Gold standard of a TKA. Conflicting goals? POLYETHYLENE WEAR THE SOLUTION: MOBILE BEARING KNEES. MOBILE BEARING A totally new approach (1977)

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1 Changing designs : the case against mobile bearing? Gold standard of a TKA Goal of a TKA: 1. Pain 2. Motion 3. Longevity Stress Guy BELLIER M.D. PARIS France Conformity = Durability w/o constraints = non restricted Motion POLYETHYLENE WEAR Conflicting goals? More Conformity = More Constraints THE SOLUTION: KNEES Detrimental effects : OSTEOLYSIS Mobile bearing A totally new approach (1977) DePuy LCS Scorpio + WHY? Mobility with congruency : Low constraint forces Reduction of poly in vitro No back-side Better kinematics Tolerance of tibial tray malrotation Patello-femoral congruency Potential for increased durability 1

2 RESULTS: TekScan Analysis Peak Contact Pressures Mobile bearing TKA Increasing articular surface conformity improves component longevity A conforming MB design substantially reduces the contact stresses (M.Pappas 1977) By reducing the stresses associated with abrasive, pitting and delamination Postak, Greenwald AAOS 1997 Debris induced osteolysis due to surface of UHMWPE bearings is a potential failure mechanism of TKR Physiological knee simulator EFFECT OF PROSTHESIS DESIGN Highly significant (p<0.01) four-fold reduction in, despite greater conformity between poly and femur POLYETHYLENE WEAR All mobile bearings are not the same In vivo kinematics of fixed- and mobile-bearing bearing TKA. H.Delport, S.Banks.. JBJS 2006 (Marss et al, 1999; Wang et al, 1996) Uni- versus multi-directional mobile-bearing design Fischer (Leeds University) Biomed Mater Eng 1999 The femur moves in an AP direction on the upper surface of the insert. The movement at the lower surface is pure rotation 2

3 WHY? Mobility with congruency : Low constraint forces Reduction of poly in vitro No back-side Better kinematics Tolerance of tibial tray malrotation Patello-femoral congruency Potential for increased durability BACK-SIDE POLY WEAR of Fixed PS TKA Wasielewski RC, CORR 1997 Tibial insert undersurface (micromotion)) as a Back-sidecontributing maysource contribute of polyethylene up to 30 % of debris the overall polyethylene (back-side ) rate of fixed bearing inserts Condit M, JBJS 2005 Sufficient volume of material to induce osteolysis Rotational pattern of scratching and burnishing at the tibia-insert insert surface P. Jayabalan HSSJ 2006 Locking Mechanism WHY? Mobility with congruency : Low constraint forces Reduction of poly in vitro No back-side Better kinematics Tolerance of tibial tray malrotation Patello-femoral congruency Potential for increased durability SELF-ALIGNING IN ROTATION malposition of the tibial component Pagnano M. CORR 2004 LRR 3.8% (vs 3.8%) Patellar tilt 11% (vs 6%) Dennis D LRR 3% (vs 12%) Internal rotation of the femoral component lift-off & patellar subluxation subluxation WHY? Mobility with congruency : Low constraint forces Reduction of poly in vitro No back-side Better kinematics Tolerance of tibial tray malrotation Patello-femoral congruency Potential for increased durability 3

4 DURABILITY OF MB TKA Multicenter worlwide study of 4743 LCS cemented RP 87 % survivorship at 14 years (Hamelynck et al. 2002) 97 % at 20 years Buechel 94 % at 10 years Sorrel 100 % at 9 years Callaghan 92 % at 12 years Huang ADVANTAGES OF Conformity is achieved without constraint Tibial malrotation in extension may be accomodated Backside is addressed Only MB knees provide acceptable stress levels (peak stress) Less gliding and shearing forces MB knee can reduce strain at the proximal tibia DISADVANTAGES OF Bearings without stops can dislocate or spin-out Less forgiving of soft tissue imbalance Normal Fixed PS LCS MB LCS RP RANGE OF MOTION TYPE Fixed PCR PASSIVE WEIGHT BEARING Fixed PS LCS MB LCS RP RANGE OF MOTION TYPE Normal Fixed PCR PASSIVE WEIGHT BEARING Geometry more important than bearing mobility (D.Dennis 2000) Mobile Bearing BACK-SIDE WEAR LCS RP : 4 years post-op 4

