62 Orbitozygomatic Fractures
Introduction
Zygoma fractures, the most common facial fractures after motor vehicle accidents, can result in disruption of orbital contents, the maxillary sinus, and the coronoid process of the mandible, and result in significant functional and cosmetic deformities. Therefore, all fractures of the facial skeleton resulting from trauma in the orbital and cheek areas should be considered for potential orbitozygomatic or even cranioorbitozygomatic fractures, and repair of the injury must be directed to restoration of an anatomically correct skeletal unit. To achieve optimal results there must be an understanding of the anatomy, comprehensive diagnosis of fractures, and accurate reduction and stabilization with limited harm to unaffected surrounding tissues when possible.
Anatomy and Fracture Characteristics
Zygoma and Malar Prominence
The zygoma is a relatively sturdy bone that provides the aesthetically important malar eminence. It joins the surrounding craniofacial skeleton through four superficial and two deep projections. Superficially, the projections contribute to two critical external arcs of contour ( Fig. 62.1 ). The vertical arc runs from the zygomatic process of the frontal bone over the zygoma to the zygomaticomaxillary (ZM) buttress area of the lateral wall of the maxillary antrum above the first molar. The longer horizontal arc runs from the maxilla in the area of the lacrimal fossa around the zygoma to the root of the zygomatic process of the temporal bone. It is parallel to, but slightly below, the Frankfort horizontal plane. Because the height of contour of the malar eminence is also just at or slightly inferior to the Frankfort plane, the point of intersection of these arcs of contour defines the position of the malar eminence, typically 2 cm inferior to the lateral canthus ( Fig. 62.1 ). The two deep projections are the sphenoid projection that articulates along the lateral orbital wall with the orbital plate of the sphenoid bone and the orbital projection that articulates with the orbital surface of the maxilla in the extreme lateral aspect of the orbital floor. The sphenoid and orbital projections lie beneath and perpendicular to the external arcs of contour in the area of the inferolateral orbital rim, thus greatly strengthening this portion of the rim.
The zygoma is the main buttress between the maxilla and the cranium. It also serves as the principal component of the superficial lateral pillar of a buttress system of platforms and pillars that surround and protect the orbit. 1 Because its convex outer surface creates the prominent contour of the cheek, it is highly susceptible to injury.
The term tetrapod fracture refers to the fracture of all four suture lines (zygomaticofrontal [ZF], zygomaticotemporal, zygomaticomaxillary, and zygomaticosphenoid) that occurs with blunt trauma to the zygoma. Typically the weaker bones with which the zygoma articulates absorb the strong impact forces directed to the zygoma and fragment. The weakest bone is the orbital floor, which can collapse into the maxillary sinus. In contrast, the ZF is the strongest buttress and it typically separates cleanly. The ZM buttress area and the medial aspect of the inferior orbital rim are frequently comminuted.
The Zingg classification system of zygomaticomaxillary complex (ZMC) injuries can be used to describe these fractures with clarity and simplicity. 2 Type A injuries, the least common, are isolated to one component of the tetrapod fracture. They are further divided into types A1, A2, and A3, depending on whether the area of involvement is the zygomatic arch, lateral orbital wall, or inferior orbital rim, respectively. Type B fractures involve injury to all four of the supporting structures, and type C fractures are complex fractures with comminution of the zygomatic bone. Types B and C account for 62% of ZMC injuries. 3
The zygomatic arch typically either fractures near its midpoint in a single location or in two places resulting in a central fragment susceptible to displacement and rotation. Therefore, fracture dislocations of the zygoma may fragment both ends of the horizontal arc of contour and the lower end of the vertical arc. The degree of this disruption and the amount of displacement of the zygoma determine the severity of the injury and thus the complexity of the needed repair. Reconstruction of the horizontal arc restores anterior and lateral projection of the cheek, and reconstruction of the vertical arc restores the height of the malar eminence in relation to the Frankfort plane.
Orbit
The bone in the concave, central portion of the orbital floor lies 3 mm below the inferior orbital rim and may be as thin as 0.5 mm or less. 4 Posteriorly the floor is convex and posteromedially it slopes upward into the medial orbital wall without a sharp demarcation ( Fig. 62.2 ). Impact forces centered over the body of the zygoma are transmitted inferiorly through the ZM buttress to the anterolateral wall of the antrum and medially through the orbital process to the inferior orbital rim and the floor of the orbit. The antral wall and the inferior rim frequently suffer a comminuted injury that results in multiple delicate fragments lying between the ZM suture line and the lacrimal fossa. The floor of the orbit almost always suffers a comminuted injury, the severity of which varies with the strength of the impact force. This injury usually involves the concave central portion. High-velocity periorbital impact forces may be transmitted to the convex posterior floor and even to the medial wall, causing serious displacement of the bone in these areas. Although the globe itself rests anterior to the convexity, evaluation and reconstruction of this area and the adjacent medial wall are as important as repair of the more accessible concave anterior portion of the floor.
