Principles of External Fixation

Principles

  • Low complication rate
  • Not obtrusive
  • Stiff enough to maintain alignment
  • Facilitate weight bearing
  • Adaptable

Classification

  • Simple – pin-rod
  • Clamp – differ from simple frame only in pin-rod connection (eg Hoffman)
  • Ring
  • Hybrid

Frame Configurations

  • Uniplanar – unilateral (encompass extremity sector < 90o)
  • bilateral (encompass extremity sector > 90o)
  • Biplanar – unilateral & bilateral

Methods of increasing stiffness in ex fix

  • Axial or bending compression may be beneficial : encourages periosteal healing
    • Shear or torsional motion may be detrimental
    • Fracture end contact (most important)
    • Increase pin diameter
    • Widely separate pins in fragment
    • Placement of pins near fracture site
    • Radial pretensioning of pin*
    • Decrease bone to rod distance
    • Increase number of support rods
    • Increase number of planes
    • predrill using drill bit slightly smaller than diameter of pin shank (0.2mm smaller than shank)
  • Longitudinal pretensioning is now NOT recommended (necrosis of compressed near cortex)

Indications

  • Open fractures
  • Fractures with severe soft tissue damage
    • Including burns, vessel/ nerve injury
  • Infected fractures
  • Nonunions
  • Fracture stabilisation in multitrauma prior to transfer
  • Limb length discrepancy or malalignment
  • Certain paediatric fractures (to avoid growth plate)
  • Arthrodesis

Fracture healing with ex fix

  • Primary & secondary bone healing depending on rigidity of construct
  • Predominantly secondary bone healing
    • Haematoma
    • Inflammation
    • Neoangiogenesis
    • Soft Callus
    • Hard Callus
    • Remodelling
  • Gap healing only if excellent apposition with rigid fixation (eg. High tibial osteotomy site)

Dynamisation

  • Two concepts
    • Late dynamisation once rotational stability afforded by callus
    • Early dynamisation to promote callus formation then make rigid at 6 weeks to allow regenerate bone to mature
  • Passive – load transmission through fracture site due to pin bending with wt bearing
  • Active axial – load transmission through fracture site with wt bearing using telescopic side rod
  • Controlled axial – using telescopic side bar to vary amount of axial compression

Safe zones

  • Avoid neurovascular structures
  • Do not transfix muscle or tendon
  • Do not enter synovial lining of joint

Prevention of pin loosening

  • Predrill with radial pretensioning
  • Cool with water
  • Insertion of pin by hand

Pin-site care

  • Most important is preventative measures on insertion of pins/ wires
  • There is NO consensus on pin site management
  • Good general protocol is
    • Longitudinal incisions
    • Detension skin around pin
    • Chlorhexidine-soaked sponge around pins/ wires
    • Leave intact for 4 days
    • Daily saline baths with cotton bud
      • Remove crusts & avoid oily compounds so not occlude outflow
    • Loose gauze dressing can be used to prevent contamination
    • Can allow to get wet after 1-2 weeks
  • (Some advocate no dressings at all using daily saline baths only)

Complications

  • Overdistraction
  • Neurovascular injury
  • Pin track infection (8% per pin for duration of frame)
  • Joint entered with septic arthritis
  • Joint contractures
  • Reduced load transmission

Internal fixation following ex fix

  • < 72 hrs : can nail straight away
  • > 72 hrs : ex fix for 10 days
    • : splint/ traction 10 days
    • : nail at 3 weeks
  • Studies by Gustilo show that nailing can be done up to 3 weeks following ex fix application
  • Earlier is better
  • If ex fix for 3 weeks or longer : then cast for same period of time
  • ? UTN at that time
  • Reported rates of infection of IM nail following ex fix 5-50%