Total Knee Replacement (TKR)
The Goals of Total Knee Replacement
Total knee replacement is one of
the most successful of all surgical procedures, and a virtual
medical miracle. Prior to the development of total knee replacement
technology, patients with advanced arthritis of the knee suffered
from chronic pain and loss of functional independence. Following
total knee replacement, more than 90% of patients have no pain, or
only slight pain, and their walking is no longer limited by their
knee. Most patients can live a full and independent life.
The goals of total knee replacement are, in order of
- pain relief
- standing and walking that is not limited by the knee
- improved knee motion
- improved knee strength
Total knee replacement is major surgery, which usually involves
a 3-4 day stay in the hospital and a period of rehabilitation which
takes about 3 months. Our team of Orthopaedic Surgeons and their
clinical team will work with you to guide your recovery, but you are
the most important member of the team! We believe that an informed
patient is the best ally in achieving success with total knee
replacement surgery. Please read this booklet carefully. Share it
with your family and friends. The information here will guide you in
preparing for surgery and it will give you insight into how to
maximize your recovery from knee replacement surgery and enjoy many
years of painless knee function.
Arthritis is a generic condition
indicating inflammation of a joint. Inflammation is the
general response of the body to injury of any type. The signs of
inflammation are pain, swelling, warmth, and sometimes redness.
There are many causes of arthritis. These include a sudden, or
acute, injury such as might occur when playing sports. Acute trauma
is actually the most common cause of arthritis. In most cases,
however, the injury does not cause permanent damage, the
inflammation subsides over a few weeks, and the joint functions
normally for the rest of that person's life. Arthritis can also
develop after many years of certain activities performed over and
over, which can be considered a form of chronic injury.
The most common form of arthritis, which necessitates knee
replacement, is osteoarthritis. In this condition, the
articular cartilage, which is the smooth gliding surface of the
joint, has worn away. This can occur for a number of reasons. If
there is a genetic defect in the quality of the articular cartilage,
then this condition is called primary osteoarthritis.
Primary osteoarthritis may affect all of the articular cartilage in
the body, not just the knees. More frequently, osteoarthritis
affects only a few joints, usually in the legs. In these cases, the
genetic composition of the articular cartilage is normal, but there
is another factor that causes damage to the cartilage in that
specific joint or joints. This is called secondary
The most common causes of osteoarthritis are related to the alignment
of the leg (too bow-legged or too knocked-kneed) and how well the
two halves of the knee joint fit together, which is called congruency.
Similar to the tyres on a car, if the leg is not properly aligned,
then the surfaces of the knee joint will wear unevenly.
Alternatively, if the two sides of the joint do not fit together
properly, they will wear unevenly. In some cases people are born
with imperfect alignment, and in other cases they develop conditions
which result in imperfect alignment of their leg or legs. In other
cases, there may have been a disease or an injury that altered the
alignment or congruency of the joint (such as an infection, a
fracture, or a torn ligament). Increased weight puts more stress on
the joint and over time this can cause damage and contribute to a
wearing out of the cartilage. Exercise or hard work, without any
other factor, does not result in arthritis. Moderate exercise
actually improves the condition of joints.
Another common type of arthritis that can affect the knees is rheumatoid
arthritis. This type of arthritis is caused by dysfunction of
the immune system. Abnormal anti-bodies are produced that get
deposited in the lining tissue of the joints (the synovium). This
causes chronic inflammation and slow destruction of cartilage. All
of the synovial joints of the body may be affected by rheumatoid
arthritis and the level of arthritis is roughly equal on both sides
of the body, i.e., both the right and the left knees, hands, etc
The knee joint includes the end
of the thigh bone (the femur), the top of the leg bone (the
tibia) and the knee cap (the patella). The weight of the
body is transferred through the femur, across the knee joint, and
into the tibia. There are large muscles in the front of the thigh
(the quadriceps) that straighten the knee (extension). The large
muscles in the back of the thigh (the hamstrings) bend the knee
(flexion). The patella functions as an important lever for the
quadriceps muscles, making the muscle more efficient. When you bend
and straighten your knee, the surfaces of the tibia and femur roll
and slide on each other and the patella moves up and down against
the front of the femur. Front and side x-ray views of a normal
knee are shown in Figures 1a and 1b respectively. The thigh
bone (femur) is on the top and the leg bone (tibia) is on the
bottom. The smaller bone in the leg is the fibula. The knee cap
(patella) can be seen in the front of the knee on the side view. The
apparent space between the bones is actually occupied by articular
cartilage and is called the joint space. Cartilage is not dense
enough to be seen on an x-ray.
