design rationale · depuy orthopaedics, a leader in producing high quality polyethylene, proudly...

For Sigma and LCS Rotating Platform Systems

Design Rationale

2

next generationWelcome to the

DePuy Orthopaedics, a leader in producing high quality polyethylene, proudly introduces AOX™

Antioxidant Polyethylene, the next generation of polyethylene for rotating platform knees.

Our mobile bearing knee is evolving. With our advanced blend of polyethylene resin and a unique

antioxidant, COVERNOX™, DePuy Orthopaedics has created a new polyethylene material that

has extraordinary efficiency in trapping free radicals and scavenging oxygen. This first of its kind

combination is designed to deliver optimal wear resistance and long term oxidative stability.

By eliminating the annealing or remelting process, AOX polyethylene delivers outstanding oxidative stability

and optimum wear resistance without compromising the mechanical properties of polyethylene.1, 2

3

Oxidative Stability

Wear Resistance

Mechanical Strength

Mechanical Toughness

AOX 3 x Annealed 10 Mrad Remelted Vitamin E Doped

3 7

3 3

3 7 3

7

3

7

3

3

7

3

3

3

next generation


Extraordinary oxidative stability

Stabilizes free radicals

Post irradiation, COVERNOX antioxidant

combines with remaining free radicals.

Protects against oxidation

The COVERNOX antioxidant molecule bonds with

free radicals and prevents oxidation, maintaining

mechanical integrity and oxidative stability.

Free R

adica

l

Hydro

gen/

Carbo

n

COVERNOX an

tioxid

ant

Oxyge

n

4

With enhanced molecular functionality compared to Vitamin E, COVERNOX is extremely

efficient at trapping free radicals and preventing oxidation.

Extraordinary oxidative stability

Under aggressive conditions sufficient to oxidize non-irradiated polyethylene, AOX

polyethylene is completely unaffected and retains its mechanical properties. AOX

polyethylene bonds with free radicals which eliminates the potential for oxidation.

Annealed polyethylenes do not eliminate oxidative potential.1,3,6

12

14

2

8

6

4

10

00 20 40 60

Oxi

dat

ion

Ind

ex (

Max

)1

Time of Aging (Days)

AOX Polyethylene

Non-Irradiated 1020

2.5

3.0

1.5

1.0

0.5

2.0

00 2 4 6

Oxi

dat

ion

Ind

ex1,

3

Accelerated Aging (Weeks)

3x Anneal

5

AOX Polyethylene

By introducing COVERNOX antioxidant into the base resin before the polyethylene is

consolidated, the process enables the antioxidant to be uniformly dispersed throughout the

material and remain blended, eliminating the risk of outward migration. The process provides

an oxidatively stable polyethylene formulation.

Maximizing wear resistance

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Maximizing wear resistanceThe polyethylene/COVERNOX antioxidant mix is exposed to a

nominal dose of gamma irradiation, 7.5 Mrad, to stimulate a

precise amount of cross-linking to deliver optimum wear properties

without compromising material strength. Difference in wear

reduction benefits between AOX and GVF are minimal and not

statistically significant as most of the wear reduction benefits are

related to the rotating platform design versus the material used.

DePuy Orthopaedics’ Rotating Platform knees were designed with

polyethylene wear reduction as a core principle. SIGMA Rotating

Platform features a highly polished Cobalt Chrome (CoCr) tibial

tray and self aligning polyethylene insert, which by virtue of

unidirectional movement results in 94% wear reduction when

compared with the older design.10 This design coupled with AOX

polyethylene provides a low wear construct coupled with long term

oxidative stability.

7

Mea

n W

ear

Rat

es

SIgMA® RPF Knee Polyethylene Wear Comparison2

gVF

AOX

Maintaining mechanical properties is important as high patient

loads have the potential to deform and break down polyethylene

over time. By utilizing GUR 1020 resin, with its better inherent

mechanical properties, and lower molecular weight compared

to GUR 10504,5, AOX polyethylene maintains high material

strength when compared to most other commercially available

polyethylene options.

Tensile testing, measuring how polyethylene reacts under pull

or stretch load, shows that AOX polyethylene loses none of its

ability to resist deformation or breakage upon irradiation.

Unlike remelting, this approach to providing oxidative stability

does not cause a decline of mechanical strength.9

Maintaining high material

30

40

50

60

20

10

0

AOX Polyethylene1 3x Annealed6 10Mrad Remelted7

Strength of Materials

15

20

25

30

10

5

0

Ult

imat

e Te

nsi

le S

tren

gth

(M

Pa)

Yie

ld S

tren

gth

(M

Pa)

8

Vitamin E Doped8

strengthMaintaining high material

9

Excellent mechanical toughnessNormal patient loads can impose high contact stresses on polyethylene knee

components, so their toughness, or resistance to surface crack initiation and

subsequent propagation leading to shear induced delamination, is critical.

