Virtual surgical planning allows the surgeon to operate more efficiently, reduces anesthetic duration and operating room costs, and enables visualization of anatomic structures during the presurgical planning period.
Patient-specific implants reduce operating time, require less intraoperative manipulation, and, compared with prebent titanium plates, are stronger and more precise.
Intraoperative navigation allows the surgeon to avoid important anatomic structures, confirm reduction of fractures, and reduces the need for revision surgery.
Surgical correction of maxillofacial injuries presents many challenges. Care must be taken when designing surgical approaches to avoid damage to vital structures that could otherwise lead to function/sensory deficits. It is also imperative to optimize placement of incisions to avoid unfavorable scarring. With regard to repair of facial fractures, the surgeon must preserve or reestablish the proper width, height, and projection of the face in order to yield an esthetic as well as functionally acceptable result. Limitations created by surgical access, soft tissue swelling, severity of injury, and attempts to optimize use of operating room (OR) resources have led to major advances in the development of virtual surgical planning techniques and technologies as an adjunct to current surgical methods to treating maxillofacial trauma.
Rationale for virtual surgical planning
Miguel de Cervantes once wrote, “The man who is prepared has his battle half fought.” The rationale for the development and use of virtual surgical planning is to optimize the surgeon’s ability to prepare for and mitigate potential struggles in the operating room when presented with complex skeletal repair and/or reconstruction.
The proper use of virtual surgical planning can help the surgeon to use his or her time in the OR more safely and efficiently. This minimizes anesthetic duration as well as OR/hospital costs. In a recent analysis of cost of OR time, one study showed average cost of OR time in California acute care hospitals to be $36 to $37 per minute. Proper presurgical planning and appropriate use of resources such as surgical navigation and intraoperative computed tomography (CT) can make the time spent in the OR more productive and potentially reduce time spent in the OR on complex cases. The ability to confirm proper bony relationships intraoperatively using surgical navigation or intraoperative CT also reduces the need for subsequent revision operations that add expense to the health care system as well as risk to the patient. The basic technique and merits of virtual surgical planning are discussed later.
Virtual surgical planning: models, occlusal splints, and surgical guides
The first step to any sort of virtual surgical planning technique is obtaining indicated radiographic imaging, with appropriate protocols for virtual surgical planning. Usually a CT scan is already performed before consultation of the facial trauma team in the hospital setting. Although the standard maxillofacial CT ordered in the acute trauma setting may be useful for diagnosis of injuries, it may not be adequate for virtual surgical planning. Often times the patient may need to have a repeat CT with smaller slice thickness. Valuable time can be saved by ensuring the imaging is adequate before submitting data to a company that will be assisting the virtual surgical planning.
Those familiar with the virtual surgical planning for orthognathic surgery will find the process for the trauma patient quite similar. The preoperative planning session typically takes place remotely via web meeting, allowing the surgeon to discuss case planning with an engineer from the company that will be assisting with fabrication of custom materials or hardware necessary for the case. After submission of the imaging data and dental casts when indicated, a virtual 3-dimensional (3D) model of the patient’s scanned anatomy is created. Virtual surgical planning software allows manipulation of the 3D DICOM dataset, enabling the surgeon to design desired osteotomies and/or bony reductions precisely. The planned osteotomies or reductions can then be guided with the use of custom cutting or reduction guides (along with the help of occlusal splints as with traditional orthognathic surgery), which are designed off of the new or “final” DICOM dataset that represents the desired surgical manipulations. The final 3D positions of various bony segments can also be saved as individual STL files representing separate anatomic segments that can be seen and manipulated individually in an intraoperative navigation (IN) software system to help guide and confirm osteotomies and reductions in real time.
Patient-specific implants (PSIs) provide several advantages over stock implants in treating maxillofacial injuries. One major advantage is the reduction in operative time as there is no need to spend significant time intraoperatively to adapt stock implants to the injured segments. PSIs are customized to the individual patient’s anatomy to aid in precise reduction, as well as optimize strength and stability of fixation. Fabrication of PSIs requires preoperative virtual surgical planning, during which time the implant is designed to fit the final/reduced fractures in their desired position. For instance, in the case of a complex mandibular repair, a custom reconstruction plate can be milled out of a titanium block using computer-aided design and manufacturing technologies. In the case of a malar or zygomatic implant, the implant is 3D printed in a material such as porous polyethylene (Medpor) or polyether ether ketone. Although PSIs are more expensive, they have the advantage of being the most accurate and require the least amount of intraoperative manipulation. Titanium reconstruction plates fabricated in this manner are also much stronger than bent plates, because they do not undergo tensile and compressive strain from bending, which would otherwise lead to fatigue and possible increased likelihood hardware failure. The custom recon plate thus allows for the use of a potentially thinner profile plate, which has the same (if not better) mechanical properties and strength as a thick plate with bends incorporated in it.
IN uses preoperative imaging to allow surgeons to correlate clinical anatomy with CT imaging, thus permitting the surgeon to better understand the anatomy of the patient in areas difficult to visualize clinically through traditional surgical approaches. IN has proved to be an important adjunct in neurosurgery and sinus surgery and in recent years has gained popularity as a tool to aid reduction of maxillofacial fractures as well, thus improving functional and esthetic outcomes for these patients. IN helps the surgeon avoid important anatomic structures, confirm reduction of fractures, and reduce the need for revision surgery.
