A microscopic analysis of cut-bevel versus pencil-point spinal needles

An in vitro examination of 25-gauge Quincke and 25-gauge and 27-gauge Whitacre spinal needles was performed after insertion in 210 consenting adult patients. In addition, 300 unused Quincke needles and 300 unused pencil-point needles were examined under a dissecting microscope. When the microscopic evaluation was performed on the needles after spinal blockade, burrs or blunting of the needle tip were noted in 24% of the Quincke needles compared with only 3% of the 25-gauge Whitacre needles and 10% of the 27-gauge Whitacre (P < 0.05). Bony contact with 25-gauge Quincke and 27-gauge Whitacre needles resulted in an increased incidence of microscopic tip damage (versus 25-gauge Whitacre). Needle-tip damage with the Whitacre needles was limited to blunting of the tip. The analysis of unused needles revealed significant differences among manufacturers of the cut-bevel needles with respect to stylet-to-needle length and burrs on the end of the stylet. The leading edge of the stylet protruded beyond the opening of the needle tip in 7% of the Quincke needles. However, only minor needle-tip abnormalities were noted with the pencil-point needles (i.e., variability in the side-port opening to needle tip distance, side-port opening integrity). In conclusion, bony contact produced more damage to the cut-bevel than to the pencil-point needle tips. In addition, fewer inherent manufacturing defects were noted with the pencil-point versus cut-bevel needles.

It has been suggested that damaged needle tips may contribute to a higher incidence of headaches after spinal anesthesia. A microscopic examination revealed that the pencil-point (versus cut-bevel) needles had fewer manufacturing flaws and were less susceptible to tip damage when bony contact occurred during the placement of the spinal needle.