Knee replacement surgery is performed to relieve pain in the pain and to increase the ability of the knee to function normally. Pain and knee damage can inhibit the knee from functioning properly. According to Cooper University Hospital, the most common reason for the need to have knee replacement surgery is osteoarthritis, which causes joint cartilage to break down. Other forms of arthritis can also cause degradation of the knee joint and signal the need for knee replacement surgery. There are three main components in knee replacements: femoral, tibial and patellar.
Femoral
The femoral component of a knee replacement serves to resurface the end of the femur, which is the thighbone. According to the American Academy of Orthopaedic Surgeons, this is a metal component that curves around the end of the thighbone and is usually one large piece. However, if the end of the thighbone is only partially damaged, a smaller piece is used to resurface only the damaged part. This is known as unicompartmental knee replacement. Some designs of this component have an internal post with a center cam. This is called a posterior stabilized design. Other designs do not have the center cam and are called cruciate-retaining.
Tibial
The tibial component of a knee replacement is a flat platform that serves to resurface the top of the tibia, or shin bone. This is a metal component that has a top surface cushion made of polyethylene. The polyethylene cushion can be a flat surface, which is used in the cruciate-retaining design, or it can have a raised surface with a center cam, which is used in the posterior-stabilized design.
Patellar
The patellar component of a knee replacement is shaped like a dome and serves the function of a kneecap. It is a polyethylene component.
Material Types
The metal components of knee replacements are alloys that are based on titanium or a cobalt-chromium combination. The polyethylene is a high-density plastic. According to the Arthritis Foundation, some newer knee placement parts are made of special ceramics or oxidized zirconium.
Cement
Some knee replacement parts are designed to be cemented in place with a special bone cement. Other types of parts are called cementless parts. These are components that are inside the bone and are porous. This allows the bone to grow into the replacement part.
