External Skeletal fixation (Lewis) Flashcards
External skeletal fixation
- transosseous pins/wires incorporated into an extracorporeal frame
- can be used as primary or adjunctive stabilization
External fixation: indications
- Comminuted fractures
- open fractures
- infected and nonunion fractures
- arthrodeses
- transarticular stabilization
- limb deformities
- gunshot wound
*Provides stable not rigid fixation
External fixation:
Advantageous properties
- Applied either open or closed
- Stable constructs that counteract axial, bending and rotational forces
- can be used as adjunctive fixation to internal fixation
- latitude to make post-op adjustments
- encourage early weight bearing
- versatile and economical
Types of external fixators
- Linear
- Acrylic
- Circular
- Hybrid
External fixation:
Nomenclature: Type I
- Type I
- utilizes half-pin splintage
- pins pass through both cortices of bone, but only one skin surface
- Uniplanar and unilateral
- Pins loaded in contilever bending
- CIs cortex: near
- trans cortex: far
- utilizes half-pin splintage
* can be used above elbow and stifle
External fixation
Nomenclature: Type II
- Utilizes full-pin splintage
- pins pass through both cortices and two skin surfaces
- Is uniplaner but bilateral
- Pins loaded in four-point bending
- holding both ends of the broom
*can’t use above the elbow, above the stifle
External fixation
Nomenclature: modified type II
- Utilizes both half and full pin splintage
- Easier to apply with comparable stability
*can’t go above stifle or elbow
External fixation
Nomenclature: Type III
- Utilizes both half and full-pin splintage
- Biplanar
- half and full-pins are oriented in pooposing planes
- Bilateral
- Applies mainly to linear and acrylic fixators
External fixation
Biomechanics
- Surgeon must determine which construct is appropriate based on both biological and mechanical factors
- Type III
- very rigid constructs
- reserved for difficult, complex cases
Fixation pins
- Weakest link in external skeletal fixation construct
- pin design and application have substantial effect on stability of bone-pin interface
- don’t use smooth pins
Positive profile pins
- Superior stiffness and axial extraction characteristics
- can be site dependent
- Effective centrally positioned threads
- pre-drill pilot hole
- approximate the core diameter of fixation pin
Kirschner-Ehmer (KE)
Apparatus
- Disadvantages
- Can’t place positive profile pins directly through clamps
- Pre-drilling pilot holes is difficult
- Difficult to place a series of parallel full-pin splintage pins
IMEX SX External fixation system
- advantages
- innovative clamp design allows pre-drilling pilot holes
- allows variability in fixation pin diameter
- better mechanics
- disadvantages
- connecting system not radiolucent
- connecting clamps only accept pins of limited diameter
- connecting rod relatively weak
IMEX SK ex fix
summary
- Inc stability
- should allow use of less complex frames
- eliminate need for double connecting bars on type I constructs
Fixation pins
Application
- Place pins through small incisions
- don’t place pins through traumatic or surgical wounds
- Close surgical wounds prior to placing pins
- Avoid large muscle masses
Fixation pins should be inserted with
Test question
- A low speed (150 rpm), high torque drill
- Place most proximal and distal fixation pins first
- twist drill bit
- Add connecting rod close to limb
- leave some room for swelling
- pin should be in middle of bone
- Pin should not exceed 30% of diameter of bone
- beveled tip of half-pin splintage pins should completely penetrate trans-cortex
- Place 3 or 4 pins in each fragment segment if possible
- Interconnect frame elements and tigten fixation clamps
- likely unnecessary
Fixation pin diameter should not exceed….
test question
30% of diameter of the bone
Stiffness of fixation pins is proportional to….
Test question
it’s diameter to the fourth power
Acrylic connecting columns
advantages
- pins can be variable diameter
- Pins don’t have to be placed in same longitudinal plane
- Most are radiolucent
- Minimize distance between connecting column and the cis-cortex of bone
- light weight
- limited inventory and expense
Acrylic connecting columns
Disadvantages
- Difficult to maintain reduction if used for primary fixation
- Polymerization of PMMA is an exothermic reaction
- Fumes generated during polymerization are noxious, toxic, teratogenic
- Difficult to make adjustements or remove individual interior fixation pins
*Something about good for a mandible fracture
