Slide 35 References Tornetta P. Rockwood and Green's fractures in adults. Philadelphia: Wolters Kluwer; 2020. Buckley R, Moran C, Apivatthakakul T. AO principles of fracture management. Davos Platz, Switzerland: AO Foundation; 2017.

1. PRINCIPLES OF EXTERNAL
FIXATION
Presenter: Dr Mohamoud A Mohamed
OT Resident MUHAS
Moderator: Dr Billy Haonga
Senior Lecturer/Consultant OT surgeon
11-02-2020

2. Outline
1. Indications of Ex-fix
2. Components, Principles and Biomechanincs of Ex-fix
3. Construct designs
4. Anatomical Considerations
5. Pin-site Care/Pin-site Infection
6. Ex-fix Reuse

3. External Fixator is a surgical device used to
stabilize bone and soft tissues at a distance from
the operative or injury focus.

4. History
• The concept of Ex-fixation dates back to 2400 years.
• Use of Ex-fix mentioned before the invention of POP cast.
• Earliest recognizable ex-fix by Malgaigne 1840.
• Ex-fix has being evolving over time and gained acceptance because of
improving pin design and frame biomechanics.
• the first AO fixator was designed by M.E. Muller in 1952.

5. Indications
• Open fractures
• Closed fractures with severe soft tissue injury
• polytrauma - DCO
• Articular fractures
• Bone or Soft tissue loss

6. Advantages
• Less damage to the bone blood supply
• Rapid application
• Stabilization of open and contaminated fractures
• Adjustment of fracture reduction and stability without surgery
• Minimal foreign body in the presence of infection
• Less experience and surgical skill required than ORIF
• Bone transport and deformity correction possible

8. Component, Principles AND Biomechanics
PINS
Types
• Schanz screws (half pins)
• Steinman pins (Transosseos/Transfixation pins)
Biomechanics And Principles
• Pin bending strength is increased to the 4th power of the increase in
the pin’s radius.
• Decreased pin stiffness causes increased stress at the pin-bone
interface, leading to micromotion and ultimate pin failure.

9. Component, Principles AND Biomechanics
PINS
• The pin <1/3 diameter to avoid
substantial stress riser that leads
to a possible fracture.
• hydroxyapatite-coated pins
provide a significantly improved
pin bone interface and a greater
extraction torque.

10. PINS
• The weakest point of a pin is the
thread-shank junction, which
forms a large stress riser.
• The shank should be buried into
the proximal cortex, doubling
the pin’s stiffness. In addition,
soft tissues become less irritated
.

11. Component, Principles AND Biomechanics
PINS
• Two pins must be inserted into each main fragment through an
anatomical safe zone.
• Pins should be spread as wide apart as possible.
• If the soft-tissue allows, pins are inserted as close to the fracture
focus as possible. avioid hematoma or degloved areas.
• If delayed internal fixation is planned, the pins should avoid potential
incisions and surgical approaches (the zone of surgery).

13. PINS
Insertion Techniques
• Know the anatomy and avoid nerves, vessels, and tendons
• Avoid the fracture focus, hematoma, degloved, contused skin and
joints.
• Insert a Schanz screw of the correct length to allow appropriate frame
construction.
• Adequate skin incision, spreading tissues to bone, using cannulation
during drill/pin insertion with the use of protective sleeves, and
stabilizing soft tissues around the pin to prevent motion (results local
infa/infe).

14. PINS
Insertion Techniques
• Predrill the cortex to avoid burning the bone (ring sequestrum is produced)
• predrilling before manual pin insertion lowered temperatures by more than
half (Mathews et al)
• Thermal damage to bone play a potential role in pin loosening.
• Irreversible changes, including osteocyte death and alkaline phosphatase
inactivation, are seen at temp of 50C.
• Methods to decrease temperatures during pin insertion include predrilling,
irrigation, and power insertion of the pin.

15. PINS
Insertion Techniques
• Self-drilling, self-tapping pins allows for the advancement speed of
the pin. However, 22% reduction in bone purchase of self-drilling pins
compared with predrilled pins has been observed. (Seitz et al)
{ stripping of the near cortex when the cutting tip hits the far cortex}

16. Component, Principles AND Biomechanics
BARS
• Sidebars, or rods, form the link between bony fragments
Types
• Aluminum alloy
• Stainless steel
• Carbon fiber rods
Biomechanics And Principles
• Carbon fiber rods are 15% stiffer in loading to failure.
• However, 85% stiff when used in ex-fix compared to stainless steel.
• Reason; Clamp tightening to carbon rods is less effective.

17. BARS
Biomechanics And Principles
• Distance of the longitudinal connecting tube/bar from the bone:
closer means stiffer
• Number of bars/tubes: two are stiffer than one.

