Abstract
This study investigates the influence of osteoarthritis (OA) disease severity on the bio-composition of the osteochondral junction at the human tibial plateau using Raman microspectroscopy. We specifically aim to analyze the spatial composition of mineralized osteochondral tissues, i.e., calcified cartilage (CC) and subchondral bone plate (SBP) from unfixed, hydrated specimens. We hypothesize that the mineralization of CC and SBP decreases in advanced OA. Twenty-eight cylindrical osteochondral samples (d = 4 mm) from tibial plateaus of seven cadaveric donors 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 tissues. 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 with SBP. Both tissues exhibited similar compositional changes as a function of histopathological OA severity. In early OA, the mineralization tends to increase, and the mineral contains fewer carbonate substitutions. Compared with early OA, mineral crystals are rich in carbonate while the overall mineralization decreases in advanced OA. This Raman spectroscopic study advances the methodology for investigating the complex osteochondral junction from native tissue. The developed methodology can be used to elucidate detailed tissue-specific changes in the chemical composition with advancing OA. Statement of SignificanceIn this study, Raman microspectroscopy was utilized to investigate the influence of osteoarthritic degeneration on the tissue-specific biochemical composition of the human osteochondral junction. Multivariate cluster analyses allowed us to characterize subtle compositional changes in the calcified cartilage and subchondral bone plate as well as in the tidemark region. The compositional differences found between the calcified cartilage and subchondral bone plate in both organic and mineral phases will serve as critical benchmark parameters when designing biomaterials for osteochondral repair. We found tissue-specific changes in the mineralization and carbonate substitution as a function of histopathological OA severity. Our developed methodology can be used to investigate the metabolic changes in the osteochondral junction associated with osteoarthritis.
Highlights
Osteoarthritis (OA) is the most common joint disease, causes pain and leads to disabilities [1]
Without any a priori information, the unsupervised identification of different tissues based on their composition allowed us to study chemical composition across this biomechanically crucial junction, and detect tissue-specific chemical changes at different histopathological OA stages
We found that the calcified cartilage (CC) is always more mineralized than the subchondral bone plate (SBP), and the mineralization in both tissue types tends to increase in early OA but decreases in advanced OA stages
Summary
Osteoarthritis (OA) is the most common joint disease, causes pain and leads to disabilities [1]. In OA, the thickening of the subchondral plate, i.e., the calcified cartilage (CC) and cortical subchondral bone plate (SBP), is well documented [3,4,7,8]; this process includes reduced bone turnover and thinning of trabeculae [7] These typically occur in the later stages of OA [7]. The cement line advances toward the CC by the chondroclastic resorption process [12] All these processes, changing the subchondral plate thickness with associated bone remodeling, involve biochemical alterations of mineralized tissues [6,13,14]. Investigating the changes in the chemical composition of the CC and SBP as a function of OA severity will help elucidate the metabolic changes associated with the disease development
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