Ch 41 Internal fracture fixation

Question 1

4 principles of fracture mgmt (AO)

Answer 1

anatomical reduction
stable internal fixation
preserve blood supply
early pain free mobilisation

Question 2

AAAA of fracture fixation assessment

Answer 2

alignment
apposition
acitivity
apparatus

Question 3

Consequences of not preserving blood supply + solution

Answer 3

delayed fracture healing, wound breakdown, infection

Bridging fixation with relative stability with MIO and locking implants

Question 4

structural properties of IF

Question 5

Area moment of inertia

Answer 5

based on the dimensions of the structurein the direction of bending.

For a circular implant, 1/4.p.r4, radius is raised to the fourth power, so small increases in diameter have a large impact on the bending stiffness.

solid rectangular structures 1/3.b.h3, thickness of a plate is an important parameter > dimension is cubed.
more complex for bone plates because of the presence of the holes for the screws

If the direction of bending is known, the surgeon can also
use this understanding of AMI to consider alternate plate locations

Plate
The AMI determined by the size and how it is oriented relative to the bending loads.
no empty holes = higher AMI than one with unfilled holes, but requires no fracture gap.

When gap > plate must span, therefore unfilled holes, and
a significantly lower AMI,
also decreasing the fatigue life.

Question 6

Working length

plate, ESF?

Answer 6

portion that spans the fracture gap (working length) influences
the deflection of the construct. This deflection determines the movement of fracture
fragments, and this influences tissue differentiation and maturation.

For implants with the same AMI, the amount of deflection is related to the span length cubed.

Plate
3.5-mm plate (AMI 5 15 mm4) with a working
length of 2 cm there will be approximately 0.3 mm of deflection. If the working
length is increased to 4 cm, the deflection would be approximately 2.3 mm.

ESF
The working length
of a fixation pin is the distance from the bone to the clamp. The working length of the
frame is the length of the connecting bar segment(s) that span the fracture. Reducing
the pin and/or connecting bar lengths increases the stiffness of the frame.

Question 7

working length

Answer 7

stiffness of the construct is inversely related to the working length cubed.

When the working length is longer, the yield bending strength may also be reduced

The longer the bending moment arm, the lower the applied load that will cause the plate to yield

The working length of a plate is influenced by the type
of plate and the direction of bending.

locking plate,
particularly if the plate is not in contact with the bone, the working length is from
the screws closest to fracture gap.

regular plate
the plate and bone act together because in contact, working length is the unsupported length

creating a construct with a longer working length (ie, placing screws more distant) will reduce the stress in the plate, making it less likely to fail by fatigue.
> not correct, and several studies have shown that, for the same applied load, the measured strain beside a plate hole is similar for constructs with 1 hole
unfilled compared with 3 or 4 holes unfilled.

locking plate model with large gap: no bone contact and a larger working length,
the construct was less stiff

Question 8

fatigue

Answer 8

Few orthopedic implants or constructs fail clinically because of a single incident of
applied load, so understanding cyclic loading and fatigue is important for guiding
implant selection.

The factors that influence fatigue:
1 load (generates stress )
2.geometry (screw holes)
3.material and how it was handled and manufactured
4.local environment

For most metals, the endurance limit is around 50% of the ultimate tensile stress.

screw holes in a plate, may cause local stress concentrations that accelerate fatigue

Very small imperfections and cracks can be initiating factors in the failure cascade

reduce fatigue effects:
1.appropriate strength
2. minimizing notching
3. client education, reducing applied loads
4. load sharing/ promote faster # healing

Question 9

surgeon assesses the mechanical and biological factors of a particular fracture

Answer 9

Fixation that is too stiff > slow development of bridging callus.

Fixation that is too weak > deform if a single large
load is applied, or fail by fatigue

comes down to clinical judgment. This judgment is often based on personal and reported experiences.

Question 10

factor affecting stiffness of construct, gap strain and fatigue

Answer 10

stiffness
1.modulus of the
material used
2.AMI of the construct
3.span across the fracture (the
working length).

gap strain
1.width of the gap
2.amount of motion between the fragments.

fatigue failure
1.yield bending strength
2.cumulative cycles

Question 11

What are the principles of biological osteosynthesis?

Answer 11

Indirect fracture reduction using limited approaches with minimal disturbance of the fracture haematoma

Bridging implants rather than anatomical reduction and rigid fixation

Limited reliance on secondary implants such as cerclage wire, interfragmentary screws etc

Limited, if any, use of bone grafts

Question 12

What are the two main types of fracture fixation using biological osteosynthesis?

Answer 12

Open but do not touch
Minimally Invasive Osteosynthesis

MIO = ESF, ILN, MIPO

Question 13

internal fixation

Answer 13

are invasive.

require a surgical approach to the bone.