The sphenoidal and orbital processes of the zygoma transmit impact forces centered over the zygoma to the deeper structures within the orbit. The weak sphenotemporal buttress formed by the zygoma, orbital plate of the greater sphenoid wing, and the squamous portion of the temporal bone absorbs impact forces directed over the lateral orbital rim. When the impact force exceeds the capacity of this buttress to absorb it, fracture dislocations of the lateral orbital wall result and, at a minimum, comminution occurs at the zygomaticosphenoid suture line. When impact forces are directed in a medial superior direction, the orbital plate of the sphenoid bone moves toward the orbital apex and decreases the orbital volume. This impaction may cause injuries to structures in the orbit, superior orbital fissure, or optic canal. More commonly, laterally and inferiorly displaced ZMC fractures correspond with fractures of the inferior or medial orbital walls. This displacement increases the orbital volume and may allow orbital fat to herniate into the maxillary or ethmoid sinuses. Reduction of the bony injuries may be necessary to restore the volume of the orbit and the contour of the orbital rim and also to remove bony impingement on vital neurologic structures. 5
Globe Position
The position of the globe is determined by the integrity of the orbital walls and the extensive network of ligaments that suspend it. 6 Recession (enophthalmos) or depression (hypopthalmos) of the globe within the orbit results from injuries that push one or more orbital walls outward, increase the orbital volume, and also damage the network of suspensory ligaments. The orbital soft tissues are then displaced by both gravitational forces and the remodeling forces of fibrous scar contracture. This usually changes the shape of the orbital soft tissues from a modified cone to a sphere, and the globe sinks backward and downward. 7 Probably the most common cause of this posttraumatic enophthalmos is the incomplete repair of a defect in the normally convex posterior aspect of the floor or failure to recognize and correct a medial wall component of the injury ( Figs. 62.2 and 62.3 ). Less commonly, the globe is displaced superiorly (hyperophthalmos) and anteriorly (exophthalmos) by medial and superior impaction of the ZMC that decreases orbital volume.
Diagnosis and Radiologic Evaluation
The initial assessment of the patient with facial fractures must include an evaluation of the airway, the hemodynamic stability, and the cervical spine. Once these have been appropriately managed, attention is focused on the head and neck examination, keeping in mind the mechanism of injury. Patients with ZMC fractures may have palpable stepoffs at the zygoma or orbital rim, or malar flattening due to medial displacement of the ZMC. These findings become less apparent as the overlying soft tissue swells. Patients may experience trismus from compression of the coronoid process of the mandible and the temporalis by the depressed ZMC. Hypoesthesia or anesthesia may result from injury involving the infraorbital nerve (V2). Associated facial fractures occur in 25% of patients sustaining ZMC fractures. 3
A thorough ocular examination is required to assess the orbital soft tissues. Upward gaze restriction and diplopia may occur as a result of entrapment of the inferior rectus muscle. Forced duction testing can reveal entrapment of any of the extraocular muscles and should be performed in unconscious patients. Globe position should be evaluated for enophthalmos, hypophthalmos, hyperophthalmos, or exophthalmos. The latter two globe malpositions indicate a decrease in orbital volume, which may be accompanied by optic nerve injury. An ophthalmologic consultation should be obtained for all patients with ZMC fractures.
Axial computed tomography (CT) scans should be considered the gold standard for radiological diagnosis of ZMC fractures. 8 Many trauma patients undergo CT scan of the brain to assess intracranial injury, and additional facial views to evaluate the facial bones can be included at this time. Axial images can be reformatted into coronal cuts with good resolution, thus obviating the need for neck flexion or extension. These CT scans provide valuable information about the fractures to guide surgical decisions.
The preoperative choice of the appropriate surgical approach for all but the most minimally displaced orbitozygomatic fractures can be made only if the horizontal and vertical arcs of contour and the lateral, inferior, and medial orbital walls are evaluated by CT. Although axial CT provides valuable information about the lateral and medial walls of the orbit, coronal CT or good coronal reconstructions are essential for evaluation of the orbital floor. This is especially true for the convex posterior floor and the area of sloping of the floor into the medial wall. Fracture dislocations in these areas can be studied in detail and decisions made regarding the need for orbital exploration and repair to prevent delayed enophthalmos. Approximately 1-cm3 displacement of orbital soft tissue or increase in orbital volume produces 1 mm of enophthalmos. 9 , 10 A change of at least 3 cm3 of orbital volume increase, or orbital soft tissue loss, is usually required before clinically perceptible enophthalmos occurs. 11
It should be noted that acute enophthalmos may not be seen in association with severe orbitozygomatic fractures. An intact but medially impacted zygoma may compensate for the increased orbital volume caused by blowout fractures of other walls, and the globe may appear normal in anterior projection and vertical position, or even be proptotic. However, reduction of the zygomatic component of the injury to restore the malar eminence unmasks the traumatic increase in orbital volume and leads to delayed-onset enophthalmos if the other fractures are not treated. Careful review of the axial and coronal CT scans will prevent this error.
