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

Key success of MIO = preservation of the early fracture hematoma as well as blood supply to the fracture site.

Experimental studies: sparing the early fracture hematoma and local blood supply is crucial to enhancing callus formation, maturation, and remodeling.

surgical cleansing of the hematoma in rats significantly decreased callus biomechanical properties 4 weeks following fracture stabilization

Answer 2

Preservation of the biology of the fracture site is a hallmark of minimally invasive osteosynthesis procedures. This implies that the external forces used during reduction maneuvers must be applied indirectly, away from the fracture site.

emphasis placed on restoration of anatomic realignment rather than anatomic reconstruction

Question 3

List the three main forms of implants used for MIO

Answer 3

Locking plates
ILN
ESF

Question 4

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

Answer 4

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 5

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

Answer 5

Fluoroscopy
Arthroscopy

Question 6

How is reduction assessed?

Answer 6

Alignment (of joints)

Apposition (of fragments)

Question 7

How does traction of a limb assist with alignment?

mechanical principle underlying indirect reduction is distraction.

Answer 7

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

Question 8

What is ligamentotaxis?

Answer 8

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

Question 9

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

Answer 9

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 10

What is the primary goal of MIO?

Answer 10

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

Question 11

What are the 2 options for C-arms?

Answer 11

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 12

What are the ALARA principles?

Answer 12

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 13

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

Answer 13

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 14

What alternatives can be used in place of a tunneler?

Answer 14

Closed Metzembaum scissors
Freer periosteal elevators
The bone plate itself

Question 15

How can ESF construct stiffness be tailoured?

Answer 15

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

Question 16

What is the primary biomechanical weakness of an ESF?

Answer 16

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 17

How can you optimise the longetivty of the pin-bone interface in ESF constructs? (9)

Answer 17

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 18

locking plates in MIO

Answer 18

safe use of monocortical screws
> reduced working length in thin cortex may jeopardize construct stability, bicortical recommended

high plate/bone ratio). Two to three locking screws (minimum of three cortices) per fragment

location of the two innermost screws determines the plate working length. Longer plate working lengths result in greater construct compliance, which may be desirable (elastic fixation in immature bones8) or deleterious if resulting in excessive interfragmentary strain or plastic deformation of the plate

Ahmad et al.
2 mm between the cis-cortex and a 4.5 mm (LCP) had little effect on construct strength, > 5 mm significantly increases the risk of plate failure.
When an appropriate plate-bone gap achieved, the mechanical behavior is similar to conventional plates. Therefore, guidelines used for conventional plating can be followed to determine optimal locking plate sizes.

Question 19

pros of locking vs DCP

Answer 19

LP similar to ESF = “internal fixators.”
Compared to ESF, the epiperiosteal location of the plate results in a significant decrease in the bending moment on the locking screws. This in turn spares the screw-bone interface from excessive stresses.

advantages
angle-stable screw-plate interface, frictional forces not needed, and anatomic contouring of the plate is not required for construct stability.

preserves the periosteal blood supply underneath the plate.

Question 20

pros of ILN

Answer 20

interlocking nails, unlike bone plates, are particularly effective in preventing malalignment in the sagittal and frontal (coronal) planes

Question 21

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

Answer 21

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 22

Which planes of malalignment may severely impede functional recovery?

Answer 22

Rotational malalignment
Varus or valgus malalignment
Sagittal malignment (pro/recurvatum) as well as loss of length tend to be fairly well tolerated

Question 23

What are some anatomical landmarks for alignment of the tibia?

radius?

Answer 23

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

With fractures of the radius and ulna, the humeral epicondyles are identified in relation to the orientation of the flexed manus

Question 24

distal limb alignment

Answer 24

Generally, flexion of the elbow and radiocarpal joints or stifle and talocrural joints will facilitate visualization of the sagittal planes

normal relationship between external anatomical landmarks

Question 25

proximial limb alignment

femur?

humerus?

Answer 25

Reliance on intraoperative imaging

ensuring that the distal part of the arciform crest that extends from the greater trochanter to the third trochanter, and serves as part of the origin of the vastus lateralis muscle, remains in a lateral position, using the femoral trochlea as the distal landmark

greater tubercle and/or position of the intertubercular groove in relation to the humeral epicondyles

Question 26

complications with MIO (6)

Answer 26

malalignment

joint space violation

neurovascular injury

delayed/nonunion

impland failure

convernsion to open technique

Question 27

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

Answer 27

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 28

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

Answer 28

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)

Because the lateral, medial, and cranial surfaces of the femur, tibia, and radius, respectively, are used for plate application and are free of significant neurovascular structures,

Question 29

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

Answer 29

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

Clinical studies have suggested that the incidence of delayed union and nonunion has decreased with the implementation of minimally invasive osteosynthesis

Question 30

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

Answer 30

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

Question 31

Development of a novel fracture fragment stabilization
system for minimally invasive osteosynthesis and in vitro
comparison to traditional Kern bone reduction forceps
von Pfeil 2020

Answer 31

Study design: In vitro experimental study.

The SMH was more difficult and took longer to assemble (P = .031 and P = .008); SMH resulted in a smaller final reduction gap

may be helpful for maintaining reduction of femoral fractures in dogs.

Question 32

Perceptions of minimally invasive osteosynthesis:
A 2018 survey of orthopedic surgeons
William P. Robinson

Answer 32

250

only 16% of respondents reported that they performed MIO regularly

Tibial fractures were most commonly selected for MIO/MIPO stabilization
techniques in both cats and dogs. Challenges in achieving adequate fracture reduction
were identified as the greatest limitations

The results of our survey provide evidence that, despite the
benefits of MIO and MIPO compared with more traditional fracture stabilization
approaches, significant barriers must be overcome before the techniques are likely
to be more widely adopted.