1. Principles of external fixation
AOTrauma External Fixation Education Working Group (February 2018):
Main author: Dankward Hoentzsch (Germany)
Reviewers and contributors: J Spence Reid (US), Vajara Phiphobmongkol (Thailand), Andrey Volna (Russia)
AOTrauma External Fixation Working Group (February 2018)

2. Learning objectives Describe the types of external fixators
Describe the indications for external fixation
Explain the “spectrum of stability” that can be achieved
Describe how to determine the stability of the frame by the method of construction
Describe how a modular frame is constructed and used to reduce and stabilize a fracture
Explain how to place anatomically safe and stable pins in the tibia

3. Types of external fixation
Monolateral fixator
Ring fixator
Types of external fixation:
Modular, a versatile pin clamp system: with pin or screws; tubes or rods: 4, 6, and 11 mm versatile. Unilateral but V shape or bilateral possible and more construction possible
Monotube systems: Clamps with defined pin placement connected with one large tube/ “body“ (monotube)
Ring: tensioned wires on a full or partial ring, pins are possible; mixture between wires and pins (recommended today)
Some name it hybrid because of the mixture of wires and pins:
Hybrid: official name for the mixture between unilateral and full or mostly partial rings (also referred to as Combination)
Hexapod: between rings are 6 oblique rods named struts, which can be lengthened and shortened. Technique well known with flight simulators. Known under the name “Taylor frame” from first medical use.

4. Why external fixation? Minimally invasive—protects the local biology
Damage control—can be quick to apply
Easy
Anywhere, any time, by anyone
Wide range of indications
Very successful outcome for management of fractures and soft-tissue handling
Good result if done properly
With “easy” we mean – easy to apply or to handle, forgiving (no second surgery required if changes are necessary), no internal surgery (external manipulation) , minimal invasive, short learning curve etc.

5. Why not external fixation?
Risk of pin infection
No or minimal experience with method
Equipment unavailable
Uncomfortable for the patient
Managing the patient in an external fixator can be challenging

6. 1. Modular system Any limb Any joint
Partial frames for each main fragment
then
Reduction and fixation/stabilization with third rod
The modular system can be applied anywhere—for an individual bone fracture or for joint bridging fractures.
First, two pins are inserted in each segment of the fractured bone. In each segment, a rod will be fixed with clamps parallel to the bone segment. This is repeated for the other segment. The clamps in these partial constructs must be fixed very well. Often this is forgotten (it is extremely important to teach this).
Finally a third rod will be loosely fixed (once again with clamps) from rod to rod.
Now you can use these partial frames as a handle to reduce the fracture and or joint with any maneuver and ligamentotaxis.
Once the reduction is performed the clamps of the third rod will be tightened so that the fracture is fixed.
This method should be used from the beginning, not as a salvage procedure.
And very important: this is the “AO recommended method”, evaluated and recommended by all experts in this field and the Expert Group.

7. Corrective procedures
2. Monotube system
Corrective procedures
Lengthening of shortened limbs
Segmental bone transport
Correction of simple deformities
Corrective procedures can be performed in order to perform:
Lengthening of shortened limbs
Segmental bone transport (in this case as mentioned up to 6 cm)
Correction of simple deformities

8. 3. Ring/Ilizarov system
Corrective procedures can be performed in order to perform:
Lengthening of shortened limbs
Correction of rotational deformities
Segmental bone transport (in this case as mentioned up to 6 cm)

9. 4. Combination system Combined use of Periarticular fractures
Partial ring or full ring with
Unilateral system
Periarticular fractures
Secondary procedures (eg, septic cases)
Alone
In combination with other implants
Hybrid fixators refer to combinations of 2 types of fixator, such as a half ring fixator plus unilateral external fixation systems.

