Fixed Bearing Knees

Function with Wear Resistance

Today’s surgeons demand a knee system that can

react to the needs of the individual patient. The

Sigma® Knee System brings together function with

wear resistance to match the needs of a diverse

patient population.

Regardless of the size, shape or activity level of

patients, surgeons can feel confident that with the

Sigma Knee system, they can choose the procedure

and implant to meet their patients’ demands.

Sigma Knee System

The Sigma Knee System offers one of today’s most comprehensive, integrated knee systems. It embraces a wide

variety of philosophies and surgical techniques and continues to develop with the addition of further implant

options and instrumentation.

The Sigma Fixed Bearing Knee Portfolio

Posterior Lipped (PLI) Curved (CVD) Curved Plus (CVD+) Stabilized (STB)

Polished CoCr Keeled Ti Ti Porocoat

Tibi

al T

ray

Poly

ethy

lene

Inse

rt

1- Post (Round and Oval)

3-Post (Round and Oval)

Inset

CR CR150 PS PS with LugsCR PorocoatFem

oral

Com

pone

ntPa

tella

Sigma Fixed Bearing KneesFunction with Wear Resistance

Femoral Components

Rounded coronal geometry maximizes contact area while minimizing contact stresses1

Accommodates high flexion with Sigma CR150

Highly Polished Cobalt Chrome Tibial Tray

Reduces backside polyethylene wear (as compared to titanium trays) by providing a smooth surface2

Retrieved CoCr trays show no locking mechanism erosion3

XLK Polyethylene

Moderately cross-linked to provide increased wear resistance versus standard polyethylene4,5

Remelted to create an oxidatively stable material

i2 Locking Mechanism

Integrity of locking tabs maintained with anterior bumper

Interference fit between the insert and the tibial tray reduces potential for micromotion

Wea

r Re

sist

ance

Func

tion

Sigma Femoral Components

The Sigma femoral components are designed to provide optimal function for high demand patients. The main

benefits of the femoral components are:

Rounded Coronal Geometry

By utilizing a round-on-round geometry, the system allows a larger contact area and lower contact stresses, both in

neutral alignment and varus or valgus lift-off , compared to flat-on-flat designs. This optimizes the trade-off between

maximal contact area and constraint of the implant.1

In contrast, lift-off of the femoral component in a flatter condylar design can lead to edge loading on the opposite

side. This may cause high concentrations of contact stresses on the polyethylene.

High Flexion

The clinically proven Sigma J-curve with extended posterior condyles

provides conforming contact through 150 degrees of flexion,

reducing the risk of point contact stress.

At 135 degrees of flexion, the Sigma CR150 knee system provides

a 31 percent increase in contact area resulting in a 19 percent

decrease in contact stress compared to the Sigma CR femoral

component. This helps to protect the tibial insert and reduce

polyethylene wear.6

To increase congruency and conformity in high flexion, the J-curve of the Sigma CR150 is extended beyond 120

degrees. In order to achieve this, Sigma CR150 requires a posterior bone resection of an additional 2 mm when

compared to the existing Sigma CR.

Optimal Function

Edge Loading

“J” Curve for Sigma CR150

120º Min

“J” Curve for Sigma CR

A highly polished Cobalt Chrome (CoCr) fixed bearing tibial tray is a unique product from DePuy Orthopaedics with

features not offered by any other competitor on the market. The main benefits of this tray are:

Highly Polished Surface

The polyethylene friendly, highly polished CoCr tray creates a smooth surface, minimizing abrasion.2

The Ra value (a measure of surface roughness) of the CoCr tray surface has been reduced by 95 percent compared to

the older Titanium tray.2

Proven Design

The CoCr tray uses the same design that was used by the original and successful P.F.C.® tibial trays. It utilizes the

same tray thickness, stem and keel, design as well as the same undersurface finish.

