Total Knee Replacement
A person with advanced arthritis of the knee joint resulting in
severe pain is a candidate for total knee replacement. When knee pain
interferes with daily activity, walking tolerance, and independence, it is time
to consider this alternative. Many individuals choose a total knee
replacement so they can maintain normal activities of daily living.
ARTHRITIS:
The end of the femur and tibia form the knee joint. They are covered
with a thin, smooth layer of cartilage. In the knee hyaline (surface) and
meniscal cartilage cushion the joint and absorb shock. Normally this
cartilage is lubricated by a few drops of synovial fluid. The lining of
the joint which produces this fluid is synovium. With cartilage debris
from wear, the synovium proliferates and produces excess fluid. Cartilage
has poor healing capabilities; as it wears away, bone becomes exposed.
Bone surfaces rubbing against each other cause pain, while cartilage has no
sensation. There are no predictable or satisfactory methods for reversing
the damage of arthritis. When nonsurgical alternatives cannot bring a suitable
level of relief, total joint replacement is a realistic alternative.
PROSTHESIS APPEARANCE:
A total joint replacement consists of three pieces. These are made of rugged
polyethylene (high density plastic) and alloy metals. These components resurface the three bones which comprise the knee joint (femur, tibia and patella).
The femoral component (the end of the thigh bone) is made of metal. The
tibial component (the top of the shin bone) has a metal tray with a plastic
insert which mates with the femoral component. The patellar component
(kneecap) also has a plastic surface which mates with a groove in the femoral
component. The knee replacement appears and functions much like a normal knee.
TOTAL JOINT FIXATION:
There are two methods of securing the prosthesis to bone. One relies on
an in-growth of the patient's bone to anchor the device, and the other uses
"cement". The cement is a plastic polymer that serves as an
adhesive grout. The method of fixation utilized is usually based on the
patient's age and the quality and condition
of the patient's bone. The
design of the prosthesis also influences the method of attachment to the bone.
TOTAL KNEE FUNCTION:
Replacement joints come in many different sizes, and are precision engineered
to feel and move as much like a real joint as possible. Most people with an
artificial knee joint are not aware of a difference between the feel of the
implant and their original knee. The knee replacement allows for less bending
than a normal knee. In the knee suitable for replacement, however, the
range of motion is often improved postoperatively. Design changes continue in existing prostheses in an effort to yield better function and longevity.
A well implanted prosthesis, in a compliant patient, usually lasts for many
years. Since many prostheses now used are improved designs, we can only
guess at their longevity. Trauma, wear or loosening may make it necessary
to replace a prosthesis. Revision replacements may have a shorter life expectancy than primary implants. Every effort must be made to prolong the
life of the total knee which is implanted first. A maximum working life of
10-15 years is reasonable, and more is possible. The physical activity
level and patient age are strongly related to the longevity of knee
replacements. The main object of a total knee replacement is relief of
pain. Other goals include the correction of deformity and restoration of
stability. Prosthetic design constraints limit the range of motion to
approximately 0-110º. It should be emphasized that total knee
replacements are not done to allow patients to return to unlimited activities.
Fitness may be maintained by swimming, bicycling, and walking. Golfing and
even skiing in some individuals may be considered, but impact loading such as
running or jumping should be minimized.
CANDIDATES FOR TOTAL KNEE REPLACEMENT
The ideal patient is over sixty years of age. Most are between 60 and 80 years
of age. Younger patients tend to be more active leading to premature loosening
of the replacement. Young age is a relative contraindication to total knee
replacement. Extreme osteoporosis (softening of the bone) is also a
relative contraindication to total knee replacement. In patients with a
significant history of past infection of the knee, total knee replacement is
contraindicated because of the risk of reactivating the infection.
A
patient with recurrent urinary tract infection secondary to chronic kidney
stones, urethral stricture, or other genitourinary problems should have urologic
evaluation prior to total knee replacement.
PRECAUTIONS:
Special precautions against infection are taken before, during and after
surgery. Antibiotics are used routinely peri-operatively. A special
surgical room and techniques for a sterile environment are used during surgery.
Although the risk is very low, the occurrence of late infection can be
catastrophic and may require the removal of the prosthesis. To minimize
the risk of infection, prophylactic antibiotics are given any time dental
manipulation, urinary tract surgery or instrumentation or significant bowel
procedures are performed. Any skin infection should also be treated with
antibiotics as well, since late prosthetic implant infection may be related to
skin infection. There is also a risk of deep vein thrombosis (clot) after
total knee replacement, and patients are generally treated with coumadin from
the day before surgery until two weeks surgery. This substantially reduces the risk of deep venous clot.
HOSPITALIZATION:
Patients are admitted on the day of surgery and hospitalized for 4-7 days.
During the hospital stay, the emphasis is placed on regaining knee motion and
strength, and activities of daily living. The faster patients are able to
return home, the better they often do. If more assistance is required, or
there is no one at home, a week or two in a rehabilitation facility will help in regaining independence to return home. Therapy should continue at home
with daily range of motion exercises and strengthening. This may be aided
by the use of a physical therapist, but in the highly motivated patient, therapy
may be done almost entirely on a home program. Straight leg raising, bending
over the seat of a chair, and maintaining extension over a rolled towel beneath
the ankle, are used with ambulation and functional exercise such as an exercise
bicycle to regain
function.
BLOOD TRANSFUSION:
Transfusions are usually required and we encourage patients to donate their
own blood prior to surgery to minimize the risk of disease transmission. Two
units of blood are usually donated, allowing one week between each unit, and one
additional week between the donation of the second unit and surgery. In
patients who cannot donate blood because of religious convictions or medical
reasons, Erythropoietin (a normal hormone which stimulates blood
production) may be used to encourage blood production before surgery. In
this way, your own blood may be adequate and you may not require transfusion.
There is some added risk of surgery without blood availability. |
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