April 11, 2024

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:

  1. Placement of the principle frame in the sagittal plane
  2. Increasing the Schanz screw spread within each main bony fragment
  3. Preloading of Schanz is automatically done by slightly oversizing (+0.2 mm) the core
  4. Increasing the number of Schanz screws in each bony fragment
  5. Reducing the distance between the bone and the longitudinal tube
  6. Attaching a second longitudinal tube in the same Schanz screw plane with the clamps of the in close contact
  7. 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

Sizes of pins in external fixator
Sizes of pins in the external fixator

Painless external fixator: Arthrodesis

When subjected to axial loading, the unilateral frames demonstrated cantilever bending with asymmetrical loading at the fracture site

Cantilever mechanism
Cantilever mechanism

See also: Ilizarov Principles