primary knees. changing patient demographics – younger source: burden of musculoskeletal diseases...

Primary Knees

Changing Patient Demographics – Younger

Source: Burden of Musculoskeletal Diseases in the United States, 2008. (RP Technology Value Dossier)

Total Knee Arthroplasty Procedures in the United States, 1991-2004

Changing Patient Demographics – Younger Pts Growth

“In the last decade, the number of TKRs performed in the U.S. doubled, exceeding 600,000 in 2009. […]

The growth in TKR use has been greatest among younger individuals, and as a result the average age at which patients receive TKR has decreased over time.”

Source: AAOS 2012 Abstract. “How Many Americans are Currently Living with Total Knee Replacement?” 54-Adult Reconstruction Knee VII. Weinstein, A.M. et al. http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=65a71ec2-6fba-429b-b9a0-97db92e78fba&cKey=8e9d5320-3ca0-403e-8e73-c682c9240961&mKey=%7bBA8AA154-A9B9-41F9-91A7-F4A4CB050945%7d

Elena Losina, PhD, Thomas S. Thornhill, MD, Benjamin N. Rome, BA, John Wright, MD, and Jeffrey N. Katz, MD, MSc; The Dramatic Increase in Total Knee Replacement Utilization Rates in the United States Cannot Be Fully Explained by Growth in Population Size and the Obesity Epidemic; 2012 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED, p.201.

Results: “In 2008, 615,050 total knee replacements were performed in the United States adult population, 134% more

than in 1999.”

Changing Patient Demands – High Function

• “An increasing number of patients in their late 40s & early 50s are undergoing TKA and will require their implants to last 30 years or more at an increased functional demand level than did older patients in initial long-term studies.”

“Designing for the future: Mobile bearing technology for increased implant longevity.” Dennis, D. A. MD, Orthopedicstoday, 7, 2010.

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Changing Patient Demands – High Expectations

• “Today, more patients opt for early intervention & expect better outcomes, including an increased range of motion of approximately 120° to 125°, greater flexion & the ability to participate in recreational sporting activities.”

“Designing implants to meet evolving patient expectations.” Ranawat, C.S. MD, Orthopedicstoday, 3, 2010.

Changing Patient Demands – Activity

Surgeons Allow More Athletic Activity After Joint Replacement1

• Average number of gait cycles per year is over 1 million1,2

• High levels of activity place increased demands on components

1. Healy et al. “Athletic Activity After Total Joint Arthroplasty” JBJS, 90-A, 2008: 2245-2252.2. Morlock et al. “Duration and Frequency of Every Day Activities…” Journal of Biomechanics, 24, 2001: 873-881.

SIGMA Fixed Bearing:

Wear Reduction Better Bearing Surface Oxidatively Stable

Polyethylene i2 Locking Mechanism

Importance of Wear ReductionSignificant Wear Found in 25% of All Revisions1

Sharkey P. “Why Are Total Knee Arthroplasties Failing Today?” CORR, 404, 2002: 7-13.

Importance of Wear Reduction“The main causes of failure and revision were loosening,

instability, & wear.”

Source: Mulhall et al., 2006. (RP Technology Value Dossier)

Historical Wear Issues• Micromotion

Insufficient locking mechanisms & rough titanium trays may cause increased motion & wear

Wear on the underside of inserts has been associated with radiographic evidence of osteolysis1

• Oxidation of Gamma-in-Air Polyethylene Inserts

Free radicals created by gamma irradiation in an oxygen environment has been shown to degrade the poly material

Wasielewski R. “Tibial Insert Undersurface as a Contributing Source…” CORR, 345, 1997: 53-59.

Wear Reduction in Fixed Bearings

Materials Matter!