Fig 3a Fig 3b The knee is a synovial joint. The tissue lining the
joint, called synovium, produces fluid that lubricates and nourishes
the surfaces of the joint. The important internal parts of the knee
include articular cartilage, meniscal cartilage, ligaments, and
tendons. There are two types of cartilage in the knee. Articular
cartilage is specialized tissue that covers the ends of the bones.
Meniscal cartilage is specialized tissue located around the
perimeter of your knee. It helps to distribute the load and provide
some stability as well as lubricate the articular cartilage. There
are several ligaments (strong bands of fibrous tissue which connect
bone to bone) attached to the femur and tibia, which provide
stability to the knee. There are also several tendons, which are
also strong bands of fibrous tissue, but they attach muscle to bone.
It is the force of the quadriceps and hamstring muscles, pulling
through tendons, that move the knee and enable you to walk, sit, get
up from sitting, climb stairs, etc.
Articular cartilage covers the
moving surfaces inside the knee. Articular cartilage is very smooth
and has very low friction. Articular cartilage is the "tread"
inside your knee. Articular cartilage is living tissue, but it has
limited potential for growth and repair. As with all tissue, the
potential for growth and repair of articular cartilage decreases
with age. If the loads on the joint, or on a portion of the joint,
are too high, either because of improper alignment, incongruency,
excessive weight, extreme activities, or a combination of these
factors, articular cartilage will degenerate and be worn away. The
process of articular cartilage degeneration is a source of
inflammation. This can result in pain, swelling and progressive loss
of motion. In advanced arthritis, the articular cartilage has been
completely worn away and the bone of the femur and tibia, and the
femur and patella, come into direct contact. This is generally
accompanied by significant pain, a decrease in motion (stiffness),
muscle weakness, and difficulty walking. The main reason to have
a total knee replacement is because of severe pain that is due to
extensive loss of articular cartilage.
Wear of articular cartilage can be seen on x-rays as a decrease in
the space between the bones. In general, extensive loss of articular
cartilage is accompanied by extensive loss of meniscal cartilage.
When the cartilage is completely worn away, the x-rays show that the
bones are now in direct contact. Loss of articular cartilage
increases the amount of stress on the ends of the bones resulting in
the growth of bone spurs, or osteophytes, at the margins of the
joint. Front and side x-ray views of an arthritic knee are shown in
Figures 2a and 2b respectively. On the front view (Figure
2A), note the absence of space between the bones as indicated by the
arrows. This loss of joint space occurs because the articular
cartilage has worn away. The bone reacts to the loss of cartilage by
making bone spurs (osteophytes). These bone spurs can be seen on the
side view (Figure 2b) as indicated by the arrows.
What is Total
Total knee replacement employs
specially designed components, or prostheses, made of high strength,
biocompatible, metals and plastics, to replace the cartilage
in your knee. The metal that is most commonly used is an alloy of
cobalt, chromium and molybdenum. The plastic is ultra-high molecular
weight polyethylene. These materials have been used in joint
replacement for about 30 years and their behavior in the body is
well-known. The components are very precisely manufactured and the
surfaces are congruent, smooth and highly polished. In this manner,
congruent, smooth, low-friction surfaces are restored to the knee.
In modern total knee replacement surgery, only the worn-out
cartilage surfaces of the joint are replaced. The entire knee is not
actually replaced. The operation is basically a "re-surfacing"
(or "re-tread") procedure. Only a small amount of bone
is removed, the collateral ligaments are left intact, and the
muscles and tendons are left intact. Alignment abnormalities can
usually be corrected during the operation by adjusting the direction
of the cuts of the bones, removing bone spurs (osteophytes), and
lengthening tight ligaments. Front and side views of a knee
following total knee replacement are shown in Figures 3a and 3b
respectively. Note that the smooth surfaces of the joint are
restored. The joint space is now comprised of polyethylene. The
operation only replaces the worn surfaces of the joint. The
ligaments, tendons and muscles are retained.
Total knee replacement is a major surgical procedure. A tourniquet
is usually placed up high around the thigh in order to limit
bleeding during the operation. An incision is made in the front of
the knee. The large quadriceps muscle covering the front of the
femur and knee is moved, temporarily, to one side, in order to
expose the surfaces of the knee joint. Specialized instruments are
used to trim off the worn-out surfaces and shape the ends of the
bones. The femoral component is metallic, and is similar in size and
shape to the end of the femur bone (thigh bone). The tibial
component, which goes on the top of the leg bone (or tibia), may
have a metallic base, but the top surface is always polyethylene.
The undersurface of the knee cap (patella) is cut flat and covered
with another polyethylene component. Since metal covers the surface
of the femur (thigh bone) and polyethylene covers the surfaces of
both the tibia (leg bone) and patella (knee cap), total knee
replacement involves metal-on-plastic articulation.
The components are attached to the bone with a specialized polymer
(polymethylmethacrylate), commonly referred to as "bone cement".
