Total Knee Replacement
Gregory Solis MD and Mervyn J Cross OAM, MD
The major reason to undergo a joint replacement is for pain that is caused by degeneration, or arthrosis, of the surfaces of the joint. This most commonly is a result of gradual wear and tear over the years but can also be due to diseases like Rheumatoid arthritis or Gout. Damage can also be the result of abnormalities in the joint caused by ligament or cartilage injuries. This damage can cause wearing away of the cartilage, which normally acts as a cushion and a smooth gliding surface between the bones that form the joint. Eventually this cartilage can wear completely away until bone is rubbing on bone in the joint. Any such changes in the normally smooth joint surfaces causes problems similar to damaged ball bearings or loss of lubricant in mechanical devices. The result of this is pain and swelling in the knee, usually made worse with increased activity. This can significantly impact on quality of life, preventing people from engaging in recreational activities, exercise and even such simple things as going to the shops.
Joint degeneration, or arthrosis, results from wear of the normally smooth linings of the joint. The normal joint is lined with cartilage and bathed in a fluid that gives a nearly friction less surface. Figures 1a and 1b show the normal anatomy of the knee joint. This joint is formed between the femur (thigh bone) and the tibia (shin bone). The "Joint Space" is actually not a space at all, but the area occupied by the cartilage. Cartilage does not show up on X-rays. In some people this cartilage can break down or wear away. Loss of the smooth cartilage lining increases wear as the two rough surfaces move against each other. This can cause pain and inflammation in the joint (arthritis). Eventually one can have complete loss of the cartilage with bone rubbing on bone (Figure 2a and 2b). This is seen by a loss or narrowing of the "Joint Space". A further sign of degeneration in the joint is the formation of "osteophytes". These are extra spurs of bone that the body forms as an attempt to increase the area of the joint and therefore decrease the loading or pressure of the joint (i.e.. the same body weight transmitted through a larger joint surface will give a lower load per square centimeter).
Because the problem with arthrosis involves the deformity and wear of the normally smooth joint surfaces, the goal of surgery is to restore these surfaces. The original knee joint has a smooth, low friction and durable surface. Over the last 30 years the techniques and materials used in joint replacement surgery have been improved, but the basic principle remains the same.
A Total Knee Replacement is basically a re-surfacing of the joint surfaces. Figure 3a shows a side view X-ray of a knee with degeneration. Small amounts of bone on the rounded end of the thigh bone (femur) and the top of the shin bone (tibia) are removed along with the worn joint surfaces (Figure 3b). A metal (Cobalt-Chromium) cap is then fitted to the end of the femur to form a new bearing surface. To the tibia a metal tray that holds a plastic component (Polyethylene) is affixed. Both of the metal pieces are initially held in place by "press fit" with additional screws in the tibial component. These pieces are coated with a special surface and calcium crystals that stimulates your own bone to grow into it to hold them securely in place. Figure 3c shows a knee with the components in place (this is a different patient and the patella was NOT replaced). The polyethylene (plastic) is between the two metal pieces and does not show up on X-ray.
Most of our patients do not need anything done to the kneecap (patella) which articulates with (forms a joint with) the front of the femur. Your normal kneecap forms a joint with a groove in the surface of the metal component on the femur (thigh bone). If we find the surface of the kneecap is degenerated, we can remove a small amount of the bone along with the joint surface, and replace it with a plastic "button". This button is held in place with a special cement. Where possible we attempt to leave the patient's own kneecap in place.
Patients undergoing joint replacement are admitted to the hospital the evening prior to surgery. Anyone with medical conditions will be evaluated prior to admission by the medical doctors on staff so they will be familiar with your history. These physicians are available 24 hours a day during your hospital stay to take care of any medical problems that may arise. Patients who wish to pre-donate their own blood for possible transfusions must arrange this a few weeks in advance with the Blood Bank.
Surgery is done under general anesthesia (going to sleep) or with a spinal block and sedation. You will generally be down in surgery approximately 3 hours, with the actual operation taking roughly one hour. The remainder of the time is spent preparing for surgery, administering and recovering from anesthesia.
Physiotherapy will begin the first day after surgery to get you walking and moving the knee. From the second day you will be able to get out of bed with a walker. It is important to work diligently with the physio while in the hospital to get the best result out of your knee. After going home it will be very important to do exercises daily to maximize the function of your knee. The total time in the hospital will be 7-9 days. Most patients go home, although some go to a rehabilitation facility for an additional week or so. Most people leave the hospital walking with the aid of a single walking stick.
In addition to relief of pain, a major goal of Knee Replacement surgery is to improve mobility and activities. After 3 months, many patients are able to play golf, bowls and doubles tennis. Patients are encouraged to remain active, and most find an improvement in the quality of life
Joint replacement is an extremely successful procedure for alleviating joint pain and restoring quality of life. Generally 95% of patients are significantly improved in terms of pain relief and activities. While these are extremely good results, no surgery is perfect. With any operation a small percentage of people will either not improve, or could even be made worse.
Despite surgery under strict sterile conditions, infection is a potential complication of all surgical procedures. Infections can be classified as superficial or deep:
Following surgery to the legs blood clots can form in the deep veins of the calf or thigh (Deep Vein Thrombosis). As this can be a common occurrence with Knee Replacement surgery, precautions are taken in all of our patients. These precautions consistent of elastic stockings to increase blood flow and medicines to thin the blood. All patients are given Ultrasound examinations to check for this condition while in the hospital.
A very rare complication, known as a Pulmonary Embolism, occurs if one of these clots breaks free and travels to the lungs. This can be life threatening, but again is very rare. These most often come from blood clots in the thigh. The incidence of blood clots in the thigh is only 0.66% in Dr. Cross' patients, with the incidence of Pulmonary Embolus being much lower.
It requires hard work in physio on your part after surgery to maximize the range of motion you will ultimately have in your knee. Occasionally the knee can become stiff due to excess scar formation (Arthrofibrosis). This may require alter surgery to remove the deep scar tissue.
Like any mechanical device, the components in Knee Replacement will not last forever. Total Knee Replacement has been performed for over 30 years. During that time many studies have been performed to determine what works and what doesn't work. These findings have enabled many refinements to be made in the procedure as well as advances in the materials that are used. Currently we expect to get an average of 15 years from a TKR before it needs to be replaced. Some may last longer, but some also can fail much earlier, particularly if any problems such as infection develop. These failures would require further surgery, and generally the revised joints do not do as well as the first. Factors that have been found to speed up the wear of TKR's are young age, increased activity and obesity. TKR is not usually appropriate in patients under 55-60 years of age due to higher wear and the possible need for multiple revisions in their lifetime.
All knee replacements are performed through an incision in the front of the knee. The first priority after surgery is to ensure the wounds heal properly. Delayed healing can be seen in patients with diseases such as Rheumatoid Arthritis and Diabetes or patients who have been taking steroids for any reason. Any problems with wound healing may increase the risk of infection.
Haemarthrosis is bleeding within the joint. Drains are normally used to help remove the blood from the joint in all of our patients. Even with this occasionally it cause problems with delayed recovery and joint stiffness. It usually responds to ice and physiotherapy.
Any time an incision is made in the skin some small nerves in the skin will be cut. This can result in areas of numbness, although this may only be temporary. Occasionally these nerves can become painful and sensitive. This typically improves with time as the scar heals.
REFLEX SYMPATHETIC DYSTROPHY
This is a poorly understood condition which can result after any surgery. It results in pain in the effected extremity with swelling, stiffness and sweating. Over activity of the sympathetic nervous system is felt to be the cause. This can be a difficult condition to treat, but is uncommon.