Fracture Mechanics and Classification Flashcards
what are the 2 (broad) types of fracture healing?
direct and indirect
what are the components of bone?
periosteum: membrane
cortical: hard bone
trabecular bone: spongy
articular cartilage at ends
what does the periosteum do?
very vascularized, separates cortical bone from trabecular bone (spongy inside )
what are osteons?
columns of compact bone, made up of vessels and lamellae/canaliculi
osteons contain osteoblasts and osteoclasts
where is the cancellous/trabecular bone? what is it made up of?
interior of bone
- osteblasts covered in endosteum in an irregular pattern
- mixture of bone marrow and hematopoietic stem cells
what do osteocytes do?
maintain bone tissue- these are osteoblasts that become encased in the bone matrix
what are osteogenic cells?
bone stem cells
what do osteoblasts do?
form bone matrix: makes osteoid = bone
what are osteoclasts?
responsible for bone remodeling
T/F: bone is constantly being remodeled
true- eventually will be no sign that something is damaged. constantly being metabolized
what determines the type of healing a bone will undergo after being fractured?
fracture gap width and stablity
is intramembranous ossification direct or indirect healing?
direct
you see a patient for a radius and ulna fracture. the radius gets a plate applied to it and the ulna doesn’t. on post-op radiographs you notice that they healed in different ways. what are these 2 ways of healing?
- direct: “intramembranous ossification”
- indirect: “endocondral ossification”
is endochondral ossification direct or indirect healing?
indirect healing
you have dog with an original fracture width of 2cm. the change in gap width under load is 0.5cm. what is the fracture gap strain?
strain = 0.5/2 (change / original)
what tissues tolerate strain well?
hematoma and granulation tissue: up to 100%
what is fracture gap strain?
change in gap width / original gap width
what tissues don’t tolerate strain well?
fibrous connective tissue and fibrocartilagee: 10-20% strain
you do post-healing radiographs of a tibial fracture 2 weeks after surgery. you notice that the fracture gap has gotten larger. your coworker panics. what do you tell them?
this is natural- the fracture gap gets bigger as healing goes on from osteoclasts coming in and resorbing bone as strain increases
what tissues tolerate strain the least?
lamellar bone! <2% strain
T/F: fibrocartilage tolerates strain the most
false
fibrocartilage & fibrous CT tolerates strain 10-20%
hematoma and granulation tissue: up to 100%
as a fracture starts to heal, is the fracture gap getting bigger or smaller?
bigger! osteoclasts come in when the strain is too high and resorbs the ends of fracture = decreasing strain, widens gap, and decreases the strain
what factor increases stability of a fracture?
bone callus diameter: the wider it is, the more it reduces strain and thus increases stability
what is the stabilizing influence factor?
radius to the 4th power = r^4
what is endochondrial ossification?
indirect/secondary ossification
hematoma and fibrocartilage come in and form a callus: these tissues don’t mind high strain and create a wide growth around bone to help stabilize. this actually allows the bony callus formation and bone remodeling
when does intramembranous ossification occur?
this is direct/primary bone healing
happens when there is a small fracture gap + small strain, the cutter cones can do the work themselves in the bone
describe the process of primary/direct bone healing
aka intramembranous ossification
there is a small fracture gap and small strain, stable fracture, so the cutter cones led by osteoclasts go through and go across the fracture chewing up the dead zone. they are followed by osteoblasts spitting out osteoid to make new bone, and leave behind osteocytes: new osteons to bridge the entire fracture gap
how quick does direct/primary bone healing occur
slower than secondary; takes months
how quick does indirect/secondary bone healing?
weeks to months
what is faster, primary or secondary bone healing
secondary: weeks to months
increased rigidity reduces strain at the fracture to promote direct bone healing. why is this not always advantageous?
can be slower, and places increased load on the implants that are stablizing the fracture over time
decreasing rigidity can stimulate indirect bone healing. indirect bone healing is faster, but why is this not always advantagous
too much movement from the decreased rigidity can impair healing and result in implant failure
what is the “idea” fixation rigidity?
a balance between the biology/variability and the mechanics/stability of the bone
anytime you take a rad of bone, what should be included with the bone?
an object of KNOWN SIZE as CLOSE TO and at SAME HEIGHT as targeted bone: can be spheres, coin on play-dough, etc
purpose: calibrating radiographs: size is affected by distance from radiographic beam = the xray is never flat on the table right at the center of the beam
what is the purpose of placing an object by the fracture on a radiograph?
gives true dimensional idea:
- how much room do we have on each side of the fracture
- where is the joint/ how far away
- implant sizing
when radiographing a broken bone, what additional image do you want to get? why?
radiograph of the opposite intact bone as a reference! can see what it’s supposed to look like, what length, etc
what is the #1 reason why CSU repeats radiographs?
they aren’t calibrated! why it’s really nice to do them yourself in house before sending them to CSU so the owner doesn’t have to pay for repeat radiographs
what are the possibilities for the cause of the fracture?
- traumatic
- pathologic: bone already weakened (ex osteosarcoma)
when is a fracture classified as open?
when the soft tissue envelope has been breached
what is a grade 2 open fracture?
significant soft tissue damage, penetration from outside
what is a grade 1 open fracture?
minimal soft tissue damage “inside out”
what is a grade 3 open fracture classification?
severe soft tissue and vascular damage, with bone loss and continued exposure
healing is proportional to what supply?
blood supply: ex: GI (fast, very vascular) compared to ligament (very low healing potential)
bone in between these 2
what is a complete vs incomplete fracture?
complete: all the way through the bone
incomplete: partially through the bone
what are the simple fracture configurations?
- transverse: straight across
- oblique: diagonal: long and short
- segmental: column of intact bone in middle
- reconstructable: could piece fracture back together as if bone were not broken
- load sharing
what is a greenstick fracture?
partial fracture/incomplete: like taking a little green sapling and trying to snap it
see these in young animals because their bones are more mineral/collagen dense
what is reconstruction?
piecing fracture back together as if it weren’t broken so the pieces could load share
if the length of the fracture is more than 2x the width of the bone at that location, what is it classified as?
long oblique
what are comminuted fracture configurations?
- majority non-reconstructable: biologic bridging approach = use something rigid enough to hold onto ends of bone until fracture healed
- reconstructable: rare, mechanical load-sharing approach
what are comminuted fractures?
multiple fracture lines all communicating with each other
how do we describe the level of the fracture?
proximal, middle, distal
how do we describe the region of the fracture?
diaphysis: middle of bone
metaphysis: towards end of bone
epiphyseal: very end of bone
articular: involving joint
physeal: salter-harris: involving a growth plate
how do we describe fracture displacment?
displacement of DISTAL segment in relation to the rest of the body
what view do you need to determine if a fracture is cranially or caudally displaced?
lateral
what view do you need to determine if a fracture is medially or laterally displaced?
AP (anterior-posterior) = front of body to back of body
what are the 4 forces applied on fractures?
- bending
- axial compression: top to bottom (taking step) if oblique fracture = shearing force
- torsion: twisting
- tension: pulling (usually bc of muscle applying tensile force)
what is your basic 10 word description of a fracture?
- cause: pathologic vs traumatic
- soft tissue damage: open vs closed, grade 1-3
- fracture configuration: incomplete/complete, simple, comminuted, recon/non recon
- location: bone, level, region
- displacement
- forces
