External fixator is used to stabilize the fracture in the proper position in case of emergency for temporary management as well as sometimes for definitive treatment
Aims after placement of Ex-fix
It should accommodate the vital limb anatomy
Injury access to debridement and secondary procedure
Placement as per mechanical demands for patient
Patient comfort should be considered
7 frame characteristics of External Fixator
The frame is characterized to increase the stiffness of the applied and diminish motion at the fracture site by following principles:
- Placement of the principle frame in the sagittal plane
- Increasing the Schanz screw spread within each main bony fragment
- Preloading of Schanz is automatically done by slightly oversizing (+0.2 mm) the core
- Increasing the number of Schanz screws in each bony fragment
- Reducing the distance between the bone and the longitudinal tube
- Attaching a second longitudinal tube in the same Schanz screw plane with the clamps of the in close contact
- Creating a two-plane unilateral frame, i.e. constructing a second half frame within the safe corridor
Simple Unilateral Frame
Gross alignment of the fracture
Insertion of the one screw in one main fragment
1st Schanz screw
Place close to joint
Put longitudinal tube and required number of clamps
2nd Schanz screw
Other main fragments to the further opposite adjustable clamp
Length and rotational alignment are taken care
Insertion of remaining Schanz screw
If the fixator has been in place for < 3 weeks and provided there are absolutely no inflammatory changes, removal of devices can be followed by immediate internal fixation
If the fixator has been in place longer, it should be removed and the limb temporarily stabilized in a cast for 8-10 days. Under antibiotics coverage, plating and nailing is the possible a minimal risk
Radial Preload
The mismatch between greater thread diameter vs core diameter of pivot hole (0.2 mm)
Prestress the bone pain interface in a circumferential pattern
Reduces chances of pin loosening
Pin diameter α r4
Bending Preload: Not recommended
Oblique fractures: Oblique Pins
Size of pin for different bones in External fixator
Painless external fixator: Arthrodesis
When subjected to axial loading, the unilateral frames demonstrated cantilever bending with asymmetrical loading at the fracture site
See also: Ilizarov Principles