18. Component, Principles AND Biomechanics
CLAMPS
Types
• Simple (ie, single) clamps connect one pin to a rod
• Modular (ie, universal) clamps allow multiple pins to be connected to a rod.
Biomechanics
• Modular clamps, there is the possibility of uneven holding strength on
multiple pins within the clamp, thus interfering with the rigidity of the
fixation.
• This problem is avoided with the use of simple clamps.

19. Construct Design

20. Circular Frames
• Allows controlled dynamic axial loading.
• Utilizes tensioned thin wires, half pins,clamps, rods and rings.
• Ring frames resist axial and bending deformation better than any
hybrid modification.
• Useful in management of bone loss, corrective osteotomies,
infections and peri-articular fractures.
• Technically demanding.

21. Hybrid Fixator
• Combines the advantages of ring fixators in periarticular areas
with simplicity of planar half pin fixators in diaphyseal bone.
• Biomechanically superior to monolateral frame.
• This is accomplished with a minimum of three tensioned wires
and if possible, an additional level of periarticular fixation using
adjunctive halfpins.

22. LCPs as External Fixator
• Mechanical studies
demonstrated slightly higher
torsional stiffness with similar
axial rigidity as the external
fixator for both titanium and
stainless LCPs.

23. LCPs as External Fixator
• In a series of seven patients LCP external fixators;
• Facilitated mobilization - Low profile
• More manageable
• Aesthetically acceptable
• Disadvantages;
• higher costs
• plates andscrews cannot be reused
• Small screws for adults (only 4.5mm available for LCP)
(Rockwood ed 9)

24. Anatomical Considerations

25. Anatomical Considerations

26. Conversion to DefinitiveTreatment
Factors to consider in the timing of conversion;
1. condition of the soft tissues
2. the initial injury
3. the need for further surgical débridement
4. fasciotomy wounds
5. the condition of external fixator pins
6. external fixator stability
7. bone or soft-tissue loss
8. vascular injury
9. infection
10. the physiologic state of the patient.

27. Conversion to DefinitiveTreatment
• For femoral shaft fractures, early definitive stabilization is thought to reduce
the risks of;
• decubitus ulcers,
• pneumonia,
• venous thromboembolic disease
• Conversion to IMN is most frequently performed as a;
• single procedure,
• staged conversion, or “pin holiday,” before definitive fixation is sometimes warranted.
• Timing of conversion to Internal fixation; remarkable reduction of
complications reported when converted with in 2 weeks.

28. Postop management
Pin-site Care
• No consensus in the literature as to the appropriate regimen for pin-
tract care and infection prevention.
• RCT compared daily pin-tract care vs no pin-tract care - No significant
difference
• The author suggested that specific routine pin-tract care is
unnecessary as long as daily hygiene for the patient and frame is
maintained.
(Camathias C 2012)

29. Pin-site Infection
• A recent metaanalysis from 1980 through 2014 documented an
overall rate of 27.4% for risk of at least one pin-tract infection.
• hybrid external fixators demonstrated a similar risk of pin-tract
infection as unilateral fixator. but lower infection rate in the ring
fixator group. (Horst K 2015)
• pin-tract infection for limb-lengthening procedures;
• rate of half-pin site infection 100%
• rate of hybrid fixators infection (78%)
• rate of ring fixator infection (33%)
(Antoki V 2008)

30. Pin-site Infection
• Trauma patients had the lowest risk for infection at 24%.
• Reconstructive and limb-lengthening frames had the highest risk at
46%.
• This was probably related to frame duration.
• fixators removed at average 88 days and
• reconstructive frame removed on average at 198 days
(Iobista CA 2016)

31. General recommendations for Pin-site Care
• Use normal saline as the cleansing agent in concert with dilute
hydrogen peroxide.
• One RCT has shown 9% lower pin-site infection with half-strength hydrogen
peroxide and application of Xeroform dressing (Lethaby A 2008)
• LLRS authors agreed there is insufficient evidence for a single particular
strategy of pin-site care.
• Ointments are not recommended for post cleansing - inhibit normal
skin flora
• Occasional removal of a serous crust around the pins using dilute
hydrogen peroxide and saline.

32. General recommendations for Pin-site Care
• Immediate postoperative compressive dressing - stabilize pin-skin
interface.
• Compressive dressings can be removed within 10 days to 2 weeks
once the pin sites are healed.
• If pin drainage does develop,
• providing pin care three times per day
• compressive dressing

33. Ex-fix reuse
• Components showing no signs of wear can be reused.
• No differences in the rates of reoperation or complications before and
after institution of the reuse.
• No mechanical failure reported of a reused component.
• Recycling of external fixator components is safe and effective.
• In one of the studies, no component used more than three
times/Local policy.
(Dirschl DR 2002) (Mahapatra 2017)

34. Pin Site Infection
Rockwood ed. 9

35. References
1. Tornetta P. Rockwood and Green's fractures in adults. Philadelphia:
Wolters Kluwer; 2020.
2. Buckley R, Moran C, Apivatthakakul T. AO principles of fracture
management. Davos Platz, Switzerland: AO Foundation; 2017.