Virtual planning and implant planning

When secondary correction of a craniofacial defect can benefit from virtual planning of the computer assisted designed (CAD) and computer assisted manufactured (CAM) patient specific implant.

Frontal bone defects alone are most often treated with patient specific implants without the use of computer assisted surgery.

However, in cases where the frontal bone defect is combined with defects of the zygomatico orbital complex, computer assisted surgery allows simultaneous reconstruction of all parts of the cranial and facial skeleton.

The clinical view shows a patient with a posttraumatic defect of the frontal bone in combination with a complex bilateral deformity of the zygomatico orbital complex.

This case will be used to illustrate the principles of the procedure.

• Introduction to CAS
• OR setup
• Cone beam vs. fan beam
• Preparation for intraoperative navigation

Proper preoperative examination of CT-scans requires multiplanar views consisting of axial, coronal, sagittal, and 3D-reconstruction.

To facilitate intraoperative navigation, titanium screws have to be inserted as fiducial markers into the skull prior to CT scanning. In a case where the maxilla is not fractured, fiducial markers can be fixed to dental splints.

Skin fiducials or laser surface scanning in craniofacial trauma are not applicable due to soft tissue changes.

The preoperative 3D-CT scan shows a posttraumatic defect of the frontal bone in combination with a complex bilateral
deformity of the zygomatico orbital complex. This result can be adjusted by the surgeon.

The first step in preoperative planning is correct orientation of the data set to the natural head position.

The second step is segmentation of anatomic regions of interest. Using autosegmentation algorithms, this procedure is performed by the software.

Virtual simulation of the midface reconstruction is performed by mirroring the unaffected side after auto segmentation, or repositioning of affected bone segments manually.

After virtual reconstruction of the midface (right) the modified dataset serves as a virtual template that can be used for intraoperative navigation, intraoperative imaging and postoperative verification of the reduction/reconstruction.

This modified dataset is also used for producing a patient specific implant for frontal bone reconstruction (PSI). This allows frontal bone reconstruction with a preoperatively fabricated patient specific implant that fits to the midface reconstruction performed at the same time.

The orbital zygomatic reconstruction is performed first using intraoperative navigation to properly position the fragments.

The patient specific implant is then inserted and fixed with titanium screws.

A postoperative 3D-CT scan is made to evaluate the accuracy of the reconstruction.

Clinical view before and after computer assisted reconstruction of the frontal bone and the zygomatico orbital complex.