This study has the title “Platelet-rich plasma (PRP) applied during total knee arthroplasty”. Dr. João Paulo Fernandes Guerreiro, a doctor within the clinical staff of Irmandade da Santa Casa de Londrina, will conduct a clinical study within this institution that involves total knee arthroplasty on 40 patients, using a currently well-established surgical technique. In 20 patients, we will apply platelet-rich plasma (PRP) before closing the wound. PRP is a substance made from a sample of the patient's own blood, collected at the time of starting the anesthesia. The objective of the study is to analyze the benefits that PRP might bring toward controlling pain and bleeding and improving healing. PRP is a part of human blood that contains a large quantity of platelets. Platelets are cells that participate in blood coagulation when blood comes into contact with wounds. The PRP used in this study will be removed from the same patient during anesthesia. Regarding the risks of the surgery, these include edema (swelling), bleeding (with possible blood transfusion during or after the operation) and/or hematoma; dehiscence of the surgical wound (breakage of stitches or opening or the surgical wound); postoperative pain; joint stiffness (movement limitation); anesthetic accidents; complex regional pain syndrome; venous thrombosis and its consequences (formation of a coagulum that causes obstruction of the veins); temporary or definitive functional incapacity (in relation to activities of daily living, work activities, sports or other activities); superficial infection; deep infection and its consequences (difficult to treat and eradicate, with the need for new hospitalizations and surgical interventions for cleaning and removal of fixation materials, and probable sequelae such as functional limitation or loss of the limb operated); neurovascular injuries (injuries to nerves that may compromise the sensitivity and movement of a given region of the body and/or limb; arterial lesions that may compromise the blood irrigation of a given region and/or limb). The mean time taken to perform the surgery is 100 minutes. Evaluations will be made by means of physical examinations during the hospital stay (generally for two days after the surgery) and then at the following times after the surgery: 7, 10 and 21 days; 2, 6 and 12 months; and annually thereafter. Radiographs of the knee will be performed 2, 6 and 12 months after the surgery and annually thereafter, in the same way as is done routinely among our patients. During the postoperative period, it is common to have some degree of pain, but this improves with the medication that will be prescribed. There may be some swelling of the knee, which can be treated with medication sand ice compresses. Slight bleeding may also occur on the first days. Any other doubt should be clarified with the doctor. 1.1. Therefore, we request your consent to include you in our study and we assure you than confidentiality will be maintained. We will make use of your participation for the scientific evaluation and possible publication of this study, within the ethical principles that must guide research and our profession. We would also like to make it clear that your participation will not imply any financial remuneration. If your do not wish to participate, you are free to opt out, both at the outset or during the course of the work, without any personal losses. If you have any queries, you can contact the researcher directly through this telephone number: (43) 3377 0900. In an emergency, you can seek assistance at the orthopedic emergency service of Santa Casa de Londrina, telephone: (43) 3373 1671. You may also contact the bioethics and research ethics committee of Irmandade da Santa Casa de Londrina, telephone: (43) 3373 1643. We thank you for your valuable contribution. _______________________________ Researcher's signature I declare that I have been informed about the study and I agree to participate. DATE: ________________  Name____________________________________________________________  _____________________________  Signature