Unit 1 - Orthopaedic Implant Mechanics & Materials Flashcards
List the criteria for a successful orthopaedic implant?
- Be tolerated by the human body
- Relieve pain and enable sufficient mobility
- Function without failure
- Implanted successfully by a surgeon of average
ability - Acceptable cost
What are the main structural requirements for an implant?
Strength and stability
What structural factors must be considered in the design of all orthopaedic implants?
- Strength
- Stiffness
- Lubrication
- Wear
- Fatigue
What kinetic factor must be considered in the design of all orthopaedic implants?
Motion
What are the important requirements of an orthopaedic implant that are essential for biocompatibility?
- Biological Integration
2. Functional Integration
Most orthopaedic implants are attached to bone and form what?
A composite structure with bone
What are the 2 types of bone?
Compact (cortical) and cancellous bone
The stiffness property of a material is defined by what?
Its Young’s modulus
Young’s modulus is a ratio of what?
Stress to stain
What does isotropic mean?
Mechanical properties are the same no matter what direction they are loaded
What does anisotropic mean?
Young’s modulus depends on the direction in which it is being loaded
What is stress shielding?
Reduction in the load that would normally be taken by a bone. This occurs because some of the load is taken by an implant. Bone resorbs when understressed and this can lead to loosening of the implant.
Structural stiffness is determined by what?
- Material stiffness
2. Geometrical stiffness
What is the formula for shear modulus?
G = shear stress/shear strain
What is the formula for stiffness?
S=Force/stress or S=E x A/L
What are the geometrical factors that affect the axial stiffness of a structural component?
- Cross sectional area
2. Length
What is the formula for axial rigidity?
R=EA
What is the formula for bending rigidity?
R=EI
What is the formula for torsional rigidity?
R=GJ
What are the 2 main methods of biological fixation?
- Porous beads
2. Ceramic coatings
What are the 3 important features required of an orthopaedic implant material ?
- High degree of biocompatibility
- Suitable structural properties
- Ease of manufacture
Name 3 types of corrosion?
- Galvanic corrosion
- Fretting corrosion
- Crevice corrosion
Name 2 methods for improving corrosion resistance?
- Nitric acid immersion
2. Titanium nitride coating
Name 7 adverse effects implanted materials can have on the body?
- Growth of a fibrous layer between the bone and the implant
- Local infection
- Body sensitisation to metals
- Tissue inflammation in regions of implant corrosion
- Tissue necrosis in the region of bone cement
- Immunological reaction to wear particles
- Tumours occurring near sites of long term implants
Which metal implant materials are thought to have the best corrosion resistance?
Titanium and its alloys
