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Answers
to your questions about knee arthroplasty
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At
Anderson Orthopaedic Institute, we encourage propective patients
to learn as much as possible about their condition and options
before choosing knee arthroplasty. While a knee
replacement can dramaticaly improve the quality of life for a
person with debilitating knee pain, we also recognize that it
is major surgery. To best serve our patients, we usually recommend
total knee replacements and partial knee replacements after other
less invasive treatments have been attempted.
To
further your understanding of knee replacements, we invite you
to read about the evolution of knee arthroplasty, as well as our
answers to the common questions seen on the sidebar.
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Dr. Gerard Engh
Director of
Knee Research
Anderson Orthopaedic Research Institute
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Q.
What historical changes in knee
replacements have helped patients?
Knee replacement
surgery was first performed in the 1960's with hinged implants
that did not work well.
Because
the hinged knee did not permit the natural rotation and bending
of the knee, the implant loosened shortly
after implantation. These early implants also had high infection
rates.
The
first design change that made the most difference to patients
with knee pain was an implant that let the knee rotate.
Called condylar total knee implants, these implants were designed
In the mid 1970s. They
also allowed the ligaments to provide stability, but they
only came in 2 sizes and were solid pieces. Initially,
orthopaedists were cautious about using the new knee implants
because of their experience with hinges, but as good results
were recognized, more surgeons performed the operations.
The next
evolutionary steps were implants that were easier to place and
better instruments that made surgery more reproducible. By the
1990s, knee replacement surgery was widely accepted as an operation
that provided excellent pain relief from arthritis.
The most
recent change is the development of the minimally invasive unicompartmental
knee replacements. These knee replacements, discussed below,
are based on research and development of partial knee replacements;
the development of improved instruments and surgical techniques
in the late 1990s have made this a good alternative for patients
with arthritis limited to one knee compartment.
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Q. What is a total knee replacement and how can it help
me function without pain?
With
arthritis, the cartilage covering the ends of the bone within
the knee joint is badly worn.
Similar
to resurfacing a road full of potholes, a total knee replacement
artificially replaces the worn and arthritic surfaces of the knee
joint. A total knee replacement puts an artificial surface on
all parts of the joint that contact each other as the knee bends.
Using precise instruments, we first remove the damaged cartilage,
along with a very small amount of bone. We then fit a knee implant
to the bone. The implant, made of metal and plastic, provides
an artificial surface that enables a patients to move without
pain.
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Q. What
is a partial knee replacement?
A
partial knee replacement -- also called a unicompartmental knee
replacement -- involves putting an implant on just one side of the
knee, rather than over the entire surface of the knee joint.
Think
of the knee as having three compartments: an inside, outside, and
a front compartment for the kneecap. Most frequently, it is the
inside compartment that becomes arthritic. A unicondylar knee replacement
is done if part of the knee joint is damaged by arthritis and the
other compartments have healthy, normal cartilage at surgery.Due
to developments over the past 5 years, Anderson Clinic physicians
now perform minimally invasive unicompartmental knee replacement,
using smaller incisions.
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Q.
What
is revision total knee arthroplasty?
A third type of
knee replacement is a revision total knee. Currently, about
1 in 10 total knee implants fail over a 10-year period, largely due to
wear-related issues. (This is the reason for AORI's
intense research in this area.) When an implant fails, the prosthesis
should be revised. The revision procedure is more complex than a total
knee replacement. This is because the bone is not as strong when an implant
is removed, and the ligaments supporting the knee may be damaged. In performing
a revision, a special implant is used that addresses these difficulties.
For example, the surgeon can fit a stem inside the canal of the bone to
provide more support for the implant. If a bone is badly damaged, a knee
replacement may require a bone graft to reconstruct the deficient area;
in such circumstances, we discuss this with the patient during the office
visit. One
advantage of a unicompartmental knee replacement is that, if a revision
is needed, the revision procedure is less complex than with a total knee
replacement.
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