Optical spectral reflectance of human articular cartilage – relationships with tissue structure, composition and mechanical properties

Jussi Kinnunen,Simo Saarakkala,Markku Hauta-Kasari,Jukka S Jurvelin,Pasi Vahimaa

doi:10.1364/boe.2.001394

Abstract

The information from spectral reflectance of articular cartilage has been related to the integrity of the tissue. This study explores more in detail the interrelations between the cartilage composition, structure and mechanical properties, and optical spectral reflectance. Using human osteochondral samples the reflectance spectral images of articular cartilage were captured and analyzed by using CIELAB color space as well as principal component analysis. With both analysis methods statistically significant correlations were observed between the reflectance and histological integrity, as assessed by Mankin scoring, tissue proteoglycan content and dynamic modulus. In thick human cartilage, the reflectance was found to be independent of the cartilage thickness, suggesting negligible influence of the underlying subchondral bone. Based on the present results diagnostically relevant information on cartilage quality can be extracted using optical spectral reflectance measurements. These measurements could be feasible during arthroscopic surgery when more in-depth information of the properties of articular cartilage is needed.

Highlights

Degeneration of the articular cartilage, typical to osteoarthritis (OA) or rheumatoid arthritis (RA), is known to produce visual changes, i.e., the loss of glisten, change in tissue color and fibrillation of the cartilage surface
The mean spectra of the samples in three groups with normal, early OA and advanced OA cartilage (Mankin score 0-1, 2-3 and >3 respectively) had similar shape, but the total reflectance was decreased in advanced OA group compared to normal or early OA groups (Fig. 2)
The optical parameters were found to be significantly related to tissue integrity, as assessed by histological, biochemical and biomechanical analyses

Summary

Introduction

Degeneration of the articular cartilage, typical to osteoarthritis (OA) or rheumatoid arthritis (RA), is known to produce visual changes, i.e., the loss of glisten, change in tissue color and fibrillation of the cartilage surface. The browning of cartilage is believed to be related to the advanced glycation end products (AGE) [2], and it is age-related. Degenerative color changes of the articular cartilage are visually assessed. This kind of assessment is subjective and the outcome depends on the evaluator. The color can be assessed by using a conventional RGB camera Both visual observation and RGB camera inspection are limited by the number of detector spectral sensitivities.

Methods

Results

Conclusion