The effects of a central stem and its length on cementless tibial tray micromovement were investigated using preserved cadaver tibial specimens. For axial loading tests, cyclical compressive loads ranging 50-1000 N were applied to the anterolateral portion of the implanted tray. With subsidence on the loaded side and lift-off on the contralateral side, micromotions on both sides and bending of the tray were measured. The three groups consisted of a stemless group, a 7.5 cm (short) central stem group, and a 15 cm (long) central stem group. For shear loading tests, shear loads ranging 20-250 N were applied to the central portion of the posterior rim of the tray anteriorly for 1,000 cycles. Displacement values for subsidence and micromotion were measured on the medial and lateral side of the trays and compared for each group. For axial tests, the long stem minimized subsidence and lift-off (P < .05) when compared to the stemless group. Although the short stem also tended to prevent contralateral lift-off, no significant difference was shown when compared to the stemless group. However for shear loading, both central stem lengths significantly reduced subsidence and micromotion (P < .05). The authors conclude that the tibial tray with a long stem can achieve better initiation fixation of the implant to bone when compared to the short stem and no stem groups.