The use of a custom made atlas as a template for corrective surgeries of asymmetric patients

Aim: The use of conventional mirror images does not adequately guide surgeons on the correction of facial asymmetries. The purpose of this study was to evaluate the utility of an individualized atlas as a template for corrective surgeries for patients suffering from mandibular asymmetry. The patientspecific atlas is calculated from both the original asymmetric mandible and the mirror of the same mandible registered on the cranial base. Material and Method: Three patients with history of favorable clinical outcome of the correction of their mandibular asymmetry were chosen for this pilot study. CBCT were taken before and 6 weeks after corrective surgery using NewTom 3G. Each volume was mirrored and rigidly registered on the cranial base. Surface models for both the mandible and its registered mirror were used to compute an atlas using deformable fluid registration. Corrective surgery was simulated based of the resulting atlas. Differences between the virtual simulated outcome and the actual surgical outcome were computed using UNC SPHARM-PDM toolbox. Results: The detected differences between the virtual simulated outcome and the actual surgical outcome, as characterized in 6 degrees of freedom, were smaller than 2 mm of translation and 5 degrees of rotation. This indicates that the location of the synthesized template is similar to the desired clinical outcome. Conclusions: The construction of patient-specific atlases using non-rigid registration has the potential to optimize and increase the predictability of the outcome of craniofacial corrective surgeries for asymmetric patients.