The knee is the most common lower-body site for osteoarthritis because of the wear and tear the joint takes throughout a lifetime.  As with other types of osteoarthritis, it is caused by genetics, injury or repeated abuse. In particular, carrying around more weight than normal - obesity - puts extra strain on the knees, leading to osteoarthritis.  The condition is painful, but it can be treated through an anti-inflammatory diet, anti-inflammatory medication and the strengthening of the muscles around the knee. This will help relieve the inflammation and the stress on the joint going forward.