ch8_wear

ch8_wear - Massachusetts Institute of Technology Harvard...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Massachusetts Institute of Technology Harvard Medical School Brigham and Women’s Hospital VA Boston Healthcare System 2.782J/3.961J/BEH.451J/HST524J 2.782J/3.961J/BEH.451J/HST524J WEAR AND CORROSION M. Spector, Ph.D. WEAR PROCESSES Total Joint Replacement Prostheses Asperity Metal Abrasive wear (THA and TKA) Adhesive wear particle transferred to metal (THA) PE Component Crack propagated by cyclic loading results in fatigue (delamination) wear (TKA) Page 1 WEAR PROCESSES WEAR TYPE Adhesive THA and TKA Abrasive (2-body) (2THA AND TKA Abrasive (3-body) (3THA AND TKA Fatigue/ Delamination TKA MECHANISM PART. SIZE Chemical adhesion of PE nm to m m to asperity on metal Plowing of metal asperity mm through PE Entrapment and plowing of mm particle ( bone, PMMA, coating) Propagation of subsurface m 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 Abrasive Wear Text removed due to copyright restrictions. Definition of abrasive wear. WEAR PROCESSES WEAR Asperity Metal Abrasive, plowing wear (THA and TKA) Adhesive wear particle adherent to metal (THA and TKA) PE Component Crack propagated by cyclic loading results in fatigue (delamination) wear (TKA) Page 3 WEAR PROCESSES Asperity Metal Abrasive wear (THA and TKA) PE Solutions are a scratch-resistant metal/ceramic counterface (and abrasion-resistant PE – x-linked PE?) WEAR PROCESSES WEAR Metal Adhesive wear PE Component Solution: X-linked PE appears to resist adhesive wear Page 4 WEAR PROCESSES WEAR Metal PE Component Adhesive wear particle transferred to metal (THA) Problem relates to lubrication WEAR PROCESSES WEAR Metal PE Component Cracks are due to oxidation and pre-existing fusion defects Page 5 γ-Radiation-Induced Oxidation Photos removed due to copyright restrictions. Fusion Defects Sutula, et al Sutula, et Radiation-induced x-linking Radiationx- WEAR PROCESSES WEAR Metal Solution: do not sterilize with g -radiation in air and start with better consolidated PE PE Component Crack propagated by fatigue (delamination) wear Page 6 EFFECT OF GAMMA RADIATION ON PE: OXIDATION Diagram of PE crystallite structure removed due to copyright restrictions. GAMMA-RADIATION INDUCED GAMMA MODIFICATION OF POLYETHYLENE Cross-linking Oxidation O C C C C C C C C Oxidation shortens PE chains Cross-linking increases the size of Crossand thus reduces strength. the molecule and thus increase strength, but this reduces ability of the PE to elongatate ( reduces toughness). Page 7 WEAR PROCESSES WEAR What is missing from this picture? Metal Adhesive Abrasive PE Fatigue (delamination) wear WEAR PROCESSES Joint Fluid* Metal Adhesive Abrasive PE Fatigue (delamination) wear * What role does the joint fluid play in the wear of TKA? Page 8 COMPOSITION OF JOINT FLUID COMPOSITION Joint Fluid Metal z PE Hyaluronic Acid Protein (Lubricin) Phospholipid Two types of Lubrication: Two •Fluid Film •Boundary Layer TRIBOLOGY Lubrication Friction Wear What are the interrelationships? Does reduced friction correlate with reduced wear? How does lubrication affect friction and wear? Page 9 WEAR IN TKR WEAR Tribology • Lubrication – 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 Image removed due to copyright restrictions. Diagram explaining coefficient of friction in artifical ball/socket joint. Example Coefficients of Friction Cartilage - Cartilage: 0.002 - 0.004 Metal - Metal (dry): 0.4 Metal - Metal (saline): 0.15-0.35 Metal - UHMWPE (serum): 0.05-0.15 Cartilage Image removed due to copyright restrictions. Cartilage-lined knee joint. Bone Figure by MIT OCW. Mechanism of lubrication? Page 11 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 LUBRICATION OF NATURAL AND LUBRICATION ARTIFICIAL JOINTS • • • • Lubrication Mechanisms Natural Artificial Hydrodynamic yes yes (?) Elastohydrodynamic yes no Weeping yes no Boundary Layer yes yes (?) LUBRICATION OF THE NATURAL AND ARTIFICIAL JOINT • • • • Composition Amount of fluid Rate of turnover Mechanical properties Page 13 ROLE OF SYNOVIAL FLUID IN THE LUBRICATION OF NATURAL JOINTS Composition of Synovial Fluid Constituent Role Hyaluronic Acid Provides viscosity-lubricity; viscosity(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 COMPOSITION Joint Fluid Metal z PE 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; Metal with lower friction even in presence of abnormal joint fluid. Page 14 WEAR PROCESSES WEAR Fluid Film Lubrication Joint Fluid Metal 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? PE Hyaluronic Acid, HA WEAR PROCESSES WEAR Fluid Film Lubrication Joint Fluid Metal z Fluid Film Lubrication; ; determine the patient’s fluid viscosity (HA conc. and MW); benefit of HA injection? Page 15 PE Hyaluronic Acid, HA h [Pa s] 10 May experience fluid film lubrication VISCOSITY OF JOINT FLUID IN PATIENTS AT PRIMARY AND REVISION TKA Viscous 1 Mid-Range 0.1 Inviscid 0.01 0.1 1 After TKA, there is a decrease in viscosity; this may affect the lubrication of TKA. h [Pa s] 10 May experience fluid film lubrication 10 Shear Stress [Pa] D. Mazzucco, et al., J. Orthop. Res. 2002;20:1157 VISCOSITY OF JOINT FLUID IN PATIENTS AT PRIMARY AND REVISION TKA Viscous Supartz 1 Mid-Range 0.1 Inviscid 0.01 0.1 Is there a value in viscosupplementation in the TKA patient? 1 10 Shear Stress [Pa] D. Mazzucco, et al., J. Orthop. Res. 2002;20:1157 Page 16 WEAR PROCESSES Boundary Layer Lubrication Joint Fluid Metal z PE 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 Metal z PE 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 Page 17 Protein Lipid LUBRICATION OF THE NATURAL LUBRICATION 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 ROLE OF SYNOVIAL FLUID IN THE ROLE 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 osteoarthritis, 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 HYALURONIC ACID HYALURONIC (provides the viscosity in synovial fluid*) • A long chain polymer with a molecular weight between 106 and 107 produced by synovial cells. • At low molecular weight (< 106) 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 of HA in the joint is less than 24 halfhours. • 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 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 CORROSION • Contributes to degradation of mechanical properties of implants • Releases metal ions that can elicit an adverse biological response Page 21 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 ...
View Full Document

Ask a homework question - tutors are online