Biomechanics of Implant Systems Flashcards
what is strain?
change in length relative to initial length
how much strain can an early/soft callous handle?
100% of strain
how much strain can a cartilage/hard callous handle?
10-30% of strain
does a large gap or small gap have high strain?
small gap typically has higher strain
what does an intramedullary pin neutralize?
bending forces
can you use cerclage wire alone in a fracture?
no
what does a tension band wire do?
converts distractive forces to compression
how is an interlocking nail positioned?
in the neutral axis of the bone
what is a bridging application of a plate like?
bone not reconstructed
plate functions to secure major bone fragments
plate carries entire load
what is the formula for strain?
strain= change in length/original length
how much strain does lamellar bone (remodeling) tolerate?
2% strain
what is the primary reason for fixation failure with an intramedullary pin?
rotational instability
what do multiple wires neutralize?
shear
compression
rotation
what do wires not neutralize?
bending forces
what can you use skewer pins for?
to reconstruct multiple piece fractures
where are tension-band wires usually placed?
greater trochanter
olecranon
tuber calcis
tibial tuberosity
what do the screws in an interlocking nail prevent?
collapse and rotation
how many pins do you need on each bone fragment with an external fixator?
at least 2
what are the factors that affect the strength of an external skeletal fixator?
frame design
connecting bar
pin number, length, and diameter
what should the fixation pin diameter be?
25-30% of bone diameter
what is the most common hardware used?
intramedullary pin
what does a single wire help with?
shear
is a single wire sufficient to neutralize compression or rotation?
no
does an interlocking nail neutralize all of the forces?
yes
what factors affect the strength of an external skeletal fixator?
frame design
connecting bar
pin number, length, and diameter
