## 4 Discussion  
In this systematic review, we investigated papers where the Bonar histopathological score, designed primarily to evaluate excess tissue degeneration, was used in the assessment of therapeutic advances in tendinopathy. The Bonar scoring system, well known and established in the quantification of tendinous tissue degeneration, revealed a new attribute in all concerned studies--a function in the evaluation of tendon treatment effectiveness. We carefully selected 22 papers that mainly focused on PRP application in chronic tendon disorders, among which animal studies prevailed. However, the results of this systematic review showed that the Bonar score could also be easily applied in human in vivo studies to assess the shift of degeneration in healed tendinous tissue. Yet, there are some issues that have to be established and determined before widespread clinical application. The studies from the investigated papers were mainly focused on the Achilles, SST, and patellar tendons; however, the results of Bonar system use in the context of treatment results in other localizations, such as the posterior tibialis tendon (PTT), the long head of the biceps tendon (LHBT), and forearm tendons, are unknown. Further, a control group was presented in each paper and based mainly on Achilles tendon specimens. This is an important issue that is obligatory in the evaluation of various therapeutic methods in chronic tendon disorders. Future human studies should also have well-standardized control groups to easier define the therapeutic effect. Finally, the treatment methods used in the selected studies varied, but PRP application predominated. Positive effects of therapeutic methods prevailed; however, in one paper, a neutral effect of PRP application was noted. We still need a standardization of PRP therapy to predict a clinical effect, but on the other hand, the presented studies revealed no side effects of this treatment method. In recent decades, increasing concern with platelet-rich plasma injections in tendon disorders has been noted. PRP therapy is a relatively inexpensive and easy-to-prepare procedure. PRP is widely used in different fields of medicine; however, the evidence base for the clinical use of PRP is still in its infancy [51]. This therapeutic method intends to augment the natural tendon healing process, supplying the tissue with specific, highly concentrated growth factors. PRP has been recommended as a treatment option in refractory tendonopathies [30]. Its injections into the patellar tendon, Achilles tendon, and tendons of digit flexors after injury have shown positive clinical results and led to superior regeneration [56]. The application of PRP in elbow tendinopathy showed promising results both radiologically and clinically [57; 58]. On the contrary, some authors revealed no functional improvement among patients who underwent PRP therapy [59]. In such situations, histopathological assessment could be helpful to augment the functional evaluation of therapeutic results. The authors of five of the six PRP studies evaluated in this systematic review showed that PRP had a positive effect on both clinical presentation and histopathology, including collagen architecture, ECM composition, tenocyte morphology, and expansion of capillaries. Moreover, [PERSON] et al. revealed that PRP therapy decreased inflammation and reduced the apoptosis rate in tendons tissue [42]. On the other hand, a study by [PERSON] et al. showed that there was no statistically significant improvement after Achilles tendon PRP treatment [16]. PRP application as a therapeutic method in chronic tendon disorders was the most widely used in the selected group of papers. However, there were other methods with a negative or positive effect on tendons tissue. [PERSON] et al. used curcumin, [PERSON] et al. used LMWH and rivaroxaban, [PERSON] et al. used vitamin C and hyaluronic acid, and [PERSON] et al.