10. 5. Hexapod system
Ring fixation system that uses six angled struts to provide six axes of movement between bone segments
Allows correction of complex deformity
Requires computer assisted manipulations to guide strut adjustments
Sometimes the Hexapod system is called “Taylor Frame”

11. Indications for external fixation
Fractures with soft-tissue damage
Polytrauma—damage control surgery
Skeletal infection
Corrective surgery (deformity or nonunion)
Definitive fracture care (pediatric and adult patients)
The external fixator can be used for many reasons and in many ways.
The two areas in which the fixator is used are traumatology and elective orthopedic surgery.
In this presentation only use of the external fixator in traumatology will be discussed.

12. Indications Fractures with soft-tissue damage
Indications for external fixation are fractures with severe soft-tissue damage:
Closed fractures with soft-tissue compromise
Open fractures with soft-tissue wounds
Closed fractures with soft-tissue compromise
Open fractures with soft-tissue wound

13. Indications Polytrauma—damage control Multiple fractures…
In a polytrauma, the external fixator has to be applied as fast as possible to stabilize the patient and save life and limb.
A polytrauma patient is often treated in different stages:
Application of (an) external fixator(s)
The definitive treatment is done later depending on the condition of the patient.
Multiple fractures…
…often resulting from road traffic accidents

14. Indications Infection When the wound, bone and/or implant is infected:
Debridement will remove all dead and infected tissue—including bone
Remove or reduce all implants
The fracture will then be stabilized temporarily by external fixation
Final osteosynthesis is done later, once the infection is cured

15. Indications Corrective surgery Limb lengthening
segment transport with callus distraction
EX Fix can be used for
Corrections,
Limb lengthening
Segment transport
with callus distraction or modulation (called Ilizarov technique)
One example:
Limb lengthening with callus distraction
6.5 cm can be achieved to restore the full length of the limb (2.5 plus 4.0 cm)
But this should not be a topic of focus for this lecture.
2.5
4.0

16. Indications V. Definitive fracture care
In children: avoid second operation for removal
Soft-tissue complication: cannot use cast
Avoid epiphyseal plate
Indications
V. Definitive fracture care
In this case with a child a single tube has achieved a good reduction and the single rod was stable enough.
This picture only shows that it is possible, however, the modular technique is not the only solution.
The AO and AO EX FIX groups recommend in this case for you to use a modular system.

17. Spectrum of external fixation stability
Damage control (optimize soft tissue)
Motion at Fracture (Strain)
Relative stability
Temporary – fracture healing not intended:
DCO: within a bone segment and across joints
Position a joint after internal fixation
Definitive application for fracture union:
Achieve relative stability in a fracture setting
Protection of a lag screw
Achieve primary bone healing via compression
Create bone via distraction osteogenesis
Absolute
stability
Stiffness of bone-frame construct

18. Stiffness of external fixator
Distance between tube (ring) and bone
Number of tubes (rings and threaded rods or struts)
Separation of tubes (rings) from each other
Number and diameter of pins (very relevant)
Relationship between pins and the fracture and between pins themselves
The system configuration
The surgeon cannot manipulate all parameters.
The distance from tube to bone is limited by soft tissue, eg, femur or not too near the skin because of secondary swelling and/or dressing.
Diameter of pins is very relevant and not well known. Do not forget the 6 mm Schanz screws, especially for the femur and pelvis & for heavy patients: see the next slides
Stiffness of bone-frame construct

19. Stiffness µ (diameter)4
Frame stiffness: pins
Pin diameter
The larger the diameter of the pin, the greater the stiffness
Stiffness µ (diameter)4

20. Frame stiffness: pins Stiffness ratio: pin diameters
4 mm vs 5 mm 1: 2.44
4 mm vs 6 mm 1: 5.06
5 mm vs 6 mm 1: 2.07
6 mm pin is more than twice as stiff as a 5 mm pin
256/625 = 2.44

21. Factors influencing stiffness of construct
Diameter and number of rods
Distance
between clamps, rods and bone
Distance
between pins and fracture site
Distance
between pins in a fragment
Diameter of screws
Go through all of the factors.
Here, it is shown firstly with the modular technique because you should learn this recommended method.
The factors are independent of the frame—modular or conventional (old one tube system).
Holding strength in bone

