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Biomechanics & Surgery Exam 3 > Internal Fixation > Flashcards

Internal Fixation Flashcards

1
Q

What are the 4 AO principles?

A
  1. anatomical reduction
  2. stable internal fixation
  3. preservation of blood supply
  4. early active pain-free mobilization
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2
Q

where does most of the blood supply to the bone come from?

A

endosteal or medullary vessels (found in inner 2/3 to 3/4 of cortcial bone)

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3
Q

which type of bone healing bypasses callus formation?

A

direct osseous repair

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4
Q

how is absolute stability achieved?

A

using compression plates or screws

  • ideal for articular fx
  • needs less than 2% of strain
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5
Q

how is relative stability achieved?

A

using intermedullary nailing, ex-fix, locking plates

*needs 2-10% of strain

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6
Q

what is strain?

A

deformation of a material when a given force is applied

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7
Q

how is strain decreased?

A

increased gap length

decreased motion

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8
Q

how does titanium compare to stainless steel?

A

titanium is more flexible, which means it can break easier but there is not as much allergic reactivity to it compared to stainless steel (which contains nickel)

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9
Q

which metal would you use for someone who is allergic to nickel?

A

titanium

avoid stainless steel

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10
Q

which is the least dense of surgically implantable materials? most dense?

A

titanium- least dense = flexible
(then stainless steel)
cobalt chromium- most dense

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11
Q

which metal is the material of choice for joint implants?

A

cobalt chromium

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12
Q

what is the un-threaded part of the screw called?

A

shaft

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13
Q

what is the threaded part of the screw called?

A

shank

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14
Q

what is the term for the place where the shaft and shank meets? what is the significance of this place?

A

runout- it is the weakest part of the screw

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15
Q

compare the size of the pitch between cortical and cancellous screws.

A

cortical screws have a smaller pitch for grasping cortical bone.
cancellous screws have larger pitches.

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16
Q

what is a pitch?

A

distance between threads on a screw

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17
Q

which type of screws are usually partially threaded?

A

cancellous screws

compared to cortical screws which are fully threaded

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18
Q

describe the lag by technique screw. what is the order according to AO techniue?

A
  1. overdrill (or glide hole)
  2. underdrill (or guide hole or thread hole)
  3. countersink
  4. measure
  5. tap (if necessary)
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19
Q

when would you use a lag screw “by technique”?

A

when inserting a cortical screw

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20
Q

how does the lag screw “by design” compare to the lag screw “by technique”?

A

one less step- don’t need to do the overdrill

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21
Q

how far do you drill for a lag screw by technique?

A

need to insert 1mm past far cortex to increase “pull out strength”

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22
Q

how far do you drill for a lag screw by design?

A

do not want to pierce far cortex because they are cancellous screws

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23
Q

what type of fragment set is this? 3.5 and 4.0mm screws? and when would you use this size

A

small frag set

*good for midfoot work

24
Q

what type of fragment set is this? 1.5, 2.0, 2,7mm screws? and when would you use this size?

A
  1. 5, 2.0, 2.7 mm screws

* good for forefoot work, metatarsal necks

25
Q

what type of fragment set is this- 4.5, 6.5 mm screws?

A

large fragment set

*good for tibia or calcaneus

26
Q

what size drill bit would you use to make a thread hole for a 1.5 mm screw?

A

1.1

27
Q

what size drill bit would you use to make a thread hole for a 2.0 mm screw?

A

1.5

28
Q

what size drill bit would you use to make a thread hole for a 2.7 mm screw?

A

2.0

29
Q

what size drill bit would you use to make a thread hole for a 3.5 or 4.0mm screw?

A

2.5

30
Q

what size drill bit would you use to make a thread hole for a 4.5 mm or 6.5 mm screw?

A

3.2

31
Q

what type of screw would you use where screw head prominence may be problematic?

A 
herbert screw (aka whipple screw) 
Ex. fusing the STJ
32
Q

When would you use K-wires?

A

stabilize hammer toe procedures or osteotomies

33
Q

When would you use Steinman pins?

A
  • stabilize larger osteotomies or fusion (calcaneus or ankle)
  • can be used as a metatarsal intramedullary nail
  • across growth plates
34
Q

when is cerclage/ monofilament wire used?

A
  • comminuted metatarsal fx
  • transverse osteotomies
  • tension band wiring
  • last resort type thing
35
Q

when would you use tension band wiring?

A

fragments that may be too small or difficult to put a screw through or when there is a soft tissue attachment pulling against you

36
Q

what kinds of forces do staples resist (and what do they not resist)?

A

resist distraction but generally not shear or bending forces

37
Q

what are some ways to achieve compression with plates?

A
  1. eccentric drilling
  2. prebending
  3. tension device
  4. tension band
38
Q

when doing eccentric drilling to achieve compression, where do you put the first screw?

A

on stable side of the fx (then place second screw on the unstable side of teh fx)

39
Q

when prebending a plate to achieve compression, where do you put the screws first?

A

put the 2 screws centrally then move your way outwards to avoid gapping

40
Q

when applying the tension band principle to achieve compression, on which side do you screw the screws?

A

put the screw on the side of teh fracture where you have tensile forces

41
Q

what is teh drawback of dynamic compression plates?

A

there is a lot of contact of the bone to the metal plate that it can cause osteonecrosis under plate. (so then limited contact DCP were created)

42
Q

what is the drawback of LC-DCP?

A

very thick and prominent

advtg is that it limits vascular trauma

43
Q

what is the function of a neutralization plate?

A

helps protect inter-frag screw by preventing rotational forces

44
Q

what type of plate would you use in a spiral fibula fx?

A

neutralization plate

45
Q

what type of plate would you use in a transverse fx?

A

compression plate

46
Q

what type of plate would you use in a tibial plateau or plafond fx? or calcaneal fx?

A

buttress plate

47
Q

what is a buttress plate?

A

stabilizes fx by being anchored to the main stable fragment, not necessarily the fragment it is supporting

48
Q

what type of plate would you use to fixate 2 main fragments followed by a graft placement?

A

bridge plate

49
Q

how is a locking plate different from a traditional plate?

A

it has threaded holes for extra stability

50
Q

what are the rules of stabilization?

A
  1. screw fixation
  2. plate stability
  3. vassals rule
  4. two screws are better than one
51
Q

what is the rule for screw fixation when it comes to stabilizing a fx?

A

the length of fx should be at least twice the diameter of the bone involved

52
Q

what is the rule of cortices for a metatarsal plate?

A

4 cortices: 2 screws on both sides of the fx

53
Q

what is the rule of cortices for ankle plates?

A

need 6-8 cortices: 3-4 screws on both sides

54
Q

what is vassals rule?

A

reduce the primary fx and secondary fx will spontaneously reduce

55
Q

what is teh ‘2 screws are better than 1” rule?

A

2 points of fixation to resist rotatory forces

56
Q

what is a MIPO (minimally invasive plate osteosynthesis) plate?

A

percutaneous plate usually used in tibia or teh femur that is anatomically pre-contoured and is a locking plate
*used to protect fx biology (minimally disruptive to soft tissue and periosteum)

57
Q

what are potential complications of internal fixation use?

A
  • prominent painful hardware
  • hardware breakage
  • hardware backing out
  • malunion
  • nickel allergy
  • sterile abscess or reaction
  • infection

Biomechanics & Surgery Exam 3 (11 decks)

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