Increased tissue damage from the approach and fragment manipulation may prolong healing.

Implants remain inside the body and can potentiate infection.

Question 14

absoulte vs relative methods

Answer 14

absolute
may take longer for the bone to reach its normal strength

further devitalize portions of the soft tissue and bone, delay healing

complications less likely after stable repair.

important for fractures involving the articular surface

rebuilt bone structure supports the fixation at the same time as the fixation supports the bone.

relative
secondary bone healing > callus and remodeling occurs.

minimized to preserve the blood supply

radiographic union and functional strength are often achieved more quickly

more discomfort for the patient,

implants experience greater stress, predisposing them to failure.

Question 15

fractures amedniable to recon

Answer 15

(1) transverse,
(2) short oblique,
(3) long oblique,
(4) segmental,
(5) minimally comminuted (e.g., those including large butterfly fragments),
(6) articular fractures

Question 16

How many twists are needed to keep a twist knot cerclage wire secure?

Answer 16

1 1/2 twists - better to cut short that to flatten if possible

more twists increase susceptible to fatigue

Question 17

What is orthopaedic wire made of?

How do you calculate its tensile strength?

Answer 17

Made of 316L stainless steel
Tensile strength = pie x radius^2

Question 18

What manipulations after formation of a twist knot cause a drop in the resting tension?

Answer 18

Vibration from cutting caused a drop of approx 10N
Pushing over to lie flat causes a decrease in resting tension from 45-90%
Cerclage wire is classified as loose is the resting tension is less than 30N

Question 19

What are the tension of each form of cerclage and their load resisted prior to loosening?

Question 20

What are the principles of application of cerclage to help to ensure success?

Answer 20

Applied to an oblique fracture (2.5 - 3 x diameter)
At least 2 wires
Spaced approximately half a bone diameter apart
The shaft of the bone around which the cerclage is placed must be completely reconstructed

Question 21

cerclage wire

Answer 21

best suited to long oblique fractures of the diaphysis

Primary role of hemicerclage is to maintain alignment while definitive fixation is applied. Because they limit rotation well in only one direction

twist and single- and double-loop knots are most commonly used

tension in the formed wire decreases with any manipulation of the knot.
if the twist was pushed over to lie flat on the tying jig, the resting load dropped by 45% to 90%

or tension-band wires, resting tension is less critical, and the twists often are more superficial. The twist may then be laid flat by bending the twist down as the last twist is performed.

Cerclage wires also loosen after a small amount of “collapse” (loss of circumference) of the bone.

lood supply damage attributed to cerclage was caused by the wires becoming loose and damaging local vessel development.

Question 22

List the 3 sizes of K-wire in inches and mm

Answer 22

0.035in (0.9mm)
0.045in (1.1mm)
0.062in (1.6mm)

Question 23

k-wire

Answer 23

often used to counter rotation by being placed in pairs or added adjacent to a screw used in lag fashion.

To counter rotation, Kirschner wires are best placed parallel to, and separated from, each other.

erpendicular to the growth plate and parallel to each other. This arrangement allows the best opportunity for longitudinal growth if growth potential remains.

Question 24

Steinmann Pins

Answer 24

1/16 to 1/4 inch (1.6 to 6.4 mm) three-faced trocar tip
sizes increase by 0.4mm

Pins are most suited to resist bending. Their strength and stiffness are determined by their area moment of inertia

Pins do not resist forces aligned with (compression) or around (rotational) their axes well because there is little friction

placed normograde or retrograde.

tie-in configurations with external skeletal fixators1 or to prevent damage to the sciatic nerve (fractures of the femur).

cross pinning
Some rotational stability is achieved if the pins are located apart from one another at the level of the fracture. In the standard crossed-pin technique, the pins gain purchase by penetrating the cortex opposite.

dynamic/rush pinning don’t engage cortex

because the physis is often extensively damaged by the fracture process,116 in most instances the implants do not influence whether the growth plate remains functional.

noromograde: tibia, femur, humerus

Question 25

What is the recommended %fill of an IM pin when placed as the only IM device?

Answer 25

70%

Question 26

List the 3 main design types of interlocking nails

Answer 26

Regular interlocking nail
Angle stable interlocking nail
Inverse interlocking nail

Question 27

List the biomechanical advantages of interlocking nails (4)

treatment of closed comminuted diaphyseal fractures of the long bones

Answer 27

1 - Nail are placed near the neutral axis of the bone and are therefore subjected to compressive rather than bending forces during weight bearing

2 - Large area moment of inertia provides more resistance in bending compared to bone plates of a similar size

3 - Locking mechanism provides stability in torsion and compression

4 - Intramedullary location eliminates risk of failure via screw pull-out

Question 28

What is the strongest construct configuration of an interlocking nail?

