Spinal Fusion Implants

1
Spinal Fusion Implants
Ben Russell Austin Deschner Claire
Vinson ---------- BME 215 Duke University Fall
2008
BEGIN
http//us.synthes.com/NR/rdonlyres/74C8AC9A-54CB-4
06C -B0AC-DFF94B98A95F/213/ClickXEnhancements3.jpg
http//img.medscape.com/pi/emed/ckb/neurosurgery /
247017-247018 1343720-1352138.jpg
2
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3
Instructions
This is an interactive PowerPoint that will
introduce you to the science and applications of
spinal fusion rod implants.
Click the button below to start a short tutorial
and overview of the navigation controls.
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4
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5
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6
Instructions
Main
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Give it a try
This is the Information Button If you see this
little green button, hover over it for quick
extra information
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There will also be several other
along the way that you can click
to learn more about particular topics. Also, some
text is shown in blue for emphasis.
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Implantation
Performance
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8
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Main
Disease State
Materials Design
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Learn about the spine anatomy and diseases
potentially requiring spinal fusion
Implantation
Performance
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References
9
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Disease State
Materials Design
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Learn about the design of spinal rod implants and
their material properties
Implantation
Performance
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10
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Disease State
Materials Design
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Implantation
Performance
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Learn about spinal fusion surgery and the
implantation of spinal rods
back to Intro
References
11
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Main
Disease State
Materials Design
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Implantation
Performance
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Learn about the effectiveness of spinal rod
implants
back to Intro
References
12
Disease State
Main
gt
Disease State
Spine Anatomy
Degenerative Disc Disease
Other Diseases Of The Spine
Chapter Summary
http//www.eorthopod.com/images/ContentImages/spin
e/ spine_lumbar/degeneration/lumbar_degeneration_i
ntro01.jpg
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Main
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Disease State
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Spine Anatomy
Spine Anatomy
Spinal elements
Primary regions Of spine
14
Spinal Elements
Main
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Disease State
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Spine Anatomy
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S. Elements

• The spine is comprised of intervertebral discs
  and vertebrae, and protects the spinal cord

Spinal Cord
Intervertebral Disc
Vertebra
http//www.sci-recovery.org/images/vertebraeandspi
nalcord.jpg
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Spinal Cord
Main
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Disease State
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Spine Anatomy
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S. Elements
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S. Cord

• The spinal cord is a bundle of nerve fibers that
  transmits electrical signals between the brain
  and the bodys limbs and organs
• The spinal cord is fed through the spinal canal

http//myhealth.centrahealth.com/library/healthgui
de/en-us/images/media/medical/hw/n5551554.jpg
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Spinal Cord
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Disease State
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Spine Anatomy
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S. Elements
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S. Cord

• Different parts of the spine host nerve routes
  that control different bodily functions

http//media-files.gather.com/images/d576/d164/d74
4/d224/d96/f3/full.jpg
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Spinal Cord
Main
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Disease State
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Spine Anatomy
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S. Elements
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S. Cord

• A compressed nerve can cause pain elsewhere in
  the body, according to the areas covered by that
  nerve shown on the right
• Unbearable pain due to problems in the spine is
  the leading reason for intervention via spinal
  fusion

http//www.ark.in-berlin.de/senszonen.svgz
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Intervertebral Discs
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Disease State
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Spine Anatomy
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S. Elements
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I. Discs

• Intervertebral discs are composed mostly of
  collagen (cartilage), proteoglycan (protein), and
  water
• The discs have 3 main functions
• They act as a ligament, holding the vertebrae
  together
• They absorb shock and help support the downward
  weight (axial load) of the body
• They act as a pivot point, allowing the spine to
  bend, rotate, and twist

• Intervertebral discs are composed mostly of
  collagen and proteoglycan (forming fibrous
  cartilage), and water

http//www.eorthopod.com/images/ContentImages/spin
e/spine_lumbar/degeneration/lumbar_degeneration_an
atomy03.jpg
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Intervertebral Discs
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Disease State
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Spine Anatomy
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S. Elements
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I. Discs

• Intervertebral discs are made of three basic
  structures
• Nucleus Pulposus
• Annulus Fibrusus
• Vertebral Endplates

http//chirogeek.com/000_Disc_Anatomy.htm
http//chirogeek.com/000_DDD_Page-2_DDD.htm
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Intervertebral Discs
Main
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Disease State
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Spine Anatomy
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S. Elements
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I. Discs

• Intervertebral discs are made of three basic
  structures
• Nucleus Pulposus
• Annulus Fibrusus
• Vertebral Endplates

http//chirogeek.com/000_Disc_Anatomy.htm
The nucleus pulposus is the water-rich,
gelatinous center of the disc. When standing
upright, the nucleus is the portion of the disc
that bears the majority of the spines axial
load. This generates a lot of pressure in the
nucleus, as shown in the figure on the bottom
right.
http//chirogeek.com/000_DDD_Page-2_DDD.htm
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Intervertebral Discs
Main
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Disease State
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Spine Anatomy
gt
S. Elements
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I. Discs

