Total Knee Replacement

A total knee replacement is a surgical procedure whereby the diseased knee joint is replaced with artificial material. The knee is a hinge joint which provides motion at the point where the thigh meets the lower leg. The thigh bone (or femur) abuts the large bone of the lower leg (tibia) at the knee joint. During a total knee replacement, the end of the femur bone is removed and replaced with a metal shell. The end of the lower leg bone (tibia) is also removed and replaced with a channeled plastic piece with a metal stem. Depending on the condition of the kneecap portion of the knee joint, a plastic “button” may also be added under the kneecap surface.

Introduction

A painful knee can severely affect your ability to lead a full active life. Over the last 25 years, major advancements in artificial knee replacement have greatly improved the outcome of surgery. Artificial knee replacement surgery is becoming more and more common as the population of the world begins to age.

Causes For Knee Joint Replacement

There are many conditions that result in degeneration of the knee joint. Osteoarthritis is the most common cause for patients who have knee replacement surgery. Osteoarthritis is commonly referred to as “wear and tear arthritis”. Osteoarthritis can occur with no previous injury to the knee joint – the knee simply “wears out”. Some people may have a genetic tendency that increases their chances of developing osteoarthritis.

The major problem in osteoarthritis is that the cartilage (the articular cartilage) on the surface of the bone inside the joint wears away. Once the slick protective surface of the articular cartilage is worn away, the results is bone rubbing against bone. Bone rubbing against bone is painful.

Fractures of the knee, torn cartilage, and torn ligaments can cause the knee joint to function abnormally. This abnormal function can lead to excessive wear and tear of the joint many years after the injury – just like an out-of-balance tire can wear out too soon.

Symptoms

The symptoms of a degenerative knee joint usually begin as pain while bearing weight on the affected knee, such as when walking. You may start to limp. The knee may become swollen with fluid. The range of motion of the affected knee can be effected. The knee will bend less than normal and may lose its ability to completely straighten out. Bone spurs will usually develop and can be seen on xray. Finally, as the condition worsens, you may feel pain may almost all of the time. Pain may even keep you awake at night.

Diagnosis

The diagnosis of a degenerative knee joint starts with a complete history and physical examination by your surgeon. Xrays are required to determine the how bad your knee joint has become. Xrays may help suggest a cause for the degeneration in your knee. Other tests may be required if your surgeon thinks that other conditions may be adding to the degenerative process. Blood tests can rule out systemic arthritis, such as rheumatoid arthritis, or an infection in the knee.

Medical Treatment

Not all degenerative knee conditions require a knee replacement as a first treatment. Your doctor may suggest several alternative treatments to put off replacing the knee as long as possible. Using a cane may help relieve some of your pain and allow you to walk more comfortably. Anti-inflammatory medicinces may reduce the inflammation from the arthritis and reduce pain.

Surgery

Most degenerative problems will eventually require replacement of the painful knee with an artificial knee joint, called a prosthesis. The decision to proceed with surgery should be made by you, your family, and your doctor and only after you feel that you understand as much as possible about the surgery and recovery process.

Once the decision to have surgery is made, there are several things that may need to be done. Your orthopedic surgeon may suggest a complete physical examination by your medical or family doctor. This is to ensure that you are in the best possible condition to undergo the operation. You may also need to spend time with the physical therapist who will be managing your rehabilitation after the surgery. The therapist will begin the teaching process before the surgery to ensure that you are ready for the rehabilitation afterwards.

One purpose of the pre-operative visit with the physicial therapists is to record baseline information. This includes measurements of your current pain levels, what you are able to do, how much swelling you have in the knee, and the amount of movement and strength of each knee.

A second purpose of the pre-operative visit is to prepare you for surgery. You’ll begin practicing some of the exercises you will use right after surgery. You will also be trained in how to use a walker or crutches. Whether or not your surgeon used a cemented or noncemented type knee prosthesis will determine how much weight you will be able to place on your foot while walking. Finally, an assessment will be made of any special needs you will have once you return home.

The Artificial Knee Joint, called a prosthesis

There are two main types of artificial knee replacements:

• Cemented Prosthesis
• Uncemented Prosthesis

Both types are widely used. In many cases, a combination of the two types are used. The kneecap, or patellar, portion of the prosthesis is usually cemented into place. The choice to use a cemented or uncemented prosthesis is usually made by the surgeon based on your age and lifestyle, and your surgeon’s experience.

The prosthesis usually consists of three to four parts:

• The tibial component, with the tibial insert replaces the end of the tibia. The tibia is commonly called the shinbone.
• The femoral component replaces the end of the femur, the groove where the kneecap slides. The femur is commonly called the thighbone. It is the largest bone in the body.
• The patellar component replaces the surface on bottom of the patella. (This component is seldom necessary to replace.) The “top” of the kneecap is the part you can feel through your skin. The “bottom” is the on the other side, and slides up and down in the femoral groove whenever you bend or straighten your leg.
• The femoral component is made of metal. The tibial component is usually made of two parts – a metal tray that is fitted directly onto the bone, and a plastic spacer that provides a bearing surface. The plastic used is very tough and very slick – so slick and tough that you could ice skate on a sheet of the plastic without much damage to the plastic.
  A cemented prosthesis is held in place using an epoxy type cement that attaches the metal to the bone. An uncemented prosthesis has a fine mesh of holes on the surface that allows the bone to grow into the mesh and attaches the prosthesis to the bone.