Age-dependent differences in response to partial-thickness cartilage defects in a rat model as a measure to evaluate the efficacy of interventions for cartilage repair

The objectives of this study are (1) to examine age-dependent longitudinal differences in histological responses after creation of partial-thickness articular cartilagedefects (PTCDs) in rats and to use this model (2) to objectively evaluate the effectiveness of interventions for cartilagerepair. Linear PTCDs were created at a depth of 100 μm in the weight-bearing region of the medial femoral condyle in rats of different ages (3 weeks, 6 weeks, 10 weeks and 14 weeks). One day, one week, two weeks, four weeks and twelve weeks after PTCD generation, spontaneous healing was evaluated histologically and immunohistochemically. Effects of interventions comprising mesenchymal stem cells (MSCs) or platelet-rich plasma(PRP) or both on 14-week-old PTCD rats were evaluated and compared with natural courses in rats of other ages. Younger rats exhibited better cartilagerepair. Cartilagein 3-week-old and 6-week-old rats exhibited nearly normal restoration after 4–12 weeks. Cartilagein 14-week-old rats deteriorated over time and early signs of cartilagedegeneration were observed. With injection of MCSs alone or MSCs + PRP, 14-week-old PTCD rats showed almost the same reparative cartilageas 6-week-old rats. With injection of PRP, 14-week-old PTCD rats showed almost the same reparative cartilageas 10-week-old rats. This model will be of great use to objectively compare the effects of interventions for small cartilagelesions and may help to advance the development of disease-modifying osteoarthritis drugs.