The
illustration above shows the knee during several stages of knee replacement.
Arthritis of the knees
can be mechanical (osteoarthritis) in which the surfaces of the knee gradually
"wear out". This may be due to either old age, angular deformity, or old
fractures. Systemic arthritis such as rheumatoid arthritis or gout affects
the synovium (the membrane tissue in the joint that normally lubricates
the joint), becomes pathologic and the surface of the joint is destroyed.
In either case when
the surface of the joint is worn away, at a certain point in time walking
and activities of daily living become very difficult. Standardized treatment
such as weight loss, anti-inflammatory medication, braces, orthotics,
steroid injections, physical therapy, etc. are all tried and if effective
that is fine.
In many cases, however,
despite the above non-surgical treatments, functional limitations persist.
Most people who are considering knee replacement are limited to walking
less than three to six blocks, or less than 15 to 20 minutes. They have
difficult time getting up out of a chair. They have rest pain. They are
taking anti-inflammatory medication and/or pain medicine on a regular
basis and the pain is generally progressive.
It is important to
realize that a knee "replacement" is actually just a "resurfacing" of
the knee joint. The femur or thigh bone is covered with a metal covering
and plastic is placed on the tibia so that instead of irregular arthritic
surfaces, one has metal and plastic articulating which produces a smooth
non-patent surface. In most cases the undersurface of the knee cap is
also replaced with a plastic surface so that this articulates with the
femoral surface.
Knee replacements
have been done since the early 1970's and our most recent designs appear
to have 85% to 90% survival at twenty years. Knee replacement in 1998
are more successful than hip replacements with a lower incidence of revision.
The actual procedure
involving knee replacement involves either general or epidural anesthesia
with a four to six day hospitalization. The surgery itself takes between
1-1/2 and 2-1/2 hours. In most cases patients donate two units of autologous
blood to be used in the postoperative period. Weight-bearing begins immediately
the first postoperative day. Patients usually use a walker for a period
of one to two weeks, going to crutches and then a cane. People are off
all walking aids anywhere from three weeks to two months.
Success rates in
knee replacements are approximately 90% with 10% not doing as well. This
can be due to either stiffness or ache or swelling in and about the knee.
The most significant complications, aside from general medical complications
(heart and lung) involve infection of the prosthesis. If this occurs,
in some cases the prosthesis can be saved and the patient taken back to
the operating room, the knee irrigated with antibiotic irrigation and
then be on antibiotics. In some cases if this does not respond, then the
entire prosthesis must be taken out and antibodies given for six weeks
and then another attempt at re-implantation of the of the prosthesis must
occur. In an extremely small percentage of cases, conceivably if the infection
could not be controlled, then one is left a knee fusion in which the femur
and tibia are fused in one bone.
Activities after
knee replacement that should produce no difficulty are simple walking,
bicycling, golfing, swimming. The prosthesis is not designed form impact
loading sports such as skiing, basketball, racquetball. People have been
know to play doubles tennis with bilateral knee replacements.
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