Total Disc Replacement

- Ujwal Parikh

Scope

• Scope of the total disc replacement is to create a disc model that would improve the longevity and functionality of the implant to reduce pain.

Anatomy

• Human spine – 24 articulating vertebrae, 9 fused vertebrae.

• Stacked to form vertebral column maintaining human body’s upright posture.

• Each segment consists of vertebrae and spinal disc.

• Spinal Disc:– Nucleus pulpous (Jelly)– Annulus fibrosis (Stronger)

Anatomy

What is TDR?• Total Disc Replacement (TDR) is surgical

procedure replacing vertebral disc by an implant.

• Surgeon removes the worn-out, painful, degenerated disc replaces by metal implant.

• The goal is to reduce pain still maintaining complete functionality of spine.

• First clinical trial performed by Fernstorm in 1966 on 125 patients, 88% reduction.

CHARITÉ Artificial Disc (De Puy Spine, Inc.)

Why TDR?

• Degeneration of intervertebral disc in lower spine may lead to chronic back pain.

• The chronic nature results in reduced functionality hindering patient’s everyday life.

• Approximately 80% of Americans experience a significant back pain in their life time.

• Treatments– Anti-Inflammatory Medication– Surgical

I Spine fusion (Traditional)II Artificial Disc Replacement

Spinal Fusion Vs. TDR

Design Input

PRODISC® (Spine Solutions, New York, NY, USA)CHARITÉ Artificial Disc (De Puy Spine, Inc.)

L4-L5 vertebrae

Steps followed….

1. Plate2. Assembly3. Polymer4. Mechanical

Plate

Plate (Contd…)

Isometric View

Superior View Lateral View

millimeter

Breadth 42

A/P length 33

Thickness 4

Posterior radius 17

Anterior radius 11

Anterior View

Plate (Contd…)

Assembly

Polymer

Assembly + Polymer

Lateral ViewAnterior View

Isometric View

Material

Ti6Al4V

Young’s Modulus (E) 114 GPa

Poisson’s Ration (υ) 0.342

Density 4.43 g/ccTensile strength, Yield 880 MPa

Urethane Type L42

100 % Modulus 2.8 MPa

Poisson’s Ratio (υ) 0.48

Density 1.07 g/cc

Tensile Strength 20.7 MPa

Analysis

Polymer

Max. Stress 2.361 MPa

Max. Displacement 5.82 mm

Analysis (Contd…)

Plate

Max. Stress 1.167 MPa

Max. Displacement 8.246mm (10 deg)

Conclusion

• Since max. stress on polymer < tensile strength of Urethane L42, polymer won’t rupture

• Also max. stress on plate < yield strength of Ti6Al4V, metal wont break either for the given force and degree of freedom.

• For a force of 43.33 N, Angular displacement= 10 deg.• Stiffness = Moment/Angular Displacement

= 1.72 Nm/deg

References

• http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641

• http://www.dsm.com/en_US/downloads/dbm/pdf002_-_Bionate_product_description-processing-properties.pdf

• http://www.americanurethane.com/aboutu1.htm• http://asm.matweb.com/search/SpecificMaterial.asp?

bassnum=MTP641• http://us.synthesprodisc.com/EN-US/• http://www.depuy.com/corporate-information/about-

depuy/history

Thank You