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 Knee Anatomy

X-ray of knee joint

The knee joint is made up of three bones:

1.  the thigh bone (femur)

2.  the leg bone (tibea)

3.  the knee cap (patella)

The knee joint is like a ‘hinge’. It is made up of two joints. The thigh bone (femur) in your upper leg is hinged to the shin bone (tibia) in your lower leg. This is called the femorotibial joint. Where the thigh bone (femur) connects with the knee cap (patella) it is called the patellofemoral joint. These two joints allow you to bend and straighten your knee.

In a normal knee, the surfaces of all three bones coming into contact with each other are covered with a smooth gliding surface. This smooth substance is known as the articular cartilage. It provides a smooth surface to let you easily move around, and it acts as a shock absorber for any stress placed on the knee.

When the knee is healthy, the knee joint moves freely. But disease or injury can wear away the cartilage between the bones in your knee joint. Without this cushioning, the bones can become rough and rub together, causing pain.

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How does the knee joint work? 

The knee joint works like a ‘hinge’. The knee joint lets the shin bone in your lower leg move back and forth on your thigh bone so you can bend and straighten your knee.

Three things help the knee joint work easily and without pain:

  1. The smooth coating over the bones, called cartilage.
  2. The slippery fluid inside the joint, called synovial fluid.
  3. The muscles and ligaments that support and move the knee.

Three things make the knee painful and hard to move:

  1. The smooth coating over the bones gets rough and worn away.
  2. The muscles get weaker.
  3. The slippery synovial fluid in the knee starts to dry up.

Osteoarthritis, rheumatoid arthritis and other diseases and injuries can damage the cartilage in your knee. If you are feeling a lot of pain and discomfort every day, you should see your doctor.

Why do I need a knee replacement?

Most people have a knee replacement because the cartilage between the bones in their knee has worn away. The bones are now rubbing against each other, making your knee very stiff and painful.

The pain may be keeping you awake at night, and affecting your everyday life.  You may have had to cut back, or stop, many of your everyday activities such as working, going for a walk, going up and down stairs, gardening and shopping.

You may need knee replacement surgery if the knee joint gets to a point when you can’t control the pain any more with other treatments. Knee replacement is the most common joint replacement surgery. It has a high success rate, and can improve your quality of life. Your pain should stop, or at the very least, you should feel less of pain and discomfort. Your new knee should be more flexible, allowing you to go about the activities of your everyday life.