Micromotion of cementless tibial components

To develop a method of evaluating the initial fixation and stability of uncemented tibial components, 27 cementless tibial trays were implanted which utilized various fixation geometries including screws, pegs, stems, and asymmetry. Specimens were loaded in a servohydraulic testing machine in six defined areas of the tibial tray (3 medial, 3 lateral). In addition, 10 scalpel blades were inserted about 1 mm under the tray into the cortex of the tibiae at the six loading points, and laser distance sensors were mounted on a low vibration stand to monitor the displacement of both the tray and bone. The test was repeated three times for each loading point to monitor repeatability Stiffness testing was also repeated four times at each loading point. Analyses of the data indicate that asymmetric designs yield lower micromotion values than asymmetric designs. Micromotion was not affected by the method of fixation and proximal cancellous bone stiffness, but affected by cortical contact area.