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
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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