Jennings Lm. Wear Of Knee Replacements Influence Of Kinematics And Design

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  • Jennings Lm. Wear Of Knee Replacements Influence Of Kinematics And Design

    1. 1. Wear of Knee Replacements Influence of Kinematics and Design <ul><li>Louise M Jennings, John Fisher </li></ul><ul><li>Institute of Medical and Biological Engineering </li></ul><ul><li>University of Leeds </li></ul><ul><li>VOCA Congress </li></ul><ul><li>September 2007 </li></ul>
    2. 2. Two Types of Polyethylene Wear <ul><li>1. Delamination or structural fatigue </li></ul><ul><li>2. Surface wear </li></ul>
    3. 3. Surface Wear in Knees <ul><li>Surface wear produces micron and sub micron size wear particles </li></ul><ul><li>Accumulation in periprosthetic tissues leads to osteolysis </li></ul><ul><li>Potential for long term failure we see in the hip occurring in the knee </li></ul>
    4. 4. Factors That Affect TKR Surface Wear in Current Polyethylenes <ul><li>Kinematic conditions </li></ul><ul><li>Prosthesis design </li></ul><ul><li>Simulator studies, 300 million cycles </li></ul>
    5. 5. Leeds ProSim Knee Simulator
    6. 6. Leeds ProSim Knee Simulator <ul><li>Anatomical Mounting </li></ul><ul><li>6 degrees of freedom </li></ul><ul><li>4 controlled axes </li></ul><ul><ul><li>Femoral Side </li></ul></ul><ul><ul><li>Axial Load </li></ul></ul><ul><ul><li>Flexion/Extension </li></ul></ul><ul><ul><li>Tibial Side </li></ul></ul><ul><ul><li>Rotation </li></ul></ul><ul><ul><li>Displacement </li></ul></ul><ul><li>2 passive axes </li></ul><ul><li>Displacement or </li></ul><ul><li>Force Control </li></ul>Tibial Rotation AP Displacement Flexion/Extension Axial Force Abduction/Adduction Medial/Lateral Translation
    7. 7. Kinematic Inputs <ul><li>Femoral - relative to Tibia </li></ul><ul><li>ISO standard (ISO 14243) </li></ul><ul><ul><li>Axial Load </li></ul></ul><ul><ul><li>Flexion/Extension </li></ul></ul><ul><li>Tibial - relative to Femur </li></ul><ul><li>Kinematics of the natural </li></ul><ul><li>knee (Lafortune et al . 1992) </li></ul><ul><ul><li>IE Rotation </li></ul></ul><ul><ul><li>AP Displacement </li></ul></ul><ul><ul><li>AP Force (ISO) </li></ul></ul>
    8. 8. Effect of Bearing Materials Fixed Bearing Knees - PFC, PFC Sigma <ul><li>Historic device and material: PFC 1020  - IR in air </li></ul><ul><li>Current device and material: PFC Sigma 1020 GVF </li></ul><ul><li>Potential material: PFC Sigma Marathon (5 MRad 1050 + re melt with GP sterilisation) </li></ul><ul><li>High kinematics (± 5° rotation, 10 mm displacement) </li></ul><ul><li>5 million cycles </li></ul>
    9. 9. Fixed Bearing Knees PFC  - IR in air PFC Sigma  - IR under vacuum and foil packed PFC Sigma Marathon
    10. 10. Effect of Kinematics on Wear Fixed Bearing Knees
    11. 11. Effect of Kinematics Fixed Bearing Knees - PFC Sigma 1020 GVF
    12. 12. Fixed Bearing Knees PFC Sigma 1020 GVF High Kinematics PFC Sigma 1020 GVF Intermediate Kinematics PFC Sigma 1020 GVF Low Kinematics McEwen et al J Biomechanics 2005
    13. 13. Effect of Kinematics <ul><li>Fixed Bearing knees : doubling the amount of internal-external rotation and anterior-posterior translation produced a five fold increase in wear rate </li></ul><ul><li>Implications for young, high demand patients </li></ul><ul><li>Wear is increased by more multidirectional kinematics due to greater cross shear on the polyethylene surface </li></ul>
    14. 14. Fixed Bearing Knees <ul><li>Multidirectional motion of the femoral component relative to the tibial bearing surface </li></ul>femoral rotation a-p translation tray femoral bearing flexion- extension
