Massachusetts Institute of Technology Harvard Medical School Brigham and Women s Hospital VA Boston Healthcare System 2.782J/3.961J/BEH.

Transcription

1 Massachusetts Institute of Technology Harvard Medical School Brigham and Women s Hospital VA Boston Healthcare System 2.782J/3.961J/BEH.451J/HST524J WEAR AND CORROSION M. Spector, Ph.D. WEAR PROCESSES Total Joint Replacement Prostheses Asperity Abrasive wear (THA and TKA) Component Adhesive wear particle transferred to metal (THA) Crack propagated by cyclic loading results in fatigue (delamination) wear (TKA) Page 1

2 WEAR PROCESSES TY Adhesive THA and TKA Abrasive (2-body) THA AND TKA Abrasive (3-body) THA AND TKA Fatigue/ Delamination TKA MECHANISM Chemical adhesion of to asperity on metal Plowing of metal asperity through PART. SIZE nm to mm mm Entrapment and plowing of mm particle ( bone, PMMA, coating) Propagation of subsurface mm m to mm cracks to the surface by cyclic compression, tension, shear Adhesive Wear Text removed due to copyright restrictions. Definition of adhesive wear. Page 2

3 Abrasive Wear Text removed due to copyright restrictions. Definition of abrasive wear. WEAR PROCESSES Asperity Abrasive, plowing wear (THA and TKA) Component Adhesive wear particle adherent to metal (THA and TKA) Crack propagated by cyclic loading results in fatigue (delamination) wear (TKA) Page 3

4 WEAR PROCESSES Asperity Abrasive wear (THA and TKA) Solutions are a scratch-resistant metal/ceramic counterface (and abrasion-resistant x-linked?) WEAR PROCESSES Adhesive wear Component Solution: X -linked appears to resist adhesive wear Page 4

5 WEAR PROCESSES Adhesive wear particle transferred to metal (THA) Component Problem relates to lubrication WEAR PROCESSES Component Cracks are due to oxidation and pre-existing fusion defects Page 5

6 γ-radiation-induced Oxidation Photos removed due to copyright restrictions. Fusion Defects Sutula, et al Radiation-induced induced x-linkingx WEAR PROCESSES Component Solution: do not sterilize with g-radiation in air and start with better consolidated Crack propagated by fatigue (delamination) wear Page 6

7 EFFECT OF GAMMA RADIATION ON : OXIDATION Diagram of crystallite structure removed due to copyright restrictions. GAMMA-RADIATION INDUCED MODIFICATION OF POLYETHYLENE Oxidation O Cross-linking C C C C C C C C Oxidation shortens chains and thus reduces strength. Cross-linking increases the size of the molecule and thus increase strength, but this reduces ability of the to elongatate ( reduces toughness). Page 7

8 WEAR PROCESSES What is missing from this picture? Abrasive Adhesive Fatigue (delamination) wear WEAR PROCESSES Joint Fluid* Abrasive Adhesive Fatigue (delamination) wear * What role does the joint fluid play in the wear of TKA? Page 8

9 COMPOSITION OF JOINT FLUID Joint Fluid z Two types of Lubrication: Fluid Film Boundary Layer Hyaluronic Acid Protein (Lubricin) Phospholipid TRIBOLOGY Lubrication Friction Wear What are the interrelationships? Does reduced friction correlate with reduced wear? How does lubrication affect friction and wear? Page 9

10 Lubrication WEAR IN TKR Tribology Depends on amount, composition and mechanical properties of joint fluid Friction Better the lubrication lower the friction Wear Lower the friction, less wear ROLE OF SYNOVIAL FLUID IN THE LUBRICATION OF ARTIFICIAL JOINTS How do the amount, composition and mechanical properties of synovial fluid affect the performance of total joint replacements? What is the mechanism of lubrication of artificial joints? If injection of hyaluronic acid helps the patient with osteoarthritis would it help the total joint replacement patient? Page 10

11 Image removed due to copyright restrictions. Diagram explaining coefficient of friction in artifical ball/socket joint. Example Coefficients of Friction Cartilage - Cartilage: (dry): (saline): UHMW (serum): Cartilage Image removed due to copyright restrictions. Cartilage-lined knee joint. Bone Figure by MIT OCW. Mechanism of lubrication? Page 11

12 Several Mechanisms of Lubrication in the Joint Boundary layer lubrication at the surface. Fluid -film (hydrodynamic) lubrication in regions where surfaces are separated - also elastohydrodynamic and weeping lubrication. Articular Surface Lubricating Proteins or Phospholipids Articular Surface Boundary Layer Lubrication of Articular Cartilage The load is supported by a monolayer of the lubricating molecules adsorbed to the surface of the cartilage. Page 12

13 LUBRICATION OF NATURAL AND ARTIFICIAL JOINTS Lubrication Mechanisms Hydrodynamic Elastohydrodynamic Weeping Boundary Layer Natural Artificial yes yes (?) yes yes no no yes yes (?) LUBRICATION OF THE NATURAL AND ARTIFICIAL JOINT Composition Amount of fluid Rate of turnover Mechanical properties Page 13

