General Adult Health Information

Total Knee Replacement (also called Total Knee Arthroplasty)

Artificial knee replacement surgery, also called total knee replacement, 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.

Finally, you may be asked to donate blood before the operation. Blood can be donated 3 to 5 weeks before surgery. Your body will make new blood to replace the donated blood. If you need to have a blood transfusion at the time of surgery, you will receive your own blood.

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. 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 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.

The Operation

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 you 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 you 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 taperd cut. The metal prosthesis is made to almost exactly match the taperd 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, an 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 cemented into place behind the patella.

The Completed Knee Replacement

Xray from the side , xray from the side compared with illustration of knee prosthesis

Xray from the front , xray from the front compared with illustration of knee prosthesis

 

Rehabilitation
While you are in the hospital:

• Range of Motion exercises
• Walking
• Exercises for strength and flexibility

The physical therapist will schedule your first visit soon after surgery. Therapy will focus on the range of motion in the knee. Gentle movement will be used to help you begin bending and straightening of the knee. If your surgeon recommends a continuous passive motion (CPM) machine, it will be adjusted for your knee. Next, you’ll go over your exercise regimen. When you are stabilized, your therapist will assist you up for a short walk using crutches or a walker. Physicial therapy will continue once or twice a day. You will be on your way home when you can safely:

• get into and out of bed,
• walk up to 75 feet with crutches or a walker,
• go up and down a flight of stairs, and
• get to the bathroom.

It is also important that you have good contraction of the upper thigh muscle, called the quadriceps, and that the range of motion of your knee is improved.

After you leave the hospital: Once your are at home, the physicial therapist will likely come to your home for treatment. This is to ensure you are safe in and around your home. Your therpist will probably see you for at least one safety check visit and to go over your exercise program again. You may need as many as three visits at home before beginning outpatient physical therapy.

As you progress: Once you begin outpatient physical therapy, several key areas will be addressed. Your therapist may choose one or more treatments, such as heat, ice, or electrical stimulation, to help reduce any persistent swelling or pain. Continue to use your walker or crutches. If you had a cemented prosthesis, you can increase the amount of weight you place on your sore leg until you feel uncomfortable. If you had a noncemented prosthesis, place only your toes down until your doctor or therapist allows you to increase the amount of weight you can bear.

Range of motion exercises will help you regain full bending and straightening of your knee. Your exercise program will include strengthening, balance, endurance, and functional activities. Your strengthening program will focus on key muscle groups in the buttocks and hips, thigh, and calf muscles. When you are allowed full weight bearing, several balance exercises will be used to further stabilize your knee. Endurance can be achieved by riding a stationary bike, swimming laps, and using an upper body ergometer (upper cycle). Finally, you will be taugh a special group of exercises that simulate your day-to-day activities, like going up and down steps, proper squatting, raising up on your toes, and bending down. Later, specific exercises may be chosen to simulate the physical demands of your work or hobby.

Complications Of Total Knee Replacement
As with all major surgical procedures, complications can occur. The most common complications following knee replacement are:

• Thrombophlebitis
• Infection in the joint
• Stiffness of the joint
• Loosening of the joint

This is not intended to be a complete list of the possible complications, but these are the most common.

Thrombophlebitis
Thrombophlebitis, sometimes called Deep Venous Thrombosis (DVT), can occur after any operation. It is more likely to occur following surgery on the hip, pelvis, or knee. DVT occurs when the blood in the large veins of the leg forms blood clots within the veins. This may cause the leg to swell and become warm to the touch and painful. If the blood clots in the veins break apart they can travel to the lung. Once in the lung they get lodged in the capillaries of the lung and cut off the blood supply to a portion of the lung. This is called a pulmonary embolism. Pulmonary means "lung". An embolism is a fragment of something traveling through the vascular system. Most surgeons take preventing DVT very seriously. There are many ways to reduce the risk of DVT, but probably the most effective is getting you moving around as soon as possible! Some of the commonly used preventative measures include:

• Pressure stockings to keep the blood in the legs moving.
• Medications that thin the blood and prevent blood clots from forming.

Infection
Infection can be a very serious complication following an artificial joint. The chance of getting an infection following total hip replacement is probably around 1 in 100 total hip replacements. Some infections may show up very early - before you leave the hospital. Others may not show up for months, or even years, after the operation.

Also, an infection can spread into the artificial joint from other infected areas. Your surgeon may want to make sure that you take antibiotics when you have dental work, or surgical procedures on your bladder or colon to reduce the risk of spreading germs to your new joint.

Stiffness
In some cases, the ability to bend the knee does not return to normal after an artificial knee replacement. Many orthopedic surgeons are now using a machine known as a CPM machine (Constant Passive Motion) immediately after surgery to try and increase the range of motion following artificial knee replacement. Other orthopedic surgeons rely on physical therapy beginning immediately after the surgery to regain the motion. It is not clear which is the best approach. Both approaches have benefits and risks, and the choice is usually made by the surgeon based on his experience and preferences.

To be able to use the leg effectively to rise from a chair, the knee must bend at least to 90 degrees. A desirable range of motion should be greater than 110 degrees. Balancing of the ligaments and soft tissues (during surgery) is the most important determining factor in regaining an adequate range of motion following knee replacement, but sometimes increasing scarring after surgery can lead to an increasingly stiff knee. If this occurs, your surgeon may recommend taking you back to the operating room, placing you under anesthesia once again, and forcefully manipulating the knee to regain motion. Basically, this allows the surgeon to breakup and stretch the scar tissue without you feeling it. The goal is to increase the motion in the knee without injuring the joint

Loosening
The major reason that artificial joints eventually fail continues to be loosening of the joint where the metal or cement meets the bone. There have been great advances in extending the life of an artificial joint. Still, most joints will eventually loosen and require a revision. Hopefully, you can expect 12-15 years of service from your artificial knee. In some cases the knee will loosen earlier than that. Just like your diseased knee, a loose joint causes pain. Once the pain becomes unbearable, another operation will probably be required to replace the knee.

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