In essence, the highly polished cobalt chrome tray provides a more polyethylene friendly environment than titanium

with no compromise in material strength or fixation. It has been demonstrated that:

• Becausemotionbetweentheinsertandmetalbackingmaybeinevitable,thewearcharacteristicsoftheinnertray

surface should be optimized to minimize debris production.7

• Polishingthetrayhasbeenshowntoimprovethewearcharacteristicsofthearticulation.7

Wear ResistanceHighly Polished Cobalt Chrome Tray

The main goal of cross-linking is to improve polyethylene’s wear properties. Improving the

wear properties of the polyethylene material is important in fixed bearing knees because of

the multi-directional stress that the insert experiences.

Gamma irradiation is a proven method for cross-linking the

polyethylene. As the dose of gamma radiation increases,

the material’s wear properties also improve.5

But higher doses of gamma irradiation have a drawback

-- gamma radiation adversely affects polyethylene’s

mechanical properties.8 Therefore, it is not advisable to

increase the dose indiscriminately. A balance needs to exist

between the amount of wear reduction that is achieved

and reduction in mechanical properties. Sigma XLK finds

that balance with the following characteristics:

GUR 1020 Resin

Sigma XLK polyethylene is made from GUR 1020 resin

which has tougher mechanical properties relative

to GUR 1050.

Moderately cross-linked

DePuy Orthopaedics uses the 5 Mrads dose as it gives the desired amount of wear

reduction without a significant drop in mechanical properties. Moderate cross-linking of

the polymer chains provides increased resistance to the multidirectional wear generated by

fixed bearing designs.9

Oxidatively Stable

Sigma XLK is remelted above the melting point of polyethylene after it is exposed to gamma

radiation to make it oxidatively stable.8

Bottom line:

Sigma XLK is remelted to eliminate free radicals and therefore is oxidatively stable –

both on the shelf and in vivo.8

10

20

30

40

50

60

0

0

5 10 15

Irradiation Dose (Mrad)

Wea

r Ra

te (m

m3 /

mill

ion

cycl

es)

XLK

GVF

Wear Resistance Sigma XLK Polyethylene

The Sigma i2 locking mechanism plays a pivotal role in reducing the amount of micromotion between the

tibial insert and the tibial tray. The two salient features of the i2 locking mechanism include:

Interference Fit

The size of the polyethylene insert is 150 microns bigger than the tibial tray pocket. Due to this difference in

size, the insert has to ‘squeeze’ inside the tray. Since the insert deforms as it goes in the tray, there is little room

for it to move, thus minimizing the rotational micromotion and potential for backside polyethylene wear.

Integrity

There is an anterior bumper on the front of the insert between the two locking tabs. This improved

design removes the load from the tabs. Since the locking tabs do not experience the stress, it reduces

the risk of tabs breaking over time. The bumper will also absorb most of any anteriorly directed force,

minimizing the anterior/posterior micromotion and potential for backside polyethylene wear.

Reduced anterior/posterior motion due to anterior bumper

150 micron difference

Wear Resistance i2 Locking Mechanism

This construct delivers the benefits of modularity while approaching the performance of a one-piece tibial design.

When compared with the older lock, the i2 lock has reduced the amount of micromotion by 85 percent.10 In fact,

16 microns of resultant micromotion in the Sigma design is the lowest among a group of implant systems as

demonstrated in mechanical testing.11

85%Reduction

PFC ∑i2 XLK

PFC ∑i2 GVF

Advance NexGen Duracon Optetrak Journey Scorpio

10.0

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.0

400

350

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250

200

150

100

50

0

Mean R & RT Micromotion by Manufacturer

RT (DEG

)

R (M

ICRO

MET

ERS)

MANUFACTURER

R

RT

R = (AF)2 + (ML)2√

RESU

LTA

NT

MO

TIO

N (M

ICRO

NS)

i2 Locking SystemPrevious LockingSystem

100

150

0

200

250

300

350

257

33

Micromotion Micromotion is the motion that occurs between the polyethylene insert

and the tibial tray. It’s a phenomenon that has been recognized as a contributing factor to backside wear of polyethylene and is an unintended consequence of modularity in total knee implant systems.12

