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Knee wear simulation

For wear simulation a modified knee simulator (KS-2-6-1000, AMTI) is used. The servo hydraulic system consists of two benches, each equipped with three actively driven wear stations and one axially loaded reference station. The simulator enables replication of knee kinematics, in detail: axial loads of up to 4.5 kN, flexion/extension of 100, internal/external rotations of 15 as well as anterior/posterior translations of 25mm. The simulator has been modified to allow simulation of physiological force transmission, as well as simulation of changed force transmission due to varus-valgus malalignment [1].

Generally, level walking according to ISO 14243 (force as well as displacement controlled) is simulated. Additionally, the simulator enables simulation of other wear relevant activities like walking stairs or even cycling. Clinically relevant ligamental situations (e.g. insufficient posterior cruciate ligament) can be simulated using a virtual soft tissue control system.

Simulations are run in a closed chamber. As a substitute for synovial fluid, bovine serum is used; this is maintained at 37 during simulation. Generally, simulations are run to a total of 5 million cycles which corresponds to an in vivo use of approximately three years.

[1] Kretzer JP, Jakubowitz E, Hofmann K, Heisel C, Kleinhans JA, Thomsen M. Design Modifications and Optimization of a Commercially Available Knee Simulator. Journal of Medical Devices-Transactions of the Asme 2008;2.

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