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Biomaterials currently used to replace intervertebral discs

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Sadi Sabti

on 28 January 2014

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Transcript of Biomaterials currently used to replace intervertebral discs

Biomaterials Currently Used to Replace Intervertebral Discs
Introduction
Degenerative Disc Disease
History of Intervertebral Disc Replacement
Current Methods of Treatment
Future Applications
Intervertebral Discs
- Fibral cartilaginous joints
- Fit between vertebrae
- Allow for bending of the spine
- Act as a ligament to hold vertebrae together

- Outer layer is the annulus fibrosus, composed of fibrous cartilage -Tough and fibrous, contains several layers
- Inner layer is the nucleus pulposus, composed of loose fibers suspended in mucoprotein gel thats soft and gelatinous
- Acts as a shock absorber and helps the spine return to its natural state after bending
- Composed of 80% water
- As time progresses, discs lose water content and shorten as people age

Health Risks Associated with Intervertebral Discs
- Herniation is caused by a tear in the annulus fibrosus which allows the nucleus pulposus to leak out
- Also known as a slipped disc
- Tears can be caused by stress and strain from physical activity or degeneration
- Discs will compress the nerves causing back pain
- A minor herniation can heal on its own but a major one may need surgical intervention

Degenerative Disc Disease
- Nucleus pulposus doesn’t get enough water in it or gets driven up into the vertebrae
- Loses its gel like properties
- Shrinks the disc, leading to a smaller area for nerves to get through which can lead to compression of the nerves causing back pain and loss of sensation
- Before age 40, 25% of people show signs of disc degeneration
- Above 40, more than 60% of people show signs of disc degeneration

Methods of Repair
A discectomy may be needed to help repair a herniation
- The removal of some of the disc or disc degeneration will lead to shortening of the intervertebral disc

Short discs lead to:
- Back pain
- Disc degeneration
- Increased pressure on other joints
- Destabilizing of the spine
- Change in properties of nucleus pulposus due to increased pressure

Need to have a method of restoring original disc height with a material that has the same properties as the original disc

Biomaterials
- A biomaterial is any matter, structure or surface that interacts with biological systems
- Examples are ceramics, polymers and metallic materials
- Insure biocompatibility
Examples: heart valve, artificial teeth, silicon implants, contact lenses and joint replacements

The Past
-Research in spinal cord injury dates back to 2500 BCE
-First documented spinal cord injury believed to be written by ancient Egyptian physician Imhotep
-Believed that spinal cord injuries were impossible to treat, “an ailment not to be treated”
- During the 19th century there was controversy as to whether or not to perform surgery
-Since spinal cord injuries were untreatable and often led to death, it was proposed by some that there was nothing to lose
-On the Contrary, some argued that surgery would cause immediate death or further damage
-The first real progression was achieved by Munro in the 1940s
-Believed that he had to help the person as a whole in order to rehabilitate movement and integrate the person back into society, rather than try to perform surgery
-John Young was responsible for implementing this in North America in the 1970s.

Spine Arthroplasty: a Historical Review
-First replacement of an intervertebral disc was a metal ball by Fernstrom near the end of the 1950s
-This caused segmental hypermobility and the prosthesis tended to sink into the vertebral bodies and endplates
-Meager results were reported by Fernstrom

-Fassio created an elastic disc that was “flying saucer shaped”
-The center was silastic and the ring was a synthetic resin that could not be compressed
-Stopped being used due to destructive approach and sinking into endplates. This lead to an intraspongious hernia
-SB Charite prosthesis was introduced in 1980s and first implanted in 1984. Though the inability to stay in place and fractures lead versions I and II to being tossed away; version III was upgraded and is widely used.

- The need for disk replacement is due to Degenerative Disk Disease (DDD)
- DDD is used to describe all intervertebral disc degeneration
- Caused by back injury and aging
- Most common cervical and lumbar discs
- DDD in cervical disc can cause pain, numbness, and tingling in the neck, arm or shoulder region depending on the level
- In the lumbar disc it can cause these symptoms in the legs
- Associated issues
o Disk herniation
o Spinal stenosis
o Bone spurs and corrosion
- If non-surgical methods don’t work for a few months, then surgery becomes an option



- Conditions that prevent you from being a candidate

o Spondylolisthesis
o Osteoporosis
o Vertebral body fracture
o Spinal tumor
o Spinal infection
o Morbid obesity
o Significant changes of facet joints
o Pregnancy
o Chronic steroid use
o Autoimmune issues
o Previous abdominal surgery

• Three different methods:
- Annulus fibrosus replacement
- Nucleus pulposus replacement
- Whole disc replacement

