Principles of External Fixation
Roman Hayda, MD
Original Authors: Alvin Ong, MD & Roman Hayda, MD; March 2004;
New Author: Roman Hayda, MD; Revised November, 2008
Overview
•
•
•
•
•
Indications
Advantages and disadvantages
Mechanics
Biology
Complications
Indications
• Definitive fx care:
• Open fractures
• Peri-articular fractures
• Pediatric fractures
• Temporary fx care
• “Damage control”
– Long bone fracture
temporization
• Pelvic ring injury
• Periarticular fractures
– Pilon fracture
•
•
•
•
Malunion/nonunion
Arthrodesis
Osteomyelitis
Limb
deformity/length
inequality
• Congenital
• Acquired
Advantages
•
•
•
•
Minimally invasive
Flexibility (build to fit)
Quick application
Complex 3-C humerus fx
Useful both as a temporizing or definitive
stabilization device
• Reconstructive and salvage applications
Disadvantages
• Mechanical
–
–
–
–
–
Distraction of fracture site
Inadequate immobilization
Pin-bone interface failure
Weight/bulk
Refracture (pediatric femur)
• Biologic
May result in
malunion/nonunion,
loss of function
– Infection (pin track)
• May preclude conversion to IM nailing or internal fixation
– Neurovascular injury
– Tethering of muscle
– Soft tissue contracture
Components of the Ex-fix
• Pins
• Clamps
• Connecting rods
Pins
• Principle: The pin is the critical link
between the bone and the frame
– Pin diameter
• Bending stiffness
proportional to r4
< 1/3 dia
• 5mm pin 144% stiffer
than 4mm pin
– Pin insertion technique respecting bone
and soft tissue
Pins
• Various diameters, lengths,
and designs
–
–
–
–
–
2.5 mm pin
4 mm short thread pin
5 mm predrilled pin
6 mm tapered or conical pin
5 mm self-drilling and self tapping
pin
– 5 mm centrally threaded pin
• Materials
– Stainless steel
– Titanium
• More biocompatible
• Less stiff
Pin Geometry
‘Blunt’ pins
- Straight
- Conical
Self Drilling and Tapping
Pin coatings
• Recent development of various coatings
(Chlorohexidine, Silver, Hydroxyapatite)
– Improve fixation to bone
– Decrease infection
– Moroni, JOT, ’02
• Animal study, HA pin 13X higher extraction torque vs
stainless and titanium and equal to insertion torque
– Moroni, JBJS A, ’05
• 0/50 pts pin infection in tx of pertrochanteric fx
Pin Insertion Technique
1. Incise skin
2. Spread soft tissues to
bone
3. Use sharp drill with
sleeve
4. Irrigate while drilling
5. Place appropriate pin
using sleeve
Avoid soft tissue damage and bone
thermal necrosis
Pin insertion
• Self drilling pin
considerations
– Short drill flutes
• thermal necrosis
• stripping of near
cortex with far cortex
contact
– Quick insertion
– Useful for short term
applications
vs.
Pin Length
•Half Pins
–single point of entry
–Engage two cortices
•Transfixation Pins
–Bilateral, uniplanar fixation
–lower stresses at pin bone
interface
–Limited anatomic sites (nv
injury)
–Traveling traction
Courtesy Matthew Camuso
Pin Diameter Guidelines
•Femur – 5 or 6 mm
•Tibia – 5 or 6 mm
•Humerus – 5 mm
•Forearm – 4 mm
•Hand, Foot – 3 mm
< 1/3 dia
Slide courtesy Matthew Camuso
Clamps
• Two general varieties:
– Single pin to bar clamps
– Multiple pin to bar clamps
• Features:
– Multi-planar adjustability
– Open vs closed end
• Principles
– Must securely hold the
frame to the pin
– Clamps placed closer to
bone increases the
stiffness of the entire
fixator construct
Connecting Rods and/or Frames
• Options:
– materials:
• Steel
• Aluminum
• Carbon fiber
– Design
• Simple rod
• Articulated
• Telescoping
• Principle
– increased diameter = increased stiffness and strength
– Stacked (2 parallel bars) = increased stiffness
Bars
•Stainless vs Carbon
Fiber
–Radiolucency
–↑ diameter = ↑ stiffness
–Carbon 15% stiffer vs
stainless steel in loading to
failure
–frames with carbon fiber
are only 85% as stiff ? ? ?
?Weak link is clamp to
carbon bar?
