An in vitro study was performed using a singular unibody design CoCr tibial baseplate with fins to test the hypothesis that the addition of cement surrounding the tibial stem decreases micromotion of the tibial tray in cemented total knee arthroplasty. Five configurations were tested. Significant micromotion occurred with a cementless stem and a 1 mm cement mantle under the tibial tray. However, if the cement mantle beneath the tibial baseplate was increased to 3 mm, excellent stability of the implant was seen regardless of whether the tibial stem was left uncemented. In this particular component design, implant stability was enhanced with the addition of cement surrounding the tibial stem unless the cement mantle beneath the tibial tray was increased to 3 mm.