Platelet-rich plasma (PRP) accelerates murine patellar tendon healing through enhancement of angiogenesis and collagen synthesis

Purpose Although platelet-rich plasma (PRP) therapy has become an increasingly popular treatment for sports-related injuries, the molecular mechanisms of PRP on tissue healing process remain poorly understood. The aim of the present study was to develop an experimental method quantifying the efficacy of PRP with murine patellar tendon injury model, leading to future elucidation of the mechanisms of PRP on healing processes. Methods Full-thickness defects were created in the central third of the murine patellar tendon. The prepared allogenic PRP gel was applied on the defect of the patellar tendon (PRP group), while the remaining mice served as the untreated control group. Mice were sacrificed at 2, 4, 6, 8, and 10 weeks after the operation, with histological sections obtained in each time point (n = 4 / time point / group). Semi-quantitative histological evaluation was performed in accordance with the Bonar score. The variables included in this scoring system were cell morphology, ground substance, collagen arrangement, and vascularity, with higher grades indicating worse tendon structures. In addition, the ratio of the collagen fibers to the entire tendon tissue (FT ratio) was measured using KS400 software as a quantitative histological evaluation. Results The total Bonar score in the PRP group was significantly lower than in control group. With regard to the variables in the Bonar score, the vascularity score was significantly higher in the PRP group at 2 and 4 weeks, while the collagen arrangement score was significantly lower in the PRP group at 8 weeks. Based on a quantitative evaluation, the recovery speed of the patellar tendon determined by FT ratio was significantly faster in the PRP group than in the control group at 6 and 8 weeks. Conclusions We have developed an experimental method for histological and quantitative evaluation of the effects of PRP on tissue healing using murine patellar tendon injury model. The results of this study suggest that the local application of PRP could enhance the tissue-healing process both directly through action on localized cells and indirectly through the recruitment of reparative cells through the blood flow. Further investigations will be needed to confirm the mechanisms of PRP in tissue-healing processes with the development of this experimental model.