Effect of synovial fluid-derived mesenchymal stem cells on repa-iring full-thickness cartilage damage in the knee

Cartilage lesions are the precursor lesion of os- teoarthritis, which is the most common cause of morbidity. Ensuring the healing of cartilage lesions to prevent the progression to osteoarthritis is important. In our study, we aimed to evaluate the regenerative effects of exosomes and mesenchymal stem cells(MSC) in the treatment of full-thickness cartilage injuries and compare them with the standard microfracture treatment. 11 New Zealand male rabbits were used. Both knees of the rabbits were subjected to full-thickness cartilage injuries after which, the procedure continued with intra-articular injections at day 0, week 4 and week 8. Group 1 received exosomes subtracted from synovial fluid-derived MSC, Group 2 received stem cells derived from synovial fluid, and Group 3 received microfracture treatment. Group 4 served as the positive control group, Group 5 as the negative control group, and Group 6 as the Sham control group. At the end of the 3rd month, rabbits were sacrificed. Healing of cartilage lesions was evaluated using the International Cartilage Repair So- ciety(ICRS) scoring system, H&E staining, and immunofluorescence staining. It was observed that the healing in the group treated with MSC and exosomes was of hya- line cartilage quality, with significantly higher ICRS scores compared to the injury and microfracture groups. Although the ICRS scores of the exosome group were slightly higher than those of the stem cell group, no statistically significant difference was de- tected. We believe that both methods provide effective treatment modalities that yield a healing tissue with low fibrous content and that resembles native cartilage structure.