The objective of this study is to compare the results of 2000 impulses of radius shockwaves per week with 2000 placebo shockwaves on the treatment of pain and functional incapacity of patients with severe primary knee osteoarthritis, who did not satisfactory respond to previous conventional treatments.

• Prospective, placebo controlled randomized and double-blind study.
• Treatment Method:

Radial extracorporeal shockwaves will be applied using the Swiss Dolorclast (EMS Electro Medical Systems, Switzerland), generated by pneumatic waves.

Intervention:

• Group 1 - Intervention group Patients will receive 2,000 impulses of radial shockwave per week, with pressure of 2.5bar to 4.0bar, at the frequency of 8Hz. The impulses will be applied at the most painful site of the knee joint interface on manual palpation, for three consecutive weeks.
• Group 2 - Control Group:

Patients will receive 2,000 impulses of placebo radial shockwave per week, without any energy flow intensity. Frequency of 8Hz will appear in the screen. The impulses will be applied at the most painful site of the knee joint interface on manual palpation, for three consecutive weeks.

Post application program for both groups: Three consecutive days of:

1. Hot packs (superficial heat) applied on the application site for 20 minutes;
2. Simple analgesics, when needed (Acetaminophen 500mg every 6 hours, or analogue in case of allergy).

Outcome Evaluation:

The evaluation of pain intensity will be done according to the VAS (Visual Analog Scale) The influence of pain on the functional capacity of patients will be measured with WOMAC (Western Ontario and McMaster Osteoarthritis Index) for knee evaluation.

Another evaluation criteria will be the level of tolerance of pressure on several muscles and other parts as the pes anserinus and patellar tendon, the knee joint interface, and the supraspinal of L1 to S1 also on the dermatomal from T12 to S2. These measures will be done by the Fisher algometry.

The evaluations will be carried out before the treatment, immediately after the treatment and 3 months after the end of the treatment.

Analgesia drut will be prescribed, if patients feel pain during the days after the application.

Inclusion Criteria:

• Clinical and radiological diagnosis of primary knee diagnosis.
• Pain intensity: Visual Analog Scale (VAS) ≥ 6;
• One of more failures with conventional treatment (drugs, Non-Steroidal Anti-inflammatory Drugs - NSAD, physiotherapy, stretching, acupuncture, orthosis and others);
• Age over 60 years;
• No use of corticosteroids in the prior 48 hours;
• No major osteoarthritis events in other joints of lower limbs (waist and ankle) and lower back;
• No clinical evidence of related neuropathy, including radiculopathy and peripheral neuropathy;
• Absence of systemic inflammatory disease (Rheumatoid arthritis, Reiter, ankylosing spondylitis, generalized polyarthritis, cancer);
• Absence of infection or cancer at the application site;
• Absence of related endocrine and metabolic diseases;
• Absence of fibromyalgia, diagnosed after the American College of Rheumatology, 1999;
• Absence of severe blood dyscrasias;
• Absence of severe psychiatric disturbances that requires psychiatric assessment;
• Availability to comply with the clinic visits and follow up evaluations along the treatment

Exclusion Criteria:

• Patients who withdraw the informed consent form at any time