A MOVING CONTACT OF ARTICULATION ENHANCES THE BIOSYNTHETIC AND FUNCTIONAL RESPONSES OF ARTICULAR CARTILAGE

Biomechanical influences play a fundamental role in the structural, functional, and biosynthetic properties of articular cartilage. During physiologic joint loading, the contact area between two surfaces migrates due to the primary and secondary motions of the joint. It has been demonstrated that a migratory contact area plays a critical role in reducing the coefficient of friction at the cartilage surface. However, a detailed analysis of the influences that a migratory contact area plays on the structural, functional, and biosynthetic properties remain to be explored. In this study, bovine cartilage explants were placed in a biotribometer. Explants were subjected to compression and shear forces of migratory contact area, namely moving contact (MC) articulation, or stationary contact area, namely stationary contact (SC) articulation. Free swelling explants were used as control. In a separate study, bovine cartilage-bone grafts were used for frictional testing. On histologic analysis, the SC group had evidence of surface fibrillations, which was not evident in the MC group. Compared to the SC group, the MC group cartilage explants had increased chondrocyte viability, increased lubricin synthesis, and comparable proteoglycan synthesis and release. MC articulation had reduced coefficient of friction as compared to SC articulation. MC articulation led to reduced surface roughness as compared to SC articulation. In conclusion, a migratory contact area can play an important role in maintaining the structural, function, and biosynthetic properties of articular cartilage. This study provides further evidence of the importance of migratory contact area and in vitro assessment of natural joint movement, which can be further evaluated in the context of cartilage homeostasis and disease.

Implications of trauma and subsequent articulation on the release of Proteoglycan-4 and tissue response in adult human ankle cartilage

The purpose of this study was to investigate the effects of trauma and subsequent articulation on adult human ankle cartilage subjected to an injurious impact. Trauma was initiated through impaction on talar cartilage explants. Articulation and loading were applied in a joint bioreactor over 5 consecutive days. The early (24 h) effects of impaction included a reduced chondrocytes viability (51% vs. 81% for non-impacted; p = 0.03), increased levels of apoptosis (43% vs. 27%; p = 0.03), and an increase in the histopathology score (4.4 vs. 1.7; p = 0.02) as compared to non-impacted cartilage explants. One of the key findings was that damage also stimulated the PRG4 release (2.2 vs. 1.5 μg/ml). Subsequent articulation for 5 days did not lead to further changes in tissue histopathology and cell viability, neither for injured nor non-injured samples. However, articulation led to an increased apoptosis in the injured samples (p = 0.03 for the interaction term). Articulation also caused a significant increase of PG/GAG release into the culture medium (p = 0.04) for both injured and non-injured samples; however, the synthesis of PG was not affected by articulation (p = 0.45) though the PG synthesis was higher in injured samples (p < 0.01). With regard to the PRG4 release, impacted samples continued to show higher amounts (p = 0.01), adding articulation led to a reduction (p = 0.02). The current study demonstrated that adult human talar cartilage increases both the PRG4 release and biosynthetic activity as an immediate cellular response to injury. Articulation played a less contributing role to biosynthesis and remodeling, behaving mostly neutral, in that no further damage emerged. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:667-676, 2017.

Surface topography of viable articular cartilage measured with scanning white light interferometry

OBJECTIVE

By means of scanning white light interferometry, develop a noncontact, nondestructive technique capable of measuring surface topography of viable cartilage.

METHODS

Using full thickness cylindrical cartilage explants obtained from bovine calf knees, experiments were performed to produce a surface preparation protocol that yields highly repeatable topographical measurements while maintaining cartilage viability. To further validate the technique, a series of human talar cartilage samples, displaying varying degrees of cartilage degeneration, was then subjected to interferometric measurements and compared to their histology.

RESULTS

A key aspect of the technique of surface topographic measurement by interferometry was the development of an optimal surface preparation process. The technique was successfully validated against standard 2-D profilometry. The intrinsic variability of the technique is less than 2%, which is much less than the average point-to-point variability of 17% observed across a cartilage specimen. The technique was hence sufficiently sensitive to readily detect differences in roughness between surfaces of healthy cartilage in different locations on the bovine knee. Thus, the average roughness of the medial explants exceeded that of the lateral explants by 0.35 microm Ra (P=0.003) and the roughness of the trochlear explants exceeded that of the condylar explants by 0.55 microm Ra (P<0.0001). Also, applying this technique to diseased human talar cartilage samples, a statistically significant increase in the average surface roughness value per unit increase in histological degeneration score was observed (> or =0.2 microm Ra, P< or =0.041), making surface roughness obtained via interferometry a useful parameter for evaluating cartilage health nondestructively.

CONCLUSIONS

The aim of developing a protocol based on white light interferometry to measure the surface topography of viable articular cartilage was achieved. This interferometric technique opens the door to monitoring the surface topography of live cartilage, as is desirable for ex vivo tests on cartilage explants.