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Tobias Volume I MS > Internal Fx Fixation > Flashcards

Internal Fx Fixation Flashcards

1
Q

Which of the following is true?
• A cerclage wire is considered loose if its tension is less than 40 N
• Vibration during cutting can cause a drop in tension by approximately 12 N
• Collapse of 1% of the diameter of the structure causes the resting tension to drop below 30N
• 3 twists are necessary to maintain adequate knot security

A

C true

A (30)
B (10)
D false, 1.5)

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2
Q

Which of the following is true?
• Kirshner wires and steinmann pins are interchangeable
• Pins resist compression and bending
• When used alone, an IM pin should fill at least 75% of the medullary cavity
o “stacked “ pinning improves rotational stability in theory, not proven

A

D is true

A (False, K-wires are the 3 smallest and steinmann pins are the largest)
B(false, just bending)
C (false, 70% and shouldn’t be used alone…)

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3
Q

Which is true?
• Stability is greater with dynamic cross-pinning than the conventional crossed-pin technique.
• Eccentric implants are exposed to bending forces during axial compression.
• AMI of ILN is πr3/3
• Area moment of inertia influences implant compression strength and stiffness.

A

B true

A (opposite - no proof for rush pinning)
C. AMI of an ILN = πr^4/3??
D. (bending)

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4
Q

What forces does the locking mechanism of the interlocking nail counteract?

A

• Stability in torsion and compression

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5
Q

Which ILN system had high concern for bending/breaking?

A

• first-generation regular interlocking nails

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6
Q

Which of the following is FALSE regarding interlocking nails?
• In older ILN implants, rotational instability may be responsible for 14% nonhealing rate
• Using an ILN in dynamic mode requires that axial load sharing is possible
• Reaming is always recommended for an ILN because it allows for larger nail placement
• A 6mm nail is appropriate for dogs between 15 and 30 kgs

A

C (controversial- nonreaming allows preservation of meduallary blood supply, associated with less infection and fat embolism, and histologically more rapid healing times)

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7
Q

Which of the following is correct in regards to placement fo ILN?
• Placing the locking device furthest from the nail/alignment guide should be first to add stability to the guide system
• The only bones that can have an ILN include the femur, humerus, radius, and tibia
• Overall success of fracture healing with various types of ILN are 83-96%
• If the most distal hole is not placed correctly, the dynamization helps speed fracture healing

A

C

A(CLOSEST)
B(NOT radius, yes ulna)
D (premature dynamization results in instability, and delayed union or non-union.

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8
Q

What is the recommended % nail filling of the medullary diameter in order to limit stress shielding?

A

(75%)

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9
Q

True or False?

• Screws intended for dense cortical bone have a finer pitch compared to those intended for cancellous bone

A

True

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10
Q

How far beyond the far cortex should a cutting screw be placed to ensure the cutting flute passes completely through the bone?

A

• 2mm

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11
Q 
The bending strength of a screw is determined by the...?
•	A. Region of purchase
•	B. Core diameter
•	C. Outer diameter
•	D. Shaft diameter
A

B core diameter

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12
Q

If the length of the fracture line is less than __ times the diameter of the bone, it is difficult to place a lag screw

A

• 1.5 times

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13
Q

Improvements with the limited contact dynamic compression plate?

A

• Scalloped plate means stress is not concentrated at the screw holes and less effects on vascularity.

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14
Q 
What is FALSE regarding reconstruction plates?
 A. Considerably weaker than DCP
B. Available in 2.0, 2.7, and 3.5 sizes
C. Can be contoured in 4 directions 
D. Made of softer steel
A

C (only 3 directions)

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15
Q

What is false regarding cuttable plates?
A. Holes are designed to produce compression
B. Plates can be stacked for increased stiffness
C. Available in 2 plate sizes, 1.5 and 2.0 sizes
D. Available in 50 hole lengths and are cut to size

A

A false

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16
Q

What force do plates NOT resist?

a. Tension
b. Compression
c. Bending
d. Rotational

A

C bending

17
Q 
A plate used in conjunction with a lag screw for an oblique fracture is called what?
•	a.    Neuralization plate
•	b.      Buttress plate
•	c.      Compression plate
•	d.      Dynamic plate
A

A neutralization

18
Q

What is false regarding bone plating?

a. It is best to place the plate on the tension side of the bone
b. When performing compression plating, prestressing a plate puts a convexity centered over the fracture
c. The area of moment of inertia are weakest around the screw hole
d. One cuttable plate is the same strength clinically as stack plating

A

D

19
Q

Which of the following is true?
• During weight bearing, axial forces are converted to tension forces
• The shear interface between the plate and screw is the weak point in a conventional plate-screw-bone construct
• Buttress osteosynthesis is where larger segments of bone are spanned without affecting the fracture itself
• The ability of conventional plates and screws to resist bending loads is related to the bending stiffness of the plate and the resistance of screws to axial pull-out

