IMPLANTS IN ORTHOPAEDICS

1. IMPLANTS IN ORTHOPAEDICS DR ABHISHEK SHETTY

2. HISTORY The basic foundation • Lord Lister– aseptic surgery in 1860 • Morton & Simpson– ether & chloroform for anesthesia • Roentgen (1896)-- xrays

3. EVOLUTION Pre Lister era • Gold, Silver, iron, platinum and many others were used as implants • Pins wires, hooks books also used • Bell (1804) and Lavert (1829)– silver and platinum implants

4. Post Lister era/ antiseptic era • Lister himself was the first to wire a patella with silver wire. • Hansman– early exponent of plate and screws, used plated sheet steel • Sir Arbuthnot Lane placed plate and screw on firm footing by using high carbon steel/ stout steel

5. Von Bayer– pins for intraarticular small fragment fixation. • Hey Grooves(1893)– advocated rigid fixation of fractures • Sherman (1912) used vanadium • During the same time stainless steel was discovered with discovery of chromium!! Stainless steel era was thus launched!

6. 1959- Ferguson and Lang published their work “ metals and engineering in bone and joint surgery” type 316 steel was recognised.. 316L is now replacing 316

7. Advances in implant of fracture fixation • Smith Peterson 1937—triflanged nail • Mc laughlin and throton introduced extra plate to S-P nail. • 60 yrs ago kuntscher– intramedullary nailing • A.O/ ASIF group– 1950 in Europe by 18 surgeons.

8. IMPLANTS • DEFINITION As a substance made of living/non living material with a specified form which can be inserted into the body through skin/ mucus membrane to sub serve a specific function and to remain there for a significant duration.

9. Common qualities • Function without breaking, distorting or deteriorating. • Not produce deleterious effect on host • Easier to insert and remove.

10. Functions • Replace a diseased damaged or worn out part • Immobilize fractures or osteotomies • Aid in correction of deformities

11. IDEAL IMPLANT • Should be inert & non toxic to the body • Corrosion proof • Easily fabricated • Great strength & high resistance to fatigue • Should be inexpensive.

12. PHYSICAL PROPERTIES • Corrosion resistance • Fatigue resistance • Shape & dimensional compatibility • Interchange ability • Sterilization • Freedom from toxic effects • Freedom from surface defects • Marking and packing

13. Testing of implants CATEGORIES • Physical • Chemical • Structural • Biological

14. Physical • appearance • Weight • Magnetism • Hardness • Microstructure

15. CHEMICAL • Molybdenum detection test • Molybdenum percentage estimation • Corrosion test

16. STRUCTURAL CHARACTERISTICS • Design specifications • Mechanical stability

17. Implant design • Possible forces acting on implant & whether implant is strong enough to neutralize these forces. • Function for considerable time • Surgical convenience • Anatomical factors • Stress protection effect • Cost

18. Methods of checking profiles • Naked eye examination & magnification photography. • Profile magnification be done by using a profile projector or a slide projector • Industrial x-rays -slot foe screw driver -canal of canulated screw -structural defects

19. METALS IN ORTHOPAEDICS • METALLIC GROUPS • Stainless steel or iron based alloys • Cobalt based alloys • Titanium based alloys

20. Stainless steel first modern alloy system corrosion resistant contains carbon, molybdenum, chromium and nickel

21. Carbon increases strength but decreases corrosion resistance • Chromium increases passivity by forming stable chromium oxide • Molybdenum counters the action of chloride ions &organic acids in body fluids & thus increases passivity • Nickel keeps structure of steel stable

22. Commonly used types • AISI 316L—implant steel • AISI 440B—instrument steel

23. Advantages & disadvantages of stainless steel • Offers good mechanical strength • Possesses excellent ductility • Shows work hardening effects • Time-tested metal • It may show local corrosing & pitting corrosion

24. DRILLBIT STEEL • Extremely hard • Can be sharpened well • Not ductile & can easily break • Not corrosion resistant

25. COBALT-BASED ALLOY • Vitallium or F75--- commonly used cobalt-chromium alloy– contains 27 to 30 % chromium, 5 to 7 % molybdenum, cobalt making up remaining

26. Advantages & disadvantages • Are inert • Posses high modules of elasticity & high strength than steel • Difficult to machine • Quite expensive • Has low ductility & bind securely to bone

27. TITANIUM • PURE TITANIUM is soft hence not commonly used • However AO grp popularising pure titanium of good strength & ductility--LCDCP

28. Advantages & disadvantages • Less prone to fatigue • Outstanding corrosion resistance • Optimal amount of torque • Technologies are not well established

29. FUTURE • TRIP( transformation-induced plasticity) steels • Refractory metals—tungsten, tantalum and molybdenum • Nickel-titanium alloys memory metals (nitinol)

30. BIOCOMPATIBILTY OF IMPLANT • CORROSION– damage of material due to action of its environment 1-change in colour 2-formation of surface film 3-disintegration of material

31. Effects of corrosion • Tissue inflammation & necrosis • Weakening of implant

32. Corrosion process • Chemical • Electrochemical

33. CORROSION CLINICAL RELEVANCE • UNIFORM ATTACK • GALVANIC OR BIMETALLIC • PITTING CORROSION • FRETTING

34. To make use of corrosion resistant material for implant manufacturing • To use same material for parts of a multipart implant • To remove broken drill bit if any, esp if it is in contact with plate • To keep damage to implant minimum • Avoid instability of fixation

35. HOST RESPONSE • Fibrine & platelets • Leukocytes • Macrophages • Lymphocytes • Fibroblats • Bone minerals • FB giant cells

36. Modified • Macrophages may remain in vicinity of implants.. • Significant number of lymphocytes & plasma cells near the implant • Multinucleated giant cells • All implants surrounded by fibrous capsule

37. CLINICAL RELEVANCE • Chronic inflammation • Loosening • Sterile abscess • neoplasia

38. IMPLANT FAILURE • Every implant is subjected to various forces because of • Gravity • Muscle action • Wt bearing

39. Forces are • Tension • Compression • Bending • Shear • torsion

40. Implant –loading in tension—more force---deformation. • As force removed implant gets back to its original shape– elastic deformation • Force excess—implant does not get back to its original shape, there after even if force is decreased material continues to deform till implant fails-plastic deformation.

41. Deformation dependant on • Force applied • Original length • Original cross-sectional area

42. Deformation with respect to original length—strain • Force applied per unit area--stress

43. Stress Strain

45. Strength • Rigidity or ductility • Yield stress, max stress, ultimate stress • Ductile failure • Brittle failure • Fatigue failure • Creep • Stress concentration