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Bearing surfaces THR

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Alternative bearing surfaces
Alternative bearing surfaces
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Bearing surfaces THR

  1. 1. Bearing Surfaces in Total Hip Arthroplasty
  2. 2. History Interpositional arthroplasty 1912- Sir Robert Jones- Gold foil
  3. 3. Mould arthroplasty 1923-Smith Peterson Restore congruous articular surfaces Bleeding cancellous bone of femoral head and acetabulum Metaplasia of fibrin clot to fibrocartilage
  4. 4. Glass Pyrex – viscalloid - celluloid derivative Bakelite Fragility and foreign body reaction
  5. 5. 1937-Venable and Stuck- Vitallium- results encouraging Aufranc
  6. 6. Judet brothers- heat curved acrylic femoral head prosthesis-fragmentation of acrylic with wear- severe tissue reaction-bone destruction Thompson and Moore – metallic endoprosthesis with medullary stems- erosion of bone on pelvic side
  7. 7. Metal on metal Urist, Ring and McKee Farrar Friction metal wear High incidence of loosening and pain.
  8. 8. Sir John Charnley -Low friction torque arthroplasty -Surgical alteration of hip biomechanics -Lubrication -Material design -Operating room environment -PMMA
  9. 9. 1 st Charnley prosthesis Moore prosthesis stainless steel femoral component Thin polytetrafluroethylene shell for acetabulum
  10. 10. Tribology Surfaces interacting under an applied load and in relative motion Study of: -Friction -Lubrication -Wear
  11. 11. Wear Types of wear: 1. Adhesive wear 2.Abrasive wear 3. Third body wear 4.Fatigue wear
  12. 12. Adhesive wear Adhesion during contact of opposing bearing surfaces Sliding breaks these contacts Strength of adhesion exceeds strength of material Particles are pulled from the material
  13. 13. Abrasive wear Hard projection on one surface cuts into the opposing surface
  14. 14. Third body wear Hard particles such as bone or PMMA if trapped between bearing surfaces cause abrasive damage
  15. 15. Fatigue wear Repetitive loading of the bearings during articulation
  16. 16. Wear modes Conditions under which the prosthesis was functioning when the wear occurred
  17. 17. Mode 1 Motion of 2 primary bearing surfaces against each other
  18. 18. Mode 2 Primary bearing surface moving against a secondary surface that was not intended to come into contact with the first
  19. 19. Mode 3 Contaminant particles directly abrade one or both of the primary bearing surfaces Third body abrasion or wear
  20. 20. Mode 4 2 secondary surfaces rubbing together Backside wear
  21. 21. Wear debris causes osteolysis Compromise fixation Complicate revision procedure.
  22. 22. Wear threshold value  0.1 mm/year
  23. 23. Threshold is modified by -Intracapsular pressure -Bone interface access -Patient reaction to debris
  24. 24. Types of bearings Hard Soft
  25. 25. Femoral Head material Metallic alloys that can be used with UHMWPE liner: -Stainless steel 316L -Cobalt chromium alloy -Titanium alloys
  26. 26. Ceramics with UHMWPE Alumina Zirconia
  27. 27. Conventional UHMWPE Ram extrusion Compression molding
  28. 28. Sterilization Ethylene oxide Gas plasma Gamma radiation in air (2.5 to 4 mrad) Gamma radiation in inert atmosphere (nitrogen, argon or vacuum)
  29. 29. Gamma radiation Cross-linking of polyethylene molecules Interaction of free radicals formed during irradiation Improved wear resistance
  30. 30. Highly cross-linked UHMWPE Higher doses of radiation Heat
  31. 31. Remelting: Heating above the melting range of polyethylene Annealing: Heating below the melting range
  32. 32. UHMWPE- Semi crystalline polymer Mechanical behavior - crystalline morphology
  33. 33. Benefits of cross linked polyethylene -High wear resistance -No toxicity -Relatively low cost -Multiple liner options (elevated rim etc)
  34. 34. Risks of cross-linked polyethylene -Reduction in other material properties -gross material failure -Increased bioactivity of wear particles
  35. 35. Metal on metal bearings Muller and Weber Wear depends on: 1.Type of cobalt chromium alloy 2.Surface finish 3.Bearing clearance 4.Sphericity
  36. 36. Fluid film lubrication 1. Bearing size 2. Clearance 3. Sphericity 4. Surface finish
  37. 37. Benefits of Metal on metal  Very high wear resistance  Favors larger diameters (lowers wear)  Long in vivo experience
  38. 38. Risks of Metal on metal Increased ion levels Delayed type hypersensitivity Carcinogenesis
  39. 39. Ceramic on ceramic bearings Alumina: 1. Hardness 2.High wear resistance 3. Chemical inertness
  40. 40. Benefits of ceramic on ceramic Highest wear resistance No toxicity Long in vivo experience
  41. 41. Risks of ceramic on ceramic 1.Position sensitivity 2.Liner chipping 3.Fracture risk
  42. 42. Material properties CoC MoM MoHCLUH MWPE HardnessM Pa 2300 350 Low # reported no +remelted
  43. 43. Tribology CoC MoM HCLUHM WPE Wear 1 25 100 Particle size <0.02and >0.2 0.05 0.4 Metal ion Not increased increased Not increased
  44. 44. Biologic effectsCoC MoM MoHCLUH WPE Cell toxicity No Yes No Local tissue reaction Low Low Low Chromo. changes NR R NR Hypersensi tivity NR R NR Carcin. NR * NR
  45. 45. Coc MoM MoHCLUH MWPE Squeaking + + - Clicking + + - Seizing - + -
  46. 46. Future *IDEAL*
  47. 47. Next generation polyethylenes 1. Sequential irradiation and annealing 2. Irradiation and solid state deformation by extrusion below melting temperature 3. Vit E antioxidant containing polyethylene
  48. 48. Metal on metal Increase in femoral head size –greater sliding velocity and increased probability of fluid film lubrication – decrease in wear Reduced risk of impingement and dislocation 32 mm and bigger
  49. 49. Ceramic on metal Alumina head Cobalt chromium alloy cup Reduced wear rate 100 fold Clinical studies underway
  50. 50. Ceramics Alumina – Zirconia combination: for increasing toughness of alumina 75 % alumina 24 % Zirconia 1 % chromium oxide - Greater bending strength - Lower wear rate - Added manufacturing complexity - Cost
  51. 51. Take home message  There is no 100 % ideal bearing surface  Hard/hard and hard/soft  Tribology –friction, lubrication and wear  Wear causes osteolysis
  52. 52.  Modern bearings: - all have low wear  Young and active patients Hard/hard bearings will produce less wear debris but noise remains a problem
  53. 53.  For hard on hard bearings cup placement is important to reduce risk of impingement, excessive wear and fracture.  Metal on metal bearings release metal ions and corrosion products and probably should not be used for patients with impaired kidney function or women of child bearing age.