The Concept of Early Osteoarthritis and Its Significance in Regenerative Medicine.

Osteoarthritis (OA) has been investigated as one of important target diseases for regenerative medicine. The concept of early OA has recently emerged under the assumption that if OA is detected and intervened early, progression of OA might be arrested or delayed before irreversible destruction of the joint occurs. This concept also matters in regenerative medicine for OA because new regenerative technologies can work better when joint damage is minimal. Diagnostic criteria for early OA have been suggested in this background to find a group of patients who have a higher possibility of developing full-blown OA. However, as currently suggested criteria of early OA are mostly expert opinions lacking higher level of evidence, clinical validations are necessary to prove their value in patient care. While new treatment methods that can suppress or prevent symptoms at an early stage of OA before progressive and irreversible changes occur are being developed, detailed definition and classification of early OA agreed upon by major stakeholders in OA field and validated by prospective studies are necessary to prove the efficacy of these methods. As clinical outcome of regenerative treatment is related to patient characteristics and the status of the whole joint, it is of critical significance to predict which patient will progress and who will be responsive to regenerative treatment. While diagnostic criteria for early OA should be highly sensitive and applicable without employing biomarkers or magnetic resonance imaging, a subclassification and comprehensive endotyping /phenotyping using these techniques might be needed to detect the population who would be responsive to regenerative medicine.