Abstract
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.
Keywords
acrylic - external skeletal fixators - pin positioning - biomechanics
