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Title: Use of Ceramics in Total Hip Arthroplasty


1
Use of Ceramics in Total Hip Arthroplasty
Begin
Arthur Mui, Cole Barthel, Kaizhen Chen
BME 215 Fall 2007
Duke University
2
Navigational Guide
  • This is an educational presentation about
    ceramic hip implants. Please refer to the
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Learn More
Clicking on this button brings the reader to more
information on the topic
3
Start by clicking on Why
ceramics? Then click on any of the four images
below to learn more
Click here to see references and surgeon and
vendor contacts
DISEASED STATE
DESIGN AND MATERIALS
SURGICAL IMPLEMENTATION
IMPLANT PERFORMANCE
4
Why Ceramics?
Excellent Biocompatibility
Good Lubrication Properties
Abrasion Resistance
High Wear Resistance
Long Lifetime
Superior Corrosion Resistance
5
Diseased State
Hip Anatomy
History of Hip Implants
Functions of the Hip
Forces on the Hip
Diseases of the Hip
Motivation for Replacement
Criteria for Hip Replacement
Chapter Summary
6
History and Development of Ceramic Implants
Click on each button to learn more about a
particular time period
Second generation ceramics, zirconia introduced
Third generation ceramics
1970s
2003
1980s
Today
Use of alumina in total hip arthroplasty
FDA approved ceramic- on-ceramic hip joints
7
1970s
  • The use of ceramic components in joint
    replacement surgery was initiated in the 1970s
    with the introduction of first generation alumina
    products, when ceramics superior resistance to
    wear in comparison to more traditional metal and
    polyethylene materials became apparent.
  • The use of alumina ceramics in total hip
    arthroplasty began in Europe. Professor Pierre
    Boutin pioneered the use of ceramics in France in
    1970, replacing traditional metal femoral heads
    with alumina. However, early ceramic components
    were prone to fracture as they had low densities
    and a coarse microstructure.

http//www.ceramtec.com/index/divisions/medical_pr
oducts/ medical_professionals/history/04020,0125,0
341,4011.php
8
1980s
  • Advances in material quality and processing
    techniques and a better understanding of ceramic
    design led to the introduction of second
    generation alumina components in the 1980s that
    offered even better performance than early
    systems. The fracture rate of ceramic Biolox
    femoral heads was 0.026 for first generation
    alumina, 0.014 for second-generation alumina,
    and 0.004 for femoral heads manufactured after
    1994.
  • In 1985, the first zirconia femoral heads were
    implanted.

9
2003
  • The FDA approved the use of ceramic-on-ceramic
    hip implants in the February of 2003. The first
    ceramic-on-ceramic hip implant was implanted in
    legendary golfer Jack Nicklaus in 1999 as part of
    Strykers clinical study.

www.belfasttelegraph.co.uk/sport/article24642...
10
Today
  • Todays third generation alumina ceramic
    material has a high density with a small grain
    size, high chemical purity and a stable
    crystalline structure. Additionally, the material
    is hot isostatically pressed which decreases
    grain size and in turn, the incidence of
    fracture. Lubrication properties are also
    improved with the decrease in grain size.
    Individual ceramic components are also
    extensively tested before they are shipped and
    sold to the surgeons, which greatly decreases
    risks of failure.

11
Anatomy of a Normal Hip Joint
http//www.mylifeinaction.com/hip/arthritisandyour
hip/images/Normal_hip.gif
12
Pelvis
  • The bony pelvis is located at the base of the
    spine and provides a strong and stable support
    for the vertebral column and pelvic organs. It
    consists of 2 large bones separated from each
    other in the back by the sacrum, an extension of
    the spinal column. The pelvis also accepts the
    bones of the lower limb, connecting them to the
    axial skeleton.

www.pdh-odp.co.uk/pelvis.htm
13
Acetabulum
  • The acetabulum is a deep fossa formed by the
    ilium, ischium and pubis. It functions as the
    socket that accepts the rounded head of the
    femur. Together, the femoral head and the
    acetabulum form the hip joint, which is
    classified as a ball-and-socket joint. A
    fibrocartilage lip called the labrum, which
    extends around the rim of the cup-shaped cavity,
    increases the depth of the acetabulum for
    articulation with the femoral head and
    contributes to hip joint stability. The
    acetabular cavity is enclosed with a joint
    capsule with a smooth synovial lining for
    lubrication.

http//www.ori.org.au/bonejoint/hip/goodbad.htm
14
Femur
  • The femur is commonly called the thigh bone. The
    upper side of the femur tapers into a neck that
    is topped with a ball-shaped head capped with a
    shiny, slippery tissue layer of articular
    cartilage. The head of the femur fits snugly into
    the cartilage-lined acetabulum, with just enough
    space to rotate smoothly.

http//www.britannica.com/eb/art-101308/
15
Function of the Hip
  • Approximately 3 times the body weight is
    distributed throughout the hip with routine
    activities due to the muscle pull and joint
    forces that occur. The range of movements of the
    hip joint include

Flexion / Extension
Lateral / Medial Rotation
Abduction / Adduction
co-me.ch/projects/phase2/p07/p07_03.en.html
16
Flexion / Extension
www.brianmac.co.uk/musrom.htm
17
Lateral / Medial Rotation
www.brianmac.co.uk/musrom.htm
18
Adduction / Abduction
www.brianmac.co.uk/musrom.htm
19
Forces on the Hip
This movie shows the multi-directional forces
experienced at the hip joint during motions like
walking and sitting.
www.lifemodeler.com/LM_Manual/T_hip.htm
20
Forces on the Hip (cont.)
This finite element analysis (FEM) model shows
the stress distribution in a ceramic ball of the
hip implant.
www.endolab.de/computer/computersimulation_e.htm
21
Diseases Affecting the Hip
Osteoarthritis
Rheumatoid Arthritis
Avascular Necrosis
Hip Dysplasia
Post-traumatic Arthritis
  • Intense chronic pain is often experienced, with
    impairment of day-to-day activities like running
    or walking. Total hip replacement is usually
    considered only if normal functions are still
    impaired even with the help of anti-inflammatory
    drugs or pain medication.

