43.internal fixation (1)

Question 1

type of implant used for complete anatomic reconstruction

Answer 1

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

Question 2

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

Answer 2

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

Question 3

anatomic reconstruction vs biological osteosynthesis in terms of bone healing

Answer 3

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

Question 4

fractures suitable for anatomic reconstruction

Answer 4

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

Question 5

principles of biological osteosynthesis

Answer 5

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

Question 6

Minimally invasive osteosynthesis main limitation

Answer 6

no direct observation of fracture segmentsmay need intraop fluoroscopically

Question 7

tensile strength of orthopedic 316 L Stainless Steel Wire

Answer 7

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

Question 8

weakest point of a wire

Answer 8

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

Question 9

4 methods orthopedic wire is used

Answer 9

1. tension band2. cerclage3. hemicerclage4. interfragmentary wire

Question 10

relative strength of 18, 20, 22 gauge orthopedic wire

Answer 10

18 g 1.020 g 0.62 x22 g 0.36 x

Question 11

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

Answer 11

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

Question 12

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

Answer 12

twist–untwistsingle loop/double loop–unbend

Question 13

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

Answer 13

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

Question 14

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

Answer 14

True (pg 579)

Question 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)

Answer 15

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

Question 16

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

Answer 16

TRUEcerclage cannot be placed in areas that may collapse

Question 17

alternative material to routine orthopedic wire for cerclage

Answer 17

multifilament cable—strongnot flexible therefor can’t knot; need crimps or clamps to secure

Question 18

fracture type that cerclage is MOST effective for

Answer 18

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)

Question 19

pins resist bending base on their area moment of inertia

Answer 19

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

Question 20

general recommendation for pin width of medullary cavity when used ALONE

Answer 20

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

Question 21

dynamic vs cross pinning technique

Answer 21

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)

Question 22

forces resisted with ILN system

Answer 22

bending, rotation and axialnot used in the radius

Question 23

biomechanial advantage to ILN systems

Answer 23

–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)

Question 24

compare ILN systems vs plate biomechanically

Answer 24

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

Question 25

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

Answer 25

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

Question 26

new angle stable ILN system advantages

Answer 26

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

Question 27

entry point of ILN/IM pin into tibia

Answer 27

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

Question 28

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

Answer 28

must be placed 2 mm beyond trans cortex

Question 29

what is the pullout strength of a screw primarily dependent on

Answer 29

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

Question 30

what is the bending strength of a screw primarily dependent on

Answer 30

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

Question 31

what is the optimal orientation of a lag screw

Answer 31

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

Question 32

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

Answer 32

TRUEmust be perpendicular to fracture plane

Question 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

Answer 33

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

Question 34

3.5 mm broad DCP advantages

Answer 34

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

Question 35

benefits of the LC-DCP

Answer 35

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)

Question 36

nonlocking vs locking screws

Answer 36

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

Question 37

difference with reconstruction plates

Answer 37

made of softer steeleasily contoured in three planesweaker

Question 38

guidelines for locking plate placement

Answer 38

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

Question 39

how to increase plate construct stiffness

Answer 39

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

Question 40

LCP advantages

Answer 40

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

Question 41

star hexagonal head for locking screws allows for….

Answer 41

increased insertional torque up to 65%

Question 42

what kind of screws to use with SOP

Answer 42

locking construct but uses standard screws allowing a press fit

Question 43

Fixin plate system

Answer 43

SS plate with titanium insert for locking screws

Question 44

ALPS screws

Answer 44

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

Question 45

most common complication seen with MIPO techniques

Answer 45

fracture mal alignment

Question 46

plate rod constructs and decreased strain

Answer 46

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