The Effect of Flexibility and Central Stem of the Cementless Total Knee Tibial Tray on Initial Fixation

Summary

The effect of material properties, central stem and its length on tibial tray micromovements were investigated using 100 preserved cadaver tibias. Both axial and shear tests were performed on independent specimens. Axial compressive loads of 100 kg were applied to the anterolateral portion of tibial trays in axial loading tests. Subsidence on the loaded side, lift-off on the contralateral side, micromotions on both sides, and bending of the tray were measured. There was significantly less subsidence, micromotion, and lift-off with the softer Ti6A14V trays than with the harder CoCr trays. Less subsidence and lift-off were also demonstrated in trays with a long central stem when compared to the other stem groups. For shear loading tests, shear loads of 25 kg were applied to the central portion of the posterior rim of the tray anteriorly. Subsidence and micromotion were measured on the medial and lateral side of the trays, and the mean values were statistically determined for each group. The presence of a central stem significantly reduced both subsidence and micromotion regardless of stem length. Therefore, we concluded that the flexible Ti6A14V tibial tray remains in better contact with the cut tibial bone surface than the more rigid CoCr tray during eccentric loading. We also concluded that the tibial tray with a long stem can achieve better initial fixation of the implant to bone when compared to the short stem and no stem.