Introduction: Osteoarthritis of the knee is a very common disease. However there are few treatment options for these patients. Botulinum toxin type A is an option for chronic pain. If the investigators prove effectiveness of its use for intra-articular analgesia, Botulinum toxin type A can be useful for treat these patients.

Objective: Compare the effectiveness of the use of intra-articular corticosteroid versus Botulinum toxin type A in the treatment of patients with knee osteoarthritis.

Methods: A prospective controlled randomized double blind studied with three groups (n = 35 each group) of patients with symptomatic osteoarthritis of the knees receive intra-articular medication in a single moment will be undertaken. The three groups will be: Botulinum toxin type A Group: patients who receive 100 units of botulinum toxin; hexacetonide of triamcinolone Group: patients who receive 40mg of triamcinolone hexacetonide, and saline group: patients who receive 2ml of normal saline. Patients will be assessed by evaluators " blind " in 4 times during 12 weeks of follow-up with clinical assessment instruments (pain, quality of life questionnaire as short form 36 questionnaire) , functional ( WOMAC questionnaire) , and ultrasound (quantitative and semi quantitative measure of synovial hypertrophy and semi quantitative Power Doppler ) .The following statistical tests will be used : Student's t test, Mann - Whitney , chi- square test and ANOVA for repeated measures . Will be considered as statistical significance the difference of 5 %.

Inclusion Criteria:

• age above 50 years
• diagnose of knee osteoarthritis using clinics and radiographic criteria
• pain for more than 6 months
• analogic visual scale among 4 to 8
• patients who agree to sign informed consent

Exclusion Criteria:

• secondary osteoarthritis
• skin lesion
• use of intraarticular corticosteroid in the last 3 months
• use of oral corticosteroid in the last 30 days
• Kellgren Lawrence I or IV
• inflammatory arthritis
• neuromuscular disease
• use of aminoglycoside antibiotics
• metalic prosthesis in knee
• peripheric neuropathy
• serious cardiovascular or pulmonary disease
• serious disorder of coagulation
• pregnancy or breastfeeding
• infections
• use of wheelchair