Metals in orthopaedics

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Metals in orthopaedics

  1. 1. METALSMETALS ININ ORTHOPAEDICSORTHOPAEDICS
  2. 2. PROPERTIES HIGH ELASTIC MODULUS HIGH DUCTILITY CAN BE FABRICATED INTO VARIOUS SIZES AND SHAPES PROPERTIES CAN BE ALTERED BY PHYSICAL PROCESSES CAN FORM ALLOYS GOOD RESISTANCE TO EXTERNAL AND INTERNAL ENVIRONMENTS
  3. 3. MAJOR METALS USED 1.STAINLESS STEEL 2.COBALT BASED ALLOYS 3.TITANIUM BASED ALLOYS NEWER METALS 1.OXINIUM 2.TRABECULAR METAL 3.NITINOL-NICKEL TITANIUM ALLOYS
  4. 4. STAINLESS STEEL PLATES,SCREWS,PINS AND RODS CONTAINS CARBON,MOLYBDENUM,CHROMIUM AND NICKEL APART FROM IRON CARBON-INCRESES STRENGTH,DECREASES CORROSION RESISTANCE CHROMIUM-INCREASES PASSIVITY MOLYBDENUM-INCREASES PASSIVITY NICKEL-HELPS TO MAINTAIN AUSTANTIC STRUCTURE OF STEEL. COMMONLY USED TYPES OF STAINLESS STEEL ARE AISI 316 L,AISI 440 B.
  5. 5. ADVANTAGES AND DISADVANTAGES GOOD MECH STRENGTH HIGH DUCTILITY SHOWS WORK HARDENING EFFECTS MAY SOMETIMES SHOW LOCAL COROSSION AND PITTING CORROSION-LOCAL IRRITATION AND WEAKENING OF IMPLANT
  6. 6. COBALT-BASED ALLOYS MAINLY HIP AND KNEE PROSTHESES CORROSION RESISTANCE AND BIOCOMPATIBILITY-EXCELLENT FATIGUE RESISTANCE AND INCRESED TENSILE STRENGTH QUITE DIFFICULT TO MACHINE EXPENSIVE VITALLIUM IS THE MOST COMMONLY USED ALLOY
  7. 7. TITANIUM-BASED ALLOYS CONTAINS ALUMINIUM,VANADIUM ALONG WITH TITANIUM MOST FLEXIBLE AMONG THE METALS USED IN ORTHOPAEDICS LIGHT WEIGHT THAN OTHER METAL ALLOYS BIOCOMPATIBLE EXCELLENT CORROSION RESISTANCE[Ca-P LAYER AND SURFACE OXIDE LAYER MAKES IT INERT] PURE TITANIUM IS ALSO USED WHERE HIGH STRENGTH IS NOT REQUIRED
  8. 8. NEWER METALS OXINIUM • OXIDIZED ZIRCONIUM IS A METALLIC ALLOY WITH A CERAMIC SURFACE. • ZIRCONIUM: A BIOCOMPATIBLE METALLIC ELEMENT IN THE SAME FAMILY AS TITANIUM • COMBINES THE BEST OF BOTH METAL AND CERAMICS. • EXCELLENT FRACTURE TOUGHNESS LIKE COBALT CHROME. • CERAMIC SURFACE THAT OFFERS OUTSTANDING WEAR RESISTANCE
  9. 9. TRABECULAR METAL • ELEMENTAL TANTALUM METAL • VAPOR DEPOSITION TECHNIQUES THAT CREATE A METALLIC STRUT CONFIGURATION SIMILAR TO TRABECULAR BONE. • CRYSTALLINE MICROTEXTURE IS CONDUCTIVE TO DIRECT BONE APPOSITION. • INTERCONNECTING PORES – 80% POROUS – 2-3 TIMES GREATER BONE INGROWTH COMPARED TO CONVENTIONAL POROUS COATINGS
  10. 10. TRABECULAR METAL MATERIAL IS MADE FROM TANTALUM OVER CARBON. IT IS STRONG, FLEXIBLE, AND BIOCOMPATIBLE. THE STRUCTURE OF TRABECULAR METAL MATERIAL IS SIMILAR TO THE STRUCTURE OF BONE. IT IS VERY POROUS, WHICH MEANS IT HAS SMALL SPACES OR PORES. NEW TISSUE CAN GROW INTO THESE PORES AND HELP HOLD THE IMPLANT IN PLACE.
