Page 132 - Advanced concepts in orbital wall fractures

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Chapter 7
clinically irrelevant as this area is rarely affected by trauma. An exact anatomical restoration of the contour of the orbital floor and medial wall is impossible when using a preformed titanium implant. Therefore, small variations of the contralateral side in orbital shape are acceptable. After mirroring over the midsagittal plane, it is possible to perform a virtual reconstruction. Virtual templates of the available implants can be used to determine which implant has the best fit and thus facilitates an optimal reconstruction. The mirrored orbital cavity can also be used for the design of a patient-specific implant to get a closer approximation of the anatomy before trauma. The mirroring technique is a fundamental process in restoring the bony orbit and is one of the pillars of virtual preoperative planning.
Intraoperative assistance and control
In surgical cases for orbital reconstruction, advanced diagnostics is followed by the execution and completion of the preoperative plan. Based on the size of the bony orbit and the fracture, the correct implant size will be selected using the virtual template of the preformed implants. The ideal position of the implant can be achieved with the virtual template obtained from the mirroring technique. The 3D reconstruction contributes to a better visualisation of the anatomy and assessment of the ideal position of the implant compared to the anatomical landmarks. During the virtual reconstruction 2D and 3D images can be used alternately to identify the most important landmarks, examine the boundaries of the fracture, and assess the expected problems. This is particularly insightful for an inexperienced surgeon and valuable for specialty trainees. In chapter 4, the preoperative plan is used as virtual guidance during surgery. Even without real-time feedback of intraoperative navigation, there is a significant improvement of the position of the implant. The accuracy is close to the outcomes of a comparable cadaver study on intraoperative navigation13. This may be due to a lack of a calibration error, adequate preparation, gaining experience during virtual reconstruction, and also because the planning can be used as a reference intraoperatively. The preoperative plan can be considered the most important step in CAS. An additional benefit of preoperative planning is that the plan can be used in the postoperative analysis to check if the targeted position is achieved. It