The objective of this study was to develop a novel method to quantify rotational micromotion of modular tibial components that incorporates physiologic loading conditions, a physiologic test environment, and constraint characteristics of the articulating surface. The methodology is reviewed and data are presented on four total knee designs. Results showed the design with a rotational stabilizing island to demonstrate the most capability in resisting rotational micromotion for a given reacted torque, followed by a full peripheral capture device, then a partial peripheral capture device, and then a full peripheral capture device with a posterior lipped edge. Under walking and stair-climbing loads, the full peripheral capture device imparts more torque to the insert than the other designs due to the higher constraint of its articulating surface and thus experiences the most micromotion. The rotational stabilizing island device reveals the least amount of motion, due to a combination of its locking mechanism and a less constrained articular surface.
As the demands for total knee arthroplasty continue to rise, the methodologies for testing current and future devices may require refinement. Current standards have not been shown to simulate wear rates and patterns seen in explanation studies. The purpose of this study was to assess a combination of potentially more physiological testing protocols. Four identical TKAs were implanted into four fresh cadaver knees and tested in a knee simulator. Each knee was tested using the ISO load control testing standard (ISO 14243-1) and five novel testing protocols representing different activities of daily living. Motions were recorded between the tibia and femur (tibial rotation, anterior–posterior (AP) motion) and between the implant and bone (superior-inferior femoral condylar motion, tibial tray vertical motion). The total tibial AP cadaver motion varied from a total of 6.2 to 7.6 mm for the six loading protocols during a cycle of motion. For the ISO gait profile and the new gait, stair ascent and stair descent profiles, the range of tibial cadaver rotation varied from 9.2° with the ISO gait to 10.2° with the stair ascent. The crossover turn had a range of 16.3° and the pivot turn a range of 18.7°. Larger tibial tray AP motion, relative to the tibia, occurred with the pivot turn and crossover turn motions, compared to the gait motions or stair activities. This study supports the viability of new and alternative loading profiles. We suggest that these novel profiles should be considered by the ASTM or ISO as they seek to supplement or replace the profiles currently in use.
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