  11. 11. THE LATEST TECHNIQUE FOR PRODUCTION OF LESS STIFF TOTAL JOINT PROSTHESES IS THE TRABECULAR METAL TECHNOLOGY. A METALLIC SPONGE MADE FROM TUNGSTEN HAS ABOUT THE SAME STIFFNESS AS BONE. WHEN A LAYER OF THE METALLIC SPONGE IS PLACED ON THE SURFACE OF THE TOTAL HIP PROSTHESIS, IT WILL MAKE A SMOOTH TRANSITION FROM THE STIFF METAL TO THE WEAK BONE. THE SCIENTISTS HOPE THAT THIS TECHNOLOGY WILL DIMINISH THE STRESS SHIELDING EFFECT OF THE TOO STIFF TOTAL HIP AND KNEE PROSTHESES
  12. 12. IMPLANTS SUCCESS OF AN IPLANT IS DETERMINED BY 1.CONDITION OF THE PATIENT 2.SURGEON’S SKILL 3.BIOCOMPATIBILITY OF IMPLANT 4.MECHANICAL PROPERTIES 5.WEAR/CORROSION RESISTANCE
  13. 13. IDEAL METAL FOR IMPLANT • BIOCOMPATIBLE – NON-TOXIC, NON-CARCINOGENIC, NON-IMMUNOGENIC • STRENGTH – COMPRESSIVE, TENSILE, TORSIONAL • FATIGUE RESISTANCE, CONTOUR ABILITY • CORROSION AND DEGRADATION RESISTANCE • OSSEO INTEGRATION (WHEN APPLICABLE) • IMAGING COMPATIBLE – MRI, CT SCAN • INEXPENSIVE
  14. 14. PROBLEMS ENCOUNTERED IN METAL IMPLANTS
  15. 15. INFECTION IN PRESENCE OF AN IMPLANT EARLY INFECTIONS THROUGH SKIN,AIR OR SURGICAL INSTRUMENTATION INFECTION DOESN’T SUBSIDE BCOZ REVASCULARISATION BLOCKED BY IMPLANT LATE INFECTIONS HEMATOGENOUS IN ORIGIN BACTERIA PROTECTED BY GLYCOCALYX PRESENT ON THE COATING FORMED ON THE SURFACE OF THE FOREIGN MATERIAL
  16. 16. BIOCOMPATIBILITY BIOCOMPATIBILITY - ( MEANS WELL TOLERATED BY BODY'S TISSUES ) ALL MODERN ALLOYS ARE WELL TOLERATED BY BONE TISSUE - IN BULK FORM. THE BEST TOLERATED IS TITANIUM IN PURE FORM. FOR THIS EXTREME BIOCOMPATIBILITY, PURE TITANIUM IS OFTEN USED AS POROUS COATING FOR THE SURFACES OF TOTAL HIP PROSTHESES.  IN DUST FORM, AS WEAR PARTICLES, ALL THESE ALLOYS, EVEN A PURE TITANIUM, MAY, HOWEVER, TRIGGER OSTEOLYSIS IF THEY LAND IN THE TISSUES AROUND THE TOTAL HIP PROSTHESIS. METALLIC WEAR PARTICLES IN THE SOFT TISSUES PAINT THE TISSUES BLACK,
  17. 17. UNTOWARD HOST RESPONSE –CLINICAL MANIFESTATIONS C/C INFLAMMATION-METALLOSIS OSTEOLYSIS AND LOOSENING STERILE ABSCESS NEOPLASIA
  18. 18. METAL FAILURE BRITTLE FAILURE – SCREW HEAD WITH POOR DUCTILITY PLASTIC FAILURE – LOAD > ENDURANCE LIMIT. IMPLANT BENDS PERMANENTLY. FATIGUE FAILURE – CYCLICAL (REPETITIVE) LOADING.
