Stability of the original Hoffmann and AO tubular external fixation devices |
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Authors: | T. K. Moroz J. B. Finlay C. H. Rorabeck R. B. Bourne |
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Affiliation: | (1) Orthopaedic Research Laboratory, University of Western Ontario, University Hospital, Station ‘A’, PO Box 5339, N6A 5A5 London, Ontario, Canada |
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Abstract: | Detailed data of the stability of external fixation devices are needed by the orthopaedic surgeon to predict successful healing of a fracture. The stability (rigidity, yield and failure criteria) of four half-frame configurations (single, stacked, double and delta) of the original Hoffmann and AO tubular frame have been analysed under four loading conditions: axial compression, torsion, and both AP- and ML-bending. Overall the two systems' rigidities were the same between similar configurations. Both systems' single half-frames were particularly weak; however, as the number of components (rods, pins, clamps, couplings) on the frame increased, the rigidity of the frame increased. The difference in performance between the two systems lies in their yield and failure characteristics. The AO system exhibited excellent failure criteria in all modes of loading, i.e. no configuration failed within the test limits, whereas most Hoffman frames yielded and failed at low loads. |
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Keywords: | Biomechanical stability Bone healing External fracture fixation |
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