Deformed spinal needle tips and associated dural perforations examined by scanning electron microscopy

Background: The tips of modern thin Quincke-type spinal needles may be easily damaged by bone contact during the puncture. The purpose of this study was to find out the frequency of tip deformation in routine clinical work and the appearance of the dural perforations made by such damaged needles. Methods: Two hundred and ninety-five Quincke-type needles (22G-29G) used in routine spinal anaesthesia were inspected by light microscopy. Scanning electron micrographs were taken of some of the damaged tips and of experimental dural perforations made by these. Results: Four per cent of the needle tips were clearly bent or hooked and 11% were slightly bent. When an introducer needle was used (19 cases), one needle was clearly bent and one slightly bent. A puncture with a bone contact was associated with clear tip damage in 7%; a puncture without bone contact resulted in an undamaged or slightly bent needle tip in 99% of the cases. The numbers of bent tips among the various sizes were: 22G-2/21, 25G-13/40, 27G-28/231, 29G-1/3. In scanning electron microscopy (SEM) images of four clearly bent needle tips the deviation of the tip was between 10 μm and 20 μm. In SEM of eleven dural perforations, the holes made by needles with clearly bent tips were almost closed and three of them exhibited an “open tin can” appearance. None of the dural perforations was badly torn. Conclusions: We verified that the tips of modern thin spinal needles are vulnerable to damage due to contact with bone. However, the holes made in dura by needles with bent tips do not appear to be excessively torn.