14 ROLE OF SYNOVIAL FLUID IN THE LUBRICATION OF NATURAL JOINTS Composition of Synovial Fluid Constituent Role Hyaluronic Acid Provides viscosity-lubricity; (GAG) viscoelastic damping of loads; hydrodynamic lubrication Phospholipid Adsorbs to the surface for (Lipid) boundary layer lubrication Lubricin Adsorbs to the surface and binds (Protein) phospholipid for boundary layer lubrication COMPOSITION OF JOINT FLUID Joint Fluid z Hyaluronic Acid Protein Phospholipid The amount and composition and properties of joint fluid in TKA patients vary widely; this could explain why some pts. have high wear. Solution; with lower friction even in presence of abnormal joint fluid. Page 14

15 WEAR PROCESSES Fluid Film Lubrication Joint Fluid z Fluid Film Lubrication; surfaces separate no friction and no wear; due to viscosity of fluid (HA conc. and MW), topography of counterfaces, and velocity: TKA? Hyaluronic Acid, HA WEAR PROCESSES Fluid Film Lubrication Joint Fluid z Fluid Film Lubrication; determine the patient s fluid viscosity (HA conc. and MW); benefit of HA injection? Hyaluronic Acid, HA Page 15

16 10 May experience fluid film lubrication 1 h [Pa s] 0.1 VISCOSITY OF JOINT FLUID IN PATIENTS AT PRIMARY AND REVISION TKA Viscous Mid-Range Inviscid Shear Stress [Pa] After TKA, there is a decrease in viscosity; this may affect D. Mazzucco, et al., the lubrication of TKA. J. Orthop. Res. 2002;20:1157 VISCOSITY OF JOINT FLUID IN PATIENTS AT PRIMARY AND REVISION TKA 10 May experience fluid film Viscous Supartz lubrication 1 h [Pa s] 0.1 Mid-Range Inviscid Shear Stress [Pa] Is there a value in viscosupplementation D. Mazzucco, et al., in the TKA patient? J. Orthop. Res. 2002;20:1157 Page 16

17 WEAR PROCESSES Boundary Layer Lubrication Joint Fluid z Boundary Layer Lubrication; protein and lipid adsorb to the surfaces to decrease friction and reduce adhesive wear; can contribute to reducing abrasive and fatigue wear Protein Lipid WEAR PROCESSES Boundary Layer Lubrication Joint Fluid z Boundary Layer Lubrication; Determine the protein and lipid content of the joint fluid; employ a metal counterface that will best adsorb the lipid and protein; Oxinium Protein Lipid Page 17

18 LUBRICATION OF THE NATURAL AND ARTIFICIAL JOINT Composition Amount of fluid Rate of turnover Mechanical properties Wear testing of a total knee replacement prosthesis in a knee simulator. Photos removed due to copyright restrictions. Page 18

19 ROLE OF SYNOVIAL FLUID IN THE LUBRICATION OF ARTIFICIAL JOINTS How do the amount, composition and mechanical properties of synovial fluid affect the performance of total joint replacements? What is the mechanism of lubrication of artificial joints? Does injection of hyaluronic acid help the patient with osteoarthritis,, and if so, would it help the total joint replacement patient? HA INJECTION FOR THE TREATMENT OF OSTEOARTHRITIS Does not reverse the degenerative changes of OA. Cannot yet determine if it slows progression. Has an analgesic effect that mimics NSAIDs and steroid injection placebo effect? Affects lubricity of the joint? Page 19

20 HYALURONIC ACID (provides the viscosity in synovial fluid*) A long chain polymer with a molecular weight between 10 6 and 10 7 produced by synovial cells. At low molecular weight (< 10 6 ) and concentration (< 1 mg/ml), HA molecules form random coils, and do not interlock with each other (lower viscosity). At higher molecular weight and concentration, HA chains interlock to form an entanglement network that has a high viscosity. *May require interaction with proteins in joint fluid. HA INJECTIONS FOR THE TREATMENT OF OSTEOARTHRITIS The half-life life of HA in the joint is less than 24 hours. The lasting effect of an HA injection may be related to its stimulation of the endogenous production of HA by the synovium. How does the synovial membrane in the TJA patients compare with that in the OA patient? Page 20

21 No difference between HA and placebo (saline) with respect to pain relief in OA pts. Graph removed due to copyright restrictions. L.S. Lohmander, et al., Ann. Rheum. Dis., 55:424 (1996) CORROSION Contributes to degradation of mechanical properties of implants Releases metal ions that can elicit an adverse biological response Page 21

22 Several slides removed due to copyright restrictions. - Diagram of concentration cell - Anodic and Cathodic reactions - Table of electrochemical series of metals with normal electrochemical potentials - How oxygen-depleted crevices foster corrosion Page 22