Mechanical stability and biological consequences of cracks in articular cartilage

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Osteoarthritis (OA), the most common form of arthritis, is a joint disease characterized by the degradation of articular cartilage. This disease is complex and dynamic, evolving over years or even decades to ultimately cause joint pain and dysfunction. OA affects over 27 million adults in the US, making it a leading cause of disability. Despite being the most common cause of disability in western nations, OA has no cure and few options for diagnosis or treatment. In the search for a treatment, the most critical knowledge gap involves understanding the pathogenesis of OA prior to converging on the late-stage disease state, which is characterized by pain, deformity, and dysfunction. Indeed, the current standard of diagnosis by late-stage radiographic changes and eventual treatment via arthroplasty has proven to be a “solution” that is far from ideal. Cracks in cartilage (i.e. breaks in the matrix) have strong potential to be one such early marker of pre-OA and increased OA risk. Cracks are often observed after joint trauma as well as in late-stage disease. Indeed, cracks are often considered when grading and classifying cartilage damage and OA progression. Recent basic-science studies have defined crack prevalence and morphology, mechanical thresholds for crack initiation, and bio-physiological changes after cracking. However, to be developed as a marker for pre-OA or to guide clinical decision-making, key questions about cracks must be answered. These questions range from basic-science research to clinical application. This proposal outlines two basic-science questions that enhance the fundamental understanding of the mechanical and biological consequences of cracks in cartilage and, in so doing, begin to test cracks as an important orthopedic biomarker. Specifically, it is unknown if existing cracks destabilize cartilage or predispose it to further biological degradation. Broadly, the applicants hypothesize that crack morphology can be used to distinguish between cracks that are benign verses cracks that indicate irrevocably damage cartilage. In this study, the applicants more specifically hypothesize that, when loaded above a threshold, cracks in cartilage will grow and induce peracute cellular deterioration. To address these knowledge gaps, this proposal has two specific aims: (1) Investigate the mechanical stability of cracks in cartilage and (2) Characterize the acute biological consequences of cracks in cartilage.