22
Osteoarthritis
  • Progressive degenerative joint disease
  • Most common cause for hip replacement surgery
  • Often a result of aging, a congenital abnormality
    of the hip joint or trauma
  • Cartilage in the hip joint becomes cracked and
    pitted
  • Movement of the joint becomes difficult and
    painful

http//www.highlands-ortho.com/degenhip.gif
23
Osteoarthritis
  • Cartilage between the femoral head and the
    acetabulum progressively wears away
  • Bones rub against each other, resulting in severe
    pain, deformity and loss of mobility
  • Bone spurs or osteophytes may develop,
    resulting in severe pain and limitation in
    mobility

http//www.oagb.net/education/hipresurface/images/
hip_compare.jpg
24
Rheumatoid Arthritis
  • Chronic, inflammatory autoimmune disorder
  • Inflammation and soft tissue swelling
  • Chemicals produced in the joint space cause it to
    become thickened and inflamed
  • Synovial fluid destroys the cartilage, leading to
    cartilage loss, pain and stiffness

http//www.gaortho.com/Portals/0/RheumatoidArthrit
isHip.jpg
25
Post-traumatic Arthritis
  • Fractures to the hip bones can result from trauma
    such as a fall or blow to the hip
  • Post-traumatic arthritis may develop after joint
    injury if the bone and cartilage do not heal
    properly
  • The joint is no longer smooth, which leads to
    increased wear on the joint surfaces, resulting
    in severe pain

http//medicalimages.allrefer.com/large/hip-fractu
re.jpg
26
Avascular Necrosis
  • Fractures or dislocations of the hip can result
    in avascular necrosis if the arteries supplying
    this area are damaged
  • It can also arise due to blockage of the blood
    vessels caused by agents such as sickle cell
    anemia, abnormal red blood cells and fat
    particles
  • Alcoholism and steroids also increase risks of
    avascular necrosis
  • Without blood, bone tissue dies and collapses,
    leading to collapse of the joint surface

http//www.mylifeinaction.com/hip/arthritisandyour
hip/
27
Hip Dysplasia
  • Abnormal formation of the hip joint in which the
    femoral head is not stable in the acetabulum
  • Refers to a hip that is subluxatable
  • or dislocatable
  • Acetabular dysplasia - acetabulum is shallow,
    rendering the hip joint unstable
  • Developmental dysplasia - child has apparently
    normal hips at birth, but develops problems in
    his/her first year of life

www.msnyuhealth.org/.../body_ganz_osteotomy.html
28
Motivation for Total Hip Replacement
One of the most reliable operations in
orthopedic surgery
Allows patient participation in gentle leisure
activities
Improves quality of life, mobility and
independence
Vastly reduces or eliminates pain of disease
www.walgreens.com/library/contents.html?docty...
29
Criteria for Hip Replacement
  • Pain experienced is enough to restrict work,
    recreation and ordinary daily activities
  • Pain is not relieved with the use of
    anti-inflammatory medicine
  • Patients X-ray shows advanced arthritis, or
    other problems like avascular necrosis
  • Age, overall health and bone density are also
    important factors to be considered before the
    operation

orthopedics.about.com/.../a/arthritis_2.htm
30
Summary Diseased State
  • The hip joint is the joint between the femur and
    the acetabulum of the pelvis
  • Its range of motion include abduction/adduction,
    lateral and medial rotation and flexion/extension
  • Some diseases affecting the hip include
    osteoarthritis, rheumatoid arthritis, avascular
    necrosis, hip dysplasia and post-traumatic
    arthritis
  • Total hip replacement is only considered if the
    pain is debilitating enough to interfere with
    daily activities, and if pain persists despite
    the use of medication
  • Total hip replacement vastly improves the quality
    of life and mobility of patients

www.dreamscape.com/cnytc/ELA.html
31
Design and Materials
Overall Schematic
Commonly Used Materials
Ceramic-Ceramic Joint
Materials Comparison
Chapter Summary
32
Design Overall Schematic
  • There are 4 components to a hip replacement
    prosthesis
  • 1) The Acetabular Shell2) The Cup3) The
    Ball4) The Stem
  • While the stem is always made out of metal, there
    are 4 commonly used combinations for the cup and
    the ball
  • 1) Metal Ball on Polyethylene Cup
  • 2) Ceramic Ball on Polyethylene Cup
  • 3) Metal Ball on Metal Cup
  • 4) Ceramic Ball on Ceramic Cup
  • This section will focus on the design of the
    ceramic on ceramic joint

Illustration of total hip prosthesis (click for
details)
Novartis Ceramic Hip Brochure
33
Illustration of a Total Hip Prosthesis
  • The following illustration shows all the parts in
    a total hip prosthesis

Stryker Ceramic Hip Brochure
34
Design Ceramic-Ceramic Joint
  • There are a few distinctive advantages of a
    ceramic-ceramic joint
  • Low Wear
  • Low Friction
  • High Hardness / Low Grain Size
  • High Lubrication
  • High Biocompatibility
  • There are a few concerns to address when using a
    ceramic-ceramic joint
  • Brittleness / Fracture
  • Cost / Patient Factors
  • Dislocation is a major problem that occurs in all
    hip joints. The chance of dislocation is related
    to
  • Jump Distance
  • Range of Motion
  • Diameter of Femoral Head

35
Wear
  • Wear of prosthetic joints is a significant
    problem, because the debris produced by wear can
    cause adverse tissue reactions that may lead to
    inflammation and massive bone loss around the
    implant and consequently loosen the implant
  • The following are wear rates of joints made of
    different materials. As shown, the
    ceramic-ceramic joint has the lowest wear rate

ceramic-ceramic1 microns / year
metal-metal4.2 microns / year
ceramic-polyethylene20 microns / year
metal-polyethylene220 microns / year
36
Wear (cont.)
  • A ceramic-ceramic joint has a wear rate of
    approximately 1 micron / year, which is up to 200
    times less than the rate of wear of a
    metal-polyethylene joint
  • Although a metal-metal joint has similar rates of
    wear, there are concerns that this coupling can
    result in potentially harmful concentrations of
    metal ions being released into the bloodstream
  • High concentrations of metal ions have been
    suspected to cause kidney and liver diseases

