Ch 43 - Minimally Invasive Osteosynthesis

Question 1

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

Answer 1

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

Question 2

List the three main forms of implants used for MIO

Answer 2

• Locking plates
• Interlocking nail
• ESF

Question 3

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

Answer 3

• 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

Question 4

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

Answer 4

• Fluoroscopy
• Arthroscopy

Question 5

How is reduction assessed?

Answer 5

• Alignment
• Apposition

Question 6

How does traction of a limb assist with alignment?

Answer 6

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

Question 7

What is ligamentotaxis?

Answer 7

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

Question 8

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

Answer 8

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”

Question 9

What is the primary goal of MIO?

Answer 9

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

Question 10

What are the 2 options for C-arms?

Answer 10

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

Question 11

What are the ALARA principles?

Answer 11

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%

Question 12

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

Answer 12

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

Question 13

What alternatives can be used in place of a tunneler?

Answer 13

• Closed Metzembaum scissors
• Freer periosteal elevators
• The bone plate itself

Question 14

How can ESF construct stiffness be tailoured?

Answer 14

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

Question 15

What is the primary biomechanical weakness of an ESF?

Answer 15

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

Question 16

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

Answer 16

• 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

Question 17

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

Answer 17

• 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

Question 18

Which planes of malalignment may severely impede functional recovery?

Answer 18

• Rotational malalignment
• Varus or valgus malalignment

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

Question 19

What are some anatomical landmarks for alignment of the tibia?

Answer 19

• 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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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)

Question 22

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

Answer 22

• 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

Question 23

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

Answer 23

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