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A Patient's Guide
to
Artificial Knee Replacement
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Disclaimer
Introduction
A painful knee can severely affect your ability to lead a full active
life. Over the last twenty five years, major advancements in artificial
knee replacement have improved the outcome of the surgery greatly.
Artificial knee replacement surgery is becoming more and more common as
the population of the world begins to age.
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Causes
There are many conditions that can result in degeneration of the knee joint.
Osteoarthritis is the most common cause that patients need to undergo knee
replacement surgery. This condition is commonly referred to as "wear and
tear arthritis". Osteoarthritis can occur with no previous history of
injury to the knee joint - the knee simply "wears out". There may be a
genetic tendency in some people that increases their chances of developing
osteoarthritis.
The major problem in osteoarthritis is that the
cartilage (the articular
cartilage) on the surface of the bone inside the joint
wears away. This results in bone
rubbing against bone, the slick protective surface of the articular
cartilage is absent. This causes pain.
Abnormalities of knee joint function resulting from fractures of the
knee, torn cartilages and torn ligaments can lead to degeneration many
years after the injury. The mechanical abnormality leads to excessive wear
and tear - just like the out of balance tire that wears out too soon on
your car. For more information of these injuries, see
A Patient's Guide to Knee Problems
Symptoms
The symptoms of a degenerative knee joint usually begin as pain while
bearing weight on the affected knee. You may limp and the knee may become
swollen with fluid. The degeneration can lead to a reduction in the range
of motion of the affected knee - the knee bends less than normal and may
lose the ability to completely straighten out. Bone spurs will usually
develop and can be seen on x-ray. Finally, as the condition becomes worse,
the pain may be present all the time and may even keep you awake at night.
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Diagnosis
The diagnosis of a degenerative knee starts with a complete history and
physical examination by your doctor. X-rays will be required to determine
the extent of the degenerative process and may suggest a cause for the
degeneration. Other tests may be required if there is reason to believe
that other conditions are contributing to the degenerative process. Blood
tests may be required to rule out systemic arthritis (such as Rheumatoid
Arthritis) or infection in the knee.
Medical Treatment
Not all degenerative knee conditions require a knee replacement as the
initial treatment. Your doctor may suggest several alternative treatments
to put off the decision for replacing the knee as long as possible. Using
a cane may help alleviate some of your pain and allow you to walk more
comfortably. Anti-inflammatory medications may reduce the inflammation
from the arthritis and reduce your pain.
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Surgery
Most degenerative problems will finally require replacement of the
painful knee with an artificial knee replacement. The decision to proceed
with surgery should be made jointly by you and your doctor only after you
feel that you understand as much about the procedure as possible.
Once the decision to proceed with surgery is made, there are several
things that may need to be done. Your orthopedic surgeon may suggest a
complete physical examination by your medical or family doctor. This is to
ensure that you are in the best possible condition to undergo the
operation. You may also need to spend time with the Physical Therapist who
will be managing your rehabilitation after the surgery. The therapist will
be able to begin the teaching process before the surgery to ensure that
you are ready for the rehabilitation afterwards.
One purpose of the preoperative visit is to record a baseline of
information. This includes your measurements of your current pain levels,
functional abilities, the presence of swelling, and the available movement
and strength of each knee.
A second purpose of the preoperative visit is to prepare you for your
upcoming surgery. You’ll begin to practice some of the exercises you’ll
use just after surgery. You’ll also be trained in the use of either a
walker or crutches. Whether the surgeon used a cemented or noncemented
approach will determine how much weight you’ll be able to apply through
your foot while walking Finally, an assessment will be made of any needs
you’ll have at home once you’re released from the hospital.
Finally, you may be asked to donate some of your own blood before the
operation. This blood can be donated 3-5 weeks before the operation and
your body will make new blood cells to replace the loss. At the time of
the operation, you will receive your own blood back from the blood bank in
case you need to have a blood transfusion.
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The Artificial Knee
There are two major types of artificial knee replacements:
- Cemented Prosthesis
- Uncemented Prosthesis
Both are still widely used. In many cases a combination of the two
types are used. The patellar(kneecap) portion of the prosthesis is
commonly cemented into place. The choice to use a cemented or uncemented
artificial knee is usually made by the surgeon based on your age, your
lifestyle, and the surgeons experience.