37
Friction
  • The friction coefficient of the ceramic-ceramic
    combination is 0.09 compared to 0.21 with
    metal-polyethylene coupling
  • Using 1000 N alternate loading with water
    lubrication, an initial running-in-wear is
    observed due to a self-polishing effect of the 32
    mm diameter ceramic head against the ceramic cup
    followed by a decease of the friction torque to a
    steady state of 0.6 Nm

Frictional torque versus time for three materials
combinations
38
Hardness / Grain Size
  • The hardness of alumina is second only to a
    diamond (Alumina has a microhardness of 23,000
    Vickers)
  • Ceramics small grain size and grain distribution
    also increases its scratch resistance. Ceramic
    grains lie between 1.5 5 microns

Illustration of Microstructure of Alumina (x1000
magnification)
Illustration of Grain Size Distribution
39
Hardness / Grain Size (cont.)
  • Comparatively, metal-metal joints can be
    scratched causing an abrasive surface. Foreign
    debris in the joint may also accelerate implant
    wear
  • A minor drawback of ceramic-ceramic joints is
    that they are reported to make a squeaking noise
    occasionally. Nonetheless, the squeaking noise
    does not affect the implant function

40
Lubrication
  • The high density of ceramics allow a very smooth
    surface finish
  • The surface roughness of alumina (Ra) is 0.02 µm,
    which is superior to any metallic finish available

Trident Ceramic Acetabular System Brochure
41
Lubrication (cont.)
  • The hydrophilic nature of alumina also affords
    better lubrication in an aqueous environment. The
    contact angle of water is 44 degrees for Alumina,
    72 degrees for 316 L Stainless Steel, 80 degrees
    for UHMWPE, and 87 degrees for Cr-Co alloys
  • A lower contact angle promotes better
    lubrication, which in turn produces less wear
    particles

42
Biocompatibility
  • Alumina, the most commonly used ceramic material,
    is known to be very biocompatible. Laboratory
    analysis has shown that ceramic debris may be
    better tolerated by the body
  • Clinical studies have also shown that the alumina
    surface is completely covered with protein
    molecules immediately after implantation, and as
    a result, the body does not recognize it as
    foreign

43
Biocompatibility (cont.)
  • Tissue biopsies show that in well fixed alumina
    (ceramic-ceramic) prostheses, alumina wear
    particles increased with time however, only a
    low macrophagic reaction has occurred, and no
    necrosis (death of tissue) was observable
  • Tissue biopsies from metal-polyethylene total hip
    prostheses showed that polyethylene wear
    particles elicited a stronger body reaction when
    compared to alumina particles. Polyethylene
    particles were bigger, with numerous giant
    macrophages directly in contact

44
Brittleness and Fracture
  • Back in 1974, as many as 1 in 300 ceramic
    components fractured however, increased ceramic
    quality and advanced cup design have reduced that
    to as low as 1 in 20,000 today
  • The first generation ceramic joints sometimes
    failed as a result of manufacturing defects,
    causing the implants to crack and shatter.
    Furthermore, the grain size was 40x larger than
    that of modern ceramics, which have grain sizes
    on the order of 1um

Fracture of Ceramic Heads in Total Hip
Replacement by B. Habermann
45
Brittleness and Fracture (cont.)
  • However, recent technological advancements have
    led to the manufacture of alumina ceramic
    components with reduced grain size, fewer
    inclusions and limited grain boundaries, which in
    turn leading to a much tougher and stronger
    material

46
Brittleness and Fracture (cont.)
  • One of the most common causes of fracture results
    from impingement of the femoral stem neck and the
    cup with the hip in hyperflexion and external
    rotation. Consequently, the cup becomes loose and
    dislocates, resulting in a large force exerted on
    the head and taper, bending the taper and
    fracturing the head
  • Strykers developed a solution to this problem by
    adding an elevating sleeve rim between the cup
    and the shell. Such a design shifts the
    impingement point from the stem neck and the cup
    to the stem neck and shell, which has a lower
    chance of damaging the ceramic insert

Illustration of the old design
Strykers New Design
Trident Ceramic Acetabular System Brochure
47
Brittleness and Fracture (cont.)
  • When the cup is vertically tilted or becomes
    vertically tilted after loosening, the contact
    stresses become high enough to generate
    subcritical cracks in the ceramic. Therefore the
    material will have an increased chance of
    fracturing

Illustration of contact stress distribution based
on cup orientation The left diagram illustrates
a normal cup and the right diagram illustrates a
dislocated cup
48
Cost / Patient Factors
  • Ceramic on ceramic implant configurations command
    premium prices, 7500 for implant components as
    compared to 5500 for metal on metal components
  • Patient Factors When choosing a material for a
    hip joint, sex, age, and diagnosis should be
    taken into consideration. Males and younger
    patients demonstrate higher average activity, and
    thus a higher risk for problems related to wear,
    such as osteolysis. Categorically, patients with
    medical comorbidities that limit activity
    demonstrate lower average wear rates and have a
    reduced risk for failure due to wear and
    osteolysis

49
Jump Distance
  • Jump distance is the distance a femoral head must
    travel to dislocate. The greater the jump
    distance, the less risk of dislocation
  • Typically, jump distance is defined as the
    vertical distance the femoral head must travel to
    dislocate after impingement. For the Stryker
    designed head, it incorporates an additional
    dislocation safety factor of 2.7 mm, which
    decreases the risk of dislocation
  • The following are the jump distances
    corresponding to different head diameters

Trident Ceramic Acetabular System Brochure
50
Jump Distance (cont.)
  • The jump distance measurement is more complicated
    than it seems since the implant cup is usually
    embedded 45 degrees into the pelvis
  • The formula used for the vertical jump distance
    is r - rcos(45) 2sin(45)
  • The following illustrations show the jump
    distance calculation in greater detail