• Intervertebral discs are made of three basic
  structures
• Nucleus Pulposus
• Annulus Fibrusus
• Vertebral Endplates

http//chirogeek.com/000_Disc_Anatomy.htm
The anulus fibrosus has a higher collagen content
and lower water content than the nucleus
pulposus, making it strong and fibrous. The
anulus is made of 15-25 concentric sheets of
collagen called the lamellae, which are held
together with proteoglycan. The lamellae
surround and contain the pressurized nucleus.
http//chirogeek.com/000_DDD_Page-2_DDD.htm
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Intervertebral Discs
Main
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Disease State
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Spine Anatomy
gt
S. Elements
gt
I. Discs

• Intervertebral discs are made of three basic
  structures
• Nucleus Pulposus
• Annulus Fibrusus
• Vertebral Endplates

http//chirogeek.com/000_Disc_Anatomy.htm
The vertebral endplates are composed mostly of
cartilage. They attach the discs to the
vertebrae. The vasculature of the vertebrae
supply nutrients to the nucleus and anulus
through these endplates.
http//chirogeek.com/000_DDD_Page-2_DDD.htm
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Vertebrae
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae
Vertebrae are composed of bone The vertebrae
maintain the structure of the spine Knowing the
nomenclature of the vertebrae is useful for
understanding the parts of the spinal fusion
system
http//www.emory.edu/ANATOMY/AnatomyManual/fig7.jp
g
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Vertebrae
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

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Vertebrae
Main
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Disease State
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Spine Anatomy
gt
S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Vertebral Body
The vertebral body is the main portion of the
vertebrae. It bears the majority of the bodys
load while standing and attaches to the
intervertebral discs.
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Vertebrae
Main
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Pedicles
The pedicles stick out of the vertebral body and
provide side protection for the spinal cord and
nerves.
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Vertebrae
Main
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Disease State
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Spine Anatomy
gt
S. Elements
gt
Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Lamina
The lamina bridges the spinous processes and
facet joints. The lamina also provides backside
protection for the spinal cord.
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Vertebrae
Main
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Spinous Process
The spinous process projects outwards from the
midline of the lamina and serves as a site of
attachment for muscles and ligaments.
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Vertebrae
Main
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Transverse Processes
The transverse processes project outwards at the
junction of the pedicle and lamina. These serve
as sites of attachment for muscles and ligaments.
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Vertebrae
Main
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Disease State
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Spine Anatomy
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S. Elements
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Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Spinal Canal
The spinal canal is the tunnel made by the
vertebrae that the spinal cord passes through.
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Vertebrae
Main
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Disease State
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Spine Anatomy
gt
S. Elements
gt
Vertebrae

• Important parts of the vertebrae to consider
  are the
• Vertebral body
• Pedicles
• Lamina
• Spinous Process
• Transverse Processes
• Spinal Canal
• Facet Joints

http//www.cedars-sinai.edu/7132.html
Facet Joints
The facet joints on each vertebra attach it with
the vertebra above and below it.
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Primary Regions
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Disease State
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Spine Anatomy
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Primary Regions

• There are four primary regions of the spine
• Cervical
• Thoracic
• Lumbar
• Pelvic/Sacral

http//www.agrabilityproject.org/assistivetech/tip
s/tractorseats_files/regionsofspine.gif
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Primary Regions
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Disease State
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Spine Anatomy
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Primary Regions

• Cervical Region
• 7 vertebrae
• Convex curve with respect to anterior
• Small size compared to other vertebrae
• C1 and C2 are specialized for joining skull and
  head rotation

http//www.mayfieldclinic.com/Images/PE-AnatSpine_
Figure2.jpg
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Primary Regions
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Disease State
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Spine Anatomy
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Primary Regions

• Thoracic Region
• 12 vertebrae
• Concave curve with respect to anterior
• Intermediate size compared to other vertebrae
• The spinal cord ends at T12

http//www.mayfieldclinic.com/Images/PE-AnatSpine_
Figure2.jpg
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Primary Regions
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Disease State
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Spine Anatomy
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Primary Regions

• Lumbar Region
• 5 vertebrae
• Convex curve with respect to anterior
• Large size compared to other vertebrae
• This region is the most common regions requiring
  spinal fusion due to degenerative disc disease

http//www.mayfieldclinic.com/Images/PE-AnatSpine_
Figure2.jpg
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Primary Regions
Main
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Disease State
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Spine Anatomy
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Primary Regions

• Sacral/Pelvic Region
• This region consists of two major parts sacrum
  coccyx
• Sacrum
• 5 fused vertebrae
• Coccyx
• 4 fused vertebrae

http//www.mayfieldclinic.com/Images/PE-AnatSpine_
Figure2.jpg
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Main
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DDD
Degenerative Disc Disease
basics
risk factors
symptoms
treatment
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Basics of DDD
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Disease State
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DDD
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Basics

• Degenerative Disc Disease (DDD) is a condition
  in which one or more intervertebral discs
  gradually shrink and become brittle as a result
  of disc cell death and disc dehydration.

