A set of styli comprised of a shaped memory or elastic metal are disclosed wherein each stylus has a different preformed curvatures for use with a cutting device for performing a selective discectomy. The device is inserted at a point chosen from contralateral, anterior or anterolateral relative to a herniation site. Once the cutting device is inserted its cutting window is moved to the desired position by inserting a first stylus having an appropriate curvature and moving the device, removing the stylus, inserting a second stylus with a different curvature relative to the first stylus before or after moving the device. By using a plurality of styli with different curvatures and using positioning movements the cutting window is positioned at the site of herniation and a selective discectomy is carried out.