Abstract
Introduction
Initial stability of cementless total knee arthroplasty (TKA) tibial trays is necessary to facilitate biological fixation. Previous experimental and computational studies describe a dynamic loading micromotion test used to evaluate the initial stability of a design. Experimental tests were focused on cruciate retaining (CR) designs and walking gait loading. A FEA computational study of various constraints and activities found CR designs during walking gait experienced the greatest micromotion. This experimental study is a continuation of testing performed on CR and walking gait to include a PS design and stair descent activity.
Methods
The previously described experimental method employed robotic loading informed by a custom computational model of the knee. Different TKA designs were virtually implanted into a specimen specific model of the knee. Activities were simulated using in-vivo loading profiles from instrumented tibia implants. The calculated loads on the tibia were applied in a robotic test. Anatomically designed cementless tibia components were implanted into a bone surrogate. Micromotion of the tray relative to the bone was measured using digital image correlation at 10 locations around the tray.
Three PS and three CR samples were dynamically loaded with their respective femur components with force and moment profiles simulating walking gait and stair descent activities. Periods of walking and stair descent cycles were alternated for a total of 2500 walking cycles and 180 stair descent cycles. Micromotion data was collected intermittently throughout the test and the overall 3D motion during a particular cycle calculated. The data was normalized to the maximum micromotion value measured throughout the test. The experimental data was evaluated against previously reported computational finite element model of the micromotion test.
Results
The maximum average micromotion was on the CR design during walking gait. The greatest CR micromotion during stair descent was 67% of the maximum. The maximum micromotion in the PS design was 55% of the CR walking maximum and occurred during stair descent. The next highest PS value was 52% during walking. The absolute difference in these values was under 3 µm. The majority of the PS micromotion values around the tray were less than 50% that of the maximum micromotion of the CR design.
Discussion
The experimental continuation of this investigation into cementless tray stability aligned with computational results in this model. The computational model predicted the PS tray would have 50% of the micromotion of the CR design, which was close to the experimental test. For CR, the computational rank order for walking and stair descent was also the same in the experimental follow-up. Future work in this investigation will include continued validation of the computational and experimental models, including more designs. Further exploration into accounting for patient and surgical variability should be explored.
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