Experimental model for controlling shear using the Ilizarov frame.

Objective: This study has been designed to ascertain whether a standard configuration Ilizarov tibial frame can control shear motion at the fracture site of an oblique fracture within acceptable limits for axial micro-motion, and therefore promote bony union. If not, are there simple modifications to the frame design that can achieve this?

Methods: Four Ilizarov frame designs were tested on a load test rig. Fracture site shear displacement was measured using a clip gauge attached to an automated data recording system.

Findings: The standard Ilizarov frame allowed 4mm of fracture site displacement at 340N of load. Our fourth frame design, the locked olive frame, allowed a maximum of 0.61mm displacement at 700N.

Interpretation: This is one of only two studies to look at circular frame fracture site control in oblique fractures. This is the only study to characterise Ilizarov frame stiffness in oblique fractures. We have shown that the standard Ilizarov frame design is inadequate for control of oblique fractures in this mechanical model. Our data show that with the application of simple principles, the Ilizarov frame can be modified to provide better fracture site control. These frame designs can be applied clinically to reduce fracture site shear motion in oblique fractures, resulting in improved union rates.