• Tray Material & Surface Finish

• Polyethylene Material

• Locking Mechanism

Polished Cobalt Chrome Tibial Tray• Cobalt Chrome Material• Polished cobalt chrome trays have been shown

to reduce backside poly wear (as compared to Ti trays)1

• Highly Polished Surface• Polishing the surface of the CoCr tray reduces

roughness by 95% compared to a Ti tray2

• Several clinical papers recommend polishing the tray to reduce wear1,3,4

95% Reduction

1. “Polished Tibial Trays in Modular Knees…” Currier et al, AAOS Podium Presentation #165.2. Data on File at DePuy Orthopaedics, Inc. WR 010120.3. “Modular Tibial Insert Micromotion…” Parks et al, CORR., 356:10-15, 1998.4. “Tibial Insert Undersurface…” Wasieleski et al, CORR, 345:53-59, 1997.

CONCLUSION “Unlike hips, knees have been shown to have significant backside wear. It is unclear whether crosslinking has significant clinical advantage.

This study shows that the finish of the tibial tray is significant predictor of wear, and crosslinking might not be.”

2012 AAOS Abstract: Metal Ions from Tibial Trays – Co is Lowest

CONCLUSION “For other metallic implant devices it is well known that metal wear products are able to interact with the immune system potentially leading to

immunotoxic effects like hypersersensitivity or the formation of pseudotumors. To our knowledge, this is the first study that analyzed the release of metallic wear

products in TKA in vitro. We found that approx. 10% of the whole wear products are metallic and we believe that these particles and ions may become

clinically relevant.”

XLK Polyethylene

• GUR 1020 Resin• Tougher mechanical properties relative to other

commercially available medical grade resin, 10501

• Moderately Crosslinked to 5 Mrads• Provides increased resistance to multidirectional wear

inherent in fixed bearing designs2

• A higher dose of radiation produces a marked deterioration in mechanical properties3

• Oxidatively Stable• Remelted above its 135° C melt point2

• Creates mobility in polymer chains & allows free radicals to recombine and crosslink

i2 Locking Mechanism

• Interference Fit• Polyethylene insert is larger than the perimeter of

the tray by 150 microns• Inhibits the ability of the polyethylene to move

inside the tray

• Anterior Bumper• Anterior bumper between the two locking tabs

prevents a “spring” effect

“A New Approach in Micromotion…” Leisinger et al, ORS #1952, 2008.

i2 Locking Mechanism

• 16 Microns of MotionA New Approach to Micromotion Characterization of Modular Tibial Implants; Poster number 1952; 54th Annual Meeting of the Orthopaedic Research Society; 2008; San Francisco, CA

Fixed Bearing Clinical Publications•“Because motion between the insert and 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.”•“Tibial Insert Undersurface as a Contributing Source of Polyethylene Wear Debris” Wasielewski et al., CORR, 345, 1997.

•“Locking mechanisms of inserts from polished trays showed no discernable wear or geometrical changes, in contrast to the matte finish counterparts…”•“Polished Tibial Trays in Modular Knees Show Reduced Backside Wear” Currier et al., AAOS #165, 2009.

•“99.6% 10-year survivorship with the Sigma CR Fixed Bearing knee. Our study confirms that the PFC Sigma knee system has performed well at midterm follow-up.”•“Midterm Results with the PFC Sigma Total Knee Arthroplasty System” Dalury et al., JOA, 23, 2, 2008.

CONCLUSION “A total of 120 patients (138 knees) were successfullyfollowed up.

Survivorship over 17 years was 92.5% [with PFC SIGMA CR Knees].”

SIGMA Rotating Platform

Materials Matter:

• Tray Material & Surface Finish

• Femorotibial Conformity

• Unidirectional Motion

• Oxidatively Stable Polyethylene - Antioxidant UHMWPE available

Polished Cobalt Chrome Tibial Tray

•Cobalt Chrome Material• Polished cobalt chrome trays have been shown to

reduce backside poly wear (as compared to Ti trays)1

•Highly Polished Surface• Polishing the surface of the CoCr tray reduces

roughness by 95% compared to a Ti tray2

• Several clinical papers recommend polishing the tray to reduce wear1,3,4

1. “Polished Tibial Trays in Modular Knees…” Currier et al, AAOS Podium Presentation #165.2. Data on File at DePuy Orthopaedics, Inc. WR 010120.3. “Modular Tibial Insert Micromotion…” CORR., 356:10-15, 1998.4. “Tibial Insert Undersurface…” Wasieleski et al, CORR, 345:53-59, 1997.