Answer 28

A nail which fills approx 80% of the IM cavity, using a nail with smaller holes and using bolts to lock to nail to the bone

Question 29

What range of diameters and lengths are avaible for interlocking nails?

What are some general recommendations for size choice?

Answer 29

Nails are available ranging from 2.5 - 10mm diameter and 62 - 230mm length

Cat and small dogs 5-15kg –> 3-4mm diameter nail
Dogs 15-30kg –> 6mm nail
Dogs up to 40kg –> 7mm nail
Dogs over 40kg –> 8-10mm nail

The diameter of the nail should be as large as possible without exceeding 70-90% of the diameter of the isthmus. 75% has been recommended when using the angle-stable nail

he interlocking nail should span most of the length of the bone.181 Imbedding the nail ends in metaphyseal and epiphyseal cancellous bone increases bending stability of the nail as well as fatigue life

Question 30

ILN

Answer 30

current angle-stable interlocking nail > improved by machining threads to the outer surface of the central portion of the Morse-tapered peg that screws into threads of nail.

provides a rigid nail/bolt interface, cortical threads in the cis and trans sections of the bolt have been eliminated.

strongest constructs with this nail system will be achieved by selecting a nail that fills approximately 80% of the medullary cavity, using a nail with the smaller holes, and using bolts to lock the nail to the bone.

Bolts are more resistant to bending forces compared to screws

Rotational instability is likely responsible for a reported nonhealing rate of 14% in dogs treated with second-generation regular interlocking nai > Development of the angle-stable interlocking nail has been shown to overcome concerns with instability in bending and torsion (pegs used as locking devices eliminate slack.)

hour-glass shape increase AMI, and allow large locking mechanism, isk for mechanical failure reduced

studies demonstrated that interfragmentary motion is reduced with use of the angle-stable interlocking nail

placed at a distance one to two bone diameters

Question 31

ILN technique

Answer 31

bility to place the implants in accordance with the principles of biologic osteosynthesis.

Dynamization, or destabilization, of a nail placed in static mode can also be achieved by removing one or more locking devices as bone healing progresses. The potential positive effect of the dynamic mode is increased axial micromovemen

effect of reaming of the medullary cavity >loss of bone and medullary blood supply
> hourglass shape of the angle-stable interlocking nail is designed to allow increased vascularity of the diaphyseal medullary cavity because of the smaller diameter (Clinical union occurred as early as 8 weeks)

Careful preoperative evaluation of radiographs should include evaluation of fracture lines, fissures, and available bone stock.

fluoroscopy during interlocking nail placement may be advantageous (aiming device reduce this need)

Sharp nail tips should be blunted

Traditionally, two locking devices are placed into the most proximal and distal. locking the nail with a single proximal and distal bolt is often sufficient.

care radial nerve distal bolt area i.e place 45 degree

Question 32

ILN outcome

Answer 32

Mean bone healing time of fractures, via minimally invasive osteosynthesis principles, was reported to be 36 ± 9 days > reflect the combined biomechanical and biological advantages

In a large clinical study (121 cases), 95% of patients had good or excellent functional outcome

complications
poor indications (e.g., use to treat a metaphyseal fracture with insufficient bone for screw insertion) or technical errors (e.g., empty screw hole near a fracture site).
no major complications were noted in 41 fractures treated with the angle-stable interlocking nail
Failure to successfully place the locking device in the most distal hole in the nail can result in premature dynamization (<1% with angle-stable)

bolt; fracture of the bone through a drill hole; fracture of the bone proximal or distal to the interlocking nail; rotational instability; osteomyelitis; radial nerve paralysis; sciatic nerve damage;

Question 33

What are the benefits of non-reaming when placing an ILN?

Answer 33

Preservation of medullary blood supply
Associated with less infection and fat embolism
Histologically proven to be associated with more rapid healing times

Question 34

What are the two possible modes of placement of an ILN?

Answer 34

Static
Dynamic

Question 35

What is the frequency of misplacement of the most distal locking device in regular and angle-stable ILN?

Answer 35

Regular: 28% misplacement
Angle-stable: less than 1%

Question 36

What is the overall success rate of ILN?

What is the mean bone healing time of fractures fixed with an angle-stable ILN?

angle stable means no slack in locking mechniasm of bolt-nail

Answer 36

Overall success 83 - 96% (mostly associated with traditional designs), more recent study 95% have good-excellent outcome

Mean bone healing time 36 +/- 9 days

Question 37

What are some benefits of angle-stable ILN?

Answer 37

Overcome concerns regarding bending and torsional instability seen with the regular locking nail
Use self-tapping, Morse tapered locking screw-cone pegs
Hourglass shape nail allowing placement of locking devices with larger diameter, thereby decreasing the risk of failure of the nail at the level of the nail hole, or of the locking device itself.
Hourglass shape also allows increased vascularity of diaphyseal medullary cavity

Question 38

How does the measurement of the area moment of inertia vary in regards to interlocking nail and a bone plate?