  19. 19. FATIGUE FAILURE
  20. 20. FATIGUE FRACTURES THE EVERYDAY LIFE PUTS ASTOUNDING DEMANDS ON THE MATERIALS OF THE TOTAL HIP JOINT. THE SHAFT OF THE MODERN TOTAL HIP PROSTHESIS WILL SUSTAIN SUCH LARGE LOADS, IF THEY OCCUR OCCASIONALLY; THE SHAFT MAY FAIL, HOWEVER, EVEN FOR LOWER LOADS, IF THEY OCCUR VERY OFTEN. THE METAL ALLOY WILL SUCCUMB TO THE SO- CALLED FATIGUE FAILURE AND BREAK. THERE IS A LIMIT, HOW MUCH REPETITIVE LOADS  THE PROSTHESIS WILL EVENTUALLY SUSTAIN. THIS LIMIT IS SPECIFIC FOR EVERY FORM OF THE TOTAL HIP PROSTHESIS AND FOR THE METAL ALLOY USED FOR MANUFACTURE.  ABOVE THIS LIMIT, THE PROSTHETIC SHAFT WILL SUSTAIN THE FATIGUE FRACTURE
  21. 21. STRESS SHEILDING STRESS SHIELDING - A TOO STIFF SHAFT. THE PROSTHETIC SHAFT TAKES OFF A PART OF THE STRESS THAT WALKING AND OTHER EVERYDAY ACTIVITIES PUT ON THE UPPER PART OF THE THIGH BONE HOLDING THE PROSTHESIS. A TOO STIFF SHAFT OF A TOTAL HIP PROSTHESIS "STRESS SHIELDS" THE UPPER PART OF THE THIGH BONE TO MUCH. THIS IS SO BECAUSE THE ALLOYS USED FOR FABRICATION OF THE SHAFT ARE MUCH STIFFER THAN THE SKELETON OF THE THIGH BONE. THE SHIELDED BONE DOES NOT THRIVE, LOSES ITS SUBSTANCE, AND BECOMES WEAK. THE TOTAL HIP JOINT HAS WEAK ANCHORAGE IN A WEAK SKELETON AND MAY FAIL
  22. 22. CORROSION DAMAGE OF MATERIAL DUE TO ACTION OF THE ENVIRONMENT EFFECTS- TISSUE INFLAMMATION AND NECROSIS,WEAKENING OF IMPLANT CLINICALY RELEVANT FORMS OF CORROSION 1.UNIFORM ATTACK 2.GALVANIC OR BIMETALLIC 3.PITTING CORROSION 4.FRETTING
  23. 23. PRECAUTIONS 1.USE OF CORROSION RESISTANT MATERIAL 2.USE OF SAME MATERIAL FOR DIFF PARTS OF THE SAME IMPLANT 3.AVOID DAMAGES DURING TRANSPORTATION 4.AVOID INSTABILITY OF FIXATION
  24. 24. METAL TOXICITY • NICKEL – CYTOTOXIC AGENT & ALLERGEN • TITANIUM – INHIBIT OSTEOCLASTIC ACTIVITY AND REDUCE OSTEOBLASTIC PROTEIN SYNTHESIS (THOMPSON & PULEO 1996). – CONTACT DERMATITIS (LAYOR ET AL. 1991). • COBALT-CHROMIUM – METALLOSIS, OSTEOLYSIS, – FORMATION OF SOFT TISSUE MASSES, – INFLUENCE PROLIFERATION AND FUNCTION OF HUMAN OSTEOBLASTS
  25. 25. POLYETHYLENE POLYETHYLENE IS A TYPE OF PLASTIC COMMONLY USED ON THE SURFACE OF ONE IMPLANT THAT IS DESIGNED TO CONTACT ANOTHER IMPLANT, AS IN A JOINT REPLACEMENT  POLYETHYLENE IS VERY DURABLE WHEN IT COMES INTO CONTACT WITH OTHER MATERIALS.  WHEN A METAL IMPLANT MOVES ON A POLYETHYLENE SURFACE, AS IT DOES IN MOST JOINT REPLACEMENTS, THE CONTACT IS VERY SMOOTH AND THE AMOUNT OF WEAR IS