Trident Ceramic Acetabular System Brochure
51
Range of Motion
  • Range of motion is critical for the patient
    because it enhances optimal movement and activity
    post-operatively
  • Clinical studies have shown that a greater range
    of motion was observed for larger heads compared
    with smaller ones

Trident Ceramic Acetabular System Brochure
52
Diameter of Femoral Head
  • Typical ceramic ball head sizes range from 28 mm
    to 36 mm in diameter
  • While a larger femoral head diameter is known to
    provide a more favorable jump distance and range
    of motion, it also reduces the chance of fracture
    due to better distribution of stress
  • An area of concern is that in some laboratory
    studies, the range of motion prior to neck-socket
    impingement leading to dislocation was increased
    as ball diameter increased. Moreover, very large
    diameter bearings, 40 mm or greater, have been
    used to stabilize hips with a history of
    recurrent instability

www.devicelink.com/mtm/archive/07/05/005.html
53
Materials Commonly Used for Balls and Cups
Click on a material to learn more
Titanium
UHMWPE
Alumina
Alumina/Zirconia
54
Titanium
  • Pros
  • High biocompatibility
  • High strength
  • Ductile
  • Cons
  • Undesirable wear rate

Learn More
Learn More
Learn More
Learn More
Uses Popular orthopedic implant material (hips,
knees, shoulders, etc.) First material
used for hip balls and still a very popular
option Ball/Cup Pairs Titanium ball with UHMWPE
cup
Titanium Ball
www.onlinetmd.com
55
High Biocompatibility of Titanium
  • Titanium has extremely low corrosion rates making
    it ideal for implantation
  • Titanium is also bio-inert which means that it
    will not react with the surrounding environment

www.timet.com/specialized.html
56
High Strength of Titanium
  • A hip joint can be loaded with multiple times
    body weight depending on the activity. As such,
    the materials used must be of high strength.
  • Titanium is a very strong metal (also used in
    aircraft parts) and can support much higher loads
    than what is seen in a hip joint

www.tirings.com/titanium_facts.php
57
Ductility of Titanium
  • As with all metals titaniums crystal structure
    is held together with metallic bonds
  • These bonds enable the atoms in the crystal to
    slide past each other when subjected to stress.
    This creates a ductile material that will deform
    before it fractures
  • Ductility is important because it greatly reduces
    the risk of fracture

Titanium Unit Crystal each atom is held to the
other through sharing of electrons (metallic
bonds)
www.msm.cam.ac.uk
58
Titanium Wear
  • The production of wear particles is a major issue
    because they can cause osteolysis (resorption of
    bone around the implant)
  • Wear occurs at the interface between the hip ball
    and acetabular cup due to the rubbing motion
    created during normal movement
  • Wear particles are responsible for most titanium
    artificial hip failures

Stryker Orthopedics Brochure
59
UHMWPE (Ultra High Molecular Weight Polyethylene)
  • Pros
  • Low friction/hard
  • Biocompatible
  • Cons
  • Undesirable wear rate

Learn More
Learn More
Learn More
Uses Low friction bearing surface in
manufacturing and biomedical applications
Used exclusively as an acetabular cup in
artificial hip joints Ball/Cup Pairs Titanium or
Alumina/Zirconia ball with UHMWPE cup
Hip and Knee bearing surfaces
www.disanto.com, www.onlinetmd.com
60
Hardness and Low Friction of UHMWPE
  • UHMWPE has a low friction coefficient and is very
    hard making it an ideal bearing surface for the
    articulation between the ball and the cup.

www.ticona.com
61
Biocompatibility of UHMWPE
  • UHMWPE consists of very large molecules and there
    are many cross-links in its chemical structure.
    Therefore, the material does not react with the
    surrounding biological environment.

www.msm.cam.ac.uk, http//www.zimmer.co.za/z/ctl/o
p/global/action/1/id/7867/template/MP/prcat/M2/pro
d/y
62
Wear of UHMWPE
  • The wear of a joint is dependent on the
    combination of the ball and acetabular
    components. In Titanium-UHMWPE combinations the
    wear rate (220 microns/year) is a major issue.
    However, in Alumina/Zirconia-UHMWPE joints the
    wear rate is greatly reduced.

Stryker Orthopedics Brochure
63
Alumina
  • Cons
  • Susceptible to cracking / slow crack propagation
  • Pros
  • Less wear
  • High strength
  • Excellent corrosion resistance
  • Good biocompatibility
  • Low friction coefficient

Learn More
Learn More
Learn More
Learn More
Learn More
Learn More
Uses One common use of alumina is in billiard
balls Introduced as an artificial hip
component in 1972 in an effort to reduce the wear
produced from titanium/UHMWPE
pairs Ball / Cup Pairs Alumina balls are almost
always paired with alumina cups Learn More
Manufacturing alumina Crystal Structure
Learn More
Learn More
64
Wear of Alumina
  • Alumina on alumina joints (1 micron/year) have a
    much lower wear rate than that of titanium on
    UHMWPE joints (220 microns/year)

Stryker Orthopedics Brochure
65
High Strength of Alumina
  • Alumina is an extremely strong material. It has
    a tensile strength and tensile modulus greater
    than even titanium.

66
Corrosion Resistance of Alumina
  • As with most ceramics alumina practically does
    not corrode at all. This increases its
    biocompatibility and means that it will not
    interact with the biological fluids surrounding
    it.

