Joint Prosthesis

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Joint Prosthesis

• Lec 06 - 08

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outline

• Anatomy
• Total Joint Replacement
• Knee joint
• 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.
• For 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 cup-shaped area of another bone.

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When Is Total Joint Replacement Recommended?

• 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

• 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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Knee joint

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anatomy

• 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

• 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.
• 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

• 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

• The other big difference between types of knee
  replacements is fixation. There are cemented,
  cementless, and hybrid (combination of cemented
  and cementless) designs.
• 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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Hip joint

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anatomy

• 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

• 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 patients 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
• Metal-on-Polyethylene The ball is made of metal
  and the socket is made of plastic (polyethylene)
  or has a plastic lining.
• Ceramic-on-Polyethylene The ball is made of
  ceramic and the socket is made of plastic
  (polyethylene) or has a plastic lining.
• Metal-on-Metal The ball and socket are both made
  of metal.
• Ceramic-on-Ceramic The ball is made of ceramic
  and the socket has a ceramic lining.
• Ceramic-on-Metal The ball is made of ceramic and
  the socket has a metal lining.

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Implant Components

• 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 patients
  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

• Your shoulder is made up of three bones
• 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

• 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

• 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 (press-fit) 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

• The elbow is a hinge joint which is made up of
  three bones
• 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

• 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