gms | German Medical Science

German Congress of Orthopedic and Trauma Surgery (DKOU 2017)

24.10. - 27.10.2017, Berlin

Fiber Bragg grating based indentation of healthy and degenerated articular cartilage – a new method and feasibility study

Meeting Abstract

  • presenting/speaker Peter Foehr - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany
  • Gabriele Marchi - Munich University of Applied Sciences, Photonics Laboratory, Munich, Germany
  • Valentin Baier - Munich University of Applied Sciences, Photonics Laboratory, Munich, Germany
  • Carmen Marthen - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany
  • Jutta Tübel - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany
  • Raimund W. Kinne - Waldkrankenhaus "Rudolf Elle" GmbH, AG Experimentelle Rheumatologie, Lehrstuhl für Orthopädie der FSU Jena, Eisenberg, Germany
  • Johannes Roths - Munich University of Applied Sciences, Photonics Laboratory, Munich, Germany
  • Rainer Burgkart - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2017). Berlin, 24.-27.10.2017. Düsseldorf: German Medical Science GMS Publishing House; 2017. DocGR15-734

doi: 10.3205/17dkou503, urn:nbn:de:0183-17dkou5033

Published: October 23, 2017

© 2017 Foehr et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.


Outline

Text

Fragestellung: Biomechanical characterization of healthy and degenerated articular cartilage is one of the basic experimental methods besides histomorphological and biochemical techniques. The aim of using either one of the three methodologies is to gain a deeper understanding of both the functional behavior and loss of function during degeneration of articular cartilage. Within this work we present a novel method to mechanically characterize biological tissue using a fiber Bragg grating based fiber-optical indenter. This very thin fiber with the added Bragg grating is capable to measure forces based on changing its optical properties, named the Bragg wavelength. Prior to introducing this measurement technology into a possible clinical application, we conducted a controlled laboratory study for verification purposes.

Methodik: Cylindrical osteochondral samples (bovine, 2 groups, n=10/group, diameter=6 mm) were harvested from the patellar grove using a clinical punch and stored in phosphate-buffered saline (PBS) at -20°C. One day before testing, the samples of the first group were thawed at room temperature and immersed for 24 h in 2.5% trypsin and cell culture medium to artificially damage the cartilage. The untreated healthy cartilage of the second group was thawed at the day of testing. The identical testing procedure was applied to all samples using a stress-relaxation protocol with an indenter diameter of 0.125 mm. Every indentation test used 15 steps with an indentation depth of 0.02 mm (ramp speed=0.27 mm/s) and a relaxation time of 120 s. To identify viscoelastic parameters from of the data sets, all steps were curve-fitted with a Generalized Maxwell model (3 springs, 2 dashpots) and clustered in five diagrams of κe, κ1, κ2, τ1, τ2 with respect to the indentation depth. Statistical analysis was performed between the healthy and damaged samples using Student's t-Test and a p-value of <0.05.

Ergebnisse und Schlussfolgerung: Biomechanical testing and parameter identification were successfully conducted for all specimen. By observing the raw data significantly lower reaction forces for the degenerated samples were observed for every indentation step >0.04 mm. After fitting the data to the Generalized Maxwell model further analysis was performed on the indentation depths of 0.1 and 0.3 mm for both groups. Statistical differences for the viscoelastic parameters were observed, e.g. for the spring constant κ1: It appears to us that this parameter is the best to compare the functional status of healthy and degenerated cartilage. It should also be noted, that the parameter fitting always reached a coefficient of correlation (R2) above 0.95.

We conclude that the new methodology is a highly reliable way to measure differences between healthy and degenerated cartilage. Based on the success of this feasibility study we will increase the study group to at least four grades of degeneration for articular cartilage.

This research was funded by the Deutsche Forschungsgemeinschaft (DFG) under grant no. RO4145/4-1.