## 4 Discussion
Further research into the durability of PRP effects over time is needed to determine its role in long-term tendon and ligament management. Moreover, future studies should include longer follow-up periods (e.g., 2-5 years) to assess the durability of PRP treatment and its impact on preventing injury. The combined use of PRP with MSCs (either from bone marrow or adipose tissue), BMMNCs, or BMAC showed promising results in several studies [40; 41; 42; 43; 55], demonstrating enhanced tissue regeneration and improved long-term outcomes. However, no randomized clinical trials or experimental studies have directly compared the effects of PRP alone, stem cells alone, or their combination to confirm a potential synergistic effect. Controlled clinical trials evaluating PRP in combination with MSCs or other regenerative products are essential to validate their potential additional benefits and to develop optimized treatment protocols. Future research should also explore the use of other regenerative therapies, such as extracellular vesicles [61; 62; 63] or gene therapy [63], in combination with PRP to further enhance tissue repair and regeneration. To the authors' knowledge, this is the first study to critically evaluate PRP preparation procedures and quality-related parameters using the modified [PERSON] and Alsousou criteria, which assess 10 key characteristics [28]. While some aspects of this discussion have been addressed in previous sections, the most important findings relate to the semi-quantitative scoring system used to assess the quality of information for each characteristic and the overall methodological rigor of the studies. Specifically, 72.72% of the reviewed studies demonstrated a poor to moderate methodological description of PRP production and quality, potentially limiting the reliability of their reported clinical outcomes. For example, studies that reported negative clinical outcomes [46; 47] also had low semi-quantitative scores of 40 and 50 (Table 11), highlighting the impact of methodological inconsistencies on outcome interpretation. At this point, a consideration that this problem has been widely documented in several systematic reviews conducted in several human medicine fields [64], including orthopedics [65], is necessary. To address this issue, future studies should adhere to standardized reporting or criteria, such as those used in this study [28], or use other guidelines, such as the Minimum Information for Studies Evaluating Biologics in Orthopedics (MIBO) guidelines [66], to improve the quality and reproducibility of PRP research. We used two risk of bias assessment tools to evaluate the studies included in this systematic review [31]: the ROBINS-I tool for non-randomized intervention trials [29] and RoB2.0 for randomized trials [30]. Overall, case series had a high risk of bias, mainly due to the lack of control groups and lack of blinding during interventions. This problem was particularly evident in studies evaluating PRP in combination with stem cells and other cellular products [40; 41; 43], as well as in one study evaluating PRP as a single treatment [39]. While the overall clinical outcomes in these studies were positive, their results should be interpreted with caution due to the methodological limitations identified in the risk of bias analysis. Future studies should prioritize the inclusion of control groups and blinding of both clinicians and owners to minimize bias and improve the reliability of the results. Regarding the risk of bias analysis of randomized clinical trials, studies with an overall score of \"some concerns\" [46] and a \"high risk\" [47] of bias reported negative clinical outcomes for PRP. Notably, these studies also had lower scores (40 and 50) for the methodological description of PRP production and quality. In contrast, the randomized clinical trials by [PERSON] et al. [44] and [PERSON] et al. [45] evaluating PRP versus saline for the treatment of ligament and tendon injuries had a low overall risk of bias.