Ch 42 ESF

Question 1

What are Duraface pins?

What biomechanical advantages do they have?

Answer 1

Duraface pins are a negative profile pin by IMEX which has a tapered transition from the shaft to the negative profile threads, avoiding the stress-riser seen with a rapid transition

When compared to the corresponding positive-profile pin, they have 55% increase in pin stiffness and an average 54% increase in ultimate pin strength and a 2.3-4.9-fold increase in cyclic fatigue.

Question 2

ESF is MIO

pros (5)?
risks (3)?
cons vs plates (5)?

Answer 2

• closed reduction or OBDNT
• preserve # haematoma and blood supply
• offer relative stability
• reduced soft tissue trauma
• can be easily dyaminised
• can be removed

long term risks:
-infection
stress protection
implant migration/failure

disadvantages compared to plates:
- increase infection risk due to percutaneous
- eccentric pacement, thus increased bending moments on pins
- not last if delayed healing occurs
- pin loosening cause morbidity
- increase owner compliance/nursing care

Question 3

When may the use of a Duraface fixation pin be beneficial?

Answer 3

Stabilisation of smaller segments
Non-load sharing conditions
Biologically compromised bone
Large soft tissue envelope requiring a longer working length

Question 4

Name the following ESF clamps

Answer 4

A - SK clamp (IMEX)

B - TITAN (Securs)

C - Securos U-Clamp (Securos)

Note the two different pin sizes and locations within the Securos clamps

Question 5

List the possible methods of augmentation to increase frame stiffness

Answer 5

1.Articulations (interconnecting bars which do NOT cross the fracture)

2.Diagonals (Interconnecting bars which DO cross the fracture gap)

interconnecting bars resist shear/bending/rotation

3.Combined IM pin-ESF frame (pin should fill no more than 40%) - resist bending

4.Combined interlocking nail-ESF

5.combined plate + ESF

increase stiffness of bars will increase overall contruct strength and redue stress on individual pins thus protect pin-bone interface

Question 6

What is the general rule for sizing of acrylic connecting bars?

Answer 6

The diameter of the acrylic bars should be 2-2.5 times the diameter of the bone, and the diameter of the scrylic bar should be 3-4x that of a comparable stainless steel connecting bar

Question 7

What is vaporization when regarding acrylic connecting bars?

Above what size does vaporization become a concern?

Answer 7

Vaporisation is a consequence of excessive heat produced within larger-diameter acrylic columns, resulting in a vacuum and potential voids within the material that can decrease the density and stiffness of the column

Vaporisation is a concern if acrylic columns are over 25mm

Question 8

List the commercially available veterinary acrylic systems

What is the full set time of these products?

What is the working time of epoxy-resin/putty? What is the full set time

Answer 8

Acrylx (IMEX)
APEF (Innovative Animal Products)
Full set time is 12-15 minutes

Epoxy putty (Knead-It) has a working time of 3-4min and a set time of 10-12 min

Question 9

Management of fractures of the long bones of eight cats using external skeletal fixation and a tied-in intra-medullary pin with a resin-acrylic bar
AJ Worth

Answer 9

eight cats ESF tied-in with resin-acrylic bar
Median time to removal = 7 weeks
versatile and lightweight and allowed highly comminuted non-load-sharing fracture configurations to be stabilised
Failure of the pin/acrylic interface did not occur
greater flexibility for the orientation and placement of fixation pins than allowed by traditional linear bar systems.

Question 10

What are the recommendations for wire size and tension for circular ESF?

Answer 10

Question 11

What is the recommended rate and rhtyhm of distraction osteogenesis?

Answer 11

Rate of 1mm/day

Rhythm of 0.5mm q12hr

Question 12

Distraction Osteogenesis

Answer 12

phenomenon in which bone is induced to form in the space between two bone segments that are pulled apart at a measured rate (Ilizarov)

If drawn apart at a rate of approximately 1 mm per day, bone is regenerated in a process that is histologically similar to active physis.

circular external skeletal fixation frames are uniquely well suited for this type of progressive distraction.

used for:
the correction of angular limb deformities,
to lengthen bone
to transport bone segments across a defect.

After an osteotomy is performed, the bone is left stable over the course of few days. This delay, called the period of latency, is necessary for the formation of a fracture hematoma

Question 13

What is a hybrid ESF?

Answer 13

An ESF with a linear componenet on one side of the fracture and a circular component on the other side of the fracture. Commonly used for juxta-articular fractures

Question 14

What are the safe corridors for the humerus, antebrachium, femur and crus?

Answer 14

Green = safe
Yellow = hazardous
Red = unsafe

Question 15

What is the relationship between the stiffness of a transfixation pin and its length?