Benefits of Modularity

Modularity allows flexibility to customize the thickness of the polyethylene insert after the tibial tray has been fixed in the patient and exchange of polyethylene bearings without revision of the entire tibial component.12

Disadvantages of Modularity

The tray and insert interface can be a source of polyethylene wear debris. In a study by Wasielewski et al, wear on the underside of retrieved modular tibial inserts was associated with radiographic evidence of osteolysis.13

Source and Significance of Micromotion

Micromotion is typically caused by inherent design characteristics of the implant. By definition, modularity requires the two components to be of slightly different size so that they can easily be assembled. The key is to minimize this difference so as to minimize the ‘play’ between the two. At the same time, it should be easy for a surgeon to assemble (and disassemble when required) the two components. Different implant designs in the marketplace have had different levels of success achieving this balance.

Solution

It is not possible to completely eliminate micromotion between the tibial tray and tibial insert in a modular design. Therefore the locking mechanism, material, and the surface finish of the tibial tray assume greater significance. If any amount of motion is taking place, the following is desirable:

• Theinsertlockingmechanismshouldsecuretheinsertandthetraywithatightfit.

• Thesurfacefinishofthetrayshouldbepolyethylenefriendly.Itshouldbeassmoothaspossibleinordertominimizethe friction between the metal and plastic components.

• Thetraymaterialshouldbeafriendlyarticularsurface.

Key Message

“The undersurface of the insert is an additional source of polyethylene debris contributing to tibial metaphyseal osteolysis. To lessen polyethylene debris produced at this modular surface, the tibial implant locking mechanism should fix the insert firmly to the metal backing to decrease relative micromotion. Because motion between the insert and the metal backing may be inevitable, the wear characteristics of the inner tray surface should be optimized to minimize wear debris production at this other articulation.”13

The combination of a highly polished cobalt chrome tray, i2 locking mechanism and moderately cross-linked polyethylene has resulted in significant reduction in overall polyethylene wear in the Sigma Knee System. Tests have shown that use of these improved technologies has reduced the polyethylene wear rates in a Sigma Fixed Bearing Knee by 88 percent under standard kinematic loads and 71 percent under high kinematic loads compared to standard polyethylene and titanium trays.14

Polyethylene has been successfully used in orthopaedic implants, including knee systems, for many decades. However

it is also often cited as the leading cause of knee revision.15

Oxidative Stability

Oxidative Stability is defined as the material’s ability to resist combining with oxygen molecules. Oxidation eventually

leads to breakdown of the polyethylene material and may contribute to implant failure.

Virgin polyethylene is a material not exposed to any gamma radiation and is therefore inherently oxidatively stable.

However, exposure to gamma radiation is an essential step in the current manufacturing processes. Gamma radiation

serves two functions:

• Cross-linking-Improvesthewearcharacteristicsofpolyethylene9

• Sterilization-Terminalsterilizationofsomeinserts

Oxidation

When polyethylene is exposed to gamma radiation, the gamma energy initially breaks either the carbon-carbon

or carbon-hydrogen bonds along the polyethylene chain and forms free radicals. If the polyethylene material with

free radicals is exposed to oxygen, oxygen molecules can combine with the free radicals. This can cause the long

molecular chains to break, creating even more free radicals in the process. Degradation of the polymer chain

continues in the presence of free radicals and oxygen molecules. Polyethylene that is not oxidatively stable has shown

mid to long-term clinical mechanical failure and elevated wear rates.16

Thus, it is of crucial importance to either:

• Removefreeradicalsfromthepolyethylenematerial

• Avoidexposureofpolyethylenematerialtooxygeniffreeradicalsarepresentinthematerial

It is desirable to remove free radicals from the polyethylene because it is not possible to avoid exposure of the

polyethylene insert to oxygen once placed in the body. Therefore, manufacturing techniques like remelting have

been developed that allow removal of all free radicals that are generated in the process of gamma irradiation. It has

been shown that cross-linking the polyethylene and then remelting above the melt point eliminates free radicals and

creates an oxidatively stable polyethylene.8

Oxidative Stability

Technical Details

**Not Available for TC3 Femoral Components

*10 mm for size 6

8 mm

9 mm*

Sagittal Shape

Coronal Shape

Size 6**

Size 5

Size 4

Size 3/4N

Size 2.5

Size 2

Size 1.5

17.8 mm Inner Box (Dimension Constant)

