Optical Imaging of Articular Cartilage: Current Status and Clinical Applications.

Osteoarthritis (OA) is a condition characterized by cartilage degeneration leading to pain, swelling and disability, while representing a substantial financial burden. Radiographs are most commonly used to evaluate the presence and progression of OA, which can reveal various structural changes within joints. Moreover, standard radiographs, magnetic resonance imaging, and arthroscopy enable visualization of cartilage surfaces and presence of any macroscopic changes. Optical imaging technologies represent nondestructive and noninvasive imaging modalities that allow for evaluation of microscopic changes in articular cartilage, such as fibrillations, clefts, collagen disorganization, and matrix degeneration. OCT and PSOCT can accurately assess cartilage surface disruption and collagen disorganization, with studies performed during arthroscopy further showing its potential to identify early cartilage degeneration. RS can identify disruptions in organization and composition of cartilage based on banding changes in the collagen microstructure. Additional imaging techniques, including photoacoustic imaging, Brillouin spectroscopy, and polarimetry-based techniques can detect articular cartilage degeneration by identifying proteoglycan loss and collagen fibril disorganization. Current clinical applications are limited by small number of human studies and techniques compatible for use during surgery as well as standardized grading systems and imaging processing techniques.