Added bar stiffness
≠
increased frame stiffness
Kowalski M, et al, Comparative Biomechanical Evaluation of Different External Fixator Sidebars: Stainless-Steel Tubes versus
Carbon Fiber Bars, JOT 10(7): 470-475, 1996
Ring Fixators
• Components:
– Tensioned thin wires
• olive or straight
– Wire and half pin clamps
– Rings
– Rods
– Motors and hinges (not
pictured)
Ring Fixators
• Principles:
– Multiple tensioned thin wires (90130 kg)
– Place wires as close to 90 to
each other
o
– Half pins also effective
– Use full rings (more difficult to
deform)
• Can maintain purchase in
metaphyseal bone
• Allows dynamic axial
loading
• May allow joint motion
Multiplanar Adjustable Ring
Fixators
• Application with wire or half pins
• Adjustable with 6 degrees of freedom
– Deformity correction
• acute
• chronic
• Type 3A open tibia fracture with bone loss
• Following frame adjustment and bone
grafting
Frame Types
• Uniplanar
– Unilateral
– Bilateral
• Pin transfixes extremity
• Biplanar
– Unilateral
– Bilateral
• Circular (Ring
Fixator)
– May use Half-pins and/or
transfixion wires
• Hybrid
– Combines rings with planar
frames
Unilateral uniplanar Unilateral biplanar
Hybrid Fixators
• Combines the
advantages of ring
fixators in periarticular
areas with simplicity
of planar half pin
fixators in diaphyseal
bone
From Rockwood and Green’s, 5th Ed
Biomechanical Comparison
Hybrid vs Ring Frames
• Ring frames resist axial and bending
deformation better than any hybrid
modification
• Adding 2nd proximal ring and anterior half
pin improves stability of hybrid frame
Clinical application: Use full ring fixator for fx
with bone defects or expected long frame time
Pugh et al, JOT, ‘99
Yilmaz et al, Clin Biomech, 2003
Roberts et al, JOT, 2003
MRI Compatability
• Issues:
– Safety
• Magnetic field displacing ferromagnetic object
– Potential missile
• Heat generation by induced fields
– Image quality
• Image distortion
MRI Compatibility
• Stainless steel components (pins, clamps,
rings) most at risk for attraction and heating
• Titanium (pins), aluminum (rods, clamps,
rings) and carbon fiber (rods, rings)
demonstrate minimal heating and attraction
• Almost all are safe if the components are not
directly within the scanner (subject to local policy)
• Consider use of MRI “safe” ex fix when area
interest is spanned by the frame and use
Kumar, JOR, 2006
titanium pins
Davison, JOT, 2004
Cannada, CORR, 1995
Frame Types
• Standard frame
• Joint spanning frame:
– Nonarticulated
– Articulated frame
• Distraction or Correction frame
Standard Frame
• Standard Frame
Design
– Diaphyseal region
– Allows adjacent
joint motion
– Stable
Joint Spanning Frame
• Joint Spanning Frame
– Indications:
• Peri-articular fx
– Definitive fixation
through ligamentotaxis
– Temporizing
» Place pins away from
possible ORIF
incision sites
• Arthrodesis
• Stabilization of limb with
severe ligamentous or
vascular injury: Damage
control
Articulated Frame
• Articulating Frame
– Limited indications
• Intra- and peri-articular fractures or
ligamentous injury
• Most commonly used in the ankle, elbow
and knee
– Allows joint motion
– Requires precise placement of hinge in the
axis of joint motion
(Figure from: Rockwood and Green, Fractures in Adults, 4th ed, Lippincott-Raven, 1996)
Correction of Deformity or Defects
• May use unilateral or ring frames
• Simple deformities may use simple frames
• Complex deformities require more complex
frames
• All require careful planning
• 3B tibia with segmental bone loss, 3A
plateau, temporary spanning ex fix
• Convert to circular
frame, orif plateau
• Corticotomy
and distraction
• Consolidation
*note: docking site bone grafted
Healed
EXTERNAL FIXATION
Biomechanics
Leave the Eiffel tower in Paris!
Understand fixator mechanics
•
do not over or underbuild frame!