Box height of Sigma PS Femoral Components

Size 1.5 14.0 mm

Size 2 14.8 mm

Size 2.5 14.8 mm

Size 3 14.8 mm

Size 4 16.7 mm

Size 4N 16.7 mm

Size 5 18.6 mm

Size 6 19.5 mm

Amount of rotation allowed by each insert:

Posterior Lipped (PLI) 15°

Curved (CVD) 10°

Curved Plus (CVD+) 20°

Stabilized (STB) 8.0°

Stabilized Plus (STB+) 2.0°

Size Keel Height M/L Keel

1.5 38 mm 37 mm

2 38 mm 37 mm

2.5 38 mm 37 mm

3 38 mm 37 mm

4 43 mm 43 mm

5 43 mm 43 mm

6 48 mm 49 mm

M/L

Keel Height

Tray Thickness (2.8 mm)

Peripheral Lip Height (6.6 mm)

Keel slopes 3 degrees posteriorly

The poly plug at the bottom of the tibial tray adds an additional 8 mm to the keel height.

Posterior Lipped Insert

(cruciate retaining only)

8, 10, 12.5, 15, 17.5, 20 (mm)

Curved Insert

(cruciate retaining only)

8, 10, 12.5, 15, 17.5, 20 (mm)

Curved Plus Insert (cruciate retaining

and cruciate sacrificing)

8, 10, 12.5, 15, 17.5, 20 (mm)

Posterior Stabilized (PS) Insert

(posterior stabilized only)

8, 10, 12.5, 15, 17.5, 20, 22.5, 25 (mm)

All Polyethylene CVD and all Polyethylene PLI Tibia not shown; 8, 10, 12.5, 15 (mm) options available for each

Size 1.5 (Curved Plus) insert only available in 8, 10, 12.5, 15, 17.5 (mm)

All Polyethylene PS Tibia not shown; 8,10, 12.5, 15 (mm) options available

Size 1.5 (PS) insert only available in 8, 10, 12.5, 15, 17.5 (mm)

Sigma High Performance Instruments

Function HP Instruments deliver Function with Wear Resistance through ease of use and improved alignment. Ease of use,

or function, impacts all healthcare providers throughout the surgical pathway including surgeons, scrub techs and surgeon assistants by creating a straightforward and efficient procedure.

Distal Femoral Resection

Efficient - Engineered for fast pinning and easy removal.

Adjustments designed to be easy to access and use.

User-Friendly - Designed for comfortable fingertip control.

Visual Cues - Line-of-site engraved marking for quick,

eye-friendly visual clarity. Secure color-coded locking

after adjustment.

Fixed Reference

Options - Anterior or Posterior referencing in one

system, available in 0, 3, 5, or 7 degrees of rotation.

Rotation Guides provide reference points to Whiteside’s

line and epicondylar axis.

Optimized profile - Cutting blocks minimize soft

tissue impingement, enable complete cuts, and are

the same M/L width as the implant.

Flexibility - Allows for easy downsizing or upsizing

changes, as well as last minute +2 or -2mm adjustments.

Wear Resistance Wear resistance is a key factor in an implant’s long-term success. It is influenced by implant alignment, which is a

combination of surgical skill and precise instrumentation.

Tibial Resection

Stability - Blocks are designed to maximize stability

against the bone, to promote a more accurate cut.

Precision - Instruments provide 1 mm resection

adjustment – which allows for optimum gap balancing.

Precise calculation sets the exact degree of slope

that the surgeon desires based on leg length.

Versatility - Multiple alignment checks/tools are

available to aid in correct placement and resection.

Tibial Preparation

Precision - 1 mm cement mantle produced by

instruments provides consistent implant fit.

Accuracy - Tray tower is designed for drill and

punch to occur at the same spot on the tibia.