Answer 38

Area moment of inertia is measured for an intrelocking nail using radius to the 4th power whereas for plates, it uses thickness to the third power
The area moment of inertia of an 8mm ILN is approx 6.8x that of a 3.5mm DCP and approx 3.5x that of a 3.5mm broad DCP
Area moment of inertia influences bending strength and stiffness

Question 39

What is considered the optimal screw tightness in relation to torque?

Answer 39

70% of the stripping torque

Question 40

List the guidelines for use of locking plates in people, to decrease plate strain and the likelihood of plastic deformation

Answer 40

1 - Spanning long segments of bone (>3x length of the fractured segment)

2 - Limiting the screw-to-hole ratio to less than 0.5

3 - Limiting the distance between the plate and bone to <2mm

4 - Leaving at least 2-3 screw holes empty over the bone defect (This results in a weaker construct which may not always be the best for veterinary patients who will bear weight on the limb. It allows for micromotion and increased production of secondary callus)

Question 41

What is the weak point of locking plate constructs?

Answer 41

The screw-plate interface

Question 42

List the 5 main locking plate systems and their characterisitic?

Answer 42

1 - Locking compression plate (LCP, Synthes) - oblong Combi holes allowing use of standard screws in compression or neutralisation mode or the use of locking screws in the threaded portion of the hole. The core diameter of these locking screws is larger than that of the same size standard cortical screws resulting in increased resistance to bending, and a star drive head allows for 65% greater insertional torque

2 - SOP (Orthomed) - Uses standard cortical screws that thread into the plate, allowing the screw head to press-fit into a recessed chamber

3 - Advanced Locking Plate System (ALPS, Kyon) - Uses a dual locking system - The plate hole has partial threads which lock the most proximal thread of the screw and the screw has a smooth tapered head that engages the matching plate hole

4 - Fixin System (Intrauma) - Uses a titanium insert which screws into the stainless steel plate. This insert then accommodates a screw with a morse taper head

5 - Polyaxial Locking Plate System (PAX, Securos) - The holes in the titanium plate have ridges and as the screw is inserted, the threaded head cuts its unique path into the ridges. Screws can be placed at an angle up to 10 degrees from vertical

Question 43

What is the recommended plate span ratio and screw density for bridging plates?

Answer 43

Recommended plate span ratio 2-3 for comminuted fractures and 8-10 for simple fractures

Recommended screw density 0.5-0.4

Question 44

conventional plate

Answer 44

Regular bone plates
secured to bone using screws such that, as the screw is tightened, the plate is compressed onto the surface of the bone.
As a general rule, if 3 bicortical screws are placed, the
fixation is considered secure. For the plate-bone attachment to remain rigid, the screws must remain tight. It is important that the plate be in direct contact with the bone
These plates also necessitate
accurate contouring

absolute stability can be achieved by compressing
fragments to one another. Several plate systems have screw holes that are
sloped hole such that, when the screw is placed at the high end of the hole, and then
tightened, the fragment that it is engaging is compressed onto the opposite fragment

When a plate is loaded in bending, the pullout load resisted by the screws is
greatly reduced when they are further from the fracture

Question 45

locking plate

develped to enhance via MIO (bridging/reduce anatomic recon/relative stablity)

weakest point = screw-plate interface

Answer 45

the head of the screw locks into the plate and holds it rigidly
in position, rather than pulling it to the bone. The most common method for locking is
a threaded screw head engaging a threaded hole in the plate

locking screws is that they are at a fixed angle to the plate and thus work together to keep plate attached to bone. 2 well-seated locked screws provide a mechanically safe attachment to a fragment.

increased resistane to axial pullout (require all screws to pull out concurrently or bone to fail, and this is more than conventional screw pull out force = mechanical advantge

advantages
plate is not compressed
to the bone, the periosteum does not need to be elevated. > help maintain the vascularity of bone
not need to be accurately contoured. However, because the plate is slightly offset, bending and shear forces on the screws are much greater.

single beam construct means bending loads distributed evenly accross all supporting screws, therefore reduce stress consentration at a single screw-bone interface

locking screws generally have a larger core diameter and, thus, a
larger AMI to resist these stresses

disadvantage
requirement to insert locking screws at a predetermined fixed angle to the bone plate
options: screw hole in the plate can either be left empty or
filled with a cortical bone screw that is directed away from
the joint. Alternatively, a shorter locking screw
» might reduce the strength

bone stronger against compression than shear

Question 46

Name the following types of screws:

cortical screws are 1.5, 2.0, 2.4, 2.7, 3.5, 4.0, 4.5, 5.5, and 6.5 mm

Answer 46

A - Cortical screw

B - Cancellous screw

C - Partially threaded cancellous screw

D - Shaft screw

E - Cannulated screw (Kirschner wire is used to maintain reduction, and the screw is placed over the Kirschner wire, thus ensuring accurate placement.)

