How much work is required to puncture dura with Tuohy needles?

The effects of needle bevel orientation and cerebrospinal fluid (CSF) press ure on dural displacement and force required to penetrate cadaveric dura we re studied using 40 samples. A constant hydrostatic pressure was applied to the subdural surface, either high or low, simulating the sitting and later al positions. A 17-gauge Tuohy needle was advanced through the dura with th e bevel oriented parallel or perpendicular to dural fibres. Travel distance and peak force at which dural penetration occurred were measured under bot h pressure conditions. The work required to produce dural penetration was c alculated. Greater force and work were required to penetrate dura in the pe rpendicular orientation (P<0.05), regardless of the subdural pressure exert ed. Dural displacement was similar under both pressure conditions.