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Slide 1
Reviewed by: Name: AGNES Purwidyantri Student ID No: D 0228005
Basics of Orthopedic Implants
Slide 2
Bone Properties Density 2.3g/cm 3 Tensile Strength 3-20MPa
Compressive Strength 15,000 psi Shear Strength 4,000 psi Youngs
Modulus 10-40 MPa Orthopedics Terms Osteoconductive The property of
a material that allows for the possible integration of new bone
with the host bone. Osteoinductive Characteristic in materials that
promote new bone growth. Bioresorbable The ability of a material to
be entirely adsorbed by the body. Trochanter The second segment of
the leg, after the coxa and before the femur
Slide 3
Screw Types OBLIQUE SCREWS In subtrochanteric and high femoral
fractures oblique screws may be required to be inserted up the
femoral neck Screws are 4.5mmX150mm
Slide 4
CANNULATED SCREW Screw Sizes 6.5mm X 102mm 4.5 X 12.5mm Screw
Types
Slide 5
CANNULATED SCREW A bulbous ended nail with cannulated 12.5 mm
screws is shown here successfully stabilizing a subtrochanteric
non-union of the femur following a failed Gamma nail Screw
Types
Slide 6
TRANSVERSE SCREWS In most subtrochanteric and upper femoral
fractures it is much easier to insert transverse screws in the
upper femur, than use oblique screws up the neck of the femur.
Screw Types
Slide 7
Transverse Screws Screw Types
Slide 8
Removing the Femoral Head Once the hip joint is entered, the
femoral head is actually dislocated from the acetabulum and the
femoral head is removed by cutting through the femoral neck with a
power saw. The steps involved in replacing a diseased hip with an
uncemented artificial hip begin with making an incision on the side
of the thigh to allow access to the hip joint. Reference: Medical
Multimedia Group (http://www.sechrest.com/mmg/) Example case
Slide 9
Reaming the Acetabulum Attention is then turned towards the
socket, where using a power drill and a special reamer, the
cartilage is removed from the acetabulum and the bone is formed in
a hemisperical shape to exactly fit the metal shell of the
acetabular component.
Slide 10
Inserting the Acetabular Component Once the right size and
shape is determined for the acetabulum, the acetabular component is
inserted into place. In the uncemented variety of artificial hip
replacement, the metal shell is simply held in place by the
tightness of the fit or by using screws to hold the metal shell in
place. In the cemented variety, a special epoxy type cement is used
to anchor the acetabular component to the bone.
Slide 11
Preparing the Femoral Canal To begin replacing the femur,
special rasps are used to shape the hollow femur to the exact shape
of the metal stem of the femoral component.
Slide 12
Inserting the Femoral Stem Once the size and shape are
satisfactory, the stem is inserted into the femoral canal. Again,
in the uncemented variety of femoral component the stem is held in
place by the tightness of the fit into the bone (similar to the
friction that holds a nail driven into a hole drilled into wooden
board - with a slightly smaller diameter than the nail). In the
cemented variety, the femoral canal is rasped to a size slightly
larger than the femoral stem, and the epoxy type cement is used to
bond the metal stem to the bone.
Slide 13
Attaching the Femoral Head The metal ball that makes up the
femoral head is attached.
Slide 14
The Completed Hip Replacement
Slide 15
The steps involved in replacing a diseased knee with an
artificial knee begin with making an incision on the front of the
knee to allow access to the knee joint. Shaping the Distal Femoral
Bone Once the knee joint is entered, a special cutting jig is
placed on the end of the femur. This jig is used to make sure that
the bone is cut in the proper alignment to the leg's original
angles - even if the arthritis has made you bowlegged or
knock-kneed. The jig is used to cut several pieces of bone from the
distal femur so that the artificial knee can replace the worn
surfaces with a metal surface.
Slide 16
Metals For Implants Must be corrosion resistant Mechanical
properties must be appropriate for the desired application Areas
subjected to cyclic loading must have good fatigue properties --
implant materials cannot heal themselves ORTHOPEDICS MATERIALS 1.