Flattened, brittle
Cell death Disc dehydration
http//chirogeek.com/000_DDD_Page-1_Aging.htm
http//chirogeek.com/000_DDD_Page-1_Aging.htm
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Basics of DDD
Main
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Disease State
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DDD
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Basics

• DDD is most commonly observed in the lower
  lumbar region, often causing lower back pain and
  leg pain.

http//www.straightfromthedoc.com/50226711/images
/lower_back_pain.jpg
http//wiki.cns.org/wiki/images/0/03/Degenerative_
disc_disease.jpg
http//chirogeek.com/000_DDD_Page-1_Aging.htm
40
Basics of DDD
Main
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Disease State
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DDD
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Basics

• The progression of degenerative disc disease
• is as follows15
• Capillaries giving nutrients to disc die off
• Cell death in nucleus pulposus
• The nucleus pulposus dries up

Click here to watch a video
http//indyspinemd.com/Images/normalAnat/Intervert
ebralDisc.jpg
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Basics of DDD
Main
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Disease State
gt
DDD
gt
Basics

• The progression of degenerative disc disease
• is as follows15
• Capillaries giving nutrients to disc die off
• Cell death in nucleus pulposus
• The nucleus pulposus dries up

Click here to watch a video
At birth, the disc cells in the nucleus pulposus
of each intervertebral disc are supplied with
oxygen and nutrients via capillary beds in the
vertebral endplates. Starting when we first stand
upright, and continuing as we age, these
capillary beds slowly die off. The exact reason
for capillary bed death is unknown, but it is
suspected that it is due to the increased axial
load on the spine, a result of an upright stance.
The majority of capillaries in the endplate have
been destroyed by the end of the first decade of
life.
http//indyspinemd.com/Images/normalAnat/Intervert
ebralDisc.jpg
42
Basics of DDD
Main
gt
Disease State
gt
DDD
gt
Basics

• The progression of degenerative disc disease
• is as follows15
• Capillaries giving nutrients to disc die off
• Cell death in nucleus pulposus
• The nucleus pulposus dries up

Click here to watch a video

• Eventually, there is not enough blood flow to the
  disc to supply the disc cells with oxygen and
  nutrients, and the disc cells themselves begin to
  die off.

http//indyspinemd.com/Images/normalAnat/Intervert
ebralDisc.jpg
43
Basics of DDD
Main
gt
Disease State
gt
DDD
gt
Basics

• The progression of degenerative disc disease
• is as follows15
• Capillaries giving nutrients to disc die off
• Cell death in nucleus pulposus
• The nucleus pulposus dries up

Click here to watch a video
Without disc cells to replace proteoglycan
aggregates as they break down, the nucleus of the
disc loses its ability to absorb water. This
causes the hydrostatic pressure in the nucleus to
drop dramatically as the nucleus dries up,
shifting the weight of the spinal column from the
nucleus to the annulus. At this point, the disc
is considered to be degenerated.
http//indyspinemd.com/Images/normalAnat/Intervert
ebralDisc.jpg
44
Progression of DDD
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Video
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DDD
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Basics

• vertebra

Intervertebral Disc
Capillaries
Intervertebral
http//chirogeek.com/000_DDD_Page-1_Aging.htm
disc cells
Click the picture to start
(you may need to click twice if replaying)
45
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Video
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Main
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Disease State
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DDD
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Basics
Progression of DDD
(you may need to click twice if replaying)
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Video
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Disease State
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
52
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Video
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Main
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DDD
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Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
53
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Video
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Main
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Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
54
gt
Video
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Main
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Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
55
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Video
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Main
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Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
56
gt
Video
gt
Main
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Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
57
gt
Video
gt
Main
gt
Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
nucleus dries up, shifting the weight of the
spinal column from the nucleus to the annulus
3)
58
gt
Video
gt
Main
gt
Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
nucleus dries up, shifting the weight of the
spinal column from the nucleus to the annulus
3)
59
gt
Video
gt
Main
gt
Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
nucleus dries up, shifting the weight of the
spinal column from the nucleus to the annulus
3)
60
gt
Video
gt
Main
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Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
nucleus dries up, shifting the weight of the
spinal column from the nucleus to the annulus
3)
61
gt
Video
gt
Main
gt
Disease State
gt
DDD
gt
Basics
Progression of DDD
Capillaries feeding nutrients to disc die off
1)
Loss of nutrients in nucleus pulposus, causing
cell death
2)
Replay?
nucleus dries up, shifting the weight of the
spinal column from the nucleus to the annulus
3)
62
Symptoms of DDD
Main
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Diseased State
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DDD
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Symptoms

• Degenerative Disc Disease itself has few major
  symptoms, aside from pain and reduced mobility in
  the affected region of the spine.
• However, degenerated discs are fragile and prone
  to further damage.
• Moderate or advanced DDD often causes other,
  more noticeable problems in the spine
• In severe cases, this may lead to nerve damage
  and cause pain in the legs

Spondyl- olisthesis
Spinal Stenosis
DDD
Disc Bulging
Annular Tears
Disc Herniation
63
Risk Factors of DDD
Main
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Diseased State
gt
DDD
gt
Risk Factors
Several factors are known to increase the rate
of disc degeneration.

