Osteoarthritis is the gradual breakdown of the material, called cartilage, that covers the joint. Cartilage is a tough elastic material that acts as a shock absorber. In osteoarthritis, the cartilage becomes thinner and may even disappear in some places. When this happens, bone rubs against bone, causing pain. Under this weakened cartilage, the bone tries to regenerate and forms growths, called spurs or osteophytes. The joint may become deformed, larger, and lose its mobility.

Osteoarthritis of the knee is the most common form of osteoarthritis affecting the lower limbs. In fact, one-third of people aged 70 and over suffer from this disorder. Although we still have a lot to learn about the causes of knee osteoarthritis, a number of predisposing factors are associated with it:

1. Advanced age
2. Heredity
3. Being overweight
4. Knee injury
5. Surgery involving the meniscus (particularly at a young age)

Normal	Diseased
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Osteoarthritis of the knee may be painless, especially at first. When the pain occurs, it is related to mobilization (movement) of the joint and is relieved by rest. Stiffness in the morning when getting up and after a period of inactivity, swelling, and cracking of the joint are other signs that may occur.

There are three compartments in the knee joint:

1. Patellofemoral (between the femur or thighbone and the kneecap)
2. Medial tibiofemoral (between the tibia and the femur or thighbone)
3. Lateral tibiofemoral

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