Rotation - Fixed Bearing instruments allow surgeons

to locate optimal implant positioning for rotation.

Printed in USA. ©2010 DePuy Orthopaedics, Inc. All rights reserved.

2.5M06100612-65-508 (Rev.1)

References

1. P.F.C. Sigma Knee System with Rotating Platform Technical Monograph. DePuy Orthopaedics, Inc. Lit. No. 0611-29-050 (Rev.1).

2. Data on File at DePuy Orthopaedics, Inc. WR# 010120.

3. Currier, J.H., M.B. Mayor, A.S. Perry, J.C. Huot and D. Van Citters. “Polished Tibial Trays in Modular Knees Show Reduced Backside Wear.” Paper 165, Podium Presentation at AAOS, February 25, 2009, Las Vegas, NV.

4. McKellop, H., F.W. Shen, W. Diamaio and J.G. Lancaster. “Wear of Gamma Cross-linked Polyethylene Acetabular Cups Against Roughened Femoral Balls.” Clinical Orthopaedics and Related Research, 1999: 73-82.

5. McKellop, H., F.W. Shen, B. Lu, P. Campbell and R. Salovey. “Development of an Extremely Wear-Resistant Ultra High Molecular Weight Polyethylene for Total Hip Replacements.” Journal of Orthopaedic Research Vol. 17, No. 2, March 1999: 157-167.

6. Data on File at DePuy Orthopaedics, Inc.

7. Collier, M.B., C.A. Engh, Jr., J.P. McAuley, S.D. Ginn and G.A. Engh. “Osteolysis After Total Knee Arthroplasty: Influence of Tibial Baseplate Surface Finish and Sterilization of Polyethylene Insert.” The Journal of Bone and Joint Surgery Vol. 87-A, No. 12, December 2005: 2702-2708.

8. Collier, J.P., B.H. Currier, F.E. Kennedy, J.H. Currier, G.S. Timmins, S.K. Jackson and R.L. Brewer. “Comparison of Cross-linked Polyethylene Materials for Orthopaedic Applications.” Clinical Orthopaedics and Related Research No. 414, September 2003: 289-304.

9. Chiesa, R., M. Tanzi, S. Alfonsi, L. Paracchini, M. Moscatelli and A. Cigada. “Enhanced Wear Performance of Highly Crosslinked UHMWPE for Artificial Joints.” Journal of Biomedical Materials Research Vol. 50, No.3, June 2000: 381-387.

10. Data on File at DePuy Orthopaedics, Inc. WR# 020159 and 040076.

11. Leisinger, S., S. Hazebrouck and D. Deffenbaugh. “A New Approach to Micromotion Characterization of Modular Tibia Implants.” 54th Annual Meeting of the Orthopaedic Research Society, Poster No. 1952, March 2-5, 2008, San Francisco, CA.

12. Parks, N.L., G.A. Engh, L.D.T. Topoleski and J. Emperado. “Modular Tibial Insert Micromotion: A Concern with Contemporary Knee Implants.” Clinical Orthopaedics and Related Research No. 356, November 1998: 10-15.

13. Wasielewski, R.C., N. Parks, I. Williams, H. Suprenant, J.P. Collier and G. Engh. “Tibial Insert Undersurface as a Contributing Source of Polyethylene Wear Debris.” Clinical Orthopaedics and Related Research No. 345, December 1997: 53-59.

14. Data on File at DePuy Orthopaedics, Inc. WR# 020085 and 30058.

15. Sharkey, P., W. Hozack, R. Rothman, S. Shastri and S. Jacoby. “Why are Total Knee Arthroplasties Failing Today?” Clinical Orthopaedics and Related Research No. 404, November 2002: 7-13.

16. Currier, B.H., J.H. Currier, M.B. Mayor, K.A. Lyford, J.P. Collier and D.W. Van Citters. “Evaluation of Oxidation and Fatigue Damage of Retrieved Crossfire Polyethylene Acetabular Cups.” The Journal of Bone and Joint Surgery Vol. 89, September 2007: 2023-2029.