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Flashcards in 43.internal fixation Deck (46):
1

type of implant used for complete anatomic reconstruction

when anatomic reconstruction (exact rebuilding) of a fracture is achieved, the rigid implant in place is a NEUTRALIZATION implant (shares or neutralized the forces being borne by the bone)bone supports fixation = fixation supports bone

2

type of implant for animals without anatomically reconstructed fractures in which you aim to achieve rigid fixation of implant > load on bone

Buttress/bridging carries all of the weight and resists all forces applied to the bone(ILN, plate rod, lengthening plates)

3

anatomic reconstruction vs biological osteosynthesis in terms of bone healing

anatomic recon --> primary healing (AO style)biological osteosynthesis --> secondary healing

4

fractures suitable for anatomic reconstruction

1. ARTICULAR FRACTURES2. transverse3. short oblige4. long oblique5. minimally comminuted (lg frags)

5

principles of biological osteosynthesis

1. indirect fracture reduction w limited surgical approach and disturbance of the fracture hematoma (OPEN BUT DO NOT TOUCH or CLOSED/MI)2. fracture stabilization using bridging osteosynthesis (less rigid)3. limited reliance on secondary implants4. limited use of bone grafts

6

Minimally invasive osteosynthesis main limitation

no direct observation of fracture segmentsmay need intraop fluoroscopically

7

tensile strength of orthopedic 316 L Stainless Steel Wire

tensile strength is related to cross sectional area = pi r squareddoubling radius, increases strength 4 fold

8

weakest point of a wire

weakest point of a wire is usually associated with the method used to secure it in generally, larger diameter wire has a higher knot strength

9

4 methods orthopedic wire is used

1. tension band2. cerclage3. hemicerclage4. interfragmentary wire

10

relative strength of 18, 20, 22 gauge orthopedic wire

18 g 1.020 g 0.62 x22 g 0.36 x

11

twist, single loop and double loop knots and load resisted before loosening

twist--tension and secure at same time 260 Nsingle loop--wire tensioner used; wire is secured by bending 260 Ndouble loop-- wire tensioner used; wire is secured by bending 666 N

12

twist, single loop and double loop knots---how do they loosen

twist--untwistsingle loop/double loop--unbend

13

based on mechanical studies, how many twists are necessary to maintain tension and produce a secure knot

1 (can cut it short)--generally recommend (AO) keeping 2-3 twistsdo not push down/flatten--will loosen

14

T/Fthe peak load resisted without regard to deformation is superior for twist knots

True (pg 579)

15

T/Fthe double loop cerclage generated more tension than both twist and single loop and was able to resist greater load before being classified as loose (30 N)

TRUEdouble initial 300-500 N resist 666 N before loosensingle initial 150-200 N resist 260 N before loosentwist initial 70-100 N resiss 260 N before loosen

16

T/Fresting tension of cerclage drops below 30 N (considered loose) with only 1% collapse of a diameter structure

TRUEcerclage cannot be placed in areas that may collapse

17

alternative material to routine orthopedic wire for cerclage

multifilament cable---strongnot flexible therefor can't knot; need crimps or clamps to secure

18

fracture type that cerclage is MOST effective for

long oblique/spiral (fracture 2.5-3x diameter of bone)at LEAST 2 wires if not MOREspaced btwn half and the diameter of the bone apartperpendicular to fracture line (skewer pin if needed)

19

pins resist bending base on their area moment of inertia

area moment of inertia = radius to the fourth powerincrease radius by 2; increase AMI by 16

20

general recommendation for pin width of medullary cavity when used ALONE

70% medullary cavity aloneif plate rod decrease to 35-40% not to exceed 50%

21

dynamic vs cross pinning technique

some rotational stability can be achieved with pins placed separate from each other at the level of the fracturedynamic pins: Rush pins (do not penetrate opposite cortex)cross pins: penetrate opposite cortex (greater stability)