Femorotibial Conformity

• 1:1 Conformity between 0°- 30° of Flexion

• Promotes alignment of the insert to the femoral component

• Limits the amount of multidirectional motion on topside of insert

• Increased Contact Area• Minimizes contact stresses on the polyethylene

Unidirectional Motion• Unidirectional Motion• Rotating platform separates complex,

multidirectional motions inherent in fixed bearing designs

• Topside motion flexion / extension

• Backside motion internal / external rotation

SIGMA Rotating Platform

Design Matters:

• Better Femoro-insert Mechanics

• Better Femoro-tibial Mechanics

Femoro-insert Mechanics• More forgiving

to malaligned femoral components because insert self-aligns to femoral component

• Increased Contact Area

• Decreased Contact Stress • Minimizes contact stresses on the

polyethylene

Femoro-tibial Mechanics

“Mobile-bearing knee prostheses have been shown toreduce stresses transmitted to the fixation interface,which could improve implant stability and decrease theincidence of implant loosening7, 8”.

7. Russo et al., 2005. Fixation of tobal knee arthroplasty improved by mobile-bearing design. Clin Orthop Relat Res. 437:186-195.8. Bottlang et al., 2006. A mobile-bearing knee prosthesis can reduce strain at the proximal tibia. Clin Orthop Relat Res. 447:105-111.

Representative Constraint Torque – Rotation Angle Curves at 0 Degree Knee Flexion

Peak limit = spin out

Femoro-tibial Mechanics

“The SIGMA PS rotating platform knee reduced peak torque by 79% and 77% at 0 and 45 degree tibiofemoral flexion, respectively, compared tofixed-bearing knee.”

Constraint torque was reached 9.4 Nm

Rotating Platform Clinical Publications•“The results of this study point toward a mobile-bearing wear rate that is lower than that reported for fixed-bearing TKAs despite the appearance of polyethylene damage…”•“Clinical Wear Measurement on Low Contact Stress Rotating Platform Knee Bearings” Atwood et al., JOA, 23, 3, 2008.

•“Mobile bearing knee replacements succeed in reducing stresses associated with abrasion, pitting, and delamination.”•“The Influence of Mobile Bearing Knee Geometry on the Wear of UHMWPE Tibial Inserts: A Finite Element Study” Morra et al., ORL, AAOS 1998.

•“This translation of complex knee motions into more unidirectional motions results in molecular orientation of the UHMWPE and reduced volumetric wear.”•“Wear of fixed bearing and rotating platform mobile bearing knees subjected to high levels of internal and external tibial rotation” McEwen et al., J of Mat Science, 12, 2001.

Sigma RP Clinical Evidence

• A Polished Tray – FB or RP – reduces backside wear

• SIGMA RP has less wear than published LCS wear

Sigma RP Clinical Evidence

JBJS March 2012; Meftah, Ranawat, & Ranawat

• Implanted 2000-2001• 138 knees; consecutive RP PS

knees• Survivorship:

• 100% w/ revision due to mechanical failure

• 97.7% w/ revision for any reason (1 infection, 2 traumatic supracondylar fx)

• 95% w/ an reoperation as end point

TKA Survivorship

• New polyethylene such as antioxidant UHMWPE and highly cross-linked UHMWPE have increased survival significantly.

• Polished CoCr tibial trays have greatly reduced backside wear of UHMWPE bearings.

• Mobile rotating platform UHMWPE bearings reduce wear even further making 25-30 year TKA survivorship possible.

Questions