CLINICS 2011;66(10):1835-1838 Platelet-rich fibrin and cartilage granules facilitate cartilage repair Kuo T-F et al. Figure 3 - Group A specimen. Image shows focal thickening of the articular cartilage and the cortical bone (insert) with a deformed articular surface. Fissuring (double arrows) and osteophytes (arrow) are shown (H & E stain). with p,0.05 indicating a significant difference observed between the groups in the values obtained for the individual parameters. RESULTS The sums of the ICRS scores were significantly different between the groups (p = 0.02). Further comparisons showed a significant difference in the cell distribution (p = 0.01) and cartilage mineralization (p = 0.03) between the groups (Figure 2). In group A (Figure 3), disorganized cell distribution was noted in six specimens. All of the rabbits showed abnormal cartilage mineralization. The cartilage from four of the six rabbits showed surface irregularities and erosion. Two lesions were covered by dense fibrous tissue. In all of the animals, cells had clearly delineated nuclei indicating partial (2/6) or predominant viability (4/6). We observed subchondral granulation in three animals, detachment at the base in three animals, and marginal osteophytes in three animals. Specimens from one rabbit in group B were excluded because of a technical failure during tissue preparation. In group B (Figure 4), only one out of the five remaining specimens showed disorganized cell distribution. Three specimens exhibited normal cartilage mineralization. Four of the five specimens showed a smooth and continuous regenerated cartilage surface, and one specimen had major fissures. All five specimens showed hyaline cartilage repair with higher structural integrity of the matrix. The cells were predominantly viable in all five rabbits. Subchondral normal or remodeled tissue was noted in four specimens. No osteophyte formation was noted. By comparing the means (¡ standard deviation) and ratios of the MRI T2 values, we observed that the value for the defective cartilage in group A (11.8¡7.4 ms; ratio: 0.5¡0.1) was lower than that of the normal cartilage of the same rabbit (23.2¡1.7 ms; ratio: 0.9¡0.2) (p = 0.06). No differences were detected in the T2 values for the regenerated cartilage in group B (18.2¡4.5 ms; ratio: 0.6¡0.2) and normal cartilage of the same animal (p = 0.15). 1837 Figure 4 - Group B specimen. Image shows a continuous surface and erosion of the regenerated hyaline cartilage (insert) in the central zone of the original defect area (area within the orange line). A cystic space (arrow) that was filled with granulation tissue in the subchondral area (blue line) with sclerosing change is shown (H & E stain). DISCUSSION Fibrocartilage contains a high proportion of type I collagen and forms coarse fibers.9 Fibrocartilage occurs frequently in areas of failed cartilage regeneration,10 as observed in our control animals. Mature hyaline cartilage is recognized by the abundant extracellular matrix, which is usually homogeneous, and by the scarcity of rounded chondrocytes that occupy well-defined lacunae, which we observed in our experimental animals. PRF contains many kinds of growth factors and cyto- kines.7 The growth factors are known to promote cell proliferation, cell differentiation, cell motility, and matrix synthesis by binding to specific cell-surface receptors.11 PRF slowly polymerizes during centrifugation. Its connected junctions allow the establishment of a fine and flexible fibrin network that supports cytokine enmeshment, cellular migration, and stem cell trapping.6 The cytokines may comprise interleukins, which are needed for inflammatory responses and repair responses to promote normal immune function. Biodegradable artificial scaffolds that are seeded with chondrocytes significantly improve the healing of cartilage defects. The scaffolds improve the redifferentiation capacity of chondrocytes by providing them with appro- priate mechanical stability.12 We hypothesize that PRF that is mixed with cartilage granules provides favorable condi- tions for cell migration and cell growth. Alterations in the MRI T2 values in cartilage correlate with changes in the water content and the organization of collagen structures that are associated with hyaline articular cartilage degradation.13,14 In our control animals, the defective cartilage matrix became more fibrotic, which reduced the T2 value. The regenerated cartilage of treated animals had higher T2 values than did defective cartilage, indicating a decrease in proteoglycans and a progressive increase in collagen content. Our study indicates that the injured cartilage in rabbits healed within three months. The use of PRF and cartilage granule without bovine thrombin represents a one-step cartilage repair surgery with potentially favorable results.