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Hasenkamp W.,Ecole Polytechnique Federale de Lausanne | Hasenkamp W.,Microsystems Laboratory LMIS4 | Thevenaz N.,Ecole Polytechnique Federale de Lausanne | Thevenaz N.,Microsystems Laboratory LMIS4 | And 11 more authors.
Biomedical Microdevices | Year: 2013

This paper describes the development of a polyimide-based MEMS strain-sensing device. Finite element analysis was used to investigate an artificial knee implant and assist on device design and to optimize sensing characteristics. The sensing element of the device was fabricated using polyimide micromachining with embedded thin-metallic wires and placed into a knee prosthesis. The device was evaluated experimentally in a mechanical knee simulator using static and dynamic axial load conditions similar to those encountered in vivo. Results indicates the sensor is capable of measuring the strain associated to the total axial forces in the range of approximately 4 times body weight with a good sensitivity and accuracy for events happening within 1 s time window. © 2013 The Author(s).

Hasenkamp W.,Ecole Polytechnique Federale de Lausanne | Hasenkamp W.,Microsystems Laboratory LMIS4 | Villard J.,TU Munich | Delaloye J.R.,University of Lausanne | And 9 more authors.
Medical Engineering and Physics | Year: 2014

Ligament balance is an important and subjective task performed during total knee arthroplasty (TKA) procedure. For this reason, it is desirable to develop instruments to quantitatively assess the soft-tissue balance since excessive imbalance can accelerate prosthesis wear and lead to early surgical revision. The instrumented distractor proposed in this study can assist surgeons on performing ligament balance by measuring the distraction gap and applied load. Also the device allows the determination of the ligament stiffness which can contribute a better understanding of the intrinsic mechanical behavior of the knee joint. Instrumentation of the device involved the use of hall-sensors for measuring the distractor displacement and strain gauges to transduce the force. The sensors were calibrated and tested to demonstrate their suitability for surgical use. Results show the distraction gap can be measured reliably with 0.1. mm accuracy and the distractive loads could be assessed with an accuracy in the range of 4. N. These characteristics are consistent with those have been proposed, in this work, for a device that could assist on performing ligament balance while permitting surgeons evaluation based on his experience. Preliminary results from in vitro tests were in accordance with expected stiffness values for medial collateral ligament (MCL) and lateral collateral ligament (LCL). © 2013 IPEM.

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