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The following is a summary of “Tibial morphological difference between metal augmentation and actual tibia for revision total knee arthroplasty,” published in the March 2025 issue of the Knee Surgery & Related Research by Sakamoto et al.

The tibial component overhang in total knee arthroplasty (TKA) can lead to soft tissue irritation, while underhang poses a risk of tibial bone resorption. However, it remains unclear whether the tapering angles of currently available metal augmentation blocks on the medial, lateral, anterior, and posterior aspects conform to the natural morphology of the proximal tibia. This study aimed to analyze the anatomical contour of the proximal tibia and assess whether the tapering angles of existing metal augmentation blocks align with the actual bony structure.

A retrospective analysis was conducted using computed tomography (CT) scans of the lower extremities from 100 consecutive knees. Three-dimensional reconstructions of the tibia were generated to evaluate anatomical variations. The primary resection level was set at 10 mm below the center of the lateral tibial plateau, with additional assumed resection levels at 5, 10, 15, and 20 mm below this reference plane. The reduction values from the primary resection level to each of these assumed levels were measured. The tapering angles at eight tibial regions were calculated and compared with the angles of currently available metal augmentation blocks, as provided by the manufacturer. The mismatch distances between the metal augmentation blocks and the native tibial bone surface were also quantified.

Results demonstrated that the tapering angle increased progressively at more distal resection levels, reaching up to 30° on the medial and lateral sides and approximately 40° on the posterior side at the 20 mm resection level. Notably, the tapering angles of current metal augmentation blocks were smaller than those observed in native tibial morphology. Furthermore, the mismatch distances varied significantly across different implants, with a maximum deviation of 11.3 mm observed in the 15 mm augmentation.

These findings highlight a substantial discrepancy between the design of currently available metal augmentation blocks and the natural morphology of the proximal tibia. This mismatch suggests that surgeons should be mindful of potential size discrepancies when selecting femoral and tibial components during revision TKA. Customization or modifications to implant design may be necessary to achieve optimal fit, ensuring better biomechanical compatibility and minimizing complications associated with poor tibial component alignment.

Source: kneesurgrelatres.biomedcentral.com/articles/10.1186/s43019-025-00262-9