Intra-observer variations of femoral bony landmarks using three different methods for the design of custom knee implant

Abstract

This study investigated the variability of the manual localization of anatomical landmarks of the distal femur using 3 different methods: CT, Mesh, and 3D printed models. From a CT database of 50 knees, 3D meshes were automatically generated and 3D printed. The main author performed twice, for each case, a registration of 11 distal femoral landmarks.We investigated for each landmark and modality the:• mean distance per modality• averages distance between each modality• deviation of each modality from the barycentre• position of the new planes and axes relative to their starting positionFinally, the study was carried out on 41 knees, 9 of which had to be excluded because of 3D printing issues. 2706 manual annotations were performed.Regarding the Intra-operator reproducibility, the average distances for each point and modality were between 1.49mm and 6.34mm. As for the analysis considering the barycenter no differences were found between the three modalities. However, some points showed more variability. But their impact on the 3 axes and the planes studied were found negligible. Mean angular variations for either axes or planes are all less than 0.5°.In summary, no differences were found between the three modalities but some points showed more variability.