Functional Assessment of Human Articular Cartilage Using Second Harmonic Generation (SHG) Imaging: A Feasibility...

Many arthroscopic tools developed for knee joint assessment are contact-based, which is challenging for in vivo application in narrow joint spaces. Second harmonic generation (SHG) laser imaging is a non-invasive and non-contact method, thus presenting an attractive alternative. However, the association between SHG-based measures and cartilage quality has not been established systematically. Here, we investigated the feasibility of using image-based measures derived from SHG microscopy for objective evaluation of cartilage quality as assessed by mechanical testing. Human tibial plateaus harvested from nine patients were used. Cartilage mechanical properties were determined using indentation stiffness (E_inst) and streaming potential-based quantitative parameters (QP). The correspondence of the cartilage electromechanical properties (E_inst and QP) and the image-based measures derived from SHG imaging, tissue thickness and cell viability were evaluated using correlation and logistic regression analyses. The SHG-related parameters included the newly developed volumetric fraction of organised collagenous network (Φ_col) and the coefficient of variation of the SHG intensity (CV_SHG). We found that Φ_col correlated strongly with E_inst and QP (ρ = 0.97 and - 0.89, respectively). CV_SHG also correlated, albeit weakly, with QP and E_inst, (|ρ| = 0.52-0.58). E_inst and Φ_col were the most sensitive predictors of cartilage quality whereas CV_SHG only showed moderate sensitivity. Cell viability and tissue thickness, often used as measures of cartilage health, predicted the cartilage quality poorly. We present a simple, objective, yet effective image-based approach for assessment of cartilage quality. Φ_col correlated strongly with electromechanical properties of cartilage and could fuel the continuous development of SHG-based arthroscopy.