F - Self-tapping screw (decreases the overall surface area of the bone-screw interface; therefore, the screw must be advanced so that the cutting flutes pass completely through (defined as 2 mm beyond) the far cortex )

Question 47

What determines the pull-out strength of a screw?

What determines the bending strength of a screw?

Answer 47

The outer diameter of the screw and the strength of the material into which it is placed
The core diameter determines the bending strength

Question 48

locking screws

With locking plates, the screw engages the plate, creating a stable fixed-angle construct. This configuration is statically secure in that the locking head screw is anchored in a mechanically stable manner in the plate

Answer 48

screw threads on the head that engage either a similar thread in the plate or cut their own thread into protrusions within the plate hole (e.g., PAX system, Securos).

thread pitch of the head is half that of the shaft because they have a double lead.

The thread profile on the shaft > finer pitch and less depth because these screws are designed less to resist pull-out and more to have bending strength.

The Fixin system (Intrauma) > threaded bushing and a conical taper of the screw head

In the string of pearls system (Orthomed), standard smooth head cortical screws are used; they lock into the “pearl” using a combination of thread at the base of the pearl and a contact “ridge” within the pear

Question 49

lag fashion

vs position screw

Answer 49

With a fully threaded screw, the hole in the near cortex (glide hole) is drilled so the threads of the screw do not engage.

As the screw is tightened, the screw head compresses the near fragment onto the far fragment to stabilize the fracture. T

he optimal orientation of a lag screw is perpendicular to the fracture plane.

A position screw is used to hold fragments in a specific location. They are placed with the threads engaging both near and far fragments (cis and trans, respectively).

Question 50

plate application principles

Answer 50

plate in bridge/axial converts axial force into bending force due to unshared laoding (eccentirc loaction therefore increases bending moment)

plate on tension surface decreased bending forces on plate
1.plate span 70% diaphysis (min. 50%)
2.contour
3.place scrw 0.5cm from #
4.compress only tranasverse or short oblique
5.minimum 4-6 cortices per fragment
6.plate size (weight, screw diameter <25-30%)

Question 51

conventional plate vs locking mechanism

studies show LP fail at greater loads than conventional

Answer 51

depend og dirct plate to bone and screw to bone friction to maintain fixation therefore rely on close contact/contour,

failure of reduction can occur when axial load is greater than friction force (due to excessive shear force on construct)

if axial overloads friction, contruct strength relies on screw to resist shear or ability of bone surrounding screw to resist compression
> construct relies on single screw pull out strength

ability of plate to resist bending related to stiff/strength of plate + resistnace of bone engaged by screw thread to shear forces (axial pull out)
bending converted to shear stres along screw axis (resist determined by screw outer diameter + bone quality)

shear strength of bone-screw interaces = weakest

locking fixed angle construct does not need to rely on screw purchase > locked screw in plate converts shear to compressive at screw-bone interface, therefore failure dt bone compression failure.

Question 52

What benefits do the scalloped underside of a LC-DCP bring?

Answer 52

Scalloping means that stress is not concentrated at the screw hole

Reduces the area in direct contact with the bone to preserve the blood supply

During contouring, a bend can be distributed over the whole plate, rather than mostly at the screw holes

The underside of the screw hole has been opened more in LC-DCP as compared to DCP. This allows screws to be angled to a greater degree

Question 53

Name the following plates:

Answer 53

A - Veterinary cuttable plate

2 sizes; one for 1.5/2.0 screws, second for 2.0/2.4/2.7 screws
Thinner in profile. can be stacker for increased stiffness

B - Semitubular plate
Due to shape fits close to bone
Much weaker that DCP, not really used in vet

C - Lengthening plate
Solid middle portion

D - Reconstruction plate
v-notched between holes and made of softer steel to allow contouring in all three directions
Weaker than equivalent DCP
Available in 2.0, 2.7 and 3.5

Question 54

What are the general recommendations for screw placement in locking plates?

Answer 54

Construct stiffness is maximised ifs screws are placed at end of plate and near the fracture

2 screws per fragment minimum, little advantage to placing more that three in regards to axial stiffness

Third screw towards fracture site increases stiffness

Additional of a 4th screw per fragment increases torsional rigidity

If the fracture gap is small (1mm) recommended to omit screws from 1-2 holes closest to fracture

If fracture gap is large (6mm), placement of innermost screws as close to the fracture as practical is recommended

Question 55

Name the following locking plates

Answer 55

A - SOP

B - ALPS (Advances Locking Plate System) Kyon

C - Fixin system

D - PAX (Polyaxial Locking plate system) Securos. Titanium

Question 56

What is the minimum number of screws per fragment when using locking plates?