Answer 15

The stiffness of a transfixation pin is inversely proportional to its length to the third power

Question 16

How far should the clamps be placed from the skin surface?

Answer 16

1cm

Question 17

What are the principles of pin insertion to preserve the bone-pin interface?

Answer 17

1 - Selection of appropriate pin size - should not exceed 25% the diameter of the bone

2 - Adequate exposure of the bone with retraction of surrounding soft tissues

3 - Predrilling - All pins should be pre-drilled with a drill bit 0.1mm smaller than the core diameter of the pin. Significantly decreased mechanical and thermal injury

4 - Low-speed pin insertion - Drill speeds under 300rpm. This decreased thermal injury while avoiding wobble of the hand-chuck

Question 18

What is the recommended timing for destabilisation when indicated?

Answer 18

Young dogs - 4-6 weeks

Adult dogs - 6 weeks

Older dogs and cats - 8-10 weeks

Question 19

What are dynamisation clamps?

Answer 19

Special clamps which allow the fixation pins to slide along the connecting bar in a controlled form of axial motion during weight bearing to stimulate healing

Question 20

How does a larger connecting bar effect frame biomechanics?

Answer 20

Increases frame stiffness

By increasing stiffness, also decreases load on individual fixation pins

Titanium, aluminium, carbon fibre and acrylic allow for use of larger-diameter and lighter weight frames (titanium is twice as strong as carbon fibre)

Aluminium, titanium and carbon fibre bars are radiolucent

Question 21

Name the following ESF configuration

Answer 21

A: Type Ia (unilateral, uniplanar)

B: Type Ib (unilateral, biplanar)

C: Type I-II hybrid

D: Type II modified (bilateral, uniplanar)

E: Type II (bilateral, uniplanar with all full pins)

F: Type III modified (bilateral, biplanar)

Question 22

Which connecting bars are amenable to contouring?

Answer 22

Acrylic
3.2, 4.8mm stainless steel
6.3mm titanium
Carbon fiber cannot be contoured

Question 23

How does the addition of an ESF to an ILN, change the biomechanics of the ILN?

Answer 23

Decreases torsional compliance by approx 25%
Decreases bending compliance by 60%

Question 24

What materials are used for acrylic bars?

Answer 24

Epoxy resin
Methylmethacrylate
Epoxy resin creates a bond with smooth pins approx 4x stronger than that of methylmethacrylate.

A knurled-pin epoxy resin interface is approx 40% stronger than that of a smooth pin

Question 25

Tensioning of a 1.6mm wire is as strong as what size of pin in cantilever bending?

Answer 25

4mm pin

Question 26

What can be used to allow linear movement of adjacent rings, without changing their relative angles?

Answer 26

Multiple parallel motors or distraction nuts

Question 27

How do wires in a Circular ESF allow axial micromotion?

Answer 27

Initially exhibit low stiffness when first loaded As load increases, there is an exponentially increasing stiffness until it levels off and becomes linear, beyond which point, tensioned wires exhibit similar stiffness to a large-diameter pin This exponential increase occurs over a short distance (less than 1mm), limiting the micromotion within the range of gap strain which can be tolerated for bone healing

Question 28

What are the available options for hybrid connecting bars? What angulation does each allow?

Answer 28

Spherical washers and nuts - 10 degrees C: Hybrid adapter - up to 65 degrees D: VariBall locking hybrid rod (IMEX) - 100 degrees

Question 29

How does adding a second hybrid bar to a hybrid frame effect is biomechanics?

Answer 29

65% increase in stiffness with a diagonal bar 69% increase in stiffness with a diagonal bar and orthogonal fixation pin

Question 30

What are the general rules for pin configuration?

Answer 30

3-4 pins per segment Far pins placed first, followed by near pins and then interpositional pins Place pins ¾ bone diameter away from adjacent joints Place pins ½ bone diameter awat from the fracture line

Question 31

In a comparison of pin insertion with and without predrilling, predrilling was shown to….

Answer 31

Increase pin end-insertional torque by 25% Increase pin pull-out strength by 13.5% Increase in thread contact area of 18% Reduce microstructural damage

Question 32

What is the recommended daily care for ESF?

Answer 32

Cleaning pin tracts with antiseptic solution Monitoring tracts for increasing redness, swelling, discharge or discomfort Checking frame stability Monitoring for changes in gait and lameness

Question 33

What is reverse dynamisation?

Answer 33

Frame components are added during healing to increase frame stiffness and improve fracture stability As callous starts to mature and become mineralised, its tolerance of gap strain decreases

Question 34

What is a critical size bone defect in a feline tibia?

