Ch 43 - Minimally Invasive Osteosynthesis Flashcards

1
Q

What occurs during the first week after a fracture which is essential for secondary bone healing?

A

Inflammatory response, domintaed by angiogenesis and controled by key factors such as hypoxaemia resulting from local vascular damage, takes place at the fracture site, leading to formation of early fibrocartilaginous callous

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2
Q

List the three main forms of implants used for MIO

A
  • Locking plates
  • Interlocking nail
  • ESF
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3
Q

What is this instrument?
What is the purpose of the hole at the tip?

A
  • Tunneler - for creating the epiperiosteal tunnel for implant placement
  • Hole at tip for used to attach the precontoured bone plate with suture and pull back through tunnel
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4
Q

What additional units may be required in the OR for successful MIO?

A
  • Fluoroscopy
  • Arthroscopy
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5
Q

How is reduction assessed?

A
  • Alignment
  • Apposition
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6
Q

How does traction of a limb assist with alignment?

A

A muscle envelope under distraction exerts concentric (hydraulic) pressure on the shaft, easing fragments into place

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7
Q

What is ligamentotaxis?

A

Closed reduction maneuvers used mostly for the treatment of intra- and/or juxta-articular fractures

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8
Q

What is the broad category of these three instruments?
Name each

A

Distraction devices
- A: Fracture reduction handles (“Joysticks”)
- B: Custom-built distraction frame (2 ESF rings with a tensioned wire with 2 motors)
- C: Purpose-designed distractoes eg “foot-and-ankle distractor”

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9
Q

What is the primary goal of MIO?

A

Restoration of alignment in the sagittal (pre/recurvatum), frontal (varus/valgus) and transverse planes (rotation), as well as restitution of length

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10
Q

What are the 2 options for C-arms?

A

Full sized C-arm
- deliver high energy beams
- Larger field of view (23-33cm)
- Wide accessible space (78cm)

Mini C-arm
- Less powerful
- More maneuverable
- Small field of view (12-15cm)
- Small accessible space (35cm)
- Inneffective when used through a surgery table

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11
Q

What are the ALARA principles?

A

Radition safety principles: As low as reasonably achieveable
- Using lowest amount of radiation possible for quality images
- Proper shielding gear
- Increase distance between personnel and radiation source

Doubling distance between surgeon and x-ray machine decreases exposure by 75%

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12
Q

How does placing the C-arm generator below the table improve radiation safety?

A

Back scattor (can represent 25-40% of the primary beam) will be directed towards the floor rather than towards the upper body of the surgical team

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13
Q

What alternatives can be used in place of a tunneler?

A
  • Closed Metzembaum scissors
  • Freer periosteal elevators
  • The bone plate itself
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14
Q

How can ESF construct stiffness be tailoured?

A
  • Frame type
  • Numer, diameter and material of connecting bars
  • Number, diameter, distribution and working length of the fixation pins
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15
Q

What is the primary biomechanical weakness of an ESF?

A

The pin-bone interface
Pins experience high bending moments and the ensuing deflection results in high stresses at pin-bone interface, which may lead to premature loosening

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16
Q

How can you optimise the longetivty of the pin-bone interface in ESF constructs?

A
  • Short fixation pin working lengths
  • Increased number of fixation pins
  • Large threaded fixation pins (up to 25% bone diameter)
  • Full-pins instead of half-pins
  • Pre-drilling
  • Optimal pin location
  • Hydroxyapetite coating
  • Pins with tapered run-out junction (Duraface, IMEX)
  • Optimal post-op restriction
17
Q

How does changes in angle in monoaxial locking plate systems effect the construct?

A
  • 10degrees off axis decreased push out load and bending force to failure of a 4.5mm LCP by up to 77% and 69% respectively
  • In polyaxial system, appropriate insertion torque is important
18
Q

Which planes of malalignment may severely impede functional recovery?

A
  • Rotational malalignment
  • Varus or valgus malalignment

Sagittal malignment (pro/recurvatum) as well as loss of length tend to be fairly well tolerated

19
Q

What are some anatomical landmarks for alignment of the tibia?

A
  • Tibial crest should be slightly medial to sagittal plane
  • Calcaneus should be slightly lateral to sagittal plane
  • Medial cortex of tibia and tibial crest should be parallel to a virtual line joining the center of the patella to the center of the talus
20
Q

What are four strategies to avoid joint space violation with locking plate MIO?

A
  • Use non-locking screws directed away from the joint
  • Shorter locking screws
  • Bend the plate to angle away from the joint
  • Slightly shorter plate
21
Q

Which bone is at the highest risk of neurovascular trauma during MIO?

A

Humerus
- Radial nerve laterally (aim to place precontoured plate under the brachialis muscle)
- Musculocutaneous, median and ulnar nerves medially (Careful creation of epiperiosteal tunner and slide plate along medial cortex)

22
Q

What steps help to avoid delayed/non unions with MIO?

A
  • Appropriate fracture approximation to avoid large residual gaps
  • Careful epiperiosteal tunneling to avoid stripping
  • Gentle remote reduction
  • Recognition of when it is appropriate to revert to ORIF
23
Q

What is the most common form of implant failure with ORIF and with MIO?

A

ORIF - Fatigue fracture of the plate due to cyclic bending loads
MIO - Fracture of screws. (Due to long working length, plate is under relatively low stress/unit length