Addition of Transcranial Direct Current Stimulation and Transcutaneous Electrical Nerve Stimulation to an Education and Exercise Program in Subjects With Chronic Pain Due to Knee Osteoarthritis

tDCS intervention will consist in placing two electrodes, the cathode on the supraorbital surface on the same side as the painful knee, and the anode on the parietal area, corresponding to the area of the primary motor cortex, on the opposite side. The intensity will be 2 milli amperes (mA) and stimulation will be 20 minutes. The placebo will generate an initial sensation, and then descend until the stimulation is turned off.

TENS intervention will consist in placing two electrodes on the sides of the patella of the affected knee. The frequency will be 10Herzts and the intensity will remain at a sensitive threshold level, without reaching the motor. The placebo will generate a sensation of current to descend to the minimum value that the equipment allows. Stimulation will last for 20 minutes.

The General Education Intervention consisting in an educational program will be applied to all groups using audiovisual material to increase the subject's knowledge about his/her pathology, about chronic pain and recommendations for supervised exercise based on the NEMEX protocol for osteoarthritis (Ageberg et al.)18: the participants will be taught analytical strengthening exercises (quadriceps and hamstrings) and neuromuscular functional exercises (getting up from the chair or going up a step), with their detailed dosage (2 to 3 series with 10 to 15 repetitions) and a home follow-up model where the participant must record compliance with exercise as well as pain during activity.