Previous IRB approval and informed consent, 180 ASA I-II adults under ambulatory knee arthroscopy will be randomly allocated to receive unilateral spinal anesthesia with 7.5 (group Levo-7.5, n=59), 9.37(group Levo-9.37, n=61) and 11.25 (group Levo-11.25, n=60) mg of HLBP 0.75% using a 27-gauge Whitacre needle at a rate of 0.1 ml/ seg. and lateral decubitus position maintained for 5 min after injection.