Answer 56

One bicortical and one monocortical
With a plate-rod construct, a lineral increase in axial stiffness can be expected when extra screws are added, up to four monocortical per fragment

Question 57

What is the relation between increasing % of IM canal filling and plate strain for plate-rod constructs?

And with overall construct stiffness?

Answer 57

For every increase of 10% canal filling , plate strain was reduced by approx 20%

Overall construct stiffness increased by 6%, 40% and 78% respectively when rods filled 30%, 40% and 50% respectively

Question 58

What is the recommended % fill of an IM pin when used as part of a plate-rod construct?

Answer 58

35-40%

Question 59

conventional plates

When the type and size of the plate are selected, the weight of the patient, the dimensions of the specific bone, the size of any fragments, the mode of application, and the expected loads must be considered. The AO group has developed guidelines

Answer 59

In the 3.5 mm system, a broad plate was developed for veterinary use that is made from the same bar stock as the 4.5 mm plate (see Figure 41.25D). Because the screw holes are smaller for 3.5 mm screws than for 4.5 mm screws, this plate is stronger than the basic 4.5 mm dynamic compression plate.

The dynamic compression plate is made so that, given a fracture with good bone contact between the major fragments, tightening the screws drives the bone ends together. This further stabilizes the fracture and, if absolute stability is achieved, allows primary bone healing

Question 60

functional application of plates

Answer 60

dynamic compression (laod sharing)

neutralisation (shiled secondary implants from physiooogical loads)

briding via MIO (resists all forces)

butress (resists compressionand shear force in metaphysis)

elastic (increased working length proprtionaml to increase compliance therefore reduce screw pull out in softer bone)

Question 61

complications

Answer 61

nonunion
osteomyelitis
sequestrum
causes: iatrogenic ST truama, disruption of fracture heamatoma, periosteol necrosis, trauma from implants

Question 62

MIO

Answer 62

Multi-fragmentary fractures of the diaphysis and metaphysis are most suitable
for MIFR.

Articular fractures: case-by-case basis but are generally better open

Simple diaphyseal fractures are potential candidates for MIFR, but the advantages over interfragmentary compression in these applications is debatable.

Question 63

MIO principles

whether “open but do not touch” or MIO

Answer 63

diaphyseal alignment is restored via indirect reduction methods the fracture site is left undisturbed

somewhat flexible, rather than rigid, fixation is achieved

longest possible plate that spans these landmarks is selected and precontoured based on radiographs of the intact contralateral bone.

inserted into an epiperiosteal tunnel created by using a blunt instrument

use of intraoperative fluoroscopy

Awareness of “safe” and “unsafe” MIFR zones/corridors
for MIFR implant placement is vital

Question 64

Perceptions of minimally invasive osteosynthesis:
A 2018 survey of orthopedic surgeons
William P. Robinson

Answer 64

Reported advantages
of MIO/MIPO techniques in human and veterinary:
- reduced postoperative pain
- preservation of the fracture hematoma
- improved vascularization of the fracture site
- more rapid healing
- fewer wound complications,
- faster return to normal function compared with open approaches.29,36

Disadvantages
- technical difficulty of the learning process
- longer operating times
- prolonged healing
- fracture malreduction
- radiation safety issues associated with intraoperative fluoroscopy.

Because of the conflicting evidence, Kulkarni et al 36 advocated an individual
approach to each fracture based on a cost/benefit analysis.

Question 65

Mechanical comparison of two small interlocking nails
in torsion using a feline bone surrogate
Marturello

Answer 65

two small angle-stable interlocking
nails (I-Loc and Targon) with that of locking compression plates
(LCP).

We showed that I-Loc nails provided greater torsional stability
than size-matched Targon nails and LCPs.

Question 66

Biomechanical Comparison of Two Conical Coupling
Plate Constructs for Cat Tibial Fracture Stabilization
Sandra L. MacArthur1

Answer 66

The augmented design of the pCCP yielded superior mechanical characteristics
during both non-destructive and destructive testings compared with constructs
employing standard CCP. The more rigid design of the pCCP suggests that this
implant may be better at withstanding greater loads, particularly when applied in a
bridging fashion, during the postoperative convalescence

Question 67

in vivo loads are extremely difficult
to replicate by ex vivo laboratory
quasistatic mechanical testing.
There are two main methods for
‘simplified’ ex vivo testing of locking screw constructs. One
method is ‘screw pushout’ from the plate hole

The second method of ex vivo mechanical testing of locking
screw-plate connections is to apply cantilever-bending
load to the screw engaged in the plate hole with a force
directed perpendicular to the screwlong axis. This

Answer 67

These results of testing by push out and cantilever bending
are not generalizable across different types and manufacturers
of locking bone plates. However, they do suggest
that deliberate off-axis insertion of a locking screw by
five degrees results in about a 50% reduction in screw
push-out strength and cantilever bending of the locking
screws. This reduced strength of a deviated locking screws
with cross threading is probably more than adequate to
maintain construct stability in canine patients, although in
vivo loads experienced by locking plateswith complete cyclic
loading are currently unknown.

