Early Detection of Cartilage Degeneration: A Comparison of Histology, Fiber Bragg Grating-Based Micro-Indentation, and Atomic Force Microscopy-Based Nano-Indentation.

Bastian Hartmann,Johannes Roths,Gabriele Marchi,Zsuzsanna Farkas,Paolo Alberton,Attila Aszodi,Hauke Clausen-Schaumann

doi:10.3390/ijms21197384

Abstract

We have determined the sensitivity and detection limit of a new fiber Bragg grating (FBG)-based optoelectronic micro-indenter for biomechanical testing of cartilage and compared the results to indentation-type atomic force microscopy (IT-AFM) and histological staining. As test samples, we used bovine articular cartilage, which was enzymatically degraded ex vivo for five minutes using different concentrations of collagenase (5, 50, 100 and 500 µg/mL) to mimic moderate extracellular matrix deterioration seen in early-stage osteoarthritis (OA). Picrosirius Red staining and polarization microscopy demonstrated gradual, concentration-dependent disorganization of the collagen fibrillar network in the superficial zone of the explants. Osteoarthritis Research Society International (OARSI) grading of histopathological changes did not discriminate between undigested and enzymatically degraded explants. IT-AFM was the most sensitive method for detecting minute changes in cartilage biomechanics induced by the lowest collagenase concentration, however, it did not distinguish different levels of cartilage degeneration for collagenase concentrations higher than 5 µg/mL. The FBG micro-indenter provided a better and more precise assessment of the level of cartilage degeneration than the OARSI histological grading system but it was less sensitive at detecting mechanical changes than IT-AFM. The FBG-sensor allowed us to observe differences in cartilage biomechanics for collagenase concentrations of 100 and 500 µg/mL. Our results confirm that the FBG sensor is capable of detecting small changes in articular cartilage stiffness, which may be associated with initial cartilage degeneration caused by early OA.

Highlights

Osteoarthritis (OA) is one of the most frequent joint diseases worldwide
We report that nano-scaled indentation-type atomic force microscopy (IT-atomic force microscopy (AFM)) was superior to detect cartilage softening induced with the lowest collagenase concentration but failed to clearly discriminate between mechanical changes induced by higher collagenase concentrations
Magnetic resonance imaging (MRI) is a powerful, non-destructive tool to detect morphological and extracellular matrix (ECM) compositional differences between healthy and osteoarthritic knee articular cartilage, MRI is currently not recommended for the diagnosis of early OA in the clinical practice due to the lack of consensus criteria [29]

Summary

Introduction

Osteoarthritis (OA) is one of the most frequent joint diseases worldwide. At an early stage, cartilage degradation starts at the molecular level, primarily affecting the structural and mechanical properties of the articular cartilage surface [1,2]. Changes in molecular composition and integrity of the articular cartilage ECM can be detected, e.g., by histochemistry and immunohistochemistry, while tissue structural and mechanical properties can be assessed by atomic force microscopy (AFM) [3,4]. During arthroscopy, the surgeon is currently dependent on the localization of the degenerated tissue by optical examination and by palpating the cartilage surface by hand or by using a hook [5,6] This presupposes a great experience of the surgeon and shows high variations resulting from the subjective judgment of the examiner. This underscores the need for measurement devices that can support the medical evaluation of the cartilage condition [7]. The applied probes have diameters of about 1–3 mm and lengths of several centimeters, which makes endoscopic integration difficult

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Discussion

Conclusion