Virtual planning and intraoperative imaging
1. Introduction
Indications
Whenever an intraoperative CT scanner is available, an intraoperative scan should be obtained for intraoperative evaluation of the reduction.
Zygomatic fractures that have a significant amount of displacement and internal orbital disruption benefit from virtual planning. After zygomatic reduction, an intraoperative CT-scan can be fused to the virtual plan to determine the adequacy of zygoma reduction and the status of the internal orbit.
When using computer assisted surgery, the reduction (and fixation if necessary) is performed according to standard procedures as described in the AO Surgery Reference. Computer assistance should be considered as an adjunct to surgical treatment.
Computer assisted surgery in treating fractures allows virtual preoperative planning of the desired reconstruction using preoperative CT scans and appropriate software.
Intraoperative imaging combined with image fusion of preoperative and intraoperative CT scans and the virtual plan allows verification of proper reduction.
Simple zygomatic fractures benefit mostly from intraoperative CT scanning to visualize fracture reduction and to determine the need for orbital wall reconstruction after zygoma reduction.
In simple orbital floor fractures radiopaque material for orbital wall reconstruction can easily be visualized by intraoperative imaging allowing intraoperative or postoperative verification of proper reconstruction.
With this technique, insufficient fracture reduction can be can be identified and corrected, eliminating the need for secondary procedures which may be necessary if only postoperative imaging is performed.
Intraoperative imaging requires an additional 10-15 min.
Useful additional reading
2. Virtual planning
Preoperative imaging
The preoperative CT scan shows a displaced fracture of the right zygomatic complex involving the orbital floor.
Virtual reduction
Virtual simulation of the zygoma reduction is performed by mirroring the unaffected left zygoma after auto segmentation. The yellow line shows the outer surface of the virtually repositioned zygoma and becomes the surgical goal for reduction.
Virtual orbital wall reconstruction is shown in green. This was achieved by mirroring of the unaffected contralateral side after auto segmentation.
3. Intraoperative assessment of reduction
To verify that the zygoma has been properly reduced, a CT scan is performed intraoperatively.
Virtual planning software allows automatic image fusion of preoperative and intraoperative CT scans along with the virtual plan for a better visualization of the achieved reduction.
Note: The reduced zygoma fits perfectly to the planned position (yellow).
The correct anatomic shape of the orbital floor can be verified after zygoma reduction in the intraoperative CT scan when virtual reconstruction in the preoperative CT scan is transferred to the intraoperative scan via image fusion. Note how the orbital floor after zygoma reduction perfectly fits the planned position (green). This confirms that there is no need for orbital wall reconstruction in this case.
Due to intraoperative visualization using a 3D C- arm after zygoma reduction, unnecessary orbital reconstructions can be avoided.
In case the orbital floor is not properly reduced, open orbital revision is recommended.