Fixator Mechanics:
Pin Factors
• Larger pin
diameter
• Increased pin
spread
– on the same side of
the fracture
• Increased number
of pins (both in
and out of plane
of construct)
Fixator Mechanics:
Pin Factors
• Oblique fxs subject to
shear
• Use oblique pin to
counter these effects
Metcalfe, et al, JBJS B, 2005
Lowenberg, et al, CORR, 2008
Fixator Mechanics: Rod Factors
• Frames placed in the same plane as the applied load
• Decreased distance from bars to bone
• Stacking of bars


Frame Mechanics:
Biplanar Construct
• Linkage between
frames in
perpendicular planes
(DELTA)
• Controls each plane of
deformation
Frame Mechanics: Ring Fixators
• Spread wires to as
o
close to 90 as
anatomically
possible
• Use at least 2 planes
of wires/half pins in
each major bone
segment

Modes of Fixation
• Compression
–
–
–
–
Sufficient bone stock
Enhances stability
Intimate contact of bony ends
Typically used in arthrodesis or to complete union of a fracture
• Neutralization
– Comminution or bone loss present
– Maintains length and alignment
– Resists external deforming forces
• Distraction
– Reduction through ligamentotaxis
– Temporizing device
– Distraction osteogenesis
Biology
• Fracture healing by stable
yet less rigid systems
– Dynamization
– Micromotion
• micromotion
formation
Kenwright, CORR, 1998
Larsson, CORR, 2001
=
callus
(Figures from: Rockwood and Green,
Fractures in Adults, 4th ed,
Lippincott-Raven, 1996)
Biology
• Dynamization = loadsharing construct that
promote micromotion at
the fracture site
• Controlled load-sharing
helps to "work harden" the
fracture callus and
accelerate remodeling
(Figures from: Rockwood and Green,
Fractures in Adults, 4th ed,
Lippincott-Raven, 1996)
•Kenwright and Richardson, JBJS-B, ‘91
•Quicker union less refracture
•Marsh and Nepola, ’91
•96% union at 24.6 wks
Anatomic Considerations
• Fundamental knowledge of the anatomy is critical
• Avoidance of major nerves,vessels and organs
(pelvis) is mandatory
• Avoid joints and joint capsules
– Proximal tibial pins should be placed 14 mm distal to articular
surface to avoid capsular reflection
• Minimize muscle/tendon impalement (especially
those with large excursions)
Lower Extremity “safe” sites
14 mm
• Avoid
– Nerves
– Vessels
– Joint capsules
• Minimize
– Muscle transfixion
Upper Extremity “Safe” Sites
• Humerus: narrow lanes
–
–
–
–
Proximal: axillary n
Mid: radial nerve
Distal: radial, median and ulnar n
Dissect to bone, Use sleeves
• Ulna: safe subcutaneous border, avoid
overpenetration
• Radius: narrow lanes
– Proximal: avoid because radial n and PIN, thick muscle sleeve
– Mid and distal: use dissection to avoid sup. radial n.
Damage Control and Temporary
Frames
• Initial frame application
rapid
• Enough to stabilize but is
not definitive frame!
• Be aware of definitive
fixation options
– Avoid pins in surgical approach
sites
• Depending on clinical
situation may consider
minimal fixation of articular
surface at initial surgery
Conversion to Internal Fixation
• Generally safe within 2-3 wks
– Bhandari, JOT, 2005
• Meta analysis: 6 femur, 9 tibia, all but one retrospective
• Infection in tibia and femur <4%
• Rods or plates appropriate
• Use with caution with signs of pin irritation
– Consider staged procedure
• Remove and curette sites
• Return following healing for definitive fixation
– Extreme caution with established pin track infection
– Maurer, ’89
• 77% deep infection with h/o pin infection
Evidence
• Femur fx
– Nowotarski, JBJS-A, ’00
• 59 fx (19 open), 54 pts,
• Convert at 7 days (1-49 days)
• 1 infected nonunion, 1 aseptic
nonunion
– Scalea, J Trauma, ’00
Bilat open femur, massive
• 43 ex-fix then nailed vs 284
compartment syndrome, ex fix
primary IM nail
then nail
• ISS 26.8 vs 16.8
• Fluids 11.9l vs 6.2l first 24
hrs
• OR time 35 min EBL 90cc vs
135 min EBL 400cc
• Ex fix group 1 infected
nonunion, 1 aseptic nonunion
Evidence
• Pilon fx
– Sirkin et al, JOT, 1999
• 49 fxs, 22 open
• plating @ 12-14 days,
• 5 minor wound problems, 1 osteomyelitis
– Patterson & Cole, JOT, 1999
•
•
•
•
22 fxs
plating @ 24 d (15-49)
no wound healing problems
1 malunion, 1 nonunion
Complications
•
•
•
•
•
•
Pin-track infection/loosening
Frame or Pin/Wire Failure
Malunion
Non-union
Soft-tissue impalement
Compartment syndrome
