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Musculoskeletal > External skeletal fixation > Flashcards

External skeletal fixation Flashcards

1
Q

What are some advantages/disadvantages of ESF?

A

Advantages: can be applied in a minimally invasive approach, minimal periosteal contact limiting damage to the local vascular supply, implants are removed (preventing long term implant related complications, i.e. irritation, infection, migration).

Disadvantages: increased risk for infection, large bending moments on the fixation pins due to eccentric placement, patient morbidity (pin loosening, pin tract inflammation, implant failure with long-term use).

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2
Q

What types of pin design can be used with an ESF?

A

Smooth, positive profile, negative profile, negative profile with a tapered thread run-out (Duraface)

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3
Q

Name the following implants.

A
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4
Q

How do positive profile pins compare biomechanically to negative profile pins with a tapered thread run out?

A

Tapered run out prevents stress riser while maximizing external shaft diameter. Shown to have increased stiffness, strength and fatigue life compared to positive profile pins

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5
Q

Why are larger ESF pin shaft diameters desirable?

A
  1. Greater resistance to bending or failure with loading.
  2. The larger diameter clamp-pin interface is more stable.
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6
Q

What is the difference between full and half pins?

A

Full pins penetrate soft tissues on both side of the bone with fixation through the centrally threaded portion of the pin.

Half pins penetrate the soft tissues on one side of the bone, with the threaded portion on the end of the pin.

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7
Q

What are the different commercially available ESF connecting clamps?

A

IMEX SK, Securos Titan, and Securos U-clamps. Designed to limit slippage along the connecting bar, slippage of the pin through the clamp, and to resist rotation about the clamp.

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8
Q

Name the following ESF clamps.

A
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9
Q

What is the effect of using a larger connecting bar on the pins?

A

A larger connecting bar results in a stiffer construct. This decreases the load/stress on individual pins (more evenly distributes load) helping to protect the pin/bone interface

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10
Q

What are some lightweight alternatives to stainless steel for use in connecting bars of ESF?

A

Carbon fiber, titanium, aluminium, acrylic. Aluminium, titanium and carbon fiber are also radiolucent.

Carbon fiber bars cannot be contoured.

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11
Q

Are titanium or carbon fiber connecting bars stronger?

A

Titanium are twice as strong as carbon fiber of comparable size.

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12
Q

Describe the different configurations of ESF

A
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13
Q

Name the following ESF configurations.

A
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14
Q

How do you increase the strength/stiffness of an ESF frame?

A

Use a more complex frame design, increased number of fixation pins, increased connecting bar size, augmentation techniques (interconnecting bars, combined frames [combine with IM pin or interlocking nail - may or may not be ‘tied-in’ via a proximal articulartion])

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15
Q

What are the two types of interconnecting bar configurations?

A

Articulations - don’t cross the fracture gap.
Diagonals - do cross the fracture gap.

Diagonals result in greater increases in stability as compared to articulations.

Greater increase in stiffness if the augmentation is fixed to the connecting bar with double clamps as compared to directly to fixation pins.

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16
Q

What type of ESF frame is shown?

A

Type 1B (use of a wide bar allows angulation of pins on either side by up to 35 degrees).

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17
Q

When using an IM-pin ESF construct, what size of IM pin should be used?

A

No more than 40% of the medullary cavity.

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18
Q

What is one potentially negative sequelae of use of a combined IM pin and ESF or interlocking nail and ESF?

A

There is prolonged direct access to the outside environment into the medullary canal and an increased risk of osteomyelitis.

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19
Q

What are two acrylic based compounds that can be used for ESF connecting bar creation?

A

Methylmethacrylate and epoxy resin.

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20
Q

What are some advantages/disadvantages of free-form ESF fixation?

A

Advantages: can be conformed to maximize the use of biologic corridors, placement of pins in numerous planes can increase construct stiffness, lighter frame.

Disadvantage: cannot adjust the apparatus, cannot perform staged disassembly.

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21
Q

What are the general recommendations of acrylic connecting bar stiffness and size?

A

Should be 2-2.5 times the diameter of bone. In order to reach similar stiffness should be 3-4 times the diameter of a comparable stainless steel connecting bar.