A

D is true

A (false, shear)
B (false, screw bone interface)
C (false, bridging)

20
Q

Which of the following regarding locking implants is true?
• They must be contoured to the bone, thereby affecting the periosteal blood supply
• The biomechanics of a locking plate/screw construct is more similar to other plate/screw constructs than external skeletal fixators
• Locking implants are angle stable, with this the shear forces caused by axial loading is subsequently converted to compression
• Guidelines for locking implant placement include spanning long segments of bone (2× the length of the fractured segment), limiting the screw-to-hole ratio to less than 0.5, and leaving at least three to four screw holes empty over the bone defect

A

C is true

A false
B (false, ESF more so)
D (span segments of bone >3x with leaving 2-3 screw holes empty)

21
Q 
Locking compression plate locking screws have a unique StarDrive head rather than hexagonal one. How much more insertional torque is created with this?
•	25%
•	35%
•	65%
•	85%
A

65%

22
Q

Which of the following statements is true?
• Neutralization mode can be used in combination with cerclage wires to resist axial compression
• Buttress plating should be anchored to the smaller metaphyseal fragment and contoured to the main stable fragment to minimize displacement
• Elastic plate osteosynthesis is for patients that are past their most rapid phase of growth
• Elastic plate osteosynthesis is beneficial because small plates permit plastic deformation

A

A is true

B Buttress plating should be anchored to main stable fragment and contoured to the smaller metaphyseal fragment
C (< 5-6 months of age)
D (plastic deformation leads to implant failure, the increased compliance is beneficial for early callus formation, and it allows preservation of the periosteum)

23
Q 
Which of the following is  NOT a characteristic of bridge plating?
•	High plate bridging ratio
•	High plate span ratio
•	Low plate screw density 
•	Screw density between 0.4-0.5
A

B LOW plate span ratio

24
Q

What is the recommendation for plate span ratio in bridge plating of comminuted fracture? ___
For simple fractures ? ___

A

2-3

8-10

25
Q

In a Plate-rod construct what forces does the plate counteract?__ How much shoudl the IM pin fill?___
How many screw purchases?__

A

• plate: compression (axial collapse) and rotation
• 35-40% for IM filling
Cortices 4 on each side

26
Q

What is the equation for tensile strength of wire?

A

■ Pie x radius^2

27
Q

What is false regarding wire?
■ A. Composed of 316L stainless steel
■ B. Cerclage can be used for fixation of short and long oblique fractures
■ C. Hemicerclage wire can never be used as a primary fixation
■ D. Tension bands convert the tensile force into compression force

A

■ B. Cerclage can be used for fixation of short and long oblique fractures

28
Q 
○     What fractures are not appropriate for anatomic reconstruction?
■     A. Long oblique
■     B. Butterfly fragment fracture
■     C. Articular fracture
■     D. Severely comminuted fracture
A

D

29
Q

What type of fracture configuration is most appropriate for cerclage wiring?

a. Short oblique
b. Long oblique
c. Metaphyseal fractures
d. Spiral fractures

A

B

30
Q

What is the minimum recommended number of twists

a. 1 twist
b. 1.5 twists
c. 2 twists
d. 3 twists

A

1 twist…

31
Q

What is true regarding twist knots and loop knots?

a. Twists knots are superior in regards to peak load resisted
b. A twist knot loosens by unbending
c. A loop knot reaches peak on a load vs deformation curve with a large amount of deformation
d. Loops should have at least 1 twists when making your own loop knot

A

A true

B (untwisting, duh)
C small amount of deformation
D (1.5 twists)

32
Q

Which of the following is true?
A A cerclage wire is considered loose if its tension is less than 40 N
B Vibration during cutting can cause a drop in tension by approximately 12 N
C Collapse of 1% of the diameter of the structure causes the resting tension to drop below 30N
D 3 twists are necessary to maintain adequate knot security

A

C is true

A (30)
B (10)
D (false, 1.5)

33
Q

Which of the following is true?
A. Kirshner wires and steinmann pins are interchangeable
B. Pins resist compression and bending
C. When used alone, an IM pin should fill at least 75% of the medullary cavity
D “stacked “ pinning improves rotational stability

A

D true
A (False, K-wires are the 3 smallest and steinmann pins are the largest)
B (false, just bending)
C (false, 70% and shouldn’t be used alone…)

34
Q

How much compression with a 3.5 dcp?

A

1mm

35
Q

How much compression with a 2.7 dcp

A

0.8mm

Gold guide gives you a Gold star for compression :D

Tobias Volume I MS (16 decks)

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