UNIT 6E: External Fixators Flashcards
What is the basic structure of an external fixator?
Pins drilled into the bone to which a metal beam is attached in parallel to the long axis of the bone
What are the advantages of external fixators?
Allows access to the soft tissues
Very versatile
List 5 uses of external fixation in orthopaedics
Limb lengthening
Limb shortening
Joint fusion (arthrodesis)
Correction of angulatory or rotatory deformity
Bone segment transportation
How can post-trauma use of external be divided?
Temporary or definitive
Which type of injuries in temporary external fixation most useful?
Open fractures with extensive soft tissue damage
What are the benefits of temporary external fixation?
Access to the tissues
Elevation of the limb
Fixation technique can be changed once soft tissues have healed
Can be used in lie threatening situations where speed is essential
What are the common sites for application of external fixation?
Tibia
Femur
Humerus
What are 2 principles to be considered when constructing frames/
The bone/frame construct should be stable (i.e. not rigid)
Pin placement must not tether soft tissues or restrict access to wounds
What are bilateral frames?
Bone pins positioned so they cross both cortices and pass through the skin and sofft tissues on both sides of the limb
What are the issues with bilateral frames?
Cause soft tissue tethering
Limit limb motion (painful and limits rehab)
Describe the design of a unilateral frame
ass through the skin on one side of the limb - enter the proximal corted - end by just passing through the opposite cortex
What are the advantages of unilateral frames?
Confer adequate stability
Permit mobilisation
Excellent access to wound
Keep soft tissue tethering to a minimum
Why is fracture stability rather than rigidity more desirable?
Rigidity may inhibit bone healing (balance so callous formation is not inhibited and fracture alignment is maintained)
What 6 factors determine the stability of an external fixator?
The configuration of the frame
The degree of contact between the bone ends
he extent of the soft tissue injury
The quality of the bone/pin interface
The degree to which the clamps have been properly tightened
The total number of pins used
Which direction of strain is thought to be a good stimulus for healing bone?
Strains along the long axis of the bone
If there is no movement at the fracture site what does not form?
Callous
What is dynamisation?
The modification of the construct which permits the transition of forces across a fracture without allowing distraction of the fragments
When is dynamisation usually used?
When soft tissues are well on the way to healing
The simple unilateral frame is to be used for definitive fracture control
What are 5 advantages of external fixators?
Can be assembled and fitted quickly
Can be adjusted later
Beam can be removed to take very clear x-rays or to feel stability of the fracture
Most fixators are versatile and can be used in many sites
Gives excellent access to soft tissues
What are 3 disadvantages of external fixation?
Bone/pin interface infection
Loosening
Soft tissue thering
How is an infected external fixator pin site treated?
Change to method of treatment
Why do bending forces cause loosening rather than damage to the pin?
The pin is stiffer than the bone
How can soft tissue tethering be reduced?
Strategic positioning of the pins
Which structure becomes tethered typically in external fixation of femur fractures?
QQQuadriceps muscle
What complications can occur in the fixator itself?
Modular components may work loose
Loss of fracture stability
What is a sign that pins may be loosening?
Painful pins
How should old loose infected pin sites be investigated and how does this affect treatment?
X-rays - if sequestra (areas of dead bone) which may be ring shaped are present these should be drilled out and the wound cleaned
How are tight infected pin sites treated?
May be retrieved by aggressive wound cleaning (surgery if necessary) and systematic antibiotics
What considerations should be taken to avoid soft tissue tethering on insertion?
Pass through as little muscle as possible
Joint position
Are fixators crossing joints good or bad?
Bad - will cause joint stiffness - should be removed as soon as possible
What should be done to minimise the incidence of malunion and nonunion?
Regular check ups (clniically and with x-rays)
If infection is present but the external fixator is holding the fracture in a stable configuration and the bone pins are not involved how should it be treated?
Local surgery and systemic antibiotics until union
What material is being investigated for fixation devices that dissolve away?
Polyglycolates
