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Custom Craniofacial Implants
Background
Craniofacial injuries are ideally treated in the acute setting. In certain circumstances, it is appropriate for treatment to be delayed. Resuscitation and treatment of life-threatening injuries in multiple trauma victims may preclude facial trauma treatment. For example, the treatment for patients with intracranial hemorrhage involves removal of portions of the skull for surgical access. The resulting brain and dural injuries are addressed acutely, but the bony reduction is sometimes suboptimal or delayed, resulting in deformity. By necessity, resultant deformities are generally treated in a delayed fashion.
For delayed reconstructions, computer-aided design (CAD) and computer-aided manufacturing (CAM) implants can be a valuable adjunct. They can provide near anatomical replication of the cranial vault and facial skeleton. If one side of the face or vault is uninjured it can be “mirrored” to reconstruct the injured side. If that is not possible, the surgeon can design implants appropriate for the situation.
The use of alloplastic materials in the reconstruction of craniofacial deformities has both inherent advantages and limitations. The use of alloplasts avoids the morbidity of autogenous bone harvest. The use of CAD/CAM implants avoids intraoperative carpentry and therefore significantly reduces operative time. However, because alloplastic materials do not integrate into the bony skeleton, they are only used as non-load-bearing onlays except for the cranial vault, where they replace missing skull to restore contour and protect the brain.
Clinical Presentation
Calvarial Deformity
These patients are typically ones who have undergone significant head trauma, often resulting in intracranial hemorrhage and emergent craniectomy. After an extended hospital course, they are often discharged to a rehabilitation facility and may regain some or most of their neurological function depending on their age. By the time they present for secondary reconstruction, they may have a noticeable depression at their craniectomy site. Some patients also undergo neurological deterioration that is related to the “Syndrome of the Trephined.” This syndrome, also known as “sunken skin flap syndrome,” is a poorly understood entity. It is characterized largely by neurological deficits after craniectomy and subsequent improvement after cranioplasty. Although the spectrum of deficits varies widely, most of the reported cases involve motor weakness, cognitive deficits, language deficits, or a combination of the three. In a recent literature review, the only consistent characteristic of those affected by the syndrome of the trephined was that greater than 90% exhibited a visibly sunken skin flap. Most patients have an improvement in their deficits within days after cranioplasty. Unfortunately, the pathophysiology is unknown. One of the leading theories is that the change in pressure seen by the brain without the structural support of the calvarium changes brain physiology, thereby causing neurological deficits.
Midface Deformity
These patients have typically undergone blunt facial trauma with subsequent facial fractures. Depending on the trauma burden, their facial fractures may or may not be treated operatively in the acute setting. For example, there may be a displaced zygoma fracture in a patient with concomitant head trauma and extremely labile vital signs which preclude operative repair. If the patient does not become stable within the first 4 weeks, repair may be deferred entirely. Alternatively, if a patient does have operative repair of facial fractures but the reduction is not perfect, they may still end up with facial asymmetries. In either case, patients present with facial deformities in a delayed fashion and have facial asymmetries such as brow malposition, lack of malar projection, enophthalmos, and/or lack of infraorbital rim definition.
Mandible Deformity
These patients have typically sustained a Le Fort pattern midface fracture as well as a mandible fracture. Operative treatment is aimed at restoring normal occlusion and involves open reduction, internal fixation, and sometimes maxillomandibular fixation. These are severe injury patterns and perfect bony reduction and facial symmetry are sometimes compromised in favor of achieving perfect occlusion. Depending on the location of the mandibular fractures, various parts of the mandible may be displaced to create a mandibular asymmetry, deformity, or bony step-offs that can be bothersome and warrant reconstruction.
Radiological Evaluation
Dedicated CT scans of the face with thin cuts are the optimal imaging modality when evaluating a patient with posttraumatic deformity. These can be reformatted to create 3-dimensional reconstructions that can aid in creating molds for surgical planning or virtually designing custom implants.
CAD/CAM Facial Implants
Computerized tomographic (CT) scans are fundamental to CAD/CAM facial implant technology. Implementation of CAD/CAM implants is a multi-step process. It requires a CT scan with sufficient data to reconstruct an accurate 3D image. The resultant image can be used to design an implant virtually or to create a model of the 3D image on which an implant design is fashioned. Implants are subsequently manufactured using milling or 3D printing techniques.
This allows for millimeter precise assessment of the contour deficit: symmetry, height, width, projection, and its relationship to the entire facial skeleton. Applying knowledge of the normal skeletal relationship and aesthetic criteria, virtual surgery can be performed to design and to correct the posttraumatic deformities.
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