Transcript File

Lec # 06 - 08
JOINT PROSTHESIS
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OUTLINE
Anatomy
 Total Joint Replacement
 Knee joint
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 Anatomy
 Causes
 Types
of implants
 Components
 Knee implant fixations
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ANATOMY
A joint is where the ends of two or more bones
meet.
 There are different types of joints within the
body.
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example, the knee is considered a "hinge" joint,
because of its ability to bend and straighten like a
hinged door.
 The hip and shoulder are "ball-and-socket" joints, in
which the rounded end of one bone fits into a cupshaped area of another bone.
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WHEN IS TOTAL JOINT REPLACEMENT
RECOMMENDED?
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Several conditions can cause joint pain and disability
and lead patients to consider joint replacement
surgery.
In many cases, joint pain is caused by damage to the
cartilage that lines the ends of the bones (articular
cartilage)—either from arthritis, a fracture, or another
condition.
If nonsurgical treatments like medications, physical
therapy, and changes to your everyday activities do
not relieve your pain and disability, your doctor may
recommend total joint replacement.
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TOTAL JOINT REPLACEMENT
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Total joint replacement is a surgical procedure in which parts of
an arthritic or damaged joint are removed and replaced with a
metal, plastic or ceramic device called a prosthesis. The
prosthesis is designed to replicate the movement of a normal,
healthy joint.
In 2011, almost 1 million total joint replacements were performed
in the United States. Hip and knee replacements are the most
commonly performed joint replacements, but replacement
surgery can be performed on other joints, as well, including the
ankle, wrist, shoulder, and elbow.
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Lec # 06
KNEE JOINT
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ANATOMY
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The knee is the largest joint in the body and having healthy knees is
required to perform most everyday activities.
The knee is made up of the lower end of the thighbone (femur), the upper
end of the shinbone (tibia), and the kneecap (patella). The ends of these
three bones where they touch are covered with articular cartilage, a smooth
substance that protects the bones and enables them to move easily.
The menisci are located between the femur and tibia. These C-shaped
wedges act as "shock absorbers" that cushion the joint.
Large ligaments hold the femur and tibia together and provide stability.
All remaining surfaces of the knee are covered by a thin lining called the
synovial membrane. This membrane releases a fluid that lubricates the
cartilage, reducing friction to nearly zero in a healthy knee.
Normally, all of these components work in harmony. But disease or injury
can disrupt this harmony, resulting in pain, muscle weakness, and reduced
function.
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CAUSES
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The most common cause of chronic knee pain and disability is
arthritis. Although there are many types of arthritis, most knee
pain is caused by just three types: osteoarthritis, rheumatoid
arthritis, and post-traumatic arthritis.
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Osteoarthritis. This is an age-related "wear and tear" type of
arthritis. It usually occurs in people 50 years of age and older, but
may occur in younger people, too. The cartilage that cushions the
bones of the knee softens and wears away. The bones then rub
against one another, causing knee pain and stiffness.
Rheumatoid arthritis. This is a disease in which the synovial
membrane that surrounds the joint becomes inflamed and
thickened. This chronic inflammation can damage the cartilage
and eventually cause cartilage loss, pain, and stiffness.
Post-traumatic arthritis. This can follow a serious knee injury.
Fractures of the bones surrounding the knee or tears of the knee
ligaments may damage the articular cartilage over time, causing
knee pain and limiting knee function.
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TYPES OF KNEE IMPLANTS
1. Fixed Bearing Implants
 The most common knee replacement implant is referred to as
a fixed-bearing implant. It is referred to as “fixed” because the
polyethylene cushion of the tibial component is fixed firmly to
the metal platform base. The femoral component then rolls
over this cushion.
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The fixed-bearing prostheses provide a good
range of motion and just as long lasting as
other implants for most patients.
 In some cases, excessive activity and/or extra
weight can cause a fixed-bearing prosthesis to
wear down more quickly. This wear can cause
loosening of the implant, causing pain and joint
failure .
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2. Mobile Bearing Implants
 If you are younger, more active, and/or overweight, your doctor
may recommend a rotating platform/mobile-bearing knee
replacement. These implants are designed for potentially longer
performance.
 The difference between a fixed-bearing implant and a mobile
bearing implant is in the bearing surface. Fixed-bearing implants
and mobile-bearing implants use the same three components.
 In a mobile-bearing knee, a similar metal implant is inserted into
the tibia, but the polyethylene tray is placed on a circular stem
that allows slight rotation of the tray on the metal tibial platform
during knee motion.
 This rotation allows patients a few degrees of
greater rotation to the medial and lateral sides
of their knee.
