Asymmetrical fracture fixation: stability of oblique fractures is influenced by orientation

Background. Although clear differences in fracture site displacement have previously been demonstrated between transverse and oblique fracture models stabilised by an asymmetrical method, the direction of the obliquity has not been examined biomechanically. Methods. Eight Sawbones tibiae were cut to represent oblique fractures: four ran from antero-inferior to postero-superior and four from antero-superior to postero-inferior. These were fixed with a Sheffield Ring Fixator and cyclically loaded in axial and off-axis compression. Direct measurements were taken of inter-fragmentary displacement. Results. Significant differences were detected between the fracture directions (P < 0.01) and inter-fragmentary displacements were generally reduced in antero-superior to postero-inferior fractures compared with antero-inferio to postero-superior fractures. Interpretation. Fixation asymmetries need to be tailored to specific fracture orientation to improve fracture site mechanics.