Methodology: Randomized double-blind clinical trial comparing intra-articular injection of Platelet-Rich Fibrin (PRF) versus intra-articular injection of corticosteroids in mild to moderate arthrosis of the knee. Inclusion criteria: Age 50 years or older, who have not improved with non-surgical treatment for at least 3 months, ability to sign informed consent, mean visual analogue scale \> 40/100 (over at least 7 days during the month anterior), mild or moderate knee arthrosis diagnosed by grade 2 or 3 radiographic imaging according to the Kellgren-Lawrence classification. Inclusion criteria: angular deviation \>10º of varus or valgus in relation to the anatomical neutral axis in the coronal plane clinically evaluated with a goniometer (femur anatomical axis x tibial anatomical axis \> 4th varus or \> 16th valgus), BMI \>35 or \<18, smoking , autoimmune inflammatory disease - rheumatologic, diabetes - with glycated Hb \> 7, chronic kidney disease, coagulopathies, severe cardiovascular diseases, infections or immunodeficiencies, malignant neoplasm in activity or under treatment, use of NSAIDs in the last month, use of corticosteroids in the last 3 months, platelets \< 150,000, recent intra-articular corticosteroid infiltration or recent Hyaluronic acid infiltration (within the last 6 months), pregnancy or suspected pregnancy, psychiatric disorders. Exclusion criteria: when one of the investigators considers that the participant may be simulating a worse health state than the real one in order to receive financial assistance with the absence from work, he will be excluded from the work. Primary outcome: WOMAC. Secondary outcomes: Visual Analogue Pain Scale. Evaluation moments: inclusion and after the procedure at 3, 6, 12, 18 and 24 months. Sample calculation: 90 patients, 45 patients in each group, considering 15% loss to follow-up and aiming to reach a power of 0.8 and an alpha value of 0.5.