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22
Q

What limits the size of an acrylic connecting bar?

A

Once diameters exceed 25mm vaporization can occur. This is a sequelae of excessive heat within the column that can result in vacuum and potential voids. This reduces the density and stiffness of the construct.

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23
Q

What are the biomechanical differences of epoxy resin and methylmethacrylate acrylic connecting bars for ESF application?

A

Epoxy resin is 4 x stiffer but methylM absorbs 6 x the energy prior to failure.

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24
Q

What can be used to increase the stability of the acrylic bar/pin interface in an ESG system?

A

Knurled pins increase the pin-epoxy resin interface strength by 40%. Epoxy resin creates a bond with smooth pins that is almost 4x as strong as with methylmethacrylate. Bending of the pins to act as a rebar may also increase pin purchase.

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25
Q

What are the set times for epoxy resin bars?

A

10-15 minutes

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26
Q

To prevent thermal injury during curing how far should an acrylic bar be positioned from the patient?

A

1cm

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27
Q

Describe the recommendations for wire size and tension based on ESF ring components

A
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28
Q

Describe the components of a ring ESF

A
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29
Q

What are stretch rings and partial rings?

A

ESF rings that are designed to accommodate awkward anatomy.

Stretch rings have an elongated straight segment on either side similar to a horseshoe.

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30
Q

What is the equivalent pin strength of a 1.6mm wire tensioned in a ring ESF?

A

Equivalent to a 4mm pin in strength

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31
Q

In ring ESFs stabilized with fixation wires only, what is the primary determinant of construct stiffness?

A

The ring size.

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32
Q

How do you minimize translation of bone along fixation wires when using a ring ESF?

A
  1. Place the fixation wires as close to 90 degrees to one another as possible (the lower the angle the less resistance to translation).
  2. Use opposing Olive wires
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33
Q

What is a drop wire?

A

Fixation of an additional wire to a circular ESF ring at a distance away from the ring using a post.

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34
Q

Why is combining linear and circular ESF components controversial?

A

The axial micromotion inherent in circular ESF constructs is not compatible with with the stability required to maintain the pin-bone interface of conventional pin fixation (can cause loosening of the linear fixation pins).

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35
Q

What are methods by which ESF rings can be connected to one another?

A
  1. Threaded rods and nuts (allow up to 10 degrees of angulation between components with addition of a spherical washer).
  2. Hinges and motors. Motors can be placed parallel if linear movement is desired (alternatively distraction nuts can be used).
36
Q

How can bone segments be moved in relation to one another using a ring ESF?

A

Can be translated, angled or transported axially

37
Q

What rate of bone movement per day facilitates distraction osteogenesis?

A

1mm per day. Bone is regenerated in the fracture gap in a process similar to an active physis.

38
Q

As it relates to distraction osteogenesis what is the period of latency?

A

The period after the initial osteotomy and the initiation of distraction. This is usually 3-5 days and allows the fracture hematoma to form

39
Q

How do tensioned fine wires in a ring ESF respond to loading?

A

Non-linear stiffness. Initial low stiffness with easy deflection, followed by an exponential increase in stiffness and then linear portion. Linear portion usually reached within 1mm of travel. This allows for axial micromotion.

40
Q

How can the axial micromotion of a ring ESF be reduced?

A

Increased tensioning of wires, larger wires.

41
Q

What are the three methods of attachment of the linear to circular component of a hybrid ESF frame, as shown in the image? How much angulation is permitted with each?

A
  1. Spherical washer: 10 degrees of angulation.
    2: Hybrid adaptor: 65 degrees.
    3: VariBall: 100 degrees.
42
Q

In a hybrid ESF what is the location of the stress riser in the construct?

A

The junction between the linear and hybrid components. Can be reduced by addition of a contoured diagonal or articulation, or by addition of a second linear frame (type IIB).

43
Q

What are the benefits of transarticular ESF fixation over external coaptation?

A

Reduced morbidity associated with muscle atrophy, pressure sores, and limited limb function.

44
Q

What are the three types of transarticular ESF?

A

Rigid (type 1a, triangulated type 1a, type II, circular), hinged, or flexible (use of elastic bands rather than connecting bars).

