Effects of screws and a sleeve on initial fixation in uncemented total knee tibial components. Aseptic loosening of tibial components remains a serious problem in uncemented total knee arthroplasties. Achieving rigid initial fixation of porous-coated components is one of the most important factors in promoting bone ingrowth. The results of a biomechanical study for micromovement of the tibial component under posteroanterior shear and axial compressive loading are presented. Forty anatomic specimen tibiae were stress tested on a servohydraulic mechanical test machine to evaluate the effects of screws and a sleeve on initial fixation of the uncemented total knee tibial component. Twenty specimens were used for posteroanterior shear loading and 20 for anterolateral axial compressive loading. Four cancellous screws were inserted through holes of the tibial tray to pierce the cortex of the proximal tibia. The methylmethacrylate sleeve was applied to the central stem. Rigidity of fixation was significantly improved by the combination of screws and a sleeve. Bone strength was also an important factor affecting the quality of fixation. 