Nonlinear optical microscopy of early stage (ICRS Grade-I) osteoarthritic human cartilage

In a synovial joint, the articular cartilage is directly affected during the progression of Osteoarthritis (OA). The characterization of early stage modification in extra-cellular matrix of cartilage is essential for detection as well as understanding the progression of disease. The objective of this study is to demonstrate the potential and capability of nonlinear optical microscopy for the morphological investigation of early stage osteoarthritic cartilage. ICRS Grade-I cartilage sections were obtained from the femoral condyle of the human knee. The surface of articular cartilage was imaged by second harmonic generation and two-photon excited fluorescence microscopy. Novel morphological features like microsplits and wrinkles were observed, which would otherwise not be visible in other clinical imaging modalities (e.g., CT, MRI, ultrasound and arthroscope. The presence of superficial layer with distinct collagen fibrils parallel to the articular surface in 4 specimens out of 14 specimens, indicates that different phases of OA within ICRS Grade-I can be detected by SHG microscopy. All together, the observed novel morphologies in early stage osteoarthritic cartilage indicates that SHG microscopy might be a significant tool for the assessment of cartilage disorder.