Osteoarthritis of the knee is a very prevalent disease. However, there are few therapeutic options for its patients. Platelet-rich plasma is a treatment option for chronic pain. If proven to be effective in its intra-articular use, Platelet-rich plasma may help in the treatment of these patients.

Goal:

Primary objective: To compare effectiveness in improving pain and function and the medium-term tolerance (12 weeks) of intra-articular injection of Platelet-rich plasma versus intraarticular injection of triamcinolone hexacetonide in patients with symptomatic primary knee osteoarthritis.

Secondary objective: To compare the medium-term effectiveness of intra-articular injection of Platelet-rich plasma versus intra-articular injection of triamcinolone hexacetonide to improve synovial hypertrophy and quality of life in these patients.

Methods: A prospective randomized controlled double-blind study with three groups (each with n = 33) of patients with symptomatic osteoarthritis of knees who will receive intra-articular infiltration in a single moment. Patients will be allocated to one of three groups: 1) Platelet-rich plasma group: patients who will receive plasma; 2) triamcinolone hexacetonide Group: patients who will receive 40mg of triamcinolone hexacetonide; And 3) Isotonic saline solution group: patients who will receive isotonic saline solution. The patients will be evaluated by "blind" evaluators in 4 assessment times up to 12 weeks of follow-up through clinical assessment instruments (rest and movement pain, joint edema, goniometry, clinical improvement scale, quality of life questionnaire as the SF36), functional (Womac questionnaire, M. Lequesne Functional Knee Index, 6 min walk test, Time up and go test), and ultrasound test (quantitative and semiquantitative measurement of synovial hypertrophy and semiquantitative Power Doppler).

Statistics: The following statistical tests will be used according to the need: Student's t test, Mann-whitney, Pearson's chi-square test and ANOVA for repeated measures. A statistical significance of 5% will be considered.

Inclusion Criteria:

• primary knee osteoarthritis
• degree II and II in Kellgren & Lawrence classification
• pain duration: more than three months
• pain in the visual analogue scale between 4 and 8cm
• agree in participate and sign the consent form

Exclusion Criteria:

• secondary knee osteoarthritis
• skin lesion in knee
• intraarticular joint injection in the previous three months
• steroids use in the previous 30 days
• degree I or IV in Kellgren & Lawrence classification
• inflammatory arthritis, gout and pseudo-gout
• cancer
• previous surgery in knee
• cardiovascular and respiratory disease that change functional status
• pregnancy and breastfeed
• coagulation disturb
• bacterial infection
• handicapped
• NSAIDs and Platelet anticoagulant in the previous month