Stryker Orthopedics Brochure
67
Biocompatibility of Alumina
  • Because alumina has a lower wear rate it is
    considered to be more biocompatible than titanium
    on UHMWPE joints
  • It is also believed that the particles produced
    from alumina have less of a biological reaction
    than those from titanium

68
Low Friction Coefficient of Alumina
  • Alumina has a very low friction coefficient which
    makes it an excellent choice as a bearing
    material
  • This also helps to reduce the amount of wear

69
Fracture Toughness of Alumina
  • One problem with ceramics in general is that they
    are brittle materials and therefore susceptible
    to fracture if stresses are high enough. Alumina
    is also susceptible to slow crack propagation in
    which a small defect can grow through continued
    loading until it is large enough that the
    material will fracture.

www.cases.bham.ac.uk/bio/femoral.htm
70
Manufacture of Alumina
  • Alumina is most commonly manufactured using
    powder processing techniques. The alumina powder
    is isostatically compressed and then shaped by
    grinding while being sintered at 1600 to 1800oC.
    The process produces a nearly pore-free
    polycrystalline solid with grain sizes of 3 to
    5µm.
  • The techniques are used partly because the
    surface of alumina must be highly controlled down
    to the sub-micron level. Because alumina is
    susceptible to cracking any microcracks in the
    surface must be either eliminated or greatly
    reduced. The grain size must also be controlled
    in order to give the best fracture toughness.

71
Manufacture of Alumina
Click on any process to learn more
72
Alumina Powder
  • The ore bauxite, which consists of Al2O3, Fe2O3
    and SiO2 is purified using the Bayer process to
    achieve aluminum powder.
  • The powder is used to make aluminum metal and can
    be used as an abrasive

www.ltdceramics.com
73
Cold Isostatic Pressing
  • The alumina powder is poured into a mold and
    compressed from all sides using static pressure
    from a fluid
  • This compacts the powder and allows manufacture
    of highly controlled shapes

205.209.102.103
74
Sintering
  • Sintering is the process of heating a material to
    below its melting temperature until the particles
    begin to adhere to one another
  • Alumina is pre-sintered before machining and then
    sintered again before use to further set the
    material

www.esrf.eu
75
CNC Tuning and Taper Cutting
  • After pre-sintering, the component is shaped
    using CNC (computer numerical control) and other
    traditional machining techniques.

http//www.computernumericalcontrol.net/CNC-lathe.
jpg, www.penntoolco.com/catalog/products/products.
...
76
Grinding and Polishing
  • After sintering at 1600oC, the part is ground and
    polished to achieve a smooth surface
  • This is very important since the part will be
    used as a bearing surface.

www.ukam.com/products.htm
77
Crystal Structure of Alumina
  • Alumina is also known as aluminum oxide and has a
    corundum crystal structure (rhombohedral).
    Alumina has the chemical formula Al2O3 and in
    commercial use it has less than 0.4 other
    alcolide metals added such as titanium dioxide
    and magnesium.
  • Aluminas highly organized crystal structure
    gives it its strength and toughness but the ionic
    bonds that connect the molecules together make it
    susceptible to fracture. The molecules cannot
    slide past one another as in metallic bonds so
    when stresses are high enough the molecules break
    apart from one another.

Aluminum Oxide Unit CellGrey Aluminum, Red -
Oxygen
videoinside.org/show/Aluminium_oxide
78
Alumina / Zirconia
  • Pros
  • Increased hardness / fracture strength
  • Cons
  • More difficult to manufacture

Learn More
Learn More
Uses Zirconia was introduced as a hip joint
material because of its higher strength
and toughness compared to alumina
It was discovered later that the zirconia
components had a high failure rates
Alumina/zirconia parts combine the properties of
both alumina and zirconia and the
failure rate is much reduced. Ball/Cup Pairs
Alumina/zirconia balls are always paired with
UHMWPE cups Learn More Alumina/zirconia material
properties
79
Fracture Strength of Alumina / Zirconia
  • By adding relatively small amounts of zirconia
    (ZrO2) to alumina (Al2O3) the hardness and
    fracture strength of the material can be
    increased.
  • Zirconia derives its fracture strength from its
    crystal structure. If zirconia is manufactured
    correctly it is in a stable tetragonal state. In
    order for the material to fracture it must
    transition into a monoclinic state. The energy it
    takes for this process to happen increases the
    resistance to cracking.

www.chemistry.pomona.edu/.../Zirconium.htm
80
Manufacture of Alumina / Zirconia
  • Alumina / Zirconia composites are manufactured
    using the same powder processing techniques as
    pure alumina, but the manufacturing of these
    composites must be controlled even more. If the
    grain size of the zirconia grains are too large
    or too small and if the percentage of zirconia is
    too large the zirconia can transition to
    monoclinic when the material is cooled, which can
    cause cracking. Commercial alumina/zirconia
    composites have 25 zirconia.

81
Comparison of Material Properties
  • Some notable comparisons
  • The hardness increases from titanium to the
    ceramic materials (zirconia hardness is slightly
    higher than alumina)
  • The ceramic materials have very high compressive
    yield strengths and flexural strengths
  • The fracture toughness of zirconia is slightly
    higher than that of alumina

82
Summary Design and Materials
  • The hip implant consists of 4 parts the
    acetabular shell, the ball, the cup and the stem
  • Commonly used materials for the ball and cup
    include titanium, UHMWPE, alumina and
    alumina/zirconia
  • Ceramic-on-ceramic joints have the lowest
    recorded wear rate among all the possible
    couplings between ball and cup
  • Alumina has excellent biocompatibility, high
    corrosion resistance, a low friction coefficient
    and low wear rate but is susceptible to cracking
    and slow crack propagation

www.dreamscape.com/cnytc/ELA.html
83
Surgical Implementation
Hip Replacement Surgery
Pre-Operative Procedures
Surgical Protocol
Hip Implant Sterilization
Rehabilitation
Chapter Summary
84
Hip Replacement Surgery
  • Removes diseased femoral head and damaged
    cartilage from the hip socket
  • Femoral head is replaced by a ball fixed to a
    stem
  • Stem is inserted into the hollow part of the
    femur
  • Socket is replaced with an acetabular shell with
    a lining cup

www.memagazine.org/.../hipnew/hipnew.html
85
Hip Replacement Surgery (cont.)
  • Femoral and acetabular components of the
    prosthesis are attached to the bone by creating a
    space slightly smaller than the prosthesis and
    then pushing it into this tight space
  • The prosthesis may be attached to the bone by
    bone cement
  • Implant components are pre-sterilized prior to
    usage, usually by gamma radiation in an air
    environment, with doses ranging from 2.5 - 4 MRad

www.dartmouth.edu/.../corr5.html
86
Hip Replacement Surgery (cont.)
All pictures from Strykers Surgical Protocol
Brochure
87
Pre-Operative Procedures
  • Pre-operative planning and X-ray evaluation aids
    in selection of the most favorable implant style
    and optimal size for the patients hip pathology.
  • Selecting potential implant styles and sizes
    ahead of time facilitates operating room
    preparation and assures availability of an
    appropriate selection.
  • X-ray detection helps detect anatomic
    abnormalities that could prevent successful
    implantation.

