Interscalene brachial plexus block: assessment of the needle angle needed to enter the spinal canal

Attempts were made to place 8-cm 22G needles into the spinal canals of four preserved cadavers using the skin entry point most commonly associated with the lateral interscalene brachial plexus block or Winnie approach (that is, at the level of the cricoid cartilage). Eleven successful attempts were confirmed by computed tomography. Needle angles that were cephalad, transverse or slightly caudad were associated with entry into the spinal canal at depths of 5.0 cm or less from the skin. The only needle entry into the spinal canal with a needle angle of > 50 degrees to the transverse plane (< 40 degrees to the sagittal plane) entered the intervertebral foramen at a depth of 7.7 cm from the skin. We conclude that the use of markedly caudad angulations of needles no longer than 5.0 cm may minimise the chances of spinal canal entry and spinal cord damage.