. At the same time, fracture defects of the orbital wall require simultaneous bone graft repair to reconstruct normal orbital morphology and orbital volume. Rontal [20] suggested that the lateral portion of the orbital floor is a safe area to begin the control of the orbital floor, and can be safely peeled back 25 mm along the inferior and lateral orbital margins, and 30 mm from the superior orbital margin and anterior tear ridge without damaging the orbital vital structures. In the correction of severe entropion, a 360° dissection of the orbital periosteum around the orbital bone is usually required to allow for adequate anterior displacement of the eye [8]. During dissection, the orbital soft tissues must be fully released from the fractured orbital wall, and the soft tissues embedded in the fracture line or in the adjacent sinus cavity must be repositioned while maintaining the integrity of the orbital periosteum to prevent rupture and spillage of intraorbital fat.
The purpose of orbital wall implant repair is to reduce the enlarged orbital cavity, reconstruct the normal orbital volume and normal anatomical shape, regardless of the repair material used. Secondary deformities of the orbital zygomatic fracture, not only fractures of the orbital floor and lateral orbital wall, but also depressed fractures of the internal orbital wall, should be repaired simultaneously. Repair of the orbital floor alone, especially if the bone graft is located anterior to the equator or equator of the eye, can only increase the vertical height of the eye, while it is difficult to move the eye forward [17]. To accommodate the anatomical morphology of the orbital bone, the implant bone should be trimmed and shaped accordingly, and sometimes two or more bone pieces need to be overlapped and fixed, trimmed and implanted in the orbit. To prevent displacement of the implanted bone, titanium nails or titanium plates can be used for fixation [7]. The autologous cranial outer plate is an ideal material for bone grafting because it has thick dense bone, is not easily absorbed after implantation, has good curvature suitable for facial bone reconstruction, plus it is often located in the same operative field with other surgeries, easy to take, large amount of bone supply, avoiding the scar left by taking bone in other parts, and has few complications [21, 22].
5. Resuspension and repositioning of soft tissues
In orbitozygomatic fracture secondary to deformity, the soft tissue of the zygomatic-cheek area sags due to the fracture of tissue structure and nerve injury, and the displacement of the inner and outer canthus, plus the loss of most of the soft tissue support structure due to extensive subperiosteal stripping when the fracture site is exposed. phillips et al [23] first recognized this problem and emphasized the importance of re-suspension of soft tissue for fixation. Suspension can be achieved by suturing the soft tissue periosteal composite to the adjacent periosteum, to a small adjacent splint, or by drilling holes through the adjacent bone [24]. The soft tissues of the zygomatic-cheek region can also be elevated and fixed by suturing the capitellar tendon of the temporoparietal flap to the deep temporal fascia at the temporal line. In older patients with facial soft tissue laxity, in addition to re-suspension and fixation of the soft tissue on the affected side, the soft tissue on the opposite side should be suspended accordingly, otherwise, asymmetry of the soft tissue on both sides of the face may result.