Question 68

What Is the Cost of Off-Axis Insertion of Locking
Screws? A Biomechanical Comparison of a
3.5mm Fixed-Angle and 3.5mm Variable-Angle
Stainless Steel Locking Plate Systems
Jakub Kaczmarek 2022

Answer 68

One study published in this issue of the journal reported that the initial
pushout forces of locking screws inserted axially with a torque of 1.5 Nm into 3.5-mm locking compression plates (4,356 266N) and 3.5-mm polyaxial locking plates
(3,992 84 N) were reduced by about half with
five degrees of off-axis insertion.2 The pushout forces for the five degree off-axis screws were increased slightly by tightening the screws to 2.5 Nm.

The 3.5 PLS is more sensitive to the screw insertion angle than to the
insertion torque, whereas the 3.5 LCP is affected by both factors. Placing 3.5 LCP
locking screws off-axis significantly reduces the screw holding strength

Question 69

Biomechanical Comparison of Cortical Lag
Screws and Cortical Position Screws for Their
Generation of Interfragmentary Compression
and Area of Compression in Simulated Lateral
Humeral Condylar Fractures

Fuchter 2023 (chris tan)

Answer 69

Study Design Ex vivo biomechanical study.
Materials and Methods Thirteen pairs of cadaveric humeri

After removal of the fragment forceps, leaving only the cortical
screw (Time point 3: T3), both the interfragmentary compression and area of
compression remain significantly greater in the lag screw group.
Conclusion Lag screws generate a greater force of compression and area of compression
compared with position screws in this mature ovine humeral condylar fracture
model.

preferred option in mature bone; however,
this would require clinical investigation to confirm

Question 70

Biomechanical evaluation of a 4.75-mm and a 5.5-mm
bone anchor at two insertion angles using one and two
strands of suture
Sarah A. Salyer

Answer 70

SAMPLE
48 synthetic bone block samples

Anchors inserted at 45° had a higher maximum load to failure than those inserted at 90°. Constructs with 2 strands
of suture had a greater pullout strength regardless of the direction of pull

The strength of the anchor construct is likely increased with the use of double-loaded anchors inserted at 45°. Clinicians
should consider using 2 strands in clinical cases.

The exact mechanism for increased strength
of the 2-stranded constructs has not been determined.

Question 71

The effect of pearl spacing on single-cycle load-tofailure
and cyclic loading parameters of 2.0 mm
pearl locking plates
P Hyndman 2021 worth

Answer 71

Conclusions: Plate A, which is wider, thicker and has a greater spacing between pearls, was
mechanically superior to Plate B in four-point bending under single-cycle load-to-failure and
sinusoidal cyclic loading.

Clinical relevance: Although mechanical differences were identified in four-point bending, in vivo biomechanical performance remains undetermined.

By selecting Plate B, the clinician may
gain bone purchase through a greater number of pearls and thus screws per unit length,
however, the inferior mechanical characteristics,

Question 72

Biomechanical Comparison of Use of Two
Screws versus Three Screws Per Fragment with
Locking Plate Constructs under Cyclic Loading in
Compression in a Fracture Gap Model
Sophie Palierne 2022

inability to incorporate the effect of fracture biology in vivo.

Answer 72

Results The three-screw constructs were stiffer than the two-screw constructs

and a construct with three
screws per fragment would survive longer than a construct with two screws per fragment.

Due to bending, the lever arm
to the middle of the gap increased with increased working
length causing larger bending moments

Question 74

Retrospective Comparison of Titanium Hybrid
Locking Plate with Stainless Steel Hybrid
Dynamic Compression Plate for Pancarpal
Arthrodesis: 23 Dogs
Wye Li Chong1 2022

Answer 74

Pancarpal arthrodesis was performed with ALPS on 15 limbs from 12 dogs,
and HDCP on 14 limbs from11dogs

Major and minor
complications and surgical site infection rates were not statistically different between
the two groups. Plate fracture occurred in 2/15 ALPS PCA and screw loosening occurred
in 4/14 HDCP PCA. Full function was achieved in 8/12 and 8/11

The use of ALPS offers comparable performance to HDCP for PCA

Question 75

Double-loop cerclage resists greater loads for more cycles
than twist and single-loop cerclage
Lauren Butare-Smith 2022

Answer 75

1.0 mm wire.
Methods: The peak load resisted by each cerclage type was determined
(n = 6).