22. Factors influencing stiffness of construct
Additional rod
Distance
between clamps, rods and bone
Distance
between pins and fracture site
Distance
between pins in a fragment
Diameter of screws
Go through all of the factors.
Here, it is shown firstly with the modular technique because you should learn this recommended method.
The factors are independent of the frame—modular or conventional (old one tube system).
Holding strength in bone

23. Modular external fixation recommended
The modular external fixation technique is recommended by the AO for reduction and stabilization
Detailed poster available
Animations of the previous few slides are also available

24. Modular technique Pin insertion Fix rods/tubes to pins
Create a “partial” frame for each main fragment
Tighten all clamps very well
Apply third rod using two rod-to-rod clamps, yet loosely
Reduce fracture
Tighten clamps
Mount the third short rod using two tube-to-tube clamps: leave the two tube-to-tube clamps loose.
The fracture is then reduced and finally fixed by tightening the nuts.

25. Modular technique
The modular method allows the external fixator to become a reduction tool
Now we want to explain the “MODULAR TECHNIQUE”
This is the key point of this lecture—this is the first choice!
Proven and recommended by
AO TK
AO EX FIX Experts and Experts Group
AO Principles book 3rd and next 4th editions.
This is the “AO recommended method”, evaluated and recommended by all experts in this field and the Expert groups.

26. Modular technique Why use a technique with three rods?
Gentle fracture reduction is performed in a second step
The fixator becomes a gentle, efficient fracture reduction tool
The modular technique with three rods allows the first two rods to be attached, one to each fragment, and when the reduction has been gained, the third rod locks the first two in that position.

27. Additional neutralization rod
Modular technique
Even with the modular technique, a “second rod” is possible if greater stability/neutralization of forces is required
Add additional rod
The modular technique with 3 rods allows the first two rods to be attached, one to each fragment, and when the reduction has bee gained, the third rod locks the first two in that position.
Even with the modular technique an “additional neutralisation rod” is possible.
If more stability/neutralization of forces is required, add an additional rod.
Additional neutralization rod

28. Modular technique Pin insertion independent of fracture reduction
Safe position of pins in tibial midshaft
Avoid tethering soft tissue
Less pain, better pins
Insert two pins on the proximal and distal parts of the bone in the safe zones.

29. Schanz screws placement in diaphyseal bone
The bicortical pin placement is very important.
When the tip of the pin is not fixed in the far cortex the pin can dangle.
Conventional: penetrate the far cortex 1–6 mm
Self-drilling in the cortex but not penetrating—why? The self-drilling tip is very sharp and dangerous.
No!
Conventional bicortical
Self-drilling

30. Schanz screws/half pins AO principles: example, tibial safe zones
Must avoid anatomical structures
Avoid tethering soft tissue
Less pain
Fewer pin-track infections
For the safe and recommended zones for the pins, look at the different instructions.
In this basic lecture it is not possible to teach all, only the tibia, as a main indication can be shown with one or two pictures.

31. Polytrauma—damage control external fixation
An example of polytrauma with femur, tibia and ankle fractures.
Treated with damage control external fixation.
The modular technique has been used for the femur.
The modular technique was used for reduction and fixation.
The basic construct was completed with an additional rod for neutralization. This rod can be curved, like in this example.
Similarly the modular technique has been used on the tibia and ankle bridging.
With external fixation in place initial physiotherapy can be done in the intensive care unit.

32. Postoperative care to prevent pin infection Controversial—no clear consensus
Removal of crusts
Saline or disinfectant solution
Cleaning
The goal is to remove any debris, such as crusts or exudates.
There is no evidence to suggest how best to do this.
Less is more.

33. Take-home messages External fixators have broad indications
Many types of fixators are available with specific functions
The stability of a fixator is surgeon-controlled
The modular technique is the standard for damage control applications
Technique and location of pin placement is important to minimize infection and pain