Monitoring Progressive, Biologically Mediated Tendon Degeneration Using Quantitative Polarized Light Imaging

Degenerative tendon tears are common, but mechanisms behind initiation and progression are not fully understood. There is a clear need to be able to track microstructural changes during progressive biological degradation to better understand degenerative tendon pathophysiology. The aim of this study was to evaluate the sensitivity of a snapshot Stokes polarimetry technique, quantitative polarized light imaging (QPLI), in monitoring the severity and progression of biologically mediated degeneration in tendon. Leveraging a collagenase mediated in vitro tendon digestion model, we assessed the effect of enzyme degradation on polarimetric outcomes from reflectance and transmission modes of QPLI, second harmonic generation (SHG) imaging, histology, and mechanical testing. Changes observed in reflectance mode QPLI (rQPLI) allowed for characterization of progression of degeneration at all digestion severities tested, whereas data acquired from transmission mode QPLI was only able to discern changes at the most severe digestion level. Outcomes from this study establish rQPLI as a powerful tool in the microstructural evaluation of musculoskeletal soft tissues, particularly in the context of monitoring progressive degradation. The findings from this study also highlight the potential multiscale nature of biological degeneration in tendon and emphasize the importance of better understanding these processes to inform regeneration and repair strategies.