Imaging in revision total knee arthroplasty: A novel 3D classification system for tibial bone defects

Abstract Purpose The primary purpose of the study was to use pre‐revision total knee arthroplasty (TKA) computer‐tomography (CT)‐images to analyse typical tibial bone defects and create a new schematic three‐dimensional (3D)‐classification system. The secondary purpose was to investigate the association between defect size and implant selection at the time of revision surgery. Methods Eighty‐four patients with preoperative CT‐scans underwent revision of a primary TKA. CT‐image segmentation with the 3D‐Slicer Software was performed retrospectively, and a new three‐dimensional classification system was used to grade tibial bone defects. The location of tibial bone defects was recorded for all cases. Volumetric 3D bone defect measurements were used to investigate the association between the bone defect volume, the indication for rTKA, and the use of modular revision components. The t ‐test, the Mann–Whitney‐ U test, and the Fisher's exact‐test were used for group comparisons, and the Kruskal–Wallis test was used for multiple group comparisons. Results The most common anatomic regions for both contained and uncontained tibial bone defects were the anteromedial epiphysis ( N = 50; mean epiphyseal‐defect: 5.9 cm³) and metaphysis ( N = 15; mean metaphyseal‐defect: 9.6 cm³). A significant association was found between patients with preoperative metaphyseal defects ( N = 22) and the use of tibial augments ( N = 7) ( p = 0.04). The use of cones/sleeves was associated with a significantly increased 3D‐CT volume of the preoperative metaphyseal bone defects ( p = 0.04). Patients with osteoporosis had significantly larger volumetric defects in the metaphysis ( p = 0.01). Conclusion Our results emphasise the importance of considering the three‐dimensional nature of tibial defects in rTKA. The findings suggest that an understanding of the volume of the defect size through CT imaging can predict the need for augments and cones/sleeves and, especially in patients with osteoporosis can help the surgeon identify larger metaphyseal defects and ensure optimal metaphyseal fixation through appropriate implant selection. Level of Evidence Level III, retrospective cohort study.