Soft Tissue Repair and Replacement 2906

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Soft Tissue Repair and Replacement2/9/06

• Organogenesis artificial skin, Artificial discs,
  breast augmentation

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General Structure of Spine

• 4 main sections
• Cervical - neck
• Thoracic - thorax bearing the ribs
• Lumbar - low back
• Sacrum- leading to the coccyx

• Lumbar Spine
• Five lumbar vertebrae
• Bigger and more solid than cervical or
  thoracic spine
• Primary axial load support

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Structure of Intervertebral Disc

• Fibrocartilaginous cushions serving as the
  spine's shock absorbing system
• Allow some vertebral motion extension and
  flexion.
• Individual disc movement is very limited
• Considerable motion is possible when several
  discs combine forces.
• No vascularization
• Made up largely of water
• Pressure due to activities decreases the amount
  of water within the disc
• Water reabsorption occurs while lying down
• As you get older the amount of fluid in your
  discs diminishes slightly

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Intervertebral Disc Components

• Outer Casing annulus fibrosis - Strong fibrous
• Interior nucleus pulposus- soft, jelly-like,
  reinforced with strands of fiber
• Endplates upper and lower borders of disc, part
  of vertebrae themselves

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Disc Mechanics
www.back.com
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Intervertebral Disc Functions

• To provide support between vertebra as activities
  are perform.
• Without discs, vertebra would grate and crunch
  every time one moved
• Allow flexibility and movement
• Discs transfer weight evenly from one vertebra
  to another

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How the disc gets damaged

• Degenerative disc
• Bulging disc
• Spinal Stenosis
• Herniated disc
• Thinning disc

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Degenerative Disc Disease (DDD)
www.nucleoplasty.com
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What is Degenerative Disc Disease?
http//www.spine-health.com
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A Misnomer?

• DDD pain does not actually get worse over time,
  it may actually even improve.
• More severe presentation of normal disc
  degeneration.
• All people will experience disc degeneration with
  age

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Treatment Options

• Chromic Pain Management
• Exercise lumbar stabilization or aerobics
• Physical Therapy
• Back brace
• Anti-inflammatory Medications
• Cortisone Injections
• Epidural Steroid Injections
• Spinal Fusion
• Total Disc Replacement

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Chronic Pain Management

• Exercise
• -use it or lose it
• Chiropractors
• Physical Therapy
• Massage
• Acupuncture

www.back.com
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Chronic Pain Management

• Alternative Therapies
• Craniosacral Therapy
• Polarity
• The Alexander
• Technique
• Reiki
• Feldenkrais
• Yoga

www.innerhappiness.com
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Spinal Fusion

• Spinal Fusion
• Bone graft (autologous or allogeneic)
• Internal devices (metal rods)
• Eliminates motion between vertebrae segments
  (decreases flexibility)
• Increased stress on the adjacent vertebral
  segments

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Surgical Intervention A Last Resort

• Laminectomy
• Removal of the lamina to relieve stress on spine
  and nerves
• Lumbar Microsurgery
• Removal of the bulging portion of the disc
• Minimally Invasive Lumbar Laminotomy/Discectomy
• Removal of a portion of the lamina and/or disc
• Spinal Fusion
• Any procedure fusing the vertebrae
• Anterior Lumbar Interbody Fusion (ALIF)
• Discectomy approached anteriorly
• Transforaminal Lumbar Interbody Fusion (TLIF)

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A Surgical Example

• Transforaminal Lumbar Interbody Fusion (TLIF)

• Surgical Goals
• Obtain fusion of lumbar discs
• Alleviate nerve compression by removing the
  damaged disc

http//www.allaboutbackandneckpain
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A Surgical Example

• Transforaminal Lumbar Interbody Fusion (TLIF)

Induced Spinal Bleed!!
http//www.allaboutbackandneckpain
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A Surgical Example
Results
http//www.spine-health.com
http//www.allaboutbackandneckpain
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Was It Worth It?

