Osteoarthritis is the most common rheumatic, degenerative disease. Chronic disease of the entire joint is characterized by destruction and loss of articular cartilage along with other articular changes. Osteoarthritis affects all joints, but most often these are the supporting joints that include the knee. Today, it is the most common joint disease of adults in the world, and its incidence increases with age. One third of people aged 65 or over, have a radiological finding of osteoarthritis of the knee. The etiology of degenerative joint diseases has not been fully investigated, but they can generally be divided into primary and secondary arthrosis according to the cause of arthrosis. Primary or idiopathic arthrosis are those in which the cause is unknown, On the other hand, secondary arthrosis are those arthrosis in which the cause is known and occurs as a consequence of injuries, congenital anomalies of the joints, metabolic and endocrine diseases and some inflammations. Risk factors for the development and progression of osteoarthritis identified in epidemiological studies can, in general, be divided into factors influencing the general predisposition to the disease and local biochemical factors influencing the development of osteoarthritis in individual joints. Osteoarthritis was initially considered a disease of the articular cartilage, but recent research has shown that the condition affects the entire joint. Articular cartilage loss is the primary change, but the combination of cellular changes and biomechanical stresses causes several secondary changes, including subchondral bone changes. Attempts at reparation cause subchondral sclerosis and osteophytes at the edges of the joint, in order to stabilize it. Synovium swells with signs of inflammation with the formation of a less viscous effusion. As joint mobility decreases, so do the surrounding, supportive muscles. Knee osteoarthritis in the foreground is characterized by pain, fatigue, decreased range of motion, joint stiffness, and crepitation. The diagnosis of osteoarthritis of the knee is made on the basis of anamnestic data and clinical examination, and is confirmed radiologically. OA treatment is complex and multimodal. It can be divided into non-pharmacological, pharmacological and surgical treatment. Before treatment, it is necessary to make a physiotherapy assessment in which subjective and objective forms of assessment are used, as well as various measurement tests and questionnaires. In treatment, great importance is given to various therapeutic exercises. Among other methods, various forms of thermotherapy, cryotherapy and electrotherapy are used.