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Because of this mobility, mobile-bearing knee
implants do require more support from the
ligaments surrounding the knee. If the soft
tissues are not strong enough, though, the knee
is more likely to dislocate.
 Mobile-bearing implants may also cost a bit
more than fixed-bearing implants.
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KNEE IMPLANT COMPONENTS
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Typical total knee replacement implants have three basic
components: femoral, tibial and patellar.
The femoral component is generally made of metal and curves
around the end of the femur (your thighbone). There is a groove
down the center of this part of the implant which allows the
patella (kneecap) to move up and down as the knee bends and
straightens.
The tibial component is a flat metal platform with a polyethylene
(plastic) insert or spacer. This component varies in structure,
depending on which type of surgery is performed.
The patellar implant is a dome-shaped piece of polyethylene that
mimics the kneecap. This implant is used in some knee
replacements; not in others.
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TYPES OF KNEE IMPLANT FIXATION
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The other big difference between types of knee replacements is
fixation. There are cemented, cementless, and hybrid
(combination of cemented and cementless) designs.
1. Cemented prostheses utilize a special kind of bone cement
that helps hold the components of the artificial joint in
place. The majority of knee replacements are generally
cemented. Cemented knee replacements have been used
successfully in all types of knee replacement patients.
Historically, some younger, more active patients had
problems with loosening cement but the material is now
much improved.
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2. Cement less implant designs become fixed by bone growth
into the surface of the implant. Most implant surfaces are
textured or coated with a porous material so that the new
bone actually grows into the surface of the implant. Screws
or pegs may also be used to stabilize the implant until bone
ingrowth occurs. Recovery does generally take a bit longer
as the bone grows into the prosthesis. Cement less implants
are not usually a viable for patients with osteoporosis, as
the existing bone must be in good shape in order to grow
into the implant.
3. Some surgeons also use a hybrid of the two methods of
fixation, though this is more common in hip replacement
surgery.
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Lec # 07
HIP JOINT
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ANATOMY
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The hip is one of the body's largest joints. It is a ball-and-socket
joint. The socket is formed by the acetabulum, which is part of
the large pelvis bone. The ball is the femoral head, which is the
upper end of the femur (thighbone).
The bone surfaces of the ball and socket are covered with
articular cartilage, a smooth tissue that cushions the ends of
the bones and enables them to move easily.
A thin tissue called synovial membrane surrounds the hip joint.
In a healthy hip, this membrane makes a small amount of fluid
that lubricates the cartilage and eliminates almost all friction
during hip movement.
Bands of tissue called ligaments (the hip capsule) connect the
ball to the socket and provide stability to the joint.
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COMMON CAUSES
The most common cause of
disability is arthritis. Osteoarthritis,
rheumatoid arthritis, and traumatic
arthritis are the most common forms
of this disease.
Osteoarthritis.
The
cartilage
cushioning the bones of the hip
wears away. The bones then rub
against each other, causing hip pain
and stiffness. Osteoarthritis may
also be caused or accelerated by
subtle irregularities in how the hip
developed in childhood.
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Rheumatoid arthritis. This is an autoimmune
disease in which the synovial membrane
becomes inflamed and thickened. This chronic
inflammation can damage the cartilage,
leading to pain and stiffness.
 Post-traumatic arthritis. This can follow a
serious hip injury or fracture. The cartilage may
become damaged and lead to hip pain and
stiffness over time.
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Avascular necrosis. An injury to the hip, such as a dislocation or
fracture, may limit the blood supply to the femoral head. This is
called avascular necrosis. The lack of blood may cause the
surface of the bone to collapse, and arthritis will result.
Childhood hip disease. Some infants and children have hip
problems. Even though the problems are successfully treated
during childhood, they may still cause arthritis later on in life.
This happens because the hip may not grow normally, and the
joint surfaces are affected.
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TYPES OF HIP IMPLANTS
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Hip implants are medical devices intended to restore mobility and relieve
pain usually associated with arthritis and other hip diseases or injuries.
Factors that influence the longevity of the device include the patient’s age,
sex, weight, diagnosis, activity level, conditions of the surgery, and the type
of implant chosen.
There are currently five types of total hip replacement devices available with
different bearing surfaces. These are:
1.
Metal-on-Polyethylene: The ball is made of metal and the socket is
made of plastic (polyethylene) or has a plastic lining.
2.
Ceramic-on-Polyethylene: The ball is made of ceramic and the socket is
made of plastic (polyethylene) or has a plastic lining.
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Metal-on-Metal: The ball and socket are both made of metal.
4.
Ceramic-on-Ceramic: The ball is made of ceramic and the socket has a
ceramic lining.
5.
Ceramic-on-Metal: The ball is made of ceramic and the socket has a
metal lining.