Alternatively, some components have a porous texture on their
under-surface, into which the bone can grow. This method of
attachment is referred to as "porous ingrowth".
Total knee replacement is elective surgery. It is life-enhancing
surgery, not life-saving surgery. The decision to undergo total knee
replacement surgery is yours. It is important that you be aware of
your options, other than total knee replacement surgery. You may
simply decide not to have surgery and live with your arthritic knee.
In this case, you may choose to avoid strenuous and painful
activities. You should, however, adopt some gentle exercise, such as
walking. You may benefit from some moist heat, massage or other
forms of physical therapy. Weight loss can be very helpful in
reducing pain from arthritic knees by reducing the stress, and is
good for your general health as well. There are a number of
medications, both anti-inflammatory medications and pain
medications, that can help you live with arthritis. There are also
medicines that can be injected directly into the knee, such as
cortisone and newer products that improve lubrication.
Unfortunately, the arthritis is progressive in most cases. A cane or
a crutch may be required in order to walk.
to Total Knee Replacement
|The following is a list of
alternatives to total knee replacement surgery you may wish to
There are specialized braces that can be helpful in some cases of
knee arthritis. These braces are designed to create a force which
transfers load from an area of the knee where the cartilage is more
worn, to an area of the knee where the cartilage is less worn. These
braces are helpful in cases where there is still some cartilage
remaining in the knee, and the pressure of the brace causes less
discomfort than the knee arthritis.
There are less invasive surgical procedures available which can be
helpful in some cases. These include arthroscopy. Arthroscopy
requires only small incisions around the knee which allow the
insertion of small instruments, which are about the size of a pen or
pencil. With arthroscopy, degenerated and worn cartilage can be
trimmed and smoothed, which reduces the source of inflammation.
Additionally, the lining of the knee (the synovium), can be trimmed,
and this also decreases inflammation. Patients who have knee
arthroscopy almost always go home the same day. Recovery from
surgery occurs over a couple of weeks. Unfortunately, the benefit of
arthroscopy decreases as the degree of arthritis increases. In
advanced arthritis, arthroscopy is of little value.
It is now possible to transplant articular cartilage from one
location to another. Healthy cartilage, from an area of the knee
that does not bear weight, can be transplanted into another area of
the knee where weight-bearing cartilage has been damaged. Cartilage
transplantation is best for localized areas of damaged cartilage in
an otherwise healthy knee. Unfortunately, in most cases of
osteoarthritis and rheumatoid arthritis, the degeneration and wear
of articular cartilage involves the majority of the joint surfaces.
Cartilage transplantation is not a good option in such cases.
Some cases, where the leg is imperfectly aligned, can be treated by
an osteotomy. An osteotomy is an operation that cuts the bone,
either above or below the knee, and re-aligns the knee to a better
position. This is a bigger operation than an arthroscopy and
patients usually stay 1 or 2 days in the hospital. It takes 6 to 8
weeks for the bone to heal. Physical therapy is usually required to
restore knee motion and strength. Complete recovery takes a number
of months. An osteotomy is a good operation, especially for younger
patients, and those where the leg is clearly not straight and the
cartilage wear is confined to one portion of the knee.
Unfortunately, the success of an osteotomy decreases as the degree
of arthritis increases.
In a few cases, only a portion of the knee joint surfaces have worn
out and need to the replaced. When only a portion of the knee is
replaced, this is called a uni-compartmental arthroplasty. Patients
usually stay 2 or 3 days in the hospital and it takes a couple of
months for the knee to recover. Physical therapy is usually required
to restore knee motion and strength. Unfortunately, in most cases of
arthritis, the joint surfaces are diffusely worn. Uni-compartmental
arthroplasty is, therefore, less commonly performed than total knee
Arthrodesis / Knee Fusion
In cases when the risk of failure of total knee replacement is
considered to be very high, an arthrodesis, or knee fusion may be
recommended instead. In this operation, the ends of the femur and
tibia bones are cut flat, the cut ends are pressed together such
that the leg is just slightly bent, and then held in this position
by pins, or plates and screws. Over a couple of months the ends of
the bones grow together, hence the term knee fusion. The knee fuses
in a nearly straight position and cannot be bent. Although the knee
no longer moves, it is not painful and most patients walk with only
a slight limp.
Total knee replacement is a major surgical procedure and there are
innumerable potential complications. In aggregate, the benefits
(improvement in the patient's quality of life) of total knee
replacement outweigh the risks (the chance of that patient having a
complication) for most individuals with severe knee arthritis. Most
patients have many years of painless knee function. If you wish to
receive the benefits of total knee replacement, you must also be
willing to accept the risks. The decision to undergo total knee
replacement surgery is yours.