45
Q

What are the three types of hinges that can be used in hybrid transarticular ESF?

A
  1. Connection of the linear connecting or acrylic bar with the hinge of the circular ESF.
  2. Proprietary joint range of motion hinge.
46
Q

Why is fixation of the stifle with a hinged transarticular ESF challenging?

A

The complex rolling a gliding motion of the stifle joint.

47
Q

What are the biologic disadvantages of using rigid transarticular ESF?

A

If used for greater than 4 weeks can result in arthrosis secondary to joint adhesions, soft tissue contracture, and degenerative articular changes. Can be partially mitigated through use of a hinged trans-articular ESF.

48
Q

Describe the safe soft tissue corridors for ESF placement

A

Corridors are either classified as safe, hazardous or unsafe.

49
Q

How many ESF pins should be placed per segment?

A

4 per segment. Additional pins will increase stiffness but not enough to offset additional morbidity.

50
Q

How far from the fracture and joint should ESF pins be placed?

A

3/4 the bone diameter from joints, 1/2 bone diameter from fracture.

51
Q

What determines the working length of the ESF connecting bar?

A

The distance between the central fixation pins. A far-near-near-far distribution is recommended to reduce stress on the construct.

52
Q

How does the stiffness of the pin relate to its exposed (extracortical) length?

A

Inversely proportional to extracortical length to the 3rd power.

53
Q

How far should clamps be placed from the skin surface?

A

About 1cm - trade-off between reducing working length of fixation pins and allowing post-op care of tracts and for swelling

54
Q

By placing pins on alternating sides of a connecting bar what divergent planar angle can be achieved?

A

Up to 35 degrees (acts like a type 1b fixator)

55
Q

What is the most common cause of weakness or failure of ESF frames?

A

The pin-bone interface.

Thermal necrosis and mechanical damage are common causes.

56
Q

What are the sequelae of failure of the pin-bone interface?

A

Pin loosening, soft tissue irritation, pin drainage, and/or pin tract sepsis.

57
Q

What is pin feed rate?

A

The rate at which the fixation pin advances into bone, and is determined by thread pitch and rotational speed. It is important to apply appropriate axial pressure to prevent interference with feed rate that may lead to cortical stripping.

58
Q

Describe strategies to preserve the pin-bone interface

A
59
Q

What is the maximum recommended size of an ESF fixation pin?

A

25% of the bone diameter (pin holes greater than 30% will weaken the bone a predispose to fracture).

60
Q

Why should predrilling be performed prior to ESF fixation pin placement?

A

The trochar tips of fixation pins do not cut bone efficiently, and do not allow for removal of bone debris during drilling. This results in thermal necrosis.

61
Q

How much does predrilling increase the pin insertional torque and pull-out strength of ESF fixation pins?

A

25% and 13.5%, respectively.

62
Q

What are some disassembly options for an ESF if the surgeon wishes to pursue dynamization?

A
63
Q

At what stage post-operative is dynamization of ESF typically performed?

A

Young dogs: 4-6 weeks.
Adult dogs: 6 weeks
Older dogs and cats: 8-10 weeks

Need to ensure sufficient stability to prevent catastrophic failure.

64
Q

What are dynamization clamps?

A

Clamps that secure pins to the connecting bar of an ESF but that allow sliding along the bar during weight bearing, facilitating controlled micromotion.

65
Q

What is reverse dynamization?

A

The process by which frame components are added during healing to increase frame stiffness and improve fracture stability

66
Q

How far should pins be placed from the physis in immature animals to avoid inadvertent disruption?

A

1 cm or 3 pin diameters

67
Q

What is the ideal location for placement of ESF pins in the humerus?

A

Lateral or craniolateral. Care to avoid the radial nerve at the distolateral one-third of the diaphysis.

68
Q

What is the ideal location for placement of ESF pins in the radius?

A

Medial and craniomedial. Care to avoid the radial nerve at the lateral aspect of the proximal radius.

69
Q

If there is limited bone availability proximally in the radius, how could proximal pin placement be achieved?

A

Placement of a proximal pin in the ulna (mediolateral), relying on the strong soft tissue attachments between the radius and ulna for stability.