88
Sterilization of Implant
Hip replacement components come to the surgeon
packaged and pre-sterilized Sterilization
techniques
UHMWPE gas plasma
Ceramics Metals gamma radiation
Other popular sterilization techniques Ethylene
Oxide, Heat
89
Gamma Radiation
  • Cons
  • More expensive than ethylene oxide
  • Not an in-house operation
  • Pros
  • Rapid
  • No residues
  • Good for convoluted shapes
  • Penetrates the material well
  • Easy to control the dosage
  • Can be sterilized in its packaging

How it works The bacterias DNA is degraded
through ionization
How its done The part is passed by radiating
rods on a conveyer belt
www.medicaldesign.com, www.medicaldesign.com
90
Ethylene Oxide
  • Pros
  • Compatibility with many materials
  • Good for heat sensitive products
  • Low cost
  • Does not compromise the mechanical properties of
    UHMWPE the way radiation does
  • Cons
  • Penetration can be difficult
  • Residues are present
  • Long process

How it works Alkylates proteins and DNA
How its done EO gas is introduced to a chamber
around the part for a specific amount of time and
then flushed away.
img.trade.tootoo.com
91
Heat (Autoclaving)
  • Pros
  • Fast
  • No residues
  • Very low cost
  • Can be used in-house
  • Cons
  • Heat sensitive parts like many polymers can not
    be sterilized this way

How it works Oxidizes and denatures enzymes
How its done The part is placed in a very hot
wet environment for a specific amount of time
www.fragoimpex.com
92
Gas Plasma
  • Cons
  • A new process that does not have in-vivo data to
    back it up
  • Pros
  • Does not compromise the mechanical properties of
    UHMWPE the way radiation does
  • Can be used for materials sensitive to
    temperature, radiation, and chemicals

How it works Uses ionized gas to deactivate
bacteria on the surface
How its done The gas passes over the part and
two electrodes create the plasma that kills the
bacteria
www.torontosurplus.com
93
Surgical Protocol
  • The hip is dislocated and the femoral head is
    removed
  • Soft tissue from the acetabulum is removed to
    gain adequate exposure for reaming
  • Excision of labrum and osteophytes

www.elib.gov.ph/edatabase/elibgetdb.php/http/...,
www.rcsed.ac.uk/journal/svol1_6/10600004.html
94
Surgical Protocol (cont.)
  • Reamer handle is oriented at 45o of abduction
  • Reaming progresses in 1mm increments until final
    sizing is achieved
  • Care is taken not to enlarge or distort the
    acetabulum by eccentric reaming
  • Final state ideally shows the hemispherical
    acetabulum denuded of cartilage with the
    subchondral plate intact and anterior acetabular
    wall preserved

www.elib.gov.ph/edatabase/elibgetdb.php/http/...,
www.rcsed.ac.uk/journal/svol1_6/10600004.html
95
Surgical Protocol (cont.)
  • Appropriately sized acetabular component is
    selected
  • The metal shell is impacted into the acetabulum
    using a mallet until a tight fit is achieved
  • Screws may be used to secure the shell
  • Ceramic/polyethylene insert is carefully
    introduced
  • Insert is turned into final pre-locking position
  • Insert is seated firmly by firm mallet blows

www.elib.gov.ph/edatabase/elibgetdb.php/http/...,
www.rcsed.ac.uk/journal/svol1_6/10600004.html
96
Surgical Protocol (cont.)
  • The hollow center portion of the femur is cleaned
    and enlarged
  • A cavity matching the shape of the implant stem
    is created
  • Top end of femur is planed and smoothed so that
    stem can be inserted flush with the bone surface
  • Stem is impacted into place using the mallet

www.elib.gov.ph/edatabase/elibgetdb.php/http/...,
www.rcsed.ac.uk/journal/svol1_6/10600004.html
97
Rehabilitation Process
  • Physical therapy and exercises to strengthen the
    artificial hip
  • Aided walking with crutches for up to 4-6 weeks
  • Use of cane for another 4-6 weeks before being
    able to walk unaided
  • High impact sports like running and aerobics are
    strongly not recommended
  • Full recovery varies from 3-6 months

www.hipsandknees.com/hip/bhr/rehab.htm
98
Summary Surgical Implementation
  • Total hip replacement involves replacing the
    diseased femoral head with a ball fixed to a
    stem, and the socket with an acetabular shell
    with a lining cup
  • During surgery, soft tissue from the acetabulum
    is removed in preparation for reaming, and the
    acetabular shell is then impacted into the cavity
    using a mallet
  • The center portion of the femur is removed for
    insertion of the femoral stem
  • Sterilization of ceramic hip implants is
    commonly done using gamma radiation and ethylene
    oxide
  • The rehabilitation process involves physical
    therapy and use of a cane or stick until full
    recovery at 3-6 months

www.dreamscape.com/cnytc/ELA.html
99
Implant Performance
Clinical Trial 1
Implant Performance
Clinical Trials Summary
Clinical Trial 2
Failure Modes
Chapter Summary
100
Implant Performance
  • The best way to evaluate the performance of an
    implant is to collect data through clinical
    trials
  • We will look into the results of 2 FDA approved
    clinical trials on a cementless
    ceramic-on-ceramic total hip arthroplasty design

101
Methods of Clinical Trial 1
  • Objective
  • Analyze the failure of a ceramic-on-ceramic hip
    implant
  • Time frame
  • Oct 1999 (rolling participation) to Apr 2005
  • Samples
  • 282 patients (315 hips) are treated with a
    ceramic-on-ceramic implant
  • Median weight of patients was 83.4 kg
  • Clinical data
  • Harris hip score (indicates range of motion)
  • Radiographs
  • Retrieval analysis (on failed explanted implants
    only)
  • Definition of failure
  • Failure was defined as fracture or displacement
    of the ceramic liner

Trial Results
  • Robert A. Poggie, Thomas R. Turgeon and Richard
    D. Coutts, Failure Analysis of a Ceramic Bearing
    Acetabular Component. The Journal of Bone
    Joint Surgery. 2007.

