Strength of commonly used spinal needles: the ability to deform and resist deformation.

Abstract

We investigated the strength of commonly used spinal needles in relation to the amount of deformation, and registered forces during standardised testing. We investigated differences between manufacturers for the same length and gauge of Luer and non-Luer needles, and examined the effect of the internal stylet in terms of needle strength. A specialised rig was designed to perform the testing in both the horizontal and axial plane, reflecting common industrial tests and clinical use. Needles from four commonly used manufacturers were used (Vygon, Becton Dickinson, B Braun, and Pajunk). Needles of 25 G and 27 G were tested in 90-mm and 120-mm lengths. We found significant differences in terms of the size of final deformation and 'toughness'/resistance to deformation between needles of different brands. There were also significant differences between horizontal tests conducted as an industry standard and our own axial test. This may have bearing on clinical use in terms of the incidence of bending and breakage. The presence of the internal stylet resulted in significantly greater toughness in many needles, but had little effect on the degree of deformation. Comparison of Luer and non-Luer needles of the same brand and size showed few significant differences in strength. This result is reassuring, given the imminent change from Luer to non-Luer needles that is to occur in the UK.