Each prosthesis is made up of four parts:
- The tibial component (bottom portion) replaces the top of the lower
bone, the tibia.
- The femoral component (top portion) replaces the two femoral
condyles and the groove where the patella runs.
- The patellar component (kneecap portion) replaces the joint surface
on the botton of the patella that rubs against the femur in the femoral
groove.
The femoral component is made of
metal. The tibial component is
usually made up of two parts - a metal tray that is attached directly to
the bone and a plastic spacer that provides the bearing surface. The
plastic used is very tough and very slick - (so slick and tough that you
can ice skate on a sheet of the plastic with out much damage to the
material).
A cemented prosthesis is held in
place by a type of epoxy cement that attaches the metal to the bone. An
uncemented prosthesis has a fine
mesh of holes on the surface that allows bone to grow into the mesh and
attach the prosthesis to the bone.
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The Operation
You can download a surgical
animation showing the steps involved in replacing a diseased knee with
an artificial knee. The steps involved in replacing the knee begin with
making an incision on the front of the knee to allow access to the knee
joint. There are several different approaches used to make the incision,
usually based on the surgeon's training and preferences.
- Shaping the Distal Femoral Bone
- Once the knee joint is entered, a special cutting jig is placed on
the end of the femur. This jig is used to make sure that the bone is cut
in the proper alignment to the leg's original angles - even if the
arthritis has made you bowlegged or knock-kneed. The jig is used to cut
several pieces of bone from the distal femur so that the artificial knee
can replace the worn surfaces with a metal surface.
- Preparing the Tibial Bone
- Attention is then turned towards the lower bone, the tibia. The top
of the tibia is cut using another of jig that ensures the alignment is
satisfactory.
- Preparing the Patella
- The undersurface of the patella is removed.
- Placing the Femoral Component
- The metal femoral component is then placed on the femur. In the
uncemented variety of femoral component, the prosthesis is held on the
end of the bone by the fact that the end of the bone is tapered, and the
metal prosthesis is cut so that it matches the taper almost exactly.
Driving the metal component onto the end of the bone holds the component
in place by friction. In the cemented variety, an epoxy cement is used
to attach the metal prosthesis to the bone.
- Placing the Tibial Component
(metal tray)
- The metal tray that will hold the plastic spacer is attached to the
top of the tibia. The metal tray is either cemented into place, or held
with screws if the component is of the uncemented variety. The screws
are primarily used to hold the tibial tray in place until the bone grows
into the porous coating. (The screws remain in place and are not
removed.)
- Placing the Tibial Component
(plastic spacer)
- The plastic spacer is then attached to the metal tray of the tibial
component. If this component should wear out while the rest of the
artificial knee is sound, it can be replaced - a so called retread.
- Placing the Patellar Component
- The patella button is usually cemented into place behind the
patella.
- The Completed Knee Replacement
- X-ray from the side
- X-ray from the front
Rehabilitation
While you are in the hospital:
- Range of Motion
- Ambulation
- Exercises
The physical therapist will schedule your first inpatient visit shortly
after surgery. Treatment will address the range of motion in the knee.
Gentle movement will be used to begin to help you regain both the bending
and straightening of the knee. If you are using a CPM (continuous passive
motion) device, it will be checked for alignment and settings. Next,
you’ll go over your exercise regimen. When you are stabilized, your
therapist will assist you up for a short outing using your crutches or
your walker. Treatment will proceed on a one to two time per day basis.
You’ll be on your way home when you can demonstrate a safe ability to get
in and out of bed, walk up to 75 feet with your crutches or walker, get up
and down flight of stairs and access the bathroom. It is also important
that you regain a good muscle contraction of the upper thigh muscle
(quadriceps) and that you gain improved knee range of motion.
After you leave the hospital:
- Home health needs
Once discharged from the hospital, your therapist will likely see you
for in home treatment. This is to ensure you are safe in and about the
home. You should be seen for at least one visit for the safety check and
to review your exercise program. In some cases you may require up to three
visits at home before beginning outpatient physical therapy.
As you progress:
- Outpatient progression
Welcome to outpatient physical therapy. Several key areas will be
addressed. Your therapist may choose one or more modalities such as heat,
ice, or electrical stimulation to help reduce persistent swelling or pain.
