Comparison between uniaxial pull-out tests and torque measurement of 2.0-mm self-tapping screws

This study investigates the retentive capacity of 2.0-mm self-tapping screws in porcine rib utilizing axial pull-out tests as well as torque measurements of insertion and stripping. These techniques have been performed independently; this analysis assesses the association between pull-out and torque values. The Goodman-Kruskel correlation coefficient between pull-out and insertional torque is 0.13, while the correlation between pull-out and stripping torque is 0.21. Partial correlation indexes control the thickness of bone, a confounding factor. Nonparametric analysis of covariance showed no significant difference between insertion of screws and pull-out of the screws, but stripping versus pull-out test was significant. Given these findings, it appears that insertional torque may be used as an alternative technique for screw retention analysis. Because insertional torque tests can be conducted in the operating room, results of clinical studies can be compared to laboratory analyses.