It is especially important in a posterior stabilized design, which is subjected

to repeated high stress loading. Fatigue crack resistance, measured as (∆)

inception, provides ample evidence of the material toughness.

The findings show an advantage in toughness for AOX polyethylene, bringing

it far closer to standard polyethylene, which is considered the gold standard in

polyethylene material properties.

Relative toughness is measured by a ‘double notched’ Izod test that shows

resistance to fracture when encountering sudden or catastrophic impact.

While the chart shows that AOX polyethylene exhibits lower toughness

than that of non-irradiated "standard" polyethylene, it is superior to other

competitive products.1,8

10

Excellent mechanical toughness

0.6

0.8

1

1.2

1.4

1.6

0.4

0.2

0

K ∆

Ince

pti

on

60

80

100

120

40

20

0

Do

ub

le N

otc

hed

Izo

d T

ou

gh

nes

s (k

J/m

2)

AOX polyethylene1 AOX polyethylene15

3x Annealed16 3x Annealed - No data available

10Mrad Remelted89Mrad Remelted16

Vitamin E Doped8Standard6

Toughness of Materials

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Functionwith wear resistance, and oxidative stability

DePuy Orthopaedics continues to lead and drive the

future in mobile bearing technology. The rotating

platform technology with 97.7 percent survivorship at

20 years, demonstrates that its less constrained axial

rotation effectively reduces wear and implant loosening

forces when compared to a fixed bearing design.10-14

Through advanced material and component design you

can now have function with wear resistance coupled

with oxidative stability of AOX polyethylene to optimize

implant survivorship.

12

Functionwith wear resistance, and oxidative stability

Central to performance and survivorship, AOX polyethylene is an excellent choice for your active patients where a mobile bearing knee system is preferred.

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Patients expect to continue their active lifestyles post-surgery, so today’s knee

implants need to meet these demands. It is our dedication to the surgeon and the

patient that drives us to constantly innovate - developing and evolving technology

for clinical success. With the introduction of AOX Antioxidant Polyethylene, only

DePuy Orthopaedics offers designs to accommodate the different philosophies of PCL

management, wear reducing benefits of rotating platform and oxidative stability.

Welcome to the next generation

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SIGMA® CR150 Knee SIGMA® RPF Knee LCS® COMPLETE™ RPS Knee

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References:

1. Data on File at DePuy Orthopaedics, Inc. WR070300.


3. Muratoglu, O.K. "Grand Rounds Presentation at the Dartmouth Hitchcock Medical Center on May 16, 2007." http://www.dnslides.org/ortho/ortho051607/msh.htm.



6. Greer, K.W. and M.S. Sharpe. "Comparison of Cross-linked UHMWPE Stabilized by Sequential Annealing or by Remelting." Poster 1784, 53rd Annual Meeting of the Orthopaedic Research Society, February 11-14, 2007, San Diego, CA.

7. Malhi, A.S., K.K. Wannomae, S.D. Christensen, C. Godleski and O.K. Muratoglu. "A Novel Processing Methodology for Improvement of Mechanical Properties in Highly Cross-linked Polyethylene." Poster No. 0657, 52nd Annual Meeting of the Orthopaedic Research Society, March 19-22, Chicago, IL.

8. Muratoglu, O.K., B.R. Burrough, A. Malhi, S. Christensen, K. Wannomac, E. Oral, S. Spiegelberg and W.H. Harris. "Two Second Generation Cross-linked UHMWPES Show Improves Mechanical Properties and Fatigue Strength." Poster No. 1661, Presented at the 51st Annual Meeting of the Orthopaedic Research Society, Washington, DC.

9. Kurtz, S. M., UHMWPE Biomaterials Handbook, 2nd ed.,page 73-74.

10. McNulty, D., S.W. Swope, D.D. Auger and T. Smith. "The Effect of Crosslinking UHMWPE on In-vitro Results in Fixed and Mobile Bearing Knees." Presented at ASTM Symposium on Crosslinked and Thermally Treated UHMWPE for Joint Replacement, November 2002.


12. Data on File at DePuy Orthopaedics, Inc.WR110009.



15. data on File at DePuy Orthopaedics, Inc. WR080219.

16. Morrison, M.L., Jani, S. "Evaluation of sequentially crosslinked ultra-high molecular weight polyethylene." Journal of Biomedical Materials Research Part B: Applied Biomaterials Volume 90B, Issue 1, July 2009, Pages: 87–100.

DePuy Orthopaedics, Inc.700 Orthopaedic DriveWarsaw, IN 46581-0988USATel: +1 (800) 366 8143Fax: +1 (574) 371 4865

www.depuy.com

©DePuy Orthopaedics, Inc. 2011.All rights reserved.

0612-59-508 2M 0711

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