Briard Jl. Are All Mb Knees The Same. Slide 1 28


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  • Briard Jl. Are All Mb Knees The Same. Slide 1 28

    1. 1. Are all MB knees the same? Is MB really better than FB? Jean-Louis Briard
    2. 2. classification <ul><li>Conformity: contact areas & designs to reduce fatigue wear </li></ul><ul><li>Motion of the bearing relative to the tibial tray +++ and its control </li></ul><ul><li>Stability </li></ul>
    3. 3. #1 Maximum Conformity Can be achieved through: Multi-radius sagittal femoral geometry with a distal sphere Constant radius sagittal FT geometry with a posterior sphere A - SPHERICAL DESIGNS B -OVOID DESIGNS Never spherical Coronal & sagittal radius are different
    4. 4. Multi-radius sagittal femoral geometry: J curve with a distal sphere: S2 Extensive area contact near to extension (R: 50mm ) But circular line contact in Flexion LCS & Generics, Interax ISA, Genesis II/ Profix, Innex, Link TACK, Cinétique A 1 SPHERICAL DESIGNS S2
    5. 5. Constant radius sagittal FT geometry with a posterior sphere Contact area more limited in extension (R: 25mm ) Larger contact in flexion Rotaglide, SAL, TRAC, MBK, Oxford TMK A 2 - SPHERICAL DESIGNS
    6. 6. <ul><li>B -OVOID DESIGNS </li></ul><ul><li>Never spherical </li></ul><ul><li>Coronal & sagittal radius are different </li></ul><ul><li>Smaller contact areas (than spherical) </li></ul><ul><li>often it is an &quot; extension &quot; from the fixed bearing line: PFC  RP, Natural , HLS …as most of the companies want to have a mobile bearing knee in their system </li></ul>
    7. 7. Moving from a fixed bearing to a mobile bearing without changing the femoral implant <ul><li>Allows to increase the conformity of the tibial insert (in rotation & ML), </li></ul><ul><li>And so, to increase the contact area which should be very beneficial for the wear issue </li></ul><ul><li>It’s like an UPGRADE ! </li></ul>
    8. 8. <ul><li>Contact area: </li></ul><ul><li>(At which flexion angle? </li></ul><ul><li>Through full ROM) </li></ul><ul><li>Large difference if: </li></ul><ul><li>-Multiple sagittal radius </li></ul><ul><li>-Single sagittal radius </li></ul><ul><li>-- PS (smaller coronal radius to allow V/V tilting) </li></ul>530 mm 2 407 mm 2 902 mm 2
    9. 9. But in face of V/V tilting and subsequent lift-off which divides the area by 2, 900 mm 2 seems safer Remember with LCS and poor PE, wear is exceptional !
    10. 10. #2 Motion of the Bearing relative to the tibial tray (H.Mc Ewen) <ul><li>Uni-directional motion </li></ul><ul><li>LCS MB/ RP </li></ul><ul><li>Natural knee (MB) </li></ul><ul><li>Genesis II/Profix (rotating only) </li></ul><ul><li>TRAC, Interax ISA </li></ul><ul><li>PFC  RP </li></ul>Multi-directional motion SAL, Rotaglide, LCS AP Glide MBK/LPS Flex, Oxford Genesis II/Profix (Rot/Translating) NB: There is a potential for increase wear due the &quot; crossing patterns &quot; motion at the BACK SIDE of the tibial bearing (file!)
    11. 11. Multidirectional Unidirectional Study conducted at Leeds University by Hannah McEwen, J.Fisher Has proven the value of the LCS concept designed 30 y ago !
    12. 12. UHMWPE Kinematics UHMWPE orientates in principle direction of sliding (Pooley & Tabor 1972, Proc.Roy.Soc.Lon.A, 329, 251) Strength increased parallel to sliding but reduced strength transverse to sliding (Wang et al. 1996, Proc.IMechE, 210H, 141) + Multidirectional works as a file ! : Consequence : # 1
    13. 13. Abrasive Wear Mono directional Multi directional # 2 Limited furrows Huge amount removed
    14. 14. Fixed vs RP Fixed bearing Multidirectional motion of femoral component relative to bearing RP Mobile bearing Bearing rotation decoupled: Linear rotation at tibial counterface with reduced rotation at femoral counterface Not to speak of Backside wear !
    15. 15. <ul><li>Control of the bearing mvt with cones, cylinders, slots, stops which may prove to be deleterious for wear </li></ul><ul><li>The poly cone (LCS RP) has proven its good function for 3 decades </li></ul><ul><li>(uniplanar motion) </li></ul><ul><li>NB: without the PS shear ! </li></ul>
    16. 16. Stability is an issue <ul><li>Possibility of dislocations such as posterior dislocations which can occur with fixed bearings as well </li></ul><ul><li>But due to the possibility of rotation with MB, this dislocation is usually asymetrical </li></ul><ul><li>And results in a spin-out </li></ul>
    17. 17. LCS spinout but very exceptional (4/2000) Stability is an issue
    18. 18. LCS RP prosthetic stability Deep Dish Jump height: 6 mm <ul><li>Relies only on the dish shape (uphill principle) of the RP insert </li></ul>jump height reflects : the &quot; forgiven &quot; laxity
    19. 19. <ul><li>But PS is attracting many surgeons for the following arguments: </li></ul><ul><li>-more secure technique, </li></ul><ul><li>-more difficult knees, </li></ul><ul><li>-better mechanics, with roll back after 70° ? </li></ul><ul><li>-and hopefully better flexion as with RPF ? </li></ul>
    20. 20. So, the PFC Σ RP <ul><li>Seems as an excellent compromise with increased conformity and still with the PS &quot; security “ but …. has half of the contact area of the LCS ! </li></ul>
    21. 21. PS RP (0-70°) <ul><li>The PS Post usually comes into contact with the bar only at 70° </li></ul><ul><li>Between 0 & 70°, it functions as a dish (like LCS) for AP stability : </li></ul><ul><li>- but the side contact between the post and the box controls the rotation of the insert and &quot; assists &quot; to maintain good relationship between the femur and the insert and prevent spin-out </li></ul>
    22. 22. <ul><li>Jump Height (engagement depth) of the FT articulation. When it is exceeded, danger of dislocation or spin-out </li></ul>TRAC HLS IB2 Importance of surgical technique to keep good stability and so allow soft tissues to function & dissipate the stresses (load sharing) that can lead to wear & loosening LCS
    23. 23. PS and MB ++++ <ul><li>During (high) flexion, some rotation of the tibial insert usually takes place </li></ul><ul><li>The ability of the insert to rotate allows to maintain excellent large contact area between the post and the cam avoiding edge contact and subsequent wear of the post </li></ul>
    24. 24. <ul><li>Probably, some bearing control mechanisms will fail! </li></ul><ul><li>All MB knees are not equal and won’t survive equally ! </li></ul>
    25. 25. LCS system Unchanged for 30 years and widely copied today ! Rotating Platform
    26. 26. Results Complications LCS RP <ul><li>Stability </li></ul><ul><li>Fixation </li></ul><ul><li>Wear and osteolysis </li></ul><ul><li>Patellar complications </li></ul><ul><li>Survivorship </li></ul>
    27. 27. LCS results a) complications <ul><li>Meniscal bearings </li></ul><ul><li>reports of early failures with meniscal bearings: dislocations, fractures </li></ul><ul><li>Reports of late failures with wear (MB exchange after 10-15y) </li></ul>abandoned !
    28. 28. LCS spinout but very exceptional (4/2000) Stability is an issue