Continue to use your walker or crutches. If you had a cemented procedure,
you’ll advance the weight you place through your sore leg as much as you
feel comfortable. If yours was a noncemented procedure, place only the
toes down until you’ve had a follow-up x-ray and your doctor or therapist
directs you to advance the amount of weight through your leg (usually by
the 5th or 6th week postoperatively). Range of motion exercises and
techniques will be used to help you regain full bending and straightening
of the knee. An exercise program will be developed including
strengthening, balance, and endurance, and functional activities. Your
strengthening program will address key muscle groups including the buttock
and hips, thigh, and calf muscles. When you are safe in putting full
weight through the leg, several balance exercises can be chosen to further
stabilize and control the knee. Endurance can be achieved through
stationary biking, lap swimming, and using and upper body ergometer (upper
cycle). Finally, a select group of exercises can be used to simulate
day-to-day activities, like going up and down steps, squatting, raising up
on your toes, and bending down. Specific exercises may then be chosen to
simulate work or hobby demands.
Complications
As with all major surgical procedures, complications can occur. Some of
the most common complications following knee replacement are:
- Thrombophlebitis
- Infection
- Stiffness
- Loosening
This is not intended to be a complete list of the possible
complications, but are the most common.
Thrombophlebitis
Thrombophlebitis, sometimes called Deep Venous Thrombosis(DVT), can
occur after any operation, but is more likely to occur following surgery
on the hip, pelvis, or knee. DVT occurs when the blood in the large veins
of the leg forms blood clots within the veins. This may cause the leg to
swell and become warm to the touch and painful. If the blood clots in the
veins break apart, they can travel to the lung, where they get lodged in
the capillaries of the lung and cut off the blood supply to a portion of
the lung. This is called a pulmonary embolism. (Pulmonary = lung, embolism
= fragment of something traveling through the vascular system). Most
surgeons take preventing DVT very seriously. There are many ways to reduce
the risk of DVT, but probably the most effective is getting you moving as
soon as possible!
Some of the commonly used preventative measures include:
- Pressure stockings to keep the blood in the legs moving
- Medications that thin the blood and prevent blood clots from
forming.
Infection
Infection can be a very serious complication following an artificial
joint. The chance of getting an infection following artificial knee
replacement is probably somewhere around 1%. Some infections may show up
very early - before you leave the hospital. Others may not become apparent
for months, or even years, after the operation. Infection can spread into
the artificial joint from other infected areas. Your surgeon may want to
make sure that you take antibiotics when you have dental work, or surgical
procedures on your bladder and colon to reduce the risk of spreading germs
to the joint.
Stiffness
In some cases, the ability to bend the knee does not return to normal
after an artificial knee replacement. Many orthopedic surgeons are now
using a machine known as a CPM machine (Constant Passive Motion)
immediately after surgery to try and increase the range of motion
following artificial knee replacement. Other orthopedic surgeons rely on
physical therapy beginning immediately after the surgery to regain the
motion. It is not clear which is the best approach. Both approaches have
benefits and risks, and the choice is usually made by the surgeon based on
his experience and preferences.
To be able to use the leg effectively to rise from a chair, the knee
must bend at least to 90 degrees. A desirable range of motion should be
greater than 110 degrees. Balancing of the ligaments and soft tissues
(during surgery) is the most important determining factor in regaining an
adequate range of motion following knee replacement, but sometimes
increasing scarring after surgery can lead to an increasingly stiff knee.
If this occurs, your surgeon may recommend taking you back to the
operating room, placing you under anesthesia once again, and forcefully
manipulating the knee to regain motion. Basically, this allows the surgeon
to breakup and stretch the scar tissue without you feeling it. The goal is
to increase the motion in the knee without injuring the joint.
Loosening
The major reason that artificial joints eventually fail continues to be
a process of loosening where the metal or cement meets the bone. There
have been great advances in extending how long an artificial joint will
last, but most will eventually loosen and require a revision. Hopefully,
you can expect 12-15 years of service from an artificial knee, but in some
cases the knee will loosen earlier than that. A loose prosthesis is a
problem because it causes pain. Once the pain becomes unbearable, another
operation will probably be required to revise the knee replacement.
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