The effects of needle type, gauge, and tip bend on spinal needle deflection

Although the use of fine-gauge spinal needles reduces the incidence of postdural puncture headache, they are associated with increased risk of placement failure as a result of deflection and bending. This in vitro study quantifies spinal needle deflection from the axis of insertion with respect to needle type, gauge, and tip bend. In addition to straight-tip needles, those with standardized 5 degrees and 10 degrees tip bends were studied. The purpose was to examine the effect of tip bend, which has been described with small gauge spinal needles after bony contact, on needle path deflection. Needles studied included Quincke (Q), Sprotte (S), and Whitacre (W) in sizes ranging from 18-gauge to 29-gauge. Needles were inserted perpendicularly into porcine paraspinous muscle followed by radiologic investigation. Measurements of needle deflection from the axis of insertion at depths of 20, 40, and 60 mm were performed in a blinded fashion. Straight-tip Q needle deflection, but not W or S, was correlated with gauge and depth of insertion. Although there were differences within needle type groups, needle deflection was generally correlated with the degree of tip bend. We conclude that spinal needle deflection is dependent on the type of needle (W < S < Q), and that the magnitude of deflection is related to gauge (large < small) and tip bend (straight < 5 degrees < 10 degrees).