    15. 15. Molecular Strain Hardening <ul><li>UHMWPE exhibits molecular orientation in the principle direction of sliding (Pooley & Tabor 1972) </li></ul>principle direction of sliding strain softening strain hardening <ul><li>Orientation leads to increased strength parallel to sliding (‘hardening’) and reduced strength transverse to sliding (‘softening’) (Wang et al 1996) </li></ul>
    16. 16. Effect of Prosthesis Design
    17. 17. Effect of Prosthesis Design Fixed Bearing PFC Sigma Mobile Bearing PFC Sigma Rotating Platform <ul><li>5 million cycles </li></ul>Fixed Bearing Mobile Bearing Rotating Platform
    18. 18. Fixed Bearing Knee PFC Sigma Mobile Bearing Knee PFC Sigma RP Engineering Comparison: Matched Intermediate Kinematics McEwen et al, J Biomechanics 2005
    19. 19. Fixed Bearing Knee PFC Sigma Mobile Bearing Knee PFC Sigma RP Clinical Comparison High Kinematics McEwen et al, J Biomechanics 2005
    20. 20. Mobile Bearing Knees <ul><li>Bearing rotation decoupled by allowing rotation at the tibial counterface </li></ul><ul><li> reduced rotation at the femoral counterface </li></ul><ul><li>Tibial counterface rotation in rotating platform (RP) mobile bearings is simple linear motion </li></ul>tibial rotation flexion- extension femoral bearing tray
    21. 21. Kinematics <ul><li>Multidirectional motion accelerates UHMWPE wear </li></ul><ul><li>(Wang et al 1996, </li></ul><ul><li>Barbour et al 1999) </li></ul>wear rate unidirectional multidirectional Friction vectors Wear path — transverse — principal RP Fixed Hip  F FR  <ul><li>Unidirectional motion reduces wear </li></ul><ul><li>Rotating platform </li></ul><ul><li>(Marrs et al 1999) </li></ul><ul><li>(Pooley et al 1962) </li></ul>
    22. 22. Wear Debris Volumetric Concentration
    23. 23. Biological Activity and Osteolytic Potential Tipper et al, Soc Biomaterials 2005 17.6 0.69 25.6 ± 5.3 Hip 1.8 0.36 5.2 ± 3.8 PFC Sigma RP 6.8 0.3 22.75 ± 5.95 PFC Sigma FBA Functional Osteolytic Potential SBA Specific Biological Activity Mean Wear Rate (mm 3 /10 6 cycles) Implant Type
    24. 24. Knee Design <ul><li>Rotating platform mobile bearings produced a substantial reduction in wear compared to fixed bearing knees </li></ul><ul><li>Osteolytic potential of knees is less than hips, debris less reactive </li></ul><ul><li>Osteolytic potential of rotating platform mobile bearing knees substantially reduced compared to fixed bearing knees </li></ul><ul><li>However… </li></ul>
    25. 25. Lift Off <ul><li>Introduced adduction moment to tibial carriage </li></ul><ul><li>1 mm of lateral femoral condylar lift off during swing phase </li></ul><ul><li>Associated M/L displacement </li></ul><ul><li>Simulated for every gait cycle </li></ul>Jennings et al ORS 2005
    26. 26. Effect of Lift Off Fixed Bearing PFC Sigma Mobile Bearing PFC Sigma Rotating Platform p < 0.05 p < 0.05 p > 0.05
    27. 27. Lift off <ul><li>Femoral condylar lift off accelerated the wear of both fixed and mobile bearing knees </li></ul><ul><li>Medial condyle displayed more wear damage under lift off conditions due to </li></ul><ul><ul><li>Elevated contact stresses as lateral lift off produced uneven loading of the bearing </li></ul></ul><ul><ul><li>Acceleration of wear by cross shearing of polyethylene in the medial/lateral direction </li></ul></ul>
    28. 28. Conclusions <ul><li>Rotating platform mobile bearing knees </li></ul><ul><li>reduced wear rate and functional osteolytic potential by a factor of four </li></ul><ul><li>However some of this benefit is lost if lift off and medial lateral shift occurs, which increases wear in both designs </li></ul><ul><li>Surgery stability and soft tissue reconstruction is important in wear performance </li></ul>
    29. 29. Thank you Co authors Hannah McEwen, Petra Barnett, Carol Bell, Amir Kamali, Dan Auger, Richard Farrar, Joanne Tipper, Alison Galvin, Mark Taylor, Martin Stone, Eileen Ingham Research supported by EPSRC, ARC, DePuy

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