Osteoarthritis (OA) is a leading cause of disability. New clinical strategies to improve evaluation, repair, and regeneration of damaged articular cartilage are needed to prevent or delay the onset of disabling pain and OA. The goal of this proposal is to perform the integrated multi-disciplinary large animal studies needed to advance clinical treatment and assessment of articular cartilage injury and degeneration in the United States. Microfracture, a simple and minimally invasive technique to access repair cells from the subchondral bone, is the most widely used cartilage repair procedure in this country. Microfracture is, however, inconsistent and generates a fibrous to fibrocartilaginous repair tissue of poor durability. Despite numerous studies that have shown that the consistency and quality of BMC based cartilage repair can be improved by processing the bone marrow to select and implant pluripotential cell fractions as well as some international human case reports, this treatment strategy has not been translated into clinical study in the US in part due to the lack of definitive one year large animal studies. This proposal tests the central hypothesis that increasing the concentration of bone marrow derived pluripotential cells delivered to the cartilage wound will improve the structural and biomechanical properties of the resulting repair tissue when compared to microfracture in a preclinical large animal model. Two different strategies to select and concentrate pluripotential bone marrow cells for in vivo cartilage repair will be used. The first will employ a single-step centrifugation procedure to generate a minimally processed bone marrow aspirate concentrate (BMAC). The second method will use the technique of increasing the number of bone marrow derived pluripotential cells through ficoll density gradient centrifugation and culture expansion of what has been classically described as mesenchymal stem cells (MSC). Both strategies will be studied for one year in an equine cartilage injury model. The resulting repair cartilage will be assessed with arthroscopy, as well as novel nondestructive imaging technologies such as arthroscopic optical coherence tomography (OCT) and high resolution quantitative MRI at 3T and 7T. The biomechanical quality of the repair tissues will be assessed by indentation testing and confined compression, while the integrity of the interface between repair and host cartilage will be assessed by tensile testing. Novel imaging, biomechanics and biomarker assessments will be compared to histology, immunohistochemistry and biochemical analyses. The results from this study will define whether the addition of concentrated BMC improves cartilage repair, and will also provide information on the identification and validation of biochemical and imaging biomarkers of cartilage injury, repair and early degeneration in a large animal model. These activities will be critical to the development and assessment of new disease modifying treatments for osteoarthritis. The potential impact of this proposal on generating long-term improvements to public health and eventual reduction in health care related costs from joint pain and osteoarthritis are major.