Knee replacement surgery is a surgical procedure designed to replace the
damaged load-bearing surfaces of the knee joint. The most common cause of this
damage is osteoarthritis.
The main symptom of osteoarthritis is pain. Pain that starts to limit people's
day-to-day activities, limit their walking distance, and eventually pain at
night even when turning over in bed. It can wake them up and affect their sleep,
such that eventually significantly affects the quality of their life and
limits their day-to-day activities.
Knee replacement surgery is done under anaesthetic and that can be either a
general anaesthetic where the patient's asleep, or a spinal anaesthetic where a
patient can be awake and may then have some sedation. The procedure takes
about an hour and a half in total to undertake, and most patients are in
hospital three to four days.
So to give you an idea of what a knee replacement actually means in practice
from a surgical point of view. This is a model of a normal knee joint, this being
the front patella, the femur, and the tibia. Now a knee replacement isn't
actually replacing the entire joint but it's actually a resurfacing operation. So
if we take this model of a knee replacement here you can see that if I
remove the component, the knee joint is largely there, but the surfaces - the
arthritic surfaces - have been removed and then resurfaced with either metal as you
can see here on the femoral side, or a combination of metal and plastic on the
tibial side, and those are replaced into the knee to cover the worn-out surfaces.
The knee is then balance nicely so that they can move in as normal a way as
possible, without causing the arthritic pain.
A knee replacement itself is made of a metal alloy, which is combination of
metals, and there's a plastic bearing.This is called ultra high molecular
weight polyethylene, plastic for short. It's a very wear-resistant
material. Because part of the prosthesis is metal, going through airports
for example can set off the alarms. Having said that millions of people have
hip and knee replacements so most airport authorities are very used to people
walking through with joint replacements.
The benefits of knee replacement surgery are to alleviate pain and improve
function, and to give you an example of this a lot of my patients might play
golf and they start to become limited in their ability to do so. Instead of
playing 18 holes they tend to play nine holes and then start using a buggy
because their knee is too painful to walk any distance. Now for most of my
patients after knee replacement surgery, they are usually back on the golf course
by about 12 weeks post-surgery, and continue to improve for a year
afterwards, so the outcomes are generally very good. Likewise some of my patients
are more active, like to play doubles tennis or even ski, and they're enabled
to do say following their knee replacement surgery.
The timing of knee replacement surgery is actually very individual, very much
depends on how much that person's knee pain is limiting their quality of life
and how much the pain is affecting them. Some people may cope very well with a
degree of pain because their activities are very limited. Other people are very
active and have high demands, and we perhaps move to knee replacement surgery
a little earlier, but the main indication is to alleviate arthritic pain.
There are risks to knee surgery but fortunately they're very
small. The main risks include infection, thrombosis, stiffness, damage to
nerves and vessels and persistent pain can be a problem in a small percentage
of people. Having said that the risks are actually very small, for instance the
risk of infection is less than 1%. The main problem we actually see is
stiffness, and people have to work very hard to regain range of movement and
function after their surgical procedure, and that involves extensive
physiotherapy, but the outcomes are still on the whole very good.
Most patients who have knee replacement surgery are in hospital for three or four
days. If they were to have their knee replacement in the morning, we would
expect that the physiotherapist would be getting them out of bed and start
walking that afternoon. That has changed a lot over the last 10 years
such that 10 years ago the average in-patients day was 10 to 11 days and
now it's 3 to 4 days on average. So our aim is to mobilise people quickly.
The advantage of that is that it helps their rehabilitation but also reduces
risks of things such as deep vein thrombosis.
One can't say how long an individual knee replacement may last but we can
refer to long-term follow-up studies to give us a guide as to how long it
will do so. For instance a lot of big studies now show that at 10 years, 97%
of knee placements are still working satisfactorily, and at 20 years, almost
90%. There are 30 year results although they're relatively small but suffice to
say we can assume that most knee replacements will last between 20 and 30 years.