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Musculoskeletal > Internal fracture fixation > Flashcards

Internal fracture fixation Flashcards

1
Q

What are the principles of biological osteosynthesis?

A
  1. Indirect reduction techniques
  2. Fracture stabilization using bridging implants
  3. Limited reliance on secondary implants
  4. Limited, if any, use of bone grafts
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2
Q

Describe the various gauge diameters and relative tensile strengths of orthopedic wire

A
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3
Q

What is tensile strength of a wire dependent on?

A

The cross sectional area (pi x radius squared). Therefore small increase in diameter has a significant effect on tensile strength

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4
Q

In how many directions will a hemicerclage counteract forces?

A

One direction only - must decide on direction in which to wrap the wire based on this

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5
Q

How many loops are required for a stable twist knot cerclage?

A

1 - 1.5

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6
Q

What are the general principles of cerclage application?

A

2 or more cerclage, 0.5 a diameter of the bone apart, perfectly reconstructed bony column. If to be used as sole fixation with IM pin must have long oblique fracture 2.5-3 times the diameter of the bone.

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7
Q

The resting tension of cerclage drops below 30N after how much of a collapse in the bony column?

A

1% collapse

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8
Q

How much does pushing a twist knot flat after twisting reduce tension?

A

45-90%

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9
Q

Describe the differences in initial tension and load before loosening for the twist, single loop and double loop cerclage

A
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10
Q

What is the size of the three available K-wires?

A

0.035, 0.045, 0.065 inch corresponding to 0.9, 1.1, 1.6mm

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11
Q

How does the area moment inertia of interlocking nails and orthopedic plates differ?

A

The AMI of interlocking nails is calculated by radius to the fourth power, plates are calculated by thickness to the third power

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12
Q

How much of the medullary cavity is ideally filled with an interlocking nail device?

A

75-80% (avoid going larger than 90% to prevent iatrogenic fracture)

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13
Q

What are the three types of interlocking nail?

A

Regular, angle stable, inverse

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14
Q

What are the main biomechanical differences between the AS-ILN and the regular ILN?

A

AS-ILN eliminates the slack that was experienced with the regular ILN (particularly severe in rotation). Hourglass shape of the AS-ILN also increases the AMI of the implant and reduces stress risers at the implant/bolt interface

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15
Q

What are the primary differences between cortical and cancellous screws?

A

Cortical screws have less pitch (distance between threads) and less depth to threads compared to cancellous screws. This is to increase core diameter to better resist bending forces (less risk of screw pull-out with locking systems)

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16
Q

What determines screw pull-out strength?

A

The diameter of the screw and the strength of the bone

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17
Q

What determines the bending strength of a screw?

A

The core diameter

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18
Q

Ideally how long is an oblique fracture to allow lag screw placement?

A

1.5 times the diameter of the bone

19
Q

What is the optimal tightness of a screw?

A

70% of stripping strength

20
Q

Identify common screw types

A
21
Q

What is generally the weakest point of a conventional plate/screw construct?

A

The shear strength of the bone screw interface

22
Q

What are the different methods of plate application?

A

Compression, neutralization, bridging, buttress (specifically for transcortical defects in metaphyseal regions), elastic plate osteosynthesis

23
Q

How do you calculate the AMI of a screw?

A

Radius to the fourth power

24
Q

How much of the medullary canal should be filled by a IM pin in a plate rod construct?

A

35-40%. One study found a 20% decrease in plate strain with each increase of 10% of canal filling. Greater than 50% canal filling may result in a too-stiff construct that minimizes axial micromotion.

25
Q

What is the minimum number of screws for a locking construct?

A

1 bicortical, 1 monocortical. Third screw if placed close to fracture gap will increase axial stiffness. Fourth screw will increase torsional stiffness regardless of location.

26
Q

What is degree of angulation is possible using the polyaxial locking system?

A

15 degrees

27
Q

According to Butare-Smith 2021 in Vet Surg, which of the following cerclage configurations was best able to resist cyclical loading?
1) Twist
2) Single loop
3) Double loop

A

Double loop cerclage

28
Q

According to Paulick 2021 in Vet Surg, which of the following 2 constructs were least resistant to cyclic loading in a feline ilial fracture model?
1) ALPS-5
2) ALPS-6
3) 2.0 LCP
4) FIXIN 1.9-2.5 series
5) DCP 2.0

A

ALPS-5 and DCP

29
Q

According to Raleigh 2021 in Vet Surg was the biomechanical performance of an interlocking thread screw or buttress thread screw greater in simulated repair of a lateral humeral condyle fracture?

A

The interlocking thread screw had less condylar fragment rotation at failure compared to a buttress lag screw, and resisted greater loads than a positional buttress screw.

