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Effect of a supplemental plate on the stiffness of a type I external fixator
Jana L Norris1, Karl H Kraus, James P O'Leary
1Orthopedic Research Laboratory, Tufts University School of Veterinary Medicine, North Grafton, MA, USA.
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.