A method for assessing 3D shape variations of fuzzy regions and its application on human bony orbits

In complex orbital defects, typically the eye globe is retruded in a pathological position. This is associated with severe functional and cosmetic post-traumatic conditions. Characteristically, the posterior orbital floor and the medial wall of the bony orbit (=region of interest, ROI) is fractured where adequate reconstruction is crucial for a satisfactory surgical outcome but difficult to achieve. By introducing the concept of preshaped, navigated orbital implants, the repair of complex orbital fracture patterns could be significantly facilitated and improved. However, this ROI, delineated according to surgical criteria, cannot be defined by distinct anatomical landmarks because of the absence of reliable anatomical features. The determination of homologous surface points therefore remains a problem in such regions. The aim of this study was to provide a method for the assessment of the 3D shape of the ROI and of its variability, respectively. By aligning an anatomically determinable region that embeds the region of interest with a thin plate spline, transformation homology can be determined suitable for subsequent state-of-the-art shape analysis. First results of shape variations are illustrated and give hints into the future of optimized implant design.