## 4 Discussion  
A single injection of PRS in the knee suffering from OA appeared to significantly improve the physical and socio-emotional well-being of these patients up to twelve months post-injection. Shortly after injection, a steep decrease of pain and stiffness in the injected knee as well as improvement of physical function was seen in the majority of the patients. After three months post-injection, however, some recurrence of discomfort could be observed. This finding could be due to an increase in activities after six weeks, as the reduction of pain and previous limitations enabled recuperation of activities that up to then had to be minimalized. This suggests the timing and effect of (possible) plural injections should be analysed in the future. Figure 8: Lysholm Instability scores of the osteoarthritis knee treated with PRS. A higher Lysholm score means less instability. Results are expressed as mean \(\pm\) standard deviation. Only significant results are marked. PRS = platelet rich stroma; ns = not significant; ** = \(p<0.01\); *** = \(p<0.001\). In a healthy joint, articular chondrocytes provide a balance between extracellular matrix (ECM) component synthesis and degradation by secretion of growth factors and cytokines [24]. In OA, the balance shifts towards ECM degradation through excessive production of pro-inflammatory cytokines and ECM degrading enzymes [25]. The imbalance in ECM remodelling results in cellular and oxidative stress, cartilage degradation and cell apoptosis [26]. Stressed cells produce more pro-inflammatory cytokines such as interleukin-1\(\beta\) (IL-1\(\beta\)) and tumour necrosis factor-alpha (TNF-alpha) and endogenous molecules such as damage-associated molecular patterns (DAMPs) [27]. Binding of these cytokines and molecules to pattern-recognition receptors on cell types like chondrocytes activates the nuclear factor k\(\beta\) (NF\(\kappa\beta\)) pathway [28]. The NF\(\kappa\beta\) pathway is involved in development of inflammation and pain and regulates tissue remodelling in joints by promoting secretion of matrix metalloproteinase (MMP-1, 3, 13) and a disintegration and metalloproteinase with thrombospondin motifs 4 (ADAMTS4) [26]. Growth factors in PRP, e.g., hepatocyte growth factor, platelet-derived growth factor, IGF and TGF-\(\beta\)1, inhibit the NF\(\kappa\beta\) signalling pathway and are therefore likely able to reduce the catabolic and anti-anabolic effects [26]. Downregulation of the NF\(\kappa\beta\) signalling results in a reduced production of ADAMTS4 and promotes production of type 2 collagen and proteoglycans in vitro [29; 30]. The decrease in inflammation might result in decreased pain and, therefore, be responsible for restoring the balance in ECM remodelling. Multiple preclinical and clinical studies have showed variable results from either PRP or SVF as a treatment for OA. Only recently, the combination of PRP and SVF is gaining interest [31; 32; 33]. The anti-inflammatory effects of PRP on osteoarthritis joints due to secretion of numerous growth factors can be strengthened by addition of non-manipulated ASCs being present in the form of SVF. In tSVF, the ASCs are still attached to the vascular fibrous matrix [19]. ASCs are able to produce growth factors such as TGF-\(\beta\)1 and IGF as well. It is, however, the combined injection of PRP and ASCs attached to their matrix that might be a prerequisite to allow for a synergistic effect. Growth factors secreted by platelets are capable of binding to the matrix, enabling slow release during the healing process [34]. [PERSON] et al. presented a PRP induced dose-dependent increase of the proliferation rate of ASCs and a dose-dependent increase of several paracrine genes, such as TGF-\(\beta\)1, IGF and fibroblasts growth factor 1 (FGF1) [35]. In contrast, gene expression of IL-1B showed a dose-dependent decrease [35]. Increased quantities of the anti-inflammatory growth factor TFG-\(\beta\)1 and decreased amounts of the pro-inflammatory IL-1\(\beta\) might reduce joint inflammation.