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Knee replacement: Understanding your knee

The normal knee

The knee joint is the largest and most complex joint in the body. It has four parts.

  • The first two parts are knuckle-like projections at the lower end of the thigh bone and the upper end of the shin bone. These areas glide against each other and allow you to bend your knee.
  • The third part, cartilage, covers all joint surfaces and is a smooth padding that allows the first two parts to touch and move together.
  • The fourth part is the patella (kneecap). The patella covers the knee joint as is what you feel when you touch your knee.

The normal knee has four parts: two knuckle-like projections, cartilage and the patella (kneecap).

The problem knee

Infection, injury or disease can affect the way the knee works; however, arthritis is the most common cause of knee joint deterioration.

Arthritis is a name used to describe a number of diseases that cause swelling of the joints and friction on the cartilage and bones.

In the problem knee, the worn cartilage no longer serves as a cushion. When cartilage becomes damaged by an injury or by disease, the knee joint can't move smoothly. As the cartilage wears away from the bones, the bones rub together and become irregular, creating a rough surface.

As the pain worsens, you will avoid using the joint. This causes the muscles to weaken and the joint to feel unstable and less able to support your body weight. An X-ray can determine the extent of joint damage. A total knee replacement is an option to relieve the pain and instability.

Cysts, bone spurs and loss of cartilage can lead to knee problems.

The new knee

The total knee replacement surgery removed damaged bone and cartilage from the knee joint and replaces both the bone and cartilage with an artificial joint (prosthesis).

The artificial knee provides a smooth surface for your bones to touch and move together.

The upper part of the artificial knee is metal (titanium, tantalum or cobalt) and fits into your thigh bone. The lower part is metal and plastic (wear-resistant polyethylene) and fits into your shin bone. If the underside of your knee cap is damaged, a round plastic piece will be cemented onto it.

The three parts touch and glide against each other just a normal knee joint does, allowing your knee to bend.

There are different approaches for total knee replacement surgery, which change as the technology changes. Your orthopedic doctor will determine which approach will work best for you, based on your:

  • age
  • weight
  • bone health
  • overall health
  • activity level
  • doctor preference (choice).

The new knee fits into your thigh bone (femur) and the skin bone (tibia).

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Source: Allina Patient Education, Total Knee Replacement, third edition, ortho-ahc-90140

First published: 10/01/2000
Last updated: 12/01/2006

Reviewed by: Allina Patient Education experts