22

forces resisted with ILN system

bending, rotation and axialnot used in the radius

23

biomechanial advantage to ILN systems

--placed within neutral axis of the bone (experience direct axial compression during wt bearing, not bending)--locking (provides stability in torsion and compression)--large area moment inertia (radius to the fourth)

24

compare ILN systems vs plate biomechanically

plates are eccentrically placed compared to neutral axis of bone, prone to bending, AMI thickness to the third power--all predispose plate to fail at lower loads vs ILNILN placed within neutral axis of bone, resist compression, lock and hi AMI radius to the fourth power; risk of implant failure with ILN is lower than plate

25

T/Fscrews in ILN are more resistant to bending than bolts

FALSEbolts in ILN are more resistant to bending forces when compared to screws bc bolts have smooth shafts and higher AMI. also improved contact with ILN

26

new angle stable ILN system advantages

attempt to overcome concerns with instability in bending and torsion--screw-cone pegs: Morse taper to eliminate slack; self center and self lock--hourglass figure with large diameter at each end to increase AMI, increased vascularity in diaphysis

27

entry point of ILN/IM pin into tibia

place stifle in 90 degrees flexionentry point is just cranial to inter meniscal ligamentand midway btwn MCL and tibial tuberosity

28

to achieve max holding power as a non self tapping screw, what must be done to a self tapping screw

must be placed 2 mm beyond trans cortex

29

what is the pullout strength of a screw primarily dependent on

outter diameter of the screw and strength of the material into which the screw is placed

30

what is the bending strength of a screw primarily dependent on

core (inner) diameter AMI = radius to the fourth power

31

what is the optimal orientation of a lag screw

perpendicular to the fracture planecis (glide hole)--overdrilltrans (far cortex)--drill normal core diameter of screw to be used

32

T/Fif the length of the fracture line is < 1.5x the bone diameter, it is difficult to place an effective lag screw

TRUEmust be perpendicular to fracture plane

33

T/Ftitanium plates have a theoretical advantage with respect to fatigue resistance but are not a stiff or as strong as stainless steel plates

TRUEtitanium plates have a theoretical advantage with respect to fatigue resistance but are not a stiff or as strong as stainless steel plates

34

3.5 mm broad DCP advantages

made from same bar stock as 4.5 mm DCP BUT screw holes are smaller to accept 3.5 mm screws (STRONGER) and because they are smaller there are more screw holes per length of plate (increases purchase, increases stability)HARDER to contour

35

benefits of the LC-DCP

limited contact dynamic decompression platescalloped underneath to maintain periosteal blood supply AND stress is NOT concentrated at the screw holeallows bending to be uniform across plategreater degree of angulation (40 long, 7 transverse)allows compression in both directions(BUT scalloping decrease AMIof the solid portion)

36

nonlocking vs locking screws

nonlocking screws compress the PLATE to the BONElocking screws tighten the SCREW to the PLATE (stable-fixed angle construct)

37

difference with reconstruction plates

made of softer steeleasily contoured in three planesweaker

38

guidelines for locking plate placement

spanning long segments of bonelimit screw:hole ratio < 0.5leave 2-3 holes over defect empty

39

how to increase plate construct stiffness

increase plate size (thickness to the third AMI)increase the number of screwsadd an IM pin (plate rob construct)

40

LCP advantages

LOCKING compression plateoblong combi holes--allow compression with std screw (ONLY IN ONE DIRECTION)--other end accepts locking screwScalloped to promote vascularity

41

star hexagonal head for locking screws allows for....

increased insertional torque up to 65%

42

what kind of screws to use with SOP

locking construct but uses standard screws allowing a press fit

43

Fixin plate system

SS plate with titanium insert for locking screws

44

ALPS screws

advanced locking system with tapered locking screws that fit into matching plate holes

45

most common complication seen with MIPO techniques

fracture mal alignment

46

plate rod constructs and decreased strain

for every 10% canal filling w rod plate strain decreased 20%

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