Unacceptable variation in the core diameters of some AO type cancellous screws

This study assesses the variability in core diameter of a series of cancellous screws and its effect on torque strength. Analysis of a series of 107 cancellous screws revealed a wide variation of the core diameters in our sample. Tests to evaluate the effect of this variation showed that torsional strength is directly proportional to the cube of the radius of the core; a 30% reduction in radius resulting in a 70% loss in torsional strength. Conclusions drawn from this experimental data indicate that variability in core dimensions below the recommended specifications is unacceptable in clinical practice.