Before CT scans were routinely obtained for ZMC fractures, orbital exploration was performed for diagnosis as well as reconstruction of orbital floor defects. The acceptance of CT scans as the gold standard imaging modality for patients with suspected ZMC fractures has contributed to a significant change in the treatment algorithm. Shumrick and colleagues assessed pretreatment scans to determine which ZMC fractures required orbital exploration/reconstruction. They reported a 70% decrease in orbital explorations in this group. 12 Ellis and Reddy, in reviewing their treatment of isolated, unilateral ZMC fractures over a 10-year period, determined that the preoperative CT scan can be used to assess the amount of internal orbital disruption for purposes of developing a treatment plan in patients with ZMC fractures. 11 For fractures with minimal soft tissue herniation and minimal disruption of the internal orbit, ZMC reduction without orbital floor reconstruction was adequate treatment. A posttreatment increase in orbital volume was noted in 8 of 65 cases where the floor was not reconstructed, but these increases were considered too small to result in clinically perceptible enophthalmos.
Surgical Technique
Restoration of the External Arcs of Contour
The precise relocation of the displaced zygoma is simplified by concentrating on reconstruction of the two main external arcs of contour. Restoration of the horizontal arc reestablishes anterior and lateral projection of the cheek, and restoration of the vertical arc reestablishes the height of the malar eminence in relation to the middle third of the face. The repositioned zygoma can then be used as a framework for repair of any associated orbital wall fractures. Treatment required to attain multidimensional restoration of the position of the zygoma becomes increasingly complex as the injury to each arc of contour increases in severity. Together, comminution of the bones with which the zygoma articulates (i.e., the lateral and medial ends of the horizontal arc and the inferior end of the vertical arc) and the amount of displacement of the zygoma itself determine the complexity of the injury and therefore the complexity of the needed repair.
Simple Fractures
Only rare cases without comminution of any of the projections of the arcs of contour should be managed with closed reduction techniques, such as the Gilles method with or without transzygomatic Steinmann pin fixation. If the adequacy of reduction of this type of injury is in doubt because of difficulty in palpating the zygomatic arch and lateral antral wall, a small gingivobuccal sulcus incision may be used for direct visualization of the lateral wall. If this is employed, a single 2.0 miniplate can be placed across the reduced fracture line in lieu of the transzygomatic pin to stabilize the zygoma against the downward pull of the masseter.
Because any type of limited-access technique relies heavily on palpation and external visualization of the position of the zygoma and its projections, it is helpful to delay these procedures for at least 7 days to allow for maximal resolution of edema. In addition, preoperative steroids may reduce intraoperative edema and further facilitate evaluation of the reduction. The repair should not be delayed more than 10 days because the masseter begins to shorten after this time and elevation of the zygoma becomes more difficult. 12 For repairs after 3 weeks, osteotomies may be necessary, and after 4 months bone grafts or synthetic implants may be needed to restore cheek position. 13 For cases where there is a surgical delay and elevation of the ZMC is difficult due to the onset of healing, McGivern and Stein recommend a method of reduction using two points of elevation. An elevator is passed through an upper buccal sulcus incision to elevate the zygoma while also elevating from the outside with a temporary malar eminence screw placed through a handle/cannula complex. 14
Frequently, the lateral wall of the maxillary antrum is comminuted even when the other projections of the arcs of contour suffer simple fractures or separation of a suture line. In such cases, a single craniofacial miniadaptation plate attached across the comminuted area is sufficient for lateral wall reconstruction ( Fig. 62.4 ). Because the fixation device is not resisting heavy occlusal forces, as would be the case with a Le Fort fracture, insertion of only two screws into the body of the zygoma above and at the maxilla below is required for stability. In addition, a prebent L-shaped plate may be used to facilitate placement of screws below the fracture lines if there is concern for the root tips of the maxillary teeth.
If the adequacy of reduction is in doubt, another projection of the zygoma can be directly visualized by means of a tunnel dissection superior to the inferior rim, with identification and protection of the infraorbital nerve, or laterally over the malar eminence to expose the zygomatic arch. Adequate reduction can then be confirmed with palpation of the lateral orbital rim and direct visualization of the inferior rim or arch fracture. Thus the position of the zygoma after less severe injuries can be restored and fixation obtained without violating the lower eyelid, assuming that no serious floor component is present. This avoids the potential iatrogenic injuries most often associated with open reduction of zygomatic fractures, lower lid retraction, and eversion. Even the experienced operator notes occasional increased scleral show or even gross ectropion in a patient who underwent a transconjunctival incision for exposure of the inferior orbital rim, a step that can often be avoided with thorough preoperative CT evaluation.
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