Authors of section

General Editor

Daniel Buchbinder

Authors

Alexander Schramm, Marc Metzger, Nils Gellrich, Bradley Strong

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STL model, virtual planning, and intraoperative navigation

1. Introduction

Indications

When a STL model is useful to plan surgery and/or pre-adapt plates, virtual planning is necessary.

Secondary Zygomatico-orbital complex correction can benefit from virtual planning of the procedure and intraoperative navigation to ensure proper execution of the plan.

The clinical view shows a posttraumatic defect of the left zygomatico-orbital complex. The left globe was previously removed and reconstructed with a prosthesis.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

2. Virtual planning

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

The preoperative 3D-CT scan shows a severe defect of the left midface.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

Segmentation of anatomic regions is performed using autosegmentation algorithms.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

Virtual reduction and reconstruction

Virtual simulation of the midface reconstruction is performed by mirroring the unaffected right side after auto segmentation or by repositioning the segmented affected bones manually.

Reconstruction of the orbital walls in unilateral trauma is achieved by mirroring the contralateral side.

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

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

Stereolithographic models can be produced based on the original CT-scan data set and
based on the modified dataset with virtual reconstruction.

Patient specific implants are produced based on the stereolithographic model where the virtual reconstruction has been made. In this case standard titanium implants have been bent and sized to fit the specific reconstruction.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

3. Midface reconstruction using intraoperative navigation

Tracking of patients head is achieved with a dynamic reference frame (DRF) attached to the cranial bone. Alternatively the DRF can be attached to a Mayfield clamp.

computer assisted surgery gunshot injury virtual planning and intraoperative navigation

Pointer based infrared navigation provides radiation dose-free placement of the titanium implants according to the virtual template created during the planning.

After positioning of the titanium implants, the tip of the pointer is moved slowly over the implant surface to correlate actual zygoma position with the contours of the virtual template via frameless stereotaxy.

This procedure has to be repeated after any changes of the implant position.

computer assisted surgery gunshot injury virtual planning and intraoperative navigation

The monitor screen shows the implant position (red) in correlation to the virtual reconstruction (orange).

A slight overcorrection after inserting the implants in secondary reconstructions as shown here is recommended.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

4. Intraoperative verification of the reduction/reconstruction

Recording of intraoperative images

Intraoperative imaging is used to control the reduction result with a 3-D C-arm. No sterile draping of the device is needed. The time necessary for setup and scanning is approximately 10-15 minutes.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

Intraoperative quality control of titanium implant placement

The correct anatomic shape of the titanium implants used for midface reconstruction can be verified in the intraoperative CT scan.

In case the implants are not properly positioned, correction of shape and position of the implant is recommended followed by a second intraoperative CT-scan.

This technique can be used for all reconstructions with radio opaque material.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

5. Postoperative control

Postoperative 3D-CT scan.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative

Clinical view after computer assisted reconstruction of the left midface with patient specific titanium implants.

computer assisted surgery zygomatico orbital complex stl model virtual planning and intraoperative