Briard Jl. Are All Mb Knees The Same. Slide 29 53

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  • Briard Jl. Are All Mb Knees The Same. Slide 29 53

    1. 1. Fixation (MB aims at relieving stress at the bone-prosthesis interface) <ul><li>No problems with cemented implants </li></ul><ul><li>Excellent with uncemented implants </li></ul>Even better today with Duofix
    2. 2. Wear and osteolysis <ul><li>Osteolysis is due to submicron PE wear particles mostly from the back side and is not encountered with the LCS RP ( Sorrells (5-12y), Buechel (20y) even with gamma-in-air irradiated PE ! </li></ul><ul><li>Remarkable ! </li></ul><ul><li>Wear at the upper surface is very rare due to overload or instability (surgical errors) or poor PE 1 case for Sorrells) + 5/598 of late dislocations with wear of Huang </li></ul>
    3. 3. <ul><li>We don’t see this: backside wear with catastrophic osteolysis as in Modular FB designs </li></ul>
    4. 4. Lab. Studies in Leeds by J.Fisher & H.Mac Ewen
    5. 5. FB wear more especially if they are submited to more stresses especially in rotation
    6. 6. Polyethylene Debris No significant difference in volumetric concentrations between fixed bearing 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) <0.1 μ 0.1-1.0 1.0-10 >10 Same particles but much less !
    7. 7. Survivorship <ul><li>Cemented Rotating Platform TKP: a 9 to 12y FU study </li></ul><ul><li>J.Callaghan , M.Squire, D.Goetz, P.Sullivan, R.Johnston in JBJS 2000 </li></ul><ul><li>86 knees </li></ul><ul><li>all poly patella, </li></ul><ul><li>no revisions </li></ul>
    8. 8. <ul><li>20y evaluation of Meniscal Bearing and Rotating Platform Knee replacements </li></ul><ul><li>by F.Buechel Sr & Jr, M.Pappas, J.D’Alessio in CORR 2001 </li></ul>
    9. 9. Endpoint: revision for any mechanical failure More failures with MB, but excellent results for RP 98.3% 97.7%
    10. 10. <ul><li>Total Condylar (PS) </li></ul><ul><li>LCS </li></ul><ul><li>AGC </li></ul><ul><li>Failure rate from 0 to 0.5% per year </li></ul>Total Condylar LCS AGC Best surviving TKA
    11. 11. <ul><li>The most important factor for best survivorhip is the quality of the PE which controls the fatigue wear </li></ul><ul><li>Arcom with pressure molding explains the results of the AGC knee (badly designed!) </li></ul><ul><li>Sterilization is essential: </li></ul><ul><li>- Avoid gamma air sterilized PE which leads to early oxydation </li></ul><ul><li>- Ethylene oxyde sterilization survived better </li></ul>
    12. 12. What is the situation today ? What do we know about MB today ? But don’t forget: all MB knees are not the same !
    13. 13. Now, I’m 90 and they reoperated on me ! #1 at 72 y
    14. 16. Leeds ProSim Knee Simulator Tests run for 5 million cycles
    15. 17. Mean Wear Rates
    16. 18. <ul><li>This strain hardening effect gives some wear resistance if sliding direction is same as the direction of orientation but may reduce wear resistance in orthogonal or other directions. </li></ul><ul><li>Hence it is postulated that a monodirectional sliding on any given poly surface is an enormous benefit. </li></ul>
    17. 19. 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 …..
    18. 20. 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
    19. 21. Fixed Bearing Knees Wear of fixed bearing knees is highly dependent 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
    20. 22. 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 of fixed bearing similar to Rotating Platform Higher wear rate of fixed bearing results in Functional Biological Activity more than three times greater than RP, therefore increased osteolytic potential So, much less osteolysis ! 2.1 0.36 LCS ® Rotating Platform 6.8 0.3 Fixed Bearing Functional Biological Activity (FBA) Specific Biological Activity (SBA)
    21. 23. <ul><li>So: </li></ul><ul><li>If you have a PFC Σ RP PS and allow the normal play in varus/valgus tilting, the contact area won’t exceed 350-450 mm 2 /2: is it enough and for which survivorship ? (under 70 y old) </li></ul>
    22. 24. Now, I’m 90 and they reoperated on me ! #1 at 72 y
    23. 25. 3-400mm 2 : significant diminution in contact stress often below 10 MPa

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