bone implants Flashcards
why do we use bone implants
ensure proper healing
-stability
- induce stress
what are implications of improper bone healing
length (muscles and ligaments affected)
orientation (joint contact forces)
decreased ROM
greater stiffness = …
less relative motion
more relative motion = …
more callus formation
design considerations for screws
threads/ surface finish, tip, strength, biocompatibility, pullout strength
what is done to ensure primary healing and proper load bearing on bone?
bone is preloaded
why is titanium a good material
good weight-strength ratio and low E
not good for wear resistance
why is stainless steel alloy a good material
strength, ductility but lower performance for corrosion resistance
fracture fixation system must
maintain geometric alignment
withstand compressive forces with min motion
avoid tensile/shear forces across fracture site
cortical screw
fine threads
designed to anchor in compact bone
cancellous screw
coarser threads
designed to anchor in the softer spongy bone
inner diameter is small
cannulated screw
used for passing a guide wire through it for accurate screw placement
external fixator
used in case of polytrauma
- low axial stiffness
-pintract infection
-secondary healing
rigidity of external fixator….
increases with pin diameter
increases w pin #
decreases w bone rod distance
increases w pin group separation
compression plate
accurate reduction
interfragmentary compression
secure permanent contact between fragment
primary healing with no external callus formed
stress shielding
may fail from fatigue
