Internal Fixation

Question 1

What are the 4 AO principles?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

which type of bone healing bypasses callus formation?

Answer 3

direct osseous repair

Question 4

how is absolute stability achieved?

Answer 4

using compression plates or screws

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

Question 5

how is relative stability achieved?

Answer 5

using intermedullary nailing, ex-fix, locking plates

*needs 2-10% of strain

Question 6

what is strain?

Answer 6

deformation of a material when a given force is applied

Question 7

how is strain decreased?

Answer 7

increased gap length

decreased motion

Question 8

how does titanium compare to stainless steel?

Answer 8

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)

Question 9

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

Answer 9

titanium

avoid stainless steel

Question 10

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

Answer 10

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

Question 11

which metal is the material of choice for joint implants?

Answer 11

cobalt chromium

Question 12

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

Answer 12

shaft

Question 13

what is the threaded part of the screw called?

Answer 13

shank

Question 14

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

Answer 14

runout- it is the weakest part of the screw

Question 15

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

Answer 15

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

Question 16

what is a pitch?

Answer 16

distance between threads on a screw

Question 17

which type of screws are usually partially threaded?

Answer 17

cancellous screws

compared to cortical screws which are fully threaded

Question 18

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

Answer 18

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

Question 19

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

Answer 19

when inserting a cortical screw

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

small frag set

*good for midfoot work

Question 24

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

Answer 24

1. 5, 2.0, 2.7 mm screws

* good for forefoot work, metatarsal necks

Question 25

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

Answer 25

large fragment set | *good for tibia or calcaneus

Question 26

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

Answer 26

1.1

Question 27

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

Answer 27

1.5

Question 28

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

Answer 28

2.0

Question 29

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

Answer 29

2.5

Question 30

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

Answer 30

3.2

Question 31

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

Answer 31

``` herbert screw (aka whipple screw) Ex. fusing the STJ ```

Question 32

When would you use K-wires?

Answer 32

stabilize hammer toe procedures or osteotomies

Question 33

When would you use Steinman pins?

Answer 33

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

Question 34

when is cerclage/ monofilament wire used?

Answer 34

- comminuted metatarsal fx - transverse osteotomies - tension band wiring - last resort type thing

Question 35

when would you use tension band wiring?

Answer 35

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

Question 36

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

Answer 36

resist distraction but generally not shear or bending forces

Question 37

what are some ways to achieve compression with plates?

Answer 37

1. eccentric drilling 2. prebending 3. tension device 4. tension band

Question 38

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

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

what is teh drawback of dynamic compression plates?

Answer 41

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)

Question 42

what is the drawback of LC-DCP?

Answer 42

very thick and prominent | advtg is that it limits vascular trauma

Question 43

what is the function of a neutralization plate?

Answer 43

helps protect inter-frag screw by preventing rotational forces

Question 44

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

Answer 44

neutralization plate

Question 45

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

Answer 45

compression plate

Question 46

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

Answer 46

buttress plate

Question 47

what is a buttress plate?

Answer 47

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

Question 48

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

Answer 48

bridge plate

Question 49

how is a locking plate different from a traditional plate?

Answer 49

it has threaded holes for extra stability

Question 50

what are the rules of stabilization?

Answer 50

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

Question 51

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

Answer 51

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

Question 52

what is the rule of cortices for a metatarsal plate?

Answer 52

4 cortices: 2 screws on both sides of the fx

Question 53

what is the rule of cortices for ankle plates?

Answer 53

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

Question 54

what is vassals rule?

Answer 54

reduce the primary fx and secondary fx will spontaneously reduce

Question 55

what is teh '2 screws are better than 1" rule?

Answer 55

2 points of fixation to resist rotatory forces

Question 56

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

Answer 56

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)

Question 57

what are potential complications of internal fixation use?

Answer 57

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