• As in any surgery, there are many possible
  complications.
• TLIF complications include
• Anesthesia
• Infection
• Blood Loss
• Nerve Injury
• Possible Re-operation
• (often due to slipping in the fusion mount)
• Lack of a Solid Fusion (5-10 of cases!)
• Continued or, occasionally, increased pain

In even the most effective spinal surgery
procedures, a minimum of 20 of surgeries do NOT
result in a reduction of lumbar pain!
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Are Artificial Discs a Better Option?
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Replacement

• Disc Replacement
• All three components of disc
• Retains mobility and flexibility
• Maintains the disc space height between bones
• Prevents nerve root irritation and/or damage
• No bone autograft (major source of post-operative
  pain with spinal fusion)
• Delay onset of arthritic changes adjacent to a
  fused level

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Material Considerations

• Fatigue resistance
• Minimize friction
• Superior wear characteristics
• Minimal debris generation
• Promote bone in-growth to allow for biological
  fixation of the implant
• Maintain the proper intervertebral spacing
• Provide stability
• Failsafe (failure of any individual component
  cannot be catastrophic--neural, vascular, and
  spinal tissues must be protected in the case of
  unexpected or over loading)
• Compatibility with computerize tomography and MRI
  for long-term evaluation

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Artificial Disc Replacement Eligibility
Requirements

• One diseased disc between L4 and L5 or between L5
  and S1
• Vertebra have moved less than 3mm
• Failed at least six months of conservative
  treatment (pain medication, back brace, physical
  therapy, etc.) without adequate results
• Disqualifications
• Infection
• Disc deterioration or instability at more than
  one spinal level
• Poor bone quality (osteoporosis or osteopenia).
• Pregnant

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Types of Disc Replacements
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Charité Artificial disc

• Worlds First Artificial disc
• Gained FDA approval in October 2004
• Has been used in Europe for over 17 years
• Allows patients to have between 0 and 21 degrees
  of motion while bending forward and backward.

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Charité Artificial disc
Endplates Cobalt-Chromium Alloy coated with
commercially pure titanium tri-calcium phosphate
layer
Sliding Core ultra high molecular weight
polyethylene
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• The Charite disc is an example of the most common
  combination design, which includes a polymer core
  in between two metal plates

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Endplate Composition

• Chromium-Cobalt Alloy
• Composed of Chromium, Cobalt and Molybdenum
  (ASTM-F-75)
• Molybdenum decreases grain size of the alloy ?
  increased mechanical properties
• Chromium oxide formation on the surface of CoCrMo
  provides corrosion resistance

Endplate
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Material Interactions CoCr

• Nickel originally added for superior corrosion
  resistance
• Concerns of possible toxicity and immunogenic
  reactivity from released Ni
• No longer added
• CoCrMo is corrosion resistant in chloride
  environments.

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Endplate Composition (continued)

• Commercially Pure Titanium Tricalcium Phosphate
  (CPTiCaP)
• 2 layers of CPTi are plasma-sprayed onto the
  CoCrMo endplates
• 1 layer of calcium phosphate hydroxyapatite which
  is electrochemically deposited on the CPTi layers
• Optimizes mineralized anchorage at vertebral
  endplates and supports osseointegration without
  breaking down or dissolving

Osteoblast cell line ingrowth on tricalcium
phosphate surface after 30 hours
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Material Interactions CPTiCaP

• Increases mineralized anchorage at vertebral
  endplates and supports osseointegration without
  breaking down or dissolving
• Materials with porous coatings have decreased
  fatigue performance due to stress concentrations
  from surface geometry.