102
Results of Clinical Trial 1
  • 14 out of 315 (4.4) ceramic-on-ceramic hips
    failed
  • Time to failure ranged from 8 to 42 months (avg
    25 months)
  • Harris hip scores indicated that the patients
    with and without failure were quite active with
    an essentially unrestricted range of hip motion
  • Retrieval analysis demonstrated stripe and rim
    wear with evidence of adhesive wear, indicating a
    potentially high-friction interaction at the
    articulation

Results Analysis
Comparison Table
Retrieval Analysis
103
Comparison of Failed vs. Non-Failed Implant
104
Analysis of Clinical Trial 1
  • Based on the results, the biggest differential
    factor between failed and non-failed implants is
    the weight of the patient
  • Median weight of the patients with a failed
    implant was 102.5 kg, while median weight of the
    patients with no failure was 83.4 kg
  • Based on the results, patients with a body weight
    of gt91 kg had a 4.76 times greater odds of
    failure
  • No significant association was found between
    failure and age, range of motion, acetabular cup
    size, stem size, stem type, or cup abduction
    angle

105
Retrieval Analysis
  • Among the 14 failed implants, 12 of the bearing
    surfaces were found to have fractured, the
    remaining 2 implants were dislocated
  • Scanning electron microscopy identified abrasion
    of the ceramic surface with grain pull-out within
    the striped wear area of the ceramic heads

106
Methods of the Clinical Trial 2
  • Objective
  • Observe the performance of a ceramic-on-ceramic
    hip implant
  • Time frame
  • Nov 1997 (rolling participation) to 2005
  • Samples
  • 79 patients (93 hips) are treated with a
    ceramic-on-ceramic implant
  • Mean weight of patients was 63.7 kg
  • Clinical data
  • Harris hip score (indicates range of motion)
  • Radiographs
  • Minimum duration of follow-up of five years
  • Definition of failure
  • Failure was defined as fracture or displacement
    of the ceramic liner

Trial Results
  • Jeong Joon Yoon, young-Min Kim, et al.
    Alumina-on-Alumina Total Hip Artroplasty. A
    Five-Year Minimum Follow-up Study. The Journal
    of Bone Joint Surgery. 2005.

107
Results of Clinical Trial 2
  • 1 out of 93 (1.0) ceramic-on-ceramic hips failed
  • The failed hip in the patient was observed after
    a motor cycle accident
  • The mean Harris hip score was 97 points at the
    time of the latest follow-up evaluation
  • Ceramic wear was not detectable in the
    thirty-seven hips in which the femoral head could
    be differentiated from the cup on radiographs

108
Summary of Clinical Trials
  • The findings in both studies indicated that
    contemporary ceramic-on-ceramic hip
    arthroplasties performed with use of a cementless
    stem are associated with excellent clinical
    results and implant stability at five years
  • It was discovered that higher body weight of
    patient leads to a higher chance of implant
    failure
  • The relatively higher failure rate in Clinical
    Trial 1 could be attributed to its higher
    patient weight
  • See Journal References for more detail regarding
    discussed clinical trials

109
Failure Modes of Ceramic Hips
  • Here are some failure modes specific to ceramic
    total hips
  • Impingement
  • Fracture
  • Loosening, post-operative infection and
    dislocation
  • Stripe Wear
  • A possible concern not leading to failure is
  • Noises from ceramic components

110
Impingement
  • In extreme hip joint positions like too much
    bending, the neck of the femoral component may
    impinge against the rim of the cup component.

www.totaljoints.info/ceramic_total_hips.htm
111
Impingement (cont.)
  • The edge of the ceramic cup receives a blow with
    every such extreme movement.
  • Eventually, continuing blows fracture the cup
    which splinters into many fragments.
  • The use of computer navigated insertion of
    components reduces the risk of faulty positioning
    of the cup and diminishes the risk of
    impingement.
  • Patient awareness of risks of extreme hip
    movements and adequate surgeon advice also help
    to reduce such possibilities of failure.

www.totaljoints.info/ceramic_total_hips.htm
112
Fracture of Ceramic Balls
  • Fractures of modern ceramic balls are extremely
    rare because the modern medical grade ceramic has
    very fine structure, produced by HIP (hot
    isostatic pressing).
  • Ceramic components are also individually tested
    before use with weights 60x patient body
    weights.
  • The reported fracture rate of modern ceramic
    balls is exceedingly small 0.004 or 4 in 100
    000.

www.totaljoints.info/ceramic_total_hips.htm
113
Fracture of Ceramic Liners
  • The fracture often starts off as a failure of the
    binding between the polyethylene sleeve and
    ceramic liner which is caused by impingement of
    the neck against the rim of the liner.
  • They appear as hair-fine fracture lines at the
    beginning and repeated small traumas will
    exacerbate the fractures till the liner
    eventually splinters and results in patient pain
    and discomfort.

www.totaljoints.info/ceramic_total_hips.htm
114
Loosening, post-operative infection and
dislocation
  • Loosening of ceramic components has been reported
    for 0.5 of components in the Lineage System.
  • Post-operative infection rate has been reported
    to be 0.7 with ceramic total hips in the USA
    study. This is similar to the rates of
    postoperative infection observed in operations
    with other total hip systems.
  • Dislocation rate has been reported for 2.4 of
    ABC systems and for 1 of the Transcend and
    Lineage systems. The rates of dislocations for
    other total hip systems varies from 0 up to 7,
    so that the dislocation rates of ceramic hips are
    not especially low, but not exceptionally high
    either.

