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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
17. 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
18. 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,
22. 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
23. 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
24. 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
25. 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
26. 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
27. 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
28. 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.
29. 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.
30. 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
31. 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.
32. 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
