BIOMATERIALS ENT 311/4

1. BIOMATERIALSENT 311/4 Lecture 11 Orthopaedic Implant: Internal Fixation Prepared by: Nur Farahiyah Binti Mohammad Date: 15th September 2008 Email : farahiyah@unimap.edu.my

2. 1.0 Internal Fixation • Purpose: To stabilize fractured bone until natural healing processes have restored sufficient strength so that implant can be removed. • Material requirement: • Biocompatible • Sufficient strength • Corrosion resistance

3. 1.0 Internal Fixation • Material used: • Stainless steel • Co-Cr alloys • Titanium alloys • Biodegradable polymer • To treat minimally loaded fractures • Eliminate the need for second surgery

4. 1.0 Internal Fixation • Types: • Wires • Pins • Screw • Plates • Intramedullary nails

5. 1.0 Internal Fixation • WIRES • Used to reattach large fragments of bone • Useful especially for spiral breaks and reattaching greater trochanter of hip • Wires suffer from twisting and knotting • The deformed region of the wire are more prone to corrosion

6. 1.0 Internal Fixation • PINS • Used to hold fragments of bone together temporarily or permanently and to guide large screw insertion. • Have different tip design • Trocar tip – most efficient in cutting - often used for cortical bone • Diamond tip

7. 1.0 Internal Fixation • SCREWS • Two types of bone screws: • Cortical (Compact) bone screw-small treads • Cancellous screws –large tread to get more thread-to bone contact

8. 1.0 Internal Fixation • It can be used alone or along with other devices. • The general principle is that bone heals better if the fracture fragments are aligned and pressed closely together. • The idea is to stabilize the fracture and keep the bone in anatomic alignment.

9. 1.0 Internal Fixation

10. 1.0 Internal Fixation • Principle application of bone screw: • As interfragmentary fixation devices to lag or fasten bone fragment together. • To attach a metallic plate to bone

11. 1.0 Internal Fixation • PLATES • Plates come in several types, and are named for their function. • In general, there are: • Dynamic Compression plates • Neutralization plates • Buttress (support) plates.

12. 1.0 Internal Fixation • The dynamic compression plate is one of the most common types of plates, and can be recognized by its special oval screw holes. • These holes have a special beveled floor to them with an inclined surface. • If desired, this inclined surface can be used to pull the ends of the bone together as the screws are tightened.

13. 1.0 Internal Fixation • Compression plates are used for fractures that are stable in compression. • They may be used in combination with lag screws, and they may provide dynamic compression when used on the tension side of bone.

14. 1.0 Internal Fixation • Neutralization plates are designed to protect fracture surfaces from normal bending, rotation and axial loading forces. • They are often used in combination with lag screws.

15. Resorbable bone plate As the strength of the fracture site increase due to normal healing processes, the resorption of the implant begins to take place. 1.0 Internal Fixation

16. 1.0 Internal Fixation • Buttress plates are used to support bone that is unstable in compression or axial loading. • These plates are often used in the distal radius and tibial plateau to hold impacted and depressed fragments in position once they have been elevated.

17. Buttress plate bridging a humeral neck fracture -

18. 1.0 Internal Fixation 5. INTRAMEDULLARY NAILS

19. 1.0 Internal Fixation • Used as internal struts to stabilize long bone fracture. • Inserted into medullary cavity • Should have some spring to provide elastic force and prevent rotation. • IM nails are better than plates at resisting multi-directional bending • However, torsional resistance is less than plate

20. 1.0 Internal Fixation • When designing IM nails: • A high polar moment of inertia is desirable to improve torsional rigidity and strength • Problems: • Destroy intramedullary blood supply.

21. 1.0 Internal Fixation • Biomaterial applications in Internal Fixation

22. Failure modes of internal fixation devices

23. BIOMATERIALSENT 311/4 Lecture 11 (cont) Orthopaedic Implant: Joint replacement Prepared by: Nur Farahiyah Binti Mohammad Date: 18th September 2008 Email : farahiyah@unimap.edu.my

24. 1.0 Introduction • Total joint replacement • An arthritic or damaged joint is removed and replaced with an artificial joint called prosthesis. • Goal - to relieve the pain in the joint caused by the damage done to the cartilage.

