Technical Brief

A New Approach to Determine Ligament Strain Using Polydimethylsiloxane Strain Gauges: Exemplary Measurements of the Anterolateral Ligament

[+] Author and Article Information
Martin Zens

Design of Microsystems,
Department of Microsystems Engineering (IMTEK),
Albert-Ludwigs-University Freiburg,
Freiburg D-79110, Germany
e-mail: martin.zens@imtek.uni-freiburg.de

Johannes Ruhhammer, Frank Goldschmidtboeing, Peter Woias

Design of Microsystems,
Department of Microsystems Engineering (IMTEK),
Albert-Ludwigs-University Freiburg,
Freiburg D-79110, Germany

Matthias J. Feucht, Herrmann O. Mayr, Philipp Niemeyer

Department of Orthopaedics and Trauma Surgery,
University Medical Center,
Albert-Ludwigs-University Freiburg,
Freiburg D-79095, Germany

1Corresponding author.

Manuscript received July 4, 2014; final manuscript received October 14, 2014; accepted manuscript posted October 17, 2014; published online October 30, 2014. Assoc. Editor: Guy M. Genin.

J Biomech Eng 136(12), 124504 (Oct 30, 2014) (5 pages) Paper No: BIO-14-1315; doi: 10.1115/1.4028837 History: Received July 04, 2014; Revised October 14, 2014; Accepted October 17, 2014

A thorough understanding of ligament strains and behavior is necessary to create biomechanical models, comprehend trauma mechanisms, and surgically reconstruct those ligaments in a manner that restores a physiological performance. Measurement techniques and sensors are needed to conduct this data with high accuracy in an in vitro environment. In this work, we present a novel sensor device that is capable of continuously recording ligament strains with high resolution. The sensor principle of this biocompatible strain gauge may be used for in vitro measurements and can easily be applied to any ligament in the human body. The recently rediscovered anterolateral ligament (ALL) of the knee joint was chosen to display the capability of this novel sensor system. Three cadaver knees were tested to successfully demonstrate the concept of the sensor device and display first results regarding the elongation of the ALL during flexion/extension of the knee.

Copyright © 2014 by ASME
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Fig. 1

All polymeric strain gauge sensor device based on PDMS materials. Conductivity of the material is achieved by adding 10.6 wt.% carbon black particles (black), and a high permittivity is achieved through mixing the base polymer with 38.75 wt.% barium titanate (BaTiO3) (white) for encapsulation.

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Fig. 2

cad image of a measurement stage developed for highly accurate passive movement of a fixed knee joint using stepper motors. An x–y-rotational stage in combination with a C-shaped arc allows the simulation of knee joint movement in any physiological direction with precise reproducibility.

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Fig. 3

(a) Exposure of the ALL. The ligament can clearly be distinguished from the iliotibial tract and the capsula of the knee joint as described by Claes et al. [21]. (b) Sensor strip mounted on the ALL using Loctite 4860®.

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Fig. 4

(a) Cyclic loading of the sensor device in a linear stage. The sensor was stretched 1000 times at 2 mm/s. (b) Measurement curves of a sensor strip at 30% elongation and different speeds. (c) Measurement curves for subsequently increasing strains without history dependency at 0.2 mm/s.

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Fig. 5

Calibration curves and polynomial fit of a capacitive strain gauge used for the characterization of the ALL. The curves were recorded on a linear stage in 10 consecutive cycles showing no hysteresis and a negligible drift.

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Fig. 6

Averaged results from three cadaver knees (knee 1: 86 ♀, knee 2: 73 ♀, knee 3: 87 ♀) that were measured through the technique described in this work




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