Pin-track Infection
• Most common
complication
• 0 – 14.2% incidence
• 4 stages:
– Stage I: Seropurulent
Drainage
– Stage II: Superficial
Cellulitis
– Stage III: Deep Infection
– Stage IV: Osteomyelitis
Pin-track Infection
Union Fx infection Malunion Pin Infection
Mendes, ‘81
100%
4%
NA
0
Velazco, ’83
92%
NA
5%
12.5%
Behrens, ’86
100%
4%
1.3%
6.9%
Steinfeld, ’88
97%
7.1%
23%
0.5%
Marsh, ‘91
95%
5%
5%
10%
Melendez, ’89
98%
22%
2%
14.2%
Pin-track Infection
• Prevention:
– Proper pin/wire insertion
technique:
• Subcutaneous bone borders
• Away from zone of injury
• Adequate skin incision
• Cannulae to prevent soft
tissue injury during insertion
• Sharp drill bits and irrigation
to prevent thermal necrosis
• Manual pin insertion
(Figures from: Rockwood and
Green, Fractures in Adults, 4th ed,
Lippincott-Raven, 1996)
Pin-track Infection
• Postoperative care:
– Clean implant/skin
interface
– Saline
– Gauze
– Shower
Pin-track Infection
• Treatment:
–
–
–
–
Stage I: aggressive pin-site care and oral cephalosporin
Stage II: same as Stage I and +/- Parenteral Abx
Stage III: Removal/exchange of pin plus Parenteral Abx
Stage IV: same as Stage III, culture pin site for
offending organism, specific IV Abx for 10 to 14 days,
surgical debridement of pin site
Pin Loosening
• Factors influencing Pin
Loosening:
–
–
–
–
Pin track infection/osteomyelitis
Thermonecrosis
Delayed union or non-union
Bending Pre-load
Pin Loosening
• Prevention:
–
–
–
–
–
–
Proper pin/wire insertion techniques
Radial preload
Euthermic pin insertion
Adequate soft-tissue release
Bone graft early
Pin coatings
• Treatment:
– Replace/remove loose pin
Frame Failure
• Incidence: Rare
• Theoretically can occur with recycling of
old frames
• However, no proof that frames can not be
re-used
Malunion
Intra-operative causes:
– Due to poor technique
• Prevention:
–
–
–
–
Clear pre-operative planning
Prep contralateral limb for comparison
Use fluoroscopic and/or intra-operative films
Adequate construct
• Treatment:
– Early: Correct deformity and adjust or re-apply frame prior to bony
union
– Late: Reconstructive correction of malunion
Malunion
Post-operative causes:
– Due to frame failure
• Prevention:
– Proper follow-up with both clinical and radiographic
check-ups
– Adherence to appropriate weight-bearing restrictions
– Check and re-tighten frame at periodic intervals
• Treatment:
– Osteotomy/reconstruction
Non-union
• Union rates comparable to those achieved with
internal fixation devices
• Minimized by:
–
–
–
–
–
–
–
Avoiding distraction at fracture site
Early bone grafting
Stable/rigid construct
Good surgical technique
Control infections
Early wt bearing
Progressive dynamization
Soft-tissue Impalement
• Tethering of soft tissues can result in:
– Loss of motion
– Scarring
– Vessel injury
• Prevention:
–
–
–
–
Check ROM intra-operatively
Avoid piercing muscle or tendons
Position joint in NEUTRAL
Early stretching and ROM exercises
Compartment Syndrome
• Rare
• Cause:
– Injury related
– pin or wire causing intracompartmental bleeding
• Prevention:
– Clear understanding of the anatomy
– Good technique
– Post-operative vigilance
Future Areas of Development
• Pin coatings/sleeves
– Reduce infection
– Reduce pin loosening
• Optimization of dynamization for fracture
healing
• Increasing ease of use/reduced cost
Construct Tips
•
•
•
•
•
•
Chose optimal pin diameter
Use good insertion technique
Place clamps and frames close to skin
Frame in plane of deforming forces
Stack frame (2 bars)
Re-use/Recycle components (requires
certified inspection).
Plan ahead!
Summary
• Multiple applications
• Choose components and geometry suitable
for particular application
• Appropriate use can lead to excellent results
• Recognize and correct complications early
If you would like to volunteer as an author for
the Resident Slide Project or recommend
updates to any of the following slides, please
send an e-mail to ota@ota.org
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General/Principles
Index
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Bhandari M, Zlowodski M, Tornetta P, Schmidt A, Templeman D. Intramedullary Nailing Following External Fixation in Femoral and Tibial Shaft Fractures. EvidenceBased Orthopaedic Trauma , JOT, 19(2): 40-144, 2005.