  26. 26. PATIENTS WHO ARE YOUNGER OR MORE ACTIVE MAY BENEFIT FROM POLYETHYLENE WITH EVEN MORE RESISTANCE TO WEAR. THIS CAN BE ACCOMPLISHED THROUGH A PROCESS CALLED CROSSLINKING, WHICH CREATES STRONGER BONDS BETWEEN THE ELEMENTS THAT MAKE UP THE POLYETHYLENE. THE APPROPRIATE AMOUNT OF CROSSLINKING DEPENDS ON THE TYPE OF IMPLANT. FOR EXAMPLE, THE SURFACE OF A HIP IMPLANT MAY REQUIRE A DIFFERENT DEGREE OF CROSSLINKING THAN THE SURFACE OF A KNEE IMPLANT.
  27. 27. CERAMICS • CERAMIC MATERIALS ARE USUALLY MADE BY PRESSING AND HEATING METAL OXIDES (TYPICALLY ALUMINUM OXIDE AND ZIRCONIUM OXIDE) UNTIL THEY BECOME VERY HARD. • THESE CERAMIC MATERIALS ARE STRONG, RESISTANT TO WEAR, AND BIOCOMPATIBLE. • THEY ARE USED MOSTLY TO MAKE IMPLANT SURFACES THAT RUB TOGETHER BUT DO NOT REQUIRE FLEXIBILITY, AS IN THE SURFACES OF A HIP JOINT.
  28. 28. COMPOSITE MATERIAL COMPOSITE MATERIALS ARE MADE BY MIXING TWO OR MORE SEPARATE MATERIALS WITHOUT CREATING A CHEMICAL BOND BETWEEN THE MATERIALS. METAL ALLOYS AND CERAMICS ARE NOT CONSIDERED TO BE COMPOSITE MATERIALS BECAUSE THEIR INGREDIENTS ARE CHEMICALLY BONDED TO CREATE A NEW MATERIAL.  ON A LARGER SCALE, TWO LAYERS OF DIFFERENT MATERIALS CAN BE COMBINED TO CREATE A COMPOSITE MATERIAL WITH THE DESIRED CHARACTERISTICS. THE STEM OF A HIP IMPLANT, FOR EXAMPLE, MAY CONSIST OF LAYERS OF TWO DIFFERENT
  29. 29. BIOABSORBABLE MATERIALS • BIOABSORBABLE MATERIALS ARE DESIGNED TO BE ABSORBED BY THE BODY WHEN THEIR JOB IS COMPLETE. • THEY ARE MADE FROM A BIOCOMPATIBLE PLASTIC THAT CAN BE DISSOLVED BY NORMAL BODY FLUIDS. • THESE BIOABSORBABLE MATERIALS MAY ALSO BE USED IN IMPLANTS THAT REATTACH SOFT TISSUE TO BONE.
  30. 30. TANTALUM TANTALUM IS A PURE METAL WITH EXCELLENT PHYSICAL AND BIOLOGICAL CHARACTERISTICS.  IT IS FLEXIBLE, CORROSION RESISTANT, AND BIOCOMPATIBLE. SILICONE SILICONE IS A RUBBERY MATERIAL THAT IS VERY FLEXIBLE. IN ORTHOPAEDICS, IT IS MOST COMMONLY USED IN IMPLANTS THAT REPLACE THE JOINTS OF THE TOES
  31. 31. THANK YOU

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