www.totaljoints.info/ceramic_total_hips.htm,
www.hrorthopaedics.co.uk/Hip20Replacement.htm
115
Stripe Wear
  • Stripe wear refers to the long, narrow area of
    wear damage observed on some alumina balls in
    ceramic total hips.
  • This results from the line contact between the
    head and the edge of the liner.
  • Another cause of stripe wear is the pistoning of
    hip bearings during walking.
  • Micro-separation of the bearing centers occurs
    during the swing phase of normal walking and
    subsequent edge loading with the heel strike
    causes the stripe.

www.totaljoints.info/ceramic_total_hips.htm,
www.hrorthopaedics.co.uk/Hip20Replacement.htm
116
Noises from Ceramic Components
  • Many patients have reported clicking or squeaking
    noises from their new hips when they change hip
    positions.
  • Noises may be caused by a tendon or scar tissue
    streak which glides over the protruding portion
    of the new total hip joint.
  • They may also be caused by small pistoning
    movements during walking.
  • These noises most likely result from faulty
    positioning of the ceramic cup.

www.totaljoints.info/ceramic_total_hips.htm,
www.hrorthopaedics.co.uk/Hip20Replacement.htm
117
Summary Implant Performance
  • Contemporary ceramic-on-ceramic total hip
    arthroplasties have produced excellent results
    and implant stability at 5 years
  • Higher body weights in patients may lead to
    higher chances of implant fracture
  • Some of the failure modes of ceramic hips include
    fracture of balls and liners, stripe wear,
    impingement, implant loosening and post-operative
    infection and dislocation

www.dreamscape.com/cnytc/ELA.html
118
Glossary of Terms
  • Dislocatable Femoral head can come out of the
    socket when stressed
  • Labrum A ring of fibrocartilage around the edge
    of an articular surface of a bone
  • Osteophyte Also known as bone spurs. These are
    bony projections that form all joints and are
    often seen in conditions like arthritis
  • Reaming To form, shape, taper, or enlarge (a
    hole or bore, for example) with or as if with a
    reamer
  • Subluxatable Unstable when stressed
  • Click here to go back to where you were

119
Web References
  • http//www.spinecarehelp.com/hip-replacement-surge
    ry.htm
  • http//www.medicinenet.com/total_hip_replacement/p
    age2.htm
  • http//www.pdrhealth.com/patient_education/BHG01RH
    08.shtml
  • http//www.oagb.net/education/hipresurface/images/
    hip_compare.jpg
  • http//en.wikipedia.org/wiki/Hip
  • http//www.hipsandknees.com/hip/hipanatomy.htm
  • www.lasvegaspaininstitute.com/pain.htm
  • www.4newjoints.com/Total_Hip.htm
  • http//hipreplacement.co.uk/Primary/Advantag.html
  • http//www.williambkurtz.com/Hip_Folder/Total20Hi
    p20Replacement.htm
  • http//www.devicelink.com/emdm/archive/06/11/019.h
    tml
  • http//www.coa-aco.org/library/clinical_topics/cer
    amic_bearing_surfaces.html
  • http//www.touchbriefings.com/pdf/1857/hawes.pdf
  • http//www.morganadcanvedceramics.com/articles/med
    ical_apps.htm
  • http//www.patentstorm.us/patents/5370694-descript
    ion.htm
  • www.totaljoints.info/ceramic_total_hips.htm
  • http//www.mghp.com/services/procedure/hipreplacem
    ent.shtml

120
Journal References
  • R. Nizard, L. Sedel, D. Hannouche, M. Hamadouche,
    P. Bizot, Alumina Pairing in Total Hip
    Replacement, The Journal of Bone and Joint
    Surgery
  • Trident Ceramic Acetabular System The Path to
    Approval Brochure
  • Matthew Sloanaker, T. Goswani, Review of Wear
    Mechanisms in Hip Implants, Science Direct
  • Thomas P. Schmalzried, M.D.. How I choose a
    bearing surface for my patients. The Journal of
    Arthroplasty Volume 19, Issue 8, Supplement 1,
    December 2004, Pages 50-53
  • Samir Sodha, M.D., Johnation P. Garinao, M.D, et
    al. Concepts of the Modern Ceramic on Ceramic
    Total Hip Arthroplasty and Early Results. UPOJ
    Volume 14, Spring 2001, Pages 1-4
  • P. Boutin, P. christel, et al. The use of dense
    alumina-alumina ceramic combination in total hip
    replacement. France, 1988
  • Kevin B. Fricka, M.D., Amanda Marshall, M.D., et
    al. Constrained Liners in revision Total Hip
    Arthroplasty An Overuse Syndrome. The Journal
    of Arthroplasty Volume 21, Issue 4, Supplement
    1, June 2006, Pages 121-125
  • A. Prof Sunil Kumar, Dr Andrew Lewies, The
    influence of the surface chemistry of metallic
    and ceramic implants wear debris particles on the
    cellular response
  • Robert A. Poggie, Thomas R. Turgeon and Richard
    D. Coutts, Failure Analysis of a Ceramic Bearing
    Acetabular Component. The Journal of Bone
    Joint Surgery. 2007.
  • Jeong Joon Yoon, young-Min Kim, et al.
    Alumina-on-Alumina Total Hip Artroplasty. A
    Five-Year Minimum Follow-up Study. The Journal
    of Bone Joint Surgery. 2005.
  • Click here to go back to summary of clinical
    trials

121
Surgeon and Vendor Contacts
Surgeon Contact Michael Bolognesi, MD Clinical
Faculty, Division of Orthopaedic Surgery Duke
University Email contact michael.bolognesi_at_duke.
edu Vendor Contact Brian Daigle Stryker
Orthopaedics Email contact Brian.Daigle_at_stryker.
com
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