Because each navigation system has its own individual idiosyncrasies, only general steps to using IN are discussed in this paper as follows :
A CT scan performed according to the specific protocols for the navigation system is uploaded to the navigation system and analyzed by the software.
The patient’s anatomy is registered so as to correlate with the imaging that has been uploaded in the software. Utilization of noninvasive methods involves placement of adhesive fiducial markers or a facemask to help correlate relationships with anatomic landmarks on the CT scan. Invasive methods include screws that serve as fiducials at specific bony landmarks that can be correlated with the CT imaging.
The accuracy of the registration is confirmed by placing the navigation wand at different, easily visualized points to ensure accurate correlation to the CT imaging. The registration process is repeated as necessary to achieve accurate correlation.
The current IN systems are shown to be accurate within 1.0 to 2.0 mm, with the noninvasive or mask registration being preferred over the invasive modality whenever possible. To ensure accurate correlation between the CT imaging and current clinical anatomy, it is important to confirm that the CT being used accurately represents any soft tissue swelling that may be present since the noninvasive fiducial markers are placed along the surface of the skin. The surgeon may need to consider obtaining a new CT scan as close to the time of surgery as possible, especially if there have been significant changes in soft tissue swelling since the original CT was performed.
Although there are some system-based difficulties to using virtual planning for anatomic materials/implants and IN in the acute trauma setting, it is still potentially feasible to incorporate these adjuncts given the appropriate infrastructure, communication, staff training, and protocol implementation by surgeons. Factors such as billing authorization, equipment availability, and emergency room (ER)/OR staff, nursing, and interdepartmental familiarity with these technologies is imperative to achieve logistical hurdles. The goal is to make the use of virtual surgical planning with adjunctive IN convenient, streamlined, efficient, and cost-effective for use in a trauma setting, while maintaining the lowest possible exposure to ionizing radiation and repeat CT.
Case 1—orbital blowout fracture with enophthalmos
A 21-year-old woman presented as an outpatient to the oral and maxillofacial surgery clinic after being discharged from an outside hospital approximately 3 weeks prior. She was a restrained passenger in a motor vehicle collision. During her previous hospitalization she was evaluated by the ophthalmology service and diagnosed with a right orbital floor blowout fracture. On the authors’ examination, she had diplopia in upward and lower gaze and was noted to have right-sided enopthalmos.
A copy of the CT scan from the outside hospital was sent to the virtual planning vendor ( Fig. 1 ), and the 3D DICOM data were manipulated to virtually reconstruct the right orbital floor by simply mirroring the left side in order to replicate its most likely contour before injury. This final position DICOM data were then used to fabricate a stereolithic model of the skull. It was also loaded into the IN system to aid with guiding implant placement during surgery.
Before surgery, a stock preshaped 3D orbital floor implant (made of porous polyethylene on titanium mesh) was sized, trimmed, and bent to precisely fit the contours of the right orbital floor and medial wall on the stereolithic model. The plate and stereolithic model were then sterilized for use in the OR. Of note, the material chosen for fabrication of the 3D model is important, as only acrylic models can be sterilized for use on the field and provide superior accuracy. Starch models cannot be sterilized, as they will dissolve and crack when exposed to the high temperature and pressure of an autoclave.
On the day of surgery, the navigation facemask was used for registration to the IN system. Exposure of the orbital floor fracture was gained by a transconjunctival incision with transcaruncular extension, and the remaining intact bony walls were identified. The plate was found to have good adaptation to the remaining bony walls and ledges in the orbit. Navigation was used to ensure that the plate was properly positioned, to rest on a solid posterior stop, as well as avoid impingement of the optic nerve posteromedially ( Figs. 2 and 3 ). IN is particularly helpful in repair of delayed enophthalmos, because not only are normal anatomic landmarks missing, but tissue remodeling and scar tissue formation within the orbit can make if far more challenging to identify remaining anatomic landmarks. After confirming proper positioning with IN, the plate was secured with two 4-mm screws. A postoperative CT showed favorable adaptation of the plate to bone ( Fig. 4 ).
A major advantage of prebending a plate in this fashion is the reduction in intraoperative swelling from repeated insertion and removal of the plate to make adjustments. It also essentially provides a plate that is fit with excellent accuracy, and is fabricated outside of the OR, thus decreasing OR time, resources, and expense, while at the same time avoiding the extra time and expense of a custom 3D-printed plate.
Case 2—gunshot wound with comminuted zygomaticomaxillary complex, zygomatic arch, and mandible fractures
This patient was a 38-year-old man who presented to the emergency department after sustaining a gunshot wound to his right face. After obtaining CT of the maxillofacial region ( Fig. 5 ), he was found to have sustained
Right zygomaticomaxillary complex and zygomatic arch fractures
Right maxillary alveolar ridge fracture
Right comminuted mandible body, angle, and subcondylar fractures
Complex facial lacerations with tissue avulsion and partial loss of facial nerve function on the right side