Moving to 3D: Quantifying Virtual Surgical Planning Accuracy Using Geometric Morphometrics and Cephalometrics in Facial Feminization Surgery

Facial feminization surgeries (FFS) aim to feminize facial features in transgender women and include frontal sinus setback, rhinoplasty, and genioplasty. FFS may be performed with virtual surgical planning (VSP) to help generate reproducible and predictable results. However, quantification of changes is challenging because these changes often occur in multiple axes and dimensions that are not easily reduced to a single error metric. The objective of this study was to apply cephalometrics and geometric morphometrics analyses to evaluate shape changes in FFS patients undergoing genioplasty and mandibular contouring. Fourteen patients who underwent genioplasty, mandibular contouring, or both, with a single surgeon and also had matching post-operative followup scans were included. Three-dimensional reconstructions of preoperative, postoperative, and VSP-guided "planned" computed tomography scans of each patient were created using 3D Slicer. Cephalometrics and geometric morphometrics were used to analyze changes. Pairwise 1-tailed t tests showed that postoperative bigonial width values significantly aligned with planned values across individuals. Geometric morphometric analyses, specifically Generalized Procrustes Analysis, demonstrated that the postoperative scans significantly aligned with planned scans in the fixed landmark data set (3-piece genioplasty) and gonial angle semi-landmark data set (mandibular contouring). Among scan sets that did not meet this hypothesis, the final postoperative shape was often between the preoperative and planned shapes, presumably due to post-osteotomy burring that is not captured on VSP. Future work using a greater number of landmarks, such as using statistical shape modeling approaches, may help to evaluate bony changes after FFS to better integrate changes in bone position with concomitant changes in bony shape.