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Research Papers

Design Modifications and Optimization of a Commercially Available Knee Simulator

[+] Author and Article Information
J. P. Kretzer, E. Jakubowitz, K. Hofmann, C. Heisel, J. A. Kleinhans

Laboratory of Biomechanics and Implant Research, University of Heidelberg, Schlierbacher Landstrasse 200a, 69151 Heidelberg, Germany

M. Thomsen

 German Red Cross Hospital, Lilienmattstrasse 5, 76530 Baden-Baden, Germany

J. Med. Devices 2(4), 041005 (Nov 06, 2008) (5 pages) doi:10.1115/1.2979746 History: Received May 08, 2007; Revised August 04, 2008; Published November 06, 2008

To determine the wear behavior of knee endoprostheses, implants are tested in knee simulators before being introduced to the market. Implants may undergo mechanical failure and wear debris is generated. The magnitude and morphology of this debris are determined to gain information about its biological reactivity. In this study, we describe the modifications made to the AMTI multistation knee simulator. The simulator is not capable to ensure a medially biased load distribution as required per ISO 14243, and therefore the usage of the simulator is limited. Thus, simulator modifications were made to implement a wear test as outlined in ISO 14243, and to improve both user-friendliness of operation and cost of simulation. In particular, this involved modifying the implant holders and controlling implant kinematics during the simulation. For component design, a 3D computer-aided design software was used. After the manufacturing of all components had been completed, the redesigned system was put into operation. In a final wear test, functionality and conformance with the ISO standard were tested for the modified simulator. After implementation of design modifications, it is possible to run wear tests with a medially biased load distribution according to ISO 14243.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Implant holders on the AMTI simulator: (a) tibia plateau holder, (b) rotational shaft, (c) load carrying cylinders, and (d) extension∕flexion shaft

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Figure 2

Sealing of the implant components on the ATMI simulator

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Figure 3

Explanted PE inlays of different designs showing larger wear scars medially

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Figure 4

Uncoupled degrees of freedom in the AMTI simulator

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Figure 5

Translating the force to the femoral condyles: (a) stainless steel tube, (b) polyurethane resin, (c) swallowtail guide, (d) offset shaft, and (e) rotational needle bearing

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Figure 6

Holder for the tibial plateau: (a) polycarbonate tube, (b) O-rings, (c) fine threads, (d) drain, (e) tibial plateau, (f) rotational supporting shaft, (g) tibial plateau holder, (h) bearing surface, (i) needle bearings, (j) needle rolling bearings, (k) ground plate, (l) bearing blocks, and (m) sliding carriage

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Figure 7

Final setup after modification

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Figure 8

PE inlay used in validation study

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