Fixation Fixation (MB aims at relieving stress at the (MB aims at relieving stress at the bone-prosthesis interface)bone-prosthesis interface)

No problems with cemented implantsNo problems with cemented implants Excellent with uncemented implantsExcellent with uncemented implants

Even better today with Duofix

Wear and osteolysisWear and osteolysis

Osteolysis is due to submicron PE Osteolysis is due to submicron PE wear particles mostly from the back wear particles mostly from the back sideside and is not encountered with the LCS and is not encountered with the LCS RP ( Sorrells (5-12y), Buechel (20y) even RP ( Sorrells (5-12y), Buechel (20y) even with gamma-in-air irradiated PE !with gamma-in-air irradiated PE !

Remarkable !Remarkable ! Wear at the upper surface is very rare due Wear at the upper surface is very rare due

to overload or instability (surgical errors) to overload or instability (surgical errors) or poor PE 1 case for Sorrells) + 5/598 of or poor PE 1 case for Sorrells) + 5/598 of late dislocations with wear of Huanglate dislocations with wear of Huang

We don’t see this: We don’t see this: backside wearbackside wear with with catastrophic osteolysis catastrophic osteolysis as in Modular FB designsas in Modular FB designs

Lab. Studies in Leeds by J.Fisher & Lab. Studies in Leeds by J.Fisher & H.Mac EwenH.Mac Ewen

FB wear more especially if they are submited to more stresses especially in rotation

Polyethylene Debris

No significant difference in volumetric No significant difference in volumetric concentrationsconcentrations between fixed between fixed bearing and Rotating Platform designsbearing and Rotating Platform designs

(Brown et al. Comparison of Wear Particles Generated by Fixed and Rotating Platform Mobile

Bearing Knee Designs, Submitted to ORS 2005)

<0.1μ

0.1-1.0

1.0-10

>10

Same particles but m

uch less !

SurvivorshipSurvivorship

Cemented Rotating Cemented Rotating Platform TKP: a 9 to 12y Platform TKP: a 9 to 12y FU studyFU study

J.CallaghanJ.Callaghan, M.Squire, , M.Squire, D.Goetz, P.Sullivan, D.Goetz, P.Sullivan, R.Johnston in JBJS 2000R.Johnston in JBJS 2000

86 knees86 knees all poly patella, all poly patella, no revisionsno revisions

20y evaluation of 20y evaluation of Meniscal Bearing and Meniscal Bearing and Rotating Platform Knee Rotating Platform Knee replacements replacements

by by F.BuechelF.Buechel Sr & Jr, Sr & Jr, M.Pappas, J.D’Alessio M.Pappas, J.D’Alessio in CORR 2001in CORR 2001

Endpoint: revision for any Endpoint: revision for any mechanical failuremechanical failure

More failures with MB, but excellent results for RP

98.3%

97.7%

• Total Condylar (PS)

• LCS

• AGC

Failure rate from 0 to 0.5% per year

Total Condylar

LCS AGC

Best surviving TKA

The most important factor for best The most important factor for best

survivorhip is the survivorhip is the quality of the PEquality of the PE which controls the fatigue wearwhich controls the fatigue wear

Arcom with pressure molding explains the Arcom with pressure molding explains the results of the AGC knee (badly designed!)results of the AGC knee (badly designed!)

Sterilization is essential:Sterilization is essential:

- Avoid gamma air sterilized PE which leads - Avoid gamma air sterilized PE which leads to early oxydationto early oxydation

- Ethylene oxyde sterilization survived - Ethylene oxyde sterilization survived betterbetter

What is the situation today ?What is the situation today ?What do we know about MB today ?What do we know about MB today ?

But don’t forget: all MB knees are not the same !

Now, I’m 90 and they reoperated on me !

#1 at 72 y

Leeds ProSim Knee Simulator

Tests run for 5 million cycles

Mean Wear Rates

This strain hardening effect gives This strain hardening effect gives some wear resistance if sliding some wear resistance if sliding direction is same as the direction direction is same as the direction of orientation but may reduce wear of orientation but may reduce wear resistance in orthogonal or other resistance in orthogonal or other directions. directions.

Hence it is postulated that a Hence it is postulated that a monodirectional sliding on any monodirectional sliding on any given poly surface is an enormous given poly surface is an enormous benefit.benefit.

UHMWPE Kinematics

Multidirectional motion accelerates UHMWPE wear (Wang et al. 1996, Proc.IMechE, 210H, 141)

Monodirectional motion

reduces UHMWPE wear (Marrs et al. 1999, J.Mats.Sci.Mats.Med. 10, 333)

Which is proven …..

Fixed vs RP

Fixed bearing

multidirectional motion of femoral

component relative to bearing

multiaxial wear path

transverse friction forces

higher wear

Rotating Platform

rotation occurs at tibial tray

multidirectional motion at femoral

unidirectional wear paths

transverse friction forces

lower wear

Fixed Bearing Knees

Wear of fixed bearing knees is highly dependent Wear of fixed bearing knees is highly dependent on displacement and rotation kinematics on displacement and rotation kinematics

Johnson et al. Wear, 250, 222, 2001. Barnett et al. J.Mats.Sci.Mats.Med, 12, 1039, 2001.

Highly active patients may produce high wear

with fixed bearing knees

Polyethylene Debris

(Brown et al. Comparison of Wear Particles Generated by Fixed and Rotating Platform Mobile

Bearing Knee Designs, Submitted to ORS 2005)

Specific Biological Activity

(SBA)

Functional Biological Activity

(FBA)

Fixed Bearing 0.3 6.8

LCS® Rotating Platform 0.36 2.1

Specific Biological Activity of fixed bearing similar to Rotating Platform Specific Biological Activity of fixed bearing similar to Rotating Platform

Higher wear rate of fixed bearing results in Functional Biological Activity more Higher wear rate of fixed bearing results in Functional Biological Activity more than three times greater than RP, therefore increased osteolytic potentialthan three times greater than RP, therefore increased osteolytic potential

So, much le

ss osteolysis !

So:So:

If you have a PFC If you have a PFC ΣΣ RP PS and RP PS and allow the normal play in allow the normal play in varus/valgus tilting, the contact varus/valgus tilting, the contact area won’t exceed 350-450 area won’t exceed 350-450 mmmm2 2 /2: /2: is it enough and for is it enough and for which survivorship ? which survivorship ? (under 70 y (under 70 y old)old)

Now, I’m 90 and they reoperated on me !

#1 at 72 y

3-400mm2: significant diminution in contact stress often below 10 MPa