Quantifying Extracellular Matrix Changes in Osteoarthritic Human Cartilage and Subchondral Bone Using Raman Microspectroscopy

Objectives

Osteoarthritis (OA) of the knee causes pain, limits activity and impairs quality of life. Raman microspectroscopy can provide information about the chemical changes that occur in OA, to enhance our understanding of its pathology. The objective of this study is to detect OA severity in human cartilage and subchondral bone using Raman microspectroscopy and explore corresponding mechanical properties of the subchondral bone.
Methods

OA tibial plateaus were obtained from total knee replacement surgery with REC (18/LO/1129) and HRA approval. Medial tibial plateau, representing a major weight-bearing area, was graded according to the International Cartilage Repair Society (ICRS) scoring system. Nine samples (3 samples of each graded as moderate, severe and very severe) were selected for Raman and mechanical analyses.
Results

A decrease in Raman intensity of glycosaminoglycan (GAG) CH3 (1380cm-1), collagen amide I (1655cm-1) and CH2 deformation (1450cm-1) was observed in cartilage with increasing severity. The calcified cartilage showed a prominent mineral peak at 959cm-1 in the Raman spectra. Meanwhile, an increase of the Raman intensity of collagen amide I (1655 cm-1) and CH2 deformation (1450cm-1), full width half maximum (FWHM) of the mineral peak (960cm-1) and elastic modulus was observed in subchondral bone with increasing severity. Carbonate-to-phosphate ratio (960/1070cm-1) decreased with disease severity.
Conclusions

In conclusion, as OA severity increases, cartilage loses GAG and collagen matrix, while bone increases its collagen matrix, with reduction in mineral crystallinity that cause increase of the elastic modulus. Detection of matrix and mineral changes by Raman microspectroscopy would facilitate the identification of OA severity, and potentially progression, and pave the way towards developing treatment.