Cannada LK, Herzenberg JE, Hughes PM, Belkoff S. Safety and Image Artifact of External Fixators and Magnetic Resonance Imaging. CORR, 317, 206-214:1995.
Davison BL, Cantu RV, Van Woerkom S. The Magnetic Attraction of Lower Extremity External Fixators in an MRI Suite. JOT, 18 (1): 24-27, 2004.
Kenwright J, Richardson JB, Cunningham, et al. Axial movement and tibial fractures. A controlled randomized trial of treatment, JBJS-B, 73 (4): 654-650, 1991.
Kenwright J , Gardner T. Mechanical influences on tibial fracture healing. CORR, 355: 179-190,1998.
Kowalski, M et al, Comparative Biomechanical Evaluation of Different External Fixator Sidebars: Stainless-Steel Tubes versus Carbon Fiber Bars, JOT 10(7): 470475, 1996.
Kumar R, Lerski RA, Gandy S, Clift BA, Abboud RJ. Safety of orthopedic implants in Magnetic Resonance Imaging: an Experimental Verification. J Orthop Res, 24
(9): 1799-1802, 2006.
Larsson S, Kim W, Caja VL, Egger EL, Inoue N, Chao EY. Effect of early axial dynamization on tibial bone healing: a study in dogs. CORR, 388: 240-51, 2001.
Lowenberg DW, Nork S, Abruzzo FM. The correlation of shearing force with fracture line migration for progressive fracture obliquities stabilized by external fixation
in the tibial model. CORR, 466:2947–2954, 2008.
Marsh JL. Nepola JV, Wuest TK, Osteen D, Cox K, Oppenheim W. Unilateral External Fixation Until Healing with the Dynamic Axial Fixator for Severe Open Tibial
Fractures. Review of Two Consecutive Series , JOT, 5(3): 341-348, 1991.
Maurer DJ, Merkow RL, Gustilo RB. Infection after intramedullary nailing of severe open tibial fractures initially treated with external fixation. JBJS-A, 71(6), 835838, 1989.
Metcalfe AJ, Saleh M, Yang L. Techniques for improving stability in oblique fractures treated by circular fixation with particular reference to the sagittal plane. JBJS B,
87 (6): 868-872, 2005.
Moroni A, Faldini C, Marchetti S, Manca M, Consoli V, Giannini S. Improvement of the Bone-Pin Interface Strength in Osteoporotic Bone with Use of HydroxyapatiteCoated Tapered External-Fixation Pins: A Prospective, Randomized Clinical Study of Wrist Fractures . JBJS –A, 83:717-721, 2001.
Moroni A, Faldini C. Pegreffi F. Hoang-Kim A. Vannini F. Giannini S. Dynamic Hip Screw versus External Fixation for Treatment of Osteoporotic Pertrochanteric
Fractures, J BJS-A. 87:753-759, 2005.
Moroni A. Faldini C. Rocca M. Stea S. Giannini S. Improvement of the bone-screw interface strength with hydroxyapatite-coated and titanium-coated AO/ASIF cortical
screws. J OT. 16(4): 257-63, 2002 .
Nowotarski PJ, Turen CH, Brumback RJ, Scarboro JM, Conversion of External Fixation to Intramedullary Nailing for Fractures of the Shaft of the Femur in Multiply
Injured Patients, JBJS-A, 82:781-788, 2000.
Patterson MJ, Cole J. Two-Staged Delayed Open Reduction and Internal Fixation of Severe Pilon Fractures. JOT, 13(2): 85-91, 1999.
Pugh K.J, Wolinsky PR, Dawson JM, Stahlman GC. The Biomechanics of Hybrid External Fixation. JOT. 13(1):20-26, 1999.
Roberts C, Dodds JC, Perry K, Beck D, Seligson D, Voor M. Hybrid External Fixation of the Proximal Tibia: Strategies to Improve Frame Stability. JOT, 17(6):415420, 2003.
Scalea TM, Boswell SA, Scott JD, Mitchell KA, Kramer ME, Pollak AN. External Fixation as a Bridge to Intramedullary Nailing for Patients with Multiple Injuries
and with Femur Fractures: Damage Control Orthopedics. J Trauma, 48(4):613-623, 2000.
Sirkin M, Sanders R, DiPasquale T, Herscovici, A Staged Protocol for Soft Tissue Management in the Treatment of Complex Pilon Fractures. JOT, 13(2): 78-84, 1999.
Yilmaz E, Belhan O, Karakurt L, Arslan N, Serin E. Mechanical performance of hybrid Ilizarov external fixator in comparison with Ilizarov circular external fixator.
Clin Biomech, 18 (6): 518, 2003.