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

• Useful both as a temporizing or definitive stabilization device

• Reconstructive and salvage applications

Complex 3-C humerus fx

Disadvantages

• Mechanical– Distraction of fracture site– Inadequate immobilization– Pin-bone interface failure– Weight/bulk– Refracture (pediatric femur)

• Biologic– Infection (pin track)

• May preclude conversion to IM nailing or internal fixation– Neurovascular injury– Tethering of muscle– Soft tissue contracture

May result in malunion/nonunion,

loss of function

Components of the Ex-fix

• Pins

• Clamps

• Connecting rods

< 1/3 dia

Pins• Principle: The pin is the critical link between

the bone and the frame– Pin diameter

• Bending stiffness

proportional to r4

• 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

Slide courtesy Matthew Camuso

< 1/3 dia

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?

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

Added bar stiffness

≠increased frame stiffness

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 (90-130 kg)

– Place wires as close to 90o

to each other

– 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 ComparisonHybrid 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

Pugh et al, JOT, ‘99Yilmaz et al, Clin Biomech, 2003Roberts et al, JOT, 2003

Clinical application: Use full ring fixator for fx with bone defects or expected long frame time

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 titanium pins

Kumar, JOR, 2006Davison, JOT, 2004Cannada, 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 FIXATIONBiomechanics

Understand fixator mechanics• do not over or underbuild frame!

Leave the Eiffel tower in Paris!

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, 2005Lowenberg, 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

close to 90o 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 = callus formation

(Figures from: Rockwood and Green, Fractures in Adults, 4th ed, Lippincott-Raven, 1996)

Kenwright, CORR, 1998Larsson, CORR, 2001

Biology

• Dynamization = load-sharing 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

• Avoid– Nerves

– Vessels

– Joint capsules

• Minimize– Muscle transfixion

14 mm

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

• 43 ex-fix then nailed vs 284 primary IM 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

Bilat open femur, massive compartment syndrome, ex fix then nail

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!

References1. Bhandari M, Zlowodski M, Tornetta P, Schmidt A, Templeman D. Intramedullary Nailing Following External Fixation in Femoral and Tibial Shaft Fractures. Evidence-

Based Orthopaedic Trauma , JOT, 19(2): 40-144, 2005.

2. Cannada LK, Herzenberg JE, Hughes PM, Belkoff S. Safety and Image Artifact of External Fixators and Magnetic Resonance Imaging. CORR, 317, 206-214:1995.

3. 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.

4. 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.

5. Kenwright J , Gardner T. Mechanical influences on tibial fracture healing. CORR, 355: 179-190,1998.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. Maurer DJ, Merkow RL, Gustilo RB. Infection after intramedullary nailing of severe open tibial fractures initially treated with external fixation. JBJS-A, 71(6), 835-838, 1989.

12. 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.

13. 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 Hydroxyapatite-Coated Tapered External-Fixation Pins: A Prospective, Randomized Clinical Study of Wrist Fractures . JBJS –A, 83:717-721, 2001.

14. 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.

15. 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 .

16. 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.

17. Patterson MJ, Cole J. Two-Staged Delayed Open Reduction and Internal Fixation of Severe Pilon Fractures. JOT, 13(2): 85-91, 1999.

18. Pugh K.J, Wolinsky PR, Dawson JM, Stahlman GC. The Biomechanics of Hybrid External Fixation. JOT. 13(1):20-26, 1999.

19. 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):415-420, 2003.

20. 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.

21. 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.

22. 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.

Summary

• Multiple applications

• Choose components and geometry suitable for particular application

• Appropriate use can lead to excellent results

• Recognize and correct complications early

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