30
Q

In a study by Nabholz 2019 in VCOT, when using a Targon interlocking nail, which bone was associated with a high rate of damage to the neurovascular structures during percutaneous placement in a cadaveric model?

A

The humerus. Placement in this bone was not recommended based on this study. Percutaneous placement was safe in the tibia and femur.

31
Q

What 3 miniature locking plate systems used to fixate radial and ulnar fractures in toy breed dogs are shown here?

A
32
Q

What is the locking mechanism of the screws in the conical coupling (FIXIN) plate system?

A

The low-profile stainless steel
CCP has titanium alloy bushings that thread into the screw
holes in the plate. The Morse taper fit design creates the locking
mechanism via friction, micro-welding and elastic deformation
between the bushings and titanium screws

33
Q

What two locking plate systems are depicted in the following image?

A
  1. Polyaxial locking plate system
  2. LCP
34
Q

In a study by Kaczmarek 2020 in VCOT which of the following locking plate systems had the highest mean amount of thread connection?
1) LCP
2) Polyaxial locking system with monoaxial screws
2) Polyaxial locking system with polyaxial screws

In an additional study by the same author in the same year, under biomechanical testing in a fracture gap model were PLS or LCP plates stronger? Did PLS plates with monoaxial or polyaxial screws perform in a similar fashion?

A

LCP had the greatest thread connection, with polyaxial locking systems with polyaxial screws the least.

The LCP was 30% stronger than the PLS plates.

Polyaxial and monoaxial screws in the PLS plate perform in a similar fashion under loading (despite only partial contact of the screw head and plate).

35
Q

What are the currently available polyaxial locking systems, and what degree of screw angulation can be achieved with each?

A

Currently available systems are the PAX (Securos, US), VetLOX (UK) and PLS (Germany).

The PAX and
VetLOX are made of titanium and represent ‘cut-in’ locking
mechanism which allows multi-directional screw insertion
up to 10° off axis. In these systems, sharp threads of the
titanium screws cut into the softer plate.

The PLS system is made of 316 stainless steel which represents ‘point
loading thread-in’ locking mechanism. The PLS plates feature
partially threaded plate holes, which allow maintenance of
the locking mechanism with screws inserted polyaxially up
to 15° off axis. The threads inside the plate hole are in five
positions at regular intervals.

36
Q

What implants are depicted in this image from Bird 2021 in VCOT?

A

Notched head T-plate and LCP

37
Q

How did the biomechanics of the 2.0mm notched head T-plate and 2.0mm LCP differ in a study by Bird 2021 in VCOT?

A

The LCP was stiffer and had less strain than the NHTP.

Increasing the working length of both plates reduced construct stiffness and increased plate strain.

38
Q

In a study by Marturello 2021 in VCOT, which of the following implants had the largest bending compliance and angular deformation when used in a feline surrogate bone model?
1) I-loc 3
2) Targon 2.5
3) LCP 2.0

A

LCP 2.0 (but the Targon implant had the lowest failure moment on testing once implants were removed, which may increase the risk of secondary fracture following implant removal).

39
Q

In a study by Kaczmarek 2022 in VCOT, what was the effect of increased angle of screw insertion on screw push-out strength for both a 3.5 LCP and 3.5 polyaxial locking system?

A

Decreased push-out strength was observed for both systems (although values for the PLS remained well above likely biomechanical loads in vivo).

Increasing screw torque improved push-out strength for the LCP but not PLS.

40
Q

In a study by Palierne 2022 in VCOT, what was the impact of adding an additional locking screw (two v. three bicortical locking screws) in a fracture gap construct?

A

Addition of a third screw increased number of cycles to failure by 13%, and increased load to plastic deformation by 24%.

41
Q

What 3 ESF pins are depicted?

A

Tapered run out, positive profile, and negative profile.

42
Q

In a study by Park 2022 in VCOT, did placement of ESF pins beyond the trans cortex and then reversed back into correct position affect pull-out strength?

A

Yes, for both tapered run out and positive profile pins bidirectional placement was associated with reduced pull-out strengths. No difference was observed for negative profile pins but pull-out strengths were reduced in general.

43
Q

What plating system is depicted here?

A

Liberty Lock polyaxial locking system (allows up to 15 degrees of screw angulation).

44
Q

In a study by Evans 2024 in VCOT, what was the effect on the biomechanical properties of increasing working length on a 2.0mm LCP in a fracture gap model? What was the effect of plate-to-bone offset?

A

Increasing working length resulted in reduced stiffness in bending and torsion, as well as increased strain.

Increased offset reduced torsional but not bending stiffness.

Musculoskeletal (30 decks)

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