• Structural Damage to the Disc
• Hereditary Risk Factors
• Mutations
• Smoking

64
Risk Factors of DDD
Main
gt
Diseased State
gt
DDD
gt
Risk Factors
Several factors are known to increase the rate
of disc degeneration.

• Structural Damage to the Disc
• Hereditary Risk Factors
• Mutations
• Smoking

Damage to nucleus
nucleus fracture or annulus disruption can cause
the nucleus to penetrate through the endplate.
Because of this, the hydrostatic pressure in the
nucleus depletes (like letting the air out of a
beach ball). This structural damage results in
an axial-load-shift (abnormal weight
distribution), which rapidly degenerates the disc.
http//chirogeek.com/000_DDD_Page-2_DDD.htm
65
Risk Factors of DDD
Main
gt
Diseased State
gt
DDD
gt
Risk Factors
Several factors are known to increase the rate
of disc degeneration.

• Structural Damage to the Disc
• Hereditary Risk Factors
• Mutations
• Smoking

Is twice as likely to get DDD
Has had disc surgery for severe disc degeneration
A study by Matsui L et al in 1998 found that
first degree family members from patients who
have had disc surgery are twice as likely to
develop degenerative disc disease than those from
patients who have not had disc surgery.
http//healthystart.cuyahogacounty.us/mother_child
.jpg
66
Risk Factors of DDD
Main
gt
Diseased State
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DDD
gt
Risk Factors
Several factors are known to increase the rate
of disc degeneration.

• Structural Damage to the Disc
• Hereditary Risk Factors
• Mutations
• Smoking

Two polymorphisms that lead to DDD have been
found within the genes that make discal collagen.
Another mutation that leads to DDD was found to
be associated with the discal proteoglycan
aggrecan molecule, which attracts and holds water
into the disc. Many other mutations have also
been found.
http//www.abacusbio.com/images/news20item20phot
os/SNP20diagram.png
67
Risk Factors of DDD
Main
gt
Diseased State
gt
DDD
gt
Risk Factors
Several factors are known to increase the rate
of disc degeneration.
His discs are 20 more degenerated than they
would be if he was not a smoker

• Structural Damage to the Disc
• Hereditary Risk Factors
• Mutations
• Smoking

A study by Battie et al in 1991 found that
smoking increases spinal disc degeneration in all
discs by 20. Many believe that smoking damages
the capillary beds that supply nutrients to the
discs.
http//skeptisys.files.wordpress.com/2008/02/smoki
ng.jpg
68
Treatment of DDD
Main
gt
Diseased State
gt
DDD
gt
Treatment

• Several non-surgical options are available for
  mild cases of DDD.
• Physical Therapy
• Chiropractic Therapy
• Spinal Injections
• Anti-Inflammatory Medications
• Traction
• For severe cases of DDD, and cases with
  complications such as stenosis or disc
  herniation, spinal fusion surgery is often
  suggested.

http//www.gkindia.com/therapies/images1/chiroprac
tic.jpg
http//www.crownvalleyspinalaid.com/images/lumbar_
stenosis_surgery03.jpg
69
Main
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Diseased State
gt
Other Diseases
Other Diseases Of The Spine
Disc Herniation
Fracture
Kyphosis
Spinal Stenosis
Scoliosis
Spondylolisthesis
70
Herniated Disk
Main
gt
Diseased State
gt
Other Diseases
gt
Hernia

• Disc herniations are common complications of
  degenerative disc disease.
• A disc herniation occurs when the nucleus of the
  disc works its way through the annulus.
• This may pinch the spinal nerve, causing pain.

http//www.dartmouth.edu/sport-trial/graphics/IDH_
ADAM.gif
71
Herniated Disk
Main
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Diseased State
gt
Other Diseases
gt
Hernia
Click here to watch a video

• A) Pinched nerve root
• B) Nucleus
• C) Torn outer annulus

http//www.eorthopod.com/images/ContentImages/spin
e/spine_ lumbar/anterior_fusion/lumbar_anterior_fu
sion_rationale02.jpg
http//www.spine-health.com/conditions/herniated-d
isc/lumbar-herniated-disc
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Herniated Disk
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Hernia
gt
Video
Nucleus
Annulus
Region containing spinal cord
http//chirogeek.com/001_Tutorial_Birth_of_HNP.htm
Ligament protecting spinal nerves from disc
contents
Click the picture to start
(you may need to click twice if replaying)
73
Herniated Disk
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Other Diseases
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Hernia
gt
Video
(you may need to click twice if replaying)
74
Herniated Disk
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Other Diseases
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Hernia
gt
Video

