Knee Topics

Preparation for Hip and Knee Replacement

Total Knee Replacement

A painful knee can severely affect a patient 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 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 are 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 x-ray. Finally, as the condition worsens, one may feel pain may almost all of the time. Pain may even keep the patient awake at night.

Diagnosis

The diagnosis of a degenerative knee joint starts with a complete history and physical examination by the surgeon. X-rays are required to determine the how bad the knee joint has become. X-rays may help suggest a cause for the degeneration in the knee. Other tests may be required if the 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. The doctor may suggest several alternative treatments to put off replacing the knee as long as possible. Using a cane may help relieve some of the pain and allow to walk more comfortably. Anti-inflammatory medicines 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 prosthesis. Once the decision to have surgery is made, there are several things that may need to be done. we orthopedic surgeon may suggest a complete physical examination by your medical or family doctor. This is to ensure that they are in the best possible condition to undergo the operation. They might also need to spend time with the physical therapist who will be managing the rehabilitation after the surgery. The therapist will begin the teaching process before the surgery to ensure that they are ready for the rehabilitation afterwards.

One purpose of the pre-operative visit with the physical therapists is to record baseline information. This includes measurements of the current pain levels, what they are able to do, how much swelling they 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 them for surgery. They will begin practicing some of the exercises the patient will use right after surgery. they will also be trained in how to use a walker or crutches. Whether or not your surgeon used a cemented or no cemented type knee prosthesis will determine how much weight they will be able to place on your foot while walking. Finally, an assessment will be made of any special needs they will have once they 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 is 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 the age and lifestyle.

Each prosthesis has four parts:

• The tibial component 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. The "top" of the kneecap is the part you can feel through the skin. The "bottom" is the on the other side, and slides up and down in the femoral groove whenever the patient bend or straighten their 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 one could ice skate on a sheet of the plastic without much damage to the plastic.

A cemented prosthesis i s 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.

The Operation

Replacing the knee begin with making an incision on the front of the knee to allow access to the knee joint. Shaping the Distal Femoral Bone

Shaping the Distal Femoral Bone

Once the knee joint is entered, a special cutting tool is placed on the end of the femur. This special tool ensures that the bone is cut keeping the proper alignment to the leg's original angles - even if the arthritis has made the bowlegged or knock-kneed. Several pieces of diseased bone are cut away from the end of the femur so that the artificial knee can be attached.

Preparing the Tibial Bone

Then the top of the tibia is cut using another cutting tool that also ensures proper alignment.

Preparing the Patella

The undersurface of the kneecap is removed.

Frontal View

This is what the prepared surfaces look like viewed from the front. The patella has been moved to allow to see the knee.

Placing the Femoral Component

The femoral component is then fitted on the femur. In the uncemented type of femoral component, the prosthesis is held on the end of the bone because the end of bone has a tapered cut. The metal prosthesis is made to almost exactly match the tapered cut of the bone. Fitting the femoral component onto the end of the bone holds the component in place by friction. In the cemented component, epoxy cement is used to attach the metal prosthesis to the bone.

Placing the Tibial Component (metal tray)

The metal tray that holds the plastic spacer is attached to the end of the tibia. The metal tray is either cemented into place, or held in place with screws if the component is the uncemented type. The screws hold the tray in place until the bone grows into the porous coating. The screws are left in the bone and are not removed.

Placing the Tibial Component (plastic spacer)

The plastic spacer is attached to the metal tray of the tibial component. If the plastic spacer wears out it can be replaced if the rest of the prosthesis is in good condition - a so called retread.

Placing the Patellar Component

The patellar button is usually cemente d into place behind the patella.

The Completed Knee Replacement

x-ray from the side compared with illustration of knee prosthesis. x-ray from the front compared with illustration of knee prosthesis.