• Going to focus on whole disc replacement

• Considerations that have to be made when creating the prosthesis:

- Normal kinematic patterns of that specific disc
- Load and pressure considerations
- high wear-resistance
- Low friction

Difficulties Encountered
• Current artificial replacements have not been entirely successful
• Difficulties occurred in durability, insufficient size and suitable mechanical properties(motion)
• Other areas of difficulty include anchorage, bony fixation and inflammatory responses

Current Biomaterials used to Create Intervertebral Discs
Cobalt-chromium alloys
- Tends to have weaker strengths than other materials
- High nickel content allows for excellent corrosion-resistance
Titanium and titanium alloys
- Excellent biocompatibility and imaging qualities
- Sensitive to high stress concentrations
Stainless steels
- Inexpensive
- Widely available
- Long clinical history

SB Charite III
• 4000 -5000 discs have been implanted worldwide (20 000 total procedures)
• Contains 2 endplates composed of high quality cobalt chromium alloy
• Endplates coated with titanium and hydroxyapatite porous coating
• Contains a high molecular weight polyethylene sliding core, placed in between the endplates to allow for movement

-Research into intervertebral discs is increasing due to the increasing numbers of DDD

-The structure of natural discs could be mimicked by using biphasic (two-phase) biomaterials with a high elastic modulus

-3D printing is allowing for complex tissue structure to be created.

Injectable Biomaterials and Vertebral Endplate Treatment
-The biomaterial NuCore Injectable Nucleus can restore the biological properties of an intervertebral disc after a micro discectomy (when a small piece of bone in spine is removed to create additional space to remove pinching and help healing)
-This material will not be attacked by the immune system and is not toxic
- The physical properties are the exact same as natural nucleus pulposus
- Testing this material in humans is currently underway

Designs of the Next Generation of Intervertebral Discs

-Currently in study, four unique designs for intervertebral disc replacements have been tested: homogenous elastomer, a multi-stiffness elastomer, an elastomer with fiber jacket, and a hydrogel with fibre jacket
-The designs without a fiber jacket limited the range of motion of the spine compared to a natural disc
-The elastomer with a fiber jacket showed good results, permitting physiological motion in all possible directions
-When the elastomer is replaced with a hydrogel, similar results were found
-Therefore in future materials for intervertebral disc replacement, the incorporation of a fiber jacket would be advantageous to provide the required range of motion

Pros & Cons
Pros
• Maintains distance from the 2 vertebrae, preventing the spinal column from collapsing
• Allows for movement and pressure distribution
• Has a life span of 40 years
• Reduces chances of further damage to the spine
• Had excellent results where 70-90% of patients stopped using pain medications within an 8 year follow up

Cons
• Approx. 8% height loss of prosthesis expected within 10 years of use
• Wear debris
• Operative complications:
- Vascular injury
- Retrograde ejaculation in males (less than 4%)
- Infection
• Migration of prosthesis leading to a repetition of the surgery (less than 1%)
• 7% of patients had device related complications

Conclusion
• Degenerating discs can cause severe pain and health risks for the patients
• Intervertebral disc replacement has shown some promise, but research is still on going
• Current concerns with disc replacement include:
- Causing less inflammation
- Including a greater range of movement
- Reducing wear and tear and height loss
• Nucleus pulposus and annulus fibrosus replacement methods also need to be further researched & tested to see if they yield better results

Emily Urban, Fabian Budnik, Sadi Loai, Tyler Jewiss
Chem Bio Eng: 2L03

Thank you for Listening
References
Carter, Andrew J., and Lawerence M. Boyd. "Injectable Biomaterials and Vertebral Endplate Treatment for Repair and Regeneration of the Intervertebral Disc." NCBI. U.S. National Library of Medicine, Aug. 2006. Web. 10 Nov. 2013.
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L. M. Boyd and A. J. Carter, “Injectable biomaterials and vertebral endplate treatment for repair and regeneration of the intervertebral disc,” Eur. Spine J., vol. 15, no. 3, pp. 414–421, Aug. 2006.
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Roberts, Sally, and Jill PG Urban. "Degeneration of the Intervertebral Disc." NCBI. U.S. National Library of Medicine, 2005. Web. 10 Nov. 2013.
Stephen Furlani, “The SB Charité III Disc Replacement,” Nov. 2003.
S. Taksali, J. N. Grauer, and A. R. Vaccaro, “Material considerations for intervertebral disc replacement implants,” The Spine Journal, vol. 4, no. 6, Supplement, pp. S231–S238, Nov. 2004.
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