Metal Orthopedic Devices with Metal Plates and screws, Pins and
Wires, rods (temporary) Total joints (permanent) Clips and staples
Plates and screws, Pins and Wires, rods (temporary) Total joints
(permanent) Clips and staples
Slide 17
Metals Used in Implants Three main categories of metals for
orthopedic implants stainless steels cobalt-chromium alloys
titanium alloys Material looked at in this project: Magnesium Foam
Generally about 12% chromium (316L, Fe-Cr-Ni-Mo) High elastic
modulus, rigid Low resistance to stress corrosion cracking, pitting
and crevice corrosion, better for temporary use Corrosion
accelerates fatigue crack growth rate in saline (and in vivo)
Intergranular corrosion at chromium poor grain boundaries -- leads
to cracking and failure Wear fragments - found in adjacent giant
cells Stainless Steel
Slide 18
Cobalt Based Alloys Co-Cr-Mo Used for many years in dental
implants; more recently used in artificial joints good corrosion
resistance Co-Cr-Ni-Mo Typically used for stems of highly loaded
implants, such as hip and knee arthroplasty Very high fatigue
strengths, high elastic modulus High degree of corrosion resistance
in salt water when under stress Poor frictional properties with
itself or any other material Molybdenum is added to produce finer
grains
Slide 19
Titanium and Titanium Alloys High strength to weight ratio
Density of 4.5 g/cm3 compared to 7.9 g/cm3 for 316 SS Modulus of
elasticity for alloys is about 110 GPa Not as strong as stainless
steel or cobalt based alloys, but has a higher specific strength or
strength per density Low modulus of elasticity - does not match
bone causing stress shielding
Slide 20
Titanium Alloys Co-Ni-Cr-Mo-Ti, Ti6A4V Poor shear strength
which makes it undesirable for bone screws or plates Tends to seize
when in sliding contact with itself or other metals Poor surface
wear properties - may be improved with surface treatments such as
nitriding and oxidizing
Slide 21
Best Performance Titanium has the best biocompatibility of the
three. Metal of choice where tissue or direct bone contact required
(endosseous dental implants or porous un- cemented orthopedic
implants) Corrosion resistance due to formation of a solid oxide
layer on surface (TiO2) -- leads to passivation of the
material
Slide 22
Metallic Foam Types of metallic foams Solid metal foam is a
generalized term for a material starting from a liquid-metal foam
that was restricted morphology with closed, round cells. Cellular
metals:A metallic body in which a gaseous void is introduced.
Porous metal: Special type of cellular metal with certain types of
voids, usually round in shape and isolated from each other. Metal
Sponges: A morphology of cellular metals with interconnected voids.
Why Foam? (Mg Foam) Open cellular structure permits ingrowths of
new-bone tissue and transport of the body fluids Strength &
Modulus can be adjusted through porosity to match natural bone
properties Why Foam? (Mg Foam) Open cellular structure permits
ingrowths of new-bone tissue and transport of the body fluids
Strength & Modulus can be adjusted through porosity to match
natural bone properties
Slide 23
Requirements for Porous Implant Pore Morphology (Spherical)
Pore Size (200 m - 500 m) Porosity High Purity (99.9%)
Biocompatibility Bioresorbable Biocompatible Osteoconductive
Osteoinductive Properties of bone can be easily attained using
varying processing techniques Why Magnesium?
Slide 24
Processing the Mg by Powder Metallurgy Techniques Powder Mg
powder 99.9% purity particle size 180 m Binder: Ammonium
Bicarbonate Spherical Shape 99.0% purity Size between 200 m 500 m
Processing Steps Blend powders until a homogenous mixture is
attained. Uniaxially press at 100MPa into green compacts Heat treat
at 200C for 5hrs, for binder burnout Sinter at 500C for 2hrs
Processing Steps Blend powders until a homogenous mixture is
attained. Uniaxially press at 100MPa into green compacts Heat treat
at 200C for 5hrs, for binder burnout Sinter at 500C for 2hrs
Slide 25
Results From Processing Optical Micrograph of Porous Mg: Small
isolated micropores distributed in the wall of the interpenetrated
macropores. The micropores are on the order of microns, while the
macropores are in the range of 200 m 500 m
Slide 26
Results of Processing SEM Micrograph of Mg: Micropores result
from the volume shrinkage during sintering and are to small for
bone growth Macropores are made on the appropriate size level to
promote the ingrowths of new-bone tissues and transport of body
fluid
Slide 27
Adsorption and Toxicity Adsorption Rates for Mg The bone will
adsorb around 40% of the Mg in the screw per year. From this the
lifetime of the screw would be between 5 7 years before no traces
are left. Toxicity Recommended dosage of Mg per day is 350mg 60% of
Mg in the body is found in bones In recent studies, a diet rich in
Mg resulted in increases in bone density in postmenopausal women
Relatively low toxicity issues, but in vivo testing would
clarify.
Slide 28
Comparisons MaterialDensityYoungs Modulus Tensile Strength
Estimated Cost Ranking Bone2.310 403 20Na Stainless Steel
7.91962901 Co Alloys8.92113454 Ti Alloys4.51052003 Mg
Foam2.3310.4762.8432