A phacoemsulsification needle for use with an ultrasonic handpiece in performing cataract surgery has a plurality of external grooves along its shaft. The external grooves are configured to convert longitudinal drive motion delivered by the handpiece at the base of the needle into torsional motion at the needle tip. The torsional motion at the needle tip has a magnitude greater than the magnitude of the longitudinal drive motion at the base, i.e. the longitudinal to torsional gain is greater than one. The grooves may be helical grooves, wherein the groove configuration is defined by a set of groove parameters including a helical pitch of the grooves, a width of the grooves, a depth of the grooves, an axial length of the grooves, and a total number of grooves.