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Sliding Core Ultra High Molecular Weight
Polyethylene (UHMWPE)

• Characteristics
• Thermoplastic
• Composed of long HMW chains that allow for
  uniform crystal structure packing ? high impact
  strength
• Contains radiopaque ring for radiographic
  localization

UHMWPE Sliding Core
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Material Interactions UHMWPE

• Resistant to lipid absorption
• Corrosion resistant
• Highly resistant to abrasion
• Low moisture absorption
• Low coefficient of friction
• Self lubricating
• Decreased rate of particulate wear due to
  cross-linking

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Implantation
Dissection of the fascia and the underlying blood
vessels allows for the exposure of the damaged
disc
An incision in the lower abdomen is made
Impact four retractor pins into adjacent
vertebral bodies and then apply a soft tissue
retractor system
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Implantation (continued)
Determine which of the 5 endplate sizes are
appropriate using the sizing gauge and
fluoroscopy. Insert trial disc
An X-ray is taken to ensure proper size,
placement and lordotic angulation
The damaged disc as well as the cartilaginous
endplates are removed using curettes
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Implantation (continued)
A pilot driver is screwed in, and then the trial
disc is removed. Using the guided impactor, the 2
endplates are inserted
Following a similar protocol, the appropriate
sliding core is inserted
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Implantation (continued)
A final X-ray is taken to ensure successful
implantation
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Risks of Disc Replacement

• Allergic reaction to the implant materials
• Bladder complications
• Bleeding
• Death
• Implants that bend, break, loosen, or move
• Infection
• Infertility
• Pain or discomfort
• Side effects from anesthesia
• Spinal cord or nerve damage
• Spinal fluid leakage
• Need for additional surgery

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General Host Response

• Inflammation
• Infection
• Unintended debris from wear and corrosion
• Sliding core creep
• Implant motion

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Debris-Induced Osteolysis
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Surgical Complications

• Implantation surgery is a complicated 90 - 240
  minute procedure performed through a 10 cm
  incision in the abdomen.
• Main risks
• The large veins and arteries from/to the legs
  need to be dissected away from front of the disk
• Improper alignment of implant - articulating
  surfaces of endplates must be parallel
• Proper training of surgeons to ensure successful
  implantation of the device
• Sliding core devices (Charité) require less
  placement precision than fixed pivot devices

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Osseointegration

• Layers of plasma-sprayed porous titanium and
  calcium phosphate were added to the Charité disc
  in 1998
• Coating provides for potential osseous ingrowth
  and long-term stability of the plates after
  implantation
• Coating not a feature of US version of Charité
  disc because it is not yet FDA approved
• Incorporation of the coating to the US version is
  important for long-term durability of the implant

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Function

• FDA studies show that the Charité device
  decreased the the load at facet joints by 50
  compared to a normal intact nonoperated segment
• Clincal studies also showed the implant allowed a
  range of motion from 0-21 (near normal range of
  motion)
• Proves that the implant functions as well as (or
  better) than normal disk - no functional
  improvements necessary

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Long Term Durability

• Lifespan of Charité implant 40 years (85
  million cycles)
• Most candidates for total disc replacement are in
  their 30s and 40s so the disk must be durable
  or easy replaced
• Studies show that in over 11 years of use, there
  is minimal deformation of the core (less than 8
  height loss) and no wear debris particle
  formation
• Knee and hip replacements made with UHMWPE have
  been known to wear out

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FDA Recommendations

• Development of ways to track patients in case of
  a future recall of the disc or other problem
• Making sure that appropriate surgeon training is
  provided
• Conducting further biomechanical studies
• Continuing with additional follow up of clinical
  study patients

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References

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  Historical Development, Materials Selection,
  Structural Requirements., Available
  http//www.me.berkeley.edu/ME117/S05/finalproject/
  pdf/IVDisc.pdf.
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• Abramson, S., H. Alexander, et al. (2004).
  Classes of Materials Used in Medicine.
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• Bao, Q.-B. and H. A. Yuan (2000). "Artificial
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• DePuy Spine, a. J. J. c. (2004). Charite
  Artificial Disc, Available http//www.charitedisc
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• DePuy Spine, a. J. J. c. (2004). Charite
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• Hallab, N. J., B. W. Cunningham, et al. (2003).
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• Kotani, Y., K. Abumi, et al. (2004). "Two-year
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