_applied sciences_  
_Systematic Review_  
**Therapeutic Advances in Tendinopathy Quantified**  
**Microscopically Using Bonar Score, with a Special Reference to PRP Therapy--A Systematic Review of Experimental Studies**  
**[PERSON] 1,2,3,*, [PERSON] 4, [PERSON] 5, [PERSON] 1, [PERSON] 2, [PERSON] 4, [PERSON] 6, [PERSON] 2 and [PERSON] 1**  
1 Department of General Orthopaedics, Musculoskeletal Oncology and Trauma Surgery, University of Medical Sciences, 61-701 Poznan, Poland; [EMAIL_ADDRESS] (L.L. ); [EMAIL_ADDRESS] (J.K.)  
2 Department of Orthopaedics, Orvit Clinic, Citomed Healthcare Center, 87-100 Torun, Poland; [EMAIL_ADDRESS] (L.P.); [EMAIL_ADDRESS] (D.S.) 3 Department of Pathology, Faculty of Medicine, Nicolaus Copernicus University in Torun, 87-100 Torun, Poland  
4 Department of Histology and Embryology, Faculty of Medicine, Nicolaus Copernicus University in Torun, 87-100 Torun, Poland; [EMAIL_ADDRESS] (M.G. ); [EMAIL_ADDRESS] (W.Z.) 5 Orthopaedics and Traumatology Department, Hacettepe Universitesi, Ankara 06-352, Turkey; [EMAIL_ADDRESS]  
6 Faculty of Medicine, Nicolaus Copernicus University in Torun, Collegium Medicicum in Bydgoszc, 87-100 Torun, Poland; [EMAIL_ADDRESS]  
7 Correspondence: [EMAIL_ADDRESS]  
**Citation:** [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON] Therapeutic Advances in Tendinopathy Quantified  
Microscopically Using Bonar Score, with a Special Reference to PRP  
**Therapy--A Systematic Review of Experimental Studies.**_Appl. Sci._**2021**, _11_, 4973. [[https://doi.org/10.3390/app11114973](https://doi.org/10.3390/app11114973)]([https://doi.org/10.3390/app11114973](https://doi.org/10.3390/app11114973))  
Academic Editors [PERSON] and [PERSON]  
Received: 1 May 2021  
Accepted: 25 May 2021  
Published: 28 May 2021  
**Published:** **Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. **C Copyright:** 2021 by the authors. License MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)]([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/))). **Abstract:** (1) Background: The Bonar scoring system serves in the microscopic evaluation of tendon pathology. However, it can be easily adapted to investigate decreasing degeneration after treatment and quantify the healing progress. We believe that there is an actual need for a connection between clinical observations and tissue alterations arising during the treatment process, to gain superior functional outcomes. Herein, we perform a systematic review of the Bonar score's application in the histopathological assessment of therapeutic advances in tendinopathy, with special reference to PRP therapy. (2) Methods: A systematic review was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The searching strategy was conducted across major databases: PubMed, Cochrane Central, ScienceDirect, SciELO, and Web of Science. The risk-of-bias assessment was made using the Cochrane Collaboration's Risk of Bias Tool and SYRCLE. (3) Results: The searching strategy produced 807 articles, and after selection, 22 studies were included. We collected 21 animal studies (n = 472) and 1 human study (n = 45). Three types of tendons were taken into account: 14 Achilles tendons, 7 supraspinatus tendons (SST), and in 1 case, Achilles and patellar tendons simultaneously. A variety of therapeutic methods were used--from intra-tendinous substance injections to surgical procedures or mechanical stimuli--but platelet-rich plasma (PRP) therapy dominated among them and was present in six studies.