Answer 34

1.5x the diameter of the bone Alternatively, a second surgery can be performed at the time of docking to debride the ends of the bone segments and introduce bone graft

Question 35

complications What can be caused by penetration and tethering of muscle bellies?

Answer 35

Periarticular fibrosis Loss of range of motion Muscle contracture pin/wire loosening and pin/wire breakage. Catastrophic mechanical failure is an uncommon occurrence and is a result of a technical failure Skin irritation occurs when pins are placed near joints (areas of motion) impalement of soft tissues such as muscles and neurovascular structures. synostosis In young small dogs with femur fractures that are stabilized using external skeletal fixation, there is an increased risk for quadriceps femoris muscle contracture if pins are placed through the muscle and tether the quadriceps mechanism.

Question 36

mandibular pins

Question 37

secured pin intramedullary dorsal epoxy resin (SPIDER) frame.

Question 38

young

Answer 38

oung animals have a strong biologic potential for healing, with the thicker periosteum providing a good soft tissue envelope for blood supply and inherent containment and stability of the fracture fragments. External skeletal fixation is well tolerated, and the application of acrylic free-form frames can provide a lighter weight frame for small animals (Figure 42.19). As with any form of stabilization in growing animals, it is crucial to avoid injury to the open physes.

Question 39

Effects of Transfixation Pin Positioning on the Biomechanical Properties of Acrylic External Skeletal Fixators in a Fracture Gap Model Joachim Lahiani 2023

Answer 39

Effects of Transfixation Pin Positioning. 24 Type I acrylic ESF pins were placed centric or eccentric Eccentric pin positioning decreased failure loads by 28% in bending No change in stiffness Conclusion Eccentric position alters the biomechanical properties > frame strength will be optimized if pins are centrally located.

Question 40

Safe corridors for external skeletal fixator pin placement in feline long bones Prackova 2022

Answer 40

humerus proximal craniolateral aspect and on the medial and lateral humeral condyles. antebrachium lateral aspect of the olecranon, the distal two-thirds of the medial antebrachium and the distal third of the lateral antebrachium. femur lateral to and just below the major trochanter, and on the medial and lateral condyles. tibia medial aspect of the entire tibia, the cranial aspect of the proximal tibia on the tibial crest and the area just proximal to the lateral malleolus

Question 41

Description of and complications associated with reinforced, free-form external skeletal fixation for treatment of appendicular fractures in cats: 46 cases (2010–2019) Yeh 2021

Answer 41

reinforced, free-form ESF cats: 46 cases bending the fixation pins and binding temporarily with orthopedic wire for rads prior to PMMA application 43/46 (93%) cats had a successful outcome fixator removal of 8 weeks 26% cats had major (n = 3) or minor (9) complications. 4 factors associated with postop complications: body weight tibial fracture use of a type 2 fixator use of destabilization large retrospective study did not find an association between ESF and postoperative nonunion in cat

Question 42

Transarticular elastic external skeletal fixator correction of a stifle rotational deformity and patellar luxation in a dog Tiffany Chen

Answer 42

External transarticular orthodontic chains connected to ESF pins placed in the femur and tibia were used to gradually correct a 90  stifle rotational deformity, and a transphyseal staple was used to correct left femoral varus.

Question 43

Postoperative Complications Associated with External Skeletal Fixators in Dogs Lee Beever 2018

Answer 43

Retrospective. 97 dogs. ESF complications. ESF complications common and significantly associated with location - overall 69.1% especially tarsus, manus and humerus - superficial pin tract infection 39.2% - implant failure 17.5% - especially tarsus (transarticular frames) - transarticular frame and age → higher risk of complication majority of complications related to implant infection.

Question 44

Stiffness of a type II external skeletal fixator and locking compression plate in a fracture gap model Muro 2021

Answer 44

Stiffness of a type II ESF and locking compression plate Quasi-static four-point bending and axial compression tests. - increased stiffness of the type II ESF in bending and axial compression compared to LCP > evidence this construct should be considered in a comminuted fracturs

Question 45

Sherman 2023 – minimally invasive linear ESF for tibial fractures → 100% radiographic union - complications: 40% overall, 18% pin loosening, 33% pin-tract related - major complications more common with open fracture - mean time to ESF removal: 71 ± 48 days

Question 46

Clinical outcomes of 119 miniature- and toy-breed dogs with 140 distal radial and ulnar fractures repaired with free-form multiplanar type II external skeletal fixation Aikawa 2019

Answer 46

free-form multiplanar Type II for distal radial and ulnar fractures - 100% union at median 60 days, ESF removal at median 89 days - malalignment >10° in 7.8%