Osteoarthritis (OA) is one of the most common joint diseases; as much as 80% of the population have radiographic evidence of osteoarthritis by the age of 65. Actually, the degeneration in the joints starts by the age of 20 years and manifests clinically by 35-40 years. Although only about 60% of patients with radiographically detectable OA have symptoms, 15 to 30% of all visits to general practitioners may be attributed to difficulty with ambulation, largely due to OA. 

The main risk factors for OA are aging, obesity, injury and birth defects. The association of obesity is stronger for bilateral than for unilateral disease and more marked in women than in men. Increased weight precedes the presentation of knee OA and is not a consequence of disease. Being overweight increases the amount of force across a weight bearing joint