Mechanical Comparison of Two Methods for Interfragmentary Fixation in a Short Oblique Fracture Model

Summary

Twenty mature and 20 immature cadaver dog femora had mid-diaphyseal osteotomies performed at 45° to the bone axis. Either a 3.5 mm cortical lag screw, or a 1.6 mm pin aligning a 1.0 mm (18 gauge) twist-tensioned cerclage wire, stabilized the osteotomy. A single episode of slow axial compression was applied to each construct. Slippage in the plane of the osteotomy occurred for all constructs. Neither bone fracture nor implant failure was observed. Forcedisplacement data were standardized with respect to bone cross-sectional surface area, and statistical comparisons of stress performed at 2%, 4%, and 10% strain. The lag screw constructs were significantly stronger at all three strain levels for mature bone, but only at 10% strain for immature bone. Both devices resisted axial compression to a degree likely to assist, but not to provide complete fracture stabilization. As such, these devices should only be employed in combination with sufficiently rigid primary fixation.

Oblique osteotomies in mature and immature dog femora were stabilized with either a lag screw or transfixation pin and cerclage wire. Constructs were loaded in axial compression and statistical analysis of stress performed at 2%, 4% and 10% strain. The lag screw constructs were significantly stronger at all strain levels for mature bone, but only at the highest strain level for immature bone.

Keywords

Interfragmentary compression - lag screw - cerclage wire - oblique bone osteotomy

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