Computer-assisted surgical planning in craniomaxillofacial trauma: Zygomaticomaxillary complex fractures and secondary reconstruction

Introduction

Zygomaticomaxillary complex (ZMC) fractures are one of the most common facial fractures, second only to nasal bone fractures. ^, The ZMC plays a key functional and aesthetic role for the face—the zygomatic arch serves as the cranial insertion point for the masseter, and the zygomatic complex provides an anatomic separation between the maxillary sinus, orbit, and temporal fossa. Aesthetically, the ZMC provides a normal cheek contour and is principal to establishing an appropriate and symmetric facial width.

As with most facial fractures, accurate reduction and expeditious surgical fixation of the ZMC is desirable because reestablishing pretraumatic facial contour is challenging after scarring and bony remodeling have transpired. ^, Given the ZMC’s numerous bony attachments and at-times complex translational and rotational displacement, computer-assisted surgical planning (CaSP) and computer-assisted design and manufacturing (CAD/CAM) can be helpful in restoring premorbid facial morphology and orbital volume. ^, This chapter will discuss clinical management using CAD/CAM in treating ZMC fractures acutely as well as in the setting of secondary reconstruction.

Clinical considerations

Depending on the vector, force, and mechanism of injury, damage to the ZMC can be highly variable, and for this reason, a litany of diagnostic classification systems exists to standardize surgical treatment and postoperative care of these fractures. These classifications typically distinguish categories based on the degree of displacement, comminution, and rotation of the bony segments. A detailed discussion of each of these systems is outside the scope of this chapter, but, broadly speaking, the morphology, displacement, and degree of comminution of the fracture pattern (as well as the presence of other concomitant facial fractures) will ultimately guide the surgeon in their maneuvers for adequate reduction and internal fixation.

Clinically, disruption of the ZMC through blunt or penetrating trauma can result in asymmetry and malar flattening with facial widening, exophthalmos or enophthalmos, increased scleral show, or trismus. If significantly displaced, step-offs and crepitus along the zygomatic arch or orbital rim can also be appreciated on palpation. Because of the proximity of the infraorbital nerve, facial paresthesia may also be present and nerve decompression may be warranted at the time of fracture fixation. As with all facial fractures, the gold standard for diagnosis and presurgical planning of the ZMC remains non-contrast computed tomography (CT) imaging of the craniofacial skeleton. Special consideration should also be taken to observe any areas of coronoid involvement as a possible cause of trismus due to impingement from a posteriorly displaced or rotated zygoma.

A special note should be made regarding ocular injury, which frequently accompanies ZMC and other midfacial fractures that disrupt the integrity of the orbital skeleton. Subconjunctival hemorrhage and corneal abrasion are the most frequently diagnosed ocular injuries in this context, but more serious complications such as hyphema, vitreous hemorrhage, retinal hemorrhage, extraocular muscle entrapment, canthal ligament detachment, and globe rupture may also be present. For this reason, in the acute setting, a thorough ophthalmologic evaluation and an assessment of visual acuity is necessary to diagnose and treat any potentially blinding complications before fracture fixation can safely proceed. Operative fracture treatment in this context should be delayed until stabilization of the ocular injury and ophthalmology clearance has been elicited, and in certain cases, it may be desirable to delay treatment further until improvement in periorbital edema to aid intraoperative visualization of the zygomaticosphenoid suture and orbital floor.

Nondisplaced or incomplete ZMC fractures may be managed nonoperatively with sinus precautions and a soft diet. For displaced ZMC fractures, however, technical considerations range from one to four points of fixation in the literature with no clear consensus. In a recent meta-analysis examining the number of fixation points for ZMC fractures, the overall quality of current evidence for the number of points of exposure and fixation of ZMC fractures was poor. That said, it is largely accepted that while some translation and rotational movement can be mitigated with the use of a single miniplate, a second or third plate provides further stability, counteracting the strong displacing forces from the masseter muscle. When analyzing the few randomized controlled trials that compared two- and three-point fixation, three-point fixation of ZMC fractures was shown to improve fracture stability and yield less long-term vertical orbital dystopia. The surgeon should, however, weigh the potential gains in stability against the risks of additional exposure, periosteal stripping, ectropion, and soft tissue scarring. Broadly speaking, in our experience, with most facial fractures, a greater degree of comminution and fracture complexity increases the need for more fixation points.

For those patients who have either missed their window for open reduction and internal fixation or for those whose fractures are inadequately reduced during prior fixation, secondary reconstruction of ZMC fractures may be required. In most ZMC fractures, the zygoma is usually displaced laterally and inferiorly due to masseteric pull, thereby increasing intraorbital volume, and development of enophthalmos. In these instances, patients may present with residual post-traumatic deformity such as malar flattening, hypoglobus, trismus, and facial asymmetry. Once again, up-to-date CT imaging of the craniofacial skeleton is important for visualizing the topography of prior fractures, noting the presence of any previous radio-opaque hardware or foreign bodies, and observing any areas of impingement or bony interference. Depending on the severity of the deformity, correction of facial projection or orbital symmetry may require soft tissue resuspension or augmentation, malar implants, or zygomatic repositioning osteotomies.