Unit 1 Flashcards
What are the 5 key values of an implant?
be tolerated in the human body with no short term and little long term risk of adverse effects
relieve pain and enable sufficient mobility for AoDL
Function without failure until it is no longer required (variable)
Designed for insertion such that a predictable outcome can be achieved by a competent surgeon
Be of acceptable cost to provide and insert (inc. hospital stay)
What 5 key things are required by an implant?
biocompatibility adequate strength cost effective manufacture practicability of insertion safety for the surgeon and the patient
Why is metal-metal contact not used in joint surfaces?
unsatisfactory bearing surface
What material is used instead of two metal-metal components in a joint replacement?
polyethylene
What metals are commonly used in implants?
titanium
cobalt-chrome
stainless steel
What important material has the same stiffness as cancellous bone?
polyethylene
Describe the range of orthopaedic materials used
limited
What does anisotropic mean?
different mechanical properties in different directions
Which important biological material is anisotropic?
bone
What is a composite structure?
A structure made from more than one material so as to enhance its properties
What is the main problem in orthopaedic implants?
infection
Why is infection so important in orthopaedics?
Bacteria adhere to cement and metal surfaces and cause devastating infection - the immune system is depleted in the presence of an implant
What are the two main structural concerns in implant design?
stability and strength
What is more expensive - a hip or knee implant?
knee
What are the 3 main performance categories under which an implant is looked at?
structural
kinematic
biocompatibility
What structural factors are a concern?
strength stiffness lubrication wear fatigue
What kinematic factor is important?
motion
What factors come under biocompatibility?
biological integration
functional integration
Why is motion important?
the range of motion must be sufficient to enable daily living functions
Why are biological and functional integration important?
harmful reactions of implant materials should not exceed accepted safe levels.
the implant should perform such that is does not adversely affect other parts of the body
What kind of structure is formed when an implant is attached to bone?
composite
Why are bones wider at the ends?
to accommodate the joints
Why is the end of the bone made from a greater proportion of cancellous bone?
it is more porous and less stiff than cortical bone giving desirable shock absorbing properties
What patterns are present in the cancellous bone?
trabecular align along the directions of greatest stress
What is the region directly beneath the articular surface made from?
more cortical - must provide a rigid underlying surface for the joint to bear on without causing excessive deformation
What are the shafts of bone made from?
mainly cortical bone - much more rigid so that it can resist deformation under bending and torsional loads
What word describes the mechanical properties of a non-biological structural material?
isotropic
what does isotropic mean?
mechanical properties are the same no matter what direction they are loaded
Rank the loading types in which bone is strongest in order
compression
tension
shear
Is diaphyseal cortical bones stronger than metaphyseal cortical bone?
yes - double
The stiffness of bone changes according to the rate it is loaded - what is thus property called?
viscoelastic
Why is cancellous bone difficult to replicate?
its mesh-like structure is difficult to recreate and in practice doesn’t provide a good enough bonding surface
What is it called where an implant takes some of the load of bone?
stress shielding
What can happen as a result of stress shielding in permanent implants?
loosening and failure
What is Wolff’s law?
bone is laid down where it is needed and resorbed here it is not
