OA is the most common rheumatic disease, and the knee is the most common sites OA. It is a chronic, gradually progressive, degenerative joint disease that is most common in the elderly population. The disease primarily affects the articular cartilage, but also all other articular structures responsible for joint function and is today regarded as a disease or a 'failure' of movement. Osteoarthritis is the result of mechanical and biological events in the wrist, which distort the balance of degradation and construction of articular cartilage and subchondral bone, and affects all tissues diartrodial joints. The main symptoms of OA is pain and loss of function of the affected joint. The diagnosis of OA is made based on subjective complaints of patients and objective clinical findings and confirmed by radiographic examination of the knee. According to NICE (National Institute for Care and Excellence) recommendations for the treatment of OA, the clinical diagnosis of OA without any other processing is permitted if a person has more than 45 years, has difficulties with the execution of daily activities due to pain in the joints and has morning stiffness less than 30 minutes or no stiffness at all. Treatment of OA can be pharmacological and non-pharmacological. The non-pharmacological treatment can be conservative and/or surgical. The non-pharmacological conservative treatment includes lifestyle modification and physical therapy. The gold standard for the treatment of OA of the knee is still physical therapy. Kinesiotheraphy and hydrotherapy are active methods of physical therapy, and also all the passive methods of physical therapy such as ultrasound, cryomassage all electrotherapy can be considered modalities.