The effect of platelet rich plasma on the treatment of articular cartilage defects of the knee. An experimental study

To evaluate the effect of injectable Platelet Rich Plasma (PRP) on the treatment of chondral injuries. The hypothesis of the study was that PRP can enhance in vivo chondrogenic differentiation of bone marrow stem cells (BMSCs) and cartilage formation after microfractures. Methods: We performed a focal full-thickness lesion of articular cartilage on the weight-bearing area of the medial femoral condyle of the right knee in 15 sheep. Chondral lesions were treated after 12 months. Animals were divided into 3 groups: Group 1: Microfractures; Group 2: Microfractures + PRP hydrogel; Group 3: Microfractures + PRP injection. Animals were sacrificed at 24 weeks. Contralateral knees were used as controls. Gross, biomechanical, and histological analysis were performed on each sample. Biomechanical analysis was performed with an electromechanical indenter. Histological appearance was scored according to a modified Mankin’s score. Mean cartilage stiffness and histological score were recorded. Comparison between groups was performed with Kruskal-Wallis test, and Tukey’s test for pairwise comparisons. Results: In group 1, repair tissue partially covered the defect; in groups 2 and 3 the defect was completely covered, but in group 3, repair tissue was less regular and consistent. Mean cartilage stiffness of group 2 approximated that of controls. Groups 1 and 3 showed a significantly lower stiffness, without a significant difference between them. At histology, we observed that in group 1, repair tissue consisted of a thin layer of fibrous tissue with some areas chondrocytes-like cells embedded in a fibrous and poorly organized extracellular matrix (ECM). Those areas showed an intense safranin-O staining. In group 2, the defect was almost completely covered; repair tissue showed a rich cellularity, an intense safranin-O staining of ECM, and a good integration with the surrounding healthy cartilage. Numerous clusters of chondrocyte- like cells were found in the transitional and radial zones and some clefts deepened to the radial zone. Tidemark was observed in some areas but it was not completely restored. In group 3, a thin layer of repair tissue covered almost completely the defect, showing an intense safranin-O staining, a great amount of cells well-organized in columns in the transitional zone and rare clusters in the deep zone. Tidemark was almost completely absent. Histological scoring was significantly lower in all groups in comparison with normal cartilage. Comparison between groups showed that score of group 2 was greater than those of the other groups, although the only significant difference was observed between group 1 and 2. Conclusions: PRP showed a positive effect on cartilage repair and restoration after microfractures. The procedure was more effective when PRP was used as a hydrogel scaffold in comparison with liquid intrarticular injection