Raman Micro-Spectroscopic Analysis of the Tissue-Specific Composition of the Human Osteochondral Junction in Osteoarthritis

Abstract

This study investigates the influence of osteoarthritis (OA) disease severity on the bio-compositional properties of the osteochondral junction at human tibial plateau using Raman micro-spectroscopy. We specifically aimed to analyze the spatial composition of mineralized osteochondral tissues, i.e. calcified cartilage (CC) and subchondral bone plate (SBP). We hypothesize that the mineralization of CC and SBP decreases in OA. Twenty-eight cylindrical osteochondral samples (d=4mm) from tibial plateaus of cadaveric donors (N=7) were harvested and sorted into three groups following histopathological grading: healthy (n=5), early OA (n=8), and advanced OA (n=15). Raman spectra were subjected to multivariate cluster analyses to identify different tissue types. Finally, the tissue-specific composition was analyzed, and the impact of OA was statistically evaluated with linear mixed models. Cluster analyses of Raman spectra successfully distinguished CC and SBP as well as a tidemark region and uncalcified cartilage. CC was found to be more mineralized and the mineral was more crystalline compared to SBP. Both tissues exhibited similar compositional changes with OA progression. In early OA, the degree of mineralization increases, and the mineral contains fewer carbonate substitutions. Compared to early OA, mineral crystals are rich in carbonate while the overall mineralization decreases in advanced stages. This study provides insight into both mineral and organic phases of the osteochondral junction with OA progression in human tissue. The results show that the mineralization is altered already from the early OA in this biomechanically crucial junction, which advances our understanding of the initiation of OA.