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Effects of Transfixation Pin Positioning on the Biomechanical Properties of Acrylic External Skeletal Fixators in a
Joachim Lahiani1, Mila Freire1, Xavier Montasell2
1Faculty of Veterinary Medicine, University of Montreal, Saint Hyacinthe, Québec, Canada.
Objective:
The aim of this study was to evaluate the biomechanical effects of transfixation pin positioning in acrylic columns of external skeletal fixators (ESF).
Study Design:
Twenty-four type I acrylic ESF were built simulating a fracture gap-model. Transfixation pins were placed centric (n = 12) or eccentric at ¼ of the column diameter (n = 12) in the acrylic columns. Six constructs from each group were subjected to axial compression and four-point bending tests. Stiffness, yield load and mode of failure were recorded.
Results:
Stiffness was not influenced by centring (p = 0.373), but it was higher in four-point bending than in axial compression (p < 0.001). Pin positioning had no influence on the yield (p = 0.535) and failure loads (p = 0.715) in axial compression, nor on the yield load in bending (p = 0.135). Eccentric pin positioning decreased failure loads by 28% in bending (p < 0.001).
Conclusion:
Eccentric position of transfixation pins within the acrylic columns alters the biomechanical properties of type I ESF constructs. While acrylic offers several advantages, when forming the columns, frame strength will be optimized if pins are centrally located.
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