• Disc Bulge Annular Tear

The disc has become degenerated
The disc has bulged and the nucleus has torn
through the annulus
75
Herniated Disk
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Other Diseases
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Hernia
gt
Video
2) Contained Herniation
The ligament is pushed outwards and a nerve root
has been pinched
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Herniated Disk
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Other Diseases
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Hernia
gt
Video
3) Non-Contained Herniation
The ligament protecting the spinal cord has
ruptured
This exposes the nerves to corrosive nuclear
material, causing severe pain
77
Herniated Disk
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Diseased State
gt
Other Diseases
gt
Hernia
gt
Video
4) Non-Contained Herniation Fragmentation
A fragment of the nucleus is detached and loose
in the epidural space, causing severe nerve
compression
Replay?
78
Spinal Stenosis
Main
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Diseased State
gt
Other Diseases
gt
Stenosis

• A spinal stenosis is the narrowing of a region
  surrounding the spinal cord.
• This can constrict the nerves in the spinal
  cord, causing pain and nerve damage.

http//www.eorthopod.com/public/patient_education/
6569/lumbar_spinal_stenosis.html
79
Spinal Stenosis
Main
gt
Diseased State
gt
Other Diseases
gt
Stenosis
A canal stenosis is the narrowing of the spinal
canal.
http//graphics8.nytimes.com/images/2007/08/01/hea
lth/adam/19527.jpg
A foraminal stenosis is the narrowing of the
canal for the nerves that branch out of the
spinal cord.
http//www.myneurosurgery.com/images/Image31.gif
80
Fracture
Main
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Diseased State
gt
Other Diseases
gt
Fracture

• A compression fracture occurs when the bones of
  the spine become fractured due to trauma, such as
  a hyperflexion injury.

http//services.epnet.com/GetImage.aspx/getImage.a
spx?ImageIID4679
http//www.uiortho.com/Spine/SpinalCord/vertebralI
njuries.htm
81
Fracture
Main
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Diseased State
gt
Other Diseases
gt
Fracture

• A burst fracture is a more serious form of
  compression fracture.
• In severe cases of fracture, spinal fusion
  intervention is often required.

http//radiology.rsnajnls.org/cgi/content-nw/full/
213/2/321/F19B
http//www.uiortho.com/Spine/SpinalCord/vertebralI
njuries.htm
82
Scoliosis
Main
gt
Diseased State
gt
Other Diseases
gt
Scoliosis

• Scoliosis is the side to side curvature or
  rotational misalignment of the spinal column.

http//www.drpittson.net/scoliosis2.gif
83
Scoliosis
Main
gt
Diseased State
gt
Other Diseases
gt
Scoliosis

• This disorder can create back pain and physical
  deformity.
• In severe cases, realignment is often required
  via spinal rod insertion

http//www.youcanbefit.com/scol.html
84
Kyphosis
Main
gt
Diseased State
gt
Other Diseases
gt
Kyphosis

• Kyphosis is the abnormal curvature of the
  thoracic spine.
• This condition is commonly known as humpback
  or hunchback.

http//healthhabits.files.wordpress.com/2008/05/ky
phosis.jpg
85
Kyphosis
Main
gt
Diseased State
gt
Other Diseases
gt
Kyphosis

• Adult-onset kyphosis is usually a result of bad
  posture.
• Scheuermanns disease is a genetic disorder
  which causes the lumbar vertebral endplates to
  die and regrow incorrectly (osteochondrosis),
  causing severe kyphosis.

http//www.bnhspine.com/en/kyphosis.asp
86
Spondylolisthesis
Main
gt
Diseased State
gt
Other Diseases
gt
Spondylolisthesis

Spondylolisthesis is the condition of having a
vertebra that has slipped forwards. This
slippage narrows the spinal canal and pinches the
nerves, causing severe pain. Realignment is
often required in severe cases via spinal fusion.
http//www.spinalunit.org/images/Spondylolisthesis
_clip_image002.gif
87
Main
gt
Diseased State
gt
Summary
Chapter Summary
Spine Anatomy Degenerative Disc
Disease Other Diseases of Spine
Hover over the green info buttons to see the
summary for each section
88
Main
gt
Diseased State
gt
Summary
Chapter Summary
Spine Anatomy Degenerative Disc
Disease Other Diseases of Spine

• The spine is comprised of vertebrae and
  intervertebral discs, and protects the spinal
  cord.
• The vertebrae are composed of bone and maintain
  the structure of the spine.
• The intervertebral discs are fibrocartilaginous
  cushions that hold the vertebrae together, absorb
  shock, and allow the spine to bend and twist.
• They are made up of the nucleus pulposus and
  anulus fibrosus
• The spinal cord is a bundle of nerve fibers that
  controls several bodily functions, and is fed
  through the spinal canal.
• The spine has four primary regions
• Cervical
• Thoracic
• Lumbar
• Pelvic/Sacral

89
Main
gt
Diseased State
gt
Summary
Chapter Summary
Spine Anatomy Degenerative Disc
Disease Other Diseases of Spine

• Degenerative disc disease is a condition in which
  one or more intervertebral discs gradually shrink
  and become brittle as a result of cell death and
  disc dehydration
• This usually occurs in the lower lumbar region,
  causing lower back pain
• Disc degeneration can lead to conditions such as
  spinal stenosis, spondylolisthesis, and disc
  herniation
• Risk factors include structural damage to disc,
  hereditary susceptibility, mutations, smoking
• Many non-surgical options are available for
  treatment of mild DDD, but spinal fusion surgery
  is often suggested for severe cases of DDD.

