Intra-operator and inter-operator reliability, and CT scan repeatability in 3D modelling of talus bone using CT imaging

Background: A talar body prosthetic implant may be indicated after a severe fracture in the talus bone resulting in avascular necrosis with collapse. This process is patient-specific, in which the geometry is copied from the healthy talus of the opposite foot to create the implant. More recently, an ‘off-the-shelf’ non-custom talar prosthetic was proposed, consisting of a standardised shape in 10 different sizes. Methods: The generic-shaped talus was determined by creating 3D models via image processing software MIMICS and further refined using Geomagic, from raw data of CT scan imaging. This study evaluated the intra- and inter-operator reliability in 3D modelling of talus bone from CT scan imaging. Results: Four operators created 3D models using CT scans of four subjects via the documented protocol. The average deviations were well within the acceptable value, and although the extreme values were large, the distributions showed that the critical deviations were either few points, or small areas. Intra- and inter-operator differences were not statistically significant in most cases. The talus bone was found to have larger deviations than the tibia due to rougher surface. Conclusions: From our results, the method of converting 2D CT images to 3D models used to develop generic talus implant is reliable within the acceptable tolerances.