No effect in primary stability after increasing interference fit in cementless TKA tibial components.

Cementless total knee arthroplasty (TKA) implants rely on interference fit to achieve initial stability. However, the optimal interference fit is unknown. This study investigates the effect of using different interference fit on the initial stability of tibial TKA implants. Experiments were performed on human cadaveric tibias using a low interference fit of 350 μm of a clinically established cementless porous-coated tibial implant and a high interference fit of 700 μm. The Orthoload peak loads of gait and squat were applied to the specimens with a custom-made load applicator. Micromotions and gaps opening/closing were measured at the bone-implant interface using Digital Image Correlation (DIC) in 6 regions of interest (ROIs). Two multilevel linear mixed-effect models were created with micromotions and gaps as dependent variables. The results revealed no significant differences for micromotions between the two interference fits (gait p = 0.755, squat p = 0.232), nor for gaps opening/closing (gait p = 0.474, squat p = 0.269). In contrast, significant differences were found for the ROIs in the two dependent variables (p < 0.001), where more gap closing was seen in the posterior ROIs than in the anterior ROIs during both loading configurations. This study showed that increasing the interference fit from 350 to 700 μm did not influence initial stability.