Conclusion: Double-loop cerclage will be tighter and are better able to resist
cycling than twist or single-loop cerclage.
Clinical significance: Use of double-loop cerclage to stabilize bone fragments or
prevent fissure propagation can be expected to provide greater resistance to loosening
than twist or single-loop cerclage, both initially and with repeated loading.

Question 76

Radiographically confirmed outcomes after fracture repair
with a PLS polyaxial locking system in 40 dogs and cats
Bassanino 2021

Answer 76

retrospective multicenter case series reports the use
of the PLS in 40 fractures in dogs and cats.

All animals achieved radiographic union, and very few complications occurred.

Ancillary fixation was used in 27 of 40 fractures.

We found that 38 of 40 fractures achieved
radiographic union without complications, which is similar to the results of other studies (81%–96.8%) in which other veterinary locking plate systems have been investigated

The use of ancillary fixation in most fractures (27/40) was justified on the basis of findings of a biomechanical study in which LCP had a greater stiffness and bending strength compared with PLS plates

Question 77

Clinical application of the small I-Loc interlocking nail in 30 feline fractures: A prospective study
Marturello 2021

Answer 77

Prospective clinical study.
Sample population: Client-owned cats (n = 29).

Open reduction and minimally invasive techniques were used in 73% and 27% of cases

nails were placed with mean MC fill of ≤50%.

no major complications

had faster healing times (7.2 weeks) than those previously reported and underwent complete functional recovery. In addition, challenging
epimetaphyseal fractures were successfully repaired by using the I-Loc. None of the cats experienced nonunion or other major complication.

Overreduction of the distal femoral fragment was performed to more deeply seat the
I-Loc

Question 78

Influence of wire configuration on resistance to fragment
distraction of tension bands placed in a greater trochanteric
osteotomy model
Thompson 2020

Answer 78

initial tension
and resistance to tensile loads in tension band constructs without the contributions
of Kirschner-wire stabilization.
Study design: Experimental study.
Sample population: A solid brass femur

4 configurations
The Double Loop was the strongest and most stable configuration, generating 2.3 to 3.5 times greater initial tension, maintaining a greater percentage of residual tension under incremental cyclic loads, and resisting 2.0 to 2.4 times greater load before failure at 2 mm. Failure load was highly correlated with initial tension.

creating more tension in a TB construct during tying means that it will resist greater loads
before it begins to loosen

Question 79

Safety and Accuracy of Minimally Invasive Long
Bone Fracture Repair Using a 2.5-mm
Interlocking Nail: A Cadaveric Feline Study
Katrin Nabholz 2019

Answer 79

Neurovascular structures were only damaged at the medial side of the distal humerus (10/32).

We conclude that the TVS can be safely applied percutaneously
to the tibia and with limitations to the femur in normal cadaveric cats without
fluoroscopy. Despite the limitations of a cadaveric study, the high number of
complications is leading us to consider the humerus not safe for the TVS. A learning
curve has to be expected and technical recommendations should be respected to
decrease complications.

Question 80

Biomechanical Comparison of Two Locking Plate
Constructs for the Stabilization of Feline Tibial Fractures
Natasha M. Hottmann 2020

Answer 80

locking compression plate (LCP) and conical coupling plate (CCP)

The LCP constructs were significantly stiffer and stronger than the CCP constructs

Clinical Significance LCP may be a more suitable implant for stabilizing complex
diaphyseal tibial fractures in cats. Additional supplemental fixation should be considered
when using CCP to stabilize unreconstructed diaphyseal tibial fractures in cats.

In previous studies that found no difference, there was no offset maintained between the plate and the bone or bone mode

Question 81

Mechanical Performance of a Polyaxial Locking
Plate and the Influence of Screw Angulation in a
Fracture Gap Model
Jakub Kaczmarek 2020

Answer 81

compare the locking compression plate (LCP)
with polyaxial locking system (PLS) using single cycle to failure 4-point bending test

The PLS plates were on average 30% weaker than LCP plates. Mode of failure
was plate bending in the single cycle to failure tests, and plate breakage in the cyclic
fatigue tests. Neither screw breakage nor loss of the screw–plate interface occurred.

micro-CT showed for both PLS and LCP that there was only partial contact of the screw head
with the plate hole.

PLS offers a durable locking system, even when the screws are placed polyaxially. where polyaxial positioning of a locking screw helps to avoid fissures, joints, other implants or to increase bone purchase

Theweaker bending properties of the PLS comparedwith LCP should be considered during preoperative planning (i.e higher stress such as bridging of a large fracture gap)

The mean amount of the thread connection for the LCP was 28.85% before
and 18.55% after destructive static test. The mean amount of the connection for the
PLS was 16.20% before and 14.55% after destructive static test