25. 1.0 Introduction

26. Joint degradation • Also called Osteoarthritis. • Is the end stage of a process of destruction of the articular cartilage. • Results in: • Severe pain • Loss of motion • An angular deformity of the extremity • Cartilage unable to regenerate • So, when exposed to a severe mechanical, chemical or metabolic injury, the damage is permanent.

27. Joint degradation

28. Types of Total Joint Replacement (TJR)

29. Implant fixation method • Three type of methods of fixation: • Mechanical interlock • This fixation achieved by press-fitting the implant • by using PMMA bone cement • Bone cement • Bone cement is a substance commonly used to hold implants in bone and filling the space between the skeleton and the total joint device. • Often cement is used for hip replacement and knee replacement surgery. • Cement implies that the material sticks the implant into the bone

30. Implant fixation method • In reality, bone cement should really be called bone grout. • The reason is that this material actually acts as a space-filler, to create a tight space for the implants to be held against the bone. • Bone cement does not stick substances together, rather it fills the void between the implant and the surrounding bone.

31. Implant fixation method • On the X-ray pictures one sees the bone cement as a white layer around the   shadows of the total hip device.

32. Implant fixation method • The microscopic structure of bone cement is made by two substances glued together. • One substance are the small particles of pre-polymerized PMMA (PolyMethylMetaAcrylate), so called "pearls. • These pearls are supplied as a white powder. • The other substance is a liquid monomer of MMA(MethylMetacrylate). Both substances are mixed together at the operation table with added catalyst that starts the polymerization of the monomer fluid.

33. Honeycomb structure gives the bone cement the ability to absorb downward (compression) loads. An important characteristics in an otherwise brittle material. the bone cement act mechanically as an shock absorber (1) The unloaded phase: the bone cement net is regular, not deformed. ( 2) Load applied by body weight impact on the total hip (its femoral component):  the bone cement net within marrow cavity deforms elastically, but does not brake and stays in contact with both total hip and skeleton. ( 3 ) When the load ceases  the bone cement's structure returns to its original regular form.

34. Implant fixation method • Biological fixation • Which is achieved by using textured or porous surface, that allow bone to grow into the interstices. • Porous in growth fixation • Pore size range should be 100 to 350μm • Pores should be interconnected with each other with similar size of opening.

35. Implant fixation method • Direct chemical bonding between implant and bone • for example by coating the implant with calcium hydroxyapatite, which has mineral composition similar to bone. • Material used as coating such as Bioglass and glass ceramic.

36. Biomaterials for TJR

37. Comparison between Specific Orthopedic Implant Prosthetic Materials

38. Comparison between Specific Orthopedic Implant Prosthetic Materials

39. Total hip replacement • Hip joint is a ball and socket joint • Can be divided into 2 types: • Monolithic: Consist of one part, less expensive, less prone to corrosion • Modular: Consist of 2 or more parts , allow customizing of the implant during future revision surgery.

40. Total hip replacement • Design aspect • Prosthetic hip component are optimized to provide wide range of motion to prevent dislocation. • Must enable implants to support loads • Proper femoral neck length will decrease bending stress

41. Total hip replacement • If femoral stem is designed with sharp corner: bone in contact with sharp corner may necrose and resorb. • Replaceability: possible to remove one part without removing the other.

42. Component or Total Hip joint: Femoral component Stem –Neck Ball/head Acetabular component Cup Backing Insert Hip joint replacement Acetabular component neck Femoral component stem

43. Cortical bone Trabecular bone Bone cement Femoral stem 4 (a). Backing of acetabular cup Insert of acetabular cup Schematic representation

44. Materials used for each component of THR

45. Possible combination of THR

46. Total hip replacement • STEM • Titanium alloy • Advantages: • Excellent corrosion resistance • Highly reactive material • Lowest rate dissolution • Disadvantages: • Wear • Generation of fine wear particles: inflammation and implant loosening

47. Total hip replacement • HEAD • Alumina: elicit minimal response from host tissue • Advantages: • High Wear resistance • Reasonable fracture toughness • Extremely stable (undergo little physical/chemical deformation)

48. Total hip replacement • Disadvantages: • Degradation in-vivo:WEAR • Weakens the material • Change shape that may effect fuction • Produce biology active particles • Low creep resistance: can influence the behaviour of joint

49. Total hip replacement • CUP • UHMWPE • Advantages: • Tough inert • Disadvantages: • Wear debris cause inflammatory reaction

50. Most frequent problems • Infection • Wear • Migration and failure of implants • Loosening