The Evaluation of Muller Weiss Diseased and Normal Feet on a Three-Dimensional Foot Model

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: The deformities associated with Müller Weis Disease (MWD) have not been well understood which inevitably impacts clinical and surgical decision making. Despite most previous studies characterizing MWD as a paradoxical flatfoot deformity, ie, a flat arch and a varus heel, some studies have treated MWD as a flatfoot deformity by performing a medializing calcaneus osteotomy, and others as an arthritic disorder treated with hind foot arthrodesis but without correcting the deformity. This study used an automatic 3D segmentation program to create an average 3D foot model for both normal controls and a large group of MWD feet, to demonstrate the deformity pattern, and to provide surgeons with a foundation for detailed alignment evaluation and surgical planning. Methods: Weight bearing Scans of 55 health feet without deformities, trauma and surgical histories, and 69 MWD feet were included in this study. The Bonelogic program (Disior, Paragon 28,) was used to automatically segment the bones and 3D information of each foot in the same group was pooled to create an average foot model for both the controls and the MWD feet. Videos were created using all feet in both groups to demonstrate the deformity patterns ranging from normal feet transitioning to MWD feet. Since current axial and angular metrics for alignment evaluation using traditional 2D imaging cannot be extrapolated to 3D this study was kept as a descriptive paper, and no traditional metrics were analyzed and reported. Results: Compared to the average normal foot, the MWD foot model demonstrated the following features: narrowing on the lateral pole and dorsal side of the navicular, lateral rotation and slight dorsal lifting of the talar head and medial rotation of the navicular, a varus heel with more opening in the sinus tarsi, proximal shift of the calcaneal tuberosity, a flat medial arch with subsidence at the talonavicular joint, decreased adduction of the forefoot, medial translation of the cuboid at the calcaneocuboid articulation, and a shortened 1st metatarsal. All of the above changes were consistently demonstrated in video one (a comparison between the two foot models), and video two (a comparison of the peritalar joint alignment between the two groups). Conclusion: The foot models were built up with pixels, with each pixel carrying its own 3D information in space allowing exploration of real 3D alignment evaluation tools. The MWD foot model clearly demonstrated and validated the deformity patterns originally described by Maceira, and subsequently by other authors using both radiographs and WBCT scans. This model facilitates evaluation of alignment from the hindfoot to the forefoot, as well as advanced 3D analysis to assess the morphology of the bones and joints and can be the foundation for surgical planning and predication of outcomes