KNEE REPLACEMENT SURGERY

SAIMA IBRAHIM
(feedback@pgeconomist.com)

Feb 14 - 20, 2011

Total knee replacement (TKR), also referred to as total knee arthroplasty (TKA), is a surgical procedure where worn, diseased, or damaged surfaces of a knee joint are removed and replaced with artificial surfaces. Materials used for resurfacing of the joint are not only strong and durable but also optimal for joint function as they produce as little friction as possible.

A total knee replacement surgery replaces your diseased knee joint with a synthetic implant and eliminates the damaged weight-bearing surfaces that are causing pain. A partial knee replacement involves an implant in just one compartment of the knee, retaining any undamaged parts. While there are non-surgical and surgical interventions short of knee replacement, which will often provide temporary relief, the long-term resolution to most knee degeneration will be joint replacement.

Overall, there are two main benefits to be gained from knee replacement surgery:

(1) Elimination of pain and (2) Improved range of motion. Of all possible surgical interventions, total knee replacement offers the greatest quality of life improvement. The procedure has a high rate of success.

The "artificial joint or prosthesis" generally has two components, one made of metal, which is usually cobalt-chrome or titanium. The other component is a plastic material called polyethylene.

The procedure has been proven to help individuals return to moderately challenging activities such as golf, bicycling, and swimming. Total knees are not designed for jogging, or sports like tennis and skiing (although there certainly are people with total knee replacements that participate in such sports). The general goal of total knee replacement is designed to provide painless and unlimited standing, sitting, walking, and other normal activities of daily living.

KNEE REPLACEMENT COMPONENTS

The knee is located at the juncture of three bones, the femur, the tibia, and the patella. The femur (the upper leg bone) and the tibia (the shinbone) are connected by the anterior and posterior cruciate ligaments. The joint is cushioned by the meniscus, a tough cartilage material, during movement. The patella (or kneecap) is a small bone, encased in tendons that glides up and down in the groove on the top of the femur when the knee is flexed and extended.

Degeneration of the joint can occur as a result of trauma or from wear and tear over time. Whatever the cause of the degeneration, it ultimately means that the patient's knee will wear down to the point that it causes substantial pain and limits meaningful motion.

The lower part of the replacement knee joint is comprised of a flat metal plate and stem that your surgeon will implant in the tibial bone. This tibial tray can be either cobalt chrome alloy or titanium alloy. It can be fixed by either cement or bone "in-growth".

Next, a polyethylene insert is clipped into the tibial tray to serve as the new knee-bearing surface. The upper part of the replacement knee joint consists of a contoured metal implant that fits around the lower end of the thighbone (femur). The inner surface can be fixed to the cut bone surfaces by the surgeon's choice of bone in-growth or bone cement. The outer surface of the contoured metal shield is shaped to allow the kneecap (patella) to slide up and down in its groove. The surgeon may choose to retain the natural kneecap or re-surface it. In this case, a polyethylene button will be cemented in place.

TOTAL KNEE REPLACEMENT IMPLANTS

A diagnosis of advanced osteoarthritis of the knee will indicate the need for total replacement of the knee joint. There are several design options the surgeon might choose from that would help you return to an active enjoyable life.

* Fixed bearing
* Mobile bearing
* Posterior Cruciate Ligament Retaining or Substituting

PARTIAL KNEE RESURFACING

Partial Knee Resurfacing is an innovative procedure designed to provide quicker recovery and improved surgical outcome for patients with osteoarthritis in only one part of the knee. By selectively targeting the portion of the knee that has become damaged by osteoarthritis, surgeons can isolate and resurface only the arthritic portion of the knee without compromising the healthy bone and tissue surrounding it. In the situation where only one compartment of the knee is affected, usually the medial compartment, the surgeon might suggest resurfacing or partially replacing damaged knee components. Preserving healthy bone stock is especially important to younger and more active individuals.

* Uni-compartmental or Partial Knee Replacement
* Uni-compartmental Inlay Knee Replacement
* Uni-compartmental Onlay Knee Replacement
* Knee Inter-positional Device
* Bi-Compartmental Partial Knee Replacement

DIFFERENT TYPES OF KNEE REPLACEMENTS

Broadly speaking, there are four basic categories of knee replacements depending on the degree of mechanical stability provided by the design of the artificial knee:

* Non-constrained
* Semi-constrained
* Constrained or hinged
* Uni-condylar

The highly successful non-constrained implant is the most common type of artificial knee. It is termed non-constrained because the artificial components inserted into the knee are not linked to each other and have no stability built into the system. It relies on the person's own ligaments and muscles for stability. This is the key feature of this group of artificial implants helping to maintain the stability of the knee.

The semi-constrained implant is a device that provides increasing stability for the knee. This type of artificial knee has some stability built into it. It is used if the surgeon needs to remove all of the inner knee ligaments, or if the surgeon feels the new knee will be more stable with this type of implant.

Constraint or hinged variety implants are rarely used as a first choice of surgical options. In this case, the two components of the knee joint are linked together with a hinged mechanism. This type of knee replacement is used when the knee is highly unstable and the person's ligaments will not be able to support the other type of knee replacements. It is useful in the treatment of severely damaged knees particularly in very elderly people undergoing a revision replacement procedure. The disadvantage of this type of knee joint is that it is not expected to last as long as the other types.

A unicondylar knee replacement replaces only half of the knee joint. It is performed if the damage is limited to one side of the joint only with the remaining part of the knee joint being relatively spared. However, even with only half of the joint destroyed, many surgeons prefer doing a total knee replacement believing this is a better procedure than the half-knee (uni-condylar) replacement.

