Effect of a supplemental plate on the stiffness of a type I external fixator.

OBJECTIVE

To assess the effect of a supplemental plate on the stiffness of a six-pin unilateral external skeletal fixator.

STUDY DESIGN

Mechanical testing performed on models.

METHODS

Wooden (birch) dowels were used to create five models of a fracture. A commercially available external fixation system was applied to the model with a uniform unilateral six-pin fixator design. The models were mechanically tested with and without a supplemental plate attached to the 2 clamps adjacent to the fracture gap. Testing was conducted in axial loading, medial to lateral bending, and cranial to caudal bending.

RESULTS

Results showed a 4.42-fold increase in stiffness in axial load, a 4.23-fold increase in stiffness in medial to lateral bending, and a 1.94-fold increase in stiffness in cranial to caudal bending with the addition of the plate.

CONCLUSIONS

The addition of a supplemental plate increases the mechanical stiffness of unilateral fixators. This was especially true in axial load and medial to lateral bending.

CLINICAL RELEVANCE

A supplemental plate can be used with unilateral fixators to increase stiffness of the fixator. Conversely, the plate can be removed to decrease stiffness without the removal of fixation pins.