5 Osteolysis in failed TKA : comparison of MB and FB Knees Huang et al, JBJS 2007 PREVALENCE OF OSTEOLYSIS 16/34 Mobile : 47% LCS RP & CR 6/46 Fixed : 13% All CR 4 years post-op Post-op MB : do they really rotate? Internal rotation in flexion Normal knee : 16.8 (2.1 to 27.1 ) PS : 10.4 (2.9 to 20.1 ) CR : 1.9 ( to 7.9 ) MB : 2.9 ( to 7.6 ) AUSTRALIAN JOINT REPLACEMENT REGISTRY MOBILE vs FIXED BEARINGS 7 prospective randomised recent studies Kim YH, CORR 2001 Price AJ, JBJS 2003 Woolson ST, JOA 2003 Pagnano MW, CORR 2004 Wohlrab D, Z.Orthop 2005 Aglietti P, J. Arthroplasty 2005 Kim YH, JBJS 2007 LRR, PF score, patellar subluxation : NO DIFFERENCE Cumulative percentage revision of Fixed and mobile CLINICAL RESULTS CLINICAL RESULTS Y.H Kim, D.Y Kim, J.S. Kim. J Bone Joint Surg [Br] 2007 ; 89-B : PFC Sgma DePuy No significant clinical advantage for a mobile bearing with an average follow- up of 5.6 years (IKS, ROM, Osteolysis) Y.H. Kim, S.H. Yoon, J.S. Kim J Bone Joint Surg [Br]] 2007 ; 89-B : The Kaplan-Meier survivorship for aseptic loosening of the anatomic modular knee and the low contact stress implants at 14.5 years was 99% and 100%, respectively, with a 95% confidence interval of 94% to 100% for both designs. We found no evidence of the superiority of one design over the other at long-term follow-up 5

6 DISADVANTAGES OF still the only answer to poly in 2008? Ligament balance : bearing dislocation Back side Higher revision rate Range of motion PF tracking : no difference Clinical scores : no difference Rotation : MB < PS < Normal knee ADVANCED DESIGN Fixed TKA with MBK features Fixed - mobility Triathlon and Scorpio NRG Conformity without constraint Rotational Freedom - Design Insert Triathlon PS Triathlon CR Spherical Arc (5 degrees of freedom) PS tibial insert incorporates a Spherical Flexion Varus-valgus Arc that allows for: AP translation Greater Rotational Freedom (±25( 25 ) ML translation Internal-external rotation Maintains single M/L radius The Importance of The Poly The AGC and 1900 (M.Ritter( M.Ritter) Challenging environment Relatively flat tibio-femoral geometry (CR) Relatively high stresses Relatively thin polyethylene >15 years clinical experience Low Low osteolysis High survivorship Relatively oxidation resistant X3 enables design evolution for higher function (with safety) 80 % 6

7 Materials are also key! Surface treatment New PE: Important (PCA, AGC) Bad experiences X3 The Concept of Fixed Mobility Tibio Femoral pressure in vitro C. Stukenborg Colsman (EFORT 2007) No increase of load on PE inlay with high flexion of modern design (Triathlon) No difference Mobile vs Fixed bearing Locking mechanism greatly affects propensity for Backside Wear in Modern Total Knee Designs P. Jayabalan et al. HSSJ 2006 Reduction in articular rotational constraint in TKA prosthetic design improves in vivo knee kinematics O. Mahoney AAOS Scorpio NRG PS, videofluoroscopy, stand to squat maneuver The maximum femoral external rotation observed for each knee at any flexion angle interval averaged 9.1 ±6.0 (range: 0.5 to 18.9 ) Femoral external rotation greater than 10 in 8 (47%) knees, and 4 (24%) knees exhibited femoral external rotation in excess of 15 at some point during the movement In Vivo Kinematics of Scorpio NRG PS TKA in Deep Knee Bending Motion T. Tomita (Osaka, Japan) 12 Scorpio NRG PS The axial rotation revealed external rotation up to maximum flexion. The average external rotation was 13 degrees (5.2 to 20.5) Axial Rotation Axial Rotation Range of Motion In Vivo Kinematics of Scorpio NRG PS TKA «MOBIFIX» «TribOS» O. Mahoney F. Catani T. Tomita 9.1 ±6.0 (0.5 to 18.9) Stand to squat 9.4 ( ) Active (chair) 2.9 Step up down 13 (5.2 to 20.5) Deep knee band Kinematic Design of Scorpio NRG and Triathlon Freedom of Internal and External Rotation Single radius Tibial Baseplate fixation Delta keel Improvement in Polyethylene Technology X3 Locking Mechanism of Insert to Tibial baseplate None of the disadvantages of Mobile Bearings 7

8 The new gold standard New Fixed Bearing Design New Materials THE CONCEPT OF FIXED MOBILITY «Get the best of both worlds» Triathlon, Scorpio NRG and X3 An alternative for MB THANK YOU 8