Objective:To compare the repair effects of three kinds of treatment methods included synovial mesenchymal stem cells(SMSCs),platelet rich plasma(PRP)and the combination of them with knee joint cavity injection on cartilage injury of rabbit.Methods:A total of 24 New Zealand rabbits were selected to establish a cartilage injury model of knee joint by using surgery in knee joint of them.The rabbits with cartilage injury model were divided into four groups using a random number table method,which included blank group,single SMSCs with joint cavity injection group(SMSCs group),PRP with joint cavity injection group(PRP group)and the combination of SMSCs and PRP with joint cavity injection group(SMSCs+PRP group),with 6 rabbits in each group.The synovium of four groups of rabbits were scraped off their joints to conduct in vitro culture of SMSCs,as well as the morphological observation and identification of SMSCs.The venous bloods of rabbits were extracted to prepare PRP by centrifugation.The contents of PRP,platelet and growth factor in blood were compared.The SMSCs and PRP were injected into the knee joint cavity of three groups of rabbits with model.After 2,4 and 6 weeks of injection treatment,the repair statuses of cartilages at defection area of different groups were evaluated according to cartilage repair scoring table of International Association for Cartilage Repair(ICRS).Results:The primary synovial cells of rabbit knee joint synovium were initially round in shape after isolation,but almost all of them were spindle shaped after passage.The positive detection rates of SMSCs surface antigen CD73,CD90 and CD105 of 4 group were respectively 100%,99.22%and 99.99%.The CD45 detection was 0.5%,which indicated that they possessed the property of stem cell.The platelet count of 4 groups showed that the platelet concentration in PRP was approximate 6 times of that in whole blood.The concentrations of platelet derived growth factor(PDGF),transforming growth factor-β(TGF-β)and vascular endothelial growth factor(VEGF)were respectively(569.15±57.48)ng/mL,(633.56±63.90)ng/mL and(1 243.55±106.04)ng/mL in PRP,which were approximately 5 times,6 times and 7 times of that in whole blood,respectively.After 2 weeks of injection treatment for joint cavity,there was no significant statistical difference in the scores of cartilage repair among 4 groups(P>0.05).At 4 and 6 weeks of injection treatment,the morphological and histological score of cartilage repair of the SMSCs+PRP group were significantly higher than those of the blank group,and the differences were significant(t4 week=6.35,9.15,t6 week=8.16,8.60,P<0.05),respectively.Conclusion:The repair effect of SMSCs combined with PRP on cartilage injury of rabbit is significantly better than that of single PRP and single SMSCs,respectively,and all of them are better than those without treatment.SMSCs combined with PRP can significantly improve the effect of self-repair of cartilage injury.