70
Q

What is the ideal location for placement of ESF pins in the femur?

A

Lateral and craniolateral aspect of the femur. Care should be taken to place the pins between the quadriceps and biceps femoris muscles to prevent tethering of the quadriceps muscle, resulting in increased morbidity and risk of quadriceps contracture.

71
Q

What is the ideal location for placement of ESF pins in the crus?

A

Craniomedial, can also place cranial but care not to engage the extensor ligaments on the distal tibia.

72
Q

Can ESF fixation pins be placed full thickness across all 4 metabones?

A

Proximally, yes. Distally the metabones assume an arched relationship which limits pin placement to either metabone 2/3, or 4/5.

73
Q

What are options for metabone fixation using an ESF?

A

Circular, free-form acrylic, combined intramedullary pin-ESF (SPIDER frame).

SPIDER frames are reported to improve fracture reduction (compared to modified type 1b or II) with a lower rate of synostosis.

74
Q

Placement of ESF frames are restricted to which aspect of the mandible?

A

Ventral aspect due to the presence of tooth roots (mechanical disadvantage as is the compression side of the bone). Free-form acrylic is preferred as an imperfectly contoured metal connecting bar will result in malocclusion.

75
Q

What type of ESF frames can be used in the mandible?

A

Type 1a and modified type II. Placement of full fixation pins between the mandibular bodies is preferred to increase pin purchase, but this is limited to the rostral portion as caudal full pin placement will result in tethering of soft tissue structures and loss of tongue function.

76
Q

What is the critical size of a bone defect where non-union is likely to occur?

A

1.5 times the bone diameter in the feline tibia (likely to depend on animal species, age, breed and bone location).

77
Q

How many pins should be placed per vertebral body when repairing a vertebral fracture with ESF?

A

2 per vertebral body: one half pin in the cranial vertebral body, and a second contralateral half pin placed caudally.

78
Q

What is the ideal angle of insertion of ESF pins in the vertebral bodies?

A

Typically between 45-60 degrees. May be challenging in the thoracic spine due to interference by the rib heads.

79
Q

Inadvertent penetration of what structures could occur during ESF placement in the vertebral column?

A

Thoracic cavity: azygous, aorta, pleura, lungs.

Abdomen: vena cava.

The psoas muscle reduces the risk of injury when present, extending from the level of the 11th thoracic to fourth lumbar vertebrae. Caudal to the fourth lumbar vertebra it courses laterally toward the less trochanter of the femur.

80
Q

What are the most common complications associated with ESF application?

A

Soft tissue injury (tethering of muscle bellies, peripheral nerve damage), pin tract infection (resulting in pin loosening), construct complications (pin/wire loosening and pin/wire breakage).

81
Q

In a study by Lahiani 2023 in VCOT, did eccentric pin positioning within an acrylic column adversely affect the biomechanical properties of the ESF?

A

Yes, eccentric placement resulted in 28% reduction in bending failure loads.

82
Q

Describe the safe corridors of the humerus for ESF placement in cats as described by Prackova 2022 in JFMS.

A

Craniolateral and medial and lateral humeral condyles.

83
Q

Describe the safe corridors of the antebrachium for ESF placement in cats as described by Prackova 2022 in JFMS.

A

Distal 2/3 of the medial antebrachium, distal 1/3 lateral. Lateral olecranon.

84
Q

Describe the safe corridors of the femur for ESF placement in cats as described by Prackova 2022 in JFMS.

A

Small area just below the greater trochanter, medial and lateral femoral condyles.

85
Q

Describe the safe corridors of the tibia for ESF placement in cats as described by Prackova 2022 in JFMS.

A

Entire medial tibia, cranial aspect of the proximal tibia on the tibial crest, and region just proximal to the lateral malleolus.

86
Q

In a study by Aikawa 2019 in Vet Surg, what was the median time until ESF removal in patients undergoing multiplanar type II ESF repair of distal radial/ulnar fractures? What were four major complications observed?

A

89 days

Premature pin loosening, elbow subluxation, osteomyelitis, and delayed union. Minor complications were observed frequently and were mainly related to the pin tracts.

Musculoskeletal (37 decks)

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