COMPLICATIONS OF KNEE REPLACEMENT SURGERY

Unfortunately, even the most minor of surgical operations carries some risk of complications occurring. Knee replacement surgery is very successful, and complications are relatively uncommon, considering the complexity of the procedure. The most common complication is blood clots in the legs. The most serious complication is infection.

Blood clots in the veins of the legs are the most common complication of knee replacement surgery. As long as the clots remain in the legs, they are a relatively minor problem. Occasionally, they dislodge and travel through the heart to the lungs (pulmonary embolism). This is a potentially serious problem, since (very rarely) death can result from embolism. The chances of this are one out of several hundred. The internist will prescribe Coumadin (warfarin), heparin or Lovenox (blood thinning drugs) to help prevent clots from forming after your surgery. Additionally, compressive calf pumps are used and leg exercises are encouraged to prevent blood clots. Blood clots can occur despite all these precautions. They are usually not dangerous if appropriately treated, but may delay your discharge from the hospital for two or three days.

Infection: The risk of an infection in first-time knee replacement is currently reported as being about 0.5 per cent. The risk of infection after joint replacement is much greater than with most other operations, unless special precautions are taken. Since bacteria can enter the open wound at the time of the surgery in a regular operating room, it will be operated in a laminar flow operating room in which special filters provide clean air, free of most bacteria. In addition, the surgeon and assistants wear a sterile space suit. The suit encloses the entire head and body, and includes a sterile facemask. Antibiotics given to you before, during, and after the operation further help to lower the rate of infection.

The risk of infection in the weeks after the operation is increased if you have rheumatoid arthritis or diabetes, if you have been taking cortisone for prolonged periods, if the affected joint has had previous infection, or if you have infection anywhere else in your body (teeth, bladder, etc) at the time of surgery. The artificial joint can become infected many years after the operation. The bacteria travel through the blood stream from a source elsewhere in the body such as from an infected wound, or a gall-bladder infection. Even regular dental work can release bacteria into the blood. Infections of the bladder, teeth, prostate, kidneys, etc. should be cleared up by appropriate treatment well before the day of surgery.

Loosening of the prosthesis from the bone is the most important long-term problem. How long the bond will last depends on a number of factors.

How well the surgery is done. This is by far the most important factor. Choose a surgeon who has had a great deal of experience with knee replacement, and preferably one who restricts his practice to joint replacement surgery.

The quality of your bones. The harder your bones are, the better the bond will be, and the longer the replacement will last.

How active you are. Excessive force on the implant can cause the bond to loosen. If you stayed in bed for the rest of your life, the implant will probably never come loose. Activities such as running and heavy lifting should be avoided.

Your weight. You should also keep your weight down because every pound you gain adds three pounds to the force to the knee.

Wound healing can occasionally be a problem after knee replacement. The skin wound over the knee sometimes does not heal completely. Parts of the skin may die after the surgery. This is a major complication, which occurs very rarely. Fat legs are more prone to this complication.

Nerve damage can (rarely) occur with knee replacement. The most common nerve damaged is the nerve to the muscles, which bring the foot up toward the face (the peroneal nerve). The odds of this occurring are probably one in many hundreds. If it does occur, the affected nerve usually recovers after 6 to 12 months. Sensation usually returns to normal within a few months.

Patellar complications can occur. Occasionally the kneecap does not track properly causing it to "jump" as the knee bends. The chance of this occurring is less than one per cent. The plastic part on the patella can wear through. These problems sometimes need reoperation for correction.

Injuries to the arteries of the leg is a remotely possible but serious complication. The major arteries of the leg lie just behind the knee joint. Arterial injury can usually be repaired by a vascular surgeon. If not, you could even lose your leg. The chance of this occurring is extremely small.

Loss of knee motion: It is difficult to regain bending motion that has been lost for many years and if the knee only bends 90 degrees before the operation, it is unlikely to bend much more after the operation. For unexplained reasons, some patients form excessive scar tissue in the knee after surgery, resulting in diminished bending of the knee (a condition called arthrofibrosis). It is impossible to predict ahead of time which patients might develop arthrofibrosis.

Fracture of the knee bones rarely occurs during knee replacement. Fractures can also occur later from any trauma such as falling down stairs, and (rarely) during manipulation for arthrofibrosis.

Bleeding complications. Sometimes bleeding can occur into the wound several days after surgery ("hematoma formation") as a result of the use of blood thinners. If it is excessive, it may require re-opening the wound under anesthesia to let the blood out. Occasionally the blood thinners may cause bleeding into the urine (or elsewhere), but this is usually temporary, and not of serious consequence.

Anesthetic complications can occur, and very rarely even death can occur from the anesthesia. Your anesthesiologist will see you before surgery and explain the risks involved.

Allergy to the metal parts of the implant has occasionally been reported. People who know they have metal allergies should be tested with extracts of the various metal components of the implant prior to surgery. Allergy to the plastic parts has never been reported. Small particles of plastic or metal from the implant may cause a reaction in the bone but this is not a true allergy.

Complications from Blood Transfusions. The risks of getting AIDS from screened, banked blood is thought to be in the range of 1 in 250,000 units transfused. The risk of Hepatitis B is estimated to be approximately 1 in 550 units, and Hepatitis C is 1 in 100. It is not known if the risk of disease transmission from directed blood is lower than the risk from ordinary banked blood. The risk of an allergic reaction (hives) is 1 in 500. The risk of a Hemolytic Transfusion Reaction is 1 in 10,000. The risk of a Fatal Hemolytic Transfusion Reaction is 1 in 100,000.

Fat Embolism. Fat from the bone marrow can get into the circulation and cause lung or neurological symptoms. This is a very rare complication.

Numbness around part of the wound is common and permanent. Never apply hot packs to the area since you could burn the skin.

Other minor complications can rarely occur. You should keep in mind that the chances of any significant complication are very small.