Are there any restrictions as to who can be a candidate for knee replacement surgery?
Basically no. However, patients do need to be 'cleared' by their
medical doctors that they are acceptable candidates for the surgical procedure.
This includes an evaluation of their overall health status, and a cardiac
work-up when appropriate. Other than that, there is no upper or lower age limits
for knee replacement surgery. As long as the pathology is present and the
patient is motivated, they are appropriate candidates for knee replacement surgery.
Are the actual knee replacement parts selected based on gender?
No. There really is no such thing as female or male knee
replacements -- that theory has been debunked. Knee replacements are based on
size. Small knee replacements are placed in patients of small stature; larger
knee replacements are placed in patients of larger stature.
Does daily exercise prolong the need for knee replacement?
Unfortunately, exercise does not prolong the need for knee
replacement surgery. Regular exercise, however, does play a very important role
in the management of arthritis. Because part of the arthritic process involves
the formation of bone spurs and subsequent loss of motion, exercise is
imperative to maintaining joint range of motion. Joint replacement surgery can
reliably relieve pain, but it cannot reliably restore range of motion. The
mantra is that the best determinant of post-operative range of motion is
pre-operative range of motion.
Is infection a big concern with knee replacement surgery?
No. The infection rate on a primary total knee replacement,
depending on which studies are cited, is between 0.4 and 0.8%. The infection
rate on revisions is a little higher because the surgical incision is made
through scar tissue from the first surgery. To keep these rates this low,
patients receive an intravenous antibiotic within an hour before the incision,
then for 24 hours after the surgery. Many of the infections that do occur are in
immunocompromised patients (such as patients with rheumatoid arthritis). These
patients are typically given more potent antibiotics and for a slightly longer
length of time. Another option for these patients is to place the antibiotics in
the cementing material used in the knee joint surgery so that it can leach out
over time in the joint to help control any local infection.
Once you have a knee replacement, are there any restrictions to activities?
There aren't many. Most doctors might prefer that their patients
are not too overly aggressive with athletic choices -- such as mogul skiing --
but that's about it.
How long do knee replacements last?
This is an excellent question. The results of early knee designs
were limited due to errors in the sterilization techniques for the polyethylene
liners (the plastic that resides between the metal resurfacing components).
These liners were originally sterilized with radiation in room air. This led to
the formation of free radicals, which in turn weakened the plastic components.
As a result, the plastic tended to fail by delamination, or splitting apart.
Since the discovery of these errors, however, the manufacturing
errors have been addressed. The polyethylene is now irradiated either in a
vacuum or in gas plasma, both methods removing oxygen from environment. As a
result, polyethylene liners are being produced with a minimum of free radical
formation. The ultimate result of this is that in lab wear simulator studies,
the plastic liners are lasting upwards of 25 years. Whether this pans out to 25
years in the human body remains to be seen, but the early results are
encouraging. Some companies are even infusing antioxidants, such as vitamin E,
into the polyethylene, which have shown even better results in laboratory studies.
That being said, there are numerous determinants of longevity of knee replacement surgery.
- How well the joint replacement is put in. Proper alignment of the
implant avoids abnormal loading of the joint, thereby allowing for natural
joint motion. This ultimately prevents accelerated polyethylene wear and
early failure.
- Activity level. Like any other mechanical device, like a car or a
doorknob, a joint replacement has a finite lifespan. Thus, also like a car
or a doorknob, the more you use it, the sooner it will wear out.
- Obesity. The data is conflicting on this, but the most recent evidence
suggests that obesity can lead to accelerated failure of joint implants.
Joseph George Jr., MD, is an orthopaedic surgeon, Lorain Orthopaedics, Cleveland Clinic
Lorain Family Health and Surgery Center
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