It is a double-blind randomized sham-controlled clinical trial to evaluate the effectiveness of resistive capacitive diathermy in subjects affected by knee osteoarthritis in comparison with a "sham" diathermy treatment. The resistive capacitive diathermy is a medical device supplying low (448 KHz) radiofrequencies with maximum output power of 200 W, used to reduce pain and inflammation and allowing healing processes. The sham diathermy treatment is administered with the device set on "on" but not active (not supplying energy). Each subject, randomly assigned to either resistive capacitive diathermy treatment (group 1) or sham-treatment (group 2) is submitted to a thirty minutes session, three times per week for a total of ten sessions. The outcome measures are the WOMAC scale (Western Ontario and McMaster Universities Arthritis Index) to assess pain and physical functioning, a visual analogic scale (VAS) for pain, the femoral quadriceps strength (MRC = Medical Research Council Scale). Outcome measures are administered at baseline (T0), at the end of the treatment protocol (T1), at 1 month (T2) and 3 months (T3) after the end of treatment.

Inclusion Criteria:

• Patients affected by Knee osteoarthritis established by clinical examination and X-ray in postero-anterior and lateral views

Exclusion Criteria:

• Neurologic Disorders involving the lower limbs
• Systemic inflammatory disorders
• pace-maker implantation
• Severe heart disease
• Acute infections or bone tuberculosis
• Acute skin diseases
• History of surgery on the affected knee
• Cognitive or psychiatric disorders