Written Exam - Fracture Fixation Methods Part 1 Flashcards
what is this instrument?
kern bone holding forceps
what is this instrument?
self-retaining retractors - gelpi retractors
what is this instrument?
soft tissue elevators
what instrument is this?
jacob’s chuck & key
regardless of method used, what is always necessary when using pins & bones?
must always use bone holding forceps to drive the pin into the bone & use a clamp as a brace to drive against
what is the desired drill settings for orthopedic surgeries?
high torque & low speed - decreases friction, won’t necrose the bone, & won’t cause complications at the bone/pin interface
what is a direct method in fracture fixation?
precise reconstruction of bone column - using IM pins & full cerclage wires
what is an indirect method in fracture fixation?
precise reconstruction isn’t desired or possible - external skeletal fixation
what types of fractures are suitable for cerclage wire & IM pin placement?
two piece long oblique fractures or spiral fractures
how many twists should remain after cutting the cerclage wire?
at least 2
how do you determine how many wires should be placed & how do you determine how tight the wires should be?
length of the fracture line - at least twice the bone diameter & spaced 2 bone diameters apart
use a periosteal elevator to try & shift the wires up & down the bone - if they shift, retighten them (if indicated)
how does a surgeon determine the length of an IM pin after it has been applied in the medullary canal?
use another pin that is the same size to determine the length
when is it appropriate to use a single IM pin as a sole means of fracture fixation?
never
how does a surgeon decide when to apply an IM pin in normograde or retrograde fashion?
fracture location & desired position for pin in the bone that is fractured
how does a surgeon decide on the size & length of an IM pin?
based on the size of the medullary cavity of the bone that is fractured & location/length of the fracture within the bone
if the surgeon was presented with a long oblique fracture of the radius, why would an IM pin & cerclage be disregarded as a fixation method?
there are no safe entry/exit points for the IM pin
the radius has a small intramedullary canal
how would you propose to use a drill in a sterile surgery if you did not have access to a sterilization method that is used for orthopedic drills (referral to a specialist is not an option!)?
sterilized pins & bits to be used
use an autoclave pouch to sterilize the drill
if your bit or pin is wobbling when the power (trigger is pulled) is applied, what could be the reason?
pin is either bent or not centered
when & why is the reverse function used in the drill?
backing up a transosseous pin - if you forcefully pull out the pin, you will strip all of the threads from the bone & it won’t be tight anymore
what degree of force should be used for drilling into bone?
steady, light pressure
what are IM pins good for?
support bending forces in all planes - so small increases in the diameter of the pin result in an exponential increase in bending support
what is the recommended size of IM pin to be used? why?
one that is no greater than 70% of the IM cavity at the most narrow point - want to avoid damaging the bone blood supply & negatively impact bone healing
why should IM pins never be used as a single method of internal fracture fixation?
they do not prevent rotation/shear or counteract axial forces (compressive & distractive)
what is the strength of the IM pin?
ability to resist bending forces
why is cerclage wire useful?
impart interfragmentary compression across a fracture & provide good rotational stability & resistance to axial compression
how is cerclage wire used properly?
the fracture must be at least twice the diameter of the bone & the fracture must be perfectly reduced
why are cerclage wires not used for comminuted fractures?
the small pieces may collapse into the fracture during tightening of the wire
what is the minimum of cerclage wires that should be used in fracture fixation? why?
at least 2 if not more - using only one causes a fulcrum
where should cerclage wires be placed in relation to fractures?
placed at least the bone diameter apart & greater than 1/2 of the bone diameter from the fracture line (proximal & distal tip of the fracture)
placed perpendicular to the bone with even tension, tight wires
what happens if the cerclage wires aren’t applied tightly enough?
loose wires damage bone blood supply
why should you not cut completed wires until all wires are placed?
wires will loosen when applying additional wires
when are IM pins & cerclage wires most useful?
cases with two-piece, long
oblique or spiral fractures and when rapid bone healing is expected (excellent
blood supply, young patients, good owner compliance).
when properly applied, this method of fracture fixation provides adequate support of the fracture forces (most
basically = bending, axial and rotational forces) needed for fracture healing!)
what is torque?
rotational force
what is the most common IM pin used?
steinmann pin - sharp end, avoid using threaded pins
T/F: pin size depends on fracture location
true
how is an IM applied?
use either a jacob’s chuck or drill
what is retrograde insertion of an IM pin?
pin is inserted from the fracture site & driven through the epiphysis (outside of the bone) & the fracture is reduced & the pin is advanced across the fracture
what is normograde insertion of an IM pin?
pin is inserted at the epiphysis outside of the bone & driven across the fracture line
what are the advantages & disadvantages of normograde IM pin placement?
advantages - much less risk of driving the pin through the sciatic nerve & less soft tissue irritation
disadvantages - more difficult pin placement & requires more experience
what are the advantages & disadvantages of retrograde IM pin placement?
advantages - technically easier & hold the limb with the hip in extension & limb adducted to minimize possible nerve entrapment
disadvantages - easy to catch the nerve & may impinge on the femoral neck
what is countersinking? how is it done?
technique used to recess pin into the bone so it won’t damage soft tissues
back the pin off a bit & cut it as close as possible to the bone, tap it in gently
T/F: it is okay to leave IM pins in permanently
true
when is a cross pin technique used?
useful in repairing all types of physeal & metaphyseal fractures - some rotational stability achieved
what are the principles of cerclage wires?
good rotational & axial support, imparts interfragmentary compression, complete reconstruction of bone column required
what is the definition of a long oblique fracture?
fracture is 2.5X the diameter of the bone
what must be done to have properly applied cerclage wires?
minimum of two - placed bone diameter apart, perpendicular to the bone, no soft tissues entrapped, & must be tight
T/F: when used correctly, cerclage wires don’t inhibit blood supply of healing callus
true
if a wire passes through a hole, its what?
hemicerclage wire
what 5 disruptive forces must be controlled to achieve fracture healing?
tension, compression with shear, torsion/rotation, bending, & combination
what are some fracture conditions that must be satisfied to achieve fracture healing?
what are some fracture conditions that must be satisfied to achieve fracture healing?
- restore anatomy
- establish stability
- perserve blood supply
- early mobilization of limb/patient
what is a bending force?
when bending forces occur, tensile forces occur on the convex surface & compressive forces occur on the concave side
what is an axial/compressive force?
stress is placed in a plane perpendicular to the applied load, so when an animal walks, ground reaction forces create an axial collapse in an unsupported bone
what is tension force?
distractive force is applied in a perpendicular fashion
what is shear force?
energy acts parallel to the bone surface & causes an angular limb deformity
what is torsion force?
occurs when a rotational force is applied along the long axis of a bone
in order for a cast to counteract the fracture forces, how must it be applied?
adequately cross a joint above & below the fracture
why are casts really only effective for fractures in distal extremities?
casts can counteract bending & rotational forces, but due to practical application, they can’t be done above the hip/shoulder
cast support with axial compression is only adequate for what fracture type? why?
greenstick fractures, fractures with an intact bone closely associated (radius/ulna), or transverse fractures that are reduced >50% apposition in orthogonal rads
axial collapse is present in all fractures, and unless the bone segments are in direct apposition during weight bearing, there is little support provided during weight bearing
why are casts not recommended for fractures involving the greater trochanter, olecranon, tibial tuberosity, & tuber calcanei?
casts are unable to resist the tensile forces created by musculotendinous insertions on bony apophyses
how long does indirect healing of a fracture take in a mature dog or cat?
8-12 weeks minimum