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IMPLANT COMPONENTS
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Many different types of designs and materials are currently used
in artificial hip joints. All of them consist of two basic
components:
 A cup : A cup (made of stainless steel or titanium) that is
placed in the patient’s acetabulum. In the cup, a liner (made
of polyethylene or ceramic) is impacted and serves as an
interface between the cup and the replacement femoral head.
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A femoral implant comprised of :
 A round head (made of stainless steel or titanium) that
is placed on the neck of the stem and articulates with
the liner.
 A neck (cone-shaped) that can be fixed on the stem or a
modular neck. When the femoral stem can
accommodate a modular neck, the surgeon can choose
between different necks that can be adapted to the
shape of the femur.
 A femoral stem (made of stainless steel or titanium)
inserted in the femur.
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The prosthetic components may be "press fit"
into the bone to allow your bone to grow onto
the components or they may be cemented into
place.
 The decision to press fit or to cement the
components is based on a number of factors,
such as the quality and strength of your bone.
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SHOULDER JOINT
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Although shoulder joint replacement is less
common than knee or hip replacement, it is
just as successful in relieving joint pain.
 Shoulder replacement surgery was first
performed in the United States in the 1950s to
treat severe shoulder fractures. Over the years,
shoulder joint replacement has come to be
used for many other painful conditions of the
shoulder, such as different forms of arthritis.
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ANATOMY
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Your shoulder is made up of three bones:
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your upper arm bone (humerus),
your shoulder blade (scapula), and
your collarbone (clavicle).
The shoulder is a ball-and-socket joint: The ball, or head, of your upper arm
bone fits into a shallow socket in your shoulder blade. This socket is called the
glenoid.
The surfaces of the bones where they touch are covered with articular
cartilage, a smooth substance that protects the bones and enables them to
move easily.
A thin, smooth tissue called synovial membrane covers all remaining surfaces
inside the shoulder joint. In a healthy shoulder, this membrane makes a small
amount of fluid that lubricates the cartilage and eliminates almost any friction
in your shoulder.
The muscles and tendons that surround the shoulder provide stability and
support.
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CAUSES
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One of the most common cause of shoulder joint
pain is arthritis. The most common types of
arthritis are:
 Osteoarthritis
(OA)
 Post-traumatic arthritis
 Rheumatoid arthritis (RA)
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COMPONENTS
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The artificial shoulder joint can have either two
or three parts, depending on the type of
surgery required.
 The
humeral component (metal) is implanted in the
humerus.
 The humeral head component (metal) replaces the
humeral head at the top of the humerus.
 The glenoid component (plastic) replaces the
surface of the glenoid socket.
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Total Shoulder Replacement
 The typical total shoulder replacement involves replacing the
arthritic joint surfaces with a highly polished metal ball attached
to a stem, and a plastic socket.
 These components come in various sizes. They may be either
cemented or "press fit" into the bone. If the bone is of good
quality, your surgeon may choose to use a non-cemented (pressfit) humeral component.
 If the bone is soft, the humeral component may be implanted with
bone cement.
 In most cases, an all-plastic glenoid (socket) component is
implanted with bone cement.
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ELBOW JOINT
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ANATOMY
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The elbow is a hinge joint which is made up of three bones:
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The humerus (upper arm bone)
The ulna (forearm bone on the pinky finger side)
The radius (forearm bone on the thumb side)
The surfaces of the bones where they meet to form the elbow
joint are covered with articular cartilage, a smooth substance
that protects the bones and enables them to move easily.
A thin, smooth tissue called synovial membrane covers all
remaining surfaces inside the elbow joint. In a healthy elbow,
this membrane makes a small amount of fluid that lubricates
the cartilage and eliminates almost any friction as you bend
and rotate your arm.
Muscles, ligaments, and tendons hold the elbow joint together.
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COMPONENTS
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In total elbow replacement surgery, the damaged parts of
the humerus and ulna are replaced with artificial
components.
The artificial elbow joint is made up of a metal and plastic
hinge with two metal stems. The stems fit inside the hollow
part of the bone called the canal.
Hinge allows the two pieces of the new joint to glide easily
against each other as you move your elbow. The hinge
allows the elbow to bend and straighten smoothly.
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The metal replacement parts are made of
chrome-cobalt alloy or titanium and there is a
liner made of polyethylene (plastic).
 The bone cement is made of
polymethylmethacrylate (acrylic, a type of
plastic).
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FIXATIONS
There are two different ways to hold the
artificial elbow in place.
 A cemented prosthesis uses a special type of
epoxy cement to glue it to the bone.
 An uncemented prosthesis has a fine mesh of
holes on the surface. Over time, the bone
grows into the mesh, anchoring the prosthesis
to the bone.
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THANK YOU
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