90
Main
gt
Diseased State
gt
Summary
Chapter Summary
Spine Anatomy Degenerative Disc
Disease Other Diseases of Spine

• Other conditions of the spine that may require
  spinal fusion surgery include
• 1) Disc herniation
• 2) Spinal stenosis
• 3) Fracture
• 4) Scoliosis
• 5) Kyphosis
• 6) Spondylolisthesis

1
2
3
4

5
6
91
Design Materials
Main
gt
Design Materials

esign Materials
Design
Materials
Chapter Summary
http//www.cati.com/images/CS_Pioneer_ quantum_spi
nal_rod_system.jpg
92
Main
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Design Materials
Design
gt
Design
Purpose of Spinal Instrumentation
General Device Components
Expediumtm Spine System Instrumentation
93
Purpose of Device
Main
gt
Design Materials
Design
gt
Purpose
gt
Spinal fusion is a surgical procedure that
involves fusing two or more vertebrae together
with a bone graft. Spinal fusion rods are
permanent implants used to immobilize and
stabilize the vertebrae while they fuse. The
immobilization of the spine increases the fusion
rate of the bone graft with the vertebrae.
Bone Graft
http//www.eorthopod.com/images/ContentImages/spin
e/ spine_lumbar/lumbar_PLIF/lumbar_PLIF_intro01.jp
g
94
General Components
Main
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Design Materials
Design
gt
Components
gt
Rods
Cross-Links
Pedicle Screws
Caps
http//www.cati.com/images/CS_Pioneer_quantum_spin
al_rod_system.jpg
95
ExpediumTM
Main
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Design Materials
Design
gt
ExpediumTM
gt
Rods
Pedicle Screws
Caps
Cross-Links
How the Parts Fit Together
Expedium Spine System Technical Monograph
96
Rods
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Rods
gt
rods for spinal fusion come either straight or
pre-lordosed (pre-bent to fit the spines
curvature). Expedium rods have diameters of
either 5.5mm or 6.35mm. Expedium rods have
lengths ranging from 30mm to 450mm.
Straight
Pre-Lordosed
Expedium Spine System Product Catalogue
97
Rods
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Rods
gt

• DePuy makes their expedium rods available in
  four different materials
• Metal (stainless steel, titanium alloy, and
  commercially pure titanium)
• Polymer (PEEK)
• These materials are evaluated in the materials
  section

http//www.istockphoto.com/file_closeup.php?id685
2678
http//www.istockphoto.com/file_closeup.php?id508
8182
http//www.theodoregray.com/PeriodicTable/Samples/
022.46/index.s12.html
http//www.sdplastics.com/peek.jpg
98
Pedicle Screws
Main
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Design Materials
Design
gt
ExpediumTM
gt
Screws
gt
The screws used in spinal fusion penetrate
through the pedicles of the vertebrae. These
screws act as firm anchor points that can be
connected with the rods.
http//www.medscape.com/content/2001/00/40/57/4057
07/art-nf1004.11.fig5.jpg
http//www.cedars-sinai.edu/7132.html
99
Pedicle Screws
Main
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Design Materials
Design
gt
ExpediumTM
gt
Screws
gt

• Expedium features three types of screws
• Monoaxial
• Polyaxial
• Uni-Planar
• The polyaxial and uni-planar screws are free to
  move accordingly until they are locked in place
  by their caps in their final arrangement.

Monoaxial Screw
Polyaxial Screw
Uni-Planar Screw
Expedium 5.5 Spine System Brochure
100
Pedicle Screws
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Screws
gt
Expedium screws incorporate a double-lead
thread. Expedium screws enters the bone twice
as fast as traditional, single-lead screws.
Expedium Spine System Technical Monograph
101
Pedicle Screws
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Screws
gt
Expedium screws are self-tapping. They
incorporate fully threaded and tapered (minor and
major diameter) tips, allowing the screw to
easily be inserted into the bone.
Expedium Spine System Technical Monograph
102
Caps
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Caps
gt
Specialized caps are used during spinal fusion
to lock the rods and pedicle screws into
place. These closure mechanisms must maintain a
balance between secure closure and implant
profile.
Expedium Spine System Brochure
103
Caps
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Caps
gt
Expedium caps incorporate a square thread. The
square thread design significantly minimizes
difference between the thread crest (a) and the
thread opening (ß), making it less likely for the
screw to skip a thread and advance off axis.
Expedium Spine System Technical Monograph
104
Caps
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Caps
gt
The square threading helps to minimize spreading
forces after tightening. In other words, the
square threading minimizes the horizontal forces
that make the cap try to pop off after tightening.
Expedium Spine System Technical Monograph
105
Caps
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Caps
gt
Expedium also features a new Dual-Innie
(DI) closure system that can lock the desired
screw angle in before securing the rod. The
first cap locks the screw in place, while the
second secures the rod.
2
1
Expedium 6.35 Spine System Brochure
106
Caps
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Caps
gt
The Dual-Innie closure mechanism, along with the
square threads, allow for an increased polyaxial
and axial slip strength. In other words, the
force required for the screw or rod position to
slip is maximized.
Expedium DI Independent Locking Technology
Brochure
107
Cross-Links
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Cross-Links
gt
When enough vertebrae are fused, cross-links are
often used to secure the rods in place during
spinal fusion. Expedium features a
cross-connector system that comes in fixed sizes
(15-36mm) and adjustable sizes (25-100mm).
Expedium SFX Cross Connector System Brochure
108
Cross-Links
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
Cross-Links
gt
Having the choice of fixed and adjustable
cross-links allows for more control in the
arrangement of the spine system. These
cross-links also increase the torsional strength
of the spine system, further securing the rods in
place.
Expedium SFX Cross Connector System Brochure
109
How They Fit
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
How They Fit
gt
Expedium DI Independent Locking Technology
Brochure
110
How They Fit
Main
gt
Design Materials
Design
gt
ExpediumTM
gt
How They Fit
gt
The system allows the screw to achieve a fixed
angle and later be secured on the rod at a
desired location.
Expedium DI Independent Locking Technology
Brochure
111
Main
gt
Design Materials
Materials
gt
Materials
Stainless Steel
Titanium Alloy
CP Titanium
PEEK
Comparison Of Metals
112
Stainless Steel
Main
gt
Design Materials
Materials
gt
Stainless Steel
gt
316L stainless steel is one of the most commonly
used materials in orthopedic implants17,19

• Chemical Composition
• 63.5 - 72 Iron
• 16 - 18.5 Chromium
• 10 - 14 Nickel
• 2 - 4 Molybdenum

• Advantages
• Stiffest available material
• Tolerant of bending and surface defects
• Stronger than CP Titanium

• Disadvantages
• Not MRI or CT Compatible
• Least resistance to corrosion
• Heavy
• Can deform over time
• Weaker than Titanium Alloy

http//www.istockphoto.com/file_closeup.php?id685
2678
113
Titanium Alloy
Main
gt
Design Materials
Materials
gt
Titanium Alloy
gt
Titanium Alloy Ti-6Al-4V has become the most
commonly used material in spinal fusion implants
in recent years17,19

• Chemical Composition
• 89 - 91 Titanium
• 5.5 - 6.5 Aluminum
• 3.5 - 4.5 Vanadium

• Advantages
• Highly biocompatible
• Good imaging compatibility
• Stiffer than CP Titanium
• Strongest Available Material
• Resistant to slow deformation
• Lightweight

• Disadvantages
• More flexible than stainless steel
• Extremely sensitive to bending and surface
  defects
• Some MRI artifacts still remain

http//www.istockphoto.com/file_closeup.php?id508
8182
114
CP Titanium
Main
gt
Design Materials
Materials
gt
CP Titanium
gt
Commercially Pure (CP) Titanium is a popular
choice for spinal instrumentation due to its high
biocompatibility17,19

• Chemical Composition
• 99.0 - 100 Titanium
• 0.0 - 0.5 Iron
• 0.0 - 0.5 Trace Elements

• Advantages
• Highest biocompatibility
• Best imaging compatibility
• Resistant to slow deformation
• Lightweight

• Disadvantages
• Extremely sensitive to bending and surface
  defects
• Weakest available material
• Most flexible available material

http//www.theodoregray.com/PeriodicTable/Samples/
022.46/index.s12.html
115
PEEK
Main
gt
Design Materials
Materials
gt
PEEK
gt
Polyetheretherketone (PEEK) is a new material for
spinal rods. Unlike other materials for spinal
rods, PEEK is a polymer.
Chemical Composition PEEK describes a range of
polymers, rather than a single compound. The
basic monomer of PEEK is shown here
http//pubchem.ncbi.nlm.nih.gov/image/structurefly
.cgi?sid698432

• Most companies making spinal rods has a
  proprietary formulation of PEEK. The properties
  of PEEK can be greatly varied by
• Inclusion of other materials such as glass or
  carbon fibers
• Inclusion of small amounts of other polymers
• Addition/removal of side chains
• Variation of polymer chain length
• Structural variation (amorphous vs. crystalline)

116
PEEK
Main
gt
Design Materials
Materials
gt
PEEK
gt

• Reason for Use
• Due to its lower stiffness as compared to metal
  instrumentation, PEEK is not suitable for
  stabilizing fusion grafts.
• However, it is ideal for correction of spinal
  deformities like Scoliosis and Kyphosis, as it
  allows a higher degree of movement than metal
  implants

http//www.sdplastics.com/peek.jpg

• Expediumtm PEEK rods
• Expedium rods are make from PEEK-Optima, a PEEK
  polymer with a proprietary composition, and the
  following material properties21
• Tensile strength 115 MPa
• Flexural Strength 170 MPa
• Elastic Modulus 4.0 GPa

http//ryortho.com/images/4_17pic3.jpg
117
Metals Comparison
Main
gt
Design Materials
Materials
gt
Compare
gt
Strength
Notch Sensitivity
Biocompatibility
Rigidity
Imaging Compatibility
Overview
118
Strength
Main
gt
Design Materials
Materials
gt
Compare
gt
Strength
gt
The strength of the material is a measure of how
much stress it is able to withstand before it
breaks. Spinal fusion rods made of weaker
materials are usually larger in diameter to
compensate.
119
Notch Sensitivity
Main
gt
Design Materials
Materials
gt
Compare
gt
Notch S.
gt
During the process of implantation, the rods must
often be bent to fit to the desired shape. This
can put notches into the rod. Additionally, the
tightening of the caps onto the rods can cause
scratches and surface defects in the rod. Some
materials remain largely unaffected by bending
and notching. However, it can severely compromise
the fatigue strength of other materials
A French bender, used to bend rods during
operations
Lindsey C, Deviren V, Zheng X, Yeh RF, Puttlitz
C. The Effects of Rod Contouring on Spinal
Construct Fatigue Strength. Spine 31(15) pp.1680-7
120
Notch Sensitivity
Main
gt
Design Materials
Materials
gt
Compare
gt
Notch S.
gt
Both CP titanium and titanium alloy are extremely
sensitive to bending and surface defects.
These materials should be treated carefully
during implantation. if a bent rod shape is
required in a titanium implant, pre-bent rods
should be used in favor of bending rods in situ
121
Biocompatibility
Main
gt
Design Materials
Materials
gt
Compare
gt
Bio
gt

• Titanium alloy has greater biocompatibility than
  stainless Steel17
• Less allergenicity
• Less corrosivity
• Less fibrogenicity
• CP Titanium has all the biocompatibility
  advantages of titanium alloy, and it has been
  shown to inhibit polymorphonucleocytes17

http//iupucbio2.iupui.edu/anatomy/GrayAnatBack.jp
g
122
Rigidity
Main
gt
Design Materials
Materials
gt
Compare
gt
Rigidity
gt
When materials are subjected to loads, they
deform. The elastic modulus of a material is a
measure of how much normal, or compressive,
stress is required to cause a certain amount of
strain. The higher the elastic modulus of a
material, the less it deforms in response to
stress.
123
Rigidity
Main
gt
Design Materials
Materials
gt
Compare
gt
Rigidity
gt
Spinal rods also undergo a large deal of bending
force. The flexural rigidity of a rod is a
measure of how much force it takes to cause it to
bend a certain amount. The higher the flexural
rigidity, the less the rod deforms.
124
Imaging Compatibility
Main
gt
Design Materials
Materials
gt
Compare
gt
Imaging
gt
CT Scan Images of Lumbar Pedicle Screws

• Compatibility with medical imaging systems is an
  important factor for any implant.
• The major imaging systems used today are CT and
  MRI.
• A MRI compatible implant cannot be even slightly
  magnetic, or it will distort the image.
• Stainless steel is slightly magnetic
• Titanium alloy and CP titanium are not
• The higher the atomic number of an element, the
  more it distorts the image in a CT scan.
• 316L Stainless Steel has a significant amount of
  Molybdenum (a.n. 42), and creates a large amount
  of distortion in CT images
• Titanium alloy TI6AL4V has a significant amount
  of Vanadium (a.n. 23), and causes little
  distortion
• CP Titanium is almost entirely titanium (a.n.
  22), and causes very little distortion

Stainless Steel
Titanium Alloy
Ebraheim NA et al. Magnetic resonance imaging
after pedicular screw fixation of the spine. Clin
Ortho Rel. Res. (279)133-7
125
Overview
Main
gt
Design Materials
Materials
gt
Compare
gt
Overview
gt
126
Main
gt
Design Materials
Summary
gt
Chapter Summary
Design Materials
Hover over the green info buttons to see the
summary for each section
127
Main
gt
Design Materials
Summary
gt
Chapter Summary
Design Materials

• The purpose of the spinal system is to immobilize
  and stabilize the spine after spinal fusion
  surgery
• The general components of the device are
• Rods
• Basis for the strength and support of the system
• Pedicle screws
• Penetrate through the pedicles of the vertebrae
  and act as anchor points that can connect with
  the rod
• Caps
• Lock the rods and pedicle screws into place
• Cross-links
• Secure the rods in place when